AS350 Astar / AS355 Twinstar [Archive Copy]
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Well, helmet fire, here's the FAA line (AC 90-95).
THE PHENOMENA OF LTE.
LTE is a critical low-speed aerodynamic flight characteristic which can result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, can result in the loss of aircraft control.
When they say "does not subside of its own accord", does this mean "without pilot input", or "even with the proper input"? So, Sammy Schweizer;s yaw stopped as soon as he was into the wind. He was just slow on the pedals. LTE?
Rebecca could well have just applied insufficient left pedal as she passed through ETL and raised collective. LTE?
Joey on the other hand experiences a rapid yaw, and even WITH application of the corrective action, is unable to stop it. What else to call this? LTE?
So when you droop your rotor RPM, and then you experience an uncommanded yaw rate which does not subside on its own accord, AND you can't stop it with the pedals, by the FAA definitions, you are experiencing LTE. The low RPM might have gotten you there, but you are there all the same.
The Rotorcraft Flying Handbook and AC 90-95 both describe low RPM as one of the contributors to LTE, along with hot & high, heavy GW, low speed, downwind ops, and right turns (in a CCW rotor helicopter). I didn't write the books, but as a CFI in the USA, I am bound to work within their guidelines.
You might be able to educate me here - if I am losing T/R thrust due to rotor droop, and I start yawing, would I not lower collective (as much as able), regain airspeed (as much as able) fly into the turn (as much as able) while applying opposite pedal?
THE PHENOMENA OF LTE.
LTE is a critical low-speed aerodynamic flight characteristic which can result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, can result in the loss of aircraft control.
When they say "does not subside of its own accord", does this mean "without pilot input", or "even with the proper input"? So, Sammy Schweizer;s yaw stopped as soon as he was into the wind. He was just slow on the pedals. LTE?
Rebecca could well have just applied insufficient left pedal as she passed through ETL and raised collective. LTE?
Joey on the other hand experiences a rapid yaw, and even WITH application of the corrective action, is unable to stop it. What else to call this? LTE?
So when you droop your rotor RPM, and then you experience an uncommanded yaw rate which does not subside on its own accord, AND you can't stop it with the pedals, by the FAA definitions, you are experiencing LTE. The low RPM might have gotten you there, but you are there all the same.
The Rotorcraft Flying Handbook and AC 90-95 both describe low RPM as one of the contributors to LTE, along with hot & high, heavy GW, low speed, downwind ops, and right turns (in a CCW rotor helicopter). I didn't write the books, but as a CFI in the USA, I am bound to work within their guidelines.
You might be able to educate me here - if I am losing T/R thrust due to rotor droop, and I start yawing, would I not lower collective (as much as able), regain airspeed (as much as able) fly into the turn (as much as able) while applying opposite pedal?
Last edited by Flingwing207; 5th Oct 2005 at 13:42.
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Flingwing207,
Your logic, if carried to extreme:
If you bash your tail cone into a mountain along the right side, and your aircraft yaws right and "does not subside of its own accord and, if not corrected, can result in the loss of aircraft control." So I guess if you hit a mountain, you experience LTE!
If you pull the rotor rpm down to your socks because you requested too much power, and you are too numb to the cues that your aircraft is screaming at you, you have LBP, loss of brain power. If you treat it as a yaw problem, you have so purely missed the point contained in "pilot in command" that perhaps it is time to hang it up.
The reason why the distinction is made is that the causes and cures are different, as is the aerodynamics. If you blur it all together, you will never actually understand nor control your environment. I know of pilots who lost roll control due to rpm droop, should we call that LCE loss of cyclic effectiveness?
Your logic, if carried to extreme:
If you bash your tail cone into a mountain along the right side, and your aircraft yaws right and "does not subside of its own accord and, if not corrected, can result in the loss of aircraft control." So I guess if you hit a mountain, you experience LTE!
If you pull the rotor rpm down to your socks because you requested too much power, and you are too numb to the cues that your aircraft is screaming at you, you have LBP, loss of brain power. If you treat it as a yaw problem, you have so purely missed the point contained in "pilot in command" that perhaps it is time to hang it up.
The reason why the distinction is made is that the causes and cures are different, as is the aerodynamics. If you blur it all together, you will never actually understand nor control your environment. I know of pilots who lost roll control due to rpm droop, should we call that LCE loss of cyclic effectiveness?
Can I have some confirmation or denial of the following, which summarises what I've read and heard about the phenomenon known as LTE:
a. Is associated with the Bell 206
b. Happens in a high left pedal demand situation at low speed
c. Is thought to be 'set off' by the not-very effective tail rotor operating at normal rpm encountering dirty air from either the main rotor vortices, or ingesting its own vortices
d. Is more likely when the relative wind comes from certain critical directions (ties in with 'c')
e. Is characterised by a very rapid right yaw that can't be stopped with left pedal
f. Can perhaps be flown out of as described by flingwing, given room to lower collective and gain airspeed, but will probably only be stopped by rolling off the throttle or crashing, or both.
Lots of definitions and acronyms being thrown around in this discussion; are these points a fair summary or not?
a. Is associated with the Bell 206
b. Happens in a high left pedal demand situation at low speed
c. Is thought to be 'set off' by the not-very effective tail rotor operating at normal rpm encountering dirty air from either the main rotor vortices, or ingesting its own vortices
d. Is more likely when the relative wind comes from certain critical directions (ties in with 'c')
e. Is characterised by a very rapid right yaw that can't be stopped with left pedal
f. Can perhaps be flown out of as described by flingwing, given room to lower collective and gain airspeed, but will probably only be stopped by rolling off the throttle or crashing, or both.
Lots of definitions and acronyms being thrown around in this discussion; are these points a fair summary or not?
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Anyone care to anal-ize this report?
KAUAI News
Helicopter crash report a case of 'he said, he said'
By Andy Gross - THE GARDEN ISLAND
The circumstances surrounding the fatal Heli USA Airways crash Sept. 23 off the Ha'ena Coast remains a "he said, he said," situation.
According to a preliminary report issued Tuesday by investigators with the National Transportation Safety Board (NTSB) and compiled by lead investigator Debra Eckrote, Heli USA pilot Glen Lampton told investigators the Heli USA Airways Aerospatiale AS 350BA, N355NT (registered to Jan Leasing LLC, of Las Vegas, Nevada) was at 2,000 feet flying along Na Pali Coast toward Kailiu Point. Lampton said he had encountered some weather in Waimea Canyon.
According to the preliminary report, as the flight approached Ke'e Beach, Lampton noted rain showers which appeared to be offshore. As he came around the point, Lampton said he "suddenly saw a MD500 coming straight for me." He made a left turn to avoid the traffic, and as the helicopter leveled out, it encountered heavy rain.
