The 68 inch diameter prop tip is going 586 FPS at 2000 RPM.
This assumes zero angle of attack and a forward speed
of 400 MPH or 587 FPS. This is still not the actually twist
as it is desirable to have the tip at this angle of attack for low
induced drag in the transonic region but most of the rest of
the blade needs a positive angle of attack to generate some thrust.
That is, as far as I can determine at this moment in time, a matter
of judgement or experience. If it was ground adjustable only several
degrees of change would be advisable. I wish I had a good CFD program
for props.
The next thing to worry about is blade area to see if
this five bladed C130 type prop will really absorb
1000 HP.
BTW The C130 prop twist at the tip does not have to be
as great as ours as it is not going 400 PH.
Check my arithmetic I have been known
to make mistakes from time to time.
Getting the prop right is probably the most difficult part
of this project. Up until the C130J it appears that little
attention was paid to this problem.
Paul Lamar
This is our competition.
I can't believe the GlasAir III aerodynamics are that much worse than a
Legacy. It is going 400 MPH while all the rest are only doing 375 MPH.
To do that with HP alone would require an enormous amount of additional
HP. Top speed is proportional to the cube root of HP. Probably well over 200
or 300 HP or more.
I do think he is using an IA720 A1A The picture looks like a dual turbo
720. Hard to beat.
Those engines are very very expensive. The crankshaft alone is supposed
to be $50,000. In 2009 a new IO-720-A1B cost $113,621 Stock is 400 HP.
We are going to need all the HP we can get. The prop is critical.
Short life of course. He does have dual turbo's which helps.
Rumour has it the extra thin metal props have a 1/2 hour life expectancy.
They all use the same CS prop more or less.
Paul Lamar
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