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S61 single engine operation overtorquing

S61 single engine operation overtorquing

S61 single engine operation overtorquing

I have reacently run into a warning for a Sea King helicopter that single engine take off and climb can overtorque transmission.  Me as a "dumb" mechanical engineer cannot understand that a single engine may produce more torque than two engines.

Probably we are not having the same overtorquing in mind.  Definitely shafts cannot be overtorqued, I am absolutely certain about that.  But maybe it is about gearing (tooth load) and housing loads which may be increased because of utilizing contingency rating (not normally utilized when both engines operational) and maybe due to asymmetrical load case.  In that case it is unclear to me how the aircraft torquemeter can indicate the increased torque since I am led to believe that it is indicating mast torque (which is definitely lower in the single engine operating case, even on contingency rating, comparing to both engines running for example on 10 minute power rating).

Please advise, I would be very grateful for the enlightening.

Best regards to you all


RE: S61 single engine operation overtorquing

what happens is you over torque the in put pinion gear is beyond its raiting. In twin engine mode you are deviding the power in to two seperate drive gears in the transmition.
the load is shared between the two engines and trans inputs,
the engines will produce more power than the trans can handle,An example when flying it takes 1700 hp to fly ,each trans pinion is rated at 900 hp/torque in %.both share the load of 1700 or 850 hp each, Oops the # 1 engine fails now the pilot has to fly and he sets up for OEI flight (one engine inopprative)  he lowers the colective and uses what power that is useable ,Below the OEI rating.but he needs power to avoid hitting the buildings in frount of him, he pulls more power and the pinion has to pass the power to the trans and you excede the limit. now you send the trans in for an early over haul,because the power to fly is 1700 hp and you over powered the #2 pinion by 800+ hp and you the pilot cost the company $45,000 for not watching the limits,Just because you have two engines dont belive it if you think one will keep you flying,

RE: S61 single engine operation overtorquing

Dear Gugu thank you, I have already lost any hope that anybody would bother enlightening me.

You confirmed my suspicion that the catch is in utilizing contingency rating when OEI.  This contingency (2.5 minute rating) is Brits' term, meaning the max possible engine power before burning it.  Thank you very much once again.

Best regards Rad

P.S. If a company did put some money in a maintenance OEI should hardly happen

RE: S61 single engine operation overtorquing

I've worked on S-61 helicopters for many many years.  The torquemeters are located at the transmission inputs for boh th #1 and #2 engines.  Firstly, they're not addressing overtorquing a "shaft" in particular, but rather the combination of gears, teeth, etc that make up the transmission as a unit.  There is a "combiner gearbox", or a section which makes up the front case of the transmission.  My experience is with GE CT58140-1 engines on those aircraft and they have a topping speed" which is 102% Nf (power turbine) speed to prevent a turbine burst.  As you pull pitch or ADD TORQUE in a single engine condition, 102% Nf is all you can get out of the engine because maximum fuel flow is reached at the engine's "topping out". When it tpos out and you are still looking for more torque the rotor speed will Droop, because that's all the engine has to give.  You're much more likely to TOP before you Overtorque in  a single engine situation. Hope that helped.

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