wayne king wrote:
In my last e-mail I forgot to ask you abou this. An experienced "rotary
head" as Osh. said the spur gear PSRU was definitely safer than the
planetary. If you went thru this b4 I don't want to dig it up but just
give me a 0 or 1, thanx, wayne
Was he selling a spur gear transmission? :)
The devil is in the design details. The vast majority
of geared aircraft engines have used planetaries.
Is a PT6 unsafe?
Paul Lamar ...No rotor no motor.
He has flown his rotary to OSH for many years so he deserves some credance
to those of us trying to sort it all out. I see that the website of the
PSRU he used is down. I wish you and/or Tracy could also have a similar
dicussion at OSH
Wayne King
First OSH is a loser. I am thinking of never going again.
You will see me at Sun N fun until I can no longer move :)
I know exactly who it is. The irony of the situation is this.
The vast majority of the time he flew to OSH he used a Ross :)
It wasn't until he started selling the spur gear transmission
that he started bad mouthing planetaries.
Any spur gear transmission has high gear separating
forces. This causes the over hung internal ring gear to deflect
away from the pinion gear assuming the pinion gear is supported
on both sides. If not supported they both deflect. This leads to uneven
tooth wear and a very heavy and stiff ring gear. It also leads
to a heavy and stiff gear box case.
In a planetary gear box all these separating forces are
evenly contained by the steel ring gear... not the gear box case.
The gear box itself can be much lighter in weight.
Problem two. For a given torque load the line contact length
is about one third as long as a six pinion planetary box all other
things being equal. Lets say the pinion gear is one inch wide
on a six pinion planetary. The line contact length is therefore
six inches. If the pinion gear is only two inches wide on a spur
gear transmission the line contact length is only two inches.
Therefor the spur gear box operates with much higher compressive
stresses in the all important line contact area. Over stressing
leads to gear tooth spalling(s?) and tooth fracture failure in the
cantilevered beam bending mode. This leads to much larger and
heavier gears and a larger gear housing. .
For these reasons just about all successful geared aircraft engine gear boxs
have been planetary's for the last 100 years. The upright V engines have
been the exception due to the need to raise the prop thrust line to
clear the ground. The most popular radial engine you can buy
is a planetary geared East European R-360 engine. Hundreads if not
thousands have been sold in the U.S. since about 1990.
Also for the price of the spur gear PSRU you can buy a six pinion
planetary Mistral gear box that will accommodate a hyd constant
speed governor and prop.
Paul Lamar ...No rotor no motor.
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