Turbopump gears for Liquid Rocket Engines.

[gearcutter]

In case you've ever wondered what it might be like to have to design gears for this most-unique of operating environments, here's an interesting paper from the NASA archives.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19750002094.pdf

 

[tbuelna]

Gearcutter-

Thanks for the link. I actually did some gear drive design on the Shuttle program, but it was for electromechanical actuation systems rather than turbopumps.

I only gave the paper a quick scan, but I definitely intend to read thru it fully when I have time. The paper was published in 1974, but the basic design approach described (ie. materials, lubricants, heat treatment, geometries, etc) is not that different than what is used today in high-performance aerospace gear drives. The only significant difference I saw was most of the designs used spur gears at PLVs between 15,000 and 27,000 ft/min. With most aircraft gear drives it would be unusual to use spur gears at a PLV beyond about 10,000 ft/min due to dynamic loading issues. But this is likely due to the very limited service life required from these turbopump gears. In my opinion, the most difficult aspect of these turbopump designs were the rolling element bearings. The combination of shaft dynamics, operating temperature extremes, and axial forces produced by the high pressures acting on the impeller/turbine present quite a challenge.

Lastly, here's an interesting story about an unusual situation involving a gear drive used on the Space Shuttle partially due to its "unique operating environment". The speed brake actuator used gears and bearings that were made of steel that was not corrosion resistant. At assembly the bearings and gear surfaces were coated all over with a special grease, and then the actuator housing was sealed airtight with RTV silicone compound. These actuators remained in service for almost 20 years with no apparent problems. Eventually one of the actuators was disassembled and rust was found on some of the gears and bearings. The cause of the rust was apparently determined to be the result of humidity in the air volume that was sealed within the housing at assembly, condensing and collecting on the bearing/gear surfaces as a result of the heating/cooling cycle during each flight.

 

[TVP]

Good article. I plan to read it as well, thanks.