Dynamic Rollover
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Joined: Dec 2002
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From: Hertfordshire
Dynamic Rollover
Sunday (5/01/03) an R22 operating out of a Bedford UK airfield, was subjected to a dynamic rollover. The machine was being used under training at the time. The QHI had just completed a 1.5 lesson with the student and was just about to lift again for another flight, when over she went. Fortunately both crew were OK.
What could have gone wrong ? (apart from the obvious).
The QHI was very experienced we know that.......
Was the Student tired ?
Was the QHI tired ?
Thoughts appriciated.......
What could have gone wrong ? (apart from the obvious).
The QHI was very experienced we know that.......
Was the Student tired ?
Was the QHI tired ?
Thoughts appriciated.......
Joined: Apr 2000
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From: EGDC
Maybe crosswind from the left - disc flaps back and more left cyclic required to maintain disc position.
Also static stability reduces as you raise the lever - this was proven by Boscombe Down after a Sea King incident.
The tail rotor produces a rolling couple to the right as you lift especially if you are a little nose down.
Usually it is not enough left cyclic for the prevailing conditions to prevent the aircraft accelerating to the right - once it starts to roll there is insufficient control margin or control power in the R22 to stop it.
Not the first and wont be the last - especially in a helo with a high Cof G and narrow skids.
Also static stability reduces as you raise the lever - this was proven by Boscombe Down after a Sea King incident.
The tail rotor produces a rolling couple to the right as you lift especially if you are a little nose down.
Usually it is not enough left cyclic for the prevailing conditions to prevent the aircraft accelerating to the right - once it starts to roll there is insufficient control margin or control power in the R22 to stop it.
Not the first and wont be the last - especially in a helo with a high Cof G and narrow skids.
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From: Texas
With no more information that this, my first inclination would be the same as Shy Torque's. The usual cause of dynamic rollover, at least on flat terrain, is a skid stuck somehow - either in mud, or under an obstruction, or something like that.
Obviously, we're all guessing here.
Obviously, we're all guessing here.
Joined: Nov 2000
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From: Pewsey, UK
It's alleged the first comment the instructor at a certain West Hampshire aerodrome made after a rollover in an R22 with an early PPL student was "Well, we don't normally cover this so early in the syllabus."
Marks for coolness in a crisis, Dave !
Marks for coolness in a crisis, Dave !
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From: too near London
Apparently happened in calm conditions on tarmac at end of the flight. After an initial fluffed landing, second attempt produced a small bounce and student rapidly raised coll and applied L pedal. Rate of roll and yaw impressive!FI (a good chap)unable to intervene quckly enough. Ended up on RH side. Nobody hurt.
The R22 control response is almost too good.
The R22 control response is almost too good.
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From: Philadelphia PA
It's not a question of control resposne. It is a very complex subject and appears to happen most often to teetering rotor helicopters.
There is a problem that once the rolling motion starts in a teetering rotor helicopter, lateral cyclic will not stop it, and the only way to correct the situation is to get rid of the thrust (i.e. dump the collective).
Another good reason to make sure that every takeoff, even from flat, hard surfaces is not rushed, and that you pause just before you lift off...
There is a problem that once the rolling motion starts in a teetering rotor helicopter, lateral cyclic will not stop it, and the only way to correct the situation is to get rid of the thrust (i.e. dump the collective).
Another good reason to make sure that every takeoff, even from flat, hard surfaces is not rushed, and that you pause just before you lift off...
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From: too near London
Shawn: I think we all know that - I was refering to the speed with which the R22 responds to the controls and the consequent reduction in time for the FI to be able do something...a Bell47 it ain't.
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From: EGDC
Shawn, there comes a point in dynamic rollover when even lowering the lever won't save you - once that roll acceleration starts nothing can stop it until you roll over, I know I have been there in an R22.
The main thing to stress in the prevention of dynamic rollover is to fly the disc as you lift to the hover and lift off gently - if you are in the habit of snatching the takeoff you are far more likely to roll over if the cyclic is not in the right place. Keep the disc level with as much cyclic as is required as you apply power and on a skidded aircraft you can afford to pause with the machine light on the skids to make sure it is not trying to drift or skid to the right or that one of the skids is not stuck in or to the ground.
The main thing to stress in the prevention of dynamic rollover is to fly the disc as you lift to the hover and lift off gently - if you are in the habit of snatching the takeoff you are far more likely to roll over if the cyclic is not in the right place. Keep the disc level with as much cyclic as is required as you apply power and on a skidded aircraft you can afford to pause with the machine light on the skids to make sure it is not trying to drift or skid to the right or that one of the skids is not stuck in or to the ground.
