true speed of the P-51B
Trey Wells
Recently on another BBS, a discussion about the P-51b was started. someone
posted this "
"The printed maximum speed in all books for the NA P-51D Mustang is 437 mph
at 25,000 ft. Absolute nonsense. The fastest speed ever actually RECORDED
for a P-51 ocurred on 20 October 1944, over Henden RAF base, England.
Following RAF complaints that the P-51 would not reach the printed speeds,
no fewer than 12 Mustangs from various units--two right off the boat, as
well--were tested with USAAF pilots. Both theodolite units and radar were
used to measure the speed. The fastest run--I should mention after
innumerable flights occupying the whole day--
was 416 mph in a P-51B (s/n 36799 "Carolina Hustler"); this speed was
sustained only for 10 seconds before the engine became seriously
over-boosted. The longest sustained maximum speed recorded was 405 mph for
55 seconds by a brand new P-51D at 23,000 ft. (s/n 472484). Most of the
machines in this evaluation were incapable of exceeding 400 mph under any
conditions whatever. The NII VVS tested their P-51B (L-L, s/n 35145) to a
maximum of 392 mph at 25,500ft, and climb to 5000m of 6.5 mins. (yes, on 100
octane gas). I suspect that this was exactly correct, despite the fact that
all Wetserners try to explain it away. These two events are the ONLY
scientific evaluation of the Mustang by any non-Company (i.e. North
American) entity in the entire history of the aircraft. Both evaluations
prove that the Company was inflating their numbers for 'advertising'
reasons....".
The reference is unknown and the poster did not allude that this data was
valid. My question is, can any of you say to whether this data may or may
not be valid. I have read in past times that the P-51B had a top speed of
over 440 MPH true at altitude.
please advise.
Trey
Guy Alcala
Gruenhagen's book on the Mustang shows a max. level speed of 441 mph @ 30kft for
the P-51B with V-1650-3 (and probably no rear fuselage tank). I'd really want
to know what the atmospheric conditions were on the day in question, as all test
results are supposed to be normed to Standard atmosphere, and whether this was
done. The claim that "these two events are the ONLY scientific evaluation of
the Mustang by any non-Company entity in the entire history of the a/c" is
patently incorrect. For instance, there used to be a web link which had the
results of the speed and climb tests performed on the Mustang Mk. I (AG 351) at
Burtonwood by the RAF. Unfortunately that link's no longer active, but
Gruenhagen states that the a/c managed a top speed of 382 mph at its best
altitude of 14,000 feet (engine critical altitude of 11,300 ft.) during those
tests, reduced from the 390 achieved in company tests because the a/c had gotten
its camouflage paint as well as having other operational equipment added.
Elsewhere he lists the same speed at 13,700 feet, which may be the value
corrected to ISA. Either way the best speed altitudes were a hell of a lot
lower than the Merlin-powered models in high blower, which were also more
powerful. Higher altitude = thinner air = less form drag = higher speed, until
the power starts to fall off or mach effects (on the prop or airframe) become
significant.
The P-51A, with a more powerful engine (Allison V-1710-81 vice -39) is credited
by Gruenhagen with 409 mph at its best altitude of 10,000 feet, mainly because
the -81 has a War Emergency MP rating of 57"/3000 RPM at that altitude, vs. the
-39 engine's military rating of 44.2"/3000 RPM at 11,300 feet; the -81 can
maintain the 44.2"/3000 RPM up to about 17 or 18,000 feet (eyeballing the
graph). Again, both of these are well below the critical and best speed
altitudes of the Merlin models in high blower, as well as being down a couple of
hundred hp compared to the Merlin. The Merlin V-1650-3 engined models made
their best speed at 30kft (give or take a few hundred, allowing for the usual
variation), while the V-1650-7 models made theirs at 25,000 feet.
Guy
Peter Stickney
I've actually been working on this very issue. If yo can be a bit
patient, I'll have data (and the methods used, and sources) available
this weekend.
--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster
None
actual combat performance as well, you know, for 'advertising'.
Ismail Gernot Hassenpflug
collectors who insist on flying them at races and whatnot, as a kind
of in-joke.
"None" <no...@none.net> writes:
> Wow, I guess the Mustang must have sucked, huh? Probably 'inflated' it's
> actual combat performance as well, you know, for 'advertising'.
--
Gernot Hassenpflug MSc.(Eng.) Kyoto University Fax: +81 (0)774 31-8463
Radio Science Centre for Space and Atmospheres Tel: +81 (0)774 38-3868
京都大å¦å®™ç©ºé›»æ³¢ç§‘å¦ç ”究センター eMail: ger...@kurasc.kyoto-u.ac.jp
WebHomePage: http://www.kurasc.kyoto-u.ac.jp/radar-group/members/gernot
CellPhone: +81 (0)90 3703-7253 CellMail: gernot.ha...@ezweb.ne.jp
robert arndt
> Wow, I guess the Mustang must have sucked, huh? Probably 'inflated' it's
> actual combat performance as well, you know, for 'advertising'.
I always wondered about the claimed 440 mph too (must be the true
speed of a P-51D Mustang after ditching the drop tank, expending half
its ammo, and diving on German a/c taking off or landing)!
Rob
Guy Alcala
> In article <P4ag9.244396$eK6.6...@twister.austin.rr.com>,
> "Trey Wells" <JWE...@satx.rr.com> writes:
<much snippage>
>
> > The reference is unknown and the poster did not allude that this data was
> > valid. My question is, can any of you say to whether this data may or may
> > not be valid. I have read in past times that the P-51B had a top speed of
> > over 440 MPH true at altitude.
>
> I've actually been working on this very issue. If yo can be a bit
> patient, I'll have data (and the methods used, and sources) available
> this weekend.
Oh, good. I was hoping you'd run the numbers.
Guy
Trey Wells
"Peter Stickney" <p-sti...@adelphia.net> wrote in message
news:kbqrla...@Mineshaft.local.net...
Trey Wells
http://216.91.192.19/forums/showthread.php?s=&threadid=64200&perpage=50&page
number=1
"Trey Wells" <JWE...@satx.rr.com> wrote in message
news:P4ag9.244396$eK6.6...@twister.austin.rr.com...
Guy Alcala
> Reference the discussion here.
> http://216.91.192.19/forums/showthread.php?s=&threadid=64200&perpage=50&page
> number=1
BTW, one other question about the Russian test - it's mentioned that they used
100 octane gas. The standard fuel in the ETO at least by the time the Mustang
entered service was 100/130, not 100. Since the octane rating maxes out at 100,
anything above that came to be called a "Performance number". 100/130 were the
weak/rich mixture performance numbers, respectively. In early '44, an attempt
was made to go to 100/150 PN fuel, but this caused considerable problems with
spark plug fouling. Later ethylene dibromide was added in an attempt to limit
plug fouling problems. It did so, but then there started to be problems with
valve seat inserts burning out )apparently the additive was separating out,
forming Hydrobromic acid and eating the inserts).
In any case, I don't know if the Russians had access to 100/130 fuel, or if they
used straight 100 octane. If the latter, they would have been restricted in the
MP (or boost) they could pull. Gruenhagen gives the performance specs for the
Rolls R.M.14 S.M. engine, with 150 and 130 fuel - WEP with the former is
80"/3,000 rpm and 2,080 hp. In high blower, power is 1,850 hp @ 22,800 feet
(presumably critical altitude). With 130 grade fuel, WEP is 1,850 hp @
70"/3,000 rpm, and only 1690 hp @ 18,500 feet. While some of this is due to the
use of ADI (Water/methanol injection), I suspect straight 100 octane fuel might
limit the MP/boost to 61"/+15.
