I thought maybe that's what you were driving at George, I just took the opportunity to vent my frustration with the almost daily phone calls I get asking "Why don't you do it this way ........." : ) No offense meant to you at all.  You and most everyone on this list have done enough fabricating on your own to know how much goes into the design of a flying widget.

 

That sun gear spline does sound nice but notice that if the flange is bolted to the damper and the oil seal runs on the smooth part of the female spline, it looks like the oil is still going to leak out through the spline interface.   This can be worked out too but the problems never end : )

 

Tracy

----- Original Message -----

From: george lendich

To: Rotary motors in aircraft

Sent: Wednesday, January 04, 2006 4:56 PM

Subject: [FlyRotary] Re: [FlyRotary]Soapbox Warning! PSRU Ratios

 

Thanks Tracy,

I wasn't advocating that you change your current manufacturing and models. I was more or less looking for problems associated with MY use of a 3.21 Ratio.

 

I guess, deep down, I would prefer a 2.5 ratio myself but haven't found one that has all the attributes on the 'wish list'. The straight cut gears and the splined sun gear were way up there on the "wish list', BTW the female splined flange has a neck sufficiently long for a bearing and a seal. It all looked too good to be true - BUGGER!

 

Good luck to Ken if he can use it, but like you said it's probably going in the wrong direction for most. I have also that similar advice from another valued source.

 

I do appreciate you going to the trouble, but from my perspective it doesn't hurt to keep looking at, and evaluating different configurations.

Thanks again!

George ( down under)

 

Hi George, glad you asked, gives me an opportunity to answer it once for everybody.

 

 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 -----

From: george lendich

To: Rotary motors in aircraft

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)