Yah all be careful out there! Actually flutter can rear it's ugly

head

at a

lot
lower speeds than 300. A Duster sailplane suffered a nasty crash

after

losing the vertical at less than 90mph. Also, if you lose a blade at
virtually
any time, you do not have enough time to shut down the engine before

it

is ripped from it's mounts. The good side to this is that well

designed

composite construction has better flutter resistance than almost all
other systems,

Speaking of 6000 rpm props, I promised to look at the difference

between

constant speed and fixed props in this range, and the results should

be

below. this was for a near stock Mazda with 160 bhp at 6000 rpm for
a 200mph capable plane on that power. The fixed prop was 34 inch
dia with about 42 in pitch. The constant speed was simulated by the
same blade area with the pitch changed to match speed. This is for a
clean installation, with free flow - interference from the fuselage
can severely degrade these predictions. The results are not half bad
for this little prop, and the gain from varible pitch appears less

than

what one would expect at a lower disk loading.
Vance J

Vance,

Thanks for looking at this problem. The real issue to me is whether the
engine produces enough torque to spin the fixed pitch prop up to speed

at

low forward speed. You would have to look at the power required vs.

power

available to find the operating point of the engine. Even if the engine

CAN

produce 160 hp at 6000 rpm, it may never get there because it does not

have

the torque to spin the prop to that rpm. As the forward speed increases,

the

operating point moves up the curve and you eventually get there. If you

took

this into account, then it looks like a small fixed pitch prop is

definitely

the preferable simple solution.

Monty

The program looks at all those things, and these curves were for a near
stock,
only 160 hp. I think you were planning something over 200hp turboed.
Torque is not the problem, if you make the power it will spin. The
lower speed portions of the fixed pitch curve were not running 6000rpm
but at the speed that the engine could turn it. - Vance

 
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