Rotor Transmission

[Sparweb]

Looking at the planetary gear arrangements on the Bell 212 transmission, 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%[sup]N[/sup] 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

 

[Intermesher]

SparWeb,

The follow values are the ones that I use. They came from a lot of digging around, a number of years ago. These values are based on aerospace quality gear mounting etc.

Cog belt; 2.5%
Bevel gear; 1.0%
Spur Gear (planetary); 0.66%

The planetary arraignment has the advantage of low heat generation and a smaller lighter box because of the multiple load paths through the many planetary gears.

Hope this is of some help.

Dave

 

[Sparweb]

Thanks, Intermesher. I'm actually reverse-engineering the thing to see if I can work up a realistic performance model. So far, so good.

Perhaps you could also comment on the requirements of the accessory drive? (The helicopter has a 300 Amp starter-generator and a hydraulic pump driven off the Xmission)
Say, 20-30HP?


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

 

[Intermesher]

SparWeb,

The following might (or might not) be of some help.

This is a reverse engineering of the Mini-550 spiral bevel,

http://www.synchrolite.com/0162.html

This is a reverse engineering of the UltraSport planetary;

http://www.synchrolite.com/B011.html

Disclaimer: Due to unknown hardnesses and other possible errors, the above may not be accurate.

Dave

 

[Sparweb]

Intermesher,

Thanks for the references. Your site is quite extensive, inviting me to go off on many tangents as I explore it. I will allow myself only one: Is that an off-the-shelf program you are using, or did you write it yourself?

I have now got something that reliably replicates the OGE hover performance at MCP and TO power, at least within the range that the engine is torque-limited. Other parts of the hover charts are limited by the EGT, so they don't apply to my rotors-only analysis.


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

 

[Intermesher]

SparWeb,

The data and algorithms are from a book by Hamilton Gear and a booklet by Arrow Gear, plus studying cutaways of the Mini and UltraSport gear boxes. The stuff was then incorporated into a large Microsoft Access database that interfaces with the web site.

Dave

 

[Sparweb]

Intermesher,

Have you read either Shapiro's Principles of Helicopter Engineering or Wayne Johnson's Helicopter Theory?


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

 

[Intermesher]

SparWeb,

Have read Johnson's Helicopter Theory. So much information at such a low price.

Have not read Shapiro's technical book. Does it have anything on twin main rotors?

Dave

 

[Sparweb]

A quick flip through reveals several sections dealing with the topic, the most extensive covering control and stability. Shapiro's book is much better illustrated than Johnson's, just as analytical, and makes lots of references to existing designs. Unfortunately, it was published in 1956. The "existing designs" are museum pieces.


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