All flying vs Stab and Elevator
Tango4
drag than the more conventional stab-and-elevator design ( no spanwise
elevator/stab joint) . In addition there are fewer moving parts and less
complexity in the all flying surface. This must make them lighter, simpler
to build and cheaper.
Apart from some perceived resistance to this type of tail configuration, why
haven't they caught on? I owned an LS1-d and it was a really nice A/C to
fly, I can't say that it was particularly pitch sensitive but it was very
responsive. The tail boom was noticably longer than most ships, which I
suppose reduced the coupling. I never got into any PIO situations with it.
Just wondering!
Ian Molesworth
Ray Corbett
problems that i can remember .
Ray Corbett
Tango4 <i...@imolesworth.demon.co.uk> wrote in message
news:957206595.3020.0...@news.demon.co.uk...
sierra1
stabilizer/elevator tail are many. First, it is a misnomer that
an all flying tail (stabilator) is lower drag. To get the same
lift out of an all-moving tail requires more deflection than the
elevator. The elevator deflection effects the camber of the
surface, not just the angle of attack. Secondly, the attachment
of a fixed stabilizer is structurally simpiler and weighs less
for the same rigidity in torsion.
An all moving tail has advantages over a large angle of attack
range so they are useful on aircraft like fighters (common all
the way back to the F-4) but are draggy for other applications
(airliners, etc.)
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Doug Hoffman
i...@imolesworth.demon.co.uk writes:
>Just looking at them, all flying tail surfaces would appear to offer less
>drag than the more conventional stab-and-elevator design ( no spanwise
>elevator/stab joint).
I believe this is correct.
>Apart from some perceived resistance to this type of tail configuration, why
>haven't they caught on?
I've often wondered that myself. My understanding is that the all-flying
stab offers less pitch effectiveness than stab-and-elevator because the
stab-and-elevator change the camber of the tailplane, which apparently
is more effective than tilting the all-flying stab. But I believe a
properly designed all-flying stab would have all of the pitch control
one would need.
I would think that the all-flying stab would offer an advantage in
accomodating differing CG settings on the same glider. The decalage,
or longitudinal dihedral if you will, is not fixed and can be
"adjusted" while flying. Whereas the fixed stab is just that,
fixed and not "tune-able" to differing CG and other conditions.
Good question. I have not a good answer...
-Doug
Bruce Hoult
<steve.linden...@delta-air.com.invalid> wrote:
> An all moving tail has advantages over a large angle of attack
> range so they are useful on aircraft like fighters (common all
> the way back to the F-4)
I believe the reason that they are universal on modern fighters is that a
stab + elevator combination suffers from a complete lack of control at a
certain near-Mach 1 speed, and from control reversals at other speeds.
That an all moving tail fixes this was probably the biggest single
discovery made by the X-1 and a highly classified secret for a while.
-- Bruce
Martin
Doug Hoffman <dhof...@oakland-info.com> wrote in message
news:8el1h...@enews3.newsguy.com...
>
> Good question. I have not a good answer...
>
I have flown many hours in a SIE-3 (with an all flying elevator) and my
conclusion is that this constructions sucks like hell!
Martin
Ian Molesworth
> conclusion is that this constructions sucks like hell!
>
> Martin
>
>
How succinctly put! I like your objective approach to the subject
and the development of your argument to your stated conclusion. A fine
specimen of constructive contribution to the newsgroup sir!
Ian
Martin Gregorie
>I've often wondered that myself. My understanding is that the all-flying
>stab offers less pitch effectiveness than stab-and-elevator because the
>stab-and-elevator change the camber of the tailplane, which apparently
>is more effective than tilting the all-flying stab.
>
Yes. This effect is well-known in the model flying world and for just
the reasons you give.
>I would think that the all-flying stab would offer an advantage in
>accomodating differing CG settings on the same glider.
>
I don't think this is true. The decalage setting is not the issue for
stability with different GC positions; the important things are (1)
the stab. moment arm and (2) the lift curve of the stab section.
----------------------------------------------------------------------
Martin Gregorie |Logica UK Ltd
gregorie |+44 (0171) 637 9111
@ |
logica |
. |All opinions expressed are solely those
com |of the author and not of Logica
----------------------------------------------------------------------
Tom Seim
> I believe the reason that they are universal on modern fighters is that a
> stab + elevator combination suffers from a complete lack of control at a
> certain near-Mach 1 speed, and from control reversals at other speeds.
