Hughes Tailspin
Another good example of terminology clouding the issues
"Tail Spin" is what stiff wingers do between Immelmann's and stall turns when showing off!
We fling wingers should call it one of the new fandangled name for it depending upon what you have experienced:
Loss of tail rotor control: You are not able to control the tail rotor pitch mechanism.
Loss of tail rotor thrust: Little spinning thing at the back stops spinning or falls off.
Loss of tail rotor effectiveness (LTE): "Newly" discovered and named in the 80's after many (in particular OH-58/B206) accidents. Although somewhat awkwardly named (as the tail rotor is still effectivly working and must be providing thrust) LTE refers to what is thought to be an injestion of main or tail rotor vorticey through the tail rotor which causes an onset of yaw in the direction induced by torque that cannot be overcome by the application of full "power pedal". The yaw rotation can build up quickly enough to fool most pilots into believing they have experienced a loss of tail rotor thrust. The concept has come under fire lately because of the early thoughts that the tail rotor enters vortex ring state being a little hard to proove. Oh - and then there is fenestron stall that possibly fits into this category too, although strongly denied as a possibility by the manufacturer whilst alledgedly being strongly experienced by the pilots!
Loss of Tail Rotor Authority(LTA): Also a new term to make the old Huey war story of "..and then I ran out of bloody left pedal and..." sound a little more sophisticated and technical. In this situation, the tail rotor does not produce enough thrust to counteract the torque/crosswind combination you require, your power pedal hits the stop, and around you go - though often quite gently when compared to LTE or loss of thrust. A lot of aircraft are susceptable to this, but the UH-1D/H Huey is famous for it - and many people have had the earth come up and smite them as a result. Someone mentioned the BK117 - it too is quite susceptible to LTA unless fitted with the C model tail rotor.
Thus BMK, you will need to give us a lot more info on your aircraft type/model, AUW, DA, manouevre you were attempting, wind strength and direction and IAS before we bull$hit artists can possibly hope to have a stab in the dark and argue around and around in circles about what caused it.
"Tail Spin" is what stiff wingers do between Immelmann's and stall turns when showing off!
We fling wingers should call it one of the new fandangled name for it depending upon what you have experienced:
Loss of tail rotor control: You are not able to control the tail rotor pitch mechanism.
Loss of tail rotor thrust: Little spinning thing at the back stops spinning or falls off.
Loss of tail rotor effectiveness (LTE): "Newly" discovered and named in the 80's after many (in particular OH-58/B206) accidents. Although somewhat awkwardly named (as the tail rotor is still effectivly working and must be providing thrust) LTE refers to what is thought to be an injestion of main or tail rotor vorticey through the tail rotor which causes an onset of yaw in the direction induced by torque that cannot be overcome by the application of full "power pedal". The yaw rotation can build up quickly enough to fool most pilots into believing they have experienced a loss of tail rotor thrust. The concept has come under fire lately because of the early thoughts that the tail rotor enters vortex ring state being a little hard to proove. Oh - and then there is fenestron stall that possibly fits into this category too, although strongly denied as a possibility by the manufacturer whilst alledgedly being strongly experienced by the pilots!
Loss of Tail Rotor Authority(LTA): Also a new term to make the old Huey war story of "..and then I ran out of bloody left pedal and..." sound a little more sophisticated and technical. In this situation, the tail rotor does not produce enough thrust to counteract the torque/crosswind combination you require, your power pedal hits the stop, and around you go - though often quite gently when compared to LTE or loss of thrust. A lot of aircraft are susceptable to this, but the UH-1D/H Huey is famous for it - and many people have had the earth come up and smite them as a result. Someone mentioned the BK117 - it too is quite susceptible to LTA unless fitted with the C model tail rotor.
Thus BMK, you will need to give us a lot more info on your aircraft type/model, AUW, DA, manouevre you were attempting, wind strength and direction and IAS before we bull$hit artists can possibly hope to have a stab in the dark and argue around and around in circles about what caused it.
Last edited by helmet fire; 3rd Jan 2003 at 22:59.
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The 206 tail spin . . .
Over here at altitude 206L4's w/no High Alt. Kit will run out of left pedal a lot sooner than you will run out of power (TQ, TOT, N1), learning this has led many pilots around here to some nasty surprises. With the L3 if you watch your wind you'll run out about the same time you reach both limits.
