R66 crash in Wikieup, Arizona, U.S.A., kills 2
Join Date: May 2010
Location: New Zealand
Age: 52
Posts: 395
Likes: 0
Received 0 Likes
on
0 Posts
obviously a little bit lost in translation. When i talk about any control movements, im talking small movements.
so aft cyclic, means a very small check backwards, not pulling full aft as hard as you can. Thats why these conversations are best done face to face, rather than over the interweb.
other than that, i think i could almost agree with whats said here...
so aft cyclic, means a very small check backwards, not pulling full aft as hard as you can. Thats why these conversations are best done face to face, rather than over the interweb.
other than that, i think i could almost agree with whats said here...
What would be interesting is to know exactly why the flick roll to the right occurs.
Normally a yaw to the left would produce a roll to the left as a secondary effect.
The only explanation I can offer is that the TR is above the vertical centre of gravity in a robbie - most of the weight (engine, fuel, pax) is below the line of the tail boom/TR.
So, when the TR is pushing to the right (to create left yaw) it is pushing the fuselage in a roll to the right about the vertical C of G. With no cyclic control (very low G) to oppose that movement, the fuselage can only go one way.
This may be worse in the cruise since the TR is even higher due to the nose down and lack of horizontal stabiliser.
Thoughts?
Normally a yaw to the left would produce a roll to the left as a secondary effect.
The only explanation I can offer is that the TR is above the vertical centre of gravity in a robbie - most of the weight (engine, fuel, pax) is below the line of the tail boom/TR.
So, when the TR is pushing to the right (to create left yaw) it is pushing the fuselage in a roll to the right about the vertical C of G. With no cyclic control (very low G) to oppose that movement, the fuselage can only go one way.
This may be worse in the cruise since the TR is even higher due to the nose down and lack of horizontal stabiliser.
Thoughts?
GeorgeM: Perhaps not exactly what you're looking for, but the NTSB special report available at http://www.rotorshop.com/sir9603.pdf (page 12) classifies two of 121 B206 fatal accidents as "LOC" by this definition:
1) LOSS of control (LOC) accidents, involved an in flight: loss of main rotor control; structural failure of the main rotor blade that did not involve preexisting fatigue of rotor blade materials; or, loss of aircraft control or collision with terrain for unknown reasons, in the absence of structural failure,encounter with instrument meteorological conditions, or pilot impairment due to drugs or alcohol.
1) LOSS of control (LOC) accidents, involved an in flight: loss of main rotor control; structural failure of the main rotor blade that did not involve preexisting fatigue of rotor blade materials; or, loss of aircraft control or collision with terrain for unknown reasons, in the absence of structural failure,encounter with instrument meteorological conditions, or pilot impairment due to drugs or alcohol.
Join Date: Apr 2014
Location: usa
Age: 65
Posts: 43
Likes: 0
Received 0 Likes
on
0 Posts
Crab, I also would like to understand the physics behind the uncommanded snaproll right. They quit teaching 0-g recoveries by the time I got my PPL, and my instructors are vague on the whole subject. Also, if the snaproll right is caused by left pedal that should be neutralized when the MR torque drops to rotational drag only, then why not a neutralized pedal recovery, leave the stick and the lever alone, and wait for gravity to take over? And yes, I fly Robbies out of necessity, not choice, so the answer to these questions is of more than academic interest.
over 3,800hrs in a JetBox, (err that has a 2 bladed teetering-head) more than half of those hours in high altitude Mountains, with seriously eXtreme turbulence, very high winds, landing up to 16,200' & never had a negative G or mast bumping issue, never ever 
not even close 
but I wouldn't wanna be up there in a Robo thingy 
Happy Happy
not even close but I wouldn't wanna be up there in a Robo thingy Happy Happy
as I said before, I don't know squat about the Robinson design. My experience with this phenomena is with the AH-1 series aircraft. The right roll is the result of T/R thrust, and yes, if you unload the tail rotor as you push over you can minimize the roll. The problem with that technique (which was explained to my 20 yr old brain by an aviator who had more time flying than I had alive) is that you are way outside the envelope and potentially millimeters away from main rotor separation (mast bump)as you try to match thrust.
