Transmission Systems
 

Hi Rotorheads,

Hope everyone is doing well. This is my first time posting on a forum, and I am also very new to the world of helicopters.

I am currently doing some research on transmission systems for my master thesis and a group design project. I am curious to know if any of you have any recommendations for books/ articles/ reports that might help me understand the design, materials used, advantages, and limitations of current transmission systems used for large helicopters (especially twin engines).

I have so far gathered enough research to understand the basic components, and I have also managed to somewhat understand the structure from looking at schematics on google images :ugh:. Youtube has also helped, however, I would love to know if YOU know of any great sources, or if you have time, to explain the transmission systems for twin engine helicopters.

Thanks for your time,

John

Here's a couple great public sources for technical information on rotorcraft transmissions:

NASA technical reports server

DTIC public access site

Also check to see if your university has access to AHS papers.

You could do some research on whether it is better to have a single input (B212, B412) or multiple inputs (the rest).

Each one has advantages - B212 with the combining gearbox drives one shaft into the main txmsn, making it fairly simple. But a driveshaft failure means you have lost both engines instead of just one (has happened).

Multiple inputs give more load pathways for redundancy, but increase the complexity of the gearbox.

Thank you riff_raff and Ascend Charlie. This is extremely helpful!

Here is a basic illustration of a multi input main gearbox with an accessory gearbox. This was used on the AH-64A. The engine inputs are are opposite sides. The accessory gearbox is actually separate from the main, this allows the generators, hyd pumps, etc. to be driven by either main gearbox or the APU. Hope this helps.

John-

Here's a couple good design handbooks for helicopter drives. One is from Sikorsky and one is from the US Army. They were published back in the 70's, but the fundamental design practices described are still in use. The major changes in the past few years are improvements in gear and bearing materials/heat treatment/manufacturing techniques, design/analysis tools, and techniques/instrumentation for monitoring condition of the drivetrain.

www.dtic.mil/dtic/tr/fulltext/u2/a069835.pdf

http://everyspec.com/ARMY/ARMY-Gener...974.050855.pdf

Here's a fairly recent (2010) NASA study for a large civil tiltrotor drivetrain:

https://mdao.grc.nasa.gov/publicatio...W-IPLC2010.pdf

I also forgot to mention one of the best resources for keeping abreast of the latest developments in rotorcraft drive systems. The US and other national patent office websites. I'd suggest searching both issued patents and patent applications.

patft » Page 1 of 1

Back in the days of ARB a 'B' licence entitled the holder to certify overhaul of transmissions and the like.I have this on my licence but havnt been able to locate my manuals but am sure you can get copies from CAA or archieves. This may be your best scource.

Great! Thank you so much guys/gals! This is extremely helpful to me!

John K

Good luck with your thesis.

I suppose that you can see the inherent elevated risk with a transmission of such complexity, so many parts that all have to work at the same time.

Many risk factors in series might nullify the advantages of 2 engines.

please let us know when your thesis comes out, will you address the increased risk assosciated with 'complex transmissions'?

US Army training document from 1991
 

This might be useful --- FUNDAMENTALS OF ROTOR AND
POWER TRAIN MAINTENANCE—
TECHNIQUES AND PROCEDURES.

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(It's the "Rotors" one)