Pilots Criticize Osprey's Testing (Washington post)
Vince Brannigan
Flaw Was Known, But Wasn't Fixed
By Mary Pat Flaherty and Thomas E. Ricks
Washington Post Staff Writers
Thursday, April 5, 2001; Page A01
JACKSONVILLE, N.C. -- The crash of a V-22 Osprey aircraft that killed
four Marines here in December was caused by a design flaw that had been
known for months but went largely uncorrected, according to pilots who
participated in an official
investigation of the accident. The pilots, all current or former
officers in the Marines' first Osprey squadron, said the design flaw in
the aircraft's hydraulic system was compounded by a software glitch that
could have been detected by more rigorous testing. But they said they
believe both problems slipped by because the Marine Corps wanted to win
Pentagon funding for full production of the plane. That approval, they
said, would have freed up money to go back to the drawing board and
re-engineer the hydraulics and software. The production decision was
postponed after two Osprey crashes last year killed 23 Marines, raising
questions about the safety of the aircraft.
The Marine Corps' report on the second crash is expected to be made
public as soon as today. It is unusual for participants in a military
"mishap board" to discuss their views, especially before the release of
a crash report. But several of the board's 12 members agreed to be
interviewed on condition of anonymity. They said they were ready to
speak out because they increasingly distrust the Corps' leadership and
worry that some of their conclusions might be omitted or minimized in
the public
report. "People who have been heroes all my life are no longer my
heroes," one board member said, conveying his dismay in the generals
overseeing development of the Osprey, a novel aircraft that takes off
like a helicopter and then tilts its rotors forward to fly like a
conventional airplane.
While "the Marine Corps has never let me down" in more than 15 years of
service, another pilot added, "this is the first time I've seen the
Marine Corps lose control." After the December crash, the Corps grounded
its initial fleet of eight remaining Ospreys and the secretary of
defense appointed an independent panel to review the program. The
release of the accident report comes just as the review panel, headed by
retired Marine Gen. John R. Dailey, is preparing its findings and
recommendations, which could decide the fate of the Osprey. The Marine
Corps has made the development of the V-22 a top priority and proposes
to buy 360 of the planes in a $40 billion plan to replace its aging,
Vietnam-era helicopters.
Within weeks of the Dec. 11 crash, Marine investigators suspected that
it was caused by a hydraulics failure combined with a software glitch.
But pilots on the mishap board say they believe senior Marine officials
-- including at least a handful of generals who oversee Marine aviation
-- knew about the hydraulics problem long before the crash and postponed
addressing it. They said they are certain that paperwork about the
design flaw was sent up the chain of command but they don't know how
high it went. A Marine spokesman, Maj. Patrick Gibbons, said the Corps
would not comment on the pilots' allegations while the accident report
was pending. "If there are concerns on the part of our Marines, we want
to deal with those, and we're confident that the investigation has
addressed all the relevant issues," he said.
Gibbons added that any mistrust among squadron members "is a subjective
thing." "Assuring them and ourselves that we have thoroughly reviewed
the Osprey program is the very reason we got the Defense Department's
inspector general involved and the independent review panel," the
spokesman said. Two of the pilots said the software glitch should have
been caught in engineering reviews while the Osprey was being tested,
before it left the experimental stage. In the December crash, they said,
the software should have triggered a backup hydraulic system after a
primary system began to leak. Instead, the software worsened the
situation each time the pilot hit a reset button. Hydraulics can be
likened to the muscles of an aircraft, and flight control software to
the brains. Hydraulics power the tilt of the engines and the pitch of
the propellers, while the software helps the pilot control the aircraft.
Both are vital to keep the aircraft flying.
The two pilots said their report raises broader questions about how such
a serious software glitch got into an aircraft that was in regular use.
They said their draft of the report recommended that the Pentagon and
the Osprey's manufacturers "address the process failure . . . that
allowed that to make it through." The hydraulics problems are even more
troubling, the pilots said. Of six who were interviewed, all but one
said the aircraft requires some fundamental re-engineering, particularly
in the areas called nacelles that house the tilt-rotor engines and are
tightly packed with hydraulic, fuel and electrical lines. The sixth
dissented, saying he thought the plane merely needed "seasoning," which
he argued is usual for a new aircraft.
The Osprey has hydraulic lines made of titanium that operate at a steady
5,000 pounds of pressure per square inch (psi), compared with 2,000 to
3,000 psi in many aircraft, a design that cuts the Osprey's weight and
gives it a longer range. The titanium lines, however, have proven
susceptible to abrasions and nicks, particularly in the tightly confined
nacelle, where lines have been found to wear thin from rubbing, exposure
to sand and jostling as the heavy engines shift from helicopter to
airplane mode.
In the past, some Marine officials have acknowledged cutting corners in
the development of the Osprey. In an interview hours before the December
crash, Lt. Gen. Fred McCorkle, the head of Marine aviation, said, "When
we built that airplane, we built it on the cheap . . . we cut every
ounce of fat that we could cut." Using inexpensive parts, such as
plastic fasteners, "hurt the maintainability and reliability of the
early airplanes," McCorkle said. But, he added, "on the next lot, all
that . . . has been fixed." The pilots and other Marine officers said
the Osprey's problems were well-known to top officials long before the
December crash, because complaints about them were filed with the
manufacturers. In addition, they said, the problems were studied in the
testing process from November 1999 through July 2000, and some led to
formal "hazardous incident" reports. Technicians "talked about that
problem of abraded hydraulic lines and leaking lines a lot. It's been a
known problem," said Philip E. Coyle, who retired this year as the
Pentagon's chief weapons tester. Coyle oversaw the nine-month testing of
the Osprey under conditions meant to resemble real operations.
During the test period, hydraulic failures were the most common
mechanical problem, including 39 instances in which the failure posed
"potential safety implications," Coyle told the Dailey panel reviewing
the Osprey program. Indeed, at about the time of the December crash,
Osprey mechanics were directed to wrap Teflon tape around the hydraulic
lines, pilots said. A Marine spokesman confirmed that account. "There
were known hydraulic problems, and titanium is, surprisingly, very
brittle," said one member of the mishap board. "We recognized that there
are fundamental problems with the hydraulics in the nacelle." Another
Osprey pilot said he believes that the aircraft's manufacturers -- Bell
Helicopter Textron and Boeing Co. -- knew about the problems from
complaints filed to them and from internal military reports that were
shared with them. "With as many [maintenance deficiency] reports as we
put in on this, Bell and Boeing have to know the hydraulics need to be
re-engineered," he said.
Both companies declined this week to answer questions submitted in
writing. "Since most of these questions deal with the accident
investigation, it would be inappropriate to comment, since the findings
of the investigating bodies have not been released," Boeing spokeswoman
Madelyn Bush wrote in response."Just ditto what Madelyn told you," said
Bell spokesman Bob Leder, adding: "We believe there are some erroneous
assumptions in the questions you asked us." He said he could not be more
specific because the assumptions were "embedded in questions about the
accident investigation, and we feel it would be inappropriate for us to
comment before the release of the mishap report."
The Marine investigation of an earlier Osprey crash, in which 19 Marines
died in Arizona in April 2000, blamed pilot error. The report also noted
that "the frequency of servicing/maintenance requirements for aircraft
hydraulic systems, though not causal in this mishap, is concerning." But
that opinion was omitted from the initial public version of the report.
It was made public only after it was quoted in a presentation to the
Dailey panel and after media outlets pushed for access to the full
report.
End quote
stan clark
Vince Brannigan <fir...@pressroom.com> wrote in message
news:3ACC672F...@pressroom.com...
> Pilots Criticize Osprey's Testing
> Flaw Was Known, But Wasn't Fixed
>
> By Mary Pat Flaherty and Thomas E. Ricks
> Washington Post Staff Writers
> Thursday, April 5, 2001; Page A01
>
> JACKSONVILLE, N.C. -- The crash of a V-22 Osprey aircraft that killed
> four Marines here in December was caused by a design flaw that had been
> known for months but went largely uncorrected, according to pilots who
> participated in an official
> investigation of the accident. The pilots, all current or former
> officers in the Marines' first Osprey squadron, said the design flaw in
> the aircraft's hydraulic system was compounded by a software glitch that
> could have been detected by more rigorous testing. But they said they
> believe both problems slipped by because the Marine Corps wanted to win
> Pentagon funding for full production of the plane. That approval, they
> said, would have freed up money to go back to the drawing board and
> re-engineer the hydraulics and software. The production decision was
> postponed after two Osprey crashes last year killed 23 Marines, raising
> questions about the safety of the aircraft.
Vince, Bell is a master at spending all of the development money without
doing the development. Their junk is accepted for production through
political means, and then they get paid again to go back to the drawing
board and re-engineer. Sadly, that 'development' money in production is
spent also without development. Nothing ever gets fixed. They just spit out
stuff that is hazardous to one's health. Corrupt coverups like on the Osprey
cost everybody.
On our LCAC program where I was the R&M Manager they used folded cardboard
to lodge the circuit boards in to protect from vibration. The first
production unit failed 6 weeks of planned round the clock OPEVAL testing in
less than two hours! What did the navy do? They fired me, claimed perfect
success proved by 'independent' testing, Bell made a fortune for fraudulent
reliability contract incentives, the navy threw away LCAC-1 into the
junkpile where it belonged, and went into full production quietly
redesigning from scratch and a clean sheet of paper - just like the marines
will do on the OSPREY. :-) If anyone is curious why there is no LCAC-1 of
the hundred or so air boats, now you know. Few know why they started
numbering from number 2, things are so compartmentalized. After 20 years all
they've been used for is to retreat from Somalia when they ran us off.
Charter flights would have been much cheaper.
Michael P. Reed
> Pilots Criticize Osprey's Testing
> Flaw Was Known, But Wasn't Fixed
<Snip>
The Osprey is one of the programs currently under review. Cheney tried to kill
it when he was SECDEF, and with all its well publicised problems, I suspect it
will be the first big ticket item cancelled under the latest QDR.
--
Regards,
Michael P. Reed
Guy Alcala
> Pilots Criticize Osprey's Testing
> Flaw Was Known, But Wasn't Fixed
>
> By Mary Pat Flaherty and Thomas E. Ricks
> Washington Post Staff Writers
> Thursday, April 5, 2001; Page A01
<snip>
The Marines briefed the December crash investigation today (Thursday April
5th) starting at 2:30 P.M. EDT at the Pentagon. The transcript isn't up on
the DoD website yet (4:45 P.M. PDT), but should be by I'd guess no later
than tomorrow. We already know the general findings (hydraulic
failure/software glitch), but it will be nice to get some more detail. I
caught a short excerpt on "The Newshour w/ Jim Lehrer."
Guy
John Phillips
<g_al...@postoffice.pacbell.net> wrote:
>
>The Marines briefed the December crash investigation today (Thursday April
>5th) starting at 2:30 P.M. EDT at the Pentagon. The transcript isn't up on
>the DoD website yet (4:45 P.M. PDT), but should be by I'd guess no later
>than tomorrow. We already know the general findings (hydraulic
>failure/software glitch), but it will be nice to get some more detail. I
>caught a short excerpt on "The Newshour w/ Jim Lehrer."
>
>Guy
I caught a lot of the press conference on c-span. The speaker was a
Marine Corps general who had line responsibility for the squadron. He
was though not an aviator but an infantry trained officer and he did
not deviate much from his prepared remarks.
He defined two root causes for the failure. The first was the rupture
of a hydraulic line that was common to two of the three hydraulic
systems on the aircraft. One result of this was AIR, that the
propeller pitches changed and slowed the aircraft. When the speed
drops below 170 (knots or mph) the flight controls correctly started
rotating the wings back toward vertical to avoid stalling. A number of
alarms were generated in the cockpit and the reset button lit up on
the flight controller.
According to the General, SOP is to push the reset button but this
when accomplished caused the engines speed or prop pitch to oscillate.
Apparently the pilots did this seven or eight times each with the same
result until the plane stalled and crashed nose down into a wet area
about eight miles from the airport.
The "incorrect' action following depressing the reset button was
defined as an "anomally"and the other root cause. I got the sense that
they hadn't discovered the flawed logical path in the software. Since
this appeared to be only an internal Marine investigation without
involvement of the suppliers, they may not have had access to the
software.
