You can find the book at http://speedwitheconomy.com $24.95 + shipping.
----- Original Message ----- From: "Colin Rainey" <[email protected]> To: "KRnet" <[email protected]> Sent: Saturday, November 04, 2006 2:54 PM Subject: KR> Props > 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 > [email protected] > > _______________________________________ > Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to [email protected] > please see other KRnet info at http://www.krnet.org/info.html