Guy
Guy Alcala
the P-51B and the F4U-1 and 1A:
http://www.geocities.com/slakergmb/id104.htm
The first two are slightly cleaned up as regards drag, making them somewhat
faster than stock (details of the mods are given in the report; the F4U-1 is
also using an engine boosted to represent something closer to the F4U-4); the
F-4U-1A is representative of an in service a/c. It's notable that the P-51B
(V-1650-3) tops out at 450mph @ 29kft. If fitted with the -7 engine, as the
P-51D and some 'B's were (when engine replacement was necessary), the speed and
climb performance curves would match more closely with those of the F4U, but the
P-51's high altitude advantage (above 24,000 feet) would be decreased.
In any case, it's just one more example disproving the ludicrous claim that no
non-contractor performance testing was ever done on the P-51B (or D), and
certainly no one would claim that the navy would try to make the P-51 look
better than it was, compared to their own a/c.
Guy
Trey Wells
prior to posting your comments the other day. Hope that was OK.
Thx
Trey
"Guy Alcala" <g_al...@junkpostoffice.pacbell.net> wrote in message
news:3D839078...@junkpostoffice.pacbell.net...
Guy Alcala
> Thx Guy. Do you mind if I post this on another BBS? I should've asked
> prior to posting your comments the other day. Hope that was OK.
Thanks for asking, and no problem. Be my guest, since I'm just steering people
to another public website.
Guy
P.S. FWIW, IMO netiquette allows free re-posting of any posts from a public
newsgroup, without requiring permission from the author, provided they aren't
used out of context in a way which misrepresents the original author's opinion.
Which isn't to say that it isn't nicer to ask first. OTOH, re-posting or
quoting private emails or portions of same, especially (but not exclusively) if
the author is ID'ed, definitely does (or should) require permission from the
author(s), again IMO. Paraphrasing someone's private comments, with or without
ID'ing them, is the biggest gray area.
Guy
Gregory W Shaw
> Trey Wells wrote:
>
> > Reference the discussion here.
> > http://216.91.192.19/forums/showthread.php?s=&threadid=64200&perpage=50&
> > page number=1
All the references I have seen give 67 in Hg on 100/130 octane WEP and
61 in Hg mil for the V-1650-3/7. 100 octane should drop the max MAP down
to about 52-53 in Hg. That basically splits the difference between mil
power 61 in Hg and normal power 46 in Hg, and should give about 1385 hp
low blower and 1225 hp high blower for the V-1650-7.
That would probably drop speed down to around 420-422 mph max, pretty
close to the Russian figures.
Greg Shaw
Trey Wells
that "slaker", the author of the website you posted a link to, must be a
warbirds simulator player.
"Guy Alcala" <g_al...@junkpostoffice.pacbell.net> wrote in message
news:3D83D209...@junkpostoffice.pacbell.net...
Guy Alcala
> RGR that-- I just want to be courteous.
And it's much appreciated.
> Thx again for the info.
Your welcome.
> I believe
> that "slaker", the author of the website you posted a link to, must be a
> warbirds simulator player.
So it appears. In any case, I think we can end this nonsense once and for all
(although I still want to see Pete's calcs):
Try this link:
http://www.fourthfightergroup.com/eagles/spit14speedchart.jpg
Please note that the Mustang III (P-51B/C) is fitted with a V-1650-7 engine
rather than a -3, as in the earlier case. You'll note that the Mustang III
tops out at 438mph @ 27,500 feet, using mil. power of 61"/+15 lb. The gross
weight of 9,200 lb. indicates that the aft fuselage tank is empty and/or
missing.
Going on to the AFDU Tactical Trials of the Spit XIV, they compare it to the
Mustang III (engine unstated, but I'd guess a -3) among others, and state that
"the maximum speed (sic) are practically identical":
http://www.fourthfightergroup.com/eagles/spit14afdu.html
Although not directly applicable, there's also a nice graph comparing the low
altitude speed of the Tempest V, Mustang III and Spit XIV, both of the latter
at +25 lb. boost (presumably this was for chasing V-1s):
http://www.fourthfightergroup.com/eagles/spit14+25lbs.jpg
BTW, this is a terrific Spitfire site in general, by another Warbirds
enthusiast:
http://www.fourthfightergroup.com/eagles/spittest.html
Guy
Mike Jones
> For instance, there used to be a web link which had the
> results of the speed and climb tests performed on the Mustang Mk. I (AG
351) at
> Burtonwood by the RAF. Unfortunately that link's no longer active, but
> Gruenhagen states that the a/c managed a top speed of 382 mph at its best
> altitude of 14,000 feet (engine critical altitude of 11,300 ft.) during
those
> tests, reduced from the 390 achieved in company tests because the a/c had
gotten
> its camouflage paint as well as having other operational equipment added.
The page has moved to http://www.fourthfightergroup.com/eagles/ag351pt.html
If you're interested, the guy who got those docs from the PRO is active on
the Warbirds board. He posted some good info on speeds of arious Allison
engined Mustangs at different boosts:
http://agw.warbirdsiii.com/bbs/showthread.php?s=6c0f288840a48a3409ee8bd6a9d2
0340&threadid=429&highlight=mustang
Guy Alcala
> "Guy Alcala" <g_al...@junkpostoffice.pacbell.net> wrote in message
> news:3D815AD8...@junkpostoffice.pacbell.net...
> > For instance, there used to be a web link which had the
> > results of the speed and climb tests performed on the Mustang Mk. I (AG
> 351) at
> > Burtonwood by the RAF. Unfortunately that link's no longer active, but
> > Gruenhagen states that the a/c managed a top speed of 382 mph at its best
> > altitude of 14,000 feet (engine critical altitude of 11,300 ft.) during
> those
> > tests, reduced from the 390 achieved in company tests because the a/c had
> gotten
> > its camouflage paint as well as having other operational equipment added.
>
> The page has moved to http://www.fourthfightergroup.com/eagles/ag351pt.html
<snip>
Thanks very much for the link. I was hoping it had moved somewhere else, but had
been unable to find it. I remember there was some discussion on r.a.m. a year
or two ago about the power used on the level speed tests, as several of us were
wondering why the engine was down about 3" and 40 rpm (41.7"/2960 rpm vs.
44.5"/3000 rpm) from its take off and presumably military rating (although
Gruenhagen's stats say max. MP for the V-1710-39 is 46", with no other
conditions specified), as there's no explanation (nor even any mention of the
discrepancy) in the report. The pressure was a bit lower than standard (29.32
vs. 29.92, and ground temp was almost right on, varying from +15 to +13 deg. C.
In any case, the 382 mph appears to have been based on the IAS corrected for
compressibility only and reduced to standard atmosphere, rather than with the
P.E. error included first. Including both of those corrections (-12.2 and -
3.5) to 308.5, my E6B gives just a smidgen under 370 TAS, close enough for
government work. The climb test appears to be for normal rather than military
power.
Guy
Peter Stickney
This is going to be redundant for a lot of people, but I've reviewed
the Bulletin Board thread that's been referenced as part of this
question, and, if you don't mind, I'd like to take the opportunity to
do a small bit of teaching for those who'd like to learn where these
numbers come from. A lot of you know this stuff, so please bear with
me, and if I've typo'ed or Thinko'ed something, please jump in and
correct me.
Let's start with a Glossary. Some of it's pretty basic, but we'll
need it to get all the ducks in a row. These are the things you need
to know if you want to figure out if a performance report is valid:
Flight is a balance of four forces: Weight, Lift, Thrust, and Drag.
When the sum of Weight and Lift is 0, you are in level flight. When
the sum of thrust & drag is 0, you are at the maximum speed.
