That R-2300 sure seems like an ideal engine for a KR - designed to get it's power at lower RPM. This is ideal for a number of reasons. The higher the RPM the more heat is generated from friction and heat, besides being totally wasted energy, is the VW's worst enemy. I have a friend who went through THREE Revmaster magnesium engine cases (R-2100) due to cracking - all because his oil temp gauge was reading low . . . and because he liked to run around at high RPM. He had more money than engine sense. He finally sold his KR and bought a Porche.
(A side note here: Aluminum cases hold up better to heat than the magnesium cases. The slight weight savings isn't worth the loss of durability, in my opinion.) If you are getting 160 MPH at 2700 RPM WOT that is absolutely excellent for a KR-2! Keeping your engine RPM's low is good, but your prop should allow something approaching to max-rated power for those rare times when you need it. Is that down low doing test flying? If so, take it up above 8000 and see what you get. I'd guess you'll see more RPM thanks to less tip-induced drag. But, as Brian mentions, 56" is a bit much for the VW due to the higher (compared to normal aircraft engines) RPM's VW's run at. Optimum tip speed is at or below 80% of Mach and if you were able to turn your current prop at 3200 or higher your tip drag losses would be extremely high. You'd probably actually go slower rather than faster due to this increased drag. You could retain your 56" diameter and re-shape your blades - broadening the center section and tapering the tips, but you aren't in the prop manufacturing business so to get something like this you would need to contact Bruce Catto or someone there locally who is familiar with the designs of Paul Lipps. Actually Catto doesn't do VW props but that may have changed. Here's some info on this subject: http://www.eaa.org/experimenter/articles/2009-02_elippse.asp Google the name "Paul Lipps" for more information on prop theory and design and on what others have to say - such as on the Van's AirForce forums where Paul was a very active participant. He has set conventional prop wisdom on its ear with his Reno-winning designs. I had the pleasure of flying up to Santa Maria and balancing the prop on his Lancair 235 and getting to know him a bit before he passed away a couple of years ago. He wasn't at all impressed with my Prince P-tip, telling me that he had taken one of Lonnie's P-tip props (he wouldn't mention the prop by name, gentleman that he was) and cut the tips off, resulting in something like a 20% improvement in performance. Every time I hear something taking off like a T-6, making a huge racket, I think of Paul. That racket is nothing more than the sound of wasted energy. Brian is correct . . . you'll get another 100 RPM for each inch you take off of prop diameter. Since your R-2300 is rated for continuous power at 2950-3000, taking an inch off of each tip will probably put you right where you want to be. Sounds like you've built a really nice airplane. Mike Stirewalt KSEE ____________________________________________________________ Do THIS before eating carbs (every time) 1 EASY tip to increase fat-burning, lower blood sugar & decrease fat storage http://thirdpartyoffers.juno.com/TGL3141/530d0d13cbffad137b02st02vuc