Based on interviews, other pilots, including Ian Bagano, who was at the helm of an McDonnell Douglas 500 (MD500, or Hughes 500D) owned by Inter-Island Helicopters, were at about 300 feet above sea level, getting out of the weather.
Bagano said he was well below 2,000 feet during this course reversal, and it wasn't until he was near Hanakapi'ai Beach, several miles to the southwest of the Kailiu Point, before he heard Lampton's mayday call.
Eckrote said she had no hard data to support the eyewitness accounts of the pilots. She said there was no radar operating in that area.
The preliminary report is a narrative, and does not draw conclusions. It is based upon interviews with pilots and other personnel, none of whom are identified in the report.
Eckrote said she hoped to have the final report finished in three to six months.
According to NTSB officials, the preliminary information is subject to change, and may contain errors which will be corrected when the final report has been completed.
During preliminary interviews and a subsequent written statement, Lampton reported that, at the completion of his lunch break, he spoke with a representative at the Princeville Heli USA Airways base, who reported no adverse weather conditions.
Preliminary interviews with other air-tour-operator pilots in the area reported that the weather off of the Kailiu Point had been building all day.
Eckrote said that, because there is no weather station in the vicinity, pilots had to depend upon each other's reports.
Lampton told NTSB investigators he could still see down and to the right to the coastline. The pilot opted to reduce airspeed to 60-80 knots, and started a 15-to-20-degree right turn over the beach. The helicopter got about 160 degrees into the turn when the airspeed went to zero and the aircraft started to rapidly descend. Lampton attempted to control the helicopter with control inputs, which had no effect.
The pilot stated that he realized that they were going to hit the beach, and applied full power. The rate of descent suddenly stopped, and the helicopter went back up in the air momentarily, and entered an immediate hard spin to the left. According to the report, Lampton instructed the passengers to open the doors, and he transmitted a mayday call as the helicopter impacted the water, bounced back into the air, then impacted the water again, still spinning, but remaining on the surface for a short time before it eventually rolled to the right.
At approximately 2:15 p.m. the Heli USA copter hit the ocean several hundred yards off the coastline at Ke'e Beach, near Ha'ena.
The flight encountered instrument meteorological conditions just prior to the accident.
According to Zoe Keliher of the NTSB, Lampton was not instrumentrated. A company flight plan was in effect. The pilot and two passengers received minor injuries. The remaining
three passengers were fatally injured. The flight departed from Lihu'e Airport at 1:54 p.m. for the intended 45-minute tour.
Lampton reported that the weather was good until he reached Waimea Canyon. Clouds were present in the canyon, therefore he exited the area at the lower microwave station, near the entrance to the canyon, and proceeded to Na Pali Coast.
The pilot flying a tour about 15 minutes prior to the accident said that he encountered the rain at the Kailiu Point and made a gradual descent to about 300 feet above ground level. The pilot was able to maintain visual reference with the coastline, and continued on his tour route.
According to the NTSB preliminary report, this pilot reported no encounter with turbulence, downdrafts, lightning or windshear, while maneuvering through the rain. One other pilot in front of the MD500 and doomed Heli USA craft also reported that he entered the rain shower and descended to 300 feet just past Ke'e Beach before he made a course reversal due to deteriorating visibility.
According to the preliminary report, Bagano also reported encountering the rain showers, and he too made a controlled descent to a lower altitude to maintain ground reference. The visibility decreased to a point where he, too, opted to reverse course.
Based upon earlier reports, the two surviving passengers, Karen Clifton, 44, and her husband Bill Thorson, 48, said they didn't believe Lampton had to maneuver to avoid hitting the other helicopter. They said they saw a helicopter below them.
KAUAI News
Helicopter crash report a case of 'he said, he said'
By Andy Gross - THE GARDEN ISLAND
The circumstances surrounding the fatal Heli USA Airways crash Sept. 23 off the Ha'ena Coast remains a "he said, he said," situation.
According to a preliminary report issued Tuesday by investigators with the National Transportation Safety Board (NTSB) and compiled by lead investigator Debra Eckrote, Heli USA pilot Glen Lampton told investigators the Heli USA Airways Aerospatiale AS 350BA, N355NT (registered to Jan Leasing LLC, of Las Vegas, Nevada) was at 2,000 feet flying along Na Pali Coast toward Kailiu Point. Lampton said he had encountered some weather in Waimea Canyon.
According to the preliminary report, as the flight approached Ke'e Beach, Lampton noted rain showers which appeared to be offshore. As he came around the point, Lampton said he "suddenly saw a MD500 coming straight for me." He made a left turn to avoid the traffic, and as the helicopter leveled out, it encountered heavy rain.
Based on interviews, other pilots, including Ian Bagano, who was at the helm of an McDonnell Douglas 500 (MD500, or Hughes 500D) owned by Inter-Island Helicopters, were at about 300 feet above sea level, getting out of the weather.
Bagano said he was well below 2,000 feet during this course reversal, and it wasn't until he was near Hanakapi'ai Beach, several miles to the southwest of the Kailiu Point, before he heard Lampton's mayday call.
Eckrote said she had no hard data to support the eyewitness accounts of the pilots. She said there was no radar operating in that area.
The preliminary report is a narrative, and does not draw conclusions. It is based upon interviews with pilots and other personnel, none of whom are identified in the report.
Eckrote said she hoped to have the final report finished in three to six months.
According to NTSB officials, the preliminary information is subject to change, and may contain errors which will be corrected when the final report has been completed.
During preliminary interviews and a subsequent written statement, Lampton reported that, at the completion of his lunch break, he spoke with a representative at the Princeville Heli USA Airways base, who reported no adverse weather conditions.
Preliminary interviews with other air-tour-operator pilots in the area reported that the weather off of the Kailiu Point had been building all day.
Eckrote said that, because there is no weather station in the vicinity, pilots had to depend upon each other's reports.
Lampton told NTSB investigators he could still see down and to the right to the coastline. The pilot opted to reduce airspeed to 60-80 knots, and started a 15-to-20-degree right turn over the beach. The helicopter got about 160 degrees into the turn when the airspeed went to zero and the aircraft started to rapidly descend. Lampton attempted to control the helicopter with control inputs, which had no effect.
The pilot stated that he realized that they were going to hit the beach, and applied full power. The rate of descent suddenly stopped, and the helicopter went back up in the air momentarily, and entered an immediate hard spin to the left. According to the report, Lampton instructed the passengers to open the doors, and he transmitted a mayday call as the helicopter impacted the water, bounced back into the air, then impacted the water again, still spinning, but remaining on the surface for a short time before it eventually rolled to the right.