When asked what should have happened? The General called on a Colonel
who with a poor choice of words replied "nothing". This lead to follow
up questions as to why have the button in the first place. My
interpretation of his unclear response is that the reset button action
is analogous to restarting a personal computer except that if it
detected reasonable data input that it would substitute the last good
values.
The General stated that the hydraulic line rupture was due to abrasion
with a wire bundle. He did state that this was typical (at least on
these aircraft) and that maintenance involved periodically inspecting
the lines.He did state that the maintenance of this particular
aircraft was ahead of schedule. When asked if this line had been
inspected he replied that this particular one was not included in the
recommended list. He later stated that they had found abrasion on this
particular line on two other aircraft an had replaced it. If I
translated his statements correctly, there may be some culpability in
not having immediately changed the inspection program once these
defective lines were discovered. There was no follow up on this issue
and the general lauded the thoroughness and quality of the maintenance
program.
There were some other peripheral issues that were significant but
purportedly not germane to the crash.
Regards,
John Phillips
To respond by e-mail, please remove the
parentheses from my address
Vince Brannigan
John Phillips wrote:
>
>
> I caught a lot of the press conference on c-span. The speaker was a
> Marine Corps general who had line responsibility for the squadron. He
> was though not an aviator but an infantry trained officer and he did
> not deviate much from his prepared remarks.
>
> He defined two root causes for the failure.
Interesting issue of vocabulary. I fully agree that they presented the
proximate causes of the accident. Hydraulic and software failure were the
proximate causes in the same way that. "the Titanic hit an iceberg, the plates
shattered and the ship sank" Don't hit the iceberg and the ship doesn't sink.
But I'm not sure that the hydraulic system and software failure gives and
adequate explanation of the "root cause" The definition of "root cause" requires
that you go back to the level where if you change the root cause you will
prevent "similar" events from occurring In the case of the V-22 the root cause
has to be somewhere "higher" than an interacting hydraulic and software
failure", since fixing the particular failure will not in any way prevent other
similar failures from occurring. I am not saying that the root cause must be
the tiltrotor design. However the possiblity has to be investigated. The reason
it could be the root cause is that the weight limitations of the tiltrotor
design force the use of 5000 psi titanium tubing riouted through the crowded
engine nacelles.
Vince
I
Guy Alcala
> John Phillips wrote:
>
> >
> >
> > I caught a lot of the press conference on c-span. The speaker was a
> > Marine Corps general who had line responsibility for the squadron. He
> > was though not an aviator but an infantry trained officer and he did
> > not deviate much from his prepared remarks.
> >
> > He defined two root causes for the failure.
>
> Interesting issue of vocabulary. I fully agree that they presented the
> proximate causes of the accident. Hydraulic and software failure were the
> proximate causes in the same way that. "the Titanic hit an iceberg, the plates
> shattered and the ship sank" Don't hit the iceberg and the ship doesn't sink.
Of course, that wasn't the issue in the case of the Titanic; she performed as she
was designed to, actually somewhat better. The cause of the accident (as opposed to
the cause of the sinking) was that they were going too fast for the prevailing
visibility conditions, with lookout procedures and lack of equipment (binoculars,
searchlight) that may have been contributing factors. It's true that going on at
full speed in clear weather at night, even when ice was reported, was a
long-standing and nearly universal practice at the time, but no one knew any better
because the safety record had been impeccable prior to the accident, and even after
it the accident and loss rate was still extremely low. It's just that, as when a
jetliner crashes now, the number of deaths is concentrated in time and spectacular,
even though the overall loss rate is infinitesimal. Anyway, the excess speed was a
human decision, rather than a design or equipment problem.
> But I'm not sure that the hydraulic system and software failure gives and
> adequate explanation of the "root cause" The definition of "root cause" requires
> that you go back to the level where if you change the root cause you will
> prevent "similar" events from occurring In the case of the V-22 the root cause
> has to be somewhere "higher" than an interacting hydraulic and software
> failure", since fixing the particular failure will not in any way prevent other
> similar failures from occurring. I am not saying that the root cause must be
> the tiltrotor design. However the possiblity has to be investigated. The reason
> it could be the root cause is that the weight limitations of the tiltrotor
> design force the use of 5000 psi titanium tubing riouted through the crowded
> engine nacelles.
Of course, you imply that such chafing and failure is unique to 5,000 PSI systems,
and nothing could be further from the truth. The F-105, prior to the incorporation
of Safety Packages I and II, was crashing/catching on fire regularly due to such
failures, and just about any other a/c with hydraulic systems has suffered similar
problems at one time or another. In the case of the F-105, are we to hold 3,000 PSI
hydraulic systems at fault, or should we instead recognize that lines containing
fluid under pressure are more subject to failure when abraded, and do what we can to
identify the locations where this is most common, take steps to mitigate the problem
(by relocation/protection) where possible, and decrease inspection/replacement
intervals where it isn't? We do that with every other a/c, so why is the V-22
special in this regard? And as to routing lines (Ti or otherwise) through "crowded
engine nacelles," where the hell else should they be routed, if not to where
hydraulic actuators are located? Are you suggesting that they shouldn't be routed
to the nacelles drives and rotors? That would certainly eliminate this particular
problem, but at a rather unacceptable cost.
The software problem will have to be fixed, but that's hardly unique to a tiltrotor
either, as the designers of the YF-22 and JAS 39 FCS software can tell you.
Guy
Ivanhoe
To clarify, any weight issues are not systemic to tiltrotors, but to the
specific V-22 design. The Navy's constraints on deck footprint set a
hard limit on rotor diameter, which sets a hard limit on max hover OGE
thrust.
The Marines' sling load expectations and the self-deployment requirements
set a hard limit on useful load. So the only variable is empty weight,
which was apparently driven down by the use of almost-all-composite
structure,
high-pressure hydraulics, and a high-speed cross-shaft among other things.
All of which are technical risks not fundamentally inherent to tiltrotors.
I'm beginning to think these hardware failures have been primarily due
to inadequate inspection schedules, caused by the attempt to massage
the maintenance manhours logged. Kinda obvious, and kinda avoidable
if they'd let the mechanics really go over the birds after every flight.
As for the possible software flaws, further proof of the dangers
of full-authority flight control systems.
John Phillips
wrote:
>
>"Vince Brannigan" <fir...@pressroom.com> wrote in message
>news:3ACE0F0F...@pressroom.com...
>>
>>
>> John Phillips wrote:
>>
>> >
>> >
>> > He defined two root causes for the failure.
>>
>> Interesting issue of vocabulary. I fully agree that they presented the
>> proximate causes of the accident. Hydraulic and software failure were the
>> proximate causes in the same way that. "the Titanic hit an iceberg, the
>plates
>> shattered and the ship sank" Don't hit the iceberg and the ship doesn't
>sink.
>> But I'm not sure that the hydraulic system and software failure gives and
>> adequate explanation of the "root cause" The definition of "root cause"
>requires
>> that you go back to the level where if you change the root cause you will
>> prevent "similar" events from occurring In the case of the V-22 the root
>cause
I may have not made it clear but if either the hydraulic line failure
did not occur or the software glitch was not present, the crash would
not have happened. Eliminate either malfunction and the Marines would
still have an airplane and crew. These are root causes in my mind.
stan clark
Guy Alcala <g_al...@postoffice.pacbell.net> wrote in message
news:3ACE336A...@postoffice.pacbell.net...
Guy, it's going to take a great deal more than merely fixing a software bug
to make that plane safe. I think Vince is saying it's an immature design
reliabilitywise and years away from being ready for going into production,
if ever. Bell's LCAC is still an immature design reliabilitywise, and it's
been in production for over 20 years. Our 3-inch gun is the same after 25
years.
The Osprey is like the F-105 though. Forty years later it's still not
ready for production! We were getting about an hour MTBF from the avionics
system 40 years ago, and I doubt it ever got any better. The higher pressure
lines and titanium piping is a case in point. I think the general said, "We
didn't know titanium was so brittle." If the plane were ready for
production, they'd have known by test. That's a simple materials problem,
not an aero one. They would have also determined by FMEA the relative
probability of a any combination of failures being so critical such as what
happened.
On the F-105 in '62 a red-light came on which told the pilot to jump - and
he did. Of course, they blamed the pilot - not the plane. That pilot had a
rough time around Nellis for a couple of months - until another pilot bailed
out claiming the same thing. They grounded all of the planes and replaced
every wire in ALL the damn things (putting me out of work), That, of course,
really screwed the plane up. The Air Force thinking was like yours about
just increasing planned maintenance. Since they controlled the maintenance
data, it showed their "tweaking" made the plane much more reliable. Their
great cure for the F-l05's sickness That's where we invented a new term
called maintenance efficiency. What's the probability of having a failure
on the sortie, right after maintenance, compared with having a failure on a
sortie that had no maintenance? It was about .80. In other words, not only
did tweaking not help - it introduced a new failure every fifth or so
sortie. We have F-105s for decoration now all over my town - so they weren't
completely worthless. I think the Coca Cola company erected them for
advertising. - since that's what they looked like. A Republic Aviation wheel
once gave me a wall picture of four of them in formation. I asked him how
he got four up in the air at the same time long enough to take their
picture. Years later I discovered the answer - it was a painting. I see the
Osprey becoming another F-105.
>
Guy Alcala
> Guy Alcala <g_al...@postoffice.pacbell.net> wrote in message
> news:3ACE336A...@postoffice.pacbell.net...
> > Vince Brannigan wrote:
<snip>
Stan, I don't disagree that it's immature as far as reliability, and also that's
it's missing some items that need to be incorporated before going into service
(relocated/improved radalt is a definite must). But Vince raised (and has done
so repeatedly in the past) the possibility that it may be the tiltrotor itself
that's too dangerous to fly, at least currently. Specifically, in this case he
wrote:
> > In the case of the V-22 the root cause
> > has to be somewhere "higher" than an interacting hydraulic and software
> > failure", since fixing the particular failure will not in any way prevent
other
> > similar failures from occurring. I am not saying that the root cause must
be
> > the tiltrotor design. However the possiblity has to be investigated.
> > The reason it could be the root cause is that the weight limitations of the
> > tiltrotor design force the use of 5000 psi titanium tubing riouted through
the
> > crowded engine nacelles.
There appears to be nothing in this accident unique to a tiltrotor. Nor does a
tilt rotor need to use 5,000 PSI systems, as the BA 609 uses 3,000 PSI. The
military went to 5,000 PSI to minimize weight and maximize lift capacity,
because the military is more willing and has greater need to trade off proven
technology against performance enhancements than the civilian market does, for
obvious reasons. If we are to condemn the use of a 5,000 PSI system in the
Osprey because it's new, then we could do the same going right back to the very
first hydraulic control system installed in an a/c. Should we also condemn
the Sikorsky S-92, because it's the first helo (to my knowledge) to use a 4,000
PSI system (albeit 4,000 PSI's already been used on the F-18 for 20 years or
so)?
>Bell's LCAC is still an immature design reliabilitywise, and it's
> been in production for over 20 years. Our 3-inch gun is the same after 25
> years.
>
> The Osprey is like the F-105 though. Forty years later it's still not
> ready for production! We were getting about an hour MTBF from the avionics
> system 40 years ago, and I doubt it ever got any better. The higher pressure
> lines and titanium piping is a case in point. I think the general said, "We
> didn't know titanium was so brittle." If the plane were ready for
> production, they'd have known by test. That's a simple materials problem,
> not an aero one. They would have also determined by FMEA the relative
> probability of a any combination of failures being so critical such as what
> happened.
If you're referring to the Marine General who presented the current report, he
is self-admittedly not a pilot, and off-hand I don't remember him saying such a
thing (I'll re-check the transcript).
