Here is Bud's opinion on planetary gears the rotaries have been
  flying with for the last 38 years.

  The truth is the planetary has six times the critical line contact
  length of any spur gear of the same width and that is why they have
  been used in all size aircraft engines for the last 100 years.

  Just because you can rebuild a racing engine does not mean you are a
  competent engine designer or gear box designer let alone aircraft
  engine designer. I know a lot of race engine builders :) Just about
  every SCCA racer builds his own engines.


  Paul Lamar


  "What about planetary gears in a PSRU? I choose to use the best for
  safety and dependability in the Geared Drive. For this reason, I am
  against the use of planetary gears in a PSRU. Consider what they were
   designed for; to change an automatic transmission from one gear and
  into another. They were designed to work at high RPM for only short
  periods of service. They are very small and turn at ultra high RPM
  when in continuous use, and from twenty plus years of personal
  experience in professional auto racing, my personal opinion is that
  there is any way that planetary gears can possibly hold up long term.
   The strongest and most dependable kind of gear is a straight cut
  spur, which is what I chose to use in the Geared Drive PSRU. "

  The next generation of high bypass jet engines from GE will use
  planetary gears to drive the fan.
  http://www.geae.com/engines/commercial/genx/ C. Smith

 Jack Kane has an interesting note on his website:

http://www.epi-eng.com/propeller_reduction_technology/implementation_overview.htm


 #######
  On that subject, a big problem we have seen when trying to use
  automotive planetary hardware in a PSRU is the fact that the needle
  bearings inside the planet gears often do not have an acceptable life
   under the applied loads. We require an L-10 life of at least 2000
  hours for rolling element bearings. We do not consider 200 hours (or
  even 500 hours) acceptable.

  Here is an example. Consider the use of a 6-planet E4OD front
  planetary gearset. The available ratios are 1.538 (Ring-driving,
  Sun-fixed, same direction), 1.857 (Sun-driving, Carrier-fixed,
  reverse direction) and 2.857 (Sun-driving, Ring-fixed, same
  direction). At 6000 input RPM, 300 HP applies 263 lb-ft of torque to
  the gearbox. Using the sun-driving, carrier fixed (1.857 ratio)
  arrangement, the planets spin at 14000 rpm and the load applied to
  each set of planet-gear needle bearings is 884 pounds. Under those
  conditions, the expected life of the planet-gear needle bearings is
  195 hours, assuming ideal conditions and fully-equal load
  distribution. In the Sun-driving, Ring-fixed configuration (2.857
  ratio), the planet speed drops to 9100 RPM but the bearing load is
  still 884 pounds, giving an expected life of 296 hours. However,
  using the Ring-driving, Sun-fixed arrangement (1.538 ratio), the
  planet-gear speed is also 9100 RPM but the bearing load drops to 475
  pounds (at the same 300 HP, 6000 RPM input). In that configuration,
  the expected life of the planet bearings is 2344 hours. Quite a
  difference depending on the gearbox configuration, yes?
 ########

 As far as i can see from RD-1C pictures on Tracy's website, outer ring
 is fixed, sun ie. middle gear is input, and planet wheel carrier
 transfers the power to the prop. So:

  2.857 (Sun-driving, Ring-fixed, same direction)
  In the Sun-driving, Ring-fixed configuration (2.857 ratio), the
  planet speed drops to 9100 RPM but the bearing load is still 884
  pounds, giving an expected life of 296 hours.

 I don't have E40D needle bearing specs, so can somebody check what's the
 validity of 296 hour@300 hp/6000 rpm claim...

 Cheers,
 Petri

 Assuming for the moment all this is true and I have not checked it yet.
 Yes but nobody runs the engine full power for 100% of the time.
 Lyc. and Cont. aircraft engines are limited to full power for 5 minutes
 during take off and climb out.

 As you climb out to altitude at full power power falls off to about %80
 power at 8000 feet. We don't have an engine that will generate 300 HP at
 6000 RPM. Yes at 7500 RPM but not at 6000. Typically people back off to
 save fuel at that point.

 Early three and four planet... Ross planetaries have as much as 2400
 hours on them so far in rotary engine powered aircraft use. The latest
 versions have six planets and are rated for Ford diesel pickup trucks
 with 650 foot pounds of torque. I have never seen one with worn out
 needle bearings. I have seen them with the sun gear teeth cleaned off
 due to poor machining of the gear box.

 The cost of overhaul is cheap as the complete gear set of off the shelf
 10 pound Ford planetary is less than $200.

 If you need more grunt there is always the Allison.

 Jack Kane would have you use one of these rock crusher porker gear sets
 :) The major problem is aluminum gear box expansions due to heating
 which increases the back lash.

 So far no Chev V8 has made it past 300 hours in an aircraft to my
 knowledge. The Orenda, after spending 50 million on re-design, had a
 final 1200 hour TBO.

 The Merlin had a TBO of 1000 hours and few made it that far due
 to combat damage or war emergency power. The planetary AC radials used
 in commercial airline service had TBO's of up to 3000 hours.

 Paul Lamar

 ------------------------------------------------------------------------

Checking from SKF calculator, at www.skf.com - Calculations - Bearing life

Assuming 16x22x20 needle bearing on v=12 oil (SAE30@100C) with nc=0.5

300 hp - 4.0 kN force (887 lb), 9100 rpm, gives L10h=260h L10ah=320h

200 hp - 2.7 kN force (591 lb), 9100 rpm, gives L10h=950h L10ah=1130h

160 hp - 2.1 kN force (473 lb), 9100 rpm, gives L10h=2190h L10ah=2600h


So, if assumptions are on the right side, 20B engine could be just too
much for an E40D unit.

Cheers,
Petri

One can always take the steel needles out and replace them with silicon nitride as used in 30,000 RPM machine tool spindles and Formula 1 cars.
They are ten times better :)


Paul Lamar