The thing about ground adjustable props is that they are not the magic bullet that one might think. The blades still have a fixed amount of twist in them, and simply rotating the blades around in their sockets doesn't really change the "washout" on the blades from root to tip, it simply rotates them around to get the most effective part of the blade correct. It's for that reason that a correctly optimized fixed pitch blade will be more efficient than a ground adjustable prop where the blades are simply rotated. Another problem with that kind of prop is that all (two or three) blades have to be set at exactly the same angle, or you'll get more or less bite from one of them, leading to an aerodynamic imbalance in the way the blade pulls, which will lead to an oscillating bending load on the end of the crank, which makes it more likely to fatigue and break.
My advice would be to check the "KR-info" list at http://www.krnet.org/kr-info.html , where there's a pretty comprehensive list of KRs, their engines, and their props. Many of these have been optimized through trial and error, and are certainly a good starting point. My advice would be to start with a choice that is known to work well (a used prop would be best), and fly the thing for while refining the aerodynamics of the plane (adding wheel pants other other such stuff). Then after learning whether you want better climb speed or better top speed, lower or higher rpm, or whatever, start worrying about getting the prop perfect. I've heard too many disparaging stories about the IVO over the years, many of which are in the CorvAircraft archives at http://www.maddyhome.com/corvairsrch/index.jsp . Just put IVO in the keyword box. Speaking of the "KR-info" list at http://www.krnet.org/kr-info.html , I only got one update last time I asked, and I know there are more planes that could stand to have their performance data updated, so send them on... Mark Langford, Huntsville, AL mail: N56ML "at" hiwaay.net website: www.N56ML.com
