Always welcome, a different perspective,
Al.
As I mentioned, there were Ross drives
that lasted longer than mine, but historically they did not last very long
under heavy usage. You may have had a later version – which I am
told some did have thrust bearings, but mine did not. We have reports of
rotary engine thrust bearings failing because of the load imposed by the Ross
(at least the version without thrust bearings) gear drive.
I guess I don’t understand –
the hammering back and forth (which I also had on mine – in fact the
splint teeth marks were evident from the hammering)- I attributed to the lack
of a thrust bearing. My failure appears to fall into your 80% of the reasons
for Ross failures. My error if there was a thrust bearing installed,
but if so - it did not stop the Ross from putting thrust loads on the e shaft
of the rotary and causing it’s bearing to fail prematurely. In
fact, I know of several folks who had their Ross drives modified to include a
thrust bearing. So I’ll modify my finding of no thrust bearing and
just say, the design was deficient in preventing thrust loads being transferred
to the rotary e shaft. Always best to be precise about these things.
There was considerably difference in
quality of the Ross gears boxes. Some (apparently you are one of them)
got good results, but others had very short life spans. I know after Lou
Ross died and his son, Chris, took over, things went steadily down hill in
quality.
Oil splashing around does absorb HP,
however, insufficient oil results in galled gears and other problems. If
I have to choose then I’ll trade some HP lost to ensure gears are
adequately lubricated. So if the galled sun gears were not due to
insufficient lubrication – then I’m at a lost as to what caused it –
would the hammering back and forth you mentioned resulted in galling of the Sun
gears?. If so, then my conclusion that it was due to lack of adequate
lubrication may also have been in error.
I agree theory is just a starting point
for anything in the real world – however, real operational life span
tends to tell me that the RWS gear box addressed the short comings of the Ross
drive. Yes, there were a couple of things that Tracy did - which he later changed - that
needed changing. Always part of the challenge when trying to design and
produce a cost-effective solution. Having also produced a few
products for aviation, I have found the doing of such always presents one with more
stringent compromise factors than you may face in other areas.
Time will ultimately provide the
final judgment, but for me, I fly with much more confidence behind the RWS gear
box and would not switch to a Ross drive if given to me –wait, I already
have one {:>). But, certainly if you are flying with a Ross and it is
giving no problems, then I wouldn’t switch it out. But, then - just my
personal opinion.
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Al Wick
Sent: Saturday, August 01, 2009
11:13 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: EC2 and
Ed's EFISM - a great combination
I flew 5 years with a Ross. I've disassembled and inspected
5 or so, just to help out other builders. Just want to offer a different
viewpoint based on my findings:
First, all of the Ross's have large bearing that absorbs the
prop thrust forces. I'm quite puzzled your statement that they don't. A very
important part of the installation is to verify you have clearance to flywheel.
I'm wondering if you are just confusing the pilot bearing damage issue with
prop thrust? Ross redrive had one significant design oversight. This oversight
caused around 80% of their field failures. Basically Ross picked a poor method
of controlling input shaft clearance. Input shaft is the short shaft that goes
between flywheel and gears. Low rpm torsionals caused that shaft to slam back
and forth between flywheel and gears. This caused pilot bearing damage, fatigue
failures on the drive plate. I changed the design by controlling thrust at the
sun gear. All of those failures then disappear.
Second, Ross decision to restrict oil flow to redrive is
very sound design. It limits flow because excess oil flow to redrive has
significant effect on hp loss. A friend actually measured hp loss related to
oil volume. I verified flow on my redrive gears & bearings, absolutely
no issues. I do believe there were lube issues on some Ross applications, but
definitely not true on mine. I don't understand why the difference.
There is a method of proving design changes that Tracy doesn't use often
enough. Basically you measure how close the design is to failure. You don't
rely on theory. For example, I verified oil flow just by placing aluminum
slivers at key oil locations. Operate drive for a minute, disassemble. Slivers
were washed away by oil flow. Likewise, you operate it, then quickly
disassemble and measure temperature of various components. A friend slapped a
plastic cover on his redrive, then watched the oil flow. These methods let
you predict future failures. Too much design theory, not enough actual
measurements. If you can force yourself to test your theories, you'll find tons
of things you believe in, that just aren't significant.
I am in agreement that Tracy
version of the Ross design is looking pretty good. When asked by builders which
redrive to consider, his gets high marks. I don't have rose colored glasses.
There have been a couple design oversights that resulted in failures. I like
the solutions.
----- Original Message -----
Sent: Friday, July 31,
2009 3:46 PM
Subject: [FlyRotary] Re:
EC2 and Ed's EFISM - a great combination
Actually, George, The RWS drive was not
just a redevelopment of the Ross drive.
Tracy basically started from scratch and engineered a redrive that was
designed to meet certain objectives while achieving a reasonable cost.
There is no other redrive I am familiar with that has anywhere near
the number of flying hours that the RWS redrive has with none of the problems
associated with the Ross.
While there is a superficial similarly to
the Ross (Prop on one end and rotary on the other, planetary gears in the
middle {:>)) in appearance, the internals are considerably ahead of anything
Ross had. Pressure lubrication of the prop shaft for one thing, an
integral thrust bearing for another, a removable propeller shaft for yet
another, full oil pressure lubrication. The Ross drive required a
restrictor in the oil line to (can you believe this) reduce oil pressure
– otherwise the thing leaked like crazy – even with the restrictor,
the rear seal frequently was a leaky mess. But, reducing the oil pressure
was one reason the Ross had marginal lubrication in my opinion. Even then, the
oil distribution inside the Ross was also not well designed.
Don’t get me wrong, I was glad to
get a Ross – because it was the only thing around at the time. Had
old man, Lou Ross, lived longer he may have eventually fixed a lot of these
issues, but unfortunately he did not and I won’t go into the situation
with his son, Chris. But, we are fortunate that Tracy took on this challenge and did it
right.
One thing I really appreciate about the
RWS design is that it has a considerably different internal set up with easily
replaceable parts – which was not the case with the Ross. If you
wanted to completely disassembly a Ross unit you most likely had to take it to
a machine shop.
Just wanted to make it clear that in my
opinion the RWS should not be associated with the Ross unit which many have
found shortcomings in.
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of George Lendich
Sent: Friday, July 31, 2009 5:20
PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: EC2 and
Ed's EFISM - a great combination
The Ross drive was redeveloped by Tracy Crook of Real World
Solutions (RWS). Tracy
now uses the 6 planet planetary (Ford Unit) and is about the best you will
get weight wise and value for money.
There are other similar units - all have slightly
different construction, however Tracy's
is well proven. I will probably make my own, but only because of the tyranny of
distance and associated costs.
Steve,
I went with the
RD-1B PSRU from RWS.
T Mann
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