Thanks Dave. it makes me feel better now that I know I was wrong. My  problem now is: I can spin my "monster prop" (static) up-to 4000RPM  and 50" MP I don't think I can get much more in motion and may not  get enough rpm for flight. I'll see first how much difference it will  make on fast taxi. John Slade also will bring his Performance prop  one day, so we can compare them.
BTW the prop tip speed formula given to me was:
Prop D" x 3.1416 x RPM divided by 720
Buly

On Dec 19, 2005, at 6:06 PM, David Leonard wrote:

> Oh, BTW Bully.  You will also note that at 6000 RPM the prop is  > doing 2750 which a lot of certified props will turn, even if 74"long.
>
> Also, short prop are not necessarily less efficient, its just that  > the speed of peak efficiency is shifted to a higher airspeed, and  > probably that peak is a little more narrow.
>
> Dave Leonard
>
>
> On 12/19/05, Buly <atlasyts@bellsouth.net> wrote:
> Yesterday somebody gave me the formulas to calculate the prop tip
> speed. I did some calculations and looks like us with the 2.17
> redrives are kind of painted in the corner. Hope I'm wrong, but if I
> want to keep the tips from going supersonic, I have to cut down the
> prop to 64" or keep the engine below 5500 RPM. The choice is either
> inefficient prop and adequate power, or efficient long prop and not
> getting all the power from the engine? Am I wrong?
> Buly
> atlasyts@bellsouth.net
>
>
>
>
> --
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>
>
>
> -- > Dave Leonard
> Turbo Rotary RV-6 N4VY
> http://members.aol.com/_ht_a/rotaryroster/index.html
> http://members.aol.com/_ht_a/vp4skydoc/index.html

Bulent Aliev
atlasyts@bellsouth.net
http://home.bellsouth.net/p/s/community.dll? ep=16&ext=1&groupid=164323&ck=