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From: Philadelphia PA
Exactly the point I was trying to make.
Every liftoff should be done slowly and deliberately - when you get light on the skids, pause to let everything settle down, then slowly apply more collective.
I can think of very few times when you need to rush a takeoff. Wish someone would invent a good device to demonstrate dynamic rollover in a simulator, or one of those seat belt demonstrators - a good convincing case would be made.
Every liftoff should be done slowly and deliberately - when you get light on the skids, pause to let everything settle down, then slowly apply more collective.
I can think of very few times when you need to rush a takeoff. Wish someone would invent a good device to demonstrate dynamic rollover in a simulator, or one of those seat belt demonstrators - a good convincing case would be made.
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Crab is right, yet again,
In a teetering rotor, the roll control depends on thrust, lower the collective fully and you have no thrust. No thrust, no control power, so once the roll rate has developed, it is possible that lowering the collective will not be effective. That being said, it is also true that NOT lowering the collective will not help stop the roll, so the best thing is to lift slowly and feel the effect of your controls, stop if not satisfied that YOU are in charge.
It is one more reason why teetering rotors are no longer used when a choice is possible.
In a teetering rotor, the roll control depends on thrust, lower the collective fully and you have no thrust. No thrust, no control power, so once the roll rate has developed, it is possible that lowering the collective will not be effective. That being said, it is also true that NOT lowering the collective will not help stop the roll, so the best thing is to lift slowly and feel the effect of your controls, stop if not satisfied that YOU are in charge.
It is one more reason why teetering rotors are no longer used when a choice is possible.
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From: Vancouver, BC, Canada
"It is one more reason why teetering rotors are no longer used when a choice is possible."
Perhaps PPRuNe's very own [2, 3 and 4-blade teetering rotor w/ offset] may, eventually, reinvigorate choices.
In fact the improved relationship of blade centers to rotor centers may drive the choice back in the other direction.
Dave J.
Perhaps PPRuNe's very own [2, 3 and 4-blade teetering rotor w/ offset] may, eventually, reinvigorate choices.
In fact the improved relationship of blade centers to rotor centers may drive the choice back in the other direction.
Dave J.
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From: too near London
Crab and Nick: I disagree - the roll CAN be stopped by lowering the lever - it's not called "dynamic" for nothing as it's a pilot induced prob in the first place . I imagine a little before the CG moves to the wrong side of the grounded skid the inertia could send the thing over, certainly after that point it's all academic, but that angle is a helluva lot and until then, gravity is definitely on your side! The instinctive response, as Shawn has already said, should be to lower the collective...
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From: Temporarily uncertain of position.
The facts!
If you must know what happenened, then read on.
After a succesful flight of EX11 (circuits), the student hover taxied the helicopter back to the apron & proceeded to land the helicopter on the tarmac surface. The instructor was following through on the controls the whole time & the student was relaxed. The student aborted the first attempt as a slight wobble had started (nothing wrong with that). On the second attempt, the left skid touched first as usual, a small hop to the right skid with a small amount of left yaw (the student was not pressing the right pedal whilst lowering the lever), with which the student immediatley applied full up collective & full left pedal. The helicopter yawed 180 to the left & rolled right at the same time. The instructor was unable to take control from the student due to the students strength (fear factor) + the lack of time approx 2.5 secs from raising the lever + full pedal, to full stop.
The wind conditions were extremely calm! & the surface was smooth!
So remember, whenever you give control to a student, trial lesson or friend, there immediate single aim in life is to try & kill you with there new found skill!!!
After a succesful flight of EX11 (circuits), the student hover taxied the helicopter back to the apron & proceeded to land the helicopter on the tarmac surface. The instructor was following through on the controls the whole time & the student was relaxed. The student aborted the first attempt as a slight wobble had started (nothing wrong with that). On the second attempt, the left skid touched first as usual, a small hop to the right skid with a small amount of left yaw (the student was not pressing the right pedal whilst lowering the lever), with which the student immediatley applied full up collective & full left pedal. The helicopter yawed 180 to the left & rolled right at the same time. The instructor was unable to take control from the student due to the students strength (fear factor) + the lack of time approx 2.5 secs from raising the lever + full pedal, to full stop.
The wind conditions were extremely calm! & the surface was smooth!
So remember, whenever you give control to a student, trial lesson or friend, there immediate single aim in life is to try & kill you with there new found skill!!!
