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Nov 07, 2017, 09:31 AM
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P-51 stab and elevator airfoils

Stab airfoils on Mustang I through P-51D/K/M are fairly ordinary, However the elevator airfoils are quite odd. The elevator is actually thicker in section than the preceding stab. It is also tear drop in shape, flowing from large LE radius, narrowing to concave reflexed aft section, terminating in a very sharp TE.

BTW- the airfoils are fully symmetrical and all ribs, skinning, and elevators will fit either right or left sides of the aircraft.

Any speculation as to why the elevators have such a radical section? Increased aerodynamic efficiency?? Gap seal issues??? Why????
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Nov 09, 2017, 12:21 AM
B for Bruce
BMatthews's Avatar
An early attempt to stop separation bubbles at the hinge line?

When I've seen that trick drawn up the idea is that the air passing over the "top" of the resulting bump doesn't see a sharp edge. Instead it sees a rounded rise and flows up and over and down the back of the deflected surface.

I've seen the same idea used on at least one modern sailplane. I just don't recall which one. But the total airfoil for the stab and elevator when together looks like two skinny tadpoles with the rear one starting to eat it's way up the tail of the one in front. The intention is that the hinge is located on the nose of the second "tadpole".

Like I say, this isn't a new idea. I've also seen in books where Frise style ailerons are hinged such that the top rounded surface can hump upwards when deflected down. Again this is intended to give the air a rounded surface to run into and go up and over and hopefully not separate and cause drag and a reduction in the lift force.
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Nov 10, 2017, 05:12 AM
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Steve Corbin's Avatar
I once read an article by Jim Bede in Sport Aviation magazine, where he claimed that when the leading edge of the control surface is larger radius than the stabilizer or wing it's attached to you get less "dead band", an aerodynamic thing that causes the control surface to have little or no effect at small deflection angles.

If the centerline of the hinge axis is moved aft enough, the leading edge radius will rise above the control surface, and the lift force produced will reduce the amount of effort required to move that surface. But ya gotta watch out, taking that idea too far can result in control surface "snatch" in icing conditions. Killed a few people, or so I've heard.

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