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)