The Air: Air, of course, is vital to making an airplane work. For
our purposes, there are 3 properties of the air that are important.
The Pressure, (P), the Density (Rho), and the Temperature (T). These
values change as altitude increases. How these values change can vary
from day to day, and from location to location. To get past these
differences, the "Standard Atmosphere" was developed. This is a
mathematical representation of the atmosphere's changes from a given
set of start conditions, how they vary with height, and from this can
be determined the changes due to, say, a difference in temperature or
pressure at ground level. This definition has changed through time,
in order to reflect our better understanding, and better ability to
measure these conditions. For this purpose, I'm using the ICAO 1979
Standard Atmosphere, which does vary somewhat from the 1930s NACA
Standard Atmosphere. (It's not that significant at these altitudes)
The thing that affects an airplane's flight the most is the Dynamic
Pressure, or 'q', This is the pressure generated by the movement of
air. q varied with the square of the velocity, so if you go twice as
fast, q is increased by 4 times.
Because the Pressure, Density, and Temperature of the air decrease as
you travel higher in the atmosphere. (Actually, temperature is
constant about 36,000' or so, but that's not relevant here), the q
generated by a particular airspeed is less than it is at lower
levels. This has led to the definition of several different measures
of airspeed. These are:
True Airspeed - the actual speed of movement through the air.
Equivalent Airspeed - the airspeed at sea level corresponding to a
particular q.
Calibrated Airspeed - the Equivalent Airspeed corrected for the
compressibility of the air at that height and speed. At the speeds
we're talking about, it may amount to 3 or 4 mph.
Indicated Airspeed - The airspeed that shows on the pilot's Airspeed
Indicator. This can be affected by the location and orientation of
the pitot tube used to measure 'q', and internal system peculiarities.
The difference between CAS and IAS is called Position Error, and
varies with the speed of the aircraft. It can be as high as 10-15
mph. We're not actually concerned about it here.
Weight: How much an airplane weighs. Weight doesn't necessarily
affect speed much, but it has big effects on Excess Acceleration, and
therefore Excess Power, and thus Rate of Climb and Maneuverability.
There's a whole bunch of weights, though. There are:
Empty Weight: The weight of an airframe without fuel, oil, crew,
Ammunition, Bomb load, or removable equipment.
Basic Weight, or, sometimes, Empty Equipped Weight. This is the
weight of the airframe with crew, removable equipment, oil, and
unusable fuel. (More or less the true minimum weight that an aircraft
can have.
Normal Loaded Weight: The Basic Weight, plus full internal fuel, and
ammunition.
Maximum Weight: The absolute most weight that you can have without
exceeding some limit. (Like Landing Gear Strength, or strength at some
G load, or engine-out rate of climb, etc.) This usually, for fighters
requires some amount of external load.
Note that there can be a big difference between a
After World War II, the U.S. Department of Defense, in order to help
make sense of it all, came up with the idea of "Combat Weight", Combat
Weight is a stylized representation of what the weight of an airplane
will be as it may be actually engaged in combat. It is defined as the
Basic Weight, + 60% of the Internal fuel (In most cases), plus, in the
case of some bomber aircraft, internal bombs.
This affects some aircraft more than others. In a World War 2
context, there's a lot more difference between a P-51B's Basic Weight,
and its loaded weight, than, say, for a Spitfire or an Me 109.
Most of that difference is fuel, or course.
Here's a quick comparison, with weights expressed as a percentage of
Basic Weight:
P-51B Spitfire IX Me 109G-6
8190# 6650# 6550#
Basic weight 100% 100% 100%
Loaded Weight 120% 110% 110%
Combat Weight 112% 104% 106%
When you consider the difference that a relatively small weight change
can make on maneuverability and climb, you'll see that there's a lot
more difference between a Mustang at it's loaded weight, and a Mustang
over the target area than there is for its contemporaries. (Just for
the record, a P-51B carried about 1600# of gas internally. The Spit 9
and 109G both could squeeze i about 650-660# of gas. You can see why
the idea of Combat Weight was considered important.
Lift: What's required to keep you separate from the ground. This is
done by, if you will, "fooling the air" into generating a lower
pressure on the top of the wing vs. the bottom of the wing. For a
given weight, in level flight, Lift is the same as the weight. How
hard the wing has to work to achieve this lift is measured by the Lift
Coefficient, Cl. Lift is defined as Cl * S (Wing Area) * q. As you
can see, since q decreases for a particular True Airspeed with
altitude, the higher you go, the harder the wing has to work. There's
a maximum limit for CL for each airfoil, called Clmax. This limits
how much lift a particular wing can generate. For purposes of Maximum
Speed, Clmax isn't important.
Drag: Drag is the resistance to something moving through the air
generated by pressure on the front parts, friction over the surfaces,
vacuum (low pressure) over the back parts, and drag produced by
generating lift. Basically, for the speeds involved in this
discussion, this can be divided into 2 components, the Profile Drag
(Drag due to shape), and the Induced Drag (Drag due to Lift).
These are expressed as the Induced Drag Coefficient (CdI), and the
Profile Drag Coefficient (CdF). The forces that these produce are
defined, similar to lift, as Coefficient * q * S, where S is a measure
of surface area. There's some difference of opinion over whether to
relate the Profile Drag coefficient to Wing Area (Easy to measure,
usually) or Wetted Area, which takes into account wing, tail, and
fuselage area exposed to the airstream. (Easier to determine the
effects of changes to clean up an airframe aerodynamically) We can
get past that by relating profile drag as an Equivalent Profile Area,
which expresses the drag in terms of an imaginary flat plate with a
Drag Coefficient of 1.0 - basically, the draggier the airplane, the
bigger the plate.
Induced Drag is the drag that's generated by the lift that the wing is
producing. The Coefficient of Induced Drag is defined as:
CdI = (Cl*Cl)/(pi * AR * e)
[pi is of course, pi, as in 3.14157..., AR is the Aspect Ration of the
wing, best calculated as (span * span)/Wing Area, and e is an
efficiency factor related to the shape of the wing.]
As you can tell, Induced Drag, depending on how hard the wing is
working to generate a certain amount of lift, is small at large values
of q. (In other words, it's less as you go faster and/or lower).
Thrust: How much force is being exerted by the aircraft's powerplant
to push it through the air. This is a toughie. Reciprocating engines
don't produce thrust directly, they produce power. (Which is defined
as Torque * rotational Speed - don't sweat that). Power doesn't
directly translate into thrust, so we'll have to do a bit of
arithmetic:
1 HP = 550 ft-lb/sec. Now, thrust is lbf (pounds force), since we're
on Earth, we can safely assume 1G - 32.2 ft/sec^2 and not sweat it)
So, to get lbs out of a horsepower number, we divide by 550
ft/sec. (Hey ft/sec, that's speed!) so, if we do a bit more figgering,
to get the speed part down, we end up with T (Thrust in lbs) = HP *
550/v (v in ft/sec). As you can see, at low speeds, we get bags of
thrust per horsepower. At high speeds, the thrust decreases.
