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zeroairspeed

Astar Torque Limits

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The reason I suspect its retreating blade tip stall is because I know that is the reasoning behind the different Vne numbers that change with gross weight. At least in the Jetranger and 500 anyway.

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Retreating blade stall at 40 Kts ??? At 35000 feet maybe.

I definitely go with the M/r T/r load share on this one. This is also why more modern aircraft measure torque from the M/r mast or transmission as opposed to engine/s output.

 

Cheers,

 

HN

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put a call into Eurocopter. the guy i sent the note too is not too sure. was going to get back to me.

have had a number of good replys, but none have been locked in as, absolutly the reason.

 

Had someone just say it was because of the twisting on the dogbone in forward flight. wondering if this was the reason of the mod to the new style bi-directional.

 

Not sure i am convinced of something in flight rather than an aerodynamic issue. why would a torque issue be different in a hover rather than fwd flight.

 

still hunting

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The K 1200 Kmax has an airspeed / torque limitation. Max 45 psi above 25 kts and below 25 kts max 58 psi. The manufacture has stated these restrictions due to excessice aerodynamic forces on the main rotor blades and hubs due to the high collective pitch settings, forward cyclic pressures and airspeed effects. This is right from their product support many years ago.

 

I surmise the same holds true for the yellow arc on the numerous Bell products (mast stress) and I would conclude the same for Eurocopter as the starflex, upper and lower sleeve assy and elastomerics would be exposed to the same. As we over engineer one component (astar mast and txsm) the next weaker components will take the heat. Never had an astar mast or transmisson problem but saw a few cracked and dressed starflex`s.

 

As an aside, every aircraft I know of or have piloted has a 5 minute, yellow arc torque limit. Yet there is no overtorque inspection in any manual for this time range exceedance.(eg 7 minutes at 95% tq or 25 minutes at 55 psi) You will not find one either, as it has to do with FAA FAR certification purposes. Again from a product support manufacture rep.

 

I do not think the previous mention of a txsm tail rotor correlation has anything to do with it myself but I would suggest contacting your friendly product support guru.

 

My proof - the Kmax does not have a tail rotor.

But it does have a semi - articulated main rotor system.

Go figure!

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I just read the AS 350 MM for an overtorque between 94%-100% in straight and level flight above 40kts, and I quote

 

" Overtorque Between 94%-100%

 

If the "OVERTORQUE" accumulated time between

two major overhauls is greater than 8 min:

a) Recondition or overhaul the MGB

B) Scrap the planet pinions, the fixed ring gear and the sun gear"

 

section 05.53.00.602 of MM para 3.1.2.1

 

I would guess after reading this excessive forward loads on the mast above 94%tq above 40kts adds extra stresses in the transmissions planetary gear system from the mast. Just my guess.

 

 

 

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Right from Eurocopter via tech rep.

 

 

The transmission is torque limited. If the torque reading was off the transmission, the number would be the same in hover and in fwd flight. But the reading as we know, is off the engine.

 

The tailrotor in hover and below 40kts takes torque from the engine. In forward flight, this load is off loaded by the shape of the vertical fin. The torque goes somewhere and that is forward to the transmission.

 

As the fine fellow above stated. you are limited to 8 minutes total time above 94%. Then the transmission gears are replaced.

 

This was fun, and actually learned what the issue was.

 

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