Mast bumping, tailboom chops and two bladed rotors (merged)
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"If you poled a 500 over, left your seat and then pulled the stick back quickly I would hate to see how close those short blades would come to the tailboom, if not contact it."
Presumably leaving your seat means the aircraft seat - rather than parting company with your own buttocks? You see there are scientific and cultural differences between Brits and Aussies.......also, in this hemisphere to be "poled" is something entirely different from your meaning.
Presumably leaving your seat means the aircraft seat - rather than parting company with your own buttocks? You see there are scientific and cultural differences between Brits and Aussies.......also, in this hemisphere to be "poled" is something entirely different from your meaning.
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Lu, you're correct that a reduction of centrifugal force would cause the blades to rise, but that's only part of the story. Reduction of the centrifugal force also means that flapping angles will increase, therin lies the danger.
Also, reduced Nr reduces lift, so lift reduced and centrifugal force reduced results in ?????
Also, reduced Nr reduces lift, so lift reduced and centrifugal force reduced results in ?????
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Bloody hell Lu, (excuse my french) all I did was point the guy at another thread for further reading. I expressed no opinion whatsoever. Do you honestly expect me to be responsible for everything everbody says in another thread??? This is the first time I've been corrected for something I didn't even post! If you really think there's a problem with what someone else said in a different thread, well then say it on that thread. I dunno, I should of stayed in bed this morning. 
Irlandés
Irlandés
Iconoclast
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In the case of your post I don't know what to put in this block.
To: helmet fire
Quote:
“The bloke in the first Robbo thread is talking about on the ground during shutdown”.
Response:
If you mean the first post in this thread the question was non-specific about when the chop would occur.
Quote:
“Haven't we cured you of centrifugal”?
Response:
If centrifugal is good enough for Frank Robinson it is good enough for me.
Quote:
“The bloke in the first Robbo thread is talking about on the ground during shutdown”.
Response:
If you mean the first post in this thread the question was non-specific about when the chop would occur.
Quote:
“Haven't we cured you of centrifugal”?
Response:
If centrifugal is good enough for Frank Robinson it is good enough for me.
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helmet fire or anyone else...
Can you please explain "droop stop pounding" on the fully articulated rotorhead and most importantly, what usually causes it?
Can you please explain "droop stop pounding" on the fully articulated rotorhead and most importantly, what usually causes it?
Last edited by Flight Safety; 20th Jul 2002 at 11:58.
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Flight Safety,
The articulated rotor heads can allow the blades to flap too much when the rotor rpm is low, during engagement or shutdown. We generally use a simple rotating stop mechanism that is held out of the way at 100% Nr, and that falls into place as the rotor winds down. This droop stop prevents the blades from flapping down enough to hit the fuselage. They are quite reliable and can be felt as they fall in during shutdown.
Droop stop pounding at full rpm - If the pilot makes large cyclic inputs while the aircraft is restrained on the ground, he can make the blades hit these droop stops. It is very hard to hit them while fully airborne, since the aircraft rotates rapidly with all that cyclic input. Generally, droop stop pounding occurs while the wheels or skids are on the ground, and the pilot puts in a big cyclic input.
A favorite way to get pounding is to use "aerodynamic braking" with back stick during a running landing. This is poor practice, and not generally recommended. This is a good way to pound droop stops and take a divot out of the tail cone with the blades, and a very poor way to stop, since it is quite ineffective. If your instructor teaches Aerodynamic braking, he/she throws in free tail cone contact lessons.
Droop stop pounding at high rpm also helps stress the blades and rotor head, since while the blade is in contact with the droop stop, it is not articulated any more, and lots of bending is experienced. The droop stops can get dented, and the hinges can crack, too. In especially bad cases, the droop stops can be launched off the aircraft and get tossed onto the ramp!
Droop stop pounding at low rpm - Droop stops also get pounded if the pilot does not find the sweet spot when shuting down and spinning up. The rotor flies downwind, so the pilot must use a little cyclic into the wind to keep the disk level and the stops unpounded. The forces at low rpm are low, so the droop stops can take this milder abuse quite well.
Pilots use the landing light at night to help keep the disk level during enganement and shutdown. I generally use the movable spot light and turn it upward to illuminate the tips.
The articulated rotor heads can allow the blades to flap too much when the rotor rpm is low, during engagement or shutdown. We generally use a simple rotating stop mechanism that is held out of the way at 100% Nr, and that falls into place as the rotor winds down. This droop stop prevents the blades from flapping down enough to hit the fuselage. They are quite reliable and can be felt as they fall in during shutdown.
Droop stop pounding at full rpm - If the pilot makes large cyclic inputs while the aircraft is restrained on the ground, he can make the blades hit these droop stops. It is very hard to hit them while fully airborne, since the aircraft rotates rapidly with all that cyclic input. Generally, droop stop pounding occurs while the wheels or skids are on the ground, and the pilot puts in a big cyclic input.
