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Warped Wing

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Old 10-05-2012, 02:00 PM
  #1
rmpRmP
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Default Warped Wing

I've just got a Trainer-style plane, almost finished, with a warped 70" wing. The front left side of the wing seems to be about 1/2" lower than the right side front. I'd like to fix it, because it seems to take all of my radio's aileron trim to keep it flying straight. Maybe more. Questions: 1) Is it better to have the front wing tips down or up? 2) In adjusting with a heat iron, is it best to start ironing on the bottom of the wing or the top? Any other suggestions?
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Old 10-05-2012, 02:10 PM
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Default RE: Warped Wing

I am assumining it has a flat bottom airfoil. If that is the case lay it flat on a table andweigh it down flat or pin it to your work table. Use a heat gun on the top side. After it cools down check it out. If not to your satisfaction you will have to prop up the low edge and reheat the top agin. After you are done check the flat side for wrinkles or excessive stretching, if needed use the heat iron to even it out.

If it has a symetrical airfoil you would have to put it in some sort of a jig to even it outand do what I described above.

I hope this helps

Rafeek
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Old 10-05-2012, 02:14 PM
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Default RE: Warped Wing

On a trainer it would be better to have the leading edge at the tips lower . The lower leading edge at the tip will reduce the tip stall tendency ,this is usualy refered to as washout. Raising the leading edge will increase the angle of attack and cause the planes airfoil to stall easier.
It really doesnt matter if you use heat on the top or bottom first but both must be done to hold the change effectively.
Eyeballing the warp on a trainer wing is not difficult to do but using an incidence meter will get you where you need to go with less guess work . If you are going to continue to assemble or build planes an incidence meter is worth adding to your tool collection
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Old 10-05-2012, 04:10 PM
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Default RE: Warped Wing

If the wing is standard balsa construction with a MonoKote type covering, it is very easy to remove warps. Simply twist the wing in the other direction until the covering wrinkles badly, hold that twist and run a heat gun over the covering to pull the wrinkles out. Check for twist now. It may require several applications but reshrinking the covering will provide enough tension to hold the twist in the wing.

Of course the best way to determine the twist is with an incidence meter, test incidence at the root vs. the wing tip, then twist and heat as needed. As CK1 said, a bit of washout can be a good thing on a trainer, but be sure you have the same amount on both wings.

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Old 10-06-2012, 02:33 PM
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Default RE: Warped Wing

Depending on the type of wing construction it may be next to impossible to remove the warp
just using heat on the covering.

If the area from the spar forward is fully sheeted & it has a full depth spar or two webbed
spars once the wing is glued together the boxed section at the front is mechanically rigid.
If this is the case you'll have to remove the top or bottom sheeting, pin the wing flat &
glue the sheeting back on. [&o] - John.
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Old 10-06-2012, 03:53 PM
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Default RE: Warped Wing

This is just not true. Every wing I build has sheeting from LE to spar and shear webs and I adjust incidence this way. You are correct that the type of construction will affect how much twist can be achieved with covering but if it is anything less that a fully sheeted wing you can get great improvement with the technique I described. The OP was discussing a "trainer style" airplane and very few of those have fully sheeted wings so I didn't feel the need to get into that discussion. I have successfully removed over 4 degrees of twist from this style of wing exactly the way I described.

One thing to be aware of, the amount of correction possible with covering is dependent on the type of covering used. MonoKote has the highest tensile strength of any covering out there and is best for this technique but even the softer coverings will give some degree of correction.

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Old 10-07-2012, 07:42 PM
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John Sohm
 
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Default RE: Warped Wing


Quote:
ORIGINAL: Boomerang1

Depending on the type of wing construction it may be next to impossible to remove the warp
just using heat on the covering.

If the area from the spar forward is fully sheeted & it has a full depth spar or two webbed
spars once the wing is glued together the boxed section at the front is mechanically rigid.
If this is the case you'll have to remove the top or bottom sheeting, pin the wing flat &
glue the sheeting back on. [&o] - John.
On a fully sheeted wing, you would be correct. However, what you're describing is nothing more than a "D" tube structure. Although it's strong and rigid, the rest of the wing is easy to remove the warp or twist from using heat and reshrinking the covering... to a certain degree.

If you were to build in a degree or two of washout, you would have a much better stalling plane that shouldn't fall off on one wing or the other. Figure out how much spacer would be needed to get that washout. Pin down the root of the wing and place that spacer under the rear of the tip rib while pinning down the front of the tip rib. Now apply the heat gun to the covering to get the wrinkles out and let cool. You probably will need to get rid of wrinkles in bottom too. Be judicious with the heat gun and make sure the upper covering doesn't reheat and return to it's old position.

Now do the same to the other half of the wing. Use an incidence meter to make sure both sides have equal washout and you should be alright. Just be careful on really hot days or keep your plane in the shade or it could return to it's old self or partly to it.

I've used this method twice in the past and it worked pretty well. Good luck.
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