Paul, I need your (group) help in helping me determine the adequacy of a
gear set. I need to know how much horsepower that the set is capable of
handing with a reasonable safety factor. This is being considered for a
psru. I hate to admit it, but it's been too long ago that I could do these
calculations.

The spur gear set is as follows:

Width:  .750"

Outside Diameter:  pinion-2.56" (26T)   driven-5.36"(52T)

Gear heigth: .200"

Material: 8620 (Rockwell 55 est) heat treated steel

Max rpm of pinion: 7,000

Thanks for the help.

Chuck H

Interesting question- so I pulled out my referenc books, and the first
good lead was Martin Gear and Sprocket catalogue no 60.
Best guess is that your gear set is about an 11 DP 20 degree pich
(strongest). That would make the pinion pitch dia 2.36 which would jibe
with your .2 tooth height.
Allowable pitch line force = (SFY/P) X (600/600+V)
S allowable safe stress - stated at 35,000 psi for hardened 40 carbon steel
F tooth face width .75 in
Y tooth form factor from table .344 for 20 degree 36 tooth
p Diametral pitch 11
V pitch line velocity fpm 4325 at 7000 rpm
Computed load 98.5 pounds
HP 98.5 lbs X 4325 fpm/ 33,000 = 12.9 hp

I knew that you would not like the answer! so the Florida Supreme Court
suggests that since this is a catalogue rated value (ie lawyer approved
24 hour day - years of life - electric motor driven) You might add a
bunch for 1000 hr reduced safety factor - but take off for pulsing
loads, and maybe think in terms of 40 hp max _Vance

 
Ken Powell wrote:

Vance,
I was surprised to see how little HP this proposed gearbox could
handle. Thanks for the calcs.  Wish that I still had a Rotax box
around to measure for comparison.  I have a belt drive PSRU on a
Kawasaki 2-stroke that I am not at all happy with so I am always
interested in these exchanges (I plan to put this engine on a
MiniMax if I can ever get the plane finished - my wife's projects
seem to get done first!) .

Ken Powell

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