George you lost me with (81-45)/2=1.8
I get .9
Bryan
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of George Lendich
Sent: Friday, July 10, 2009 3:21
AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re:
Interested in cog-belt PRSUs?
The calculations for ratio of this kind is (ring gear
divided by sun gear). Using teeth numbers on the ring gear divided by
the teeth numbers on the sun gear; If you had 81 teeth on the ring gear and 45
teeth on the sun gear i.e. (81/45=1.8).
Now if there were an intermediate gear as on the planetary
i.e. planetary gear - then the calculation for the planetary gear teeth. is;
ring gear minus sun gear divided by two i.e.( 81- 45)/2 = 18. As a
planetary runs with 3 gears, the prop runs the same way if the planetary
is held (in place) by the ring gear, the calculations are 1.85 +1 =
2.85:1 Ratio.
As the rotary runs anti-clockwise in out orientation ( from
the rear of the motor forward ) we have a clockwise prop direction when using a
planetary PSRU, with ring gear held. With the planet housing held it would run
anti-clockwise and would be 1.8:1
However we only have two gears (sprockets) in this belt PSRU so ir must
run in the direction the motor runs i.e. anti-clockwise. The ratio is similar to
the Ford planetary which is 1.85:1.
I don't really know the numbers of the teeth on the belt
PSRU sprockets but used the numbers abovementioned as demonstration only.
"With the rotary, that would mean an anti-clockwise
prop rotation, view from
the cockpit, 1.8:1 is right on the mark as compared to the Ford planetary
reduction which is 2.85:1 with clockwise rotation i.e. 1.85+1.
George (down under)."
I am totally confused about having two different ratios going from clockwise
prop rotation to anti-clockwise for the same engine speed and prop speed. I am
way out of my depth here. HELP!!! Bernie