Good afternoon Paul

 There is my revised design i tend to use Tracy prop shaft
 who as been tested for several hours, i know i will have some
 weight but for the first test i will go this way and then i can
 redesign or improve after testing for several hours and
 different rpm.

 The main trust line can be located inside of spool bolts surface
 and back plate, the way i locate it will be hard to install it.

 The second trust bearing between prop shaft and spool can be
 omitted and use the bushing only what you think

 The back plate will be perforated at 4 points to received the
 rubber bushings mount and each side of front part with 4 gussets
 and 2 of them will have 2 rubber bushing mount
 I know you are in favor of carbon fiber tubing but at this speed
 we need a good lubrication bearing with oil circulation and
 cooling and carbon fiber resin are not good friend with oil.


 I will draw on drawing board on my return to USA.

 If someone have comments about this design they are free to let me know.


Jean Prudhomme

Tracy says his output shaft is not suitable for a 50 pound constant
speed prop. I agree.

Are you still placing the engines nose to nose in the tail?
The fuselage will have to be 80 inches wide.

Paul Lamar

Jean, As you might have guessed I have ben following your project on the
news letter, and have been looking at your current post. IMHo the use of two
thrust bearings doesn't seem like a good idea. Only one of the bearings wll
be carying thrust loads at a time, If you had a perfectly clearenced
assembly, when it comes up to operating temperature the different thermal
expansions of the aluminum housing and the steel prop shaft will push the
prop shaft forward towards the prop. this will put the thrust load on the
smaller thrust bearing and unload the bearing on the spool. I  downloaded
the technical specification pdf  on the helicopter bearing literature that

Paul posted last week. This is a thin section bearing well suited to this
application, however by it's thin section nature, the depth of the grooves
in the ball races is relatively shallow and unloading the bearing will not
guarantee that the bearing balls roll rather than slide even if you spec the
low breakaway bearing separator. Evem more problematic is that if the spool
and shaft are rigidly coupled the critical gear clearance will decrease and
bad things should be expected there. The use of splines would mean  a
coresponding female splined addition on the spool adding still more
weight.In addition the prop shaft you  show in your sketch is much too
short. By the time you get to a wing thickness where you can hide the pinion
drive shaft and the safety cover around it the prop will also be inside the
wing planform. A propeller or fan blade just can't run close to an edge that
shears the air flow off the blade. there is a pressure build up in front of
the blade and then a low pressure after passing the  obstruction which
causes cyslic bending of the blades.

I once redesigned a fan system in a
lumber drying kiln that had this problem and a dump truck full or nearly 300
broken  blades for the 60" fan blades. I moved the offending frame piece
back 8" and lost only an additional 3 blades which were installed previous
to the modification, and none the following years. Can you think of any twin
which had prop blades 3" in front of the leading edge of the wing. This
leads me to the additional two rubber bushings out near the prop flange.
There doesen't seem to be any spar or structure out there to attach the
bushings to. As for the rear bushings I am undecided. Considering the
traditional aircraft engine there is a large mass of engine very close to
the prop with little leverage for any imballance to shake the relatively
heavy engine. In the wing mount gearboxes there is a design imperitave to
keep the weight down combined with a longer distance out to the prop to
magnify any imballance  both mechanical and from P-factor. and this is at
least a 450HP airplane.


I would lean towards using the flexibility of the
fiberglass structure to dampen vibration an not use the bushings due to the
power being applied back at the fusaloge and the smooth running nature of
the rotaty engine itself. As far as hot oil and composites are concerned
also IMHO the carbon or kevlar fibers are completly incapsulated in the
resin and should be impervious to their surroundings. It is the resin which
could soften at elevated temperatures and be prone to chemical attack at
higher temperatures. I am sure nobody is advocating using the pro-set or
aeropoxy that you use in the airframe. There are many familys of resin
systems for use in high temperature and chemical resistance. I looked them
up when designing my cowling and  saw some for use at 2 thousand degrees.
For my application I didn't require ceramic cloth. I buy all my cloth at
Thayercraft in high point Nc and Steve didn't have a mechanicl properties
sheet for the  ceramic cloth we were looking at so I just specd S2 glass
which I get in 73" widths and have plenty of scraps to beef up the cowling.
These high temp resins have a LOT of precautions /warnings concerning fumes
and contact with the product and look downright dangerous to be around. But
like explosives used in phosphate mining they are  usefull in the right
application.

I was envisioning the light weight steel spool and bonded
carbon fiber propshafts having a short  steel sleeve slid over the OD of the
tube during layup to mount the inner race of the support bearing  and for
the housing oil seal to run on. The outer bearing race and oil seal would be
in a second carbon fiber tube surrounding the prop shaft and bonded to the
gear case housing.  the oil would be pressure fed to the support bering and
pinion bearings and sprayed on the ring gear and thrust bearings.The oil
would be scavenged from both the support bearing and gear case to go to the
cooler. There is no need to maintain a lot of oil in the housing. The oil
being removed and cooled would reduce the heat build up. The prop shaft tube
would  have the steel prop mount end cap slightly smaller than the bearing
race sleeve OD and once the pinion gear is removed from the housing the
shaft and spool would be removable through the back cover opening.As far a
the installed width of two engines nose to nose would be. Whatever the
e-shaft length is ( approx 16.891"?) per engine plus the front belt sheave
and  about 3" past the eshaft on the other end to put  a coupling and
bearing mounting plate on each engine and about two inches between the
engines we are looking at 42 inches wide. Being right against the rear
seatback that may not be a deal buster.

the pinion shaft bearings and
starter motor (rotated down to the forward side of the engine) would be
inside the strake and not add to installed width. You may need to add a
couple inches for clearance to the fusaloge on each side and some
soundproofing material and that would be 46"     If you take the weight and
ballance sheet from your pevious cnnard build and subtract the moment for
the power train then add the weight and balance estimates for the proposed
installation you can get an approximate location fore and aft for the
engines  and see what dimensions the fusaloge would need. If you omit the
battery weight that will give a fudge factor as it can be on either side of
the CG to trim the weight later.

george grimes