The ring gear is exactly 7 inches in diameter. So a 8 inch OD tube
with 1/2 inch wall is just right. A 7.5 might work if you shave some
meat off the outside of the ring  gear.

The bulk heads can be cut from aluminum plate on a band saw (or you
can buy rounds) and trued up in the  lathe. Use a bunch of extended
point set screws to center and lock the ring gear. The nose can be
bar or tube. Best to just bolt the parts together with a bunch of 1/4
inch bolts.

One might get two housings out of one 12 inch long tube.

BTW the ring gear alone weighs 4.2 pounds. Cutting it down to the
width of the planet gears will get it down to roughly 3.6 pounds.

the input shaft and sun gear are 6 pounds.

The planet carrier, un machined, is 17 pounds. One may get it down to
10 pounds by machining it. It is very VERY expensive to cut it down
so don't even think about it. Take the planets out and make a new
planet carrier out of 6061 T6.

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

This is it. No separate planet carrier.

The front and back flanges become the planet carrier further
reducing the cost and weight. A custom aluminum planet cage would
cost a lot in therms of NC machining time.

The Allison comes with 3 planet gears but you can put in up to six.
If you only use three the other three can be larger in diameter
spacers up to one inch which will stiffen it up. I think three are
enough as this is a real heavy duty transmission. Those planet gears
are rather heavy.

The bolts are ordinary  grade 8.... 7/16th bolts. The hollow planet
shafts are about 5/8th OD and must be hardened and ground for the
needle bearings in the planet gears.

The correct size  shoulder bolts are hard to find. Also very
expensive.

I put in the Jerry Bass helical gear thrust bearing. It is the blue
bearing in the 3D's.

The planet shafts are recessed into the front and back flanges for
accuracy and torsional stiffness.

Paul Lamar

Planet rebuild kits are readily available from Allison.  I would
think Ti or Gama TiAl would be the way to go for the planet carrier.
Better fatigue resistance and lighter than the steel. There is one
transmission that has a 3.5:1 low gear without being compound. I
think it is a MT640.

Dale Davies

This one is 3.1 to one according Aubrey.

Here it is put together. Very compact. Good for 1300 HP Reno 4
rotor. I  suspect it will be around 30 pounds. 5 pounds less than the
Bell 47 with out the Sonja :-)

Paul Lamar

Now all we need to do is make the end housing do double duty as the
rear of the redrive to save another few pounds.

Chris Cosman


Right on Chris. Your hired.

Paul Lamar

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