Paul Yaw wrote:

Paul wrote:

Paul Yaw wrote:

This may top the silly question list, but a bit of embarrasment before
the new year will be OK since I will forget all about it when I open my
gifts on Saturday.  There were two Ivo props shown in a previous
message. One of them was rated at 100 to 700 horsepower.  The 100 to 700
hp version was used on an airplane which had a 260 hp 13B that I built.
74" diameter I think.  With the engine at full throttle, (43" mp) the
rpm never dropped below 6,200 rpm no matter how the prop was set.  If a
260hp engine can spin it 2850 rpm (2.17 reduction ratio.) what is going
to happen with 700 hp on tap?  What am I missing? Before anyone answers
please consider that I know nothing about props (Or airplanes for that
matter.) so make it easy to understand.

Paul Yaw

Good question Paul I don't really know but I can guess.
The prop is made out of rubber so the pitch flattened out?
Perhaps the blades went into torsional flutter without
failing?

The 700 HP is a bad joke?  I mean how many people are going to
test it with 700 HP? Your average PT6 jock is not going to
put an IVO on his Cessna Caravan now is he?

Paul Lamar

I'm not sure I understand your answer.  Is the 700hp quote just a bunch
of BS?

PY

I would say yes to that Paul. 

There are a lot of unknowns with the
IVO prop. Most prop blades have their neutral twist axis about
the center of the cord. That includes the IVO. The center of lift
is about 25% back from the leading edge. That means the prop blade
is subjected to a twisting force as well as a bending force. Therefor 
as the blade twist the angle of attack increase and the blade bends more. 
If this angle of attack increase  causes the blade to stall the center 
of aerodynamic force moves back along the blade cord to more or less 
the 50% cord point. 

This in turn  reduces the twisting force that caused the blade to
twist in the first place releasing all the torsional and bending energy 
now stored in the blade and the blade snaps back and goes into a negative
angle of attack mode. Things start all over again and the cycle repeats
at the natural frequencies of bending and torsion. The mass distribution 
in the blade also enters into the equation.

This is the classic wing flutter mode. It can be very destructive.

It can happen with prop blades and particularly with blades made
from low modulas of elasticity materials such as a foam core with
very few layers of glass fiber skin. This is how the IVO is made.

The thing about glass fiber is it has a high tensile strength but
it is a rubber band (or low modulas of elasticity) when it comes to 
deflection. This all means that the blade could be fluttering and 
absorbing a lot of engine HP in the process and still not failing 
structurally.

You might want to run it at night and put a strobe on it to check
for this possibility.

Paul Lamar
 
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