Tail Rotor Problems
Guest
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Flight Safety,
I don’t recall mentioning SOPs in relation to your comments, however I did feel your remark below was unrealistic:
“What puzzled me was why the pilot didn't apply more collective and climb, so he could straighten it out with a little altitude and attempt a landing on the surrounding flat terrain. I know this would have increased the spin rate, but as long as the airframe structure can tolerate the increased spin, this would have been far better than destroying the helo in the rocky ravine.
So that's my idea, why can't pilots do what "GulfPLt" did, and just climb if needed while enduring a higher spin rate, if that's what it takes to get out of trouble following the loss of T/R, especially at low altitude above an uninviting landing area? “
The following extract from the Uk’s AAIB on an AS355 last year makes interesting reading on this subject:
“…..diverted to a second task which involved hovering at 500 to 600 feet agl over a residential area near the M4 motorway. The visibility was good with a last reported surface wind of 200°/12 kt. Sunset was at 1910 hours and daylight was fading, but the pilot was still able to fly by visual reference.
The helicopter had been hovering in the area for about 10 to 15 minutes, facing in a south-westerly direction, when it suddenly made an uncommanded yaw to the left through some 180 degrees. The pilot immediately applied full right yaw pedal to counter this yaw. However, although the helicopter stabilised for a moment, it then yawed more rapidly to the left. At this time he called out to the two observers on board to warn them of a problem with the helicopter. He partially lowered the collective lever in an attempt to regain control and applied some forward cyclic to gain forward motion and airspeed, but the helicopter then entered a steeply spiralling/yawing descent to the left. The pilot realised that he would not be able to recover full control of the helicopter and abandoned his attempt to fly out of the situation. He concentrated on keeping the helicopter as level as possible whilst looking out through the right side window for visual reference, since he found the forward view too confusing due to the rapid yawing motion. He adjusted collective to achieve what he judged to be the best combination of rate of descent against yaw, and when he caught sight of the surface in his peripheral vision he pulled the collective lever fully up to cushion the impact. “
(Full report at; http://www.aaib.detr.gov.uk/bulletin/jan01/gsaew.htm)
So, I was not intending to cause offence to anyone, merely to add some words of caution to those on this thread who profess to be low time and in search of wisdom. Mind you, most of us are low time when it comes to TR failures, and long may that continue!
As has been said ( I think I may have done too, but obviously in invisible ink) in a teetering head design the resulting fueselage movements that might ensue following a high rate of yaw, could and probably would result in main rotor contact and break up.
The advice of Test pilots is invaluable without doubt, but remember also that any deliberate examination of handling characteristics in this regime will be done in a controlled and systematic approach following extensive briefings and simulations. They are of well above average skill and in current practice with handling extreme situations. Your average line pilot who may not have done even an autorotation for many months or years, and at the end of a hard days flying will probably have a very tough time indeed dealing with a loss of TR drive, in any flight regime, unless in the cruise in a Dauphin perhaps.
You may get away from a TR failure in one piece, on the other hand you may not; it depends on many factors not the least of which will be LUCK!
------------------
Another day in paradise
I don’t recall mentioning SOPs in relation to your comments, however I did feel your remark below was unrealistic:
“What puzzled me was why the pilot didn't apply more collective and climb, so he could straighten it out with a little altitude and attempt a landing on the surrounding flat terrain. I know this would have increased the spin rate, but as long as the airframe structure can tolerate the increased spin, this would have been far better than destroying the helo in the rocky ravine.
So that's my idea, why can't pilots do what "GulfPLt" did, and just climb if needed while enduring a higher spin rate, if that's what it takes to get out of trouble following the loss of T/R, especially at low altitude above an uninviting landing area? “
The following extract from the Uk’s AAIB on an AS355 last year makes interesting reading on this subject:
“…..diverted to a second task which involved hovering at 500 to 600 feet agl over a residential area near the M4 motorway. The visibility was good with a last reported surface wind of 200°/12 kt. Sunset was at 1910 hours and daylight was fading, but the pilot was still able to fly by visual reference.
The helicopter had been hovering in the area for about 10 to 15 minutes, facing in a south-westerly direction, when it suddenly made an uncommanded yaw to the left through some 180 degrees. The pilot immediately applied full right yaw pedal to counter this yaw. However, although the helicopter stabilised for a moment, it then yawed more rapidly to the left. At this time he called out to the two observers on board to warn them of a problem with the helicopter. He partially lowered the collective lever in an attempt to regain control and applied some forward cyclic to gain forward motion and airspeed, but the helicopter then entered a steeply spiralling/yawing descent to the left. The pilot realised that he would not be able to recover full control of the helicopter and abandoned his attempt to fly out of the situation. He concentrated on keeping the helicopter as level as possible whilst looking out through the right side window for visual reference, since he found the forward view too confusing due to the rapid yawing motion. He adjusted collective to achieve what he judged to be the best combination of rate of descent against yaw, and when he caught sight of the surface in his peripheral vision he pulled the collective lever fully up to cushion the impact. “
(Full report at; http://www.aaib.detr.gov.uk/bulletin/jan01/gsaew.htm)
So, I was not intending to cause offence to anyone, merely to add some words of caution to those on this thread who profess to be low time and in search of wisdom. Mind you, most of us are low time when it comes to TR failures, and long may that continue!
As has been said ( I think I may have done too, but obviously in invisible ink) in a teetering head design the resulting fueselage movements that might ensue following a high rate of yaw, could and probably would result in main rotor contact and break up.
The advice of Test pilots is invaluable without doubt, but remember also that any deliberate examination of handling characteristics in this regime will be done in a controlled and systematic approach following extensive briefings and simulations. They are of well above average skill and in current practice with handling extreme situations. Your average line pilot who may not have done even an autorotation for many months or years, and at the end of a hard days flying will probably have a very tough time indeed dealing with a loss of TR drive, in any flight regime, unless in the cruise in a Dauphin perhaps.
You may get away from a TR failure in one piece, on the other hand you may not; it depends on many factors not the least of which will be LUCK!
