Paul,

Is there a link somewhere detailing the work on the 20B HR 2 ?  I have considered building a plane like this (not for time-to-climb) and wondered what kind of modifications the builder has made to handle the power.  Also, what kind of top / cruise speeds he's expecting.

Also thinking about 13B Mustang 2, but like the higher speeds of the HR better.

Dennis Lithgow, PE


By "HR" I think you mean the Harmon Rocket.
The 20B 3 rotor is more or less just the same as a 2 rotor installation only longer MM tubes.
The Harmon Rocket would accommodate the extra weight of a stock 3 rotor no problem.

The motor mount tubes would be longer and the latest Ford six pinion based
PSRU would be strong enough for a non turbo 3 rotor. We will be using
the silicon rubber coupling on the TTC engine with the Bell 47 gear box..

In P-port form you would have 375 HP to work with at 7500 RPM.

We are working on the all aluminium time to climb 2 rotor  engine with
turbo and it weighs less than 200 pounds.  Far less weight than the 6 cyl the HR normally
uses and with the pilot is in the back seat we have an aft CG problem.

Modifications were made to accommodate the necessary tanks for oil, water
and alcohol fuel. Nothing was done to the air frame as the anticipated climb speed
is about 100 MPH at a 45 degree angle of attack. Considerable modifications
where made to our normal cooling system to accommodate the 45 degree
angle of attack and vastly increased HP. I have no idea how fast it would go
as we have not  thought about a cowling yet.

You would not have those problems with a  stock 3 rotor converted to p-ports.

Dan Gray is a good man at SZP that could help you finish the air plane.
He has now  and will have lots more  experience. I won't be around for ever :-)

Paul Lamar


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