Has anybody survived mast bumping?
When I was training, about 20 years ago, there was a story about a chap who managed to land a 22 after a mast bump and survived. I don't know how true this was.
When I was training, about 20 years ago, there was a story about a chap who managed to land a 22 after a mast bump and survived. I don't know how true this was.
Join Date: May 2010
Location: New Zealand
Age: 52
Posts: 395
Likes: 0
Received 0 Likes
on
0 Posts
crab, you are correct, roll to the right is from the high TR position. now think UH1's it is even worse than a robbie.... but we have a little more weight to start with.
this is another reason for slight aft cyclic BEFORE you start bouncing through those hills. as you slow down, you end up with less nose down, therefore the TR also comes down, compared to MR level, and can produce less of a turning moment on the fuselage when you start to get bounced, if the bounce even produces a loss of G, or because you already have the disk well loaded you may just get a bounce.
worst combination is 1 up, low on gas, returning to base at VNE, in the lee of some big hills on a windy day, and how many of us have done that? luckily the ol JR doesn't really want to get to VNE straight and Level...
this is another reason for slight aft cyclic BEFORE you start bouncing through those hills. as you slow down, you end up with less nose down, therefore the TR also comes down, compared to MR level, and can produce less of a turning moment on the fuselage when you start to get bounced, if the bounce even produces a loss of G, or because you already have the disk well loaded you may just get a bounce.
worst combination is 1 up, low on gas, returning to base at VNE, in the lee of some big hills on a windy day, and how many of us have done that? luckily the ol JR doesn't really want to get to VNE straight and Level...
Bell and many military officials have insisted that mast bumping will never occur unless a critical part fails or the pilot flies beyond the limits set for the helicopter. But the only person to survive a catastrophic mast bumping disputes their contention.
Col. Larry B. Higgins has told his superiors — and the Star-Telegram — that he was flying a Cobra helicopter within its operating limits last August when a rotor blade sliced through the cockpit, killing his co-pilot instantly. Higgins was able to parachute to safety only because the blade cut off the front of the cockpit, giving him an instant escape route.
Col. Larry B. Higgins has told his superiors — and the Star-Telegram — that he was flying a Cobra helicopter within its operating limits last August when a rotor blade sliced through the cockpit, killing his co-pilot instantly. Higgins was able to parachute to safety only because the blade cut off the front of the cockpit, giving him an instant escape route.
Some occupants are not killed instantly, however.
A Marine Corps major was aboard a helicopter at the test pilot school in 1980 when a mast bumping and separation killed his pilot but left him alive. Equipped with a parachute, he pulled his door handle in an effort to bail out, but was unable to open the door. Finally, he broke the handle.
But by the time he was outside the helicopter and had pulled his ripcord, he had hit the ground. An instant later, the helicopter fell on him, according to the Navy investigation.
In a 1981 Australian crash for which Bell is being sued, the Australian military tried to determine why a helicopter crew chief was unable to parachute to safety.
Investigators suggested that he may still have been shaken because of a troubling flight in the same helicopter the week before. He may have frozen in shock when -- after the mast bumping occurred -- the rotor blade came through the cockpit and decapitated the pilot sitting in front of him.
"In this accident, the visual scenes confronting him would have been horrific," the investigators said, noting the crew chief had up to 12 seconds to escape. "This, coupled with (his) already high state of anxiety, may well have been sufficient to freeze him in a state of immobile terror."
A Marine Corps major was aboard a helicopter at the test pilot school in 1980 when a mast bumping and separation killed his pilot but left him alive. Equipped with a parachute, he pulled his door handle in an effort to bail out, but was unable to open the door. Finally, he broke the handle.
