Sorry I missed the first post. Bill, sounds like you're working on a spar
system similar to one I'm building at the moment. It's my first design of a
"big" plane at 120". I have two spars like you say, but I placed them so
that they are at 90% wing thickness so as not to compromise strength too
much. This places one spar at about 17% and the other at around 42% if
memory serves.
The spars converge in the outer panels as strength requirements decrease.
This allows me to use three panels and have two joiners equally sharing the
load at the two midspan joints. These two joiners are significantly smaller
than the solid joiners typically found in the center of a wing because the
load on the joiner increases roughly by the distance from the wingtip
squared.
I have an almost solid spruce spar (well, two of them actually) 3/8" wide in
the center, and no joiner to further complicate things in this already
compromising area. The spar tapers by steps of 1/16" to 1/8" as the load
decreases. It's still a ways from launch, so I don't know if it will work
at all, but theoretically, the wing will sustain 8g--that's 36lb. I don't
know if this is typical, but back engineering a couple 2m and a 100" plane
gave an average value of about 6g.
I don't know if this approach captures what you have in mind. If you're
interested, I could fire you off the spreadsheet I used to design the spar
system. It's pretty flexible and designed to work w/ the PlaneGeometry
spreadsheets, but can be used as a stand alone.
Tony Rogers
Product Design Engineer [EMAIL PROTECTED]
Precision Interconnect 503/603-4750
> -----Original Message-----
> From: Michael Imsic [SMTP:[EMAIL PROTECTED]]
> Sent: Wednesday, May 31, 2000 12:38 AM
> To: RCSE
> Subject: RE: [RCSE] Wing Spar Design
>
> I am sorry this thread did not take off, it is a really interesting one I
> think. Perhaps everyone was to busy contemplating Inge's fashion sense?
> Here are some links I have relating to spars.
>
> http://www.geocities.com/Pipeline/Halfpipe/4579/spars.html
> http://www.cstsales.com/SparBuilding.htm
>
>
> Does anyone have any other links?
>
> Kindest regards
>
> Michael
>
> Melbourne, Australia
> ICQ 3481522
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> Sent: Saturday, 20 May 2000 4:03 AM
> To: RCSE
> Subject: [RCSE] Wing Spar Design
>
>
> Let's discuss wing spar design, and as a spinoff, the modes of spar
> failure.
> I'm specifically looking at built-up wings, strong enough to withstand
> heavy-pedal winching.
>
> I'll chime in more as the discussion heats up, but my initial spar design
> in
> built around spruce main spars with CF laminations, shear webs of
> vertical-grain balsa or ply, and possibly a ply box structure to contain
> the
> wing joiner rod. I like the idea of a secondary spar at 2/3 chord with a
> light joiner rod to keep the wing halves from twisting. The center of the
> wing panels(s) should be sheeted and 'glased, and a D-tube LE gives
> torsional rigidity.
>
> I'll fine-tune this the more I build, but from an intuitive view, it seems
> correct.
>
> I've not seen any (sailplane) failed wings, but it seems to be the
> stresses
> involved in winching would put the lower surface in tension and the upper
> surface in compression.
>
>
> --Bill
>
>
> RCSE-List facilities provided by Model Airplane News. Send "subscribe"
> and
> "unsubscribe" requests to [EMAIL PROTECTED]
>
>
> __________________________________________________
> Do You Yahoo!?
> Talk to your friends online with Yahoo! Messenger.
> http://im.yahoo.com
> RCSE-List facilities provided by Model Airplane News. Send "subscribe"
> and "unsubscribe" requests to [EMAIL PROTECTED]
RCSE-List facilities provided by Model Airplane News. Send "subscribe" and
"unsubscribe" requests to [EMAIL PROTECTED]