> That an all moving tail fixes this was probably the biggest single
> discovery made by the X-1 and a highly classified secret for a while.
>
Why doesn't this happen to the ailerons?
Tom
Reb Byrne
>
>Tom
It does. Most modern fighters use differential stab movement for roll
control as well as ailerons. Amount of differential stab is varied
depending on airspeed, altitude, g-loading/angle of attack. Coordinated
rudder is also input so it is possible to fly with your feet flat on the
floor, although use of "more" rudder at low speed/high AOA provides
dramatically better roll rates.
Reb Byrne
Zuni N42KH
one time F-15 driver
sierra1
elevator.
Marc Ramsey
> You may be right, but the X-1 had a fixed stabilizer and
> elevator.
My understanding is that the transonic "control reversal" myth
comes from the early 50's British movie "The Sound Barrier."
In that flick, brave British pilots attempting to be the first
to break the sound barrier (I guess they hadn't heard about Yeager)
by diving their jets, were making smoking holes in the ground until
the hero tries moving the stick forward, rather than aft, to pull
out of the dive.
A number of piston engine fighters would experience control problems
during high speed dives due to transonic airflow, but I believe the
solutions were known by the time of the X-1...
--
_____________________________
Marc Ramsey, ma...@ranlog.com
http://www.ranlog.com/ramsey/
Sent via Deja.com http://www.deja.com/
Before you buy.
Nolaminar
reversal at high speed.
GA
Shaber CJ
>comes from the early 50's British movie "The Sound Barrier."
>In that flick, brave British pilots attempting to be the first
>to break the sound barrier (I guess they hadn't heard about Yeager)
>by diving their jets, were making smoking holes in the ground until
>the hero tries moving the stick forward, rather than aft, to pull
>out of the dive.
>
>A number of piston engine fighters would experience control problems
>during high speed dives due to transonic airflow, but I believe the
>solutions were known by the time of the X-1...
>
The F7F Togercat could run into control reversal in a high speed dive.
SoarHead
15 which also flew well. No pitch sensitivity at all.
To SIE-3 guy. If it sucks...why fly it?
Vince Miller
Bruce Hoult
<steve.linden...@delta-air.com.invalid> wrote:
> You may be right, but the X-1 had a fixed stabilizer and
> elevator.
No, it started that way but they changed it during the program.
-- Bruce
Doug Hoffman
greg...@see.sig.for.address writes:
>>Doug Hoffman wrote:
>>I would think that the all-flying stab would offer an advantage in
>>accomodating differing CG settings on the same glider.
>>
>I don't think this is true. The decalage setting is not the issue for
>stability with different GC positions; the important things are (1)
>the stab. moment arm and (2) the lift curve of the stab section.
>
Sorry. I wasn't clear. I was not referring to stability
advantages of adjustable decalage. I meant to say that the
efficiency, or minimum drag possibility, of an adjustable decalage
would seem to be an advantage of the all-flying stab vs. the
fixed stab. Especially when given the variables of differing
CG, airspeed, flying weight, pilot proficiency, etc.
In general we can say that the more decalage angle the more
stable the glider becomes, but at a cost of increased drag.
I believe.
-Doug
Bruce Hoult
<steve.linden...@delta-air.com.invalid> wrote:
> You may be right, but the X-1 had a fixed stabilizer and
> elevator.
Just found this...
From <http://www.dfrc.nasa.gov/gallery/photo/X-1/>:
For the first time in a transonic-capable aircraft, an all-moving
stabilizer was utilized.
From <http://www.dfrc.nasa.gov/History/X_1.html>:
The moveable horizontal stabilizer was developed from data supplied by
NACA based on its tests on the XP-42. The unit had a deflection of 5
degrees up and 10 degrees down. It was fitted with a screwjack operated,
ultimately, by a pneumatic motor. The stabilizer was initially capable of
one-degree, later three-degree, and finally two-degree per second
adjustments.
The need for a movable stabilizer became critical in the upper transonic
speed range when the XS-1 #1 reached an indicated Mach number of 0.94 and
its elevators lost their effectiveness. So important was this discovery
that nearly every transonic and supersonic aircraft since that time has
had an all-movable horizontal stabilizer, although the Air Force managed
to keep the information about it classified for about five years. This was
long enough to give the later versions of the U.S. F-86 used by American
pilots in the Korean War a decided advantage over the MiG-15s used by
their opponents, because the F-86s had all-movable stabilizers and the
MiGs did not.
