control actions reversed at transonic speed??
Martin
(just after ww2) when conventional aircraft dived from height
and their speed approached M1.
The stories state that the action of the control surfaces (particularly
the elevators) were reversed, so they had to push the stick forward
to raise the nose.
If these stories are true, how could the control surface actions become
reversed? Maybe the elevators-down increased drag and reduced
tail-lift, or maybe the CoG moved backwards for some reason??
Does anyone know about this to save me guessing and coming up
with any more stupid answers?!
Martin
ent...@staffs.ac.uk
dr...@mit.edu
writes:
|> Martin (ent...@staffs.ac.uk) wrote:
|> : I've heard the stories about the early days of high speed flight
|> : (just after ww2) when conventional aircraft dived from height
|> : and their speed approached M1.
|>
|> Lockheed P-38 was undergoing test flights. As the airplan approached
|> high subsonic speeds (usually while diving) the airplane tended to
|> nose over. This put the plane in an even steeper dive and, if the
|> plane didn't become "locked" into position, it was exceptionally
|> difficult to pullout of the dive.
|>
|> This "tuck-under" (or "Mach Tuck") effect was the result of
|> commpressibility effects on the main wing of the P-38. When critical
|> Mach was reached, the downwash angle was drastically reduced. This
|> means that the horizontal tail's angle of attack (and therefore
|> positive lift) was greatly increased. This lead to a strong pitching
|> moment as it shifted the aerodynamic center to the rear of the CG.
The effect you are referring to is just the usual decrease of tail
effectiveness due to wing downwash. It has nothing to do with transonic
effects.
"Mach Tuck" is due to the wing airfoil's pitching moment coefficient (Cm)
becoming more negative as the suction-surface shock moves back at higher
Mach numbers. This effect is not seen at lower Mach numbers, since the
Cm is more or less constant then.
Mark Drela First Law of Aviation:
MIT Aero & Astro "Takeoff is optional, landing is compulsory"
Jason C. Bowman
>break the sound barrier in level flight. The control instabilities
>that the aircraft experienced were mainly due to: 1) the "Mach tuck"
>effect - which is a nose-down moment caused by the shift of the
>aerodynamic center rearwards at high transsonic speeds, and 2)
>unstable wing wakes impinging on the elevator surfaces as the airflow
>went critical (i.e. locally supersonic) over the wing surface before
>actual Mach 1.
>
>I will leave a technical discussion of these phenomena to those who
>know better than I.
Just thought I'd add my $0.02. I think Yeager said in his
autobiography that they found that using the variable incidence tail
was one of the keys to breaking Mach 1. Yeager found this out after
losing elevator effectiveness on the way to Mach 1. I don't know the
original purpose of having the variable incidence, but it turned out
to be a blessing in disguise. It is interesting to note that the
F-86 appeared with an all moving tail shortly thereafter, and the
Mig-15 still had the old elevator. But I tend to think the F-86
had the all moving tail in the original design since the difference
in time between Yeager's flight and the F-86 was something like
6 months.
Ed Hahn
Date: 14 Oct 1994 10:01:07 -0500
The stories state that the action of the control surfaces (particularly
the elevators) were reversed, so they had to push the stick forward
to raise the nose.
Control surfaces do not reverse themselves at transsonic speeds. This
myth was started by the British film, "Breaking the Sound Barrier",
which is a fictionalized account about DeHaviland's attempt to break
the sound barrier after WWII.
In the movie, several pilots get killed trying to break the sound
barrier due to control problems near Mach 1. The method they use to
break the sound barrier is to perform a power-on dive at altitude and
attempt a pull-up afterwards, as you described. The movie's
protagonist gets himself into the same situation, and after trying to
do a normal pull-up, "discovers" that the controls are reversed. He
then pushes the stick forward and the airplane is saved, and he breaks
the sound barrier, hurrah!
As you know, the USAF in real life used the rocket powered X-1 to
break the sound barrier in level flight. The control instabilities
that the aircraft experienced were mainly due to: 1) the "Mach tuck"
effect - which is a nose-down moment caused by the shift of the
aerodynamic center rearwards at high transsonic speeds, and 2)
unstable wing wakes impinging on the elevator surfaces as the airflow
went critical (i.e. locally supersonic) over the wing surface before
actual Mach 1.
I will leave a technical discussion of these phenomena to those who
know better than I.
ed
//////// Ed Hahn | eh...@mitre.org | (703) 883-5988 \\\\\\\\
The above comment reflects the opinions of the author, and does not
constitute endorsement or implied warranty by the MITRE Corporation.
Really, I wouldn't kid you about a thing like this.