> On the F-105 in '62 a red-light came on which told the pilot to jump - and
> he did. Of course, they blamed the pilot - not the plane. That pilot had a
> rough time around Nellis for a couple of months - until another pilot bailed
> out claiming the same thing. They grounded all of the planes and replaced
> every wire in ALL the damn things (putting me out of work), That, of course,
> really screwed the plane up. The Air Force thinking was like yours about
> just increasing planned maintenance. Since they controlled the maintenance
> data, it showed their "tweaking" made the plane much more reliable. Their
> great cure for the F-l05's sickness That's where we invented a new term
> called maintenance efficiency. What's the probability of having a failure
> on the sortie, right after maintenance, compared with having a failure on a
> sortie that had no maintenance? It was about .80. In other words, not only
> did tweaking not help - it introduced a new failure every fifth or so
> sortie. We have F-105s for decoration now all over my town - so they weren't
> completely worthless. I think the Coca Cola company erected them for
> advertising. - since that's what they looked like. A Republic Aviation wheel
> once gave me a wall picture of four of them in formation. I asked him how
> he got four up in the air at the same time long enough to take their
> picture. Years later I discovered the answer - it was a painting. I see the
> Osprey becoming another F-105.
Considering that the F-105 was the workhorse of the Rolling Thunder period
('65-'68) of the Vietnam War, flying the most hazardous missions over North
Vietnam and having the highest sortie total (matched by the highest number of
losses, natch), I don't consider that a bad thing at all. The a/c was made far
safer, and for the period it was adequately safe (its loss rate wasn't
significantly different from other fighter a/c of the period, and better than
many), and its MMH/FH had decreased considerably from its days in the 4th TFW (I
take it that was when you had your experience with it, when they and the 57th at
Nellis had it?), although it was never an easy a/c to work on. The 388th at
Korat achieved a 99.77% take-off rate (0.23% abort rate) in one month in the
summer of '67, and they were averaging 70 hours per month per a/c _in combat_.
In short, it had matured. Its combat loss rate was better than the F-4's flying
the same missions in the same period, despite the fact that it only had one
engine, and the pilots loved the a/c. It wasn't perfect; the hydraulic control
lines ran next to each other, and until a mod was installed a single flak hit
could result in both PC-1 and PC-2 losing all their fluid and the a/c having to
be abandoned over N. Vietnam. But for its day, it was a superb combat aircraft.
If the Osprey can equal the Thud's reputation, or more to the point the CH-46's
(which suffered 6 or maybe it was 7 fatal crashes in a two month period due to
the rear rotor pylon falling off the a/c, two years after it achieved IOC and 6
months after it was introduced to combat), it will have achieved what the
Marines hope for from it. Naturally, the Osprey must meet much higher standards
for acceptable operational loss rates than those a/c, designed in the fifties
and sixties, had to.
Guy
curious
>>> John Phillips wrote:
>
>I may have not made it clear but if either the hydraulic line failure
>did not occur or the software glitch was not present, the crash would
>not have happened. Eliminate either malfunction and the Marines would
>still have an airplane and crew. These are root causes in my mind.
>
John,
The root causes are those things that, if fixed, would have prevented this
accident, and all other similar occurrences.
The obvious (now, in retrospect) software glitch and chafing problems are only
the beginning. Working back up the time line, the crews wrote of how poorly
the program communicated. They also spoke about how the problems were ignored
or shelved, and that any critisizm was considered a threat to the program, so
it was shuffled under the rug.
Note that after the last accident (should we number them to make it easier to
keep them separate?) they inspected the remaining aircraft and found
similar chafing on eight of the aircraft, even though there was an accident
caused by this years ago. A careful program would relentlessly hunt down and
fix all line routing problems, take photos, train crews and impose
reinspections. A bad program would not do these things, and more accidents
could happen.
A bad program would have the Comanding General of the USMC swear in public how
maintainable the aircraft is by feeding him false data.
The root cause of this accident is probably the attitude the Marines have
always had, the "Can Do" attitude that is very important on a beach landing,
and very unhealthy when developing a flying machine.
Curious
John Phillips
wrote:
>
>>>> John Phillips wrote:
>
>>
>>I may have not made it clear but if either the hydraulic line failure
>>did not occur or the software glitch was not present, the crash would
>>not have happened. Eliminate either malfunction and the Marines would
>>still have an airplane and crew. These are root causes in my mind.
>>
>
>John,
>
>The root causes are those things that, if fixed, would have prevented this
>accident, and all other similar occurrences.
>
>The obvious (now, in retrospect) software glitch and chafing problems are only
>the beginning. Working back up the time line, the crews wrote of how poorly
>the program communicated. They also spoke about how the problems were ignored
>or shelved, and that any critisizm was considered a threat to the program, so
>it was shuffled under the rug.
>Note that after the last accident (should we number them to make it easier to
>keep them separate?) they inspected the remaining aircraft and found
>similar chafing on eight of the aircraft, even though there was an accident
>caused by this years ago. A careful program would relentlessly hunt down and
>fix all line routing problems, take photos, train crews and impose
>reinspections. A bad program would not do these things, and more accidents
>could happen.
I have not been following the issue and have no disagreement with your
comments.
>
>The root cause of this accident is probably the attitude the Marines have
>always had, the "Can Do" attitude that is very important on a beach landing,
>and very unhealthy when developing a flying machine.
Do you expect an internal Marine report to list this as a root cause?
The Marine spokesman referenced a panel that I assume is looking at
the entire program.
George S Collins
>If the Osprey can equal the Thud's reputation, or more to the point the CH-46's
>(which suffered 6 or maybe it was 7 fatal crashes in a two month period due to
>the rear rotor pylon falling off the a/c, two years after it achieved IOC and 6
>months after it was introduced to combat), it will have achieved what the
>Marines hope for from it. Naturally, the Osprey must meet much higher standards
>for acceptable operational loss rates than those a/c, designed in the fifties
>and sixties, had to.
>
>Guy
The point being that, absent the political pressure applied to and by
the USMC, there is no credible reason for using live (for the time
being) Marines as crash test dummies. The program is faulted, either
fix it or cancel it. And, if the decision is to fix it, disqualify the
A/C from flight until such time as it can be reasonably reliable.
The F-105 is irrelevant, as it was built at a time when non-flight
testing/simulation was in its infancy.
George
George S Collins
>
>Do you expect an internal Marine report to list this as a root cause?
>The Marine spokesman referenced a panel that I assume is looking at
>the entire program.
>
>
>Regards,
>
>John Phillips
>
Unfortunately, they are looking at how to save a flawed program (and,
as a result, their careers). The deaths of a few Marines no longer
seems of any import to those at the top of the Corps. That is an
extremely troubling circumstance.
George
Guy Alcala
> >If the Osprey can equal the Thud's reputation, or more to the point the CH-46's
> >(which suffered 6 or maybe it was 7 fatal crashes in a two month period due to
> >the rear rotor pylon falling off the a/c, two years after it achieved IOC and 6
> >months after it was introduced to combat), it will have achieved what the
> >Marines hope for from it. Naturally, the Osprey must meet much higher standards
> >for acceptable operational loss rates than those a/c, designed in the fifties
> >and sixties, had to.
> >
> >Guy
>
> The point being that, absent the political pressure applied to and by
> the USMC, there is no credible reason for using live (for the time
> being) Marines as crash test dummies. The program is faulted, either
> fix it or cancel it. And, if the decision is to fix it, disqualify the
> A/C from flight until such time as it can be reasonably reliable.
And I don't disagree that it needs to be fixed to reach an acceptable standard of
reliability, including most or all of the operational equipment and testing that
received waivers for Opeval, land shouldn't be put into operational service prior to
that time. I don't think that it's possible for the a/c to ever reach a stage where
human beings won't sometimes be forced to act as crash test dummies, any more than
any other a/c can (Boeing 747/TWA 800, for instance). Unfortunately, problems are
often only noticed/identified because there's a crash, and the more complex the
system, the more impossible it becomes to predict every possible failure or fault
that may develop.
>The F-105 is irrelevant, as it was built at a time when non-flight
>testing/simulation was in its infancy.
I wasn't the one who brought up the 105, that was Stan Clark, and I was just replying
to some of the claims made in relation to it, as it was used as an analogy to the
V-22. I agree that it is, although I think the conclusion that should be drawn is
the opposite one that Stan put forward. And specifically, abrading
hydraulic/electric lines is the sort of thing that is only likely to be discovered
through inspection after use under operational conditions, or unfortunately, as a
result of crashes.
Guy
Vince Brannigan
Guy Alcala wrote:
I suspect you missed my point. I'll try again. My point has nothing to do with the
5000 psi system as such. That is a symptom of the root cause which is the inherent
lack of lift. The V-22 has an inherent fundamental disadvantage relative to a
helicopter using the same advanced technology. It gains its higher flight speed by
tolerating a substantially reduced payload. The reduction in payload comes both
from the less efficient rotors and the extra weight of the tilt-rotor equipment.
Most of the cost and complexity problems of the V-22 arise form the need to
miimize weight.
Vince
Coridon Henshaw
Prof Vince et el:
RISKS Digest has an interesting article on the latest V-22 loss. The
general gist is that the USMC investigation didn't look deeply enough. The
whole article can be found at
http://catless.ncl.ac.uk/Risks/21.33.html#subj1
--
Coridon Henshaw -- http://www3.sympatico.ca/gcircle/csbh
"..To expect a good deal from life is puerile." -- D.H. Lawrence
Hang Fier
the Marine investigation didn't go deep enough. More that they were
disappointed that the Marines didn't explain exactly how the
computer/software error came about and who made it. I would guess these
computer programs are rather complicated and releasing the actual code with
notations on which lines of code affected which other lines of code and
ended up affecting the aircraft's flight would not help the average person
much.
But I think some in this NG would rather blame the whole aircraft than to
isolate and correct the problem. To the extent that this computer-related
problem may be symptomatic of other possible existing problems, it does seem
that more research is needed on the software and how it behaves under
anomalous conditions. I wonder why the computer reset light came on in the
first place in this situation. A burst hydraulic line shouldn't affect the
computer system.
I guess the computer system may have noticed the hydraulic failure and
assumed that the reading was a symptom of a computer failure.
I once read that the Space Shuttle has three redundant computers. It seems
to me that if the Osprey had had redundant computers, or maybe a peer to
peer system, the computers could check up on each other. If all the
computers find that they have the same weird readings, they would be able to
determine that the problem was not likely to be a computer problem (hence
resetting would not do any good and the reset light would not light up) but
a REAL problem. No doubt this is an oversimplified analysis.
I also liked the article about the prisoner escaping down the computer
cable.
"Coridon Henshaw" <"csbh<R"@datahit.com wrote in message
news:Xns907ED9010...@206.172.150.51...
Hang Fier
>
> Unfortunately, they are looking at how to save a flawed program (and,
I am sorry but you will have to be more specific if you wish to be
persuasive.
What is your definition of a "flawed" program?
Do people have to die to make a program flawed?
How many people are allowed to die before the program is cancelled? One?
Two? How many?
Would you apply the same "death limitation" to RPVs too? Or could we dump
billions onto a bad RPV as long as nobody died?
And if you found a prgram which met your definition of "flawed" what should
be done with it? Axe it? Put more money into it to fix the flaws? What?
> as a result, their careers). The deaths of a few Marines no longer
> seems of any import to those at the top of the Corps. That is an
> extremely troubling circumstance.
Maybe they believe that in the long run the V-22 will result in more lives
saved on the battlefield than have been lost, or are likely to be lost, in
testing.
>
> George
Guy Alcala
> Guy Alcala wrote:
<snip>
> > There appears to be nothing in this accident unique to a tiltrotor. Nor does a
> > tilt rotor need to use 5,000 PSI systems, as the BA 609 uses 3,000 PSI. The
> > military went to 5,000 PSI to minimize weight and maximize lift capacity,
> > because the military is more willing and has greater need to trade off proven
> > technology against performance enhancements than the civilian market does, for
> > obvious reasons. If we are to condemn the use of a 5,000 PSI system in the
> > Osprey because it's new, then we could do the same going right back to the very
> > first hydraulic control system installed in an a/c. Should we also condemn
> > the Sikorsky S-92, because it's the first helo (to my knowledge) to use a 4,000
> > PSI system (albeit 4,000 PSI's already been used on the F-18 for 20 years or
> > so)?
>
> I suspect you missed my point. I'll try again. My point has nothing to do with the
> 5000 psi system as such. That is a symptom of the root cause which is the inherent
> lack of lift. The V-22 has an inherent fundamental disadvantage relative to a
> helicopter using the same advanced technology. It gains its higher flight speed by
> tolerating a substantially reduced payload. The reduction in payload comes both
> from the less efficient rotors and the extra weight of the tilt-rotor equipment.