At approximately 2:15 p.m. the Heli USA copter hit the ocean several hundred yards off the coastline at Ke'e Beach, near Ha'ena.
The flight encountered instrument meteorological conditions just prior to the accident.
According to Zoe Keliher of the NTSB, Lampton was not instrumentrated. A company flight plan was in effect. The pilot and two passengers received minor injuries. The remaining
three passengers were fatally injured. The flight departed from Lihu'e Airport at 1:54 p.m. for the intended 45-minute tour.
Lampton reported that the weather was good until he reached Waimea Canyon. Clouds were present in the canyon, therefore he exited the area at the lower microwave station, near the entrance to the canyon, and proceeded to Na Pali Coast.
The pilot flying a tour about 15 minutes prior to the accident said that he encountered the rain at the Kailiu Point and made a gradual descent to about 300 feet above ground level. The pilot was able to maintain visual reference with the coastline, and continued on his tour route.
According to the NTSB preliminary report, this pilot reported no encounter with turbulence, downdrafts, lightning or windshear, while maneuvering through the rain. One other pilot in front of the MD500 and doomed Heli USA craft also reported that he entered the rain shower and descended to 300 feet just past Ke'e Beach before he made a course reversal due to deteriorating visibility.
According to the preliminary report, Bagano also reported encountering the rain showers, and he too made a controlled descent to a lower altitude to maintain ground reference. The visibility decreased to a point where he, too, opted to reverse course.
Based upon earlier reports, the two surviving passengers, Karen Clifton, 44, and her husband Bill Thorson, 48, said they didn't believe Lampton had to maneuver to avoid hitting the other helicopter. They said they saw a helicopter below them.
zdfwflyer: i would care to comment....that report is totally irrelevant to the thread, however i am sure that flingwiing can safely conclude it was an LTE event that caused the accident, after all, it hit the water and spun uncontrollably left.
AOTW,
Some points on your summary;
95% of LTE have been on B206, as Nick points out. Bell claim it is not limited to the 206, but few other types have had a record of the event. This ties in with the claim of "a new aerodynamic theory or phemomena" rather than any acceptance of deisgn flaw.
re your point 'f", the recovery technique was as you say. A 1995 ish B206 accident in the Australian Army was an LTE event and the pilot did just that - he tried to lower lever but had insufficient height, and then rolled the throttle off in accordance with the checklist procedure, writing the aircraft off and sustaining injury to himself and his pax. The checklist actions were reviewed and the recommendation was to lower the lever if hieght permits, otherwise attempt a flyaway using out of turn cyclic rather than roll the throttle off, particularly when faced with adverse terrain. I dont know if Bell ratified this recommendation, but it certainly makes sense. The danger is trying to discern LTE from Loss of T/R thrust whilst you are spinning around madly staining your shorts.
As a sideline, senior pilots very unfairly critised the junior pilot involved who carried out the taught checklist procedure to perfection in harrowing circumstances. well done that man. He did what the senior pilots had taught him, and what Bell recommended. Where do they get off??
AOTW,
Some points on your summary;
95% of LTE have been on B206, as Nick points out. Bell claim it is not limited to the 206, but few other types have had a record of the event. This ties in with the claim of "a new aerodynamic theory or phemomena" rather than any acceptance of deisgn flaw.
re your point 'f", the recovery technique was as you say. A 1995 ish B206 accident in the Australian Army was an LTE event and the pilot did just that - he tried to lower lever but had insufficient height, and then rolled the throttle off in accordance with the checklist procedure, writing the aircraft off and sustaining injury to himself and his pax. The checklist actions were reviewed and the recommendation was to lower the lever if hieght permits, otherwise attempt a flyaway using out of turn cyclic rather than roll the throttle off, particularly when faced with adverse terrain. I dont know if Bell ratified this recommendation, but it certainly makes sense. The danger is trying to discern LTE from Loss of T/R thrust whilst you are spinning around madly staining your shorts.
As a sideline, senior pilots very unfairly critised the junior pilot involved who carried out the taught checklist procedure to perfection in harrowing circumstances. well done that man. He did what the senior pilots had taught him, and what Bell recommended. Where do they get off??
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In the UK the CAA released a FODCOM (Jan 04) after 2 "LTE" filming incidents in 03. The FODCOM of course made no reference to the facts that the two machines involved were 206 models.
A year later (!!) the BBC released an internal Health & Safety Alert to all production departments, referring to the CAA alert and stating that all productions must ask any helicopter operator they book a series of questions about LTE.
What a mucking fuddle that caused. It flashed up on the BBC internal email system as a major alert making everyone drop their media glasses onto the tips of their noses and panic. Suddenly, all helicopters were going to kill you.
God save us from the clipboard and box-ticking mentality.
LTE isn't a cause of accidents. It's a symptom of bad driving.
A year later (!!) the BBC released an internal Health & Safety Alert to all production departments, referring to the CAA alert and stating that all productions must ask any helicopter operator they book a series of questions about LTE.
What a mucking fuddle that caused. It flashed up on the BBC internal email system as a major alert making everyone drop their media glasses onto the tips of their noses and panic. Suddenly, all helicopters were going to kill you.
God save us from the clipboard and box-ticking mentality.
LTE isn't a cause of accidents. It's a symptom of bad driving.
Ok, Ok.....now that everybody who is visiting this thread for the first time, is thoroughly confused with:
LTE / LTA / LTC / overtorqueing etc etc...would anyone out there who thinks they have a handle on this, care to summarise for the benefit of many ab initio pilots and 206 drivers...what, IN VERY BASIC TERMS is LTE.
So they can go away and log it ready for easy recall when needed:
I thought I had this nut cracked...now I'm not too sure?
LTE / LTA / LTC / overtorqueing etc etc...would anyone out there who thinks they have a handle on this, care to summarise for the benefit of many ab initio pilots and 206 drivers...what, IN VERY BASIC TERMS is LTE.
So they can go away and log it ready for easy recall when needed:
I thought I had this nut cracked...now I'm not too sure?
Thanks, helmet fire.
The revision to the recovery technique of trying to use out-of-turn cyclic sounds a bit dodgy to me, gut-feeling wise; I'd be more inclined to cyclic into the turn slightly, or at least keep it centered (given the room to move) and try to do some kind of an ugly ascending, accelerating and hopefully slipstreaming climb out.
Using a heap of left cyclic as the machine was spinning rapidly right sounds a bit like a recipe for rolling it over or mast bumping -as I say, gut feeling, so maybe the test pilots can comment further.
