As long as the diameter is not too large for the maximum rpm, greater
diameter is more efficient.
If you imagine a graph of speed on the horizontal axis and efficiency on
the vertical axis, increasing the diameter causes the efficiency to go
up. Lowering the pitch causes the efficiency to occur at a lower speed.
Of course you've got to make sure that your prop isn't too long for the
engine. And that takes a balance between pitch and diameter, plus some
of the art of building props. And that art, alas, is beyond me. I'm
merely an engineer.
David Paule
----- Original Message -----
From: gliderx5@comcast.net
To: pietenpol-list@matronics.com
Sent: Thursday, November 19, 2009 7:26 PM
Subject: Re: static thrust
David
All true. I must admit that making the prop (per Alvin Schubert) was
probably my favorite part of building the Piet so far. I did build it
66 inches, with the intent of trimming an inch or two to get more RPM if
needed. I will have to see what more RPMs but a smaller disk does to
the thrust. Experimental aircraft right!
Malcolm Morrison
----- Original Message -----
From: "David Paule" <dpaule@frii.com>
To: pietenpol-list@matronics.com
Sent: Thursday, November 19, 2009 9:17:49 PM GMT -05:00 US/Canada
Eastern
Subject: Re: static thrust
=EF=BB
A lower-pitch prop will give you higher static RPM and greater static
thrust. If you are otherwise happy with the prop, that's the only change
needed. Besides, your next prop will be faster to make and possibly
better, right?
David Paule
----- Original Message -----
From: gliderx5@comcast.net
To: pietenpol-list@matronics.com
Sent: Thursday, November 19, 2009 6:37 PM
Subject: Re: static thrust
Dan
I have the results of my static thrust testing at
http://home.comcast.net/~mmorrison123/engine_test.html. Corvair with a
homemade prop. 2500 RPM static giving 280 lbs thrust. I spoke with
William Wynne at Oshkosh, and he indicated that for a Piet I should be
more like 2700 RPM and 350 lbs thrust. I may look at getting a Warp
prop. It is highly likely that the factory can make a better prop than
I can.
Malcolm Morrison
----- Original Message -----
From: helspersew@aol.com
To: pietenpol-list@matronics.com
Sent: Thursday, November 19, 2009 7:49:50 PM GMT -05:00 US/Canada
Eastern
Subject: Re: static thrust
Gentlemen,
Has anyone done a static thrust test on their flying airplane (or
almost flying?). I have measured 265 lbs. with my Model A and my 76/46
prop. I would be curious how this stands up to others.
Dan Helsper
Poplar Grove, IL.
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