Planetary gear efficiency

[Sparweb]

I'm looking at a planetary gear transmission (no it ain't on a car), and I would like to know what would be a reasonable figure for its efficiency. I have found in one reference that a spur gear can be counted upon to have 98% efficiency. With that in mind, will 98%^N work (where N is the number of stages)?
Seems I get a rather small result if I do so.

Also, can I count on bevel gears to be as efficient at transmitting power as straight spur gears? My reference books don't give that information, either.

Any references would be helpful. Thanks.


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[Tmoose]

If the pitch line velocity gets over some tiny value the lovely 9X% efficiency will get undermined and maybe even hornswoggled by the churning losses when the teeth squish the lube. 9HP to drive a 50 HP gearbox at full speed with zero torque output is not very good efficiency.

 

[drawoh]

SparWeb,

Are you designing this gear train, or ordering something from a catalogue?

Dudley's Gear Handbook, Dennis P. Townsend, McGraw Hill has a whole section on Gears in Action. This covers efficiency of all sorts of gears, including bevel and hypoids. It covers planetary drives.

I haven't read the section carefully or applied any of it, so you are on your own. Probably, the book is on Amazon.

JHG

 

[GregLocock]

SparWeb, are you intending to use straight cut gears, or hypoids?

Cheers

Greg Locock

 

[Sparweb]

All,

I'm doing some reverse-engineering, actually, so the configuration is quite fixed. This is the transmission on a Bell helicopter. The 1350hp engine drive is output horizontally to a bevel gear driving the planetary reduction gear which in turn drives the mast.

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[Sparweb]

To continue... (was cut off yesterday) ... The point of the reverse engineering is to simply fine-tune a rotor performance model. I'm realy only interested in the aerodynamics of the system so a simplified idea will suffice. So far the feedback from various sources has indicated that only a few percent of the torque will be lost through this system. Any nay-sayers?

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[IRstuff]

Not my specialty, but I would think from a plausibility perspective that the efficiency must be quite high, otherwise the power loss must be manifested as heat generation, which would be deleterious to the engine and the gear.

TTFN