Jon Kimmel wrote: >> Something I found interesting with the new airfoil is that it looks like the sweep is different than what is in the plans.<<
The sweep is different because the airfoil shapes (AS405x and RAF48) are different with regards to thickness vs coordinates, so to make the airfoil fit the stock dimensioned spars, a slight fore/aft adjustment had to be made to get the best fit compromise between airfoil and front and aft spar dimensions. This was done at root and tip and then cross-sections were cut through the wing model at the Y-axis template locations to define the scale and spar locations at those cross sections. The term "new airfoil" seems funny now. It's been so long since I made those templates I'm starting to forget the details! It was inevitable, but time has proven that it's a worthwhile improvement, despite the naysayers.... It'll take a few beers to make me finish that sentence at KMMV! Also, Richard Mole, an English aerodynamicist and good friend, did a "full blown" analysis of the KR2 at about the time of the new airfoil inception (20 years ago now!) and concluded that the aft 2" of the CG range was unsafe. This was many years after the first KR2 pilots concluded the same thing, the hard way. This was done in way more detail than is usual, including stability derivatives and considering a lot of characteristics specific to the plane. I think his words were something like "I sure hope nobody's tried to fly one of these with the CG that far aft!". Anybody wondering how far forward you can fly a KR, consider N891JF. Jim Faughn set the CG with him and full fuel right at the forward end...exactly on it. It's not a handful in smooth air, and will do the phugoid thing all day, as long as it doesn't drift off left or right. Needless to say, it requires some nose-up trim to keep it level, but it still turns in some respectable speeds and efficiency, even with the RAF48 airfoil. Mark Langford ML at N56ML.com http://www.n56ml.com
