If you mean 'what problem would it be for me' the answer is "No
problem at all". Except for scrapping every part of the current
design, scrapping all the tooling developed for it, scrapping all
the production procedures (this is no small thing) and replacing all
this with new stuff.
Obviously, there has to be a good reason to do this to make it worth
while. It has to solve an existing problem (are there any?),
significantly improve performance (would it?) or reduce cost enough
to justify all the work and expense of changing (does it?).
I'm sure that Dodge gear set is a fine piece of hardware but what
does it give us? It has a smaller diameter ring gear (4.4" vs 5.0")
narrower gears (about 3/4" vs 7/8") and one less planet. On
paper, this looks like a minus, not a plus. The availability of
straight cut gears is a possible bonus but on the other hand, I have not
had any problem dealing with the helical gear thrust so
far.
The splined sun gear might be nice but so far we are paying a pretty
high price for it. A lot of other factors need to be
considered. For instance, How do you isolate the oil in the gear box
when using that mating splined part? Is there a place to put an oil
seal? There are literally hundreds of questions like this that must
be answered during the course of designing a gear reduction
drive.
As far as the ratio goes, 2.85 : 1 is actually a bit higher than
optimum for most applications. Going even higher is the wrong
direction. Note that I said "most applications". There will of
course be some that would favor a higher one. A detailed discussion
of this would be interesting but is way more involved than I
can detail in an email message. But, to summarize, I
believe fuel economy, engine life, and proper matching with a suitable
prop would suffer with a higher ratio.
Anecdotal data from people in the auto transmission industry has been
contradictory at best. It's the Chevy vs Ford vs Mopar thing
all over again. I give the Ford guys as much credit as the
Dodge boys - Zero.
I know Paul L. pushes for more power at every turn (higher rpm
(requiring higher ratios), P porting, etc) but I think this focus is
counterproductive in too many other areas. I'm more in tune with
Richard Vangrunsvan's goal - Total Performance.
You also asked why I was previously opposed to changing from 2.17 to
2.85. Note that I did not change. The 2.85 is in addition to
the 2.17 which is still in production. There are plenty of
applications where the 2.17 is clearly a better choice than the
2.85. There are still times when I would prefer the 2.17 on my own
plane. Some of the reasons are subtle and not
quantifiable. I like the BMW better than the Chevy I drove but I
couldn't give you any hard reasons for it.
Tracy (now stepping off soap box)
----- Original Message -----
Sent: Tuesday, January 03, 2006
5:56 PM
Subject: [FlyRotary] PSRU
Ratios
A question for Tracy.
What problems would you envisage using a
3.21 ratio instead of the 2.85.
One of the Lads on the other site has found
this 'U-beaut' Planetary out of a Cummings Diesel (
overdrive).
There are two 5 planet arrangements, one
with angle cut ( opposite to the Ford unit) whereby the thrust
is between the sun gear and planet ( internal thrust gear
arrangement).
The other is a straight cut 5 planet
arrangement ( no thrust).
The beauty of this planetary is that the
sun gear has a spline at the aft end with a matching female splined
flange ( for bolting to the damper plate).
The ring gear is externally notched as in
the Ford 2.17.
The planet housing is similar in design and
size to the Ford 2.85.
Advice from people in the industry are that
the Dodge units are superior to the Ford units, however that would
have to be confirmed.
Originally you were opposed to going from
the 2.17 to 2.85 for a number of reasons - can quite remember why? Was
it because of higher RPM ( engine workload)? overspeeding the water pump
and alternator? Anything else ?
What problems do you envisage with a 3.21:1
ratio?
George ( down
under)