Minimum Gear Diameter

Question

Minimum Gear Diameter

Wittenborn (Aerospace)

(OP)

27 Aug 03 15:11

Greetings,

Being an aerospace design guy, with zero gear design experience, I am stumped with my latest task.

I am trying to get a feel for the size of a 90 degree gearbox to go into a turboprop aircraft. The horsepower of the engine is ~240 shp max, and the output shaft RPM from the engine is 3000. I need to step this up in the 90 degree gearbox to 7,600 RPM. And of course I have to do this using the least amount of volume possible. Obviously, I need to minimize the gear diameter to minimize the gearbox housing dimensions.

Right now, I just need a rough set of dimensions to put in the CAD model (i.e. 6"x8"x8").

Can someone explain to me the relationship between horsepower (or torque if you'd like), RPM and minimum gear diameter?

Any help will be greatly appreciated.

Best regards,
Grant Wittenborn

Regards,
Grant Wittenborn
Aerospace Engineer
www.darcorp.com

EnglishMuffin (Mechanical) · Answer 1 · 2003-08-27 17:04:13

I presume you want to use spiral bevels ? I have just picked up my Arrow spiral bevel standard gear catalog, and for a 3:1 ratio and 7.5" od gear, it lists 3.78HP per 100 rpm on the pinion, so as a rough guess I would say it looks doable. This particular gear set has a face width of 1.125 and is 6 DP. The gear will take 7142 lbf.in and the pinion 2381 lbf.in. These are nickel alloy case hardened AGMA 9, but you'd want something better than that for Aerospace and those speeds, probably ground and AGMA 11 or 12. But its just to get a rough idea. You can get into the details using Dudley's Practical Gear Design, for example.

Wittenborn (Aerospace) · Answer 2 · 2003-08-27 17:13:08

Thanks English,

Can you tell me where to get a catalog?

Regards,
Grant Wittenborn
Aerospace Engineer
www.darcorp.com

EnglishMuffin (Mechanical) · Answer 3 · 2003-08-27 17:19:45

I'm not of course suggesting that you actually get them from Arrow Gear, although you could. But I always use them as a guide - gives you somewhere to start.

http://www.globalspec.com/Supplier/OnlineCatalog/ArrowGear/?se=av

Wittenborn (Aerospace) · Answer 4 · 2003-08-27 17:23:19

English,

I figured I could look all that information up, so you don't have to waste your time. I just needed a place to start.

Thanks again for the source and info.

Grant

Regards,
Grant Wittenborn
Aerospace Engineer
www.darcorp.com

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