------------------
Another day in paradise
Guest
Posts: n/a
Also culled from the same report 212man got his bit from :
"Prior to joining the company he had flown helicopters in the Royal Navy for a number of years. In 1993 he was involved in an accident to a Westland Sea King helicopter in which the tail rotor drive shaft had failed. He had witnessed, on that occasion, a change in engine sound or mechanical noise associated with the loss of control, whereas on this occasion he had not heard any such changes."
Prior experience counted for him when he had his second problem !!
"Prior to joining the company he had flown helicopters in the Royal Navy for a number of years. In 1993 he was involved in an accident to a Westland Sea King helicopter in which the tail rotor drive shaft had failed. He had witnessed, on that occasion, a change in engine sound or mechanical noise associated with the loss of control, whereas on this occasion he had not heard any such changes."
Prior experience counted for him when he had his second problem !!
Guest
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Thanks 212man. I apologize that I reacted as strongly as I did, and I understand your desire that no one be misinformed, especially the new and low time pilots. I'm glad we're still friends. 
I agree with your comments and I understand the decision made by the pilot in the accident report.
One think that still troubles me is why loss of anti-torque spins in helos are so daunting to most pilots. In FW flying, aircraft have to meet design certification requirements for spins, and pilots have to be trained in spin recovery techniques. Why is it that airframe design for spins and pilot training for spins is such a relatively "unexplored" area in helicopter flight (other than "lower the collective, chop the throttle and autorotate")? Is it because the "egg-beater" can be sat down anywhere (which is only a partial truth because in reality it can't be sat down just "anywhere") that not much effort has been put into "flying" spin recovery techniques?
I also want to look at the FARs (when I get some time) for helo certification, to see exactly what the certification requirements are for alternative anti-torque and spin stability, and to see what requirements actually exist.
For what it's worth, I think more work needs to done on method 2 listed above (the low/mid torque, run-on landing method) so that this loss of T/R recovery method is not nearly so daunting to most pilots.
I guess after seeing the ANG Blackhawk (loss of T/R) crash video last year mentioned above, I just started thinking that other alternatives have to be available other than just entering into a flat spin, and accepting the fact that you have to go down in a totally inhospitable area, that for those pilots and crew just destroyed their helo and seriously injured some of them. What was weird is that while the spin before descent was brief, it didn't really look that unstable. The helo just hovered for a moment, in a nice (not too rapid) flat spin before it started descending, and the descent was pretty flat as well.
It's the characteristics of these flat spins that I don't think are very well understood, and a "flying" recovery from these spins certainly isn't well understood. The only recovery method that is fairly well understood is the "autorotate, you're going down" recovery method.
It's what guys like GulfPLt were able to accomplish, that make me think that loss of anti-torque spins don't have to be as daunting as we perceive then to be now. I'm just hoping that research and investigation can provide some better options in the future, as the options we have now for loss of T/R recovery are pretty limited in my view.
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Safe flying to you...
[This message has been edited by Flight Safety (edited 02 July 2001).]
I agree with your comments and I understand the decision made by the pilot in the accident report.
One think that still troubles me is why loss of anti-torque spins in helos are so daunting to most pilots. In FW flying, aircraft have to meet design certification requirements for spins, and pilots have to be trained in spin recovery techniques. Why is it that airframe design for spins and pilot training for spins is such a relatively "unexplored" area in helicopter flight (other than "lower the collective, chop the throttle and autorotate")? Is it because the "egg-beater" can be sat down anywhere (which is only a partial truth because in reality it can't be sat down just "anywhere") that not much effort has been put into "flying" spin recovery techniques?
I also want to look at the FARs (when I get some time) for helo certification, to see exactly what the certification requirements are for alternative anti-torque and spin stability, and to see what requirements actually exist.
For what it's worth, I think more work needs to done on method 2 listed above (the low/mid torque, run-on landing method) so that this loss of T/R recovery method is not nearly so daunting to most pilots.
I guess after seeing the ANG Blackhawk (loss of T/R) crash video last year mentioned above, I just started thinking that other alternatives have to be available other than just entering into a flat spin, and accepting the fact that you have to go down in a totally inhospitable area, that for those pilots and crew just destroyed their helo and seriously injured some of them. What was weird is that while the spin before descent was brief, it didn't really look that unstable. The helo just hovered for a moment, in a nice (not too rapid) flat spin before it started descending, and the descent was pretty flat as well.
It's the characteristics of these flat spins that I don't think are very well understood, and a "flying" recovery from these spins certainly isn't well understood. The only recovery method that is fairly well understood is the "autorotate, you're going down" recovery method.
It's what guys like GulfPLt were able to accomplish, that make me think that loss of anti-torque spins don't have to be as daunting as we perceive then to be now. I'm just hoping that research and investigation can provide some better options in the future, as the options we have now for loss of T/R recovery are pretty limited in my view.
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Safe flying to you...
[This message has been edited by Flight Safety (edited 02 July 2001).]
Guest
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I'll start by saying I think from Gulfplt's description that it was a partial loss of T/R control. Not so?
My experience has all been simulated thus far, in the simulators at Bell/FlightSafety (FS) in Fort Worth and with the Canadain Military (CF) in Gagetown, N.B.
It was mentioned before that FS's assessment of vertical stab effectiveness was optimistic. The CF agreed and adjusted their aerodynamic programming accordingly. In the sim the response was pretty basic, lower collective, roll off throttles if you have time to think about it, and cushion at the bottom. Like most of these items, practice allows you to land something that was extremely difficult the first couple times.
I have also simulated countless stuck pedals of varying degrees in the hover, climb, cruise, descent, even on the ground prior to T/O. This is in the RH22, RH44, and BH06. I have seen several pilots try to pull pitch and climb away when the right yaw got away from them and they wanted to go around and try it again. I make a point of maintaining the failure, just so they can see why this is such a lousy idea.
Invariably the right yaw accelerates beyond their ability to focus on the horizon and they lose the ability to maintain a level aircraft, any wind/airspeed and associated weathervaining only exacerbate the situation as the tail whips through 90-180ish yaw. I rarely let it go more than one full rotation and never yet has the pilot thought that I took it too early. The reaction I teach in this situation is to stop the a/c (cyclic flare to zero groundspeed) and perform the failure as per the hover. They are already close to ground now so it's a short hover chop to the ground.
