Ray, Thanks for the great report! I'm glad to know that this worked so well! An extra tidbit on mass balancing polyhedral wings: You want to locate the lead spanwise with some care. There is an effective torsional axis of the wing about which the wing is twisting. The tip is above the axis and the poly break is below the axis. This means that these points move fore and aft as the wing twists during the flutter cycle. You want to eyeball the location of the lead close to the axis so that it does not act to reduce the natural frequency in the twist mode. For instance, locating the weight right at the tip of a poly wing could cause as much harm by reducing the frequency as it helps with the mass balance. I would guess from your description that you intuitively picked the right spot on the wing. Anyway, thanks again for the report, and glad to hear of your success! Regards, Blaine Beron-Rawdon Envision Design San Pedro, California ---------- >From: Raymond DiNoble <[EMAIL PROTECTED]> >To: [EMAIL PROTECTED], [EMAIL PROTECTED] >Subject: Wing Flutter Fix via RCSE >Date: Thu, Aug 24, 2000, 10:47 AM > > Blaine and Aaron - wanted to pass along and confirm that your recent RCSE > item solved a very bad wing flutter concern here in Las Vegas. Great > work, men. > > BACKGROUND/HISTORY > > One of our more senior members Dan Foster (retired from San Fernando > Valley area) designed a 1980s type floater (open bay- non D tube built up > wing, ~ Clark Y airfoil, T tail, pod/boom fuse) with a 116 inch span. The > dimensions are: main panels 35 inches, the tip (poly) panels are 23 > inches. Main cord 10 inches, poly panel cord 10 tapering to 6.5 inch > tip. > > First flew in SoCal and exhibited severe wing flutter on launch. He > shelved the plane for about 5 years. After moving to Las Vegas, Dan > rebuilt the wing using truss braces from the T.E. to the Spar, ala > Sagitta. Recovered with M.Kote - absolutely no help with the flutter. > > My experience with this plane on launch was such that the violent flutter > started immediately after rotation. The most gently touch on the winch > was required to launch without flutter. Another easily induced flutter > point was just before release - certainly not a zoom - but about the > same location in the launch profile. > > I read your notes on RCSE and talked Dan into trying it. Because I'm a > retired engineer (ME, Ford Motor Co. - R & D Design) Dan felt my > analysis of your proposal must be OK. Wow - no pressure on me. > > RESULTS > > Last Tuesday we taped 1.75 ounces of thin sheet lead, to each poly panel, > about 3/4 distance to the tip (measured on the poly section). The lead > was wrapped around the LE (about half on top/half on bottom) to keep it > weight forward of the spar. > > First launch, I very gently tapped the winch for a full launch with NO > hint of flutter! A quick landing and a much more aggressive launch again > NO flutter. I put the plane into a rather high speed (?) dive with NO > flutter. > > I was extremely pleased and Dan was ecstatic. We did NOT try to optimize > the weight or it's location after these two launches. Dan already had > plans to go home, cut the covering and epoxy the lead to the adjoining > ribs and recover ASAP. > > Perhaps not as scientific as I would like to report but Dan Foster, the > owner, is too pleased for words. That's what counts. > > Thanks again, > > Ray DiNoble > Las Vegas Soaring Club > > Newsletter Editor > LFS Coordinator > Chief Instructor Pilot > > Too busy to fly my own stuff! RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
