|
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.
-al wick
----- 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
__________ Information from ESET NOD32
Antivirus, version of virus signature database 3267 (20080714)
__________
The message was checked by ESET NOD32 Antivirus.
http://www.eset.com
|