From <http://www.pbs.org/wgbh/nova/barrier/men.html>:
Yeager: Obviously the reason we kept it
classified was to keep the rest of the
world from finding out about a flying tail
that's necessary to control the airplane
through the speed of sound. It resulted in
a kill ratio of 10 to 1 between the F-86 and
the MiG 15. That one simple thing, of
putting a flying tail on the F-86, because
we knew that it would dive to the region of
the speed of sound, and it pitted it against
the MiG 15 in Korea, in 1951, '52, and '53,
and we had a kill ratio of 10 to one. And
when I flew the MiG 15 over there for the
first time I was amazed, because it was a
good airplane, just like the Hawker-Hunter
was or the MD-452, that Dassault built for the
French air force, but it didn't have a flying
tail on it.
-- Bruce
David C. Rolley
parts count advantage in manufacturing.
The primary disadvantage of an all-flying stab in our (low speed glider)
applications is that it doesn't always behave the same way a
conventional tail aircraft does.
One example of this behavior is an uncommanded pitch up at the beginning
of tow or shortly after liftoff while holding forward stick. Pushing
the stick further forward does not necessarily bring the nose down if
the horizontal tail is stalled. Returning the control to neutral is the
correct action to regain control. But who, trained by the lightplane
(including glider) in the USA, would ever pull the stick (or yoke) to
break an impending stall?
Another good idea which some folks like but most have some level of
difficulty with is a flap only glider (no separate spoilers or dive
brakes). I owned and flew a Concept 70 for 8 years and several hundred
hours. I loved it. You come down like a yard dart! Folks on the ground
used to ask to see a full flap (90 degrees) approach and some never
wanted to see one again because the steepness scared them. I liked it
and miss that capability in my current ship. BTW, I once had a high
time instructor tell me that I shouldn't reduce my flap setting once I
deployed my flaps. Glad I knew he didn't understand the meaning of LOTS
of drag. You adjust ANY drag device to meet the circumstances. But
flap only gliders aren't the norm. However, an ASW-20 ought to be a
blast, 60 degree flaps ("A" model) AND spoilers! The best of both
worlds? Well, the later models of the -20 had somewhat less maximum
flap deflection. 60 degrees of flap by itself generate lots of drag
and, I'm making an assumption here, I'd guess a lot of folks weren't
prepared to deal with having to adjust BOTH spoilers and flaps if things
go bad on short final. So perhaps that was too much of a good thing.
Different isn't necessarily bad. But deviations from the "normal"
control behaviors or "standard" system configurations can lead to
problems when training and mentoring fall short.
Remember, today's high performance world championship winner is, maybe
20 years from now, someone's low priced first ship.
Dave Rolley
Martin
Ian Molesworth <i...@imolesworth.demon.co.uk> wrote in message
news:957264999.1441.0...@news.demon.co.uk...
You're welcome.
BTW you are right, I should have been more specific. In this case it is
probably a SIE-3 problem. The ship just isn't stable and the all flying
elevator surely contributes to this problem.
Martin
Martin
SoarHead <soar...@aol.com> wrote in message
news:20000502195257...@ng-fk1.aol.com...
Do you really think I still fly it?
Martin
Sula
>The all-flying stab does have some aerodynamic advantage.
Against this is the problem of fairing the junction between it and the
vertical tail.
>It also has a parts count advantage in manufacturing.
Possibly, though this isn't obvious when you consider the stab's support and
its drive mechanizm.
Geoff Butler
>
>>Apart from some perceived resistance to this type of tail configuration, why
>>haven't they caught on?
>
>stab offers less pitch effectiveness than stab-and-elevator because the
>stab-and-elevator change the camber of the tailplane, which apparently
>properly designed all-flying stab would have all of the pitch control
>one would need.
I flew an all-flying tailplane for many years, on a Dart. There was no
problem with pitch effectiveness, but a lot of problems with pitch
accuracy. It may have been a matter of design, but there was very little
feedback through the stick, so it was very difficult to keep a constant
attitude by feel. The result was speed wandering all over the place
whenever you concentrated on looking anywhere other than straight ahead.
Geoff Butler
David C. Rolley
Sula wrote:
> Against this is the problem of fairing the junction between it and the
> vertical tail.
>
The Nimbus 2 that I salvaged a few years back had a simple fairing that did a
pretty good job except at the extremes of travel. Which isn't a position you
would normally use in flight.
>
> Possibly, though this isn't obvious when you consider the stab's support and
> its drive mechanizm.
In some types of manufacturing, you can estimate the cost of fabrication by
counting the parts required to make up the assembly.
