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Bryan,
The trouble with understanding the planetary is that you can get two different directions and ratios, WITH THE SAME GEARS AND PARTS. It is the basics of how an automatic trans works. I hate trying to figure things out. You can take the drive, (assuming you are driving the sun gear), from the planet carrier or the outer ring gear. The current RD-1C drives the prop from the planet carrier, giving correct rotation and a 2.83:1 ratio. The 1-B takes drive from the ring gear and turns opposite and has a 2.18:1 ratio, clear as mud right?
Bill Jepson
-----Original Message-----
From: Bryan Winberry <bryanwinberry@bellsouth.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Fri, Jul 10, 2009 3:35 pm
Subject: [FlyRotary] Re: Interested in cog-belt PRSUs?
Thanks George,
I caught my math error, but that +1 thing still evades me a little. There’s some good animation out there on the internet. I’ll need a little time to wrap my head around it.
All I really care about is that my RD-1C makes me go fast in the forward direction :>)
BW
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of George Lendich
Sent: Friday, July 10, 2009 5:53 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Interested in cog-belt PRSUs?
I understand your confusion, as I had to get my head around this stuff a long time ago.
That's 85 minus 45 = 36 divided by 2 =18 which is the number of planet teeth. I see what you have done, you have divided 85 by 45 - that's the overall ratio 1.8 then divided by 2 to get .9.
There are 4 major components of the planetary the ring gear, the planet gear housing, the planet gear itself and the sun gear.I threw the calculations for planet teeth as a bonus for those unfamiliar with the process, thinking it may be confusing, but for the overall picture it's a necessary part of a planetary system, as is the difference between holding the planet housing as compared to holding the ring gear, the difference here is + 1. The + 1 is when you run the planetary opposite to the crank. In our case we hold the ring gear to attain the +1.
=0
D
Showing the reason for the +1 was necessary to show the comparison between a 3 gear system (like the planetary 2.85) and the 2 gear system ( 1.8) like the belt and pulleys/ sprockets.- which are very similar in ratio but turn the opposite direction.
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 rati
o 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
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