Tracy Crook wrote:

One disadvantage of the New Horizons PSRU is its weight at
about 50 pounds. This is probably due to the use
of large ball bearings for the prop shaft.
It is a bullet proof design but a switch to tapered
Timken roller bearings would lighten the weight with
no loss in strength. The other interesting thing
about the design is the use of sprag clutches
to decouple the torsionals.

newhorz.

I suspect the weight of this PSRU is the gearhousing hogged out of solid
stock aluminum.  Ball bearing in my drive weighs .23 kg.  Total weight is
about the same as Ross,  (37 lb.)

Tracy Crook
   rws@altavista.net
Web site:   http://www.rotaryaviation.com

What is your shaft diameter Tracy?
Lets see... 2.2 pounds per Kilo .5 pound. If your output shaft
size is 1.181 that is probably a 30 mm bore bearing with
a 62 mm or 2.4409 OD "light" ball bearing. Your housing
should then be about 2.75 inch dia or 2 7/8 inch dia on
the prop end since you are using one ball bearing
on the prop end and one plain bearing on the planetary
end.

>From looking at the box I would guess New Horizons 
is using more like a Lycoming shaft size so
with the same "light" series bearing at 65 mm or 2.5591
ID and 120 mm or 4.7244 OD the bearing weight would
be 2.40 pounds each or 4.8 pounds for both and of course
the housing would then be about five inches or more in diameter.
The bigger housing plus the bigger shaft and bearings could
easily account for the 12 pounds heavier weight of the 
New Horizons PSRU. Things rapidily add up.

BTW The load for 2500 hour average life of a 30 MM "light" bearing 
at 2400 RPM is 985 pounds.

The load for 2500 hour average life of a 65 MM "light" bearing 
at 2400 RPM is 3030 pounds.

The OD for a 65 mm ID tapered roller would be 4.133 so the 
housing could be reduced in size to about 4.5 OD. The length
of the housing could also be shortened to save additional
weight due to the greater effective spread of tapered rollers.
The radial  rating would be about the same as 
a ball bearing but the thrust rating would be much higher 
as would the ridgidity. 

IMHO the thrust rating is very important when dealing with both 
the helical gears as found in the Ford C6 planetary and
the thrust of the prop.

Unfortunately I don't have a weight for the tapered rollers
but I would guess they would be about the same as the 65 MM
ball bearings.

As I said I would like to see the New Horizons design 
converted to tapered rollers to reduce the weight.

Paul Lamar
 
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