The KR-2 Plans have a serious error regarding Weight & Balance. The designer, Stu Robinson, chose the RAF48 Center of Lift 2 inches to far forward. The KR-2S supplement does correct this error. Here is an excerpt from the archives: http://www.krnet.org/as504x/ -------------------------- There are three different ways to use the new airfoil. For new construction, the best is probably using the 18% AS5048 at the root, tapering to the 15% AS5045 at the tip. This uses a main spar that is 8.19" tall at the root, making it 17% stronger than the stock spar. It also adds almost 20% to the capacity of the wing tanks. The materials required are exactly the same as the plans call for, except the vertical spacers between the caps are slightly longer. If your spars are already built, the 16% AS5046 is almost a perfect match, requiring only a lamination of 1/8" of spruce to the upper main spar cap to bring it up to proper dimension. ------------------------- If you use the KR-2 Plans dimensions as is and the location called out for the VW engine, your KR-2 will have an extremely poor aft CG problem. Big engines such as a Corvair or O-200 with the heavier weights up front and/or extended engine mounts will solve the problem. The CG range numbers called out in the stock KR-2 Plans are wrong. Numbers should be 6 to 14 inches.
Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA PS: Sorry about my previous post; hit the send button instead of the paste. ------------------------------------------------------------------------------------- The plans call for using 8 inches - 16 inches of the wing cord. So forward point would be 8 inches aft of the wings front edge. Aft would be 16 inches. This is for the RAF 48 airfoil. I wonder if the new airfoil would be different???? ------------------------------ Most aircraft use 15% to 35% mac. The forward limit is influenced by the distance to the horizontal and size. The aft limit is not. I think most go wrong in the mac. The mac for a kr2s is slightly smaller than for a KR2 and the plans are for a kr2. The governing factors are taper and sweep. You can measure both easily. Something I found interesting with the new airfoil is that it looks like the sweep is different than what is in the plans. https://sites.google.com/site/mykr2stretch/ https://sites.google.com/site/mykr2stretch/parts-for-sale On Aug 17, 2015 5:40 PM, "Chris Prata via KRnet" <krnet at list.krnet.org> wrote: > The plans call for using 8 inches - 16 inches of the wing cord. So forward > point would be 8 inches aft of the wings front edge. Aft would be 16 > inches. > This is for the RAF 48 airfoil. > I wonder if the new airfoil would be different???? >
