Willie said : Today was my 2nd flight with "Shreg" (the green KR2). This time I was not
so nervous. Congrats on number two! Alot of builders have played with props, and there has been much discussion about pitch and length. The archives are filled with them. And as always EVERYONE has an opinion about what is best. Here is what my research has found. For your given application if you find that your speed is okay but you cannot reach peak rpm at cruise, then typically you will be over pitched, especially if your climb rate is also down. Using a prop of the same length and less pitch from the same manufacturer should yield a better climb and faster cruise, as long as the prop doesn't cavitate or tips break the speed of sound (best efficiency is tip speed between 80 & 90% of speed of sound). If you find yourself with a fantastic climb rate and engine over speeding at cruise, that is unable to use full throttle at cruise because of engine over speed, then you are pitched too little and need more pitch given that you will use the same length and manufacturer. The reason I say the same maker and length is because each maker will measure the prop slightly differently, just like different cam companies will advertise the same lift and duration, but get different results with the "same" cam. By using a different length you introduce a new variable of larger disc area, which brings its own changes to thrust and hp required etc... Even people running the same engine in the same model of airplane may get very different results given the same prop. Establish a baseline, and then make one change at a time. It takes more time that way but you will be able to measure your results better as to what actually yielded benefits, and what changed little or nothing. Also, get the book "Speed with Economy" to evaluate your plane better for better cruise numbers and get that climb rate up. Then you will have a fast and low risk 2 seater.... Colin Rainey brokerpi...@bellsouth.net
