What would happen if... ??
Thread Starter
Joined: Aug 2000
Posts: 121
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From: Australia
What would happen if... ??
R22....
Flying along, fat, dumb and happy... Drive shaft between the upper sheeve and transmission (the two flex plates on each end) fails and drive between engine and transmission is lost.
Which way would the aircraft yaw in this scenario?
Flying along, fat, dumb and happy... Drive shaft between the upper sheeve and transmission (the two flex plates on each end) fails and drive between engine and transmission is lost.
Which way would the aircraft yaw in this scenario?
Joined: Mar 2004
Posts: 224
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From: UK
Not quite sure where you are thinking the break would be, either forward of the sheave or aft of it or both?
If it breaks forward of sheave, the engine will still drive the tail rotor, but no torque reaction required since the main rotor is no longer driven. Therefore the a/c will yaw left needing right pedal but the lever will need dumping.
If it breaks aft of the sheave, main rotor is still driven, tail rotor isn't therefore the a/c will yaw right (left pedal needed, except that won't work so lever gets dumped).
Breaks at both places, simple engine failure scenario, sort the pedals out after you have dumped the lever!
Can see a pattern here - most important thing is what is happening to the lever rather than the pedals.
Can someone remind me where the govenor receives its RRPM/ERPM information from?
PS you should never be fat, dumb and happy in an R22!, well not all at the same time!!
If it breaks forward of sheave, the engine will still drive the tail rotor, but no torque reaction required since the main rotor is no longer driven. Therefore the a/c will yaw left needing right pedal but the lever will need dumping.
If it breaks aft of the sheave, main rotor is still driven, tail rotor isn't therefore the a/c will yaw right (left pedal needed, except that won't work so lever gets dumped).
Breaks at both places, simple engine failure scenario, sort the pedals out after you have dumped the lever!
Can see a pattern here - most important thing is what is happening to the lever rather than the pedals.
Can someone remind me where the govenor receives its RRPM/ERPM information from?
PS you should never be fat, dumb and happy in an R22!, well not all at the same time!!
Joined: Feb 2003
Posts: 261
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From: LEAX, Spain
The craft will yaw left, just as with an engine failure.
If, as you seem to be wondering, drive to the tailrotor is maintained, the yaw will be more pronounced than with engine failure. However, the regulatory boot full of right pedal together with the usual rapid lowering of the collective should see you home in time for Tiffin just the same.
If, as you seem to be wondering, drive to the tailrotor is maintained, the yaw will be more pronounced than with engine failure. However, the regulatory boot full of right pedal together with the usual rapid lowering of the collective should see you home in time for Tiffin just the same.
Joined: Mar 2002
Posts: 267
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From: Queensland Australia
TC
Yes..but hopefully the yaw and the falling RRpm indicator and/or the low rrpm horm will give you the hint that there's something that requires dropping the collective.
The robbie has a very good mechanical correlator which will wind off the ERPM as you do and hopefully it will drop it back to an idle or close to it.
But what you have to hope is that when the short shaft fractures the stump attached to the MRGB doesn't spin outwards and jam or at least slow down by hitting the surrounding bits. I think that is what happened in the west australian crash that stimulated the A.D. requiring the inspections for unauthorised mating compounds under the clutch sleeves.
RR
Yes..but hopefully the yaw and the falling RRpm indicator and/or the low rrpm horm will give you the hint that there's something that requires dropping the collective.
The robbie has a very good mechanical correlator which will wind off the ERPM as you do and hopefully it will drop it back to an idle or close to it.
But what you have to hope is that when the short shaft fractures the stump attached to the MRGB doesn't spin outwards and jam or at least slow down by hitting the surrounding bits. I think that is what happened in the west australian crash that stimulated the A.D. requiring the inspections for unauthorised mating compounds under the clutch sleeves.
RR
Joined: Apr 2002
Posts: 593
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From: UK
What about the huge engine overspeed ?
Depends how quick you react. But assuming you catch it within a second (and to avoid rotor decay you would need to at least hit this target), there'll be some popping and banging before you shut the throttle.