Thomas coupling,
as a relative newcomer to the 206 I was keen to find out what this LTE business was all about, and the summary I wrote above is about the best I've been able to glean.
We all know about the obvious things that can happen to any tail-rotored helicopter, such as loss of tail rotor drive, or damage to the tail rotor itself; as has been mentioned, machines like the Huey can get short on tail rotor authority (ie high power hover, left pedal banging on and off the stops, but not whipping around to the right), but when I started flying the 206 people would talk about this LTE thing; apparently a rapid right yaw in high power low speed situations that can be brought on when the wussy tail rotor gets dirty air and can't cope, exacerbated by winds from certain directions (must check the chart again, the 8 o'clock springs to mind).
Hope this is of some use.
The revision to the recovery technique of trying to use out-of-turn cyclic sounds a bit dodgy to me, gut-feeling wise; I'd be more inclined to cyclic into the turn slightly, or at least keep it centered (given the room to move) and try to do some kind of an ugly ascending, accelerating and hopefully slipstreaming climb out.
Using a heap of left cyclic as the machine was spinning rapidly right sounds a bit like a recipe for rolling it over or mast bumping -as I say, gut feeling, so maybe the test pilots can comment further.
Thomas coupling,
as a relative newcomer to the 206 I was keen to find out what this LTE business was all about, and the summary I wrote above is about the best I've been able to glean.
We all know about the obvious things that can happen to any tail-rotored helicopter, such as loss of tail rotor drive, or damage to the tail rotor itself; as has been mentioned, machines like the Huey can get short on tail rotor authority (ie high power hover, left pedal banging on and off the stops, but not whipping around to the right), but when I started flying the 206 people would talk about this LTE thing; apparently a rapid right yaw in high power low speed situations that can be brought on when the wussy tail rotor gets dirty air and can't cope, exacerbated by winds from certain directions (must check the chart again, the 8 o'clock springs to mind).
Hope this is of some use.
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headsethair,
If it is not possible to get LTE in a Black Hawk, nor in a Lynx, nor in a H-500, nor most helos. How is it purely "bad driving" if you get it virtually only in a Bell 206?
The whole Bell helicopter campaign to create the label LTE is a move to make you say that, so that you don't demand a helicopter with adequate tail rotor authority (and more precisely, so that your lawyer doesn't get to make such a case.)
The definitions are this:
LTE (Loss of Tail rotor Effectiveness) - occurs on a very few helicopter models, caused by that helicopter model's inadequate tail rotor authority, when you can lose tail rotor control while inside the normal envelope. Is the cause of a significant percentage of those model's accidents. Prevented by using very conservative flying techniques, and preparing recovery escape maneuvers, or by re-designing the tail rotor to assure adequate thrust. The typical LTE involves an approach to a spot with moderate cross wind, at altitude, and a loss of yaw control when the approach is terminated near the hover. Once entered, recovery is very difficult without descending, often ground contact is unavoidable.
LTA (Loss of Tail rotor Authority) - occurs on almost any helicopter, when operated outside its normal envelope, typically when the rotor rpm is abused, or when very high torque is demanded. Is a symptom of this mishandling, not a separate cause. Does not cause a significant percentage of accidents in those models, often zero accidents. Prevention does not involve preplanning except regarding weight/power performance. The typical LTA involves a takeoff or landing when the helicopter hits its engine topping, and the rotor rpm droops below the green arc, causing loss of yaw control. Recovery often can be made by lowering collective to recover rpm without significant descent, so that ground contact is often avoidable.
LTC - (Loss of Tail rotor Control)- The tail rotor system is broken, and no longer does its proper job. A true emergency. Can be a stuck control (left pedal, right pedal, or center) or it can be a total loss of thrust (broken drive shaft or gear box). Can occur on any helo, but relatively rare. Part of the training on every helo.
If it is not possible to get LTE in a Black Hawk, nor in a Lynx, nor in a H-500, nor most helos. How is it purely "bad driving" if you get it virtually only in a Bell 206?
The whole Bell helicopter campaign to create the label LTE is a move to make you say that, so that you don't demand a helicopter with adequate tail rotor authority (and more precisely, so that your lawyer doesn't get to make such a case.)
The definitions are this:
LTE (Loss of Tail rotor Effectiveness) - occurs on a very few helicopter models, caused by that helicopter model's inadequate tail rotor authority, when you can lose tail rotor control while inside the normal envelope. Is the cause of a significant percentage of those model's accidents. Prevented by using very conservative flying techniques, and preparing recovery escape maneuvers, or by re-designing the tail rotor to assure adequate thrust. The typical LTE involves an approach to a spot with moderate cross wind, at altitude, and a loss of yaw control when the approach is terminated near the hover. Once entered, recovery is very difficult without descending, often ground contact is unavoidable.
LTA (Loss of Tail rotor Authority) - occurs on almost any helicopter, when operated outside its normal envelope, typically when the rotor rpm is abused, or when very high torque is demanded. Is a symptom of this mishandling, not a separate cause. Does not cause a significant percentage of accidents in those models, often zero accidents. Prevention does not involve preplanning except regarding weight/power performance. The typical LTA involves a takeoff or landing when the helicopter hits its engine topping, and the rotor rpm droops below the green arc, causing loss of yaw control. Recovery often can be made by lowering collective to recover rpm without significant descent, so that ground contact is often avoidable.
LTC - (Loss of Tail rotor Control)- The tail rotor system is broken, and no longer does its proper job. A true emergency. Can be a stuck control (left pedal, right pedal, or center) or it can be a total loss of thrust (broken drive shaft or gear box). Can occur on any helo, but relatively rare. Part of the training on every helo.
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Nick, "If it is not possible to get LTE in a Black Hawk, nor in a Lynx, nor in a H-500, nor most helos. How is it purely "bad driving" if you get it virtually only in a Bell 206?"
There are many ways that many machines can be made to kill or maim people. In helicopters, a lot of machines have their own - er - characteristics. Whether it's carb heat or "once only" autos in an R22 - or apparently LTE in a 206.
My point is that if you know a machine has a characteristic, shouldn't you do everything possible to avoid aggravating that area ?
We all know that helis can get into vortex ring on the main rotor - so we avoid getting into that situation. Why can't a 206 pilot have the same attitude to LTE ?
I am delighted to note that your company's Blackhawk products do not get LTE. Neither does my R44. When it comes to rebuild, I'll consider replacing it with a Blackhawk. I quite like the one G Bush had at G8 in Scotland.....is it leased ? Might it become available when he's finished with it ?