I would love the opportunity to get in a light helicopter sim and compare rotation rates with what we get for varying aounts of stuck right pedal in the hover. What I generally use is a stuck right pitch sufficient to maintain a right rotation in the hover despite immediate closing of the throttle.
Now, to respond to soem comments above:
Spins: A fixed wing spin and a rapid yaw are two completely unrelated beasts. The autorotation is the closest rotary equivalent to a plank spin, and is handled quite well. Control in the spin gets quickly out of hand because you are sitting out in front of the center of rotation, trying to look at a world that is moving too quickly to focus on. The immediate (normal) reaction is to focus in tighter to the a/c to pick up details, taking the horizon out of the picture, and pitch control gets ugly. Additionally, if the a/c is rotating at, lets say, 60 RPM, easily achievable, then the RRPM is effectively 530 - 60 = 470 RPM (this is for the R22) or 89%. For the R44 it is 85% and the 206 it is even less. Even more pitch is now needed to effect that climb, meaning more power, a higher rotation rate, and a lower effective RPM. Overtorque or overpitch follow and game over.
Running Landings: Nice if you have a place to do it I guess. Here we rarely fly in anything close to hospitable terrain and always teach a spot landing using cyclic flare and landing as per failure in the hover. When I was on mediums in the IFR world the running landing was standard but there is a lot more machine to toss around.
Of course, these are my opinions, they won't cover every situation, and feel free to disagree and tell me so.
My experience has all been simulated thus far, in the simulators at Bell/FlightSafety (FS) in Fort Worth and with the Canadain Military (CF) in Gagetown, N.B.
It was mentioned before that FS's assessment of vertical stab effectiveness was optimistic. The CF agreed and adjusted their aerodynamic programming accordingly. In the sim the response was pretty basic, lower collective, roll off throttles if you have time to think about it, and cushion at the bottom. Like most of these items, practice allows you to land something that was extremely difficult the first couple times.
I have also simulated countless stuck pedals of varying degrees in the hover, climb, cruise, descent, even on the ground prior to T/O. This is in the RH22, RH44, and BH06. I have seen several pilots try to pull pitch and climb away when the right yaw got away from them and they wanted to go around and try it again. I make a point of maintaining the failure, just so they can see why this is such a lousy idea.
Invariably the right yaw accelerates beyond their ability to focus on the horizon and they lose the ability to maintain a level aircraft, any wind/airspeed and associated weathervaining only exacerbate the situation as the tail whips through 90-180ish yaw. I rarely let it go more than one full rotation and never yet has the pilot thought that I took it too early. The reaction I teach in this situation is to stop the a/c (cyclic flare to zero groundspeed) and perform the failure as per the hover. They are already close to ground now so it's a short hover chop to the ground.
I would love the opportunity to get in a light helicopter sim and compare rotation rates with what we get for varying aounts of stuck right pedal in the hover. What I generally use is a stuck right pitch sufficient to maintain a right rotation in the hover despite immediate closing of the throttle.
Now, to respond to soem comments above:
Spins: A fixed wing spin and a rapid yaw are two completely unrelated beasts. The autorotation is the closest rotary equivalent to a plank spin, and is handled quite well. Control in the spin gets quickly out of hand because you are sitting out in front of the center of rotation, trying to look at a world that is moving too quickly to focus on. The immediate (normal) reaction is to focus in tighter to the a/c to pick up details, taking the horizon out of the picture, and pitch control gets ugly. Additionally, if the a/c is rotating at, lets say, 60 RPM, easily achievable, then the RRPM is effectively 530 - 60 = 470 RPM (this is for the R22) or 89%. For the R44 it is 85% and the 206 it is even less. Even more pitch is now needed to effect that climb, meaning more power, a higher rotation rate, and a lower effective RPM. Overtorque or overpitch follow and game over.
Running Landings: Nice if you have a place to do it I guess. Here we rarely fly in anything close to hospitable terrain and always teach a spot landing using cyclic flare and landing as per failure in the hover. When I was on mediums in the IFR world the running landing was standard but there is a lot more machine to toss around.
Of course, these are my opinions, they won't cover every situation, and feel free to disagree and tell me so.
Guest
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I have to say I'm with Nick's last sentance.
I've been conditioned to treat a anti-torque failure as an immeadite auto condition, as at this pint I've not the skills (I may feel differently later on as I gain experience) to try to continue flight with the condition. Also, once established, adding small amounts of power as he stated withthe "glide extention" could be done.
But I love reading the varied respnses here on this thread !
Nick,
Tell us more about the Commanche!
Am I correct in that it is single stick for cyclic and you rotate it for tail inputs?
(this I have heard and cannot confirm)
It seems to be a joy to fly ..... I missed gettin gto see it when it was brought down to Ft. Laud beach.
I'd love to fly up to Vero to get a once over, but alas .....
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Marc
[This message has been edited by RW-1 (edited 03 July 2001).]
I've been conditioned to treat a anti-torque failure as an immeadite auto condition, as at this pint I've not the skills (I may feel differently later on as I gain experience) to try to continue flight with the condition. Also, once established, adding small amounts of power as he stated withthe "glide extention" could be done.
But I love reading the varied respnses here on this thread !
Nick,
Tell us more about the Commanche!
Am I correct in that it is single stick for cyclic and you rotate it for tail inputs?
(this I have heard and cannot confirm)
It seems to be a joy to fly ..... I missed gettin gto see it when it was brought down to Ft. Laud beach.
I'd love to fly up to Vero to get a once over, but alas .....
------------------
Marc
[This message has been edited by RW-1 (edited 03 July 2001).]
Guest
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Helo teacher,
exactly! The FSI sim at DFW (not the level D one, I can't comment on that) is far to easy to control. I even carried out landings on the aircraft carrier at night in it (for fun) after taking off and losing the TR gearbox at 60 kts on climb out. Very ego boosting but not realistic.
On the other hand, the level C+ SAS 212/412 sim at Stockholm is great; you are upside down and wirling like a Pitts special in a flick roll if you don't dump the collective AND roll off the throttles (good lesson for those who friction too tightly).
Also as you say (and I did too), the transition from seemingly controlled flight to total loss of control when dealing with stuck pedals, is very rapid and needs to be well understood (before hand) as you are then in a really bad situation.
Must go, I'll have think about the FW spins but I don't have time now. I any case the aerodynamic loads will be considerably less.
