KW_Counter

I have been reading a lot about washout lately.
All of the solutions seem to involve warping the wing.
Is there an easier way such as adding some type of wingtip?
I see many planes with tips that point up or down, is this for washout?
I am not referring to side force generators.

Thanks,
KW_Counter

AA5BY

I think the answer is basically no. The washout area needs to include the aileron area because if the wing stalls in all of the aileron area, there is no roll control.

Washout is not used on fully aerobatic designs that require as good inverted characteristics as upright. Now to the basically part of the no answer. Simulated washout is possible and quite easy to do on wings with barn door ailerons where there is a servo for each aileron and a spare channel to separate the left aileron to an aux ch. When doing that, the ailerons are given a mix from the throttle so that they start trimming up at perhaps half throttle and become trimmed up perhaps 3/16" at low throttle. This actually makes a nice setup because the model has no washout under power to possibly harm inverted flight, but has some forgiveness when powered down for landing.

There are of course wing tips that can reduce air flow losses on the tip and assist in preventing tip stall by keeping the end of the wing including the aileron area from stalling.

JohnBuckner

My Feedback: (1)

Yes indeed there are other simple solutions although not as often used simply because warping is so easy and effective contributing to for example a great flying but heavy tricked out warbird.

One of the first is the very simple expediant reflexing both ailerons "up" above the intrail neutral position just a few degree. This is done just by a few twists of some clevis on both side.

Another method is to trip a stall at the wing root first before the tips simply by the addition of a sharp corner on the leading edge just in the area of the roots. This method is very common in the full scale world and used on most Mooneys for example. On our airplanes just glueing on a bit of tri stock just to the wing roots leading edge does the trick.

There are other methods that are not so practical for our purposes also such as airfoils transforming from ones of different stall characteristics at the tip and the roots.

John

pimmnz

John is right, however a caution about using a 'stall generator' at the wing root. As a fix it simply means that the airplane will stall at a higher speed/lower angle than before, that is, before the tips get a chance. This can make landing and slow speed manuvering even more difficult. On full size, as often as not, they are used to provide a bit of turbulence at higher AOA's so that the pilot fells a bit of a bump through the controls, a 'stall warning' or stick shaker, just to indicate that he's reaching the limits. Some full size aircraft will stall without much aerodynamic fuss, hence the use of the leading edge addition.
Evan, WB #12.

fredsedno

I keep it simple: balsa aileron stock just under 1/2 wingspan long, 1/4" thick. Pin thin edge under trailing edge at wing root, swing thick edge
of aileron stock [1/4"] under trailing edge of wing at wing tip and pin. Complete wing construction, 1/4" washout for full len. of wing.
Depending on desired amt. of washout simply use aileron stock of a different thickness. fredsedno

JohnBuckner

My Feedback: (1)

The leading edge stall trips at the wing roots do function by 'tripping a stall at a slightly lower angle of attack, however its my belief that they are in no way something to be wary of anymore that the other methods of causing the wing roots to stall first before the region of wing where the ailerons are.

That is the whole point of twisted wings, a spanwise airfoil change and of course root region stall trips.

This method has also been well tested by prolific and brilliant model aerodynamics researcher Andy Lennon and published many times over the years.

I actually did use this method one time to help a desparate friend and it was a wonderful success. This was about five years ago and my friend purchased an early CMP P-40 arf. He did the maiden and promptly crashed. After repairs I tried the next maiden but did survive but just barely. You could not slow it down at all without it wanting to immediately depart. On the next flight attempt I crashed it.

Well heck with this after next set of repairs I glued two short sticks of tri stock in seconds to the wing roots and the transformation was remarkable. The airplane became completely managable. Over weight, sure and definatelely not a pattern airplane but managable and actually fun. That ship has survived to this day.

This simple solution (leading edge tri angle stock at the roots) is a viable solution for many airplanes that may have problems and takes only a minute to stick on a couple of sticks where its not practical to twist an already constructed wing. 'Simple'


John