An excellent point John and one that I must admit I had not thought about. But now that you mention it, it is quite obviously true.
Tony
To: Indoor_Construction_at_yahoogroups.com
From: john.barker783_at_ntlworld.com
Date: Thu, 8 Apr 2010 22:24:27 +0100
Subject: Re: [Indoor_Construction] Propeller camber
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 - 14:35:06 CEST
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