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Another day in paradise
exactly! The FSI sim at DFW (not the level D one, I can't comment on that) is far to easy to control. I even carried out landings on the aircraft carrier at night in it (for fun) after taking off and losing the TR gearbox at 60 kts on climb out. Very ego boosting but not realistic.
On the other hand, the level C+ SAS 212/412 sim at Stockholm is great; you are upside down and wirling like a Pitts special in a flick roll if you don't dump the collective AND roll off the throttles (good lesson for those who friction too tightly).
Also as you say (and I did too), the transition from seemingly controlled flight to total loss of control when dealing with stuck pedals, is very rapid and needs to be well understood (before hand) as you are then in a really bad situation.
Must go, I'll have think about the FW spins but I don't have time now. I any case the aerodynamic loads will be considerably less.
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Another day in paradise
Guest
Posts: n/a
I also forgot to add that at least in the cicare simulator (a full size flying sim itself that volar has, uses a rotax to power it) I can experience either a T/R control failure, or a full blown loss of tail rotor failure without worry of killing myself, this is one of the good things about that simulator, which is really a one person heli in a "frame", which I described some time ago.
So while I may not try to fly out of a full blown tail rotor loss, I might at least not be panicked when it happens having experienced the sudden quickly developing yaw.
For a pic of it and description, go to:
http://orbita.starmedia.com/~cicarehelicopteros/
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Marc
So while I may not try to fly out of a full blown tail rotor loss, I might at least not be panicked when it happens having experienced the sudden quickly developing yaw.
For a pic of it and description, go to:
http://orbita.starmedia.com/~cicarehelicopteros/
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Marc
Guest
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Flight Safety,
For my sins, I am a helicopter and aeroplane instructor and have demonstated and taught low level aerobatics in both aircraft categories.
In a stiff wing spin, depending on the aeroplane, the pitch/roll/yaw rate is actually relatively slow. However, the pilot is unable to control the attitude during the spin and the aeroplane generally consumes sh*tloads of altitude while you sort it out. After gross anti-spin control (remember that all controls are still working) defeats the spin, one then recovers from the steep nose-down unusual attitude and flies away. Alternatively, you eject/parachute/strike the ground.
In a helicopter, life is considerably different. If one loses T/R authority in the cruise, there is a reasonable chance of keeping it all together. If it happens in the hover, the onset of rotation is rapid and eye-watering. Unlike our aeroplane, the helo pilot must make control inputs to maintain some semblance of a survivable attitude - the machine has no inherent ability to keep all of its bits in the intended location.
Here is the scene: the helicopter has started to spin rapidly at the torque currently set and the options are:
a. reduce the torque and slow the spin in order to bring the reaction time for survival manoeuvres closer to your capabilities, or
b. increase the torque substantially to generate vertical movement, knowing that one will dramatically increase the yaw rate and the demand for control inputs that are required simply to keep the rotating bits between you and the sun. In most cases, this requires a conscious move to take the reaction time for survival manoeuvres further from your capabilities.
Now I reckon 'b' is a poor option unless, as I have found myself, falling into the mouth of an active volcano is the only alternative. In that case, sangfroid is but a dream.
I used to teach loss of T/R authority in the high hover, simply because the almost automatic entry to autorotation created its own, very real, problems. Thus, the height took all the fun out of a relatively straightforward recovery. Suffice it to say, the control motions required to keep the sunny side up while trying to gain sufficient forward speed to alleviate the rotation and permit either a running landing or some sort of fly-away manoeuvre were always illuminating, both for me and the victim.
And one could never ignore the gut feeling that both Mr Bell amd Mr Robinson's mast stop margins were always threatened to a point that neither could have contemplated.
Bottom line - the only similarity between F/W and R/W spins is that a rotation is involved - that is all.
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Stay Alive,
[email protected]
For my sins, I am a helicopter and aeroplane instructor and have demonstated and taught low level aerobatics in both aircraft categories.
In a stiff wing spin, depending on the aeroplane, the pitch/roll/yaw rate is actually relatively slow. However, the pilot is unable to control the attitude during the spin and the aeroplane generally consumes sh*tloads of altitude while you sort it out. After gross anti-spin control (remember that all controls are still working) defeats the spin, one then recovers from the steep nose-down unusual attitude and flies away. Alternatively, you eject/parachute/strike the ground.
In a helicopter, life is considerably different. If one loses T/R authority in the cruise, there is a reasonable chance of keeping it all together. If it happens in the hover, the onset of rotation is rapid and eye-watering. Unlike our aeroplane, the helo pilot must make control inputs to maintain some semblance of a survivable attitude - the machine has no inherent ability to keep all of its bits in the intended location.
Here is the scene: the helicopter has started to spin rapidly at the torque currently set and the options are:
a. reduce the torque and slow the spin in order to bring the reaction time for survival manoeuvres closer to your capabilities, or
b. increase the torque substantially to generate vertical movement, knowing that one will dramatically increase the yaw rate and the demand for control inputs that are required simply to keep the rotating bits between you and the sun. In most cases, this requires a conscious move to take the reaction time for survival manoeuvres further from your capabilities.
Now I reckon 'b' is a poor option unless, as I have found myself, falling into the mouth of an active volcano is the only alternative. In that case, sangfroid is but a dream.
I used to teach loss of T/R authority in the high hover, simply because the almost automatic entry to autorotation created its own, very real, problems. Thus, the height took all the fun out of a relatively straightforward recovery. Suffice it to say, the control motions required to keep the sunny side up while trying to gain sufficient forward speed to alleviate the rotation and permit either a running landing or some sort of fly-away manoeuvre were always illuminating, both for me and the victim.
And one could never ignore the gut feeling that both Mr Bell amd Mr Robinson's mast stop margins were always threatened to a point that neither could have contemplated.
Bottom line - the only similarity between F/W and R/W spins is that a rotation is involved - that is all.
------------------
Stay Alive,
[email protected]
Guest
Posts: n/a
just wanted to comment on the chute idea mentioned a ways back - a possible problem with this idea is the overall increase in parasite drag which will slow the machine down (which isn't preferable in TR failure situations) to maintain speed then requires an increase in pitch/power which in turn increases torque - and your yaw problem.