Here's another table that shows this: (remember that 550 ft/sec = 375
mph)
Speed Thrust (1 HP) HP (1# of thrust)
100 mph 3.75# 0.266
200 mph 1.88# 0.533
300 mph 1.25# 0.800
400 mph 0.94# 1.067
500 mph 0.75# 1.333
As you can see, as speed goes up, thrust drops off alarmingly. But,
of course, there's more to it. A reciprocating engine generates its
thrust by turning propeller, which is basically a set of rotation
wings, which turn torque into thrust by moving a large volume of air
from in front of the propeller disk to behind it. This of course,
isn't 100% efficient. While the propeller can be considered a set of
wings, it moves through a complicated airmass. The airspeed that a
propeller's airfoil sees is defined by the rotational speed of the
propeller, and by the forward motion of the airplane. There are also,
of course, altitude effects. An airplane propeller stalls at low
speeds, and has transonic problems at higher airspeeds. The
efficiency of a propeller isn't constant. At low speeds, it can be
rather poor, and it drops off at high speeds. The altitude effects
also mean that a given propeller setting is only most efficient at a
particular combination of Torque, RPM, airspeed, and altitude. This
led to problems in the 1930s, when airplanes with wide speed ranges
were beginning to be developed, and supercharged engines, which
produced their best power at higher altitudes, were introduced. As an
example, the Boeing Monomail transport prototype, with a supercharged
Pratt & Whitney Hornet engine, couldn't take off with its propeller
set for the cruising design point of the airframe/engine combination -
the propeller efficiency was too low. When the propeller was set for
takeoff performance, there was a hefty hit on cruise speed. This was
resolved by producing variable pitch and constant speed propellers.
Basically, the pitch change allows the peak efficiency to be
maintained over a wide combination of engine power/ airspeed and
altitude combinations. What this means for this analysis is that the
thrust produced for a particular horsepower isn't dependant on
altitude.
Oh, yeah, there's one other factor as well. Because the combination
of airplane airspeed and the propeller's rotational speed can get
quite high, there's a loss of efficency as the propeller's blades
approach the speed of sound. To get past that, the propeller shaft is
geared down to keep the total speed low. The Mustang's V1650 had a
gear ratio of 0.479. For every 1000 engine RPMs, the propeller turned
479.
The efficency of an airplane propeller is best referenced by the
Advance Ratio, or 'J'. 'J' is defined as J = V(true airspeed) /
n(rotational speed)* d (diameter). For a typical WW 2 fighter airplane
propeller, the highest efficiencies are reached at Js between 1.5 and
3.5.
Now that we've got the propeller out of the way, we need to take a
look at what is driving it. All WW 2 fighter engines were
supercharged. Most airplanes started the war with single-stage (one
compressor) single-speed (one peak altitude) superchargers. This
gives the maximum engine performance at a particular height. There
are two problems with this combination - It takes engine power to run
the supercharger, so the more you want it to compress (better at
higher altitudes), the less power is available for the propeller.
This leads to less power being available for takeoff, and at lower
altitudes. There were basically 2 ways to get around this. One was
to have multiple ratio gear drives, like a car's manual transmission,
to drive the supercharger. With a slower drive speed, the peak power
was developed at low altitude, and less power was used to drive the
supercharger. Another possibility was to have a variable speed drive
for the supercharger, like the torque converter on a bulldozer or
tank. This meant that the supercharger used only as much power as
needed to produce a certain engine power, but at a cost in
efficiency.
There is also a limit for how much a single compressor can squeeze
the air. This limited just how high an airplane engine could go and
produce peak power. (Typically about 20,000'). This was solved by
using multi-stage superchargers, basically using two superchargers in
tandem so that the main stage (engine stage) supercharger is working
on the already compressed air of the initial (auxiliary stage). This
could take a number of forms. Turbosupercharged engines, such as the
Allison V1710 on the P-38, and the Pratt & Whitney R2800 of the P-47,
are one form. The turbosupercharger delivered "sea level" air
pressures to the single-speed engine supercharger at heights ranging
from Sea Level to over 25,000', with no additional cost of shaft
horsepower to run th auxiliary stage. There are drawbacks in that
the turbosuperchargers were fairly heavy, took up a lot of volume, and
required tens of yards of ducting to move air all over the place
within the airframe. Another approach was to have a separate
Mechanical supercharger, that could be shifted when appropriate to
deliver the best power. This was the type used on the F4U Corsair and
F6F hellcat. The drawbacks to this type are also the weight of the
system, and that the power consumed by the supercharger reduces the
power available to the propeller. (For example, at 20,000', for the
same RPM and Manifold pressure, the R2800 on an F4U produces about
1650 HP, while the turbosupercharged R2800 on a P-47 produces 2000
HP. The missing 350 HP is driving the supercharger.
Another possibility, which saved weight and bulk, was to have s ingle
supercharger drive that ran both compressors. This was the type used
on the V1650 Merlin on the Spitfire and P-51. The advantages are that
the engine wasn't much bigger or heavier than the single-stage
Merlin. The disadvantages were that it still consumed Shaft
Horsepower, and required very careful design to match the performance
of the two compressors. Luckily, Rolls had Stanley Hooker, who was
able to sort this all out.
Oh, yeah, and still another thing! If you design the intake system to
you superchargers right, you can take advantage of thy dynamic
pressure you're generating to basically fool the engine into thinking
its at a lower altitude. This is referred to as "Ram Recovery", and,
for typical airplanes is in the range of 65-80%. Well designed
systems can give recoveries higher than 90%. This is why an
airplane's max speed can occur at altitudes higher than the engine's
best altitude, and for purposes of finding an airplane's maximum
speed, can be critically important.
The data that is presented in the popular references is not a good
basis for accurately determining what the true performance of an
airplane is. While the data reported is correct, as far as it goes,
context information, which is vital to determining if the numbers are
valid or not, is lacking. You've basically got to have the following
data before an airframe's performance can be determined - Airspeed,
Specific Excess Power, Altitude, Weight, and Power produced by the
engine(s) . (Note that Max Speed is a case where Specific Excess Power
= 0.)
You'll generally get a Max Speed Number, sometimes an Altitude to go
with it, and, very rarely, a weight. Power setting information is
almost impossible to find. In fact, in most references, anything
other than the takeoff power of the engine is impossible to find.
Now to the subject of testing.
Well, there was (And still is) a _lot_ of non-contractor testing that
is performed for any military aircraft. This testing takes the form
of flying instrumented aircraft over instrumented ranges, wind tunnel
testing, systems testing, the whole gamut. After acceptance, the
aircraft are often run through test series other times, in order to
provide, for instance comparisons to other aircraft.
The date provided in these tests is normalized, or corrected to
whatever the Standard Atmosphere of the era is, so that comparisons
can be quickly and accurately made.
The data from these tests goes into developing the performance tables
in the Pilot's Operating Handbooks, and also into the data presented
in the (In the U.S. case), Standard Aircraft Characteristics (A
distilled summation of aircraft performance data used as a Staff
Reference ).
Now, for some time, I've been a bit leery about the P-51s Standard
Aircraft Characteristics data. (A reasonable source for some of these
numbers is Ray Wagner's _American_Combat_Planes_ (Doubleday, several
editions). The performance numbers he presents are apparently taken
from the "Basic Mission" table of the current "Standard Aircraft
Characteristics". I've found this correspondence in about 40 test
cases, so it's fairly safe to presume that the data is from a reliable
source.)
At that time, the USAAF performed their testing at, basically, 5,000'
intervals, measuring the performance at SL, 5,000', 10,000, etc. These
numbers in themselves are accurate, but they don't necessarily
represent the actual points of peak performance of the airplane.
Not a big deal, really, unless you're an obsessive gearhead/Wing Nut
who plays with CFD for fun. (Guilty)
Now, to the case of the P-51.
I have immediately available to me a number of reports, or data from
reports, that include P-51B/C performance. These are the Central
Flying Establishment graphs that Guy mentioned in another post, the
comparison report of the P-51B and a pair of F4U-1s made by the Navy
Flight Test Center at Pax River, Also mentioned by Guy, although I'd
obtained my copy from the Navy Historical Office in DC a few years
back. It, BTW, provides excellent context, describing what was done
to clean up the airplanes before the tests. (And, yes, the Corsairs in
the tests definitely were cooked.)
