Posted Tuesday, December 1, 2009 @ 01:59 PM
Greetings:
After reading over the Poly Fiber manual on fabric and how to attach Poly Fiber fabric to the wing (specific wing stitching on ribs to prevent "fabric lift"
I wonder if the fabric is really trying to separate from the wing as a function of lift. Is there a "low pressure" area above the wings caused by the shape of the wing (Bernoulli) or does the wing act as an air deflector (Newton).
Newton makes more sense to me but I wonder if the Poly Fiber people are in the Bernoulli camp and make some of their recommendations, e.g., tapes, stitching, etc. based on theory (???)rather than actual experimentation or evidence. From the Poly Fiber manual:
Aircraft fabric cement is made for shear loads, not peel. But in flight, and aircraft is subjected to constant peel loads from the center of lift on the top of the wing. The giant vacuum cleaner called LIFT is always trying to peel your wing fabric off the top surface. Additionally, any ultralight or very light aircraft you plan on keeping for more than just a couple of years needs RIB LACING! (page 31)
I am still a few months away from working on the wings so I thought it might be wise to get some other perspectives. For example... if you fiberglass the plywood parts of the wing (leading edge, etc.) should you Poly fiber fabric the leading edge also... or can you glue it down with just an inch or two hold down on the fiberglass and glued to the trailing edge?? Do you need overlapping tape as Poly Fiber recommends?? Do you need to completely cover the wing with fabric and use the fiberglass as a more stable surface than the plywood??
Here is NASA's take on HOW IS LIFT GENERATED?
There are many explanations for the generation of lift found in encyclopedias, in basic physics textbooks, and on Web sites. Unfortunately, many of the explanations are misleading and incorrect. Theories on the generation of lift have become a source of great controversy and a topic for heated arguments. To help you understand lift and its origins, a series of pages will describe the various theories and how some of the popular theories fail.
Lift occurs when a moving flow of gas is turned by a solid object. The flow is turned in one direction, and the lift is generated in the opposite direction, according to Newton's Third Law of action and reaction. Because air is a gas and the molecules are free to move about, any solid surface can deflect a flow. For an aircraft wing, both the upper and lower surfaces contribute to the flow turning. Neglecting the upper surface's part in turning the flow leads to an incorrect theory of lift.
Again, my goal is to rebuild the RF-4 wings and use the best knowledge/products I can. I know the fabric I currently have on the wings (Ceconite 103) was not put on correctly.... and I would hate to have fabric come off in flight.
What do you think??
