George Lendich wrote:

I have been trying to keep up with the discussion on props - to no avail,
but I know I will have to come to terms with it at some stage.

If you are ignorant - like me ! there is an interesting article in the #54
Contact Magazine written by Larry L. Olson (Cozy MkIV with Mazda 13B)  This
was very good for me at my level of understanding. He mentiones the popular
Warp Drive (Ground adjustable) prop and discusses why it works so well and
are so popular.
It would appear because they are so thin and have a very low coefficient of
drag. They develop more thrust per horsepower than most fixed pitch props.

I believe the negative thrust at the inner portion of the prop was mentioned
as a problem for ground adjustable props but I will have to read the article
a couple of times and let it all sink in.

I you can get hold of it ( and your like me and not very knowledgeable) it's
a good read!!
George (down under)

George, The problem with the warp drive blades is they have very little twist.
Fine for an ultra light that takes off, cruises and stalls all about the same speed.

To illustrate how important the correct  twist is for a high speed airplane 
take a look these lift to drag curves for different airfoils. Notice how 
a small change of one or two degrees  in local pitch or angle of attack  
can make a large difference in the lift to drag ratio for that section of
the blade. Each blade segment characteristics add up to the whole lift 
to drag ratio of the prop.
 
Paul Lamar
 
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