Phil According to Robert Finch the number of blades helps distribute the torque loads across the different blades, allowing for lighter/smaller blades that make less drag. Also multiple blades smooth out the engine harmonics that can reflect from just a 2 blade design which is why it is not recommended to use anything but wood against your VW if it is direct drive. 2blade metal props are known to cause crank failures due to cracking, and multiple blade metal props are very expensive compared to composite. By using a PSRU you take away these harmonic vibrations, and then using a 3 to 5 blade prop makes it quieter and smoother. Most of the information I have been told that is NOT leading edge technology from established folks in the aviation industry is about getting you to use something that they know about, or their product, not because it is necessarily better. Look at the proponents for not using automotive electronics in Lyc & Cont engines. Yet the engines that are gaining ground right now for certification and use are the converted diesels that are totally electronic controlled or FADEC. They will have no mixture control by the pilot, but rather will be computer controlled. They also burn the more readily available Jet A/kerosene fuels. This may be points for those KR builders who have not chosen their engine yet to think about. The only down side to multiple blades is cost. Done properly more blades is more thrust provided it is properly matched to the engine like any combination. If one were to use say a 2180VW with a belted PSRU, and say a 3 blade Warp Drive he should see a dramatic improvement in the climb performance and the cruise performance, and should also be able to extend the engine life due to the fact that the rpms can be reduced somewhat and still deliver good torque to the prop for cruise, kinda like adding another gear into the transmission. If I don't go with the 6 cylinder this winter then that is what I am going to do: add the belt PSRU to this 1915cc VW. I will post test numbers before and after to show the results, so hopefully we can see a useable benefit. Being done on the same plane in the same configuration with only the change of prop and addition of PSRU, but prop set for the same pitch and using the same diameter should be a reasonable comparison. We shall see....
Tentative re-inspection date set today is Sept 8-9, will find out next week, so sorry gang but no KR2 from me flown to the Gathering this year. Maybe Sun n Fun.... Colin & Bev Rainey KR2(td) N96TA Sanford, FL crain...@cfl.rr.com http://kr-builder.org/Colin/index.html