I remember there was this really tall building I used to fly out of with a TV crew, and somedays the thing would hover IGE about 12 inches from the ground with 75% TQ, but the left pedal would be almost all the way in, any increase in power would start the nose going right and no pedal to stop it, so in order to clear the pad you had to start pulling pitch 180 deg. from the desired exit, the L4 would climb as it yawed right with the left pedal all the way in, then as I reached the desired heading being now 20-30 feet high, I would lower collective slightly to stop the yaw, and push CYCLIC forward until I had some airspeed, needless to say when the aircraft sank I now had plenty of altitude to clear my tail from the edge of the building.
Returning to the pad heavy was a completely different story, but I guess easier since it requires less power to land than to take off, but you had to have the wind help you.
My pics,
http://homepage.mac.com/helipilot/he...toAlbum15.html
I remember there was this really tall building I used to fly out of with a TV crew, and somedays the thing would hover IGE about 12 inches from the ground with 75% TQ, but the left pedal would be almost all the way in, any increase in power would start the nose going right and no pedal to stop it, so in order to clear the pad you had to start pulling pitch 180 deg. from the desired exit, the L4 would climb as it yawed right with the left pedal all the way in, then as I reached the desired heading being now 20-30 feet high, I would lower collective slightly to stop the yaw, and push CYCLIC forward until I had some airspeed, needless to say when the aircraft sank I now had plenty of altitude to clear my tail from the edge of the building.
Returning to the pad heavy was a completely different story, but I guess easier since it requires less power to land than to take off, but you had to have the wind help you.
My pics,
http://homepage.mac.com/helipilot/he...toAlbum15.html
Last edited by BlenderPilot; 3rd Jan 2003 at 19:05.
FWIW, here is my Ops Manual supplement on LTE for the B206. Any (constructive) criticism gratefully received, it was written 15 years ago, and could always do with updating!
D3.1 INTRODUCTION
D3.1.1 Unanticipated right yaw, or loss of tail rotor effectiveness (LTE) is when an uncommanded right yaw occurs which does not subside of its own accord, and which, if not controlled, can result in the loss of control of the helicopter.
D3.2 CONTRIBUTING FACTORS
D3.2.1 The following factors will contribute to the onset of LTE:
(a) High gross weight and high temperature.
(b) Tail wind component
(c) Low airspeed
(d) Loss of translational lift.
D3.3 SYMPTOMS
D3.3.1 The following symptoms may be experienced prior to the onset of LTE:
(a) In the event of an unanticipated right yaw, the tail rotor will have insufficient authority to control the yaw.
(b) The helicopter will commence a rapid right rotation, with a nose down attitude.
D3.4 RECOVERY TECHNIQUE
D3.4.1 The following recovery techniques should be employed:
(a) Simultaneously input full left pedal, and forward cyclic to increase airspeed.
(b) When recovery technique takes effect, control the helicopter to recover to normal flight.
(c) Collective pitch reduction will assist the reduction of yaw, but should be used with caution in view of the resulting increased rate of descent.
(d) Should loss of tail rotor effectiveness occur at low altitude (below 1000 ft agl) and reduced collective be used to assist recover, the increased collective pitch subsequently required to reduce the rate of descent may lead to increased yaw rate and reduce rotor RPM.
(e) Should uncontrollable yaw continue to low altitude, the pilot should consider a full autorotation to the ground. Full left pedal should be maintained until the spin stops, then adjusted to keep heading into wind for landing.
D3.4.2 Recovery actions as laid down in the appropriate Flight Manual will take precedence at all times.
D3.5 AVOIDANCE
(a) Operations at low or hovering airspeeds OGE should be avoided in a relative wind that has a tailwind component.
(b) For low speed operations, eg orbiting a ground feature during aerial filming, close attention should be paid to the airspeed in order to avoid loss of translational lift. Constant airspeed must be flown, not constant groundspeed.
D3.6 BELL 206B/206L FLIGHT MANUALS
D3.6.1 The performance section of these manuals deal with "Critical Wind Azimuth Area", and its effect on helicopter performance is shown in the HIGE and HOGE graphs.
D3.7 CLOCKWISE ROTATION ROTOR SYSTEMS
(a) Loss of tail rotor effectiveness will result in LEFT yaw in helicopters with clockwise rotor systems, eg AS350B.
(b) In this case, recovery is as described for right pedal demand instead of left pedal.
D3.8 REFERENCE READING
(a) Bell Helicopter Textron "Rotor Breeze" July/Aug 1984
(b) Bell Operational Safety Notice OSN 206-83-10 Oct 1983
(c) Bell Information Letter 206-84-41/206L-84-27 Jul 1984
(d) Department of Aviation Central Office Paper Apr 1983
(e) Air Safety Digest 128/86 Autumn 1986
D3.1 INTRODUCTION
D3.1.1 Unanticipated right yaw, or loss of tail rotor effectiveness (LTE) is when an uncommanded right yaw occurs which does not subside of its own accord, and which, if not controlled, can result in the loss of control of the helicopter.
