Here 's a peek at how the hingleless or flex hinge looks with the e297 tail airfoils at +/- 21 degree deflection... it's cleaner looking, and simple, but will it work? I was imagining that the width of the flex-hinge would be about 0.25 inches, and the thickness about 0.010 inches.. Material: S-glass cloth/epoxy composite.. perhaps vacuum-bag molded along with the parts. The stiffness of the flex-hinge can be adjusted either by adding extra thin glass cloth plies to increase stiffness, or perhaps cutting a few slots in it with a diamond-wheel Dremel tool to soften it, then taping over it to seal it.
I tried this flex hinge once on my Kestrel mini-UAV project for the Air Force.. but it never flew because I didn't get the stiffness matched to the wimpy servos I was using, and we were running out of money on the contract, plus the little nylon RC hinges were working fine at the time. More on the Kestrel at:
http://home.comcast.net/~compositex/
RC guys use a similar trick called a "living hinge" with a layer of Kevlar fabric molded into the epoxy laminate. After curing, you softened the epoxy around the Kevlar by scoring it with an intentionally dull exacto knife that can't cut through the Kevlar, but the epoxy cracks up.. so it's a soft fabric hinge molded into the hardened airfoil structure, and it works great. There is also a cool tape hinge sort of like a Jacob's ladder with Z-shaped tape strips applied.. probably not suitable for full scale aircraft, but it's a slick idea.
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Hi Dan,
ReplyDeleteOn the Aerosonde UAV, the Skin Hinge I settled on was Peel ply encapsulated with glass like you described the Kevlar hinge. Peel ply sounds a bit wrong to put in the wing, but it works well on this aircraft (and many f3B gliders) (max speed 50m/s). It does not rip, its easy to get rid of the resin completely with a light score, and as the resin wets right through the cloth on either side,the material stays attached. I had trouble getting all of the resin out of the Kevlar in production. Whatever the method, you have to love full span, gap sealed hinges!
Sounds like a cool hinge setup, 3dWozz! A Spectra or Dyneema sailcloth cloth might be even better for the living hinge than nylon or polyester peel ply.. epoxy doesn't stick to it, and there is negligible UV degradation. Still, I'm a little sheepish about putting it on a manned aircraft... it's fine for RC models, but when it's your own ass being strapped into it, your attitude changes. ;)
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