Certainly, and I've no argument there. If you want to compare lift from a VTO, a helo
will win hands down. And a helo has an inherent fundamental disadvantage to any
comparable fixed wing for payload/range/speed, if runway length is available to suit.
And a tiltrotor is a compromise between the two.
Of course, you need to be more specific, and state that a side-by-side configuration
tiltrotor _where the nacelles don't extend clear of the nose during or after rotation_
suffers most from less efficient rotors. Pushing the rotor disk path clear of the nose
during rotation (assuming such a thing is possible) would allow larger rotors to be
used, including intermeshing ones, but that would either require an increase in allowed
height, or else a very snub-nosed design. Assuming that one could be built instead with
fuselage end mounted rotors, one pushing and one pulling, then the rotors could be as
large as any other tandem chopper, able to overlap and/or intermesh (boy, that's a
transition I'd like to see, and talk about nightmare complexity;-) ). But enough time
spent in Tomorrowland and/or Fantasyland.
Let's not forget that the V-22's rotor size is specifically limited by an outside
factor, i.e. LHA/LHD compatibility. Lacking that requirement, the wings and rotors
could (would, according to the designers) be longer, and disc loading lower, presumably
increasing vertical lift at the cost of some cruise speed.
> Most of the cost and complexity problems of the V-22 arise form the need to
> miimize weight.
No, most of the cost and complexity comes from the need to maintain control while
reliably transitioning large rotating masses through an unstable part of the envelope,
for the very first time in any production a/c. Minimizing weight to maximize payload is
a major factor in every a/c ever built, especially in military ones.
Guy
Guy Alcala
<snip>
> I guess the computer system may have noticed the hydraulic failure and
> assumed that the reading was a symptom of a computer failure.
>
> I once read that the Space Shuttle has three redundant computers. It seems
> to me that if the Osprey had had redundant computers, or maybe a peer to
> peer system, the computers could check up on each other. If all the
> computers find that they have the same weird readings, they would be able to
> determine that the problem was not likely to be a computer problem (hence
> resetting would not do any good and the reset light would not light up) but
> a REAL problem. No doubt this is an oversimplified analysis.
Any FBW system has redundant computers for just this sort of error correction.
Typically there are three, operating on the majority vote system. Indeed, I
believe that was the cause of the very first Osprey crash, as two of the three
lateral control circuits had been wired backwards, so the majority vote by the
computers said they were right and the single correctly wired circuit wrong.
GIGO applies.
Guy
Peter Skelton
<g_al...@postoffice.pacbell.net> wrote:
>
>No, most of the cost and complexity comes from the need to maintain control while
>reliably transitioning large rotating masses through an unstable part of the envelope,
>for the very first time in any production a/c. Minimizing weight to maximize payload is
>a major factor in every a/c ever built, especially in military ones.
One bit of the design I don't understand is the location of the
engines on the wings. Aren't they interconnected so that one can
drive both propellors? If so, why not locate them above or in the
fuselage. That should make for a more space around them than
there is in the nacelles. It would also make for smaller nacelles
with less running into them.
____
Peter Skelton
Hang Fier
the largest rotor diameter possible. The larger the rotor, the greater the
lift in helo mode and, maybe to a lesser extent, the greater the forward
acceleration and power in airplane mode.
Placing the engines as far away as possible is dictated by a design which
uses the props within the airframe "shadow" when in airplane mode. In other
words, although the props may be above the airframe "shadow" when in helo
mode, they are not outside the airframe "shadow" when in airplane mode. If
they were too long, but not long enough to touch, the V-22 would be able to
fly well in helo mode but would chop itself to pieces in airplane mode.
It just struck me that one solution to this airframe "shadow" problem could
be a pusher - puller design. The nose puller prop could rotate up so that it
was pulling the aircraft up, while the rear pusher propeller could rotate
down so that it was pushing the aircraft up. I guess all the landing gear
would have to be in front. I wouldn't want to be standing near the tail when
it landed. :) I am sure there are many physical problems with this idea,
but hell, it was just a thought.
"Peter Skelton" <Skel...@home.com> wrote in message
news:3ad39d28.7673451@news...
Peter Skelton
<Hf...@hotmail.com> wrote:
>The engines have to be as far away from the fuselage as possible to allow
>the largest rotor diameter possible. The larger the rotor, the greater the
>lift in helo mode and, maybe to a lesser extent, the greater the forward
>acceleration and power in airplane mode.
There is shafting sufficient to drive the props between the
nacels now. The engines and gearboxes do not need to be behind
the propellors.
Another option would be to do without single engine capability.
That would eliminate the shafts and some gearing freeing space in
the nacels.
____
Peter Skelton
Paul Baechler
<Hf...@hotmail.com> wrote:
> The engines have to be as far away from the fuselage as possible to allow
> the largest rotor diameter possible.
Given current tilt-rotor design, the only things that have to be on the
ends of the wings are the prop/rotors and 90-degree gearboxes to drive
them. The engines could be located anywhere along the connecting shaft, or
anywhere that engine drive shafts could feed gearboxes located along that
shaft. There is no design requirement that mandates the engines be located
as far from the fuselage as possible.
--
Paul Baechler
pbae...@bellsouth.net
Dwayne Allen Day
I went to the Navy League's Sea-Air-Space exhibition in Washington
today. Bell had a big floor display, but I got the impression that they
were seeking a lower profile for the V-22. Not much literature to hand
out at their display.
D
--
Hang Fier
"Paul Baechler" <pbae...@bellsouth.net> wrote in message
news:pbaechle-100...@host-216-76-234-223.hsv.bellsouth.net...
Oh yeah, sorry, misunderstood the question. Now that I think about it, the
question makes more sense. If one engine can power both props, why can't
both engines be situated closer to the fuselage and power the props from a
distance.
Hope we get an answer.
>
> --
> Paul Baechler
> pbae...@bellsouth.net
Nick Lappos
Bury the engines in the fuselage: This would make the cross shaft continuously under full flight loads, so it would have to be more robust than the current design, which carries only half an engine's worth of power, and only when one engine is effectively off line. Also, the engines would need a gearbox to turn the rotation 90 degrees if they were in the fuselage, adding weight, complexity and failure modes. Additionally, the mass of the engines at the wing tips adds a degree of torsional stability to the system, helping the designer tune the structure to avoid the flutter modes that were a great problem before the XV-15.
Eliminate he cross shafting: Wow, this would make synchronizing the engines a flight critical problem, because the rotor rpm will vary thrust greatly and easily swamp the rotor pitch control. The cross shaft is a great insurance policy to keep both rotors at exactly the same rpm. Also, (and maybe most importantly) the shafting keeps the machine under control if an engine fails.
Make the rotors extend past the nose so they can be larger: The balance of the vehicle makes this very hard to do, mostly because typical CG ranges make the principle payload want to be at the 1/4 chord of the wing, and there must be room for the cockpit. Also, there are strong reasons to make the rotor small because when it is a prop this keeps the dysymetry forces smaller at high speed (note the thickness of the prop roots on a prop fighter).
Make the rotors much bigger if there is no shipboard deck spotting requirement: The rotors cannot grow much bigger without seriously affecting the structural stability of the whole system. As the rotor grows, the wing must be even stiffer to keep the dynamic vibrations of the rotor and wing under control. As the system gets bigger, the natural frequency gets much lower, and the modes become more difficult to control. The large envelope of the V-22 is a real credit to the Boeing and Bell dynamicists who identify the vibrations and tune the structure and flight controls to make it all work. These dynamic modes are believed to be the reason why the enormous Russian V-12 was unsucessful. In the end, for a given sizing, a helicopter will have about 2.5 times the rotor area as a tilt rotor, and thus will lift about twice as much payload.
Note that the Bell 609 has two engines that produce about 2200 Horse Power at peak rating for a gross weight of 15,000 pounds. The Black Hawk uses engines with that power to fly at 22,000 pounds. The difference is the trade off price of a tilt rotor. Of course, the speed advantage is almost the reverse, and that's why we have horse races!
Nick
Brian Sharrock
major ship
> > Most of the cost and complexity problems of the V-22 arise form the
need to
> > miimize weight.
>
> No, most of the cost and complexity comes from the need to maintain
control
> while reliably transitioning large rotating masses through an unstable
part
> of the envelope, for the very first time in any production a/c.
> Minimizing weight to maximize payload is a major factor in every a/c ever
built,
Agreed! The design mantra is;- "Add more lightness!"
Brian
Peter Skelton
<nla...@snet.net> wrote:
>
>--------------8A44CC9D3ED466E2DC9DB329
>Content-Type: text/plain; charset=us-ascii
>Content-Transfer-Encoding: 7bit
>
>The packaging of a tilt rotor is a touchy thing, and some of the ideas expressed
>here seem OK at first, but tend to cost weight or increase risk.
>
>Bury the engines in the fuselage: This would make the cross shaft continuously
>under full flight loads, so it would have to be more robust than the current
>design, which carries only half an engine's worth of power, and only when one
>engine is effectively off line.
Are you certain? The maximum is the loading when an engine fails
the other starts, these transients are much higher than the
ongoing load.
>Also, the engines would need a gearbox to turn
>the rotation 90 degrees if they were in the fuselage, adding weight, complexity
>and failure modes.
Reduction gearing is needed in any event. It's twenty-mumble
years since I participated in a gearbox design but, at that time,
a right angle reduction set-up was not remarkably more complex
than an straight-line one. The hellicopter manufacturers
preferred a straight drive, so that's what we did. (They also had
the option of mounting the engines to avoid a right angle
gearbox, but chose not to. They had good reason for both
choices.)
> Additionally, the mass of the engines at the wing tips adds
>a degree of torsional stability to the system, helping the designer tune the
>structure to avoid the flutter modes that were a great problem before the XV-15.
What do you mean by torsional stability?
>Eliminate he cross shafting: Wow, this would make synchronizing the engines a
>flight critical problem, because the rotor rpm will vary thrust greatly and
>easily swamp the rotor pitch control. The cross shaft is a great insurance
>policy to keep both rotors at exactly the same rpm. Also, (and maybe most
>importantly) the shafting keeps the machine under control if an engine fails.
Hellicopters with fore and aft engines do not have such shafting.
If the complexity introduced by the cross-shafting adds more
crashes than its presence eliminates, it is a bad idea.
____
Peter Skelton
Dr. George O. Bizzigotti
wrote:
>Another option would be to do without single engine capability.
Is that a realistic option for the Osprey, though? My (admittedly
hazy, so forgive me if this is a red herring) understanding is that it
cannot land as a conventional aircraft would because of the rotor
diameter, so it must tilt the rotors and land as would a helicopter.
Conventional flight on one engine is analogous to ordinary
twin-engined aircraft, but could a helicopter-like landing be
controlled with only one rotor turning?
Regards,
George
**********************************************************************
Dr. George O. Bizzigotti Telephone: (703) 610-2115
Mitretek Systems, Inc., MS Z313 Fax: (703) 610-1558
7525 Colshire Drive E-Mail: gbiz...@mitretek.org
McLean, VA 22102-7400
**********************************************************************
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Peter Skelton
<gbiz...@mitretek.org> wrote:
>On Wed, 11 Apr 2001 02:19:10 GMT, Skel...@home.com (Peter Skelton)
>wrote:
>
>>Another option would be to do without single engine capability.
>
>Is that a realistic option for the Osprey, though? My (admittedly
>hazy, so forgive me if this is a red herring) understanding is that it
>cannot land as a conventional aircraft would because of the rotor
>diameter, so it must tilt the rotors and land as would a helicopter.
>Conventional flight on one engine is analogous to ordinary
>twin-engined aircraft, but could a helicopter-like landing be
>controlled with only one rotor turning?
Turbine engines are very reliable. If the shafting introduces
more failures through crowding and weight than it prevents, it's
a bad idea. (If the plane is a bad idea once that's done, so be
it.)
____
Peter Skelton
Sean trost
Curious as to what you refer to as fore and aft engines. If you are referring to the
Chinook then you are mistaken on the cross shaft because althogh they have two main
rotors the engines that drive them are located on the rear pylon with a shaft driving
the forward rotor.
