[fixer]

Hi; I have just acquired a Tiger Moth. I think it is the model originally sold buy Hobby King as a 1250mm ARF electric. The fellow I bought it from said that it would fly OK fast, but if slowed to scale speed it would tip over to the left severely. (Like full aileron for a left bank would cause)
Upon close inspection I noticed that the starboard wings are warped at the tips such that they are providing a greater angle of attack than their roots, and than the port wings. The port wing tips have a very slightly lessor angle than their roots. Together I see this as a logical cause for the scale flight problems. At higher speed I'm assuming the trim can compensate.
My question is, which way to adjust/correct the warp, and how? The next part of the puzzle is, what is the correct angle of attack for this bird? I don't want to just re-warp the starboard side to match the roots if that would give the wrong angle of attack. Same for the port wings.
Looking at the plane from the side it would appear that the wing bottom, which is flat, should be parallel with the white stripe on the side of the fuse. The stripe seams to run horizontal to the fuse in level flight. That is how it appears in some of the pictures I have seen of the Moth, but the detail may not be clear.
I can provide pics I think if it would help.

[cassat]

Hi Bob,

Congratulations on diagnosing the problem. You are off to a good start!
Yes the horizontal line thru the fuselage is a good reference line.
The bottom of the wing root should be parallel to this line.
At the tips, you can make them 2 or 3 degrees negative ( trail edge up, lead edge pointing down. This is known by the term " washout" and keeps the wing from stalling at
slower speeds.
The best way to do this is by using a heat gun or hot hair dryer carefully and a homemade guage you can make using your kids protractor or geometry set.

Regards,
Dave

[fixer]

Hi Dave; Thanks for the quick reply and detailed instruction. I see it's a little more complex than I thought. I understand what your saying though, but I'm not sure where to apply heat to adjust the wing. Is it simply a matter of holding the wing in the shape that's required and then applying heat to the entire wing covering to shrink/stretch it to the new shape? Bob

[cassat]

Yes,Bob if it is covered with plastic film, then you would twist and heat. Keep in mind it will want to flex back so you may have to twist a bit extra. All trial and error.
Also, keep in mind this can all change in 20 minutes if left in a hot car on a hot day!

[fixer]

Thanks again for your help Dave. I would really like to get this plane to fly scale, and if I can it will never see any undue heat.

[kip51035]

I use 12" rulers, a yard stick, bungee cord and a hair dryer. Put the yard and some shims stick under the wing so when it is pulled down the wing will be twisted the opposite to what it is now. Then I position the hair dryer (less heat will not burn the covering) so it will warm the part of that part of the wing. If the wing does not get warm to the touch put a light blanket over it. I have left them for more than two hours. The first thing I do before I release the pressure is re iron all the covering I can get at. Let cool for a couple of hours then release the pressure. If your problem is solved then iron the other side of the wing if not turn it over and repeat the process. Note the wood has to get warm too.

[fixer]

Hi Kip51035; Thanks for the procedure, I have used a heat gun when covering a plane but I have never attempted to adjust the incidence,so to speak, after one is covered.
Let me see if I have this right. Shim and tie down to the new shape, heat the area that needs to change "warm to the touch". When cool re-iron all available surface. Should that be lite pressure, medium heat, say 200*. I don't know what temp has been used on the covering before as it was ARF. I guess I could experiment to see at what temp the cover shrinks a little.
Next is to let it cool and re iron the other side after tying it down to it's new shape. Repeat as required.

I've had a closer look at this plane and discovered the fuse to be slightly warped too. I am hoping that I can correct this buy simply pulling the vert/horiz stab off and replacing it shimmed level with the wings. There is also some misalignment between the wings looking down on them. ie; One is flying to the left and the other to the right. Measures about 3/8" difference at the tips. I will attempt to correct it.
I am wondering if the people who build these arfs even know what an airplane is?

[kip51035]

Before you go to all that work, try flying it some times just readjusting the neutral position of the necessary flight controls you might be able to make it track reasonable.

[fixer]

Hey Kip; The previous owner who is a much more accomplished pilot than I, tried many things to correct the prob but nothing would allow it to fly stable at scale speeds. He did not want to bother with rebuilding it. I'm a fixer.
I know that this plane can fly at scale and I believe it to be aerodynamically superior to many other bipes that fly stable at scale. As I mentioned above, it has so many build faults I'm surprised it flies at all. As they say, "like a piano". It should fly like a moth and sting like a bee
Thanks again for your help and interest.

[fixer]

I have built a jig/ironing board like structure to use to rewarp my wings. It is simple and works like a charm. If anyone is interested in details I will be posting in the construction ideas, hints and tips.