A favorite way to get pounding is to use "aerodynamic braking" with back stick during a running landing. This is poor practice, and not generally recommended. This is a good way to pound droop stops and take a divot out of the tail cone with the blades, and a very poor way to stop, since it is quite ineffective. If your instructor teaches Aerodynamic braking, he/she throws in free tail cone contact lessons.
Droop stop pounding at high rpm also helps stress the blades and rotor head, since while the blade is in contact with the droop stop, it is not articulated any more, and lots of bending is experienced. The droop stops can get dented, and the hinges can crack, too. In especially bad cases, the droop stops can be launched off the aircraft and get tossed onto the ramp!
Droop stop pounding at low rpm - Droop stops also get pounded if the pilot does not find the sweet spot when shuting down and spinning up. The rotor flies downwind, so the pilot must use a little cyclic into the wind to keep the disk level and the stops unpounded. The forces at low rpm are low, so the droop stops can take this milder abuse quite well.
Pilots use the landing light at night to help keep the disk level during enganement and shutdown. I generally use the movable spot light and turn it upward to illuminate the tips.
Iconoclast
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To: Irlandes
I in no way cast any stones or any other kind of aspersions in your direction. I simply stated that the writer was wrong in what he said.
Although most of what the writer stated is true relative to the mechanics of the rotorhead he got one thing wrong. If the helicopter is in flight and the rotor speed drops the rotors will not droop.
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R22 Mast Bumping
Just a quick query: If you are unlucky enough to experience mast bumping in an R22, and I assume an R44, which part of the head actually hits the mast? My boss was telling me the other day that the tusks (droop stops) snap off and this causes the blades to flap down and voila, hit the mast. However I am not convinced. I always thought that it was the part where the coning bolt goes through the head, and that it comes down and hits those small plastic pads that are attached to the mast. (that's a bit vague, but anyone with a diagram please post it.)
Iconoclast
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Yes, Yes and No.
You are correct about the point of contact and your boss is correct as well but only under certain circumstances. If the head and blades are moving as a unit during the flapping excursions the point of contact will be as you described. If the blades are flapping independently from the head the tusk(s) can make contact with the cone stops and the energy of the blade can cause the rotorhead to deviate from the rotational plane and contact will made at the teeter stops against the mast. However, if the energy of the blade is so great as to cause the tusk to fracture one of two things can take place. Either the energy of the blade acting against the inertia of the head can cause the tusk to fracture moving the head to the point that the head contacts the mast or, the blade will continue to flap downwards and make contact with the tail boom or hit the cabin area.
IMHO
IMHO
Last edited by Lu Zuckerman; 10th Feb 2003 at 16:43.
Iconoclast
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Ask another question.
The question you should also ask is why the flapping excursions occur and under what conditions. What is there about the Robinson rotor system that causes extreme flapping?
The Robinson POH indicates that flapping excursions can occur under three and possibly more conditions. They are, Flying out of trim, Flying in a sideslip or having entered into a zero G condition and under certain conditios of low rotor RPM.
The POH suggests that the pilot avoid these conditions yet the certification documents require that the helicopter demonstrate flying out of trim by 10-degrees and flying in a sideslip by 90-degrees. Since the FAA certification requirements state that these maneuvers must be demonstrated why is the FAA now stating that these maneuvers must be avoided.
One question that I propose is would the Robinson design be certifiable if Robinson told the FAA that the R-22/44 could not be flown out of trim or in a sideslip per the certification requirements?
But then again I have said this in the past and I was crucified for saying it.
The Robinson POH indicates that flapping excursions can occur under three and possibly more conditions. They are, Flying out of trim, Flying in a sideslip or having entered into a zero G condition and under certain conditios of low rotor RPM.
The POH suggests that the pilot avoid these conditions yet the certification documents require that the helicopter demonstrate flying out of trim by 10-degrees and flying in a sideslip by 90-degrees. Since the FAA certification requirements state that these maneuvers must be demonstrated why is the FAA now stating that these maneuvers must be avoided.
One question that I propose is would the Robinson design be certifiable if Robinson told the FAA that the R-22/44 could not be flown out of trim or in a sideslip per the certification requirements?
But then again I have said this in the past and I was crucified for saying it.
Senis Semper Fidelis
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Mast bumping can occur on any "Teetering Head" system the R22, R44 B206 the Huey and many other well known Helicopters have that sort of head, Lu is quiet right in his explanation of the way to cause mast bumping, it is something that is normally drummed into most Helo pilots to avoid at all costs( the cost being your life and or that of your pax) with the rotor going one way and you and the heli going the other, it is apparantly a problem that is easier for converted fixed wing pilots to get into than pilots trained on Helo from scratch, the main reason being a fixed wing pilots reactions are to push the stick forward at the sign of any problems this action will cause the Teetering head Heli to get into the condition of Negative G, this is a most dangerous position to get into and require's quick but accurate action to recover, it has been demonstrated to me by a very experienced Heli pilot, with the cyclic loosing all feeling of being attached to anything, very dangerous dont go there!
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Why does it roll to the right?
Can anyone give me a SIMPLE answer in words of one syllable please .....