D3.2 CONTRIBUTING FACTORS
D3.2.1 The following factors will contribute to the onset of LTE:
(a) High gross weight and high temperature.
(b) Tail wind component
(c) Low airspeed
(d) Loss of translational lift.
D3.3 SYMPTOMS
D3.3.1 The following symptoms may be experienced prior to the onset of LTE:
(a) In the event of an unanticipated right yaw, the tail rotor will have insufficient authority to control the yaw.
(b) The helicopter will commence a rapid right rotation, with a nose down attitude.
D3.4 RECOVERY TECHNIQUE
D3.4.1 The following recovery techniques should be employed:
(a) Simultaneously input full left pedal, and forward cyclic to increase airspeed.
(b) When recovery technique takes effect, control the helicopter to recover to normal flight.
(c) Collective pitch reduction will assist the reduction of yaw, but should be used with caution in view of the resulting increased rate of descent.
(d) Should loss of tail rotor effectiveness occur at low altitude (below 1000 ft agl) and reduced collective be used to assist recover, the increased collective pitch subsequently required to reduce the rate of descent may lead to increased yaw rate and reduce rotor RPM.
(e) Should uncontrollable yaw continue to low altitude, the pilot should consider a full autorotation to the ground. Full left pedal should be maintained until the spin stops, then adjusted to keep heading into wind for landing.
D3.4.2 Recovery actions as laid down in the appropriate Flight Manual will take precedence at all times.
D3.5 AVOIDANCE
(a) Operations at low or hovering airspeeds OGE should be avoided in a relative wind that has a tailwind component.
(b) For low speed operations, eg orbiting a ground feature during aerial filming, close attention should be paid to the airspeed in order to avoid loss of translational lift. Constant airspeed must be flown, not constant groundspeed.
D3.6 BELL 206B/206L FLIGHT MANUALS
D3.6.1 The performance section of these manuals deal with "Critical Wind Azimuth Area", and its effect on helicopter performance is shown in the HIGE and HOGE graphs.
D3.7 CLOCKWISE ROTATION ROTOR SYSTEMS
(a) Loss of tail rotor effectiveness will result in LEFT yaw in helicopters with clockwise rotor systems, eg AS350B.
(b) In this case, recovery is as described for right pedal demand instead of left pedal.
D3.8 REFERENCE READING
(a) Bell Helicopter Textron "Rotor Breeze" July/Aug 1984
(b) Bell Operational Safety Notice OSN 206-83-10 Oct 1983
(c) Bell Information Letter 206-84-41/206L-84-27 Jul 1984
(d) Department of Aviation Central Office Paper Apr 1983
(e) Air Safety Digest 128/86 Autumn 1986
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As a general rule, true LTE is very hard to induce in most helicopters. It is certainly not endemic in all single rotor helicopters, in spite of the FAA/Bell publications that try to insinuate that any helo has a propensity to lose tail effectiveness.
The factors that get you close are generally not laxity on the pedals, they are more likely cause by using using too much main rotor power/collective pitch, especially at the bottom of an approach. If the approach is made with too much speed and rate of descent, arresting the descent at the bottom will take an armful of collective. The extra torque, above that needed for the hover after all the approach transcients have settled, is all a problem for marginal tail rotors. Most LTE accidents occur in the termination of an approach, sometimes downwind, or in a cross wind. Most LTE accidents also occur in only one or two types of helicopters.
In a study I did a few years back, surveying all reported helicopter accidents for a 2 year period, some interesting facts about LTE came out:
1) 90% of all LTE accidents occurred to Bell 206 and Bell 205 helicopters, the other 10% were spread across a great number of types.
2) None occurred in modern helicopters designed to higher yaw control standards, such as those that the Black Hawk, Apache and OH-58D had to meet. Pertinent to this thread, no LTE accidents occurred to Hughes/McD helos (in that study)].
3) For all helicopters LTE was a small accident contributer (less than 2%) but for the Bell 206, it was the cause of more than 10% of all accidents.
4) A high percentage of LTE accidents caused major damage, but few resulted in loss of life (low altitude, low rate of descent).
The factors that get you close are generally not laxity on the pedals, they are more likely cause by using using too much main rotor power/collective pitch, especially at the bottom of an approach. If the approach is made with too much speed and rate of descent, arresting the descent at the bottom will take an armful of collective. The extra torque, above that needed for the hover after all the approach transcients have settled, is all a problem for marginal tail rotors. Most LTE accidents occur in the termination of an approach, sometimes downwind, or in a cross wind. Most LTE accidents also occur in only one or two types of helicopters.