There are many ways that many machines can be made to kill or maim people. In helicopters, a lot of machines have their own - er - characteristics. Whether it's carb heat or "once only" autos in an R22 - or apparently LTE in a 206.
My point is that if you know a machine has a characteristic, shouldn't you do everything possible to avoid aggravating that area ?
We all know that helis can get into vortex ring on the main rotor - so we avoid getting into that situation. Why can't a 206 pilot have the same attitude to LTE ?
I am delighted to note that your company's Blackhawk products do not get LTE. Neither does my R44. When it comes to rebuild, I'll consider replacing it with a Blackhawk. I quite like the one G Bush had at G8 in Scotland.....is it leased ? Might it become available when he's finished with it ?
Last edited by headsethair; 6th Oct 2005 at 13:12.
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headsethair,
You are certainly right that there is lots of middle ground, and one should fly appropriate to the type he is strapped into.
I just want to be sure that we don't tar all helos with the brush invented to excuse the bad behavior of a few. While a test pilot for a manufacturer, I had to stop an effort by the FAA, fueled by Bell, to have that LTE Advisory Circular regurgetated into the flight manuals of all helos. This would have been the ultimate victory for the apologists, and a defeat for those who think we might actually try to fix the helo instead of blame the pilot, even if only on alternate Tuesdays.
You are certainly right that there is lots of middle ground, and one should fly appropriate to the type he is strapped into.
I just want to be sure that we don't tar all helos with the brush invented to excuse the bad behavior of a few. While a test pilot for a manufacturer, I had to stop an effort by the FAA, fueled by Bell, to have that LTE Advisory Circular regurgetated into the flight manuals of all helos. This would have been the ultimate victory for the apologists, and a defeat for those who think we might actually try to fix the helo instead of blame the pilot, even if only on alternate Tuesdays.
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Nick, h'fire, whups - I guess you missed the part where I agree. As an instructor operating under the auspicies of the FAA, I am forced to reconcile the party line with reality (the party line being the RFH, and AC). BTW, the AC eliminates mechanical issues as a cause of LTE.
Anyway, as to what I think and teach as far as LTE versus all the other reasons a helicopter might go 'round on you - my (personal) definition of LTE is when the main rotor is creating more torque than the tail rotor can counter (at full pedal). All the other stuff (weathercock, vortex, MR vortex) are ways to experience unanticipated yaw, but not LTE.
Nick, I'm not trying to debate your point that letting RPM droop is a pilot error, and I agree that if you keep RPM up, there are very few helicopters that will experience LTE. However, once the pilot MAKES that error, you may reach the point where the tail rotor cannot overcome the torque of the main rotor. You yaw, and no application of pedal can stop it. Physically, aerodynamically and result-wise, the only difference between (shall we call it B206 LTE?) and low-RPM LTE is how you arrived. Important difference to be sure.
Anyway, I think the frustrations lie with having to toe the FAA line while trying to teach new students what's really going on. If I tell a pre-private student "there is no LTE except in a Jet Ranger", they aren't going to have a good time defending that statement with a DPE holding a copy of the Rotorcraft Flying Handbook or the AC. Better to have them understand the principles and mislabel them as LTE.
Anyway, as to what I think and teach as far as LTE versus all the other reasons a helicopter might go 'round on you - my (personal) definition of LTE is when the main rotor is creating more torque than the tail rotor can counter (at full pedal). All the other stuff (weathercock, vortex, MR vortex) are ways to experience unanticipated yaw, but not LTE.
Nick, I'm not trying to debate your point that letting RPM droop is a pilot error, and I agree that if you keep RPM up, there are very few helicopters that will experience LTE. However, once the pilot MAKES that error, you may reach the point where the tail rotor cannot overcome the torque of the main rotor. You yaw, and no application of pedal can stop it. Physically, aerodynamically and result-wise, the only difference between (shall we call it B206 LTE?) and low-RPM LTE is how you arrived. Important difference to be sure.
Anyway, I think the frustrations lie with having to toe the FAA line while trying to teach new students what's really going on. If I tell a pre-private student "there is no LTE except in a Jet Ranger", they aren't going to have a good time defending that statement with a DPE holding a copy of the Rotorcraft Flying Handbook or the AC. Better to have them understand the principles and mislabel them as LTE.
Last edited by Flingwing207; 6th Oct 2005 at 19:43.
In defense of the 206, I can't recall ever hitting the left pedal stop. But I certainly can vouch that I have done that in other helicopters. It's never a comfortable feeling.
My one and only encounter with "LTE" was in a LongRanger. Up high, photography flight, hovering downwind. Pullling more and more power to hold position, I had "some" left pedal in but didn't sense that I was about to hit the stop and in fact had not. Suddenly...snap!...around she went. In the happy comfort of retrospect, I guess the vertical fin just blocked off enough of the tail rotor's inflow (or something) that the T/R just couldn't hack it at the high power-setting.
The rotation was so abrupt that I thought I had a tail rotor failure. Alternatively, had I known more (but not enough!) I might have assumed that the tail rotor had "stalled" like the wing of an airplane gives up the ghost. Having all of 1,000 big hours, I was bamboozled and pretty much just along for the ride, thrown sideways against the front seat passenger who was likewise thrown sideways against his door. I uttered an expletive phrase that began, "What the...?" Luckily we had plenty of altitude. I do remember lowering the pitch and banking into the spin. We did fly out of it. I thought to myself, "Don't do THAT again!" And I did not.
Sometime later I read the FAA Advisory Circular on the subject. I was surprised to learn that the tail rotor is *not* stalled during the event, and is still producing thrust. The recommendation was to go to FULL left pedal and hold it there. In my own experience, I do not remember doing that. I vowed to not make that mistake again. And I wonder how many "LTE" accidents occur because the hapless "low-time" pilots, like me, failed to stuff the pedal all the way in quickly enough because they were already low, down near the trees, concentrating on something outside the aircraft, something other than the theory of tail rotor inflow versus huge, blocking vertical fins.
So now when I'm operating in situations that demand high power and a wind off the tail, I'm very, very careful about yaw rates. And now I know what to expect if it snaps again.
Do I believe that the 206 tail rotor "stops working" and/or will spin "out of control" in an LTE event? No. It will spin until the pinhead at the controls (me) pushes in and holds the left pedal and perhaps reduces the torque if possible until a) the weathervaning tendency takes hold or b) the tail rotor gets a good "bite" again.
