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Old Jul 17, 2012, 08:22 AM
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United States, MI, Adrian
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Help!
Washout Question

Looking for some help.

I have a GP Electricub on order and I read in the manual that when finishing the wings that I should put a 1/4" of washout into them.

I've also read on here that doing this when applying the covering is somewhat complicated and not very reliable.

With this being my first larger scale build ( several guillows style builds), my question or questions are, Should I just build the washout into the wing when assembling? And if so, how do I go about doing this? Do I just put a 1/4 block under the TE when doing assembly?

Any help would be great.
John
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Old Jul 17, 2012, 08:39 AM
CA...gimme the CA...
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I built one kit where I placed a spacer under the wing and tightened the covering. I wouldn't say it was unreliable, but it definitely changed over time as the covering aged and the seasons changed. I would check it from time to time and make any adjustments required....typically a quick session with the heat gun did the trick.

Building the washout into the wing will certainly have longevity, but it can't be changed if needed....or it would be extremely difficult at best.

So pros and cons for both methods! Guess it depends on your point of view and building skill/confidence.
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Old Jul 17, 2012, 09:53 AM
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The the current edition of the GP Electricub has ailerons !! Does yours have ailerons ?? If so, you are fairly well precluded from washout. You could create flaps by cutting the ailerons in half, using the inner half as flap and the outer half as aileron. This would require putting a servo in each wing to control the ailerons. You could raise each aileron a little (with the servo centered) thus creating effective washout. I don't think there is really much value though to having flaps on a Cub.

Oh, if your Cub doesn't have ailerons, then build the washout into the wing structure...best choice IMHO..

Old_dude
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Old Jul 17, 2012, 10:54 AM
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Even with ailerons, in fact BECAUSE of the ailerons, adding some washout is still a good idea.

Pigcop2, I'm not familiar with the GP Cub's framework. If it uses a "D tube" style leading edge where the leading edge is sheeted and the spar setup is a full depth so that the sheeting and spar forms a "D" shape then this produces a very stiff wing. In that case it's often best to warp the building board to build in the washout. Although I have used the covering to hold the washout in even with such a wing with good success.

If it's some other more open style of structure and assuming you're not using some super light and flexible parkflyer covering then using the covering to hold in the washout is the normal method used by the majority of us. With Monokote or Ultracote I've seldom or never needed to reset the warps once they were put in with a second use of the iron. Mind you the world is a slightly cooloer place up this way. In hotter climates it may be a different story.
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Old Jul 17, 2012, 12:22 PM
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I've done the twist in after method on a glider wing that was already built... The thing was a snapping fool until I twisted in about 1/4 of washout. It is a 2 piece wing, so when I rubber bnad them together, I slide a 1/2" scrap of balsa between the 2 tips that keeps the twist in during storage. I think I built it in 98ish... still is just fine. I think the key is the 1/2" wedge at the tip during storage..

I've also corrected some nasty tip stalls for guys at the field on sport ships by raising both ailerons up slightly.

I'm not familiar with the Great Pains ElectricCub, but I'm guessing 1/4 washout wouldn't hurt and can only do good. Heck even my Sig Kougar which is a fast SNAPPY machine has washout which makes for really nice, slow nose high landings.
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Old Jul 18, 2012, 01:15 AM
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The thing is that simply rasing the ailerons is a bit of a bandaid. Raising the ailerons changes the airfoil at the same time it adds some washout. The problem is that it adds reflex and removes some of the camber amount at the same time that it sneaks in a little washout. But a reflexed, camber reduced airfoil will tend to stall at a lower angle of attack than the proper airfoil shape which is correctly washed out.

So while reflexing the ailerons a little works it's not as good as properly warping in some washout.
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Old Jul 18, 2012, 07:46 AM
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Thanks for the input so far. I just received the box of sticks in the mail, so I'll be studying the plans a bit closer. . I plan on putting the washout in. Just not sure wich way is best. I think I would like to build it in. Just not sure how hard that is to do.

Old Dude: It does have ailerons.

Bruce, The leading edge is not sheeted. It has a D shaped "spar" that runs along the length of the wing. There is some sheeting in the center of the wing near the wing root. The plans call for me to put a 1/4in block under the TE to use as a guide. Would I be able to do the same thing by placing it under my building board? Or is it more involved than that?