Please bear in mind that the V-22 was supposedly designed to suffer catastophic
failure induced by small bits of high velocity metal, or rocket propelled explosive.
Modern gas turbines are rather reliable nowadays but they still are not all that
robust when it comes to surviving ballistic damages. Or even trying to food process
the odd bird.
The point of the cross shaft is valid for the aircraft, (in my opinion)
all the best
Sean Trost
Peter Skelton
wrote:
>Peter,
>
>Curious as to what you refer to as fore and aft engines. If you are referring to the
>Chinook then you are mistaken on the cross shaft because althogh they have two main
>rotors the engines that drive them are located on the rear pylon with a shaft driving
>the forward rotor.
Yes
>Please bear in mind that the V-22 was supposedly designed to suffer catastophic
>failure induced by small bits of high velocity metal, or rocket propelled explosive.
>Modern gas turbines are rather reliable nowadays but they still are not all that
>robust when it comes to surviving ballistic damages.
What are the chances that the hydraulics will survive an engine
failure induced by ballistic damage?
Or even trying to food process
>the odd bird.
The PT-6 family (Viet Nam era) was pretty much FOD/bird etc.
proof. The twin pak could (often did) absorb the destruction of
one engine with continuous power flow from the gearbox (the
single gearbox saved a fair amount of weight, but not half of
course). I'd think there are more modern twin paks now, if not
I'm sure the nice folks at P&W would whip one up.
> The point of the cross shaft is valid for the aircraft, (in my opinion)
If the cross-shaft doesn't improve reliability (introduces more
failures than it eliminates) it's a bad idea. That leaves a plane
that can't survive an engine failure. If that's a bad idea (I
agree that it is) the aircraft is a bad idea. That idea is a
thinking exercise.
____
Peter Skelton
Ogden Johnson III
As a survivor of a couple externally induced turbine engine failures
in CH-46 aircraft, I can assure you that military rotor craft and
their turbine engines are exposed to unique hazards - people sometimes
shoot at you, or more importantly your engines - that similarly
engined civil aircraft aren't.
OJ III
[Frequent autorotation practice is your friend.]
Peter Skelton
The nacels are so crowded that resulting failures are common.
Enough time has gone by that I don't think whipping maintenance
people harder will fix things.
The only things I can think of that can be removed are the
engines and the cross-shafting. Removing the engines means a new
plane design.
If the cross-shafting is essential (I'm inclined to believe it,
having seen a lot of supporting documentation), crowding in the
nacels can't be reduced appreciably. Where does that leave us?
____
Peter Skelton
Paul Baechler
> Hellicopters with fore and aft engines do not have such shafting.
> If the complexity introduced by the cross-shafting adds more
> crashes than its presence eliminates, it is a bad idea.
Fore and aft engines? Cuold you cite an example?
--
Paul Baechler
pbae...@bellsouth.net
Sean trost
Peter Skelton wrote:
> On Wed, 11 Apr 2001 13:45:09 GMT, Sean trost <str...@nc.rr.com>
> wrote:
>
>
> "What are the chances that the hydraulics will survive an engine
> failure induced by ballistic damage?"
Dont know, but as most hyd. pumps are driven off of the accesory gearbox of an engine I
would have to say that chance is pretty high. (helicopter notwithstanding, as i think that
hyd. power is derived from the main rotor trans. as long as the rotor turns at least
partial hyd power is available) That is A. why twin engines(redundancy on hyd. failure due
to two engines. assuming that there are two pumps) B. why spread out on the tip of the
wing.(to minimize the effects of combat damage) C. the cross shaft synchronizes the
prorotor and provides a means for limited flight due to loss of one engine.
as for packing the nacell full of stuff. why not enlarge the nacell ?. the housing I
believe is not a structural member, and composit so ergo redesign it to provide more
space.
>
> The PT-6 family (Viet Nam era) was pretty much FOD/bird etc.
> proof
Huh ?, Im from Missouri "show me". I am assuming that due to air intake designs that all
that the Fod/bird parts were filtered out ? Have not heard of a tubine that is Fod
tolerent. let alone fod proof. could be wrong tho.
>
>
>
>
> If the cross-shaft doesn't improve reliability (introduces more
> failures than it eliminates) it's a bad idea. That leaves a plane
> that can't survive an engine failure. If that's a bad idea (I
> agree that it is) the aircraft is a bad idea. That idea is a
> thinking exercise.
>
With limited data on hand yup you could argue that. But the first raid performed by the
V-22 in which multiple aircraft come back home on one engine would blow that theory out of
the water.
Okay, Im not convinced that the V-22 is the best solution to a complex problem. Im not
even sure I like it, however it is a solution that does seem to have a possibility of
success and a possibility of being implemented. Good thoughts all. inovation and success
dont come in a vaccum.
Sean Trost
Peter Skelton
wrote:
>
>
>Peter Skelton wrote:
>>
>> The PT-6 family (Viet Nam era) was pretty much FOD/bird etc.
>> proof
>
>Huh ?, Im from Missouri "show me". I am assuming that due to air intake designs that all
>that the Fod/bird parts were filtered out ? Have not heard of a tubine that is Fod
>tolerent. let alone fod proof. could be wrong tho.
>
It is a reverse plenum design, air in at the rear, out at the
front of the combustion chamber. Naturally the air inlet was at
the front of the engine, so there was a duct to take the air to
the rear. Solids tended to go to the outside and get trapped at a
corner (I hope this is understandable.) If not there are pictures
on pratt-whitney.com - look for PT-6A. (The cobra engine is the
PT6T/T400, I think, the numbers have changed.) Its a good engine,
the agricultural version has a TBO of 3000 hr. in crop-dusting
service.
PT6 seies engines are easily recognized on the wing by exhausts
near the front, usually on top. The design originated with a
desire to replace radials in center applications.
>> If the cross-shaft doesn't improve reliability (introduces more
>> failures than it eliminates) it's a bad idea. That leaves a plane
>> that can't survive an engine failure. If that's a bad idea (I
>> agree that it is) the aircraft is a bad idea. That idea is a
>> thinking exercise.
>>
>
>With limited data on hand yup you could argue that. But the first raid performed by the
>V-22 in which multiple aircraft come back home on one engine would blow that theory out of
>the water.
You did not understand. If the damn thing can't fly reliably with
the nacels so croiwded and the crowding in the nacels can't be
reduced it's no GD good to anybody. Shitcan the f*er now, we have
an adequate collection of bodybags.
>
>Okay, Im not convinced that the V-22 is the best solution to a complex problem. Im not
>even sure I like it, however it is a solution that does seem to have a possibility of
>success and a possibility of being implemented. Good thoughts all. inovation and success
>dont come in a vaccum.
>
>
>Sean Trost
>
____
Peter Skelton
Sean trost
With ya on the the overcrowding of the nacels too. Shitcan or redesign is now the question. And
yes to keep flying after aircrew have died by the book is not a solution.
All the best
Sean Trost
George William Herbert
>>>Another option would be to do without single engine capability.
>>
>>Is that a realistic option for the Osprey, though? My (admittedly
>>hazy, so forgive me if this is a red herring) understanding is that it
>>cannot land as a conventional aircraft would because of the rotor
>>diameter, so it must tilt the rotors and land as would a helicopter.
>>Conventional flight on one engine is analogous to ordinary
>>twin-engined aircraft, but could a helicopter-like landing be
>>controlled with only one rotor turning?
>
>Turbine engines are very reliable. If the shafting introduces
>more failures through crowding and weight than it prevents, it's
>a bad idea. (If the plane is a bad idea once that's done, so be
>it.)
Turbine engines, and in particular their gearboxes,
aren't *that* reliable. My father in law had an "exciting"
combat autorotation in a Huey once, and of the rotary wing
pilots who fly single engine birds that I know probably a
quarter have had to autorotate at some point.
With a Osprey, if you don't link the two engines/props,
then every single engine failure during takeoff or approach
conditions becomes an aircraft loss of control crash with
likely full fatalities. I don't think that's considered
adequately safe flight conditions.
-george william herbert
gher...@retro.com
George William Herbert
>"Hang Fier" <Hf...@hotmail.com> wrote:
>> The engines have to be as far away from the fuselage as possible to allow
>> the largest rotor diameter possible.
>
>Given current tilt-rotor design, the only things that have to be on the
>ends of the wings are the prop/rotors and 90-degree gearboxes to drive
>them. The engines could be located anywhere along the connecting shaft, or
>anywhere that engine drive shafts could feed gearboxes located along that
>shaft. There is no design requirement that mandates the engines be located
>as far from the fuselage as possible.
The advantage of not continuously driving via a crossshaft is
that the shaft as is doesn't need to be design rated to a large
lifetime. It's only used with serious torque applied in
emergencies; if its design lifetime is as low as a couple of
hours, it will fulfil its necessary emergency role. Its weight
was a critical item, and its construction is in fact relatively
limited in lifetime as a result if I recall the details
properly.
-george william herbert
gher...@retro.com
Nick Lappos
>> (If you) Bury the engines in the fuselage: This would make the cross shaft
> continuously
>>under full flight loads, so it would have to be more robust than the current
>>design, which carries only half an engine's worth of power, and only when one
>>engine is effectively off line.
>
>Are you certain? The maximum is the loading when an engine fails
>the other starts, these transients are much higher than the
>ongoing load.
>
Nick sez:
Yes I am certian. The torque on the shaft on a V-22 is only that needed to
drive a rotor with half the engine's power, since the single engine would have
to drive both rotors. If the engine were in the fuselage, the shaft to its
rotor would have to carry all the engine power to its rotor. Start-up torque
is usually less than half of full engine power in most cases.
Peter said:
>Reduction gearing is needed in any event. It's twenty-mumble
>years since I participated in a gearbox design but, at that time,
>a right angle reduction set-up was not remarkably more complex
>than an straight-line one. The hellicopter manufacturers
>preferred a straight drive, so that's what we did. (They also had
>the option of mounting the engines to avoid a right angle
>gearbox, but chose not to. They had good reason for both
>choices.)
Nick sez:
Nope! If there were fuselage engines on a tilt rotor, there would need to be
two extra gearboxes to connect the engines to the shaft, in addition to the
gearboxes at the rotor. Only if the engines were sideways, and the rotor
drive shafts were connected directly to drive outputs would there be a
possibility of eliminating the extra gearboxes, but the packaging of the
engines side by side, within spitting distance of the wing spar and with
turned inlets and exhausts, would be a nightmare.
Nick said:
>> Additionally, the mass of the engines at the wing tips adds
>>a degree of torsional stability to the system, helping the designer tune the
>>structure to avoid the flutter modes that were a great problem before the
> XV-15.
Peter asked:
>What do you mean by torsional stability?
Nick sez:
The big design challange in a tilt rotor is the ability of the rotor to bend
the wing and start a high frequency flutter where the wing pumps the rotor and
the rotor pumps the wing, a flutter effect that caused the crash of the XV-3
tilt rotor back 30-40 years ago. This is well supressed in the latest tilt
rotors by using advanced math and computers to help separate the natural
frequencies, and also by stiffening up the wing and making the rotor controls
unable to pump the wing at the critical frequencies. The designer is not free
to use any combination of wing chord, depth and span based purely on
aerodynamics, he must carefully work the wing stiffness to keep its natural
frequencies in a narrow slot of acceptable properties. This was well done in
the XV-15 and the V-22.
Peter said:
>Hellicopters with fore and aft engines do not have such (cross) shafting.
>If the complexity introduced by the cross-shafting adds more
>crashes than its presence eliminates, it is a bad idea.
Nick sez:
The packaging of multi engine helos is done so that all engines feed the main
gearbox directly, eliminating the need for cross shafting. The tilt rotor
needs cross shafts as long as its engines are at the wing tips.
Peter, were you a PT-6 designer? Good work, that is one reliable engine!
Nick
Matt Clonfero
Sharrock <bria...@pavilion.co.uk> wrote:
>Agreed! The design mantra is;- "Add more lightness!"
The full quote was "Simplicate and add lightness."
Aetherem Vincere
Matt
--
To err is human
To forgive is not
Air Force Policy
Peter Skelton
William Herbert) wrote:
>Peter Skelton <Skel...@home.com> wrote:
>>>>Another option would be to do without single engine capability.