I laugh at that LTE Wind Chart that Bell puts out. According to it, you're susceptible to LTE with wind from virtually every quadrant except a tiny slice of area to the front right. Silly me! I didn't realize you could get into LTE with wind off the left. But Bell wants to have ALL their bases covered, I guess. And truthfully, as I've admitted here before, all of my helicopter flight time is at relatively low altitudes - below 5,000 feet. So I cannot comment on the 206's tail rotor performance at altitude. But down here in the thick air, I do chuckle when flying in a 206 with newbies who seem preoccupied with LTE when making an approach with a wind from the left-front. "Heh, go fly a B-model offshore," I tell them. "Offshore, where you'll be making max-gross landings to confined-area drilling rigs and the wind will be nowhere NEAR that little slice of clear area on the LTE chart." You'll be flat-out amazed that 206's aren't spinning out of the sky all over the place and falling into the water.
I kind of agree with headsethair. The phenomenons we ascribe to the main rotor as VRS or SWP can be excited while operating inside the flight envelope. Military OH-58 accidents aside, it seems to me that the number of civilian accidents attributable to "LTE" are small. I'll accept that, like the main rotor, the tail rotor has some performance limitations too, even considering N. Lappos' contention that this is unacceptable. (Listen to Nick screech on this subject long enough, and you get the impression he wishes that the FAA would just ground the Bell 206, that unsafe P.O.S. and be done with it.) You know, all things considered, for a helicopter that was designed over forty years ago, I believe the JetRanger ain't half bad.
Your mileage may vary
Afternoon Edit: What was I, sleeping? Happened to crack open a 206 AFM today and what to my wondering eyes should appear, but the Critical Wind Azimuth Chart! The "avoid area" is much smaller than my memory lead me to believe: only extending from 050 degrees (relative to the nose) then back around to about 210 degrees. For some reason, I thought it encompassed the entire left side of the a/c. Ah, the failing memory of old age.
Apologies.
My one and only encounter with "LTE" was in a LongRanger. Up high, photography flight, hovering downwind. Pullling more and more power to hold position, I had "some" left pedal in but didn't sense that I was about to hit the stop and in fact had not. Suddenly...snap!...around she went. In the happy comfort of retrospect, I guess the vertical fin just blocked off enough of the tail rotor's inflow (or something) that the T/R just couldn't hack it at the high power-setting.
The rotation was so abrupt that I thought I had a tail rotor failure. Alternatively, had I known more (but not enough!) I might have assumed that the tail rotor had "stalled" like the wing of an airplane gives up the ghost. Having all of 1,000 big hours, I was bamboozled and pretty much just along for the ride, thrown sideways against the front seat passenger who was likewise thrown sideways against his door. I uttered an expletive phrase that began, "What the...?" Luckily we had plenty of altitude. I do remember lowering the pitch and banking into the spin. We did fly out of it. I thought to myself, "Don't do THAT again!" And I did not.
Sometime later I read the FAA Advisory Circular on the subject. I was surprised to learn that the tail rotor is *not* stalled during the event, and is still producing thrust. The recommendation was to go to FULL left pedal and hold it there. In my own experience, I do not remember doing that. I vowed to not make that mistake again. And I wonder how many "LTE" accidents occur because the hapless "low-time" pilots, like me, failed to stuff the pedal all the way in quickly enough because they were already low, down near the trees, concentrating on something outside the aircraft, something other than the theory of tail rotor inflow versus huge, blocking vertical fins.
So now when I'm operating in situations that demand high power and a wind off the tail, I'm very, very careful about yaw rates. And now I know what to expect if it snaps again.
Do I believe that the 206 tail rotor "stops working" and/or will spin "out of control" in an LTE event? No. It will spin until the pinhead at the controls (me) pushes in and holds the left pedal and perhaps reduces the torque if possible until a) the weathervaning tendency takes hold or b) the tail rotor gets a good "bite" again.
I laugh at that LTE Wind Chart that Bell puts out. According to it, you're susceptible to LTE with wind from virtually every quadrant except a tiny slice of area to the front right. Silly me! I didn't realize you could get into LTE with wind off the left. But Bell wants to have ALL their bases covered, I guess. And truthfully, as I've admitted here before, all of my helicopter flight time is at relatively low altitudes - below 5,000 feet. So I cannot comment on the 206's tail rotor performance at altitude. But down here in the thick air, I do chuckle when flying in a 206 with newbies who seem preoccupied with LTE when making an approach with a wind from the left-front. "Heh, go fly a B-model offshore," I tell them. "Offshore, where you'll be making max-gross landings to confined-area drilling rigs and the wind will be nowhere NEAR that little slice of clear area on the LTE chart." You'll be flat-out amazed that 206's aren't spinning out of the sky all over the place and falling into the water.
I kind of agree with headsethair. The phenomenons we ascribe to the main rotor as VRS or SWP can be excited while operating inside the flight envelope. Military OH-58 accidents aside, it seems to me that the number of civilian accidents attributable to "LTE" are small. I'll accept that, like the main rotor, the tail rotor has some performance limitations too, even considering N. Lappos' contention that this is unacceptable. (Listen to Nick screech on this subject long enough, and you get the impression he wishes that the FAA would just ground the Bell 206, that unsafe P.O.S. and be done with it.) You know, all things considered, for a helicopter that was designed over forty years ago, I believe the JetRanger ain't half bad.
Your mileage may vary
Afternoon Edit: What was I, sleeping? Happened to crack open a 206 AFM today and what to my wondering eyes should appear, but the Critical Wind Azimuth Chart! The "avoid area" is much smaller than my memory lead me to believe: only extending from 050 degrees (relative to the nose) then back around to about 210 degrees. For some reason, I thought it encompassed the entire left side of the a/c. Ah, the failing memory of old age.
Apologies.
Last edited by PPRUNE FAN#1; 6th Oct 2005 at 18:30.
Flingwing, I do see your point, and know it is difficult to translate official stuff into student speak to get the message across, however, I think perhaps you are slightly missing the point: LTE is not the correct term for all T/R problems. LTE relates to a specific aerodynamic event that has a history of association with B206 models.
Your personal definition of the main rotor producing too much torque for the T/R to counter is, unfortunately, wrong. And it concerns me you are teaching another generation of pilots that definition of LTE. Look how you have even confused poor old PPRUNE Fan. lol.
Look back over the thread (you too tc) for the simplified LTE v LTA v LTC definitions. All different. All require different reactions to rectify, and all are derived from "official" theory. That is what you can teach to your students.
BTW PFan, a stalled aerofoil still produces lift, and it may be because you have never hit the left pedal stop that you got to experience LTE. So did I for the same reason.
Your personal definition of the main rotor producing too much torque for the T/R to counter is, unfortunately, wrong. And it concerns me you are teaching another generation of pilots that definition of LTE. Look how you have even confused poor old PPRUNE Fan. lol.
