snip

Picture the shock wave shape as it moves across the front and back of the
prop tip. The front of the blade with air moving a bit faster has a curved
shape. The back of the blade has a more nearly uniform shape. As the shock
wave grows across the blade tip, it acts like a giant clamp with the jaws
misaligned, trying to twist the blade tip first one way then the other. The
blade tip twists into more pitch then into less pitch at a very high
frequency. They will howel and carry on when this occurs. Metal props are
little affected but eventually will start dropping little pieces off the
tips. Wood props just split open. If you hear a loud buzzing sound at full
throttle, shut down and check the blade tips for a split. Write down the RPM
that will get your prop above 900 FPS and don't go there.

Lynn E. Hanover
lehanover@aol.com

And...don't you need to add the vector for your forward speed when you
figure that 900 fps?

Charlie

 
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