>>>
>>>Is that a realistic option for the Osprey, though? My (admittedly
>>>hazy, so forgive me if this is a red herring) understanding is that it
>>>cannot land as a conventional aircraft would because of the rotor
>>>diameter, so it must tilt the rotors and land as would a helicopter.
>>>Conventional flight on one engine is analogous to ordinary
>>>twin-engined aircraft, but could a helicopter-like landing be
>>>controlled with only one rotor turning?
>>
>>Turbine engines are very reliable. If the shafting introduces
>>more failures through crowding and weight than it prevents, it's
>>a bad idea. (If the plane is a bad idea once that's done, so be
>>it.)
>
>Turbine engines, and in particular their gearboxes,
>aren't *that* reliable. My father in law had an "exciting"
>combat autorotation in a Huey once, and of the rotary wing
>pilots who fly single engine birds that I know probably a
>quarter have had to autorotate at some point.
(TBOs are over 3000 hrs these days. MTBF is *much* higher.)
>With a Osprey, if you don't link the two engines/props,
>then every single engine failure during takeoff or approach
>conditions becomes an aircraft loss of control crash with
>likely full fatalities. I don't think that's considered
>adequately safe flight conditions.
FIne. Now think it through. There have been a number of failures
and near failures that seem to be caused by excessive crowding in
the nacels. The number seems grossly larger than an expected
number for engine failures. If removing the cross-shafting
reduces crowding enough, it makes the plane safer.
What you're saying is that the thing is too dangerous to fly and
that you have no clue how to make it safe enough.
____
Peter Skelton
Peter Skelton
William Herbert) wrote:
The amount you can take out of a well designed twin gearbox
(compared to two geraboxes) probaably excedes the weight of the
shaft.
____
Peter Skelton
Peter Skelton
Lappos) wrote:
>Nick said:
>>> (If you) Bury the engines in the fuselage: This would make the cross shaft
>> continuously
>>>under full flight loads, so it would have to be more robust than the current
>>>design, which carries only half an engine's worth of power, and only when one
>>>engine is effectively off line.
>>
>Peter asks:
>>Are you certain? The maximum is the loading when an engine fails
>>the other starts, these transients are much higher than the
>>ongoing load.
>>
>
>Nick sez:
>Yes I am certian. The torque on the shaft on a V-22 is only that needed to
>drive a rotor with half the engine's power, since the single engine would have
>to drive both rotors. If the engine were in the fuselage, the shaft to its
>rotor would have to carry all the engine power to its rotor. Start-up torque
>is usually less than half of full engine power in most cases.
You're thinking of start-up from stopped. Think about the
transient when bot engines are running and one suddenly stops.
>Peter said:
>>Reduction gearing is needed in any event. It's twenty-mumble
>>years since I participated in a gearbox design but, at that time,
>>a right angle reduction set-up was not remarkably more complex
>>than an straight-line one. The hellicopter manufacturers
>>preferred a straight drive, so that's what we did. (They also had
>>the option of mounting the engines to avoid a right angle
>>gearbox, but chose not to. They had good reason for both
>>choices.)
>
>Nick sez:
>Nope! If there were fuselage engines on a tilt rotor, there would need to be
>two extra gearboxes to connect the engines to the shaft, in addition to the
>gearboxes at the rotor. Only if the engines were sideways, and the rotor
>drive shafts were connected directly to drive outputs would there be a
>possibility of eliminating the extra gearboxes, but the packaging of the
>engines side by side, within spitting distance of the wing spar and with
>turned inlets and exhausts, would be a nightmare.
Now there is a gearbox on each engine, and two right angle
connectors for the shaft.
If the engines were moved, why would there be gearboxes at the
rotor? There's a common, but larger gearbox on a twinpak. It
replaces both rotor gearboxes. Then you need the two right-angle
connections which have to be for continuous duty at full load, so
they'll gai weight. Depending on how the engines are mounted
there may or may not have to be a right angle at the engines. (If
the application warrants custom design, this one won't cost
weight if it can be integrated into the TP box.)
>
>Peter, were you a PT-6 designer? Good work, that is one reliable engine!
>
No, i did some statistics for them. Yes it is, failure work leads
one to a thorough appreciation of thin data.
____
Peter Skelton
Brian Sharrock
"Matt Clonfero" <Matt@[127.0.0.1]> wrote in message
news:$dC6DFAC...@ntlworld.com...
> In article <zpTA6.79993$BA3.9...@monolith.news.easynet.net>, Brian
> Sharrock <bria...@pavilion.co.uk> wrote:
>
> >Agreed! The design mantra is;- "Add more lightness!"
>
> The full quote was "Simplicate and add lightness."
>
"If at first you don't succeed, use a bigger hammer!"
Brian
Guy Alcala
> The packaging of a tilt rotor is a touchy thing, and some of the ideas
> expressed here seem OK at first, but tend to cost weight or increase
> risk.
<snip>
> Make the rotors extend past the nose so they can be larger: The
> balance of the vehicle makes this very hard to do, mostly because
> typical CG ranges make the principle payload want to be at the 1/4
> chord of the wing, and there must be room for the cockpit. Also,
> there are strong reasons to make the rotor small because when it is a
> prop this keeps the dysymetry forces smaller at high speed (note the
> thickness of the prop roots on a prop fighter).
I figured Cg might be a problem, aside from height limitations, but
thought I'd throw it out as a possiblity, especially given FBW and
artificial stability. OTOH, it wouldn't be the first time an a/c had
wing mounted props further forward then the cockpit. The DH Sea Hornet
is one, and there are a few others, so it is doable.
> Make the rotors much bigger if there is no shipboard deck spotting
> requirement: The rotors cannot grow much bigger without seriously
> affecting the structural stability of the whole system. As the rotor
> grows, the wing must be even stiffer to keep the dynamic vibrations of
> the rotor and wing under control. As the system gets bigger, the
> natural frequency gets much lower, and the modes become more difficult
> to control. The large envelope of the V-22 is a real credit to the
> Boeing and Bell dynamicists who identify the vibrations and tune the
> structure and flight controls to make it all work. These dynamic
> modes are believed to be the reason why the enormous Russian V-12 was
> unsucessful. In the end, for a given sizing, a helicopter will have
> about 2.5 times the rotor area as a tilt rotor, and thus will lift
> about twice as much payload.
Don't disagree with any of this, although Bell or Boeing designers
(forget which) did say that ideally (i.e. if the LHA requirement hadn't
been there), they would have boosted the wing span/rotor diameter about
4-5 feet. Unfortunately I can't remember where I read this, so I can't
give a cite.
> Note that the Bell 609 has two engines that produce about 2200 Horse
> Power at peak rating for a gross weight of 15,000 pounds. The Black
> Hawk uses engines with that power to fly at 22,000 pounds. The
> difference is the trade off price of a tilt rotor. Of course, the
> speed advantage is almost the reverse, and that's why we have horse
> races!
Yup! And we try not to use race horses to pull plows, or plow horses to
race, but use each for the job they're best suited for.
Guy
Guy Alcala
> The packaging of a tilt rotor is a touchy thing, and some of the ideas
> expressed here seem OK at first, but tend to cost weight or increase
> risk.
>
> Bury the engines in the fuselage: This would make the cross shaft
> continuously under full flight loads, so it would have to be more
> robust than the current design, which carries only half an engine's
> worth of power, and only when one engine is effectively off line.
> Also, the engines would need a gearbox to turn the rotation 90 degrees
> if they were in the fuselage, adding weight, complexity and failure
> modes. Additionally, the mass of the engines at the wing tips adds a
> degree of torsional stability to the system, helping the designer tune
> the structure to avoid the flutter modes that were a great problem
> before the XV-15.
The other reason the engines weren't buried in the fuselage or closer
together on the wings was apparently to limit combat damage from engine
fires or a Golden BB taking out both at the same time.
Which reminds me, in the same AvLeak issue which had some articles on
the S-92 (including numerous comments from the S-92 Program Manager, who
shall remain nameless;-) ), there was an article about a Euro-consortium
that was gearing up to design a tilt-wing to compete with commercial
tilt-rotors. As described, their tilt-wing would have a fixed wing
center section, with an engine mounted on each side at the inboard end
of the tilting section, with drive shafts from there to the rotors at
the tips. IIRR, among the claims made in this article for the tilt-wing
as opposed to the tiltrotor was that this configuration was lighter, and
that it had much better transition to descent characteristics.
Now, it seems to me that Boeing and other manufacturers have stuck
engines well O/B along the span to improve span loading and thus lighten
them, so I don't understand the first claim at all. In the case of the
second claim, I'm not sure if they're referring to the fact that they
plan to use 4 bladed rotors and a stalky undercarriage that allows a
larger rotor diameter, or if there's some specific benefit to a
tilt-wing that I'm missing. Rotating a wing so that it's vertical to
the relative wind would certainly act as a huge airbrake, but I can't
see that it would be much good in helo mode if you had to move forward
or backward any distance. Since tilt-wings and tilt-rotors were tested
side-by-side way back when, with the tilt-rotor being selected as the
best compromise, I don't know what if anything has changed in the
intervening years. Can anyone (Nick?) shed any light?
Guy
James Bell
html/search-bool.html&r=1&f=G&l=50&co1=AND&d=pall&s1='grumman+698'&OS="grumm
an+698"&RS="grumman+698"
Guy Alcala <g_al...@postoffice.pacbell.net> wrote in message
news:3AD62256...@postoffice.pacbell.net...
Matt Clonfero
Sharrock <bria...@pavilion.co.uk> wrote:
>
>"Matt Clonfero" <Matt@[127.0.0.1]> wrote in message
>news:$dC6DFAC...@ntlworld.com...
>> In article <zpTA6.79993$BA3.9...@monolith.news.easynet.net>, Brian
>> Sharrock <bria...@pavilion.co.uk> wrote:
>>
>> >Agreed! The design mantra is;- "Add more lightness!"
>>
>> The full quote was "Simplicate and add lightness."
>>
>Matt, You had your teacher ... I had mine! :)
The `simplicate' quote was from the designer of the A-4 Skyhawk
(Heinman, IIRC).
>"If at first you don't succeed, use a bigger hammer!"
Clankies. I'm beset by clankies :>
Yak
"Matt Clonfero" <Matt@[127.0.0.1]> wrote in message
If it doesn't fit,force it. If it breaks it didn't fit anyway.
Jim
Nick Lappos
>> The torque on the shaft on a V-22 is only that needed to
>>drive a rotor with half the engine's power, since the single engine would have
>
>>to drive both rotors. If the engine were in the fuselage, the shaft to its
>>rotor would have to carry all the engine power to its rotor. Start-up torque
>>is usually less than half of full engine power in most cases.
Peter said:
>You're thinking of start-up from stopped. Think about the
>transient when bot engines are running and one suddenly stops.
>
Nick replied:
Nope! The torque spike when both are running and one engine quits is about
130% of one engine's torque, which is 65% of twin torque, much less than a
normal two engine takeoff, which is 200% of one engine's torque.
>>Nick said:
>>Nope! If there were fuselage engines on a tilt rotor, there would need to be
>>two extra gearboxes to connect the engines to the shaft, in addition to the
>>gearboxes at the rotor. Only if the engines were sideways, and the rotor
>>drive shafts were connected directly to drive outputs would there be a
>>possibility of eliminating the extra gearboxes, but the packaging of the
>>engines side by side, within spitting distance of the wing spar and with
>>turned inlets and exhausts, would be a nightmare.
Peter said:
>Now there is a gearbox on each engine, and two right angle
>connectors for the shaft.
Nick replied:
Whoa! In the V-22, there is a gearbox at the engine output to make the 6000
rpm of the engine match the 350 (approx) of the rotor. If you put the engine
in the fuselage, you have to turn the drive output 90 degrees (that's one
gearbox so far) and then turn and reduce the rpm at the wing tip (that's now
two gearboxes for each engine). Also, as another reader has said, the shaft
and the two gearboxes will see much more time at much higher torque, so
they (and the shaft hangar bearings) will need to be much more heavy and
robust.
Nick asked:
>>Peter, were you a PT-6 designer? Good work, that is one reliable engine!