Look back over the thread (you too tc) for the simplified LTE v LTA v LTC definitions. All different. All require different reactions to rectify, and all are derived from "official" theory. That is what you can teach to your students.
BTW PFan, a stalled aerofoil still produces lift, and it may be because you have never hit the left pedal stop that you got to experience LTE. So did I for the same reason.
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The danger area for LTE in the bell 206 is in the sector from approx 240 - 280 degrees relative bearing at wind speeds of 10 to 25kts. This is where the tail rotor can experience vortex ring state. LTA is different as stated above.
helmet fire:
In my LTE event, I got the impression that the tail would have spun around even *if* I was at full pedal. It was that abrupt - bordering on violent. I doubt that even full pedal, had I utilized it, would have had any appreciable effect once the yaw rate got started. But back in those days I was so far behind the aircraft that I could barely keep it in sight on a good visibility day.
spag:
I've met and flown with pilots who've said this very thing, in a very worried tone of voice! It's humorous, in a way. Those of us who've got lots of 206 time know...we KNOW that 240 to 280 is not the dangerous place for the wind. In fact, wind off the left assists by providing increased weathervaning stability. Anyone who gets a 206 to actually spin with the wind at 280 just isn't pushing on the left pedal hard enough and that ain't the fault of the aircraft.
Sure, wind from that quadrant will force your feet to dance on the pedals to keep the nose straight as the downwash from the main rotor impinges on the tail rotor. But that's no big deal. It's when the wind gets behind you in a 206 that you are flirting with disaster, especially if you're down low, over the trees and slow.
It provokes one to wonder: If flown in the Scout role, would an Agusta 109 be having LTE accidents since it's got a similarly large vertical fin? Enqiring minds want to know!
BTW PFan, a stalled aerofoil still produces lift, and it may be because you have never hit the left pedal stop that you got to experience LTE.
spag:
The danger area for LTE in the bell 206 is in the sector from approx 240 - 280 degrees relative bearing at wind speeds of 10 to 25kts. This is where the tail rotor can experience vortex ring state. LTA is different as stated above.
Sure, wind from that quadrant will force your feet to dance on the pedals to keep the nose straight as the downwash from the main rotor impinges on the tail rotor. But that's no big deal. It's when the wind gets behind you in a 206 that you are flirting with disaster, especially if you're down low, over the trees and slow.
It provokes one to wonder: If flown in the Scout role, would an Agusta 109 be having LTE accidents since it's got a similarly large vertical fin? Enqiring minds want to know!
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...it is not possible to get LTE in a Black Hawk, nor in a Lynx, nor in a H-500, nor most helos...
LTE relates to a specific aerodynamic event that has a history of association with B206 models.
LTE relates to a specific aerodynamic event that has a history of association with B206 models.
Should it be possible on AS 350? And how can an experienced driver, after more than xx rotations on the same the day, on the same route, on the nearly same weight, suddenly loss the a/c directional control?
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Two comments:
Use the controls to the fullest. It is not LTE if you don't use the pedal all the way, it is "shy pilot". I have tested helos for 30 years, and hit every stop on every control at one time or another. You must use your machine, not ride in it, if you expect to earn your pay.
greenthumb, you have few facts, and many assumptions here. Without knowing what torque he pulled, and his Nr, you do not know what he did to the machine (he might not either!). OGE, with a sling load literally calls for over pitching as a possible cause. Was the 6th time at higher OAT? Where are the facts, not just the broad circumstances?
Use the controls to the fullest. It is not LTE if you don't use the pedal all the way, it is "shy pilot". I have tested helos for 30 years, and hit every stop on every control at one time or another. You must use your machine, not ride in it, if you expect to earn your pay.
greenthumb, you have few facts, and many assumptions here. Without knowing what torque he pulled, and his Nr, you do not know what he did to the machine (he might not either!). OGE, with a sling load literally calls for over pitching as a possible cause. Was the 6th time at higher OAT? Where are the facts, not just the broad circumstances?
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First off, thanks everyone for your interest and input in this - these discussions are why a lot of my non-flying (or fixing, or ground-schooling) hours are spent on-line!
OK so here's where we are (or I am, anyway):
=================
Nick Lappos:
Most LTE's are due to rotor rpm drooping when too much power is commanded. Lowering the rpm reduces the available tail rotor authority, and is really not LTE, but rather over-pitching, a good British term.
LTE is... <snip> ...how a helicopter can lose control while within its normal envelope. In contrast, if a pilot takes on an excessive crosswind (beyond the flight manual limits) or is he pulls too much torque or operates at too much gross weight or pulls the rotor rpm down below normal, the resulting loss of yaw control is not really LTE, it is LTA.
It is not LTE if you don't use the pedal all the way, it is "shy pilot".
helmet fire:
LTE refers to what is thought to be an ingestion 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".
There is a real difference between LTE and rotor drooped LTA... ...let me assure you, LTE does exist.
======================
So let me make sure I've got this. LTE is when you get a yaw when everything else is OK. It's NOT when M/R torque overcomes T/R thrust - that would be LTA.
So we get LTE because of a disturbance in airflow, then the yaw starts, and only when when we can't stop it with full pedal it's LTA?
(BTW, I'm not sure when the topic of loss of thrust (as in something breaks) or loss of pitch control (stuck pedal/busted linkage) got mixed into this - certainly it wasn't in anything I posted. I realize that you would react differently if the T/R stopped turning or the pedals no longer controlled T/R pitch.)
Bottom line, I am actually concerned enough to be asking for clarity from you guys on a few things:
1) Is the basic FAA description of LTE correct - as a definition of LTE ("LTE is a critical low-speed aerodynamic flight characteristic which can result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, can result in the loss of aircraft control.")? IOW, the aircraft yaws while in a "normal" flight envelope, and if the pilot doesn't respond properly, the yaw can go out of control.
2) LTA is when full (power) pedal won't arrest a yaw? This could be due to any number of reasons, including low RPM, high density altitude, high gross weight, big crosswind, OR an undersized/underpowered tail rotor.
3) For LTE to become an emergency, does it have to become LTA? I would think so, or else you would arrest the yaw, at which point you are no longer experiencing LTE or LTA. If the Bell issue is due to an undersized/underpowered T/R, I would think it would also be more susceptable to LTA, which is the real emergency.
4) If 1) is true, are you then more susceptable to LTE (or can non-Bell helicopters become susceptable to LTE) if operating near or beyond the edges of the flight envelope as described in 2? Or is it simply that ALL helicopters become more susceptable to LTA, but Bell helicopters have the additional gremlin of LTE which increases the chances of LTA?