Guest
Posts: n/a
I've been busy the last couple of days, and been wanting to add some final comments about this. I want to add how I think the run-on landing method (method 2 listed above) can be improved for any helo, and how a possibly safe way of conducting a high torque climb after loss of T/R could be accomplished (method 3 above). After this post, I think I'll be finished with the subject.
Regarding the possible future improvement of the run-on landing after loss of T/R, Nick made the following opening statement in his very excellent post:
He then followed with an excellent discription of how to enter into this form of recovery. My focus however will be on his opening statement.
We all know that he's very correct in his statement about the size (or area) of the vertical stab being limited, but this raises the question of whether other possible means of increasing the aerodynamic anti-torque of the airframe might be available aside from the vertical stab. One possible solution would be to use something like FW delta fins mounted in rougly the same position as they are on FW aircraft, that is under the tail boom near the rear.
Here are the reasons why I think delta fins might work to improve aerodynamic anti-torque on a helo. If they were mounted at an angle that was more vertical (down) than sidways, then they could serve as additional sources of vertical stability (anti-torque) on the helo in forward flight. These could then replace the vertical area lost to the restrictions placed on the vertical stab, since being mounted under the tail boom would place them out of the airflow path for the tail rotor. Size (area), placement, mounting angles, and distance from the end of the tail boom (the moment arm) could all be determined by computer simulation, wind tunnel testing, and flight test.
Delta fins could also solve a couple of other problems. Being mounted under the tail boom, they would not pick up much rotor downwash like the horizontal stab on a helo sometimes does, and therefore would not contribute much to a pitch problem in hover. Delta fins would offer very little drag in forward flight, thus the normal aerodymanics of the airframe in forward flight would be little effected by them. There's also the possibilty that the range of the helo could be extended slightly, if the anti-torque provided by the delta fins is more efficient than that provided by the tail rotor in forward flight. If so, then power diverted to the tail rotor for anti-torque could be reduced in foward flight, thus adding a little to the range.
One possible problem with delta fins is what effect they might have in crosswinds, since the area of the side of the tail boom would effectively be increased by them. The test methods mentioned above could determine this possible effect.
Increased vertical area provided by delta fins could help a lot with providing alternative anti-torque in the event of loss of T/R, and might make performing a run-on landing much easier to accomplish.
Now to go on to the issue of trying to make a high torque climb safer following loss of T/R.
Several facts were pointed out in these posts that are very good points. Someone pointed out that drogue chutes are really useful for spin recovery in FW aircraft during flight test. Nick and I exchanged a brief e-mail where he pointed out to me the problems of using a drogue chute, especially as a "fly home" device because of the excessive drag. He also pointed out that the increased drag only adds to the anti-torque problem. He did however point out that a drogue might be useful in spin recovery.
Someone else pointed out that the vertical stab on a helo can impart a roll to the helo airframe if it's in a main rotor torque spin, since side air force on the stab would provide a lever arm rolling the tail boom from top to bottom.
So here's how I think a high torque climb following loss of T/R might be made safer.
The delta fins mentioned previously could offer an additional advantage in this scenario. They could offset the area of the vertical stab in a main rotor torque spin, by offering air resistance BELOW the tail boom roll center, thus offsetting the lever arm of the vertical stab. This issue could be addressed at the same time when designing delta fins for the foward flight anit-torque problem discussed above. It should be possible to design the delta fins so that the moment arms of the fins and the vertical stab cancel each other out in a main rotor torque spin. Adjustments in the area of the vertical stab and delta fins could be made so that there's no roll component at all in a main rotor torque spin.
Besides delta fins, the next item I think is needed to make a main rotor torque spin safer is a drogue chute. This could work by using the chute for what it's historically been good at, spin recovery.
Someone pointed out the disorientation of the pilot in a spin, especially the faster it gets. Someone else pointed out that there would be a loss of main rotor RPM in a spin because the speed governor's RPM reference is to the airframe, and if the airframe is spinning, the governor would slow the main rotor RPM in response.
The droque chute could be the solution here. It would have to be mounted at the end of the tail boom (to maximize the lever arm) and at the roll center so it wouldn't produce its own roll component in a spin. Poping a drogue chute could significantly slow down the rate of a torque spin because of the anti-torque that it would provide. Thus it might prevent a significant main rotor RPM loss, and prevent pilot disorientation.
The size of the chute would have to be determined by the test methods listed above, and the tail boom might have to be strengthened to handle the shock of the chute's deployment (it's already been designed to handle the standard anti-torque loads).
With delta fins and a drogue chute, I see a future hypothetical high torque climb working something like this:
You're hovering at low altitude over a forest doing logging work, when suddenly the T/R losses all thrust. You could autorotate into the tops of the trees, or you could climb out and try to fly it to a run-on landing.
You quickly decide to climb out. The spin must be at least partially established so the chute will fill upon deployment and not get foiled. You won't have to to wait long, as the spin will already be established by the time you decide to climb out. So you hold the collective where it was previously in the hover, hold the cyclic in the center, and pop the chute.
The spin stabilizes quickly and you apply small collective inputs, both to compensate for the slightly lowered main rotor RPM and to start a slow climb, as a slow climb lowers the anti-torque requirement and produces a slower spin rate. You also continue to hold the cyclic in the center to keep the rotor disk flat. Forget about directional control as you won't have any, you'll just drift with the wind during the climb. If you start drifting close to an obstacle, you might have to think about increasing the climb rate to avoid it, but only if absolutely necessary. The only instruments you can count on in the spin are the baro altimeter and perhaps the VS indicator to monitor the climb.
When sufficient altitude has been reached to transition to forward flight, it's time to terminate the climb and exit the spin. To do this, you lower the collective to start a brief autorotation. With no main rotor torque the drogue will quickly slow the spin and as the spin slows to a stop, you apply forward cyclic to start forward airspeed. This should be done before the spin stops completely as again you want to keep the chute filled so it won't foil. The chute should help to keep the pointy end forward as airspeed builds up. When airspeed is sufficient so that aerodynamic anit-torque provided by the vertical stab and delta fins can take over, then you can jettison the chute and fly to a proper location to perform a run-on landing. (My instincts tell me however that this spin recovery would be a little more complicated than presented here, due to the nose down moment caused by the chute when the collective is lowered).
