AEROBATICS
Wynn Paul
Another trimming question has been sent in, this time by Paul Barros of South Dartmouth, MA. He says he is flying a stock Gieseke Nobler and that on any type of outside loop or outside corner the outboard wing pops up, the plane starts to float, the lines become slack, the plane goes over its head, and he loses control. This also happens in the upper right-hand corner of the hourglass, the outside loops in the horizontal eight, the upper right-hand corners of the outside square in the square eight, and in the outside loops of the vertical eight.
My first comment is the need to know what the plane does in level flight and what happens on the inside maneuvers. Level flight should tell you if the wing is warped because of the attitude of the wing in level and inverted flight. Paul should also have told us how much tip weight he is using and if he has adjustable leadouts. In order to cover all bases, let's review first and remember that all maneuvers should be done directly downwind. Some fliers may forget this all-important factor. A little too much to your right on the hourglass and your super stunter will go all over the place, especially in windy conditions.
Diagnosing the problem
In view of the fact that Paul states his plane pops the wing up on all outside maneuvers, and considering that he is referring to a kit-built Gieseke Nobler, I would bet that he has a warped wing. It's quite difficult to keep those built-up wings from warping no matter how good the kit or the wood. After consulting with Dr. Fancher, the famous bellcrank surgeon, and Dr. Hunt, the noted diving expert, we concluded this must be a case of the right wing panel and/or flap warped down and/or the left wing and/or flap warped up. It's very difficult to have a straight wing and warped flaps, so I would bet on the warped wing.
In normal level flight, if the right wing tip flies down and the inboard tip flies slightly up (when viewed from the outside of the circle), then you have the outboard tip warped up and/or the inboard tip warped down. To cure this you need to "tweak" the flaps or bend the wing. In this instance you would bend the outboard flap down and the inboard flap up. If the normal flight had the outboard tip flying up in level flight with the inboard tip down, and the opposite in inverted flight (inboard tip down and outboard tip warped up), then you would bend the outboard flap up and the inboard flap down. In both examples both right-side-up and inverted flight should be observed.
Measuring wing warp
You may want to try measuring the wing for warp, remembering that a 1/8" warp can cause big trouble. Recommended procedure:
- Block the plane on a flat surface with the leading edges parallel to the surface.
- Measure the trailing edges at similar spots on both sides of the wing.
- Alternatively, sight over the wing from the front if you are careful and take your time — this can show if one wingtip is higher than the other. Measuring is preferred.
Correcting warp (dewarping)
The easiest way to correct minor warps is to "tweak" the flaps. Apply firm pressure with thumb and forefinger on both flaps at the point where the horn wire is embedded in the flap, bend, and hope you don't hear cracking wood.
For more severe warps you may want to steam the wing to bend it back to normal. Two common methods:
- Hold the wing panel over a large pan of steaming water until it becomes soft and pliable.
- Wrap the wing panels in towels and pour boiling water over them until the wood loosens up.
In either case, after the wing seems pliable you must block it up about 1/8" to 1/4" in the direction you want the change and let it set overnight. When you take it loose it should spring back slightly and be straight. It may take more than one operation to get it right.
Other possible causes
- Leadouts too low relative to the center of gravity (especially likely with an inverted engine). As Chris Lello pointed out in his trimming articles, improper vertical balance can cause the outboard wing to fly up.
- Excess inboard flap causing the inboard wing to stall on outside maneuvers; the result is the outboard wing coming up. On inside maneuvers there may be just enough tip weight to counterbalance the stall, so it is not noticed.
- Insufficient tip weight. Adding tip weight can help hold the plane out on outside maneuvers, particularly in the hourglass and vertical eights. However, too much tip weight will make the wing start dipping on inside squares (the familiar hinging action).
Recommendations
- First check for wing warp and correct by tweaking the flaps or steaming/dewarping as needed.
- Check leadout height relative to the CG and adjust if necessary.
- Try adding tip weight as a simpler, temporary fix; check how it affects inside maneuvers.
To conclude, I still feel Paul probably has a built-in warp of the wing and will either have to "tweak" the flaps or steam the wing.
Letter from Larry Miles
Larry Miles, 695 Foxridge Drive, Mission, KS 66202, writes:
"I frequently see kids and adults who would like to get into UC flying. But I am ignorant as to what good UC planes are available. All the magazines seem to be strangely silent about beginners' UC. What's a guy like me and the hundreds of others to do about advising newcomers about easy to build, sturdy, inexpensive and flyable beginners' planes? Nobody is looking after the beginner UC needs and that doesn't make good sense, seeing as how UC is the most adaptable to city dwellers' use and is easiest to learn. Cox has come out with an electric UC for about $7.00 at K-Mart and Woolco. They claim it is the easiest UC plane ever to fly. I'd like to see a product review on that plane. If Cox's claims are true and it has no serious defects, it would be ideal for beginning pilots."
If you have any suggestions or information, send them to me.
For information on precision aerobatics or PAMPA, write Wynn Paul, 1640 Maywick Drive, Lexington, KY 40504.
Transcribed from original scans by AI. Minor OCR errors may remain.
