Yes, people do take the different types of stretch into account. At least for FAI events using mono line.
For F3B you want a line with predominately elastic stretch, because the energy for the zoom comes predominately from the energy stored in the stretched line. However for F3J you can trade off a bit of the instant energy recovery for absolute stretch. This is because more of the zoom energy comes from the towers and the faster line speed, so the tradeoff is slighly more toward starting the zoom higher due to the amount of stretch, rather than the fast elastic recovery for zoom energy. Ciao - Chris ****** Chris Kaiser (mailto:[EMAIL PROTECTED]) Auckland, NEW ZEALAND > -----Original Message----- > From: Bill Johns [mailto:[EMAIL PROTECTED]] > Sent: Friday, 19 July 2002 4:00 p.m. > To: Mark Drela; [EMAIL PROTECTED] > Subject: Re: [RCSE] one more comment about zooming, and then I swear > I'll stop > > > At 11:17 PM 7/18/2002 -0400, Mark Drela wrote: > > > >>In my archives I have comments from others on this subject. > > >>Mark Drela: "a vertical zoom dive is better...On my 2m glider a > > >>vertical-to-vertical zoom seems the best." > > > > > >The above may have been taken out of context, but if Mark > Drela believes > > >this I would like to read the explanation of how this > technique would be > > >best for a zoom off of a winch launch. > > > >The purpose of the dive is to convert the elastic energy in the line > >into kinetic energy of the glider. > > This is the factor that has always had me wondering and for which > I see no > data or consideration. The polymer based lines we are using have three > components to stretch: 1) pure elastic, immediately available recoil, 2) > viscoelastic, will come back to it's starting length but takes a bit of > time, 3) plastic, which is permanent stretch. The pure elastic component > will be there as an instant shortening with reduced load, i.e. reducing > load by diving. The viscoelastic component might take a bit longer. If > the total time period of loading in the initial part of the launch is > perhaps 2.5-3 seconds (SWAG here) then it is reasonable to assume > that the > recovery to original length might take as long. That viscoelastic energy > is not available in a 0.4 second zoom-dive. The plastic component can be > safely ignored after a few launches with a new line. > > So how much of the energy stored in the line is pure elastic and how much > viscoelastic? I have no idea. I appreciate that the > elastic/viscoelastic > qualities of line vary from polymer type to polymer type and that > braid/various polymer characteristics all matter. Has anyone considered > this energy storage aspect of our launch lines? > > Just curious. > > Bill > > -- > Your conscience never stops you from doing anything. It just stops > you from enjoying it. > > Bill Johns > Pullman, WA > > 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]
