That is absolutely correct, Dave. The wings on my refurbished '72 Windfree
flex a lot-- the wingrods and wing spars are "matched" in strength. The
problem is that I have to carefully modulate the winch pedal else the wings
will fold, and this limits my launch height.
If I just used stiffer wingrods, the wing panels would indeed fail. If I
just used stronger wing spars, the wingrods would fail (5/32" is pretty
marginal!) Everything has to be considered as a functional unit: if I
strengthen A, then B must also be beefed up.
I believe that if I increase the spar stiffness by using a CF/composite spar
coupled with a larger wingrod that the strength of the entire wing assembly
will be usefully increased. I can do reasonable winch launches, although I
do not see doing the zippy-da-do-da zooms that you get with a polycarbonate
technowonder...
Intuitively, "off the top of my head", I'm thinking that a 5/16" steel or
3/8" aluminum wingrod will be a good match to a wing of 99" wingspan and 555
in^2 area. It might well be that a 1/4" steel rod would be appropriate.
And then again, in the Ray Hayes incarnation of the Windfree, he may already
use larger wingrods and stiffer spars than the original '72 kit, so I may
end up going with his recommendation.
But good comments...
--Bill
>From: "Dxxx" <xxx.net>
>To: "Bill Harris" <[EMAIL PROTECTED]>
>Subject: Re: [RCSE] Next project...
>Date: Thu, 28 Jun 2001 14:38:56 -0700
>
>Bill,
>I recommend that you don't use larger rods in the Windfree. I saw a 30
>year
>old one fly last weekend, and it does develop MUCHO dihedral on launch, but
>the wings never broke. I suspect that Mark and Rod Smith designed it using
>the stock rods, to keep the wings intact. If you use larger (read
>stiffer)
>wing rods, you will move the stress to the end of the rod, and it will fail
>there. IMHO, the wing needs to flex to survive.
>Just my .02 worth.
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