Airfoiled Tail Surfaces
05-13-2007 | 04:58 PM
#26
Senior Member
RE: Airfoiled Tail Surfaces
Aerodynamically, a streamlined flat plate stab is superior to an airfoiled stab. It will stall, of course, at a much lower angle of attack than an airfoiled stab, but downwash from the wing reduces the angle of attack experienced by the stab sufficiently that the wing will always stall before the stab, even if the CG is at the aft limit of stability. The flat plate airfoil also develops a slightly steeper slope of lift versus angle of attack, so that a flat plate stab can be a few percent smaller in area while developing the necessary stability in pitch.
A T-tail arrangement will reduce the downwash, and also reduce the needed stab area, but a flat plate T-tail might tend to stall before the wing, causing a rather abrupt stall pitch-up when the CG is near the aft limit.
Structurally, a flat plate stab has serious limitations, normally requiring wire bracing except at very low airspeeds. The wire bracing adds more drag than the additional drag of an airfoiled stab. The only remaining justification for a flat plate stab is structural simplicity. In other words - crude but effective.
A T-tail arrangement will reduce the downwash, and also reduce the needed stab area, but a flat plate T-tail might tend to stall before the wing, causing a rather abrupt stall pitch-up when the CG is near the aft limit.
Structurally, a flat plate stab has serious limitations, normally requiring wire bracing except at very low airspeeds. The wire bracing adds more drag than the additional drag of an airfoiled stab. The only remaining justification for a flat plate stab is structural simplicity. In other words - crude but effective.
05-13-2007 | 08:53 PM
#27
Senior Member
Joined: Aug 2005
Posts: 1,333
Likes: 0
Received 0 Likes
on
0 Posts
From: Austin,
TX
RE: Airfoiled Tail Surfaces
ORIGINAL: longdan
I am scratch building a plane at the moment that has a foiled horizontal stab. The foil is added on to the top and bottom surfaces of the built up stab like ribs. They increase the overall thickness of the stab from 1/4" to about 1/2", but the spars are still only 1/4" thick, so the foil does nothing to add strength. And it's hardly a speed demon either - it's a Tyro Major, a 3 channel trainer from the 70's.
I am scratch building a plane at the moment that has a foiled horizontal stab. The foil is added on to the top and bottom surfaces of the built up stab like ribs. They increase the overall thickness of the stab from 1/4" to about 1/2", but the spars are still only 1/4" thick, so the foil does nothing to add strength. And it's hardly a speed demon either - it's a Tyro Major, a 3 channel trainer from the 70's.