>>
Peter said:
>No, i did some statistics for them. Yes it is, failure work leads
>one to a thorough appreciation of thin data.
Nick replied:
I had an engine failure in a PT-6 in an S-58T and the team that came from
Pratt Canada didn't know what to ask me, since they'd never investigated an
engine failure before!
Nick
Nick Lappos
>> Make the rotors much bigger if there is no shipboard deck spotting
>> requirement: The rotors cannot grow much bigger without seriously
>> affecting the structural stability of the whole system. As the rotor
>> grows, the wing must be even stiffer to keep the dynamic vibrations of
>> the rotor and wing under control. As the system gets bigger, the
>> natural frequency gets much lower, and the modes become more difficult
>> to control. The large envelope of the V-22 is a real credit to the
>> Boeing and Bell dynamicists who identify the vibrations and tune the
>> structure and flight controls to make it all work. These dynamic
>> modes are believed to be the reason why the enormous Russian V-12 was
>> unsucessful. In the end, for a given sizing, a helicopter will have
>> about 2.5 times the rotor area as a tilt rotor, and thus will lift
>> about twice as much payload.
Guy responded:
>Don't disagree with any of this, although Bell or Boeing designers
>(forget which) did say that ideally (i.e. if the LHA requirement hadn't
>been there), they would have boosted the wing span/rotor diameter about
>4-5 feet. Unfortunately I can't remember where I read this, so I can't
>give a cite.
Nick replies:
Yep, but that 4 to 5 feet doesn't do much. The disk loading of the V-22 is
now 22 pounds per square foot at 50,000 pounds. An S-76 or Bell 412 is about
7 pounds per square foot. If you add 5 feet to the diameter of a V-22, and do
not raise the gross weight, the disk loading would still be 17 pounds per sq
ft. My guess is that the extra wing and rotor weight would be quite
appreciable, as would the extra drag because there is even more flat wing
exposed to the downwash. For that you also get an air vehicle that is 98 feet
across, tip to tip. About like the Wright Brother's first flight, all for
20,000 pounds of payload. For half the gross weight, half the horsepower and
1/4 the cost, you could get a helo to do that!
Guy said:
>Yup! And we try not to use race horses to pull plows, or plow horses to
>race, but use each for the job they're best suited for.
>
Nick responded:
And we don't use horses tp pull things anymore because they are simply too
expensive for the job!!! Sound familiar?
Nick
Peter Skelton
Lappos) wrote:
>Nick said:
>>> The torque on the shaft on a V-22 is only that needed to
>>>drive a rotor with half the engine's power, since the single engine would have
>>
>>>to drive both rotors. If the engine were in the fuselage, the shaft to its
>>>rotor would have to carry all the engine power to its rotor. Start-up torque
>>>is usually less than half of full engine power in most cases.
>
>Peter said:
>>You're thinking of start-up from stopped. Think about the
>>transient when bot engines are running and one suddenly stops.
>>
>Nick replied:
>
>Nope! The torque spike when both are running and one engine quits is about
>130% of one engine's torque, which is 65% of twin torque, much less than a
>normal two engine takeoff, which is 200% of one engine's torque.
130% of one engine's torque is 130% of what it takes to drive a
propellor. The engies are between the propellors, the shafting
only needs to carry the torque for one. (Incidentally your 130%
is ludicrously understated, IIRC a GT can operate at 150% rated
for several seconds to a couple of minutes, depending.)
>
>>>Nick said:
>>>Nope! If there were fuselage engines on a tilt rotor, there would need to be
>>>two extra gearboxes to connect the engines to the shaft, in addition to the
>>>gearboxes at the rotor. Only if the engines were sideways, and the rotor
>>>drive shafts were connected directly to drive outputs would there be a
>>>possibility of eliminating the extra gearboxes, but the packaging of the
>>>engines side by side, within spitting distance of the wing spar and with
>>>turned inlets and exhausts, would be a nightmare.
>
>Peter said:
>>Now there is a gearbox on each engine, and two right angle
>>connectors for the shaft.
>
>Nick replied:
>
>Whoa! In the V-22, there is a gearbox at the engine output to make the 6000
>rpm of the engine match the 350 (approx) of the rotor. If you put the engine
>in the fuselage, you have to turn the drive output 90 degrees (that's one
>gearbox so far) and then turn and reduce the rpm at the wing tip (that's now
>two gearboxes for each engine). Also, as another reader has said, the shaft
>and the two gearboxes will see much more time at much higher torque, so
>they (and the shaft hangar bearings) will need to be much more heavy and
>robust.
Why would you reduce the speed at the wingtip? Why have separate
right angle gearboxes at the engine? (the two combine nicely) Why
snip what I wrote on the subject without understanding it? I've
already answered the points you raise here.
>
>Nick asked:
>>>Peter, were you a PT-6 designer? Good work, that is one reliable engine!
>>>
>Peter said:
>>No, i did some statistics for them. Yes it is, failure work leads
>>one to a thorough appreciation of thin data.
>
>Nick replied:
>
>I had an engine failure in a PT-6 in an S-58T and the team that came from
>Pratt Canada didn't know what to ask me, since they'd never investigated an
>engine failure before!
I was working through Viet Nam experience. ISTR mostly things
like something cracked a housing and the oil fell out.
____
Peter Skelton
Guy Alcala
Yes, and the CH-53E is at about 14.9 @ 73,000. So the question is, at what point
does it become too high for whatever job it is you have to do.
> My guess is that the extra wing and rotor weight would be quite
> appreciable, as would the extra drag because there is even more flat wing
> exposed to the downwash.
Ah, but with no requirement to fit on a carrier, there's no need to stow the wing
either (I'll leave the power-blade fold on, although a commercial a/c wouldn't
need that), and that's a lot of weight and cost. Going to four blades might also
improve things considerably, and I wonder why they chose not to (too much weight?
difficult to fold?). And it also assumes that the aspect ratio would remain
unchanged, just increasing the area; that's ne approach, but they might instead
chose to leave the area alone and instead just increase the aspect ratio,
improving cruise efficiency and possibly decreasing the area exposed to downwash
(or at least keeping it the same).
> For that you also get an air vehicle that is 98 feet
> across, tip to tip.
Yes, 98 feet wide and 57 feet long, for a total box of 5,586 sq. ft.. The CH-53
is 99 feet 1 inch long, and 79 feet wide (tip to tip), for a total box of 7,827
sq. ft. The CH-53D is 88 ft. 3 in. long by 72 ft. 3 in. wide, for a total box of
6,376 sq. ft., and the same 20,000 lb. payload. It's certainly cheaper for that
20,000 lb. payload, but we know that it can only carry a 6,000-6,600 lb. payload
to a 50nm combat radius, while the V-22 can carry 10,000 lb. that far (see the
DOT&E report). Of course, we can assume a modern composite helo of the same
payload would do better, but there will always come a range at which the
tiltrotor's better cruise efficiency will win out.
> About like the Wright Brother's first flight, all for
> 20,000 pounds of payload. For half the gross weight, half the horsepower and
> 1/4 the cost, you could get a helo to do that!
Ah, but if you've got a more efficient rotor for vertical lift, then you can also
use a less powerful (and lighter) engine, can't you? And you can't get a helo to
do any of it as fast, for any price. And if there's a ground run available, then
the payload climbs much faster than a helo's does, and the longer the range the
more advantage that a tiltrotor has (because the slope of a helo's payload/range
line is much steeper than a tilt-rotor/tilt-wing).
> Guy said:
> >Yup! And we try not to use race horses to pull plows, or plow horses to
> >race, but use each for the job they're best suited for.
> >
> Nick responded:
> And we don't use horses tp pull things anymore because they are simply too
> expensive for the job!!! Sound familiar?
Actually, depends how you cost it. The main problem isn't necessarily that
they're too expensive, but that they're too slow. I come equipped with a pair of
feet, and the only fuel they require is food. But it's a fairly slow way to
travel, isn't it, and as the distance I need to go lengthens, I'm willing to spend
more to get there faster. A horse or bicycle is more expensive, but faster, and
engine-powered vehicles are more expensive and faster still. And there are places
where horses are still used, because they're the most suitable for the job.
Guy
Nick Lappos
>130% of one engine's torque is 130% of what it takes to drive a
>propellor. The engies are between the propellors, the shafting
>only needs to carry the torque for one. (Incidentally your 130%
>is ludicrously understated, IIRC a GT can operate at 150% rated
>for several seconds to a couple of minutes, depending.)
>
I'll try one more time, Peter: We are comparing the two possible shaft
designs, one where the engine is at the rotor wing tip and the cross shaft
goes from it to the other wingtip (call that the V-22 case) and the other,
postulated by you is where the engines are in the fuselage, and the shafts run
from them to each rotor (call that the Other case). Let's agree that the max
torque of one engine in a failure of the other engine might go to 150% torque
(I have tested helicopters for 25 years, and this is achievable, but extreme,
and less likely with limiters, but it is our number).
In the V-22 type system, the 150 torque is divided between TWO rotors, so the
shaft to the other rotor carries roughly half the total torque, or a maximum
of 75%. Half of the engine's torque goes to the rotor directly connected to
the engine, of course. In the Other case, on every normal takeoff, the shaft
to each engine must carry all the rotor's torque, about 100%. The other rotor
is also consumnig 100% torque. Thur, in a normal takeoff, the Other system's
shafts must carry more torque than the V-22's shaft in the worst case.
Peter asked:
>Why would you reduce the speed at the wingtip? Why have separate
>right angle gearboxes at the engine? (the two combine nicely) Why
>snip what I wrote on the subject without understanding it? I've
>already answered the points you raise here.
Nick replied:
Sorry if you don't like my snipping, done for space and clarity, not to hide
your points. I really don't like the threads that get to hundreds of lines as
everyone just adds on. Maybe I got carried away, but my motives were pure.
I give up trying to describe the what ifs and wherefores, Peter, its not all
that important, it is confusing, and there are many ways to design the system!
Nick
Peter Skelton
Lappos) wrote:
>Peter said:
>>130% of one engine's torque is 130% of what it takes to drive a
>>propellor. The engies are between the propellors, the shafting
>>only needs to carry the torque for one. (Incidentally your 130%
>>is ludicrously understated, IIRC a GT can operate at 150% rated
>>for several seconds to a couple of minutes, depending.)
>>
>Nick sez:
>
>I'll try one more time, Peter: We are comparing the two possible shaft
>designs, one where the engine is at the rotor wing tip and the cross shaft
>goes from it to the other wingtip (call that the V-22 case) and the other,
>postulated by you is where the engines are in the fuselage, and the shafts run
>from them to each rotor (call that the Other case). Let's agree that the max
>torque of one engine in a failure of the other engine might go to 150% torque
>(I have tested helicopters for 25 years, and this is achievable, but extreme,
>and less likely with limiters, but it is our number).
>
>In the V-22 type system, the 150 torque is divided between TWO rotors, so the
>shaft to the other rotor carries roughly half the total torque, or a maximum
>of 75%. Half of the engine's torque goes to the rotor directly connected to
>the engine, of course. In the Other case, on every normal takeoff, the shaft
>to each engine must carry all the rotor's torque, about 100%. The other rotor
>is also consumnig 100% torque. Thur, in a normal takeoff, the Other system's
>shafts must carry more torque than the V-22's shaft in the worst case.
Now you've got it. Next, the strength of a shaft increases with
the square of its weight (a bit faster in reality). We are not
talking big differences here.
>Peter asked:
>>Why would you reduce the speed at the wingtip? Why have separate
>>right angle gearboxes at the engine? (the two combine nicely) Why
>>snip what I wrote on the subject without understanding it? I've
>>already answered the points you raise here.
>
>
>Nick replied:
>
>Sorry if you don't like my snipping, done for space and clarity, not to hide
>your points. I really don't like the threads that get to hundreds of lines as
>everyone just adds on. Maybe I got carried away, but my motives were pure.
>I give up trying to describe the what ifs and wherefores, Peter, its not all
>that important, it is confusing, and there are many ways to design the system!
>
I don't like snips followed by text that reintroduces the
questions the snipped material covered. I know it was
inadvertent.
Yes there are many ways to d the design. None is clearly lighter
with the data we have.
