Asymmetrical Washout Concern
Asymmetrical Washout Concern
(OP)
I have a composite, kit built aircraft that I'm dealing with that was assembled with one wing in an incorrectly aligned jig. The result: the right wing is right on spec, with 2 degrees of washout. The left wing, however, only has .3 degrees of washout. The outer two cradles were out of alignment when the builder closed the wing (locking in the geometry). The problem wasn't discovered until after the first flight when a significant right banking tendency was discovered (no surprise there). The bulider took careful measurements along both wings and compared his measurements to the factory specs and blueprints.
The kit company suggested using eccentrics to get rid of the banking problem, tip the right wing up and the left wing down. I know the certified companies routinely use eccentrics to get planes flying straight, but that's with symmetrical (or nearly symmetrical) wings.
The builder installed eccentrics to adjust the wing incidence at the roots. Now the plane flies straight in cruise but the stall characteristics are not ideal, a right wing drop at the stall (no surprise there either). At least theoretically, the right wing now has more incidence at the root, so it stalls first, followed by the entire left wing, then the right tip stalls last.
Now to the question, is the eccentrics solution acceptable, or should the builder insist of re-closing the wing in properly aligned wing cradles?
I don't consider a "straight flying airplane" to be the same as a "straight built airplane". Tipping one thing one way to compensate for something else that's crooked isn't a solution in my opinion.
The original wing designer, Rick McWilliams, put those two degrees of washout in there for a reason. Some washout is important for lift distribution on a tapered wing, but it really makes the plane controllable at the onset of the stall, the ailerons still work. In addition, the lift distribution along that left wing is way off from the original design, structural issues???
I'm curious to hear what some experts have to say on the issue.
Thanks in advance,
Mike Easley
Colorado Springs
The kit company suggested using eccentrics to get rid of the banking problem, tip the right wing up and the left wing down. I know the certified companies routinely use eccentrics to get planes flying straight, but that's with symmetrical (or nearly symmetrical) wings.
The builder installed eccentrics to adjust the wing incidence at the roots. Now the plane flies straight in cruise but the stall characteristics are not ideal, a right wing drop at the stall (no surprise there either). At least theoretically, the right wing now has more incidence at the root, so it stalls first, followed by the entire left wing, then the right tip stalls last.
Now to the question, is the eccentrics solution acceptable, or should the builder insist of re-closing the wing in properly aligned wing cradles?
I don't consider a "straight flying airplane" to be the same as a "straight built airplane". Tipping one thing one way to compensate for something else that's crooked isn't a solution in my opinion.
The original wing designer, Rick McWilliams, put those two degrees of washout in there for a reason. Some washout is important for lift distribution on a tapered wing, but it really makes the plane controllable at the onset of the stall, the ailerons still work. In addition, the lift distribution along that left wing is way off from the original design, structural issues???
I'm curious to hear what some experts have to say on the issue.
Thanks in advance,
Mike Easley
Colorado Springs





RE: Asymmetrical Washout Concern
maybe ... MAYBE ... the same appraoch can be used on a kit plane, i'm only posting as an example solution ... "straight flying" is (atleast can be) almost as good as "straight"
RE: Asymmetrical Washout Concern
Mike Halloran
Pembroke Pines, FL, USA
RE: Asymmetrical Washout Concern
I talked to a Beechcraft "old timer" today. He said that they do some tweaking at the factory to get the Bonanzas to fly straight. The small stall strips on the leading edge are taped on to start with, tested until the plane drops straight ahead in a deep stall, then they permanently attach the stall strips before the bird is delivered.
Interesting....
My assumption is that a Lancair is built with a very high performance airfoil, not very tolerant of any build errors.
I walked around my home airport today with my digital level, checking the various certified aircraft sitting out where I could get at them. I had Pipers from the 70s, Bonanzas from the 50s. And everything in between. I took measurements from both wings, just to compare left to right at the same places, checking for wing incidence symmetry. I was pretty impressed. Virtually every aircraft was within a few tenths of a degree anywhere along the wings I checked. One Piper Archer from the 70s was dead on at three different places.
RE: Asymmetrical Washout Concern
It appears you have 3 choices: Leave it like it is. Split the wing and reglue it. Buy a new wing from from the factory.
I did not think that the airfoil used on that aircraft, which I believe is the NLF (1)-0215F, has a particularly sharp stalling characteristic, so even with the lack of washout apart from the fact that one wing drops first the stall should not be violent.
Since the aircraft is flying, have you done a test flight series? Checking the stall characteristics in the turns. Checking for a tendency for an over the top spin entry into the wing without enough washout. If the machine behaves itself leave it alone. If it does not, then fix it.
B.E.
RE: Asymmetrical Washout Concern