Bill:
Is there any belt PSRUs that you have seen that you would recomend? What
brand would you choose?
Also, what would you do to improve it, and why? I like the idea of a belt
drive, myself. They seem to have
been around for a long time with a pretty good track record from what I have
heard. Cheap to maintain also.
Rich Gillen

The big problem with a belt drive is they waste precious space inside the

cowl by

uselessly lowering the engine. This almost precludes using one rad under

the engine.

It gives more room of course over the engine which is of little use in most
airplanes. In only a few designs like the Kis Cruiser and the Lancair
320/360 is room above the engine real tight and that only by an inch or
two.

Paul Lamar

There are at least four critical issues with the belt type PSRUs.  I'll
tackle them in the
order that  I have seen the most problems with the myriad of units out there.

First and foremost:   Many belt type PSRUs ignore the very high (~1000 lbs)
side loads
that the belt (ANY belt) imposes on both of the shafts.  Each shaft needs a
pair of bearings
to pick up these side loads.  A key design requirement of any PSRU is that
it must keep the
loads in the engine the same as the car application, i.e.  ONLY torque
coming out
of the crank - side and thrust loads must be very small.  This implies a
crankshaft pulley
that has two bearings (one on each side of the pulley) and a
misalignement-capable
coupling.  There are various commercial couplings available, such as the
double row
roller chain wrapped around two closely located sprockets, that permit SMALL
angular
and lateral misalignment.

Second - Rolling element bearings have absolutely finite life and fail
dramatically.   They
MUST be properly designed for the load-speed combination and then replaced at
regular intervals (hours of use, not condition) and inspected at perhaps
1/4th of expected
life intervals.  So, if the design manual says B10 life is 3000 hours, I
would want to look
at the rolling elements and race every 750 hours or less.  BUT - since we
all make errors,
I would want to look at the first one ever made every 250 hours.   Sealed
bearings
eliminate the requirement for separate seals and a lot of effort to make
them work,but
preclude inspection of the bearing.   I don't like this. An open bearing
with removable
seals can be opened up, degreased, inspected, regreased and resealed.  More work
and design effort, but much safer.

Third -  The output shaft and flange should look just like the end of the
crank on
a similar HP Lyc or Continental.  Many look like a 1/2 scale replica.  Since
the
life of these is proportional to the DIAM to the FOURTH POWER !!!!!   A little
too small is WAY too weak.   This is critical as the small shaft will
fatigue and break.
Many under sized PSRUs survive because they only fly 10-20 hrs per year and are
crashed in a couple of years.  Not enough time to fail, YET.  Also, most
aircraft
conversion make nowhere near the claimed HP, which also saves a bunch of butts.

Fourth - The belt system must be properly engineered TO THE MANUFACTURE'S
RECOMMENDED HORSEPOWER AND TORQUE AND SPEED design factors.
This is often ignored.  They will work for a while, but are probably
overheating and
ovewrstressing the rubber and fabric.   Bad news.

This is not a condemnation or recomendation of any specific belt-type PSRU.
This is
just how this particular cowardly mech eng would evaluate one if my soft, pink,
irreplacable butt is going to ride around in the air behind it.

Bill Freeman
Long EZ builder & pilot
BSME, MSME

The AirCraft Rotary Engine NewsLetter.              Powered by Linux.
ACRE NL web site.
http://home.earthlink.net/~rotaryeng/            http://www.linux.org