Caution; trying to claim 100% right on
either end of the spectrum can be equally wrong.
Let’s not mix up to two issues of
spur gears vs helical; planetary vs non-planetary. Note that most of
those big WWII engines used planetary, but they used spur gears. Helical gear
were developed and used primarily for the lack of noise. We don’t
like whining noises in our commercial vehicles. Helical gearing has the
disadvantage of significant axial loads which add both stress and the friction.
Contact area, even when computed correctly (looking at how many teeth are in
contact, and the area of contact on each) is only one factor in a more complex
design process.
Using a planetary for a compact,
lightweight design is a good idea. We use helical gears because they are
readily available at a very reasonable price. Using a custom designed
spur gear planetary in our case could be a better approach, but at what cost? It
could maybe eliminate some of the lost power that goes into heating of the
gears and oil – not much, but something. When I disassembled my
drive after about 40 hours, the only evident wear was where the thrust bearing
bears onto the mounting plate, and evidence of heat on the nylon snubber washers
– the things that take the axial loads from the helical gears.
And I would think most gear designers
would agree that using a lubricant optimized to the gears could be better than
using engine oil. But it certainly adds complexity, and is it worth it?
FWIW, just another point of view.
Al
-----Original Message-----
From: Rotary motors in
aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Saturday, July
28, 2007 5:27 PM
To: Rotary motors in
aircraft
Subject: [FlyRotary] Re: Gear mesh
area? Was [FlyRotary] Re: Gear redrives.com
Suspicions confirmed! It just
seem a more sophisticated method of transferring power from shaft to shaft than
a Spur gear. But, as you mentioned, as long as it is designed to me the
loads, conditions and environment, any number of methods of power transfer
work, belts, gears, hydraulic, turbine wheels, etc. However, for
simplicity, weight and cost, its hard to beat a planetary gear set. Just my
opinion of course.
----- Original Message -----
Sent: Saturday,
July 28, 2007 6:57 PM
Subject: [FlyRotary]
Re: Gear mesh area? Was [FlyRotary] Re: Gear redrives.com
My quick & dirty answer is that the 6 pinion
planet set is equivalent to a spur gear drive with a gear width totaling the
width of all 6 planets. That would be:
6 * .785" = 4.71" Thats a
mighty big & heavy spur gear!
That's bigger than the one in a P-51 R.R. Merlin
engine I think. Not an apples to apples comparison due to the difference
in bending strength of the tooth root but the biggie factor in power
handling capability is indeed the gear contact patch.
On 7/28/07, Ed Anderson <eanderson@carolina.rr.com>
wrote:
Well, Tracy, its sort of like
flying 400 hours with a "Plugs Up" installation - can't possibly work
- the "experts" have said so {:>).
It continues to amaze me (as
it does you) how people can just accept something sprouted out by some little
(or unknown) self-styled expert without attempt to ascertain whether
there are any independent sources/ facts supporting that
position.
As several individuals have pointed
out most high powered (1500+) engines of WWII had planetary gear boxes not to
mention the dozens of different turboprop engines. But, I guess all
of that evidence does not out-weigh the opinions of "experts".
I have not done this but it would
be interesting to calculate the teeth mesh area of one of the spur gear
PSRU and then compare it to the area of the six pinion sun and planetary gear
area engaged to transfer a similar amount of power. I could be
wrong, but my gut feel is that the sun and planetary probably have more metal
to metal contact area for transferring power than the Sun gear.
But, like I said - just a
hunch, would be interesting to know. Anybody have a quick answer??
----- Original Message -----
Sent: Saturday,
July 28, 2007 1:47 PM
Thought I'd see what else I was doing wrong so took a
fresh look at the geareddrives.com
website.
The kiss of
death for a set of gears is in not using the proper lubrication. Separate lubrication systems are required for
safety and for proper engine and gear function. Sharing engine oil with the
PSRU is asking for engine and/or PSRU failure in advance.
There is
absolutely nothing I'm doing right!
But the company does not look like it is for sale
though. But Gershwinder (Sp?) drive company is for sale now. Their
chain drives were among the best I've seen.