After looking at this more, and with this good advice, instead of 1/4" wide
sparcaps, I'll use 3/8" wide sparcaps, tapered to 1/4", and maybe from .042
to .060 thick, as well as a stiffer 5/16" wingrod. A bit moer weight, but
I'll look for other places to save weight.
Take care,
--Bill
>From: "Matt Gewain" <[EMAIL PROTECTED]>
>To: "Bill Harris" <[EMAIL PROTECTED]>, <[EMAIL PROTECTED]>,
><[EMAIL PROTECTED]>
>Subject: RE: [RCSE] spar-sizing calculations
>Date: Thu, 9 Aug 2001 07:21:06 -0700
>
>Bill;
>
>This calculation gives you the minimum spar cap size and the maximum
>deflection at the maximum load. The stress in the spar caps (sigma) will
>be
>reduced in proportion to any increase in the cross section area of the spar
>caps. Therefore, if you double the size of the spar caps the stress and
>the
>tip deflection go to half the previous value. Then you can stand on the
>winch without any problems.
>
>Matt Gewain
>
>
>-----Original Message-----
>From: Bill Harris [mailto:[EMAIL PROTECTED]]
>Sent: Wednesday, August 08, 2001 8:57 AM
>To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
>Subject: [RCSE] spar-sizing calculations
>
>I'm building a Windfree nostalgia sailplane with strengthened wings, and
>utilizing a balsa-core carbon spar construction with the built-up wing, per
>the Allegro-Lite.
>
>Using Mark Drela'a "spar sizing" suggestions at:
>http://www.charlesriverrc.org/articles/allegro2m/spar_sizing.txt
>I get a spar that uses .042 and .028 single tapered (to .007) CF laminate
>with a spar width of .25" and a spar height of .60" with a .25" steel
>wingrod. This should withstand a "reasonable" winch load for this class of
>sailplane, as well as be very light. In a way, this is a similar to the
>"de-rated" spar used on the Allegro-Light-Electric.
>
>All looks good until I get to the estimated tip deflection calculation.
>Yikes!!! It comes out to be 28 inches! Not much I can do here... the only
>variable I could work with is the spar height, and that can't change.
>
>What does this "tip deflection" mean? Under what conditions does it occur?
>From the formula d= b^2 sigma / (4Eh), there is no input for wing/winch
>load, so I assume that this is the maximum deflection that the _spar_ will
>take before failure. I'm guessing that the D-tube sheeting and LE/TE might
>also fail before this maximum spar deflection is reached.
>
>It may not matter, but I'm picking at the details on this building
>exercise...
>
>--Bill
>
>
>
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