In a study I did a few years back, surveying all reported helicopter accidents for a 2 year period, some interesting facts about LTE came out:
1) 90% of all LTE accidents occurred to Bell 206 and Bell 205 helicopters, the other 10% were spread across a great number of types.
2) None occurred in modern helicopters designed to higher yaw control standards, such as those that the Black Hawk, Apache and OH-58D had to meet. Pertinent to this thread, no LTE accidents occurred to Hughes/McD helos (in that study)].
3) For all helicopters LTE was a small accident contributer (less than 2%) but for the Bell 206, it was the cause of more than 10% of all accidents.
4) A high percentage of LTE accidents caused major damage, but few resulted in loss of life (low altitude, low rate of descent).
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Tecpilot
....thanks for your input ...I do however stand by my post...the Bk Torque restriction is I believe <40kts IAS but having said that it has been a year since I read the manual !!!
and I do believe (?) that the restriction goes away if the "C" model T/R is fitted.....
and if the Bk crash due loss of tailboom pylon is the accident you are refering too ( the Colgate aircraft), then if you investigate it you will find that it was due to a maintenance fault due to use of incorrect rivets used on doublers to repair frame cracking ....which was probably caused by vibration. ...
cheers all the best for the New Year everyone
....thanks for your input ...I do however stand by my post...the Bk Torque restriction is I believe <40kts IAS but having said that it has been a year since I read the manual !!!
and I do believe (?) that the restriction goes away if the "C" model T/R is fitted.....
and if the Bk crash due loss of tailboom pylon is the accident you are refering too ( the Colgate aircraft), then if you investigate it you will find that it was due to a maintenance fault due to use of incorrect rivets used on doublers to repair frame cracking ....which was probably caused by vibration. ...
cheers all the best for the New Year everyone
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We live in an imperfect world.
Loss of Tail Rotor Effectiveness is one of those imperfect things. It can happen in just about any helicopter if the conditions are right. The Gazelle had it, and the UK military had plenty of examples of it happening. I know, as I was at Boscombe Down when the first reported loss due to this happened. It has been widely reported on the OH-58/206 series - in fact Bell Helicopter deserves tons of thanks from the helo community for delving into the problem - one of their test pilots won the Test Pilot of the Year award for this work.
Aerodynamics at the tail rotor are very complex, and have more variables than we probably know.
I've had LTE in a couple of strange places, but at least had been prepared for something like this and could fly away.
Like everything else- preparation and a prior plan will keep you out of trouble in the long run.
High power settings, or large power changes, wind not right on the nose, slow to put in a pedal input are all things that contribute. My recommendation is to always turn left (if you have to do turns at slow speed) in CCW main rotor helicopters - this means if you're doing photowork, put the photographer in the left side; make sure you always approach into wind, and know what to do if you get the loss of tail rotor effectiveness. The consistent advice seems to be add full left pedal, forward cyclic and get airspeed across the vertical stab.
For what it's worth.
Loss of Tail Rotor Effectiveness is one of those imperfect things. It can happen in just about any helicopter if the conditions are right. The Gazelle had it, and the UK military had plenty of examples of it happening. I know, as I was at Boscombe Down when the first reported loss due to this happened. It has been widely reported on the OH-58/206 series - in fact Bell Helicopter deserves tons of thanks from the helo community for delving into the problem - one of their test pilots won the Test Pilot of the Year award for this work.
Aerodynamics at the tail rotor are very complex, and have more variables than we probably know.
I've had LTE in a couple of strange places, but at least had been prepared for something like this and could fly away.
Like everything else- preparation and a prior plan will keep you out of trouble in the long run.
High power settings, or large power changes, wind not right on the nose, slow to put in a pedal input are all things that contribute. My recommendation is to always turn left (if you have to do turns at slow speed) in CCW main rotor helicopters - this means if you're doing photowork, put the photographer in the left side; make sure you always approach into wind, and know what to do if you get the loss of tail rotor effectiveness. The consistent advice seems to be add full left pedal, forward cyclic and get airspeed across the vertical stab.
For what it's worth.
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Shawn may be technically correct in that LTE "can happen to any helicopter" but in fact, it does not. If the helicopter is designed right, the probability of incurring LTE is nil. LTE is actually a misnomer, the tail rotor never looses effectiveness in LTE accidents, it is merely too small to do the job when it is swamped by events. The poorer the tail rotor, the more easily those events can be arranged.
