Some experimental work done by Bell Helicopter indicates that you don't
actually need as much duct length as a lot of theory indicates, they
were getting big efficiency gains with what amounted to a ring around
the tail rotor.  I think that the overriding factor in Perry's case is
the efficiency loss with the reduced diameter (cube function), which he
makes up at lower speeds with the duct, but it kills him at higher
speeds.  When he gets some PP power that will make a huge difference.

Perhaps a small duct about 6 inches long 1/2 thick might have most of
the low speed thrust and less drag at higher speeds.

I am amazed by his bravery flying with stock 2nd gen RX-7 electronics
which in my experience are prone to constant problems like they were
built in Great Britain or something.

The re circulation problem is well known with a short duct. The
helicopter flow field around the tail rotor is entirely different.
For one thing it is embedded in a vertical stabilizer that effectively
blocks re circulation.

Paul Lamar

Tail rotor is mostly operating with static air, tangential to primary
airflow?

The 2nd gen ECU is well made and has not proven to be a reliability
problem in the car. There are other electronics in the car that are bad,
the wiper controls, the clock.

Perry

 
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