An conventional tail with a fixed horizontal stab and two elevators has 6 skins
that need to be bonded. The conventional system has two spars with one of them
at the rear of the fixed portion to anchor the hinges, plus the hinge mounting
points in the elevators and the hinges themselves (4 to 6). A quick count
indicates 12 to 20 major parts not counting nuts, bolts and washers.
The all flying tail has 2 skins that need to be bonded. It probably does have 2
spars and reinforcements (2 to 4) in the attach area. The hinge count will be
offset by the pivot mechanism (2?). A quick count indicates 10 major parts not
counting nuts, bolts and washers.
Then you have the assembly fixtures and jigs for each subassembly.
Remember glider component fabrication and assembly is largely hand labor.
Skilled touch labor is always expensive. So, if you can reduce the overall
number of parts, or the the number of assembly operations, or the amount of
fabrication / assembly fixtures you should reduce your cost to produce and item.
Having said all that, which supports some level of advantage to the all flying
tail, the problem with all flying tails (and other unconventional solutions) is
its "different" behavior in some realms of flight compared to the "conventional"
approaches.
Dave Rolley
Richard Friday
Regarding abrupt pitching on takeoff. I fly an IS29D with all flying tail
and have found that if I commence the takeoff ground roll with too much
forward stick there is quite a delay before obtaining elevator authority.
When it does occur the tail becomes airborne very abruptly.
The reason I believe is that with the tail on the ground, combined with the
rather tall main undercarriage of the '29 plus full forward stick the
elevator is close to its critical angle of attack and therefore partially
stalled at pre take off speeds. At some point during the ground roll
sufficient lift is generated which begins lifting the tail. This subsequent
reduction is AoA then allows the tail to rapidly unstall and then produce a
dramatic and unexpected amount of lift as we are now in the tail up attitude
with far too much forward stick. I can see how this can lead to Pilot
Induced Oscillations (the key word here being "pilot" as it is the pilot who
is susceptible and not the glider).
Experience has taught me to commence the takeoff with slightly forward of
neutral stick, concentrate on wings level and steer with rudder. At some
point (depending on headwind etc.) a conscious effort can be made to raise
the tail in a controlled manner. I would be interested to hear if this
theory is sound.
RF
Robert Whelan
>
>Regarding abrupt pitching on takeoff. I fly an IS29D with all flying tail
>and have found that if I commence the takeoff ground roll with too much
>forward stick there is quite a delay before obtaining elevator authority.
>When it does occur the tail becomes airborne very abruptly.
The same effect occcurs in my Zuni, though on the one takeoff during which I
experienced it (was consciously trying to lift the tail ASAP to reduce rock
damge from main gear debris), while below fuse liftoff speed & above "normal
tail raising speed", but with tail still firmly planted, I "did a quick
guess" and eased the stick aft. The tail immediately/abruptly lifted, and I
continued the launch. Later that flight, in more or less still air, I did a
series of zoomies to see if I could replicate the effect, & thought I
could - for both forward and aft stick. What seems to happen is the tail
drag noticeably increases when stab flow is "highly separated", while the
directional force reduces significantly. In other words, rather than
increasingly larger stick motion resulting in continually increasing pitch
rate changes, the rate of pitch change DEcreases with increasing stick
motion. The actual pitch motion remains in the expected direction, though.
I view the characteristic as an interesting curiosity/quirk rather than
black and white "bad". I'd flown the ship for several hundred hours without
noticing the characteristic, before making that particular takeoff. Except
for the one takeoff and when actively experimenting, in ~2000 additional
hours, I've never had occasion to move the stick to the positions inducing
the quirk.
>The reason I believe is that with the tail on the ground, combined with the
>rather tall main undercarriage of the '29 plus full forward stick the
>elevator is close to its critical angle of attack and therefore partially
>stalled at pre take off speeds. At some point during the ground roll
>sufficient lift is generated which begins lifting the tail. This
subsequent
>reduction is AoA then allows the tail to rapidly unstall and then produce a
>dramatic and unexpected amount of lift as we are now in the tail up
attitude
>with far too much forward stick. I can see how this can lead to Pilot
>Induced Oscillations (the key word here being "pilot" as it is the pilot
who
>is susceptible and not the glider).
>
<snip>
>I would be interested to hear if this
>theory is sound.
>RF
Based on what you've written you've experienced, *I* think it's likely to
be. I came to the same conclusion about my bird in the mid-eighties.
Regards,
Bob Whelan