Other reports are from a test series at Eglin Field as part of the
P-51B acceptance trials, and performance test series EE393 conducted at
Wright Field in early 1943. I'm not counting the Tactical Reports by
the British Air Fighting Development Unit at Farnborough, but they
make interesting reading. If Mike Williams is listening in, Thank
You! The work that you've done obtaining and putting the A&AEE
reports on the web have been invaluable.
Another useful resource is the NACA Technical Reports Server. Some of
the good folks at NASA have been spending a not inconsiderable amount
of time digitizing and cataloging thousands of the older Tech Reports,
Research Memoranda, and Wartime Reports from 1921 onward, covering
everything from determining the turning circle of a Los Angeles class
rigid airship to Anti-Satellite vehicle trajectories.
Wartime Report L-108 was most useful. This was a study of a number of
mid-war aircraft tested in the Langley Full Scale Wind Tunnel to
determine the effects of cleaning up these airframes.
As a cross check of these numbers, Rate of Climb figures were
calculated and compared to test figures, if they were available. The
rate of climb, and best speed for rate of climb crosscheck the drag
and thrust calculations at a mid-point in the performance, rather than
just at the end points.
Anyway, here are the performance numbers
CFE Report, Mustang III (P-51B/C with V1650-7 engine at 61" MAP/3000R
Test Weight 9200#
Max Speed 438 mph @ 27500'
412 moh @ 14000'
Rate of Climb 2600'/min @ 23000'
3420'/min @ 11100'
The rate of climb numbers match within 5%, and the best climb speed is
175 mph IAS.
These numbers yield an equivalent Profile Area of 4.1702 sq ft, and a
Ram Recovery of 95%
U.S. Navy Patuxent River Comparison Tests V1650-3 engine at 67" MAP/3000R
Test Weight 9423#
Max Speed 450 mph @ 29200'
426 mph @ 12600'
No Climb data specifically called out.
Equivalent Profile Area is 4.1812 sq ft, with a Ram Recovery of 95%
Best Rate of Climb speed is also 175 IAS.
Eglin Field tests V1650-3, 67"/3000RPM
Test Weight 9640#
Max Speed 435 mph @ 27000'
420 mph @ 13100'
No Climb Data
Equivalent Profile Area 4.3315 - note - this aircraft had the wing
pylons attached. Ram Recovery 85%
Wright Field EE 393 tests V1650-3 67"/3000RPM
Test Weight 9200#
Max Speed 450 mph @ 28200'
420 mph @ 15300'
Rate of Climb 2666'/min at 28550'
3450'/min at 11857
Equivalent Profile Area 4.0763 Ram Recovery 95%
Note - Calculated Max Rate of Climb at 12000' is 3400'/min at 175 IAS.
NASA Wartime Report data on P-51B
"Beat Up" CdF, 0.0208, for an E.P.A. of 4.84 sq ft.
"Cleaned up" CdF 0.0173, for an E.P.A. of 4.0309 sq ft.
So, the numbers I'm getting fall into the middle of the range,
corresponding to polishing the airplane and sealing up the gun ports.
As a check, I ran data for an "Average" P-51B with a CdF of 0.01800,
and a Ram Recovery 0f 90%. At a weight of 9200#,
With a V1650-3, this gave me the following numbers:
Vmax, 67"/3000R (Emergency Power) 450 mph @ 30000'
427 mph @ 19000'
350 mph @ Sea Level
Vmax, 61"/3000R (Military Power) 445 mph @ 31000'
425 mph @ 20500'
335 mph @ Sea Level
Vmax, 46"/2700R (Normal Power) 415 mph @ 34000'
380 mph @ 22000'
300 mph @ Sea Level
The logic I'm using for when the supercharger speeds should shift may
need some tuning.
All in all, I'd say that the numbers that are in the reports quoted
above are valid. They match with NACA's drag data, and they are
internally consistent.
Note that it's rather pointless trying to pin things down too
closely. Individual airplanes vary, and engine performance varies as
well. Even coming off the factory floor, a variation of about 5% or
more in the performance numbers is to be expected.
As for the Soviet numbers, I'd be interested in more detail. From
reading reports from Soviet Pilots flying Merlin Engines Hurricanes
and Spitfires, they seem to have had some trouble getting the full
amount of oomph from their Merlins. Although the slightly over 400 mph
number at 22,000' sounds pretty close for a V1650-3 airplane in low
blower/Max Cont. Power. As for limits using 100 Octane rather than
100/130, I had an opportunity to ask a P-51 owner about that way back
when. (Don Davidson, when he owned "Double Trouble II") about running
his airplane on 100LL rather than 100/130. He limited his power to
61" for takeoff. (Which was the usual value.) Of course, he didn't run
it at more than 46"/2700 very much. Since at that time, a Merlin only
cost a quarter of a million bucks, we can safely assume that he
wouldn't risk it needlessly.
If you've made it this far, thanks for bearing with me, and I hope
that this helps. If anybody can find a way to express some it in a
more understandable way, please pipe up.
Oh, and teuton, if you _have_ to look for German Superiority in all
things, don't ignore the fact that major players on the design team
were Kindelberger and Schmued. And that it was flown into battle by
guys named Schilling and Zempke. :)
Dudley Henriques
Now tell the truth Pete. Your wife bought you a new keyboard; it's raining
like hell; and you've been champing at the bit to try it out all day
long...RIGHT??? :-)
How can I best describe this post? Well, I could say, in the words of
Charlie Brown, who, while practicing sending smoke signals for his Boy Scout
merit badge in the Nevada dessert, and looking up just in time to see an
Atom Bomb test exclaimed, "GOOD GOD!!! I wish I'd said THAT!!!!" :-))))
Or I could opine about James A. Michener's forth grade teacher, who once
told James after he was late for class to bring a note from his mother the
next day explaining why he was late. James wrote the note himself and gave
it to the teacher. She read, "In the beginning, there were volcanos, and
great dinosaurs roamed the earth." She hesitated, looked him in the eye, and
exclaimed, "James, is this going to be a long story?" :-)
Or I'll just have to compliment you instead on a very accurate post, which
of course has been done with your usual accuracy and technically correct
manner.
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/Certificated Flight Instructor
Retired
Peter Stickney
Well, I had a fantastic, highly educational, 700 line reply to this
all made up. I sent it out, and the power glitched half-way through
the update from my local server to the outside world. Fudge!
Here's the short form:
Lots of testing gets done on any aircraft by the customer before
acceptance. Anybody who believes that the U.S. Army doesn't wring out
an aircraft before selecting it for service should check out the
history of the Curtiss P-46, the annointed successor to the P-40, and
an immediate precurser to the NA-73 (P-51 prototype), This failed
testing so miserably that Curtiss decided that they's start with a
clean sheet of paper (And did no better with the P-60 series), and
sold the engineering data to North American, who used it as an example
of what not to do. The Brits had been testing P-51s before the
U.S. had. After all, it was designed to their specifications. There
was some disbelief on the part of the RAE about the Mustang's
performance numbers as reported from California, but testing of the
first examples to reach the U.K. showed that the numbers were valid.
(The stuff that Guy's pointed out was part of that testing) It's
possible that the story you've had posted was a conflated version of
that.
There were, of course, a number of tests run on every model of the
P-51 throughout its career.
I've been able to pull useful data from 4 test series, and use them to
reverse-engineer the basic aerodynamics of the airplane.
I'll digress a bit here and there, to bring up a few interesing bits
about sources, and other such stuff.
What I've done was to take information from official tests and
technical literature, apply all the basic rules of aerodynamics to
them to determine the basic coefficients that define how an airplane
is going to perform, and then recalculate the airplane's performance
through it's entire flight envelope. (This allows me to crosscheck the
date vs. things like Rate of Climb, Cruise Speed, and Ceiling data.
