Wing Washout?

[moy71]

Hi there. I am now in the process of covering my GP Electricub with monokote. The instructions says I should make a wing washout by twisting the wing so the trailing edge is higher than the leading edge, then cover it.

Has anyone had any experience with this so-called washout? Does it really make a difference?

rgds.

[CalmAir]

Hi Moy71,

The wing washout they are talking about is at the trailing edge of the wing, at the wingtip. If you lay the wing on a flat surface the trailing edge, at the wing tip itself, would be up off of the table a small amount. Typically that is about 1/4", but use the distance that your manual calls out.

Wash out does make a difference. The reason for adding washout at the wingtip is to keep the tip from stalling later than the main part of the wing. When the tip stalls it will cause that wing to drop very quickly. By slightly raising the rear of the wingtips you are changing the angle of attack of the tips. What happens is the main section of the wing will stall before the tips. This will cause the plane to mush out and lose altitude, or drop the nose during a stall, rather than dropping a wing drastically. This does not mean you could not tip stall the aircraft, but it will make it much less likely.

I have always added the washout after the wing is covered, but that is using heat shrinkable material such as Monokote, Econocote, etc. I do this by holding the wing in the center with one hand and slightly twisting the wingtip with the other hand and passing the wing over a heat gun until the wrinkles caused by the twisting disappear. This does not take long. Continue holding until the wing cools. If you are looking for 1/4" washout then twist about 1/2" and when the wing cools it will spring back a little giving you the 1/4". If you are covering the model with a different kind of covering then some of the other folks could give you instructions for doing that.

Dont spend hours trying to get the washout just perfect, just make sure you do not have any wash-in.

Dale

[BrokenChild]

You did a very good job of describing the trick, but if I'm not mistaken you made one small error in the middle stanza or middle paragraph

"By slightly raising the rear of the wingtips you are changing the angle of attack of the tips."<--- this is true, but for the tips to stall out later than the center of the wing, it would need to be the front edge of the wing twisted higher, not the rear. Sorry if this seems offensive, but if he is uncertian of what he is doing or doesnt have the concept in his mind as well as you and I do then he just crashed an airplane.

respectfully,
bc

[2NG]

Wing tip, to be raised. Greatly need for the CUB

[Dave Robelen]

Hi Brokenchild,
There does seem to be a mixup in the labeling. If the tip were twisted so that the leading edge were higher than the TE, that would be labeled washin, and that is bad news. The concept behind the use of washout deals with the fact that the portion of the wing with the highest angle to the oncoming airflow will stall first. By using washout (tip angle reduced relative to root) the wing will usually begin stalling near the center first giving some warning that you are flying too nose high. A model with washin is likely to suddenly do an uncommanded snap roll when flown too nose high. That is best avoided ;)
Regards, Dave