But by the time he was outside the helicopter and had pulled his ripcord, he had hit the ground. An instant later, the helicopter fell on him, according to the Navy investigation.
In a 1981 Australian crash for which Bell is being sued, the Australian military tried to determine why a helicopter crew chief was unable to parachute to safety.
Investigators suggested that he may still have been shaken because of a troubling flight in the same helicopter the week before. He may have frozen in shock when -- after the mast bumping occurred -- the rotor blade came through the cockpit and decapitated the pilot sitting in front of him.
"In this accident, the visual scenes confronting him would have been horrific," the investigators said, noting the crew chief had up to 12 seconds to escape. "This, coupled with (his) already high state of anxiety, may well have been sufficient to freeze him in a state of immobile terror."
This was the first time I read about helicopter air crew being equipped with parachutes btw. Maybe not the worst idea when one has to fly a robinson...
Has anybody survived mast bumping?
Thread Starter
over 3,800hrs in a JetBox, (err that has a 2 bladed teetering-head) more than half of those hours in high altitude Mountains, with seriously eXtreme turbulence, very high winds, landing up to 16,200' & never had a negative G or mast bumping issue, never ever not even close but I wouldn't wanna be up there in a Robo thingy
Happy Happy
not even close but I wouldn't wanna be up there in a Robo thingy Happy Happy
Join Date: Nov 2007
Location: Massachusetts
Age: 67
Posts: 172
Likes: 0
Received 0 Likes
on
0 Posts
Sorry, haven't been reading in a couple weeks so I had a bit of catching up to do. I hope you'll bear with this long posting. Having been a CFI before/during/after the entire SFAR 73 debacle I think I have a few good things to add to the discussion.
This is correct. When I first did the safety course in the mid 80-s Frank still taught some of it himself. He mentioned that R22 TR thrust could produce roll rates in excess of 100° per second, quote "faster than an F16 can roll".
Robinson (and the Army's training video that was included as part of the SFAR-73 training) recommend gentle aft cyclic to regain gee forces, and then once gee forces are restored you can roll level. They have never advocated addition of collective pitch and I've never tried that - I've always used aft cyclic as recommended. It's worked so far.
I'm not 100% certain, but I think this is likely incorrect. I don't disagree that at very low gee the fuselage will not respond because of the low thrust, but you are still in command of the rotor. Aft cyclic will load the rotor, and as it loads back up gee force will increase and you'll be back in command of the fuselage once again. My experience as an instructor teaching low gee right rolls for almost a decade before the FAA finally put a stop to it is that in a normal demonstration of a cyclic pushover resulting in a right roll, we would push until we would get a right rolling motion and then we would command aft cyclic. I never remember there being any delay, i.e. the aircraft would respond immediately to aft cyclic with gee force increasing. I suspect we were not very low gee but I have no way of knowing what percent of gee we would get the roll at.
I did have an experience with a student in an R22 where at the entry of autorotation he pushed the cyclic to the forward stop as hard as he could, i.e. it was a very quick application of full forward cyclic, along with the normal lowering of collective and application of right pedal. We ended up pretty close to 90° nose low (I know because we were above the end of the runway and the numbers of the runway were straight ahead in the windshield). Again, no way to know how low gee we actually achieved, but my guess would be pretty darn close to 0 gee.
I applied gentle aft cyclic and after what seemed like an extended time, the gee forces built up and the nose finally came up. The thing is, I'm not really sure that it was an extended time, it's very possible that the adrenaline and time dilation just made it seem like a long time. Certainly it worked fast enough that from 500 feet and 90° nose low, we avoided hitting the earth!
After we landed I spent some time thinking about why we were not dead and it occurred to me that it was because we pushed right pedal as we lowered the collective, i.e. there was no TR thrust to roll us (and indeed, there was no roll, just a violent nose pitch down). This is a long way of saying that even at extremely low gee the cyclic will in fact be effective. Whether the collective would work as you mention, I simply don't know.