Only some helos regularly experience LTE, and those are demonstrably poor in anti-torque control margin. LTE is actually been eliminated by modern military design rules that require more powerful tail rotor designs by specifying more rigerous yaw maneuver capabilities. Unfortunately, the civil regulatory folks have actually allowed LTE to continue in new designs by blaming pilots for LTE, and by allowing explanations such as these to stand in the place of a demand for proper yaw control capability.
The award that was mentioned above for the team that promulgated the training words about LTE was also un-earned (in my opinion) because that same group fought any improvements in yaw control regulations, thus assuring LTE would be around for years more in newly approved helicopters. In fact, there are newly approved helos that have no yaw control power when loaded fully. Beware of those machines that are approved for " Cat B, 9 passengers or less," and that require the wind to be only from the nose during hover. Those are code words for helicopters whose tail rotors are so poor that no yaw capability exists, and LTE is one inch away.
I actually fought a move to include the LTE words in ALL single rotor helicopter flight manuals, because we saw the real handwriting on the wall, where if we allow the blame to be placed on the pilot, we don't have to worry about fixing the aircraft. See my above post for the actual statistics on LTE. LTE is not a pervasive single rotor helicopter problem, LTE can be cured by modern design rules, and LTE is not something we as pilots must accept forever.
Only some helos regularly experience LTE, and those are demonstrably poor in anti-torque control margin. LTE is actually been eliminated by modern military design rules that require more powerful tail rotor designs by specifying more rigerous yaw maneuver capabilities. Unfortunately, the civil regulatory folks have actually allowed LTE to continue in new designs by blaming pilots for LTE, and by allowing explanations such as these to stand in the place of a demand for proper yaw control capability.
The award that was mentioned above for the team that promulgated the training words about LTE was also un-earned (in my opinion) because that same group fought any improvements in yaw control regulations, thus assuring LTE would be around for years more in newly approved helicopters. In fact, there are newly approved helos that have no yaw control power when loaded fully. Beware of those machines that are approved for " Cat B, 9 passengers or less," and that require the wind to be only from the nose during hover. Those are code words for helicopters whose tail rotors are so poor that no yaw capability exists, and LTE is one inch away.
I actually fought a move to include the LTE words in ALL single rotor helicopter flight manuals, because we saw the real handwriting on the wall, where if we allow the blame to be placed on the pilot, we don't have to worry about fixing the aircraft. See my above post for the actual statistics on LTE. LTE is not a pervasive single rotor helicopter problem, LTE can be cured by modern design rules, and LTE is not something we as pilots must accept forever.
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Nick:
You are, of course, correct - LTE cannot happen in some helicopters that have been designed to meet military requirements. Sorry for the slip up.
It is interesting to note that the design standards only call for sufficient tail rotor authority to handle winds of at least 17 knots from any quadrant, at maximum weight, and typically 7,000' density altitude. If the helicopter is not using maximum power in these conditions, then what is the pilot to do who wants to takeoff and climb vertically (and has enough power to do this)? He will probably run out of tail rotor authority, because there is no certification requirement for this!
But what do we do about the examples given for the 206L series that appears to run out of tail rotor well before the certification requirements? Was it overloaded for the density altitude? Should an incident report have been sent to the FAA about the lack of tail rotor authority?
Interesting discussion.
You are, of course, correct - LTE cannot happen in some helicopters that have been designed to meet military requirements. Sorry for the slip up.
It is interesting to note that the design standards only call for sufficient tail rotor authority to handle winds of at least 17 knots from any quadrant, at maximum weight, and typically 7,000' density altitude. If the helicopter is not using maximum power in these conditions, then what is the pilot to do who wants to takeoff and climb vertically (and has enough power to do this)? He will probably run out of tail rotor authority, because there is no certification requirement for this!
But what do we do about the examples given for the 206L series that appears to run out of tail rotor well before the certification requirements? Was it overloaded for the density altitude? Should an incident report have been sent to the FAA about the lack of tail rotor authority?
Interesting discussion.
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Shawn,
It is worse than you think. The FAA has approved a bunch of aircraft for weights at which there is NO side flight capability, using a change to 27/29 that allows them to abrogate the 17 knot demonstration. They retain just the ability to hover and approach/depart with nose into the wind. Look at:
http://www.bellhelicopter.textron.co...licopters/430/
page 22, step 2 shows how to calculate the weight at which you have no sideflight capability, whic is the weight for Cat B, 9 pax or less operations. They have similar charts for the 412 family and ohers. They have proposed these weights for Saudi mountain rescue operations in the 412!
