Many years ago one of our top rubber flyers told me that he carved his propellers with the rear face flat because the model climbed better than if he carved undercamber into the blades. These were outdoor propellers but the same principles still apply. I was puzzled by this claim for quite a while but eventually the penny dropped and it then seemed blindingly obvious why the model should climb faster. The puzzle now is that I have never seen the point mentioned by anyone else!
If a propeller is made on a form or carved from a block it should have the same pitch on the back face. However if the propeller blade is cambered then the greater the camber the greater the zero lift angle of the propeller blade. A moments doodling with a pencil will demonstrate that increasing the camber has the same aerodynamic effect as increasing the pitch. My colleague's flat backed propeller was climbing better because it had effectively a lower pitch. If he had started with a lower pitch on the back face and carved in some undercamber it would probably have climbed better still.
I fear I have not been very succinct. What about; It is not enough to measure the pitch on the rear face without taking camber into account.
John Barker - England
Received on Thu Apr 08 2010 - 14:25:00 CEST
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:46 CET