Paul Carey wrote:

Hi Paul

I have been researching the Wright PT for installation on our blown
20B, and had a question for you to ponder.

The wright engine uses a complex gear/fluid drive scenario. What do
you think of us using just a belt drive?
The ratio would be roughly 2:1, with the engine @ 8000rpm, and the
PT @ 16,000rpm. I was thinking of a wider (3inch) grooved belt, so
some slip during rapid accereration would prevent damage. I have
read that was why Wright used the fluid drive - to settle the drive
train down a little. Looks to me like the PT has some sort of clutch
in the can. I am off to the airport tomorrow to question our
resident Neptune operator - he has spare PT's lying around.

Regards

PC


                 Aviation Consultants
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com.au                   fax: (08) 9371 9644
.com.au               mobile:  0418 959 892

Thanks for the great pictures Paul. I am glad to see
you are pursuing this potential rewarding configuration.

The problem with a belt in this application is HP.
You are looking at 20% of the power you have now which
will be well over 1000 HP. That means you are unlikely
to find a belt that will transmit 200 HP or more.
You also need the belt between the final gear reduction
and the e-shaft as you don't want torque pulses from the main
engine feeding back into the turbine reduction gears
to destroy them.

I think you are stuck with a fluid coupling or some other
torque isolator such as the rubber device Don Dunbar is using.
The torsional dynamics are a bear otherwise.

As Vance quotes some Englishman  "An ounce of rubber is worth
a pound of engineering." :)

Paul Lamar

Pauls,

don't give up on the belts quite yet!

If there is a problem it would be with the high speed, but not with the
power.
Robinson Helicopters uses all belts to transmit up to 280 hp .
There are 4 double V-belts (look like 2 single V-belts glued together...) in
the system, but only 2 of them would be capable of transmitting all the
power. Max continous power is only 205 hp, but if needed there are 280
available. I frequently use it. Never had any belt slip or brake. If
alignment of the sheaves is correct, they will last at least the helicopters
TBO of 2200 hrs airtime, which will turn into about 2500 hrs engine running
time when TBO comes up. I understand on stationary industrial applications
these belts last way over 5000 hrs.
However I have no idea what the max speed and the smallest radius would be.
The Robinson sheaves are about 6" radius......100% rpm is about 2700.
Additionally: Robinson uses the same belts as a clutch!! ....to engage the
running engine (55% rpm - idle) to the Mainrotor Trans. As an average you
can bet on a complete engage/disengage cycle for every flighthour....
Works via an electric-motor driven worm gear. A special leafspring
arrangement will switch micro switches to maintain the correct tension
(pushing the upper sheave away from the lower one...)
Thomas J.

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