Check out page B101 of AC 29-2C:
http://www.airweb.faa.gov/Regulatory...569cf00737a9d/$FILE/Chap2_pgB46-B124.pdf
It is worse than you think. The FAA has approved a bunch of aircraft for weights at which there is NO side flight capability, using a change to 27/29 that allows them to abrogate the 17 knot demonstration. They retain just the ability to hover and approach/depart with nose into the wind. Look at:
http://www.bellhelicopter.textron.co...licopters/430/
page 22, step 2 shows how to calculate the weight at which you have no sideflight capability, whic is the weight for Cat B, 9 pax or less operations. They have similar charts for the 412 family and ohers. They have proposed these weights for Saudi mountain rescue operations in the 412!
Check out page B101 of AC 29-2C:
http://www.airweb.faa.gov/Regulatory...569cf00737a9d/$FILE/Chap2_pgB46-B124.pdf
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Nick:
I would be slightly happier with this state of affairs if we had a good low airspeed sensing / indicating system for helicopters, but sadly that is not the case.
I guess we just need more educated users and procurement people so we don't get snookered by this sort of thing in the future.
I would be slightly happier with this state of affairs if we had a good low airspeed sensing / indicating system for helicopters, but sadly that is not the case.
I guess we just need more educated users and procurement people so we don't get snookered by this sort of thing in the future.
John Eacott, that is a great Ops manual explanation. A couple of points from a different perspective:
It does not distinguished LTE from loss of tail rotor thrust in the opening explanation.
Para D3.3 does not explain the symptoms "prior" to LTE, rather it details symptoms of developed LTE.
Para D3.4 (c) and (d) say the same thing. For para (e), this recovery technique came in for critisim afetr an Australian Army B206 suffered from LTE in a fifty odd foot hover and the (low time) pilot correctly carried out checklist actions: Lower collective - if insuffcient height remains to enable the collective to be lowered: conduct autorotation. Further investigation of the accident concluded that the checklist could be ammended to reflect a revised approach to an LTE situation which was to maintain collective (where low altitude prevented lowering it) and use cyclic to fly out of the spin with forward and out of turn cyclic application. Obviously, such action requires the pilot to be full conversant with the difference between LTE and loss of tail rotor thrust - hence my first point.
As an aside, and quite disappointingly, the fact that the pilot correctly carried out the checklist actions in the above accident did not seem to help him fight critisim of his actions by more senior pilots.
Para D3.5 (b) (probably unitentionally) implies a limitation on your aerial filming operations to be conducted above translational lift regardless of helicopter type or conditions. This may indeed be prudent in B206 Ops with low time pilots, but I think it is not appropriate in AS350 or BK117 ops.
It does not distinguished LTE from loss of tail rotor thrust in the opening explanation.
Para D3.3 does not explain the symptoms "prior" to LTE, rather it details symptoms of developed LTE.
Para D3.4 (c) and (d) say the same thing. For para (e), this recovery technique came in for critisim afetr an Australian Army B206 suffered from LTE in a fifty odd foot hover and the (low time) pilot correctly carried out checklist actions: Lower collective - if insuffcient height remains to enable the collective to be lowered: conduct autorotation. Further investigation of the accident concluded that the checklist could be ammended to reflect a revised approach to an LTE situation which was to maintain collective (where low altitude prevented lowering it) and use cyclic to fly out of the spin with forward and out of turn cyclic application. Obviously, such action requires the pilot to be full conversant with the difference between LTE and loss of tail rotor thrust - hence my first point.
As an aside, and quite disappointingly, the fact that the pilot correctly carried out the checklist actions in the above accident did not seem to help him fight critisim of his actions by more senior pilots.
Para D3.5 (b) (probably unitentionally) implies a limitation on your aerial filming operations to be conducted above translational lift regardless of helicopter type or conditions. This may indeed be prudent in B206 Ops with low time pilots, but I think it is not appropriate in AS350 or BK117 ops.
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I was studying my aerodye stuff the other day and came up with this very question......can you get a "settling with power" effect on the tail rotor?. then I read this bit on this thread
1. The tail rotor gets into a vortex ring state of its own, possibly due to interference from the wake or downwash of the main rotor. The tail of the ship "settles with power" sideways. This manifests itself as an uncommanded yaw rate.
I really hope this is the way things happen because it was about how I was thinking......other wise its back to study to get the right answer to my own question. (god I hate wanting to know everything, all it does is continually raise more questions)
What would the right recovery actions be? lower collective and cyclic forward? would a slight decrease in power help? how does this effect machines that decrease power when lowering the collective? (governer/corrilator?)
Has anyone had this problem with the R22? I would expect the machine would be in the worst sorts of conditions all the time whilst mustering in the north bit of oz.