This is an important point I believe. If you think about the arc you need to fly in order to reach 0.5 gee, it's dependent on speed. In an R22 it takes a pretty good push before you get the right roll, but R22s cruise at 85-90 knots. In an R44 doing 110 knots it takes a gentle application of forward stick to start feeling yourself get light in the seat. In an R66 at 130 knots, it would be even less of a push. So, the faster the aircraft you are flying, the easier it is to push enough forward cyclic to get low gee rolls. It's something I worry about soloing an R44 student versus an R22 student. In turbulence it pays to fly a little slow.
Again, I don't agree with you that at zero gee aft cyclic won't work. Perhaps it will take a little longer to work than at 0.5 gee, I'm not sure. As to whether collective would help or hurt, I don't know but my concern would be that adding power and adding pedal will just increase TR thrust and probably keep things at least as bad as they are, and that adding power and not adding pedal would put you out of trim and the resulting tuck probably isn't going to be helping the head->mast clearance situation. I'll be curious to have one of the test pilots comment on that.
This I very much agree with. I always train people that the first time you find yourself in a low gee right roll, you are very likely going to do the instinctive thing and push the cyclic to the left. Better is to associate the light feeling in the seat of your pants with the need to move the stick aft, i.e. load the rotor back up long before you get to a gee factor low enough to allow the right roll to develop. And also what everybody says: slow down.
I don't think this is correct. I think that the TR alone will cause the mast to be bumped, pushing left cyclic probably just makes it happen more quickly. If Frank is right that the TR can cause roll rates of 100° per second, it won't take long to roll past the 12° of flapping clearance in the robby.
I seem to remember that a couple guys were out in an R22 Mariner (fixed float) when they did a practice autorotation at VNE and did a complete 360° tail-over-nose flip, i.e. Red Bull kinda move and that they bumped the mast but landed okay (and the VNE was then reduced to 95 knots).
Sorry for the long post, but obviously an interesting discussion for many of us. And, as to the design of the rotor... I've wondered for a long time why someone doesn't make a hingeless 2 bladed system? I like the idea of no low-gee restrictions but still being able to tuck a bunch of aircraft in a hangar skid-to-skid... (and I feel like the slow response of the fuselage in a 2 bladed system like the Robby or Bell makes it more difficult to teach hovering to a new student compared to an articulated system with some hinge offset).
[email protected]: What would be interesting is to know exactly why the flick roll to the right occurs.
The only explanation I can offer is that the TR is above the vertical centre of gravity in a robbie - most of the weight (engine, fuel, pax) is below the line of the tail boom/TR.
The only explanation I can offer is that the TR is above the vertical centre of gravity in a robbie - most of the weight (engine, fuel, pax) is below the line of the tail boom/TR.
Lonewolf_50 asked: In an event like that, is the correct response to load the head using collective before using cyclic to maneuver/roll? Never flown a Robinson, so I have no idea.
[email protected] says: At zero G in a teetering head helicopter, you have no control power (ie how much you have to move the cyclic to affect the attitude of the fuselage). You can wave the cyclic around as much as you like but it won't affect the attitude of the fuselage.
At zero G you have no cyclic control power so therefore aft cyclic won't be effective and can make things worse (ie chopping off the tail) - the only thing that will save you is to restore positive G and that would have to be with the collective.
At 0.99 G you have a very small reduction (probably imperceptible) in control power so aft cyclic will immediately (if you have any forward speed) restore normal operation.
There is a big sliding scale between those bookends of performance - the lower the G, the lower the control power and somewhere (I don't know exactly) there will come a point where the control power is sufficiently low to render aft cyclic ineffective in restoring G (and therefore control power).
At zero G you have no cyclic control power so therefore aft cyclic won't be effective and can make things worse (ie chopping off the tail) - the only thing that will save you is to restore positive G and that would have to be with the collective.
