Hi, I've just started building the wings of my PT-40 and I have come across a problem. The spars are warped but it says this is ok. It says that there is a right way to be warped. But one set of mine do not warp the right way. The spars warp away from each other and the manual says that this will build a warped wing. What should I do? Should I try to warp them with weights or just build the wing? Any help would be great thanks

Damien

If you can get to a hobby shop just buy replacement spars after checking them for straightness. If the wood is not straight the finished wing will not be straight. And building a straight, correctly aligned plane is more important than getting a fancy finish on it.

Dsegal,
I to am building a PT40 and sort of encountered the same issue one set made a (matched warp) and the other was warped 90degrees from the other. The amount of warp over the length of the spar was maybe a 1/16 of and inch or less. Is this enough to be concerned about.

Randy

Hello Guys:

What you need to do is find 2 spars that are warped about the same. You put them with the warps opposite each other. This is the accepted procedure, BUT. I would warn you. Check the grain on the ends of the spars. You want the grain to go as close to verticle as you can. This yields the strongest wing. If you cannot match them up. Get on the horn to Great Planes (or Tower if you bought it there) and explain that you cannot match up the warps. They should send new spars. Both have a reputation for good service. As I recall the wing has small turbulator spars in the front. If these are the spars that are warped. I would see how much. If they are only warped a little I probably would use them. The kit I built had some warp in these and did not effect the wing in any way. However the main spars are different. As I said before thy matching spars or replace them. The main spars will have a significant effect on the wing.
I hope I did not confuse you. I tend to be long winded and repeat myself. Too much exhaust fumes in the shop I fear.

If the spars are badly warped, replace them (Or email GP and ask THEM to replace them).

But if they aren't off by much, don't worry about it. As long as everything is held straight with pins and/or weights, once the shear webs and sheeting are in place, the wing will hold it's shape.

Any minor variences can be straightened by shrinking the covering.

Besides, in a Trainer, it's really not that critical.

I agree with Minn. I've built some very straight structures from some very warped wood inmy day. Just keep it straight on the board as the parts to together, and everything will hold itself straight. FWIW, when I have a warped spar, I usually try to make the warp go for-aft rather than vertically. The LE, TE, ribs, and other spar will help keep it straight.

If the spars are not severely warped then don't worry, if you read ahead in the manual you will see that you are going to be building washout (twist) into the wing anyway. I would also like to recommend that you build the "sport version" with ailerons and wing bolts instead of rubber bands.

Bkf1970,

Thanks for the input, thats where I'm heading.

Randy

Sometimes, if the spars aren't too badly warped, you can draw it against the edge of a table while bowing it away from the warp. In other words, bend the spar slightly against the warp while pulling it across a table edge. This sometimes works.

Hope I explained it OK.

bax