____
Peter Skelton
Hans Conser
>
> Of course, that wasn't the issue in the case of the Titanic; she performed as she
> was designed to, actually somewhat better. The cause of the accident (as opposed to
> the cause of the sinking) was that they were going too fast for the prevailing
> visibility conditions, with lookout procedures and lack of equipment (binoculars,
> searchlight) that may have been contributing factors. It's true that going on at
> full speed in clear weather at night, even when ice was reported, was a
> long-standing and nearly universal practice at the time, but no one knew any better
> because the safety record had been impeccable prior to the accident, and even after
> it the accident and loss rate was still extremely low. It's just that, as when a
> jetliner crashes now, the number of deaths is concentrated in time and spectacular,
> even though the overall loss rate is infinitesimal. Anyway, the excess speed was a
> human decision, rather than a design or equipment problem.
Hmmm, I read in Popular Science a while back that there was a metalurgy problem with
the hull plates and they fractured rather than buckling. They tested some samples from
the wreck to arrive at this conclusion.
Hans Conser
vincent Brannigan
Hans Conser wrote:
TITANIC was actually a very complex mix of design, materials, human factors and other
problems. The similarity to the "system failure" of the V-22 is eerie. As just one
example the design of the TITANIC was that she was under ruddered for her visibility
distance at night. (sort of like the night vision glasses on the V-22) She could not turn
in her sighting distance and therefore was designed to hit any obstruction head on. Also,
similar to the vortex ring state, turning the Titanic by backing one engine also meant
shutting down the center turbine. this reduced the control forces on the rudder and
aggravated the turning problem. . The materials problem was the steel, which cracked
instead of bending. TITANIC only had a single hull for cost reasons. TITANIC was under
-tested, and the flaws in her and her sister's design were not uncovered before production.
There had been a preliminary accident, a collision between the OLYMPIC and an RN cruiser,
which if properly analyzed would have led to an understand of the steel plate problem. It
was not analyzed.
Im not saying the two cases are identical, but in both cases a complex new technology was
put into service with very little real understanding of the vulnerability to common
disaster scenarios.
vince
Guy Alcala
> Hans Conser wrote:
>
> > Guy Alcala wrote:
> >
> > >
> > > Of course, that wasn't the issue in the case of the Titanic; she performed as she
> > > was designed to, actually somewhat better. The cause of the accident (as opposed to
> > > the cause of the sinking) was that they were going too fast for the prevailing
> > > visibility conditions, with lookout procedures and lack of equipment (binoculars,
> > > searchlight) that may have been contributing factors. It's true that going on at
> > > full speed in clear weather at night, even when ice was reported, was a
> > > long-standing and nearly universal practice at the time, but no one knew any better
> > > because the safety record had been impeccable prior to the accident, and even after
> > > it the accident and loss rate was still extremely low. It's just that, as when a
> > > jetliner crashes now, the number of deaths is concentrated in time and spectacular,
> > > even though the overall loss rate is infinitesimal. Anyway, the excess speed was a
> > > human decision, rather than a design or equipment problem.
> >
> > Hmmm, I read in Popular Science a while back that there was a metalurgy problem with
> > the hull plates and they fractured rather than buckling. They tested some samples from
> > the wreck to arrive at this conclusion.
There is considerable controversy about whether this mattered or not, and FWIW I recommend
that you be very careful in getting scientific/technical information from any magazine with the
word "Popular" in the title;-) Here's another view of the metallurgical question, and you can
undoubtedly find others in technical journals.
-------------------------------------------------------------------------
The current myth of "inferior steel" evolved from pure hindsight. It is true that the steel
provided
to Harland & Wolff by Dalzell and D. Colvilles & Co. was produced in acid-lined open-hearth
furnaces, which allowed for impurities (such as sulfur and phosphorous) in the steel. These
impurities led to low fracture resistance, especially in cold water conditions that reduced
ductility (ability of the steel to deform without yielding), by reducing the amount of
manganese
present to bind to the residual sulfur. With insufficient manganese, the sulfur combined with
the
iron to form the ferrous sulfide, which created paths of weakness (especially along grain
boundaries) along which fractures could propagate. The manganese-sulfur ratio of Titanic's
steel
recovered from the wreck site has been determined to be 6.8:1, low in comparison to steels
produced today that have ratios as high as 200:1. The presence of phosphorous, even in minute
quantities, also played a significant role in the initiation of fractures.
However, most of steel used by British shipyards during this period was produced using the
open-hearth method; in fact, the metallurgy of the steel did not change significantly until
after
1947, when wartime experiences prompted closer examination of the elemental properties of
steel. At the time of her construction, Titanic's builders used top-quality steel that would
remain
the industry standard for years to come. The steel used in the R.M.S. Queen Mary, which
survives to this day, was produced by the same mill that provided steel for Titanic and is
essentially the same in composition. To accuse Titanic's builders of using "inferior steel" is
unfair, as it would be decades before the minor elements of steel would be more fully
understood.
------------------------------------------------------------------------
Whether the above matters or not depends on the nature of the damage she suffered. It seems
clear from the Inquiry that the ship didn't have a single gash torn in her, but rather several
small holes spaced along the hull (Edward Wilding from Harland & Wolff estimated that the total
area of the holes was only about 12 sq. ft.). Whether this was due to rivets fracturing and
opening seams, or just plates having holes punched in them, is still a matter of contention, as
it depends very much on the nature of the interaction of the hull, water, and iceberg. Even if
the hole punching theory is correct, there's no certainty that modern steels would have made
any difference. One scientist who has studied this wrote he was lucky enough to have the
cruise ship he was on in Alaska give him an unintentional demonstration of underwater iceberg
damage similar in impact to the Titanic's. The Captain was kind enough to have him rowed
around the ship, and he was also allowed to inspect it in the dry dock. Apparently, modern
steels can be holed just as easily by ice as the Titanic's plates were, because of the
mechanism involved (I don't remember the details, and didn't quite understand them in any
case).
> TITANIC was actually a very complex mix of design, materials, human factors and other
> problems. The similarity to the "system failure" of the V-22 is eerie. As just one
> example the design of the TITANIC was that she was under ruddered for her visibility
> distance at night.
> (sort of like the night vision glasses on the V-22) She could not turn
> in her sighting distance and therefore was designed to hit any obstruction head on.
That is entirely dependent on what the visibility distance is, and the speed. Saying a ship is
under-ruddered has to be qualified by stating the conditions. Are all the cars in a chain
reaction pile-up on I-5 "under-braked" and "under-steered" because, when traveling at 70 mph in
fog which reduces visibility to 50 yds or less, they can't stop/avoid the crashed cars in
front? Or is it rather the fault of the drivers, who are traveling too fast for the visibility
to possibly react in time to avoid an accident? She wasn't under-ruddered for her job, just
traveling at too high a speed to turn or stop before hitting an obstacle that was spotted at
too close a range. If she'd been traveling slower, she would have had time to back the
engine(s), stopping and/or turning out of the way. Titanic had steerage way at speeds as low
as 6 knots, quite good for a ship of her size and sail area, but was traveling at 22 knots or a
bit more, i.e. > 700 yds./min. Even then, with the iceberg sighted well within that distance,
she almost avoided it.
> Also,
> similar to the vortex ring state, turning the Titanic by backing one engine also meant
> shutting down the center turbine. this reduced the control forces on the rudder and
> aggravated the turning problem.
Irrelevant, since there was no time to reverse the engines before impact. If she'd been
traveling slower there would have been time. The only evidence that the engines were backed
before the impact was from an officer's testimony (either Boxhall or Lightoller, I forget
which), and the testimony from other sources in the engine/boiler rooms is overwhelming that
his memory is inaccurate on this point.
> . The materials problem was the steel, which cracked
> instead of bending. TITANIC only had a single hull for cost reasons.
As did other ships, for the same reason. She did have a double bottom, which was carried up
around the turn of the bilge for much of the ship. As a result of the accident, the Olympic
was given a double hull, as were many other ships (I don't know if it was made a regulation for
passenger ships or not). That _might_ protect her against this very specific accident
(although at least one puncture in the Titanic would have penetrated both. See Edward
Wilding's testimony), but not against the far more likely one, a collision with another ship,
which is what her subdivision was designed to protect against. It certainly wouldn't (or at
least, didn't) help the Andrea Doria any. For a discussion of the practical advantages and
disadvantages of double bottoms by Wilding, see
http://www.titanicinquiry.org/BOTInq/BritInq18Wilding4.htm
starting around question 20035. BTW, this is one of the wonders of the internet. A group of
dedicated volunteers transcribed the entire texts of both the American and British enquiries
(brit. spelling) so that they would be available to all. I recently spent my spare time for a
couple of weeks reading almost all of the British one, and selections from the American one.
For a good laugh, be sure to read the speech given by Senator Smith at the conclusion of the
Senate inquiry (it's the next to last item under Final Report). We may think that speeches by
politicians are nothing but hot air now, but we can't hold a candle to these guys when it comes
to purple prose. Here's a sample:
"We went to the side of the hospital ship with purpose and pity and saw the almost lifeless
survivors in
their garments of woe - joy and sorrow so intermingled that it was difficult to discern light
from shadow,
and the sad scene was only varied by the cry of reunited loved ones whose mutual grief was
written in the
language of creation."
There's lots more in that vein. Oddly enough, except for the speeches the report is quite
well done and made some excellent recommendations. The British report, thank goodness, doesn't
have any of this rhetoric.
> TITANIC was under
> -tested, and the flaws in her and her sister's design were not uncovered before production.
> There had been a preliminary accident, a collision between the OLYMPIC and an RN cruiser,
> which if properly analyzed would have led to an understand of the steel plate problem. It
> was not analyzed.
By that standard, every ship, in fact virtually every technological implement ever built, is
under tested. Precisely what flaws are you referring to? We've already disposed of the
"under-ruddered" silliness, the metallurgy was the standard for the time (indeed, IIRR it was
as only as a result of "Operation Rusty" in the late '40s that data was actually gathered
scientifically on the effects of cold water temps on various types of ship steel, rivetting and
welding. Cracks in rivetted ships were stopped sooner, BTW). The only possible "design flaw"
you've mentioned is that she didn't have a double hull, which might have helped with some of
the fairly gentle but widespread impact damage she suffered, but not in a more violent
collision. Even so, she floated for 2.5 hours, vs. the 1-1.5 hours that Andrews estimated
immediatley after the collision (of course, his calculations weren't made in the most leisurely
circumstances, so if he was wrong we won't hold it against him).
If you want to speak of serious design "flaws," then the longitudinal coal bunkers on the
Lusitania/Mauretania would be high on my list (and that of the Admiralty, which tried to ban
any of their cruisers which had them from submarine waters, but were unable to shift them in
time before the Aboukir, Hogue, and Cressy all capsized and sankquickly, from single torps
fired by the same sub as they steamed up in sequence to rescue the previous ship's company.
Lusitania herself rolled on her side and sank within 18 minutes after taking a single torpedo
(and the subsequent internal explosion, either coal dust or munitions). OTOH, Britannic
(Titanic's sister) stayed up for 55 minutes after suffering similar damage from a mine.
Indeed, in that particular instance it seems entirely possible that the double bottom/hull
caused more damage, due to shock effects; her keel was destroyed over about 60 feet.
> Im not saying the two cases are identical, but in both cases a complex new technology was
> put into service with very little real understanding of the vulnerability to common
> disaster scenarios.
Except that, certainly in the case of the Titanic, there was nothing 'common' about this
scenario at all. There had been, I think 1 collision by a passenger steamship with an iceberg
in the previous 70 years or so, and that happened in poor visibility. The Guion Line's
Arizona, 5,150 tons, just under 16 knots, was proceeding at full speed in misty weather on the
Grand Banks, about 5 months after she'd entered service in 1879, when she hit an iceberg head
on. Although the bow was crumpled, the collision bulkhead apparently held, and she was able to
make it into St. John's under her own power. Indeed, Wilding estimated that, if the helm
hadn't been put over and the Titanic had hit the berg head-on, althugh the first 100 feet or so
of the ship would have been crushed and many of the crew in the forecastle would have been
killed, the ship would probably have survived. Not that anyone suggested that it would be
reasonable to expect or require a ship's officer to deliberately collide instead of trying to
avoid it.
Guy