At 0.99 G you have a very small reduction (probably imperceptible) in control power so aft cyclic will immediately (if you have any forward speed) restore normal operation.
There is a big sliding scale between those bookends of performance - the lower the G, the lower the control power and somewhere (I don't know exactly) there will come a point where the control power is sufficiently low to render aft cyclic ineffective in restoring G (and therefore control power).
I did have an experience with a student in an R22 where at the entry of autorotation he pushed the cyclic to the forward stop as hard as he could, i.e. it was a very quick application of full forward cyclic, along with the normal lowering of collective and application of right pedal. We ended up pretty close to 90° nose low (I know because we were above the end of the runway and the numbers of the runway were straight ahead in the windshield). Again, no way to know how low gee we actually achieved, but my guess would be pretty darn close to 0 gee.
I applied gentle aft cyclic and after what seemed like an extended time, the gee forces built up and the nose finally came up. The thing is, I'm not really sure that it was an extended time, it's very possible that the adrenaline and time dilation just made it seem like a long time. Certainly it worked fast enough that from 500 feet and 90° nose low, we avoided hitting the earth!
After we landed I spent some time thinking about why we were not dead and it occurred to me that it was because we pushed right pedal as we lowered the collective, i.e. there was no TR thrust to roll us (and indeed, there was no roll, just a violent nose pitch down). This is a long way of saying that even at extremely low gee the cyclic will in fact be effective. Whether the collective would work as you mention, I simply don't know.
Arrrj says: Second thing, the 66 is really powerful (3/4 fuel, 5 up, confined area, 30 degrees, up, up and away) and fast. 60% torque, 130 knot cruise.
[email protected] says: As I said, it depends on how little G you have - at zero G aft cyclic will not have an effect other than to move the disc nearer to the tail boom - that will get people killed.
Please explain how using the collective will get people killed??
Please explain how using the collective will get people killed??
[email protected] says: As has been said before the answer is prevention...
Hughesy says: An addition to this. Neg G will not cause mast bumping. It's the incorrect pilot actions that causes it.
topradio asks: Has anybody survived mast bumping?
When I was training, about 20 years ago, there was a story about a chap who managed to land a 22 after a mast bump and survived. I don't know how true this was.
When I was training, about 20 years ago, there was a story about a chap who managed to land a 22 after a mast bump and survived. I don't know how true this was.
Sorry for the long post, but obviously an interesting discussion for many of us. And, as to the design of the rotor... I've wondered for a long time why someone doesn't make a hingeless 2 bladed system? I like the idea of no low-gee restrictions but still being able to tuck a bunch of aircraft in a hangar skid-to-skid... (and I feel like the slow response of the fuselage in a 2 bladed system like the Robby or Bell makes it more difficult to teach hovering to a new student compared to an articulated system with some hinge offset).
Paul - a very informed and interesting post - you have clearly been there, seen that and got the T shirt as far as Robbie flying is concerned
The quoted rate of roll from the TR thrust is rather sobering - and that was from the bloke who designed it - wonder if he ever thought there was a better way?
I still believe that at zero G in a teetering head helo, you can wave the cyclic as much as you like but, whilst you are changing the disc attitude, the rotor has no effect on the fuselage attitude until some positive G is restored - in the case of your 90 nose down, the fact that you started to accelerate towards the ground restored the G which allowed your aft cyclic to take effect.
The rotor head has to pull the fuselage around the sky on a teetering head helo which requires the weight of the fuselage to be pulling down on the rotor - this can't happen at zero G.
I may be wrong about my suggestion to use collective but it makes sense from the physics.
The quoted rate of roll from the TR thrust is rather sobering - and that was from the bloke who designed it - wonder if he ever thought there was a better way?