1. The tail rotor gets into a vortex ring state of its own, possibly due to interference from the wake or downwash of the main rotor. The tail of the ship "settles with power" sideways. This manifests itself as an uncommanded yaw rate.
I really hope this is the way things happen because it was about how I was thinking......other wise its back to study to get the right answer to my own question. (god I hate wanting to know everything, all it does is continually raise more questions)
What would the right recovery actions be? lower collective and cyclic forward? would a slight decrease in power help? how does this effect machines that decrease power when lowering the collective? (governer/corrilator?)
Has anyone had this problem with the R22? I would expect the machine would be in the worst sorts of conditions all the time whilst mustering in the north bit of oz.
Last edited by the wizard of auz; 5th Jan 2003 at 11:17.
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Low / high speed sensing system.
To: Shawn Coyle
I believe such a system was developed by a firm called J Tech. It was originally designed to be used in underwater operations to detect water currents. It worked just as well in air. It operated on the principle of vortex shedding with the vortex frequency being detected by an ultrasonic detector. The individual units were coupled to provide airspeed in four directions
Another system is employed on the Apache and the USCG HH-65 but I believe in the case of the Apache, it is used to detect wind direction with this information being fed into the main computer to calculate windage for the chain gun. On the HH-65 I believe it is used to detect wind direction to correct for drift when in a hover. At least that is what I believe to be the reason for the systems.
I would be slightly happier with this state of affairs if we had a good low airspeed sensing / indicating system for helicopters, but sadly that is not the case.
Another system is employed on the Apache and the USCG HH-65 but I believe in the case of the Apache, it is used to detect wind direction with this information being fed into the main computer to calculate windage for the chain gun. On the HH-65 I believe it is used to detect wind direction to correct for drift when in a hover. At least that is what I believe to be the reason for the systems.
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Nick, you may believe that modern helicopters designed to military standards cannot experience loss of tail rotor authority, but I don't. I think any helicopter can experience it, with enough gross weight & altitude. The UH60 that crashed & rolled down the mountain under the gaze of CNN experienced it. Certainly some models have more margin than others, but I don't believe it's impossible in any model.
GLS:
I would draw a distinction (see my earlier post) between LTE and LTA, and the UH60 most certainly did not have LTE.
As for LTA, I think that most helicopters would experience it at such extreme DA's when attempting to operate the aircraft outside it's maximum performance envelope. I still do not know what happened in that accident, but it simply looks like they ran out of power (whether by low side failure or simply hitting the limiter). Losing main rotor RPM costs you exponentially more loss of lift from your tail rotor due to loss of tail rotor RPM (because of V is squared in the lift equation). Thus the tail rotor is no longer able to provide the lift you require even though you are at full pedal, and around you go - just like the UH60. Just like any single rotor helicopter at such extreme DA's with a main rotor that is bleeding off. No certification is required for helicopters to maintain tail rotor authority at extreme DA's with out of limits decayed RRPM.
The difference between these "modern" designs and say the UH-1H is that the poor old Huey runs out of left pedal at high DA's before you even get to the bleed. In fact I think there is a warning about this in the FM for DA's above (now I am stretching the memory) 4000 ft and weights above 8300 lbs (9500lbs is MGTOW - reduced from 10500 in the original design).
In other words, Nick is quite correct and the UH60 accident does not contradict him at all.
I would draw a distinction (see my earlier post) between LTE and LTA, and the UH60 most certainly did not have LTE.
As for LTA, I think that most helicopters would experience it at such extreme DA's when attempting to operate the aircraft outside it's maximum performance envelope. I still do not know what happened in that accident, but it simply looks like they ran out of power (whether by low side failure or simply hitting the limiter). Losing main rotor RPM costs you exponentially more loss of lift from your tail rotor due to loss of tail rotor RPM (because of V is squared in the lift equation). Thus the tail rotor is no longer able to provide the lift you require even though you are at full pedal, and around you go - just like the UH60. Just like any single rotor helicopter at such extreme DA's with a main rotor that is bleeding off. No certification is required for helicopters to maintain tail rotor authority at extreme DA's with out of limits decayed RRPM.
The difference between these "modern" designs and say the UH-1H is that the poor old Huey runs out of left pedal at high DA's before you even get to the bleed. In fact I think there is a warning about this in the FM for DA's above (now I am stretching the memory) 4000 ft and weights above 8300 lbs (9500lbs is MGTOW - reduced from 10500 in the original design).
In other words, Nick is quite correct and the UH60 accident does not contradict him at all.
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Hughes Tailspin
BMK, check out http://www.lighthorseaircav.com/s-a-history-lesson.html for a similair incident during the SEA era. Regards.