I know this is very forward thinking, and if I had an R/C model helicopter (which I don't), I'd modify it to at least test the basic aerodynamics of these ideas (the human physiology aspects aside). It would need a channel to neutralize the tail rotor pitch (to simulate the loss of T/R), a channel to pop the chute and a channel to jettison it.
Gee I wrote a book, sorry about that guys.
------------------
Safe flying to you...
[This message has been edited by Flight Safety (edited 06 July 2001).]
Regarding the possible future improvement of the run-on landing after loss of T/R, Nick made the following opening statement in his very excellent post:
<font face="Verdana, Arial, Helvetica" size="2">Loss of tail rotor is a big problem in any helicopter, especially since the vertical fin (which now must provide all your anti-torque) is often reduced in size to reduce blockage of the tail rotor to help increase tail thrust for better crosswind control.</font>
We all know that he's very correct in his statement about the size (or area) of the vertical stab being limited, but this raises the question of whether other possible means of increasing the aerodynamic anti-torque of the airframe might be available aside from the vertical stab. One possible solution would be to use something like FW delta fins mounted in rougly the same position as they are on FW aircraft, that is under the tail boom near the rear.
Here are the reasons why I think delta fins might work to improve aerodynamic anti-torque on a helo. If they were mounted at an angle that was more vertical (down) than sidways, then they could serve as additional sources of vertical stability (anti-torque) on the helo in forward flight. These could then replace the vertical area lost to the restrictions placed on the vertical stab, since being mounted under the tail boom would place them out of the airflow path for the tail rotor. Size (area), placement, mounting angles, and distance from the end of the tail boom (the moment arm) could all be determined by computer simulation, wind tunnel testing, and flight test.
Delta fins could also solve a couple of other problems. Being mounted under the tail boom, they would not pick up much rotor downwash like the horizontal stab on a helo sometimes does, and therefore would not contribute much to a pitch problem in hover. Delta fins would offer very little drag in forward flight, thus the normal aerodymanics of the airframe in forward flight would be little effected by them. There's also the possibilty that the range of the helo could be extended slightly, if the anti-torque provided by the delta fins is more efficient than that provided by the tail rotor in forward flight. If so, then power diverted to the tail rotor for anti-torque could be reduced in foward flight, thus adding a little to the range.
One possible problem with delta fins is what effect they might have in crosswinds, since the area of the side of the tail boom would effectively be increased by them. The test methods mentioned above could determine this possible effect.
Increased vertical area provided by delta fins could help a lot with providing alternative anti-torque in the event of loss of T/R, and might make performing a run-on landing much easier to accomplish.
Now to go on to the issue of trying to make a high torque climb safer following loss of T/R.
Several facts were pointed out in these posts that are very good points. Someone pointed out that drogue chutes are really useful for spin recovery in FW aircraft during flight test. Nick and I exchanged a brief e-mail where he pointed out to me the problems of using a drogue chute, especially as a "fly home" device because of the excessive drag. He also pointed out that the increased drag only adds to the anti-torque problem. He did however point out that a drogue might be useful in spin recovery.
Someone else pointed out that the vertical stab on a helo can impart a roll to the helo airframe if it's in a main rotor torque spin, since side air force on the stab would provide a lever arm rolling the tail boom from top to bottom.
So here's how I think a high torque climb following loss of T/R might be made safer.
The delta fins mentioned previously could offer an additional advantage in this scenario. They could offset the area of the vertical stab in a main rotor torque spin, by offering air resistance BELOW the tail boom roll center, thus offsetting the lever arm of the vertical stab. This issue could be addressed at the same time when designing delta fins for the foward flight anit-torque problem discussed above. It should be possible to design the delta fins so that the moment arms of the fins and the vertical stab cancel each other out in a main rotor torque spin. Adjustments in the area of the vertical stab and delta fins could be made so that there's no roll component at all in a main rotor torque spin.
Besides delta fins, the next item I think is needed to make a main rotor torque spin safer is a drogue chute. This could work by using the chute for what it's historically been good at, spin recovery.
Someone pointed out the disorientation of the pilot in a spin, especially the faster it gets. Someone else pointed out that there would be a loss of main rotor RPM in a spin because the speed governor's RPM reference is to the airframe, and if the airframe is spinning, the governor would slow the main rotor RPM in response.
The droque chute could be the solution here. It would have to be mounted at the end of the tail boom (to maximize the lever arm) and at the roll center so it wouldn't produce its own roll component in a spin. Poping a drogue chute could significantly slow down the rate of a torque spin because of the anti-torque that it would provide. Thus it might prevent a significant main rotor RPM loss, and prevent pilot disorientation.
The size of the chute would have to be determined by the test methods listed above, and the tail boom might have to be strengthened to handle the shock of the chute's deployment (it's already been designed to handle the standard anti-torque loads).
With delta fins and a drogue chute, I see a future hypothetical high torque climb working something like this:
You're hovering at low altitude over a forest doing logging work, when suddenly the T/R losses all thrust. You could autorotate into the tops of the trees, or you could climb out and try to fly it to a run-on landing.
You quickly decide to climb out. The spin must be at least partially established so the chute will fill upon deployment and not get foiled. You won't have to to wait long, as the spin will already be established by the time you decide to climb out. So you hold the collective where it was previously in the hover, hold the cyclic in the center, and pop the chute.
The spin stabilizes quickly and you apply small collective inputs, both to compensate for the slightly lowered main rotor RPM and to start a slow climb, as a slow climb lowers the anti-torque requirement and produces a slower spin rate. You also continue to hold the cyclic in the center to keep the rotor disk flat. Forget about directional control as you won't have any, you'll just drift with the wind during the climb. If you start drifting close to an obstacle, you might have to think about increasing the climb rate to avoid it, but only if absolutely necessary. The only instruments you can count on in the spin are the baro altimeter and perhaps the VS indicator to monitor the climb.
