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Freewing construction

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rtfm

Well-Known Member
Joined
Jan 3, 2008
Messages
3,900
Location
Brisbane, Australia
Hi,
I have recently discovered this forum, having spent some considerable time on the Rotary Wing Forum very profitably. However, since I am designing/building a gyro/fixed wing hybrid aircraft, the rotary guys were only able to help for the particularly gyro-aspects of the project.

I am currently trying to figure out the best way to build wings, and it seems that my thinking is very similar to ideas expressed in recent threads dealing with spar-less wing design.

I plan to have my wings machined in a local CNC shop out of polystyreme. Since the wings are not rectangular, but gently curved with upturned wingtips, this seemed to me the only way to achieve the required precision. However, since having this sort of work done isn't cheap (and I may want additional sets of wings further down the track), I thought that the wisest way forward would be to:

(1) Use the basic wing plugs to pull female molds from (top and bottom skins)
(2) Sacrifice the foam wings by first slicing out the "spar", and then by slicing out the ribs.
(3) Armed with my top and bottom skin molds, all I now need to do is to use the cut out parts as molds for both spar and ribs. The spar would be made according to the Marske method of Graphlite (pultruded carbon fibre rods) spar caps laid in a female mold and vacuum bagged into place with a layer of fibreglass. This would give me a "U" shaped spar. Place two back-to-back for a very light and extremely strong "I" beam spar which should fit between the top and bottom skins perfectly. Similarly with the ribs.

This should give me sufficient molds to create as many wings as I wish should I screw up the first one..

I might also add that I'm going to be employing the "freewing" design, so there is little (if any) torsional stresses on the wing in flight. And the free pivoting wing also limits possible G-forces to about 1.5G (this is what I have read - and can't currently confirm this).

However, some of the many imponderables at the moment consist of things like:
What wing area will I require?
If I wish to cruise at X knots, what part will wing geometry play in this?

I recently came across a very poorly photocopied article on the freewing (very little technical information is available, which doesn't make life easier...). It indicates that by moving the pivot point of the wing forwards or backwards, one can trim it to fly at a given airspeed. This seems a bit strange to me. Can anyone shed any light on this? I've attached the grainy photocopy FYI.

Regards,
Duncan
 

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