When in negative g in a Robbo (or similar), why does the craft roll to the right, rather than the left? I understand that in such a situation the disk is not loaded and that the tail rotor thrust then comes to bear on the situation, but when I imagine this situation in my mind, I envisage the tail coming up and continuing to be pushed to the right, with a subsequent roll left and pitch downwards. Trouble is, I know the roll is to the right but I just can't see why.
As I say, a really basic explanation would be great.
Thanks
Helo
When in negative g in a Robbo (or similar), why does the craft roll to the right, rather than the left? I understand that in such a situation the disk is not loaded and that the tail rotor thrust then comes to bear on the situation, but when I imagine this situation in my mind, I envisage the tail coming up and continuing to be pushed to the right, with a subsequent roll left and pitch downwards. Trouble is, I know the roll is to the right but I just can't see why.
As I say, a really basic explanation would be great.
Thanks
Helo
Off the top of my head, it's because the T/R is above the vertical C of G. Air pushing to the left ( if viewed from behind ) creates a couple around the C/G which rolls the a/c right.
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Another nail in the coffin for the R22.
I'm surprised that people want to fly it with all the problems that are associated with it's design.
Fit for purpose springs to mind and duty of care by the manufacturer are still relevant with this machine.
However, the boys in Australia herding the cattle seem to be able to fly these in their day to day tasks quite successfully. How do they cope with these problems?
I'm surprised that people want to fly it with all the problems that are associated with it's design.
Fit for purpose springs to mind and duty of care by the manufacturer are still relevant with this machine.
However, the boys in Australia herding the cattle seem to be able to fly these in their day to day tasks quite successfully. How do they cope with these problems?
Iconoclast
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Cows don't move very fast.
As much as I may criticize the Robinson design I was absolutely amazed at the agility and responsiveness of the R-22 when involved in cattle mustering as shown on a Discovery channel program. It is my opinion that the rotor system does not enter into the regime of high flapping loads at the low speeds encountered in mustering. If they tried the same maneuvers used in mustering at normal flying speeds they might get into trouble.
Then again there is a display flying team in California that flies R-22s in aerobatics flying with the full knowledge of Robinson and they constantly violate the FAA’s recommendations about flying out of trim and sideslipping. On their web site they show an R-22 flying in formation with a Stearman and the R-22 is flying backwards.
One of their high time pilots (20,000 + hours) was killed along with his first flight student when the rotor came off. It was decided that the student over controlled the helicopter when they really did not know who was at the controls. The flight terminated after fifteen minutes of flight.
Then again there is a display flying team in California that flies R-22s in aerobatics flying with the full knowledge of Robinson and they constantly violate the FAA’s recommendations about flying out of trim and sideslipping. On their web site they show an R-22 flying in formation with a Stearman and the R-22 is flying backwards.
One of their high time pilots (20,000 + hours) was killed along with his first flight student when the rotor came off. It was decided that the student over controlled the helicopter when they really did not know who was at the controls. The flight terminated after fifteen minutes of flight.
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Mast Bumbing R22
Hi all,
I have a question regarding Low G and Mast Bumping in R22s. In the R22 POH it states that "Pushing the cyclic forward following a pull-up or rapid climbor even from level flight produces a low-G (weightless) condition"
My question is .... If it's possible to induce Low G by moving cyclic forward in level flight, just how abrupt would the movement have to be? Increasing speed requires a similar action ... doesn't it?
I was taught that to level off from a climb you should apply fwd stick to accelerate to cruise speed and then lower the lever to set cruise power.
Have I misunderstood the POH? Just what would you have to do to induce low G this way.
Paranoid Sneetch
I have a question regarding Low G and Mast Bumping in R22s. In the R22 POH it states that "Pushing the cyclic forward following a pull-up or rapid climbor even from level flight produces a low-G (weightless) condition"
My question is .... If it's possible to induce Low G by moving cyclic forward in level flight, just how abrupt would the movement have to be? Increasing speed requires a similar action ... doesn't it?
I was taught that to level off from a climb you should apply fwd stick to accelerate to cruise speed and then lower the lever to set cruise power.
Have I misunderstood the POH? Just what would you have to do to induce low G this way.
Paranoid Sneetch
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It would have to be a very large input. Just imagine a rollercoaster. If it is a gentle downslope from going straight you don't feel much strain. Now if you are moving level and it drops off to a 45 degree slope you will feel quite a strain. Just remember if you ever feel weightless in your seat to pull in aft cyclic until the feeling goes away. If you don't feel weightless you are fine.
The Original Whirly
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I had this demonstrated to me on my instructors course, and cyclic movement does have to be pretty abrupt. It's easy to correct, as Jcooper says, by aft cyclic. The main problem, it seems to me, is that the helicopter begins to roll (left I think, can't remember for certain), and you may instinctively want to correct that. DON'T!!!! Aft cyclic first to reload the rotors, then whatever corrections are needed. So you have to be able to recognise what's happening.
Of course, the best thing is to always make reasonably gentle (ie normal) cyclic movements, and then it won't happen.
Of course, the best thing is to always make reasonably gentle (ie normal) cyclic movements, and then it won't happen.