When sufficient altitude has been reached to transition to forward flight, it's time to terminate the climb and exit the spin. To do this, you lower the collective to start a brief autorotation. With no main rotor torque the drogue will quickly slow the spin and as the spin slows to a stop, you apply forward cyclic to start forward airspeed. This should be done before the spin stops completely as again you want to keep the chute filled so it won't foil. The chute should help to keep the pointy end forward as airspeed builds up. When airspeed is sufficient so that aerodynamic anit-torque provided by the vertical stab and delta fins can take over, then you can jettison the chute and fly to a proper location to perform a run-on landing. (My instincts tell me however that this spin recovery would be a little more complicated than presented here, due to the nose down moment caused by the chute when the collective is lowered).
I know this is very forward thinking, and if I had an R/C model helicopter (which I don't), I'd modify it to at least test the basic aerodynamics of these ideas (the human physiology aspects aside). It would need a channel to neutralize the tail rotor pitch (to simulate the loss of T/R), a channel to pop the chute and a channel to jettison it.
Gee I wrote a book, sorry about that guys.
------------------
Safe flying to you...
[This message has been edited by Flight Safety (edited 06 July 2001).]
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By chance, I'm at the stage in my 155 course where we covered TR problems today. It has to be said that the Fin on a fenestron a/c makes the whole process infinatley easier than a conventional type, though it does require a reasonable amount of space.
I was pleasantly suprised by how controllable the final touchdown was, and the benefit of right roll to reduce the speed still further before the nose aligns with the runway.
Definately no need for an auto with this one.
------------------
Another day in paradise
I was pleasantly suprised by how controllable the final touchdown was, and the benefit of right roll to reduce the speed still further before the nose aligns with the runway.
Definately no need for an auto with this one.
------------------
Another day in paradise
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Some fun from my model bretheren (I have 2 heli's myself)
Hehe, these guys decided to stop the rotor while doing an auto, and figured they would still have enough negative collective pitch (which models do have) to recover. I had stated that they would lose the bird, not from exceeding crit AOA on the blades, but because they would suffer blowback as the model then accellerated with stopped blades.
Well I'll let you see the video:
http://ronlund.com/hhsmall.avi
Blades departed shortly after stopping
Heli: totalled., a bummer, but made a nice video.
------------------
Marc
Hehe, these guys decided to stop the rotor while doing an auto, and figured they would still have enough negative collective pitch (which models do have) to recover. I had stated that they would lose the bird, not from exceeding crit AOA on the blades, but because they would suffer blowback as the model then accellerated with stopped blades.
Well I'll let you see the video:
http://ronlund.com/hhsmall.avi
Blades departed shortly after stopping
Heli: totalled., a bummer, but made a nice video.
------------------
Marc
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Posts: n/a
212man,
Presumably you are referring to in-cruise failure? Or did you deal with fenestron failure in the high hover?
------------------
Stay Alive,
[email protected]
Presumably you are referring to in-cruise failure? Or did you deal with fenestron failure in the high hover?
------------------
Stay Alive,
[email protected]
4dogs,
yes, in the cruise followed by run on landing. Obviously in a the hover you'd be pretty poorly placed and would need to lower the lever and acept the yaw (can't "chope throttles in this one").
yes, in the cruise followed by run on landing. Obviously in a the hover you'd be pretty poorly placed and would need to lower the lever and acept the yaw (can't "chope throttles in this one").
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Hi Peeps.
Sorry to join this a bit late! (I've been on me hols!)
Firstly....any tail rotor failure in a high hover is very bad news. Each aircraft has different handling capabilities. I've had two tail rotor 'problems' one was a drive shaft failure & one was a control failure.
The most significant difference was the change in noise. When the drive shaft failed the noise change was obvious, the control failure didn't noticeably alter the noise.
Some have talked of pulling power & climbing. People if you manage it my hat is off to you. Amazing courage. My drive shaft failed at 40' just coming in to land, the obvious solution was to just dump it on the ground & live to fight another day. I lost T/R control at some 550' in the hover.
Should I have climbed? You may think so...I was there & I can assure you it was never an option! The rate of spin may from the outside have looked sedate, but in the cockpit it felt horrendous! The centrifugal force was initially enough to lean me (& hence the cyclic) to the right. Climb & increase the rate of spin???? Forget it!
Some would say chop the throttles & take away the torque reaction! Ha! Forget that! An autorotation from a 550' hover in a As355F2!!! The word SPLAT springs to mind!! No people...I can assure you I had plans for my engines & they were staying right where they were! The best plan I could come up with was to fight the aircraft down as gently as possible! It appears that between Lady Luck & me we did OK. The AAIB described the impact as relatively benign! Oh & by the way to make it benign I used everything BOTH engines had to offer! Chop them??? No way!
Forward flight failures are a different kettle of fish, as are jams etc! The variables are countless!! What I would say is that my military & civil (thanks to the North Sea & a couple of fantastic sim instructors!) proved invaluable! There ia an old addage in aviation.....I won't teach you to suck eggs.....but we walked away.
By the way...with relation to the simulator training....it teaches you what to do in many of the scenarios.....but the sim can never prepare you for the violence of the rotation! Particularly in the high hover, in a heavy aircraft legendary for it's poor tail rotor authority!!
[ 07 July 2001: Message edited by: Roofus ]
Sorry to join this a bit late! (I've been on me hols!)
Firstly....any tail rotor failure in a high hover is very bad news. Each aircraft has different handling capabilities. I've had two tail rotor 'problems' one was a drive shaft failure & one was a control failure.
The most significant difference was the change in noise. When the drive shaft failed the noise change was obvious, the control failure didn't noticeably alter the noise.
Some have talked of pulling power & climbing. People if you manage it my hat is off to you. Amazing courage. My drive shaft failed at 40' just coming in to land, the obvious solution was to just dump it on the ground & live to fight another day. I lost T/R control at some 550' in the hover.
Should I have climbed? You may think so...I was there & I can assure you it was never an option! The rate of spin may from the outside have looked sedate, but in the cockpit it felt horrendous! The centrifugal force was initially enough to lean me (& hence the cyclic) to the right. Climb & increase the rate of spin???? Forget it!
Some would say chop the throttles & take away the torque reaction! Ha! Forget that! An autorotation from a 550' hover in a As355F2!!! The word SPLAT springs to mind!! No people...I can assure you I had plans for my engines & they were staying right where they were! The best plan I could come up with was to fight the aircraft down as gently as possible! It appears that between Lady Luck & me we did OK. The AAIB described the impact as relatively benign! Oh & by the way to make it benign I used everything BOTH engines had to offer! Chop them??? No way!