I still believe that at zero G in a teetering head helo, you can wave the cyclic as much as you like but, whilst you are changing the disc attitude, the rotor has no effect on the fuselage attitude until some positive G is restored - in the case of your 90 nose down, the fact that you started to accelerate towards the ground restored the G which allowed your aft cyclic to take effect.
The rotor head has to pull the fuselage around the sky on a teetering head helo which requires the weight of the fuselage to be pulling down on the rotor - this can't happen at zero G.
I may be wrong about my suggestion to use collective but it makes sense from the physics.
Join Date: Nov 2007
Location: Massachusetts
Age: 67
Posts: 172
Likes: 0
Received 0 Likes
on
0 Posts
[email protected]: I still believe that at zero G in a teetering head helo, you can wave the cyclic as much as you like but, whilst you are changing the disc attitude, the rotor has no effect on the fuselage attitude until some positive G is restored
Originally Posted by [email protected]
I may be wrong about my suggestion to use collective but it makes sense from the physics.
Might that tend to mitigate the right roll associated with this hazard? Interesting theoretical point ... but ... it looks as though the less complicated approach is the gentle aft cyclic to load the head. Getting the control of the aircraft back probably benefits from KISS principle, per the experienced Robbie flyers (and thanks Paul for sharing your experiences as CFI)
The other point to take away "in turbulent air, slow down" is good advice.
I make the assumption that anytime one adds collective one adds left pedal, (almost as a conditioned response).
Might that tend to mitigate the right roll associated with this hazard? Interesting theoretical point ... but ... it looks as though the less complicated approach is the gentle aft cyclic to load the head. Getting the control of the aircraft back probably benefits from KISS principle, per the experienced Robbie flyers (and thanks Paul for sharing your experiences as CFI)
The other point to take away "in turbulent air, slow down" is good advice.
Might that tend to mitigate the right roll associated with this hazard? Interesting theoretical point ... but ... it looks as though the less complicated approach is the gentle aft cyclic to load the head. Getting the control of the aircraft back probably benefits from KISS principle, per the experienced Robbie flyers (and thanks Paul for sharing your experiences as CFI)
The other point to take away "in turbulent air, slow down" is good advice.
Join Date: Apr 2014
Location: usa
Age: 65
Posts: 43
Likes: 0
Received 0 Likes
on
0 Posts
Thank you Paul for the comments based on experience. I had a conversation with my FAA flight examiner on this topic last week. His assertion was that low G from turbulence was an entirely different animal compared to low G from a pushover. This due to relative wind past rotor in pushover vs relative wind up through rotor in turbulence. I'm not buying his explanation, but he's got 10,000 hrs flying Robbie's in the mountains here so I am not going to argue with him. Do you agree with him?
Also, I can not figure out why the correct and quicker response to the right roll is not right pedal along with the collective easy back? Your experience with the R22 student who pushed over with pedals neutral would seem to support that neutralizing the pedals did away with the roll.
Also, I can not figure out why the correct and quicker response to the right roll is not right pedal along with the collective easy back? Your experience with the R22 student who pushed over with pedals neutral would seem to support that neutralizing the pedals did away with the roll.
Thank you Paul for the comments based on experience. I had a conversation with my FAA flight examiner on this topic last week. His assertion was that low G from turbulence was an entirely different animal compared to low G from a pushover. This due to relative wind past rotor in pushover vs relative wind up through rotor in turbulence. I'm not buying his explanation, but he's got 10,000 hrs flying Robbie's in the mountains here so I am not going to argue with him. Do you agree with him?
Also, I can not figure out why the correct and quicker response to the right roll is not right pedal along with the collective easy back? Your experience with the R22 student who pushed over with pedals neutral would seem to support that neutralizing the pedals did away with the roll.
Also, I can not figure out why the correct and quicker response to the right roll is not right pedal along with the collective easy back? Your experience with the R22 student who pushed over with pedals neutral would seem to support that neutralizing the pedals did away with the roll.
Aft cyclic is the safest/most practical and proven recovery technique.