If they match as well, then the numbers I'm generating are
consistant.)
The tests that I'm using are:
Appendices E and F of a report by the British Central Flying
Establishment, 1946. These are charts comparing the speed/altitude
and climb/altitude performance of a Mustang II with a V1650-7 engine,
a Spitfire XIV, a Hornet I, and a Meteor III. The tests were done in
early '46. (In fact, they're the same ones that Guy pointed out. Mike
Williams has done some great work by ferreting out these reports, and
should be recognized.) The second set of numbers comes from a test
series flown at Eglin Field in early 1943. The third set is from Test
Series EE 393, performed at Wright Field in early mid '44, The last
numbers come from comparison tests of the P-51B vs. two versions of
the F4U-1 Corsair, performed by the U.S. Navy at Patuxent River.
(Guy also managed to find an online copy of this report as well. I
got mine from the Navy History Office a few years back)
I also cross-checked this data with NACA Wartime Report WR-L-108,
which was a series of tests performed in the Langley Full Scale Wind
Tunnel on various mid-war aircraft with a view to improving their drag
coefficients.
Here are the numbers, and the results of the run. (The data for each
test run turns out to be about 80-100 pages, so I'll just distill it
down a bit. The data points are at the critical altitude for both
supercharger gear ratios for the appropriate power setting.
CFE: Mustang III with V1650-7 engine, Military Power (61"/3000R)
Test Weight: 9200#
Vmax: 438 mph @ 27500'
412 moh @ 14000'
These numbers give a CdF of 0.0179, and a Ram Recovery of 95%
Eglin: P-51B with V1650-3 engine, Emergency Power (67"/3000R)
Test Weight: 9690# (Pylons attached)
Vmax: 435 mph @ 27000'
420 mph @ 13100'
This gives us a CdF of 0.0185, and a Ram Recovery of 85%
EE 393: P-51B with V1650-3 engine, Emergency Power
Test Weight 9200#
Vmax: 450 mph @ 28200'
430 mph @ 15300'
This gives a CdF of 0.0175, and a Ram Recovery of 95%
Pax River: P-51C with V1650-3 engine, Emergency Power
Test Weight 9423#
Vmax: 450 mph @ 29200'
426 moh @ 15600'
CdF 0.017945 Ram Recovery 97%
CdF is the profile drag. Ram Recovery is the efficency of the
supercharger inlet duct in capturing the dynamic pressure of the air
moving through it. This can increase the critical altitude of an
engine by, in this case, 6000'.
So, we've got 4 tests, with these results for CdF:
0.0179
0.0185 - with wing pylons.
0.0175
0.0179
The NACA Wartime Report L-108, "A Summary of Drag Results From Recent
Langley Full-Scale-Tunnel Tests of Army adn Navy Airplanes", 1945,
shows the P-51B to have an initial CdF of 0.0208 (Beat-up condition)
which was reduced to 0.0173 (Cleaned up, with cowling gaps sealed.)
The drag coefficents seen above are consistant with aircraft having
had a moderate clean up, basically a wax job and taping the gun ports.
I can go into much more detail later, if you'd like. But, I'd have to
say that the numbers reported here are correct. They check out
mathematically, and are within the basic coefficents are in line with
what NACA determined as part of their testing.
Trey Wells
would certainly like to post this information with credit to you of course.
Would that be alright with you?
Thx
Trey
"Peter Stickney" <p-sti...@adelphia.net> wrote in message
news:u3d3ma...@Mineshaft.local.net...
Trey Wells
Holy smokes! I will buy you a manicure and a new keyboard.
Thx Peter
Trey
"Peter Stickney" <p-sti...@adelphia.net> wrote in message
news:p7e3ma...@Mineshaft.local.net...
Guy Alcala
<much good stuff snipped>
Pete, the only thing I'm wondering about is how they managed to pull 67" so high.
Gruenhagen's (I know you've got him) specs for V-1650-3 and -7 high blower
critical altitudes are as follows:
-3
WE, 67"/3000 rpm, 1330 bhp @ 23,000 ft.
Mil, 61"/3000 rpm, 1210 bhp @ 25,800 ft.
-7
WE, 67"/3000 rpm, 1505 bhp @ 19,300 ft.
Mil, 61"/3000 rpm, 1370 bhp @ 21,400 ft.
Here's how they stack up:
CFE, -7, 438 mph @ 27,500 ft. @ 61", 6100 feet above Mil. high blower crit. alt.
Pax, -3, 450 mph @ 29,200 @ 67", 6200 feet above WE high blower critical altitude.
Eglin, -3, 435 mph @ 27,000 ft. @ 67", 4000 ft. above WE h.b. critical altitude
(which seems more reasonable to me).
Wright, -3 , 450 mph @ 28,200 ft. @ 67", 5200 ft. above WE h.b. crit. alt.
And then your numbers with 90% ram recovery and an 'average' CdF:
-3, 450 mph @ 30,000 ft. @ 67", 7000 ft. above WE h.b. crit. alt.
-3, 445 mph @ 31,000 ft. @ 61", 5200 ft. above Mil. h.b. crit. alt.
Obviously there'll be some variation between individual engines, and the Mustang
really was head and shoulders (hoofs and fetlocks?) above everything else in ram
recovery efficiency. I'm just wondering if these altitude gains (other than
Eglin) due to ram seem reasonable to you. Maybe I'm mentally still back with our
high altitude Lancaster exercise of a year or two ago, when we were dealing with
much lower speeds and no doubt poorer ram, but at first glance these altitude
gains seem a bit high. If the speed/altitudes attributed to WE @ 67" were instead
achieved at Mil. power of 61", I'd be more comfortable, but the curves available
don't seem to show that (and the CFE graph is at 61" and still +6100 feet). Of
course, it may just be that Gruenhagen's numbers are wrong [oh, please, say it
ain't so;-) ], or maybe I'm just clueless (always a distinct possibility).
Anyway, excellent job, and thanks for all the effort.
Guy
Peter Stickney
Guy Alcala <g_al...@junkpostoffice.pacbell.net> writes:
> Peter Stickney wrote:
>
> <much good stuff snipped>
Thank you, and thank you as well, Dudley, for your kind words. (Even
if I didn't see them directly. Sometimes Store-and-Forward protocols
are Store-and-Lose. The posts musta gone through the Chicago Post
Office.)
Well, the numbers boggled me, too, the first time I say them, and I
spent part of the weekend sorting though the NACA Tech Reports Server
looking for some verification. There's nothing specific on the P-51,
but a bit of work was put in before the war on designing ramming
inlets for teh best pressure recovery. Curtiss used this for the
P-40, and I'm certain that North American used it as well. Basically,
the rules are: no abrupt curves in the duct, have long straignt
sections as much as you can, and use guide vanes in the duct when the
direction changes. The P-51B's duct to the updraft carb is quite
long, and doesn't require the multiple bends that the ducts to the
Allison's downdraft carbs required. 95% was, perhaps, possible, but
there's enough of a gray area in the differences between the NACA
Standard Atmosohere, and the RAE Standard Atmosphere, and the ICAO
Standard Atmosphere tht I'm using that I'd rather be a bit
conservative. As for why it works out to about a 6,000' difference at
those altitudes, remember that the air pressures that we're dealing
with are rather low, and the differences between them are rather
small, and that, at 450 mph, the q values that we're looking at are a
significant fraction of the Static Pressure at that height.
The 1979 ICAO Standard Atmosphere model gives a stativ pressure of
917.6psf at 21400' (The V1650-7 case, and 704.41psf at 27500'.