Forward flight failures are a different kettle of fish, as are jams etc! The variables are countless!! What I would say is that my military & civil (thanks to the North Sea & a couple of fantastic sim instructors!) proved invaluable! There ia an old addage in aviation.....I won't teach you to suck eggs.....but we walked away.
By the way...with relation to the simulator training....it teaches you what to do in many of the scenarios.....but the sim can never prepare you for the violence of the rotation! Particularly in the high hover, in a heavy aircraft legendary for it's poor tail rotor authority!!
[ 07 July 2001: Message edited by: Roofus ]
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Thankfully I never had a real failure yet, but have lost tail rotor authority on a number of occasions (very slow flight, OGE, well out of wind, strong w/v. A little alarming but easily surviveable).
However, from previous experience as a sim instructor (including an RAF trial on tail rotor malfunctions on the Puma for general guidance of said type's pilots) and other experiences on French and American types (different directions of main rotor rotation), to avoid confusion in my own mind, here are a few rules that I now always bear in mind:
Rule 1: If the tail rotor driveshaft fails I expect an engine off landing either immediately or at some very imminent stage. Note that if this occurs, the (bad) yaw is towards the advancing blade of the main rotor (advancing side is therefore bad, read on). Fly accordingly and be aware!
Rule 2: If the tail rotor suffers another type of failure i.e. cable / control / stuck pitch, aim to keep the nose of the aircraft on the main rotor's RETREATING blade side and set the aircraft up for a running landing in that configuration. That way any increase in collective to cushion the touchdown will bring the nose towards 12 o'clock and with good judgement will give nil or minimum yaw on touchdown. If the nose goes through the 12 o'clock position towards the advancing blade side, increase airspeed and / or go around.
Also, with a tail rotor control problem, if possible keep the wind on the RETREATING blade side on final approach. This gives "weathercock effect" assistance in the correct direction. (Note that this helps offload the tail on ANY normal approach).
Personally, I have always found the American teaching "lucky left / rotten right" potentially confusing as I have alternated between American and French types.
Retreating blade side is ALWAYS lucky.
Hope this helps someone someday!
SC
However, from previous experience as a sim instructor (including an RAF trial on tail rotor malfunctions on the Puma for general guidance of said type's pilots) and other experiences on French and American types (different directions of main rotor rotation), to avoid confusion in my own mind, here are a few rules that I now always bear in mind:
Rule 1: If the tail rotor driveshaft fails I expect an engine off landing either immediately or at some very imminent stage. Note that if this occurs, the (bad) yaw is towards the advancing blade of the main rotor (advancing side is therefore bad, read on). Fly accordingly and be aware!
Rule 2: If the tail rotor suffers another type of failure i.e. cable / control / stuck pitch, aim to keep the nose of the aircraft on the main rotor's RETREATING blade side and set the aircraft up for a running landing in that configuration. That way any increase in collective to cushion the touchdown will bring the nose towards 12 o'clock and with good judgement will give nil or minimum yaw on touchdown. If the nose goes through the 12 o'clock position towards the advancing blade side, increase airspeed and / or go around.
Also, with a tail rotor control problem, if possible keep the wind on the RETREATING blade side on final approach. This gives "weathercock effect" assistance in the correct direction. (Note that this helps offload the tail on ANY normal approach).
Personally, I have always found the American teaching "lucky left / rotten right" potentially confusing as I have alternated between American and French types.
Retreating blade side is ALWAYS lucky.
Hope this helps someone someday!
SC
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My first tail-rotor failure was actually a self-induced tail-rotor drive-shaft failure. The drive-shaft jumped out and flailed because the first hangar-bearing behind the jet exhaust (in an Iroquois) got overheated and failed due to a lubrication break-down. The reason the lubrication broke down was because I'd been hovering downwind winching trainee crewmen up and down for over 30 minutes. Not a significant downwind component either -just about 4 or 5kts. However it was sufficient to pool the hot exhaust gases around the No 1 hangar bearing and cause it to seize and jump out.
Of course you could always criticise anyone for hovering out of wind however given that the target was a rock in the middle of a creek and that the only hover reference was out of wind, it seemed a reasonable idea at the time. But full marks to the crewman instructor who cut the cable and dropped the two guys in the creek before we landed on the bank (luckily without spreading the skids). Naturally I got criticised, but up until that time nobody had ever mentioned that particular vulnerability of the tail-rotor drive-shaft. No doubt others have managed to do the same trick since - and others yet unborne will repeat it. It was interesting that I had a buzz of about 30 sec duration (only) through the T/R pedals before it broke lose with a loud bang.
Of course you could always criticise anyone for hovering out of wind however given that the target was a rock in the middle of a creek and that the only hover reference was out of wind, it seemed a reasonable idea at the time. But full marks to the crewman instructor who cut the cable and dropped the two guys in the creek before we landed on the bank (luckily without spreading the skids). Naturally I got criticised, but up until that time nobody had ever mentioned that particular vulnerability of the tail-rotor drive-shaft. No doubt others have managed to do the same trick since - and others yet unborne will repeat it. It was interesting that I had a buzz of about 30 sec duration (only) through the T/R pedals before it broke lose with a loud bang.
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>>Rule 2: If the tail rotor suffers another type of failure i.e. cable / control / stuck pitch, aim to keep the nose of the aircraft on the main rotor's RETREATING blade side and set the aircraft up for a running landing in that configuration. That way any increase in collective to cushion the touchdown will bring the nose towards 12 o'clock and with good judgement will give nil or minimum yaw on touchdown. If the nose goes through the 12 o'clock position towards the advancing blade side, increase airspeed and / or go around.<<
Oh man, that is one rule I will try to incorporate into my memory!
Thanks SC!
Oh man, that is one rule I will try to incorporate into my memory!
Thanks SC!
Tail rotor failures - CAA report
The CAA have published a report into tail rotor failures. It's accessible via their web site, here.
It's 255 pages so I haven't yet read it, but I imagine it will cause some discussion. And I wonder if Roofus will start a company dedicated to training t/r failures . . .
It's 255 pages so I haven't yet read it, but I imagine it will cause some discussion. And I wonder if Roofus will start a company dedicated to training t/r failures . . .