Knowledge Challenge...Horizontal Stabilizer

[Hawg11]

Be the first to correctly identify why most fighters' horizontal stabilizers rotate as one piece (as opposed to elevators).

[SwingKid]

Supersonic?

 

-SK

[Hawg11]

Supersonic?

 

Rgr that!

[Hawg11]

It was discovered early in flight testing (for the X-1) that while supersonic, elevators were too unstable. The X-1's horizontal stab. actually rotated as a single piece. It was disguised (due to the emerging cold war) with paint to make it look like an elevator.

[SwingKid]

It was disguised (due to the emerging cold war) with paint to make it look like an elevator.

 

Is that true? I thought it really was hinged:

 

"this was first discovered in the Bell X-1; fortunately, although the tailplane was conventional in design, Bell Aircraft Corporation had included an elevator trim device that could alter the angle of attack of the entire tailplane; this saved the program from a costly and time-consuming rebuild of the aircraft"

 

http://en.wikipedia.org/wiki/Tailplane

 

I admit, I don't know which story is correct.

 

-SK

[Weta43]

Stability ? - not simply to lower deflection angles ( larger area = greater volume of air moved & more force for a given angle of deflection & drag) & lower actuator pressures needed at high (supersonic) speeds (down pressure at one end cancels out up pressure at the other & results in lower net forces needed for a given deflection)

 

Don't know jack Shi* about it, but this would have been my guess.

[Hawg11]

Is that true? I thought it really was hinged:

 

"this was first discovered in the Bell X-1; fortunately, although the tailplane was conventional in design, Bell Aircraft Corporation had included an elevator trim device that could alter the angle of attack of the entire tailplane; this saved the program from a costly and time-consuming rebuild of the aircraft"

 

http://en.wikipedia.org/wiki/Tailplane

 

I admit, I don't know which story is correct.

 

-SK

 

It had an elevator trim, (kind of like the trim tabs on the A-10), which, in turn, moved the entire control surface (unlike the A-10, which uses the trim tabs only to adjust the heavy elevators. It essentially lets the wind do the work). *I think*

 

http://en.wikipedia.org/wiki/Elevator_(aircraft)

 

"Supersonic aircraft lack elevators, because of early supersonic flight research that revealed that shock waves generated on the tailplane rendered separate hinged elevators ineffective. Instead, on supersonic aircraft the entire tailplane moves to control pitch."

 

Hmm, so yeah (now that I think about it), I guess the hinges do probably work. Damn! I hate being wrong. Anyway, they aren't elevators in the conventional sense...and, instead, are used to rotate the entire stabilator.

 

Sorry, it says I have to spread more rep around b4 i can give it to you again.

 

Now I've gotta go re-read my history. I could have sworn I read that the horizontal stabs were disguised with paint.

[Weta43]

Told you ...

[Hawg11]

Maybe it was the F86 I read that about?

 

"As sufficient aerodynamic data were not available, Bell developed a precautionary backup in which the entire tail plane could be moved as an emergency measure. The solution worked so well that it was later adopted as standard on all supersonic aircraft. It also became a well-guarded military secret, accounting in significant part for the ascendancy of F-86 Sabre over Mig-15 during the Korean conflict."

 

http://www.ipmsstockholm.org/magazine/2001/11/stuff_eng_bell_x1_part1.htm

[ARM505]

Just reading Yeagers autobiography, I think he mentions that it did have a conventional elevator, but with an all moving horizontal stabilizer actuated for trim functions. They discovered that approaching the sound barrier, when shockwaves started to form over the surfaces just prior to breaking the barrier, only the trim (therefore the movable stab) remained effective. It was then modded to allow the whole stab to move with with primary flight controls.

 

Something like that. Supersonice shockwaves start to form just before the sound barrier as airflow is accelerated over the surfaces of the aircraft, and airflow behind the shockwave is unable to be used for control as easily (VERY generalised, and I'm on VERY shaky ground here, passed my subjects a long time ago, and it's not like I use supersonic theory too much in a 737!)

 

I await the forthcoming corrections :)

[Guest EVIL-SCOTSMAN]

If i remember correctly, it was the british who first figured out that problem, with instability due to the sound barrier, the britsh then made a horizontal stabilizer instead of elevators...

 

Seen it in a program on discovery about chuck yeager and the sound barrier attempts.

 

basically, it was with elevators, the higher the speed, the less it actually worked due to its small size, so thats why we now see all supersonic aircraft with horizontal stabilizers instead...

[nscode]

Yup... almost had it them Brits.. damn politicians cut the funding