For teh V1650-3 case, it's 857.25psf at 23,000. and 652.87 psf at
29200'. (Or, more familiarly, 1.480 and 1.419 psi, respectively.) As
you can see, it doesn't take a big pressure difference to equal a
large altitude difference at that height. Don't forget that there's
also a contribution from the prop wash. Hmm - come to think of it, I
wonder if the cuffed blades on the prop were a part of it?
(An anecdote - Back in the late '70s, when I was just out of college,
part of my work a Kollsman Instrument was testing barometric
altimiters for accuracy at heights over 100,000'. This involved, of
course, couplling the static system port to a vacuum pump & pumping
it down. when you were trying to stabilize the system pressure at
100,000', it didn't take much of a twitch on the regulator valve to
get a 10-15,000' excursion.)
So, I'd say it's a win/win situation. Gruenhagen's numbers are right,
and the Mustang's inlet really could be that efficent. BTW, a
Mosquito's inlets work out at about 85% ram recovery. I don't know if
that's with the screen on or not.
Al Sumrall
Guy Alcala
> In article <3D8608AF...@junkpostoffice.pacbell.net>,
<snip>
> So, I'd say it's a win/win situation. Gruenhagen's numbers are right,
> and the Mustang's inlet really could be that efficent. BTW, a
> Mosquito's inlets work out at about 85% ram recovery. I don't know if
> that's with the screen on or not.
Okay, you've sold me ;-)
Guy
Peter Stickney
"Trey Wells" <JWE...@satx.rr.com> writes:
> Thx Peter! The horse is dead over at that BBS, however if you dont mind, I
> would certainly like to post this information with credit to you of course.
> Would that be alright with you?
Certainly. Please feel free to do so.
John Keeney
> Well, the numbers boggled me, too, the first time I say them, and I
> spent part of the weekend sorting though the NACA Tech Reports Server
> looking for some verification. There's nothing specific on the P-51,
> but a bit of work was put in before the war on designing ramming
> inlets for teh best pressure recovery. Curtiss used this for the
> P-40, and I'm certain that North American used it as well. Basically,
> the rules are: no abrupt curves in the duct, have long straignt
> sections as much as you can, and use guide vanes in the duct when the
> direction changes. The P-51B's duct to the updraft carb is quite
> long, and doesn't require the multiple bends that the ducts to the
> Allison's downdraft carbs required. 95% was, perhaps, possible, but
With a long straight duct you can build up significant momentum
in the intake charge. This can keep the charge moving into the
valve area even when the valve is closed.
Some automotive engines/intake-manifolds have been able to
exhibit greater than 100% volumetric efficiency even on the dyno.
Dennis Jensen
"John Keeney" <jdke...@iglou.com> wrote in message
news:3d86b...@news.iglou.com...
Yeah, my engine is one of them:) It is not really so much the momentum that
is the issue, it is the pulse caused by opening and closing valves. You have
to remember that, although the airflow is sometimes modelled as continuous,
it is anything but.. You have zones of compression and rarefaction along the
length of the inlet (and exhaust, come to that, hence tuned length
extractors). By optimising the length and diameter of the intake for a given
rpm condition, you can have these "standing waves" aligned so that the
region of compression arrives at the inlet valve at the time that the valve
opens. This is sometimes called pulse charging.
--
Dennis Jensen
Author of "The Flying Pigs"
http://www.ebooks-online.com/ebooks/search.asp
NOW ONLINE
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Harry Andreas
<jen...@ozzienet.net.nospam> wrote:
> Yeah, my engine is one of them:) It is not really so much the momentum that
> is the issue, it is the pulse caused by opening and closing valves. You have
> to remember that, although the airflow is sometimes modelled as continuous,
> it is anything but.. You have zones of compression and rarefaction along the
> length of the inlet (and exhaust, come to that, hence tuned length
> extractors). By optimising the length and diameter of the intake for a given
> rpm condition, you can have these "standing waves" aligned so that the
> region of compression arrives at the inlet valve at the time that the valve
> opens. This is sometimes called pulse charging.
Fascinating thread.
If I'm not mistaken, the standing waves generated by flow through a
pipe is very dependent on mass flow rate (engine RPM) so pulse charging is
usually only effective over a small range of RPM, n'est pas?
--
Harry Andreas
Engineering raconteur
Peter Stickney
Quite true. Back in my Hot-Rodding days, I designed a few cross-over
exhaust systems for V-8s. (These are dual exhausts connected at
strategic locations along the pipes to use the pulse-charging (more
like pulse-pumping, in this case) to improve scavenging. It was only
an improvement at a narrow range around the design point, and when off
design, could actually be a problem. I finally threw up my hands and
went with Turbosuperchargers, improving scavenging by forcing air in,
rather than by sucking it out.
The concept isn't new. Pulsejets use the same idea to pull air in at
low speeds, which is why they can run while not moving. The old
"Peace Pipe" mufflers that motorcycles and model airplane engines used
to use in the 1940s & '50s was sort of the same idea, too.
Gregory W Shaw
>
> All the references I have seen give 67 in Hg on 100/130 octane WEP and
> 61 in Hg mil for the V-1650-3/7. 100 octane should drop the max MAP down
> to about 52-53 in Hg. That basically splits the difference between mil
> power 61 in Hg and normal power 46 in Hg, and should give about 1385 hp
> low blower and 1225 hp high blower for the V-1650-7.
>
> That would probably drop speed down to around 420-422 mph max, pretty
> close to the Russian figures.
>
> Greg Shaw
>
>
Brain fart, I don't know how I got the speed figures mixed up, that
420-422 is still 30 mph faster than the russian claims.
I did find an old soviet chart I found online somewhere, probably the
"All about Warfare" sight. It definitely shows 438-440 mph at 8km for a
P-51D, doesn't identify the engine but that's right in line with a
V-1650-7.
Greg Shaw
Dennis Jensen
news:andreas-1709...@x-147-16-144-157.rsc.raytheon.com...
Absolutely correct. My engine has dual intake runners, with long runners at
low revs, and short runners at high revs. You could have an infinitely
variable runner length, whereby you could have pulse charging throughout the
rev range.
Scott Peterson
> Both theodolite units and radar were
>used to measure the speed. The fastest run--I should mention after
>innumerable flights occupying the whole day--
>was 416 mph in a P-51B (s/n 36799 "Carolina Hustler"); this speed was
>sustained only for 10 seconds before the engine became seriously
>over-boosted.
Coming into this discussion late, but what radar would have been
available in 1944 that could give this kind of information? As far as
I'm aware, radar at this time could give reliable bearing and altitude
information but speed would be derived by timing a blip over a known
distance on the screen.
Was there radar available in 1944 that could measure speed in
10-second or smaller increments?
Scott Peterson
--
The plural of "anecdote" is not "data."
Thom
wrote:
>Hi all. Please allow me to query this knowledgable group of individuals.
>Recently on another BBS, a discussion about the P-51b was started. someone
>posted this "
>"The printed maximum speed in all books for the NA P-51D Mustang is 437 mph
>at 25,000 ft. Absolute nonsense. The fastest speed ever actually RECORDED
>for a P-51 ocurred on 20 October 1944, over Henden RAF base, England.
