I just built a Dumas Bear Cat... 30" w/s. Anyway my question is: What aileron configuration would best help prevent tip stalls. (Yes I already added wash out.) I would like to know--From all you aerodynamistss out there if the ailerons should be slightly raised, slightly lowered or perfectly faired.
All comments are welcome!
Thanks in advance.
Sincerely... J

J.......I can share with you what I have found on the bigger "warbirds"....I fly 85" WS and larger.....I have "tinkered" with aileron adjustments and have found by "flying" that a slight "droop" works the best....I am assuming the tip stalling you are refering to is at/near stall speeds during landing......My P-47(Ziroli) I have about 1/16" droop in each aileron and with 45* of flap on a 36# plane I can slow it up and make very good wheel landings without being concerned about the "Bottom falling out".....I dont know much about the smaller planes but try small adjustments starting from neutral(Thats what I did)...and see what works best for you.......BTW...one reason I tried "drooping" the ailerons is thats what alot of the new generation large commercial aircraft (Boeing/Airbus) ...have for landing flap configuration......Bill......

.
As you already have the washout, don't do anything.
Tip stalls come from a couple of sources:
Too much elevator.
Aft c.g.
..
Don't yank the plane off the ground on takeoffs if it's underpowered.
Keeping the airspeed up prevents tip stalls when landing.
If these conditions are considered and fixed as appropriate, tip stalls are highly over rated as problems.
.
ps. Drooping the ailerons -removes- the benefit of washout!

Tall Paul........I am aware that aerodynamically speaking that "down"aileron will remove "some" of the washout............but from trial and error testing It has some benefit for slow speed landing configurations.....I can't explain it using aerodynamic nomenclature and the like ...but it works in the real flying world.........Bill....

I have no doubt that "down" ailerons helped in your case, but I've had the opposite results. Drooping ailerons have lead to erratic pitching on some of my planes, raising the ailerons has resulted in a more solid feel in the air and a reduction in aileron flutter problems. I've also noticed less of a tendancy to tip stall. But I'm willing to believe that some planes and some airfoils may act differently.

Hey guys!!! I just answered a question similar to this a couple of days ago in another thread. Basically to prevent tip stalling you want the inboard section of the wing to stall before the tip. To do this you can do a few things...

1... Add a 4" long piece of triangular stock to the leading edge of the inboard sections. This creates the effect of sharpening the leading edge, inducing a stall in the inboard section...keeping the wings level.

2... You are correct in that drooping ailerons only work for some aircraft. It all depends on how it effects the angle of attack relative to the airflow. In some situations it effectivly increases the camber of the airfoil, giving you flap like characteristics, which is like reducing the stall speed of the section.... preventing the tip stall. If washout is built in it has a negative effect, because gross angle of attack is now too high in the wrong diection ( if that makes any sense ) in that it will just produce too much drag and have messy tenancies.

I dont like messing with the ailerons. It is far better and more effecting to add the triangular stock and modify the airfoil. It makes all the difference.

When outboard ailerons are drooped to act as flaps (if they are) on a full-scale 200 ton airliner, the plane is NOT going to be manuvered any more than the slight corrections needed to keep it on the glide path.
The situation is NOT directly transferable to a 10 oz model airplane which will be flung around.

Tall Paul.....I certainly understand your concern using "alternative" flt control rigging....but I'm not flying 10 oz or even 10 lb airplanes.... all are WWII vintage aircraft and the lightest I have is 29 lbs and my biggest is a Ziroli B-25 @ 40 lbs loaded with fuel and bombs.....Being an Aircraft Mechanic and working on large commercial aircraft daily has given me some insights on different ideas to try.......and I qualify that by saying its done using "small" changes to flt control rigging....and then flying my planes to see how they respond....and I read your posts along with several other of your Aerodynamic sharpies with great interest....I have learned alot from you guys.......but with that said....I do experiment time-to -time trying to gain an edge by making changes...and if they appear to work better....why not share that....even if at times it seems contradictory to mainstream aerodynamic thinking......Bill

But they do use them on DeHavilland Canada aircraft. In the world of STOL they really do work and work very well.

I believe there are several things going on here. The Reynolds Number effects start to get to the smaller airplanes I think.

Bill, I think I can assume that you are fairly competent in your ability to fly, observe and correct the flight of your airplanes, knowing when a stall is about to occur, knowing just how to nuge the up elevator on landing, etc., so that when you did something to increase the CL of the airfoil you knew how to take advantage of it. It is a carefully considered refined change combined with lots of experience and you end up with a successful change.

Now transfer to a 30inch span model. The little monsters hardly know when you are trying to finesse them much less do anything right. I have a lot of them in the garage of that size and find that the effects of washout is readily noticable, aileron droop - more difficult to determine if you have done anything other than make the change from flying to stall a little more abrubt. Most of my experience along this line has been with a GWS Zero.

A big difference from your monsters.

1. Drooped ailerons are used on full scale aircraft in conjunction with flaps to gain a little extra lift on approach. I don’t think you will find them used in an otherwise clean configuration.

2. Every drop of a wing, or sudden snap is not necessarily tip stall. Anything that produces yaw when operating close to the stall angle of attack can cause one wing to stall before the other resulting in a sudden roll. The stall is not always at the tip, but it will still produce a snap. Full scale aircraft have an advantage in that the pilot is controlling the rudder and doesn’t allow yaw to develop, and many of the larger aircraft have a full time yaw damper that positively prevents yaw. On the other hand model pilots have no way to directly perceive coordinated flight. Some have formed the habit of using the rudder only for small heading changes on short final, while others tend to fly with ailerons only with no rudder input to correct for adverse yaw. Both habits introduce yawing moments which normally cause no problem, but if the speed gets a little too slow, or in presence of gusts it can be enough to trip it over the edge. Keeping the speed up is the simplest way to avoid the problem, but if that is not feasible, a habit of never moving the ailerons without a little rudder may be the solution.