Bill Freeman wrote:

Perry,

 Many years ago, I looked at what would be a good, safe
and least cost method of using any car motor in direct
drive mode.  Since the primary issue is to only have torque
load of the crank ( no thrust, no bending) , the method that I
came up with was very simple, and after looking at your new
mount pix, it is something that you can easily do yourself.

What I had envisioned was a steel tube truss coming off of
available mnt points on the engine block (much like your
mount) and supporting a steel mounting plate (perhaps 1/8th
to 1/4 inch ) which has a large central hole and has a machined
(aluminum?) bearing housing bolted to it.  This would have
a pair of large diameter (2.5" ID?)  tapered rollers back to back
supporting a short prop shaft (steel, much like Tracy's output shaft)
and driven by a thinwall tubular driveshaft with either two auto U-joints
or at least one CV joint to avoid alignment issues.  The driveshaft
could be alum or carbon, too.  If you use a single universal
there are bad things put into the shaft due to the inherent design
of a Hooke-type (cross) Ujoint.  Two Hooke joints cancel
it out, so are OK.  One constant velocity joint (outboard car
front wheel drive driveshaft) is ok - the "constant velocity" is
the key point.  Two CVs would work fine by are heavy.

This could be either grease lubed or oil fed and is much like
what Charlie Airesman is using on his VariEze.  I think
this might be reasonably easy to add to your system and would
be an improvement in reliability as you take the motor
back to a being a torque generator, which is what it was
designed to do.  I suspect that his could weigh in at about
25 lbs or possibly less.   I can help you design it if you want.

I don't know enough about the Mazda construction details
to assess the commentary from the Australian dude, but
he could be right.  Of course, torsional vibrations are possible,
with any shaft system but your very light prop helps this a lot.

Bill
Long EZ builder & pilot
mechanical engineer

Good ideas Bill.  There are convenient mounting points for that truss
on the rear of the engine where the transmission bell housing bolts,
but I use three of those already to mount my duct to.

The general lack of response indicates that no one really knows
for sure how this engine handles direct-drive thrust.  I guess I'm doing
a little trailblazing in this area.  Maybe Leon was just being conservative.
The only related real racing failures he mentioned were cracked thrust
plates.

Paul's comments about the strength of the bolts and the front housing
seem a little more realistic.  I can't believe those parts are that weak.
One idea I had was to statically load a front housing and thrust plate
with lots of weight.  I'm sure it would take a lot of weight to make it
fail, probably more than you could realistically stack on it.  Maybe
some kind of hydraulic press would be required to test its ultimate
strength.

I think I'm going to stay with what I've got for the next couple years.
By then Tracy's redrives will be out in the field with some experience on
them.  I'm not wedded to the direct-drive concept, even though I really
do like it.

Now that I'm flying more cross-countries, I'm already wishing I had a
little more speed.  Especially since the airframe is capable of so much
more than I'm getting.  But hopefully my experiments with ducted fans
will help some others out there, like the gyro people. That, I believe is
an ideal application for ducted fans.
--
Perry J. Mick
Mick Duckt N7XR
http://www.ductedfan.com

That front cover is essentially a sandwich panel so to speak. It has two thick
cast iron skins perhaps 1/4 inch thick each separated by water passage directors or 
channels making it over an inch thick total. These act like the core of a 
sandwich panel. As such it is extremely strong. I would not be a bit surprised 
if it took over 10,000 pounds axial load applied to those six, six mm bolts to 
break that front housing.

I would not worry about it Perry.

There is a factor to be considered with the stock thrust bearing and that is RPM.
Racers will shift the gears at up to 9100 RPM which is the upper limit for that
thrust bearing. Also they are using heavy duty racing clutches. That could 
explain why the racers are having problems with it.

We of course never get anywhere near that as the prop loads down the engine
at high RPM and severely limits the RPM.

Paul Lamar

 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

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