>Following RAF complaints that the P-51 would not reach the printed speeds,
>no fewer than 12 Mustangs from various units--two right off the boat, as
>well--were tested with USAAF pilots. Both theodolite units and radar were
>used to measure the speed. The fastest run--I should mention after
>innumerable flights occupying the whole day--
>was 416 mph in a P-51B (s/n 36799 "Carolina Hustler"); this speed was
>sustained only for 10 seconds before the engine became seriously
>over-boosted. The longest sustained maximum speed recorded was 405 mph for
>55 seconds by a brand new P-51D at 23,000 ft. (s/n 472484). Most of the
>machines in this evaluation were incapable of exceeding 400 mph under any
>conditions whatever. The NII VVS tested their P-51B (L-L, s/n 35145) to a
>maximum of 392 mph at 25,500ft, and climb to 5000m of 6.5 mins. (yes, on 100
>octane gas). I suspect that this was exactly correct, despite the fact that
>all Wetserners try to explain it away. These two events are the ONLY
>scientific evaluation of the Mustang by any non-Company (i.e. North
>American) entity in the entire history of the aircraft. Both evaluations
>prove that the Company was inflating their numbers for 'advertising'
>reasons....".
>
>
>
>The reference is unknown and the poster did not allude that this data was
>valid. My question is, can any of you say to whether this data may or may
>not be valid. I have read in past times that the P-51B had a top speed of
>over 440 MPH true at altitude.
>
>
>
>please advise.
>
>
>
>Trey
The point must be made that the top speed of a fighter is really
unimportant except when your doing a short run to escape someone you
can't get off your tail. The Germans used a different tactic by
installing a GM-1 Fueled Booster called the MW-50. Many an Allied
pilot got a big surprise the first time a German Fighter just zipped
away and many a German pilot got chewed out by his maintaince chief
for over using the 50.
Theres another factor too and that's how controlable was the P-51 over
400mph. Most WW2 types on both sides were very stiff on the stick
over 350mph. Fighters today, even ones capable of Mach 2+ do all
their fighting below mach around 600mph and it was the same back then
with air battles between fighters at 270 to 325mph! The Heavies flew
at 180mph so the fighters were buzzing around at 180 to 250mph most of
the time.
THOM
Also consider this, your on a mission over Germany and Herman's boys
just jumped you and made you drop your tanks. If you start messing
around at 400mph you ARE NOT getting home! Remember that your
economic cruise is around 65-83% power (usually on the lower end) and
thats around 300mph but if you were escorting 180mph bombers etc etc.
Gerry was operating with partial fuel from local airbases, the 51's
were loaded and coming from England. The extar weight of fuel and
ammo also had to be factored into the performance equation especially
if you had to climb. AVGAS weighs 7 pounds a gallon remember.
Peter Stickney
I've been meaning to reply a bit more to this one for a while, now
seems like a good time. As far as the supposed Soviet test goes,
there is no evidence that the Soviets ever received more than 10
Mustang Is (Allison powered P-51As). The serial number quoted, 35145
does not correspond to _any_ P-51 batch ever produced.
As to the question of whether there were radars that could track an
airplane fairly accurately at that time, yes, there were. The most
likely candidate for such use would be the SCR-584 gunlaying radar.
This was the first auromatic-tracking conical scan radar in service,
and was used to feed azimuth, elevation and range data to the
predictors (analog computers) that provided firing solutions to heavy
anti-aircraft guns. (On the U.S. 90mm and 120mm guns, the predictors
actually controlled the guns remotely) When used with teh proximity
fuze, this type of radar, allied with the heavy AA guns, is credited
with most of the V-1 kills during 1944. SCR-584s are still being used
on tracking ranges in the U.S. IIRC, China Lake still uses a few.
If you want one of your own, Radio Research in Connecticut has them in
stock. (I'm saving up for the MD-5 FCS with the B-47 tail turret,
myself)
That being said, a momentary track isn't enough for good data. The
normal precedure when performing high speed tests is to fly 3 passes,
each pass at a bearing 60 degrees off from the previous one. (An
equilateral triangle). This is because the ground-based instrumenta
are measuring Ground Speed, not air speed, and using the three offset
legs would cancel out any wind effects on teh ground speed. (Of
course, this is only true if the wind is steady.
> The point must be made that the top speed of a fighter is really
> unimportant except when your doing a short run to escape someone you
> can't get off your tail. The Germans used a different tactic by
> installing a GM-1 Fueled Booster called the MW-50. Many an Allied
> pilot got a big surprise the first time a German Fighter just zipped
> away and many a German pilot got chewed out by his maintaince chief
> for over using the 50.
A couple of things, here. First off, GM-1 and MW-50 aren't the same
things at all. MW-50 was Standard Issue Anti-Detonant Injection
(ADI, or Water Injection). (The MW stands for Methanol-Wasser, the 50
for a half&half mix. The Methanaol was there to prevent the mixture
from freezing) This has the effect of allowing the engine to pull more
manifold pressure. This increases the available horsepower, but only
at lower altitudes where the engine's supercharger can develop the
required amount of boost. The Germans had to resort to such systems
because, basically, their AVGAS was crap. The Normal German AVGAS was
rougly equivalent to the Economy Unleaded you'll find at the local gas
station.
GM-1 was much different. It was a system to inject Nitrous Oxide into
the induction system, to provide more available Oxygen in the fuel-air
mix, and thus increase power at altitudes above the critical altitude
of the engine. Again, this was a lash-up that was required because
most German engines weren't able to be supercharged to have critical
altitudes as high as the Allied aircraft with multi-stage
superchargers. BTW, while some airplanes were big enough to allpw
both MW-50 adn GM-1 to be fitted, you couldn't use them both at the
same time.
As for overusing them, there were microswitches in the MW-50 system that
would cut back the Manifold Pressure Regulators when the ADI fluid ran
out. (AN Me 109 carried about 10 minutes, worth, IIRC) You couldn't,
if all was well, overuse the system. Of course, running at those power
levels for any length of time is a bad idea.
>
> Theres another factor too and that's how controlable was the P-51 over
> 400mph. Most WW2 types on both sides were very stiff on the stick
> over 350mph. Fighters today, even ones capable of Mach 2+ do all
> their fighting below mach around 600mph and it was the same back then
> with air battles between fighters at 270 to 325mph! The Heavies flew
> at 180mph so the fighters were buzzing around at 180 to 250mph most of
> the time.
The P-51's redlines were 505 mph IAS between Sea Level and 10,000',
400 mph IAS between 10,000 and 20,000'
325 mph IAS between 20,000 and 30,000'
(From the FAA Type Cerificate Data Sheet, L-11-3)
Limiting Mach number was Mach 0.78.
Dudley or Vlado would be much better at answering this, but I haven't
come across anything that says that a P-51 has any significant
problems at those speeds. The 109, however, heavied up considerably,
and the Fw 190 had surprisingly low redlines.
One thing that has always mystified me was teh lack of effort the
Germans put into investigating and ameliorating transonic effects, for
all their vaunted high-speed expertise. Basically, their approach to
dealing with the problem was to put a red line on the Airspeed
Indicator, and a boldface note in the Pilot's Handbook saying "Thou
Shalt Not..." In the meantime, the NACA, the RAE, the manufacturers,
the USN, USAAF, RAF, and FAA were finding ways to make airplanes
usable at those speeds.
> Also consider this, your on a mission over Germany and Herman's boys
> just jumped you and made you drop your tanks. If you start messing
> around at 400mph you ARE NOT getting home! Remember that your
> economic cruise is around 65-83% power (usually on the lower end) and
> thats around 300mph but if you were escorting 180mph bombers etc etc.
>
> Gerry was operating with partial fuel from local airbases, the 51's
> were loaded and coming from England. The extar weight of fuel and
> ammo also had to be factored into the performance equation especially
> if you had to climb. AVGAS weighs 7 pounds a gallon remember.
With the low fuel capacity of the German fighters, they were just as,
if not more contrained by reasons of fuel economy as the
P-51s. Consider that P-51s were capable of flying Combat Air Patrol
over jet airfields in Czechosovakia, and returning to England.