|
Bryan,
I know it's sometimes hard, but something's you
have to take things ( like the +1) as a given. I think I remember seeing it
explained somewhere on the Net, but can't remember how it was explained.
It's a bit like trying to explain how to find a
square root of a very large number (with pencil and paper) it can be done but
everyone uses a calculator.
But your right, as long as it does the
job.
George (down under)
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.
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 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
|