Thomas A Washington
|>
|> Just thought I'd add my $0.02. I think Yeager said in his
|> autobiography that they found that using the variable incidence tail
|> was one of the keys to breaking Mach 1. Yeager found this out after
|> losing elevator effectiveness on the way to Mach 1. I don't know the
|> original purpose of having the variable incidence, but it turned out
This is fun!! Ill add my $0.02 also...
The reason this turned out to be a "blessing in disguise" is because
the shock waves which formed on the tail were located at (or ahead) of
the hinge line. This was believed to have caused the "elevator
ineffectiveness" due to possible boundary layer separation behind the
shock. The natural solution to regain control: move the whole
tail....
Thomas Washington
Mark Shaner
: I've heard the stories about the early days of high speed flight
: (just after ww2) when conventional aircraft dived from height
: and their speed approached M1.
These problems actually began occuring during 1941 and 1942 while the
Lockheed P-38 was undergoing test flights. As the airplan approached
high subsonic speeds (usually while diving) the airplane tended to
nose over. This put the plane in an even steeper dive and, if the
plane didn't become "locked" into position, it was exceptionally
difficult to pullout of the dive.
This "tuck-under" (or "Mach Tuck") effect was the result of
commpressibility effects on the main wing of the P-38. When critical
Mach was reached, the downwash angle was drastically reduced. This
means that the horizontal tail's angle of attack (and therefore
positive lift) was greatly increased. This lead to a strong pitching
moment as it shifted the aerodynamic center to the rear of the CG.
There is a good expanation of this and the solution which NACA came up
with in INTRODUCTION TO FLIGHT by John D. Anderson. (McGraw-Hill 1989,
3rd ed.)
--
"Sometimes gentle, sometimes capricious, sometimes | Mark Shaner
awful, never the same for two moments together; almost | sha...@eng.umd.edu
human in its passions, almost spiritual in it tenderness | U of MD at College
almost divine in its infinity" --John Ruskin, THE SKY | Park, USA
------------------------------------------------------------------------------
John F Carr
Ed Hahn <eh...@fairlite.mitre.org> wrote:
>Control surfaces do not reverse themselves at transsonic speeds. This
>myth was started by the British film, "Breaking the Sound Barrier",
>which is a fictionalized account about DeHaviland's attempt to break
>the sound barrier after WWII.
Ailerons do reverse at high speed, but the reversal speed could be less
than or greater than Mach 1 depending on how stiff the wing is. Typical
speeds for WWII fighters were 450-800 mph (obviously the high range is
based on theory, not flight tests).
--
John Carr (j...@mit.edu)
Rune Winther
> From: ent...@staffs.ac.uk (Martin)
> Date: 14 Oct 1994 10:01:07 -0500
>
> The stories state that the action of the control surfaces (particularly
> the elevators) were reversed, so they had to push the stick forward
> to raise the nose.
>Control surfaces do not reverse themselves at transsonic speeds. This
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>myth was started by the British film, "Breaking the Sound Barrier",
>which is a fictionalized account about DeHaviland's attempt to break
>the sound barrier after WWII.
In fact, if we talk about control surfaces in general, there have been
situations were the effect of the control surfaces has been reversed.
A couple of years ago I read Jeffrey Quills (?) account of the
development of the Spitfire. When reaching a certain speed, the force
of the ailerons twisted the wing with the net effect that the aircraft
rolled in the opposite direction.
I know that the original poster on this thread was most concerned
about the effect of the elevators at transsonic speeds. However, this
little story did seem related so I thought I'd give it a try.
Rune
--------------------------------------------------------------------
Rune Winther
Rogaland University Center
P.O.Box 2557 Ullandhaug
4004 Stavanger
Norway.
e-mail : r...@hsr.no
Telephone : + 47 51 83 18 78
: + 47 51 68 95 43 (priv.)
Fax : + 47 51 83 10 50
John R. Boatman
> The stories state that the action of the control surfaces (particularly
> the elevators) were reversed, so they had to push the stick forward
> to raise the nose.
One scenario is that when the elevator is deflected at "extreme"
speeds (for which the aircraft was not designed) it causes the entire
horizontal stabilzer to deflect. The elevator thus acts like a trim
tab which does act "in reverse."
Bill McCune
The word around here is that the X-1 horizontal stabilizer actuator
was purchased at a hardware store...in Lancaster, CA...
Well, it worked!
[Moderator's note: The shocks for the landing struts for the Spin
Research Vehicle were heavy-duty Cadillac shocks from the Lancaster
Sears store. MFS]
-Bill
Bill McCune
rav...@spaceworks.com