At 08:50 AM 11/5/2004, you wrote: >-----Original Message----- > >Don > >Can teel us why you went for a longer chord? > >What are the advanages you gained and at what cost, proformance wise?
My KR based plane was designed for a gross of 1450 pounds. I wanted to keep approximately the same wing loading. The plans built KR 2 has a wing loading of about 11 lb/ft^2 and the 2S is a little higher. Mine will be 14.5 lb/ft^2. I also increased the span so that the span loading would also be comparable. I finalized the design before I really started studying airfoil design and I simply picked one of the best NACA airfoils. If I were to do it all over, I would design my own airfoil to meet my needs. The NACA 747a315 that I picked has a reasonably low drag, gentle stall, is resistant to bug debris, and has an extremely low pitch moment. Most airfoils have a higher (more negative) pitch moment. This must be counteracted with additional download at the tail. This download is a negative lift that acts just like the plane has a higher gross weight. The low drag and negligible pitch moment will result in a low overall drag. That is, a plane with wing that has a low drag coefficient but a high pitch moment can have a higher overall drag than one with a higher drag and lower pitch. I think that the performance will be comparable. I am also spending a lot of time with drag reduction by surface finish, tolerance of gaps and part fit, and engine cooling, among others. If I do it right, I hope that I will be able to keep up with any KR. Don Reid - donreid "at" peoplepc.com Bumpass, Va Visit my web sites at: AeroFoil, a 2-D Airfoil Design And Analysis Computer Program: http://www.eaa231.org/AeroFoil/index.htm KR2XL construction: http://users.erols.com/donreid/kr_page.htm Aviation Surplus: http://users.erols.com/donreid/Airparts.htm EAA Chapter 231: http://eaa231.org Ultralights: http://usua250.org VA EAA State Fly-in: http://vaeaa.org
