PPRuNe Forums - View Single Post - S97 Raider
Thread: S97 Raider
View Single Post
Old 28th May 2015, 02:22
  #71 (permalink)  
riff_raff
 
Join Date: Sep 2007
Location: USA
Posts: 601
Likes: 0
Received 0 Likes on 0 Posts
...Frankly, the transmission diameter of most helos is sized by the main "bull" gear diameter, which establishes the basic diameter of the box....
I would agree with this point. A torque split configuration should help reduce the plan view profile of a (intermediate or final) bull gear stage. One major consideration when sizing a bull gear stage is the L/D limit of the bull pinions. A spur gear pinion is limited to an L/D of around 1.0 or less. If more pinions are used to drive the bull gear, each mesh will need to transfer proportionally less torque. This means the diameter of the pinions and bull gear can be reduced while maintaining an appropriate L/D and the required stage gear ratio. A coaxial counter-rotating MRGB configuration would have the same effect on plan view profile (vs. a single rotor config) since there is an additional torque split at the two output drives. The drawback with this configuration is that the vertical length grows due to the extra space required for the dual coaxial outputs.

I was not familiar with the term "standpipe" as used in NickLappos' posts. I had always heard such a device referred to as a "static mast". So out of curiosity I did a search of recent published US patent applications from Sikorsky using the term "standpipe", and sure enough I found a couple documents. Interesting stuff.
riff_raff is offline