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-   -   How to build wash out in a foam wing (http://www.rcuniverse.com/forum/scratch-building-aircraft-design-3d-cad-174/654801-how-build-wash-out-foam-wing.html)

Ragz 03-28-2003 05:57 PM

How to build wash out in a foam wing
 
Hi,
This is going to be my first attempt at foam wings. I need to incorporate a 1/8 inch wash out in it. I have the root and tip rib template. Can someone walk me through the procedure. I am going to wire cut the wing.

Anurag

FLYBOY 03-28-2003 05:59 PM

How to build wash out in a foam wing
 
When you put the templates on the core, put the washout in them then so it is there when you cut it. Put the tip trailing edge up the amount of washout you want.

Ragz 03-28-2003 06:08 PM

How to build wash out in a foam wing
 
just to clarify...wash out means, the leading edge of the tip rib has a positive incidence...with the tip rib trailing edge still in line with the root rib trailing edge.

anurag

FLYBOY 03-28-2003 08:27 PM

How to build wash out in a foam wing
 
You mean negative. You want the center of the wing to stall before the tip. If the tip stalls first, the plane will start a spin. you want the trailing edge higher or negative relitive to the rest.

Take for instance a flat wing trainer. they have you twist the wingtip trailing edge up 1/4 inch or so and shrink the covering so it will stay. That way the tip keeps flying when the center is stalled.

FLYBOY 03-28-2003 08:36 PM

How to build wash out in a foam wing
 
The most used method to make a wing stall more gentle is to use washout in the wing. This is accomplished in the following way. The wing is twisted slightly with the root rib being set parallel with the flight path and the tip rib being set with a little bit of negative incidence as shown in figure 2a and 2b. When the angle of attack of the wing is increased it will be greater in the center of the wing than out toward the wing tips. Since the angle of attack is greater in the center section then it will stall first while the tips are still flying. The plane will start losing altitude because of the loss of lift but will still be flying straight and true. If the angle of attack is increased more, the stall will start spreading toward the tips and they will eventually stall also.

Info copied from this web site.
http://webpages.charter.net/wrhardin/gs/why2.html

Take a look. It will answer all your questions.

Ragz 04-01-2003 07:17 AM

How to build wash out in a foam wing
 
great info flyboy..thanks...

lslewis 08-09-2003 05:13 AM

Thanks
 
I really did not understand washout. Did a search and must say your explaination is the best. Thank You

cometravi 08-20-2003 02:05 AM

How to build wash out in a foam wing
 
Flyboy is right. When you make the foam cutting templates, the washout should be there but I guess Ragz, u were asking how exactly to cut. The problem compounds a bit since you have tapered wings so you need to consider the wire speeds as well.
I read a few posts a while back, cant remember where exactly, but the best way to cut a washout into a wing will be to cut the wing in one go.. i.e. two wires top and bottom moving together over the foam block via the templates with washout built in.

Do get your washout in Ragz. It goes a long way in making your model really last. People underestimate its value especially considering that 60% of the crashs will start with a tip stall at slow speeds. Its another matter that people dont admit it!!!

The only negative aspect of the washout is of course the wash in!!!! i.e. when flying inverted it becomes wash in!! so during low inverted passes always keep the speed well over the limit!!!

johnnyo 08-21-2003 03:12 AM

washout
 
I must say there is a simple way and it works just fine. Assumeing you understand, that when cutting a tapered wing, that the cutting wire has to cut the foam from end to end at a different rate at each end. (The root needs to be traveling much faster than the tip) For example, the wire travels the width of the wing without stopping, but both ends have to enter and exit the foam at the same time.. If you have that already figured out, simply add a 1/8" spacer to the trailing edge of your tip template only not to the foam. Let the wire cutter do the rest.
If you have a buddy around with a feather cutter, buy him a six-pack and a burger, he'll be glad to help out
JohnnyO


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