Hello Paul,
We are a small engineering firm in central Oregon.
We are in the process of researching the use of a Mazda 13B coupled to a
Bell 47 Final Drive for propelling an aircraft.
Reading through your website (http://www.rotaryeng.net/index.html), I
can see you are familiar with similar installations; I also noticed in
the */Power to Weight/* information, posted on 10-14-07, it is disclosed
that the final drive of a Bell 47 is capable of handling 1000 HP at 6000
RPM.
It would be very useful to us if we could find the source of this
information.
Would you please provide information that may help us?
Thank you very much for your time,
Regards,
Alex
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Alex Baraybar
Kawak Aviation Technologies, Inc.
The source was the Bell engineers that designed it. Dave Garber contacted them back
in the early 70's and he asked them what if the input RPM was 6500? How much HP can
it handle? As I am sure you are well aware the HP is a function of both the torque
and the RPM. It is a high torque low input RPM box The only possible down side is
excessive heat and that can be handled by an oil circulatory system and cooler.
I was mightily impressed with the engineering of that box. For the torque it is
capable of it is extremely light weight. I ran it up at Sun n Fun one year. Dave
flew the airplane several times so it worked as is. The only thing I would do is
extend the prop shaft and space the bearings out several inches to handle the bending
load as a result of stalling or spinning the airplane. With a 50 pound prop that is
about 650 ft pounds with a pitch rate of one radian per second.
Also it will probably rattle badly at input RPM below 2000 so don't do that:)
There is no way around it and it is probably due to the inevitable gear back lash.
The torque pulse from any intermittent combustion engine is the cause. The magnitude
of the 2 rotor rotary torque pulse is way less than a 4 cylinder but never the less
it is still there. I know Jim Mederer is concerned with the .002" (if that) off set
of the e-shaft input. A bit anal IMHO :) I would not worry about it. Planetary gears
are self aligning.
Feel free to ask any question. We have dozens of airplanes flying with hundred's of
hours with the Ford C6 auto tranny planetary gear set. Both four pinion versions and
six pinion version. This Ford based AC box design has been around since 1973.
For details on the rubber coupling we use just ask. Not that it helps much. We idle
ours at 1800 RPM or above.
I saw a Pratt and Whitney version at the factory about the same size as the Bell
that would handle 50,000 HP with a turbine driving it. It was intended for a geared
by pass fan.
Paul Lamar
Paul,
Thank very much you for the information, it looks like you have been having a lot of fun.
The B47 final drive installation looks great.
Regards,
Alex
Here is the Prat gear set.
Paul Lamar
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