I have a feeling that the Robinson Lycoming is so under-stressed in the cruise that it can't have any physical damage in the event that the load is suddenly removed. (Could be different in the hover where the load tends to be much greater.)
It'll be like that glorious moment I have witnessed on several occasions when some tw*t starts a Robinson with a wide open throttle.
Put it this way - the engine will be the least of your problems.
Why do you need to know?
Depends how quick you react. But assuming you catch it within a second (and to avoid rotor decay you would need to at least hit this target), there'll be some popping and banging before you shut the throttle.
I have a feeling that the Robinson Lycoming is so under-stressed in the cruise that it can't have any physical damage in the event that the load is suddenly removed. (Could be different in the hover where the load tends to be much greater.)
It'll be like that glorious moment I have witnessed on several occasions when some tw*t starts a Robinson with a wide open throttle.
Put it this way - the engine will be the least of your problems.
Why do you need to know?
Joined: Aug 2003
Posts: 45
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From: Colorado
No overspeed would occur. The governor will snap the throttle shut faster than you could ever react and the RPM wouldn't jump up very high.
Same thing with a belt failure. The rotor RPM starts dropping, but engine RPM remains the same.
Same thing with a belt failure. The rotor RPM starts dropping, but engine RPM remains the same.
Joined: Feb 2003
Posts: 373
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From: ON A HILL
What would happen if... ??
If the front flex plate shears, I would have thought that the drive shaft would flail around and take out the wiring loom , tail rotor linkage, and fuel tank. If the top sheave gets too far out of line it would ( assuming the rear flex plate remains intact for a few seconds) rip the tail rotor drive shaft out. Best not to think about this for too long
Thread Starter
Joined: Aug 2000
Posts: 121
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From: Australia
Decent responses,
The real reason I posted the question was because I was bored 5hitless sitting here in the office waiting for the proverbial launch codes...... but having said that, this exact thing did happened to a bloke I know..... many moons ago now though.
He was flying along doing a wonderful job of being fat, dumb and happy, when the shaft let go due to a small crack that originated at the bolt holes under the flex plate.
His reaction was obviously correct because he put it down without a scratch from a couple of hundred feet.
The thing he recalls the most is the major engine overspeed (may be due to the fact that we were flying un-governed 22's at this stage).
Having a study of the problem it was noted that the tail rotor was still being driven by the engine but as there was no longer any drag from the main drive system the tail rotor was literally free to spin in sympathy with the increased engine RPM.
All other indications were synonomous with a basic belt come donk failure.
It has always stood out in my mind as a great story to get the head thinking as to what to expect. If the engine RPM isn't brought into check due to the excitement and maybe concentration with getting RRPM sorted out first then there could well be a conflict of indicators that would otherwise help to put a picture in your head as to what is going on behind you. How will the tail rotor react at the flare if you forget to roll the throttle all the way into the detent? Have I just had a catestrophic failure that has taken out the tail rotor controls as well? etc etc........
Just passing the time.....
The real reason I posted the question was because I was bored 5hitless sitting here in the office waiting for the proverbial launch codes...... but having said that, this exact thing did happened to a bloke I know..... many moons ago now though.
He was flying along doing a wonderful job of being fat, dumb and happy, when the shaft let go due to a small crack that originated at the bolt holes under the flex plate.
His reaction was obviously correct because he put it down without a scratch from a couple of hundred feet.
The thing he recalls the most is the major engine overspeed (may be due to the fact that we were flying un-governed 22's at this stage).
Having a study of the problem it was noted that the tail rotor was still being driven by the engine but as there was no longer any drag from the main drive system the tail rotor was literally free to spin in sympathy with the increased engine RPM.
All other indications were synonomous with a basic belt come donk failure.
It has always stood out in my mind as a great story to get the head thinking as to what to expect. If the engine RPM isn't brought into check due to the excitement and maybe concentration with getting RRPM sorted out first then there could well be a conflict of indicators that would otherwise help to put a picture in your head as to what is going on behind you. How will the tail rotor react at the flare if you forget to roll the throttle all the way into the detent? Have I just had a catestrophic failure that has taken out the tail rotor controls as well? etc etc........
Just passing the time.....