BMK,
Quite a long article , as on my last , here it is pasted to save time:
In D Troop, 3rd Squadron, 5th Cavalry, the Scouts, call sign "War Wagons", carried their gunner/observers in only the left front seat with the pilot in the right. With the rear of the ship nearly empty there was always room for picking up a crew that had been shot down. Each aircraft had a 7.62mm mini-gun mounted on the left side. The gunner had an M60 machine gun and we only made left-hand turns. Left hand turns required a little more power but the possibility of encountering "Hughes tailspin" was minimized. The tailspin arose during slow right turns at high power settings, finally resulting in loss of tailrotor effectiveness and the helicopter would spin out of control. Not a good condition when flying very close to the ground!
Regards.
BMK,
Quite a long article , as on my last , here it is pasted to save time:
In D Troop, 3rd Squadron, 5th Cavalry, the Scouts, call sign "War Wagons", carried their gunner/observers in only the left front seat with the pilot in the right. With the rear of the ship nearly empty there was always room for picking up a crew that had been shot down. Each aircraft had a 7.62mm mini-gun mounted on the left side. The gunner had an M60 machine gun and we only made left-hand turns. Left hand turns required a little more power but the possibility of encountering "Hughes tailspin" was minimized. The tailspin arose during slow right turns at high power settings, finally resulting in loss of tailrotor effectiveness and the helicopter would spin out of control. Not a good condition when flying very close to the ground!
Regards.
Following on from John Eacott's informative post.
Can this situatiion always be flown away from, provided the helicopter has enough altitude and room for manouvre.
Can this situatiion always be flown away from, provided the helicopter has enough altitude and room for manouvre.
Last edited by LordGrumpy; 5th Jan 2003 at 10:43.
Helmet,
Thanks for the comments, I'll see what I can amend to cover some of them. Point taken about low level ops being restricted if applied to other aircraft, but this is specifically the Bell 206 supplement. I'd hoped that Para D3.4 (c) and (d) were dealing with separate issues, but I see how they can be read to be the same, and I'll research the issue of para E. It was all written a few years ago....
Lord G,
I'd venture to suggest that it is in the lap of the Gods whether it can always be flown away from. Given a trained and capable pilot, and as you say suffient altitude and airspace, it should be recoverable, BUT it happens extremely quickly, and will consume heaps of altitude before all stops whizzing around
Those I know who have encountered LTE and recovered could not stress enough how sudden and sever the onset is, often with little or no warning.
Thanks for the comments, I'll see what I can amend to cover some of them. Point taken about low level ops being restricted if applied to other aircraft, but this is specifically the Bell 206 supplement. I'd hoped that Para D3.4 (c) and (d) were dealing with separate issues, but I see how they can be read to be the same, and I'll research the issue of para E. It was all written a few years ago....
Lord G,
I'd venture to suggest that it is in the lap of the Gods whether it can always be flown away from. Given a trained and capable pilot, and as you say suffient altitude and airspace, it should be recoverable, BUT it happens extremely quickly, and will consume heaps of altitude before all stops whizzing around
Those I know who have encountered LTE and recovered could not stress enough how sudden and sever the onset is, often with little or no warning.
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I have over 1200 hours in the OH6A and fly for a police department. The OH6A has numerous references in the Operators manual (-10) which cautions about right hand turns when you are close to the ground and at a slow speed.
In the OH6a, (500C) the V tail can develope lift and force the nose of the helicopter down and to the right when you have a right quartering tail wind. This is not loss of tail rotor authority. It is the wind exerting a force on the LARGE stabalizers. If you do not have enough altitude you may not be able to correct the attitude without ground contact.
I have experienced this on a number of occassions but because of altitude been able recover. Other unpleasant things can happen at High gross weight, Density altitude, slow airspeed, etc.
What type of a "tail spin" are you refering to? Is it the nose being force down during slow flight or LTE? Provide some more information and possibly I can provide you with more information.
If you would like like can email me.
[email protected]
In the OH6a, (500C) the V tail can develope lift and force the nose of the helicopter down and to the right when you have a right quartering tail wind. This is not loss of tail rotor authority. It is the wind exerting a force on the LARGE stabalizers. If you do not have enough altitude you may not be able to correct the attitude without ground contact.
I have experienced this on a number of occassions but because of altitude been able recover. Other unpleasant things can happen at High gross weight, Density altitude, slow airspeed, etc.
What type of a "tail spin" are you refering to? Is it the nose being force down during slow flight or LTE? Provide some more information and possibly I can provide you with more information.
If you would like like can email me.
[email protected]