Lonewolf_50- Just a couple final comments regarding the challenge of designing a split torque gearbox.
First, back in 2003 under the AATD RDS-21 program, Sikorsky demonstrated they could get load sharing within 1% in a split torque gear drive using their torsionally compliant quill shaft concept (somewhat similar to what is used at a larger scale in the 53K MRGB). I can tell you from experience that getting load sharing within 1% in any split torque gear drive is pretty impressive. Apparently they were not able to achieve anywhere close to the same result with the 53K MRGB in testing, since they are currently going thru a major redesign. In fact, I would speculate the bull pinion load sharing variation they saw in bench testing of the 53K MRGB was much more than "an order of magnitude" greater than 1%. In my opinion, even a 10% variation in load sharing between the 12 bull pinions would be quite acceptable.
Second, in case you don't get your hands on a copy of the AHS paper I linked, here's the most interesting quote:
"Summary and Conclusion A trade study on two different design configurations of the CH-S3K main gearbox, a new split torque MGB vs. an improved planetary MGB, was performed. The three focusing parameters of the trade study include performance, cost and risk. The advantage and disadvantages of both design configurations were thoroughly studied. The geartrain systems, mounting bearings, and supporting housings of the two different MGB‘s were designed and analyzed for detailed weight calculations. Results of the trade study are summarized below.
1.The split torque MGB design has a significant weight saving (more than 500 lbs) over the improved planetary.
2. The Split torque MGB can save millions of dollars per aircraft in total cost which includes development and production cost.
3. The Split torque design bears slightly higher risk than the improved planetary design due to Sikorsky’s lack of production experience in split-torque gearboxes. But the risk-reduction test of the quill shaft lowered the risk level of the split-torque MGB to the same level as that of the improved planetary.
In conclusion, the split torque main gearbox is a better design and was chosen for the new CH-53K."