Thanks again.
John
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Old Jul 18, 2012, 11:31 AM
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Quote:
Originally Posted by BMatthews View Post
The thing is that simply rasing the ailerons is a bit of a bandaid.
Yea, I realize it is a bit of a bandaid, but good for a quick fix at the field to see if it really is the issue
Quote:
Originally Posted by pigcop2 View Post
Would I be able to do the same thing by placing it under my building board? Or is it more involved than that?

Thanks again.
John
Not sure I understand that part of the question..... You will want just the tip raised, not the whole TE.

What ever you do, don't raise the root.
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Old Jul 18, 2012, 12:10 PM
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Rc: this was in a previous post. "In that case it's often best to warp the building board to build in the washout."

Should I do that? Or could I just put a 1/4 block under the trailing edge wingtip while I build the wing?
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Old Jul 18, 2012, 12:18 PM
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I can't say for sure, but the easiest way would be to use shim stock under the TE. Shim the tip of the TE to 1/4" (for example) and the pin the root to the board. Use fill shims to keep the TE straight; i.e. no bow. Kinda hard to explain, but this would be the long edge of a 90 degree triangle if you drew it out on a piece of paper.

To warp the building surface you would have to replicate the twist desired in the wing, to the board...
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Old Jul 18, 2012, 02:19 PM
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It's far, far simpler to shim the whole board. Trying to use just the right shim under each rib all along the span is going to pretty much guarantee that the final result will be wiggly like old McGee's walking stick. If the board is reasonably stiff but with enough flexibility so that it can be twisted and clamped down to form the twisted surface then the twist will be nicely and evenly graduated all along the span.

Because you are raising one corner the board will want to be "tippy". So on the two oppsite corners the idea is to either heavily weight them down so they are in contact with the bench top or to clamp or screw those two diagonal corners down to again ensure they are in contact with the bench.

Note that for the other wing to get the proper twist you will need to move the shim and weights, clamps or screws to the adjacent corner. You can't build both wings on the board with the shim in the same spot or one wing will be washed in and the other wing washed out. And that's never a good thing....
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Old Jul 18, 2012, 03:39 PM
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Build in the washout using shims, it's not difficult. Washout is not a complete twist along the entire wing. Putting washout in after the build via twist and reheating covering is generally for the outer 1/2 of the wing anyways. Don't warp the board... that will be to difficult and then what.. you'll need another flat board. Cubs are gentle flying highly stable planes once in the air. Washout will help on slow speed during landing but is not completely necessary though I recommend it. Differential will be worthwhile to program in and you will need to fly with the rudder for nice turns and apply it on takeoff as well if you want nice scale ROG..
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Old Jul 18, 2012, 04:08 PM
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Hmmmm. Thanks for the input guys. I think I'll build the washout in. I have some time to think about and play with how to go about it as I have a Diehls free flight Typhoon to finish up. When I start this one I'll be sure to post it. As I'll need plenty more advise and guidance.
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Old Jul 19, 2012, 02:17 AM
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Quote:
Originally Posted by pigcop2 View Post
...Bruce, The leading edge is not sheeted. It has a D shaped "spar" that runs along the length of the wing. There is some sheeting in the center of the wing near the wing root. The plans call for me to put a 1/4in block under the TE to use as a guide. Would I be able to do the same thing by placing it under my building board? Or is it more involved than that?

Thanks again.
John
To get a better answer for you I downloaded and looked at the manual for the Electricub. It's very much an open style flexible wing frame.

Simply put with a wing of this style there is just no need to shim the wing or the building board on this design to "lock in" the washout they suggest. Any covering suitable for a model of this size will easily be able to hold in the washout by you simply heating and shrinking in the washout desired. If there's any trick to it at all it's simply to ensure that you heat up and "shrink" both the top and the bottom covering evenly over a wide area to allow the covering to "take" to the warp you are putting in place. There should not be any need to go back for a follow up warping session. But if the covering you choose does require it then a second session to touch it up would be all it'll need.

I've done a fair number of gliders and other models with open and flexible structures similar to the Electricub. I've never built in the washout in any structures of this sort. I've always relied on the covering and I've yet to be dissapointed or let down.
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Old Jul 19, 2012, 06:26 AM
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Thanks Bruce and everybody. Like I said, this is my first large scale build so I'll be back for more advise. Hope I don't get too annoying. Haha.
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