5) Since the FAA doesn't single out make/model, is it fair to allow a student to go to a checkride with the following: all helicopters are susceptable to LTA if you push things enough. The "phenomenom" of LTE is the susceptability of a helicopter to enter a uncommanded rapid yaw while still in a "normal" envelope - while all helicopters are susceptable to uncommanded yaw, certain makes/models will yaw earlier, faster and further than others. Certain makes/models can also experience LTA while in a normal envelope. If you experience a rapid uncommanded yaw which then leads you into LTA, the amount of trouble you are in is inversely related to your altitude, but it is trouble no matter what.
OK so here's where we are (or I am, anyway):
=================
Nick Lappos:
Most LTE's are due to rotor rpm drooping when too much power is commanded. Lowering the rpm reduces the available tail rotor authority, and is really not LTE, but rather over-pitching, a good British term.
LTE is... <snip> ...how a helicopter can lose control while within its normal envelope. In contrast, if a pilot takes on an excessive crosswind (beyond the flight manual limits) or is he pulls too much torque or operates at too much gross weight or pulls the rotor rpm down below normal, the resulting loss of yaw control is not really LTE, it is LTA.
It is not LTE if you don't use the pedal all the way, it is "shy pilot".
helmet fire:
LTE refers to what is thought to be an ingestion 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".
There is a real difference between LTE and rotor drooped LTA... ...let me assure you, LTE does exist.
======================
So let me make sure I've got this. LTE is when you get a yaw when everything else is OK. It's NOT when M/R torque overcomes T/R thrust - that would be LTA.
So we get LTE because of a disturbance in airflow, then the yaw starts, and only when when we can't stop it with full pedal it's LTA?
(BTW, I'm not sure when the topic of loss of thrust (as in something breaks) or loss of pitch control (stuck pedal/busted linkage) got mixed into this - certainly it wasn't in anything I posted. I realize that you would react differently if the T/R stopped turning or the pedals no longer controlled T/R pitch.)
Bottom line, I am actually concerned enough to be asking for clarity from you guys on a few things:
1) Is the basic FAA description of LTE correct - as a definition of LTE ("LTE is a critical low-speed aerodynamic flight characteristic which can result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, can result in the loss of aircraft control.")? IOW, the aircraft yaws while in a "normal" flight envelope, and if the pilot doesn't respond properly, the yaw can go out of control.
2) LTA is when full (power) pedal won't arrest a yaw? This could be due to any number of reasons, including low RPM, high density altitude, high gross weight, big crosswind, OR an undersized/underpowered tail rotor.
3) For LTE to become an emergency, does it have to become LTA? I would think so, or else you would arrest the yaw, at which point you are no longer experiencing LTE or LTA. If the Bell issue is due to an undersized/underpowered T/R, I would think it would also be more susceptable to LTA, which is the real emergency.
4) If 1) is true, are you then more susceptable to LTE (or can non-Bell helicopters become susceptable to LTE) if operating near or beyond the edges of the flight envelope as described in 2? Or is it simply that ALL helicopters become more susceptable to LTA, but Bell helicopters have the additional gremlin of LTE which increases the chances of LTA?
5) Since the FAA doesn't single out make/model, is it fair to allow a student to go to a checkride with the following: all helicopters are susceptable to LTA if you push things enough. The "phenomenom" of LTE is the susceptability of a helicopter to enter a uncommanded rapid yaw while still in a "normal" envelope - while all helicopters are susceptable to uncommanded yaw, certain makes/models will yaw earlier, faster and further than others. Certain makes/models can also experience LTA while in a normal envelope. If you experience a rapid uncommanded yaw which then leads you into LTA, the amount of trouble you are in is inversely related to your altitude, but it is trouble no matter what.
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Some explanation of how LTE occurs:
1) Every tail rotor has minor variations in its thrust output, based on the precise flow it is experiencing. If you put some turbulence into a rotor, the thrust will drop a bit. I have experienced this thrust change in every helicopter I have flown.
2) When you are operating at peak thrust, (max pedal angle) there is no more yaw control available. Should any turbulent flow enter the tail rotor, there is no more thrust available.
3) Main rotor torque is big, tail rotor thrust is small. A 5% increase in main torque can completely swamp a tail rotor that is at maximum thrust, and therefore at its control margin. A 2% increase in main torque beyond maximum yaw control will look like a wild ride, with the tail whipping around.
4) Most helicopters have excess tail rotor thrust, so that small thrust changes do not unleash the beast. A tail rotor that is very marginal will experience the same slight loss of thrust, but is more likely to experience LTE because it is riding on the edge and has little to help recover.
5) Sometimes the main rotor wake slips into the tail rotor, it can be heard and felt, and it can cause a 5% loss in tail thrust. That is why the azimuth diagram exists on the Advisory Circular, to help show where this occurs.
6) If the helo has little extra tail rotor thrust and collective is misused slightly at the bottom of an approach, so that the torque is somewhat above hover torque at the bottom, LTE can occur. The best way to make LTE occur is to make the approach too fast, so that you make a quick stop at the bottom, and suck in a lot of collective to stop the descent. That is precisely where most LTE's occur.
LTE occurs when a marginal helicopter runs out of yaw control while inside its envelope, LTA occurs when a proper helicopter is pushed outside its envelope. Both have run out of yaw control, but the LTE bird is in far worse shape, because there is nowhere to fix it. The LTA bird asks that we lower the collective, stop pulling too much power (stop climbing, usually) reduce the engine power, and all gets right.
1) Every tail rotor has minor variations in its thrust output, based on the precise flow it is experiencing. If you put some turbulence into a rotor, the thrust will drop a bit. I have experienced this thrust change in every helicopter I have flown.
2) When you are operating at peak thrust, (max pedal angle) there is no more yaw control available. Should any turbulent flow enter the tail rotor, there is no more thrust available.
3) Main rotor torque is big, tail rotor thrust is small. A 5% increase in main torque can completely swamp a tail rotor that is at maximum thrust, and therefore at its control margin. A 2% increase in main torque beyond maximum yaw control will look like a wild ride, with the tail whipping around.
4) Most helicopters have excess tail rotor thrust, so that small thrust changes do not unleash the beast. A tail rotor that is very marginal will experience the same slight loss of thrust, but is more likely to experience LTE because it is riding on the edge and has little to help recover.
5) Sometimes the main rotor wake slips into the tail rotor, it can be heard and felt, and it can cause a 5% loss in tail thrust. That is why the azimuth diagram exists on the Advisory Circular, to help show where this occurs.
6) If the helo has little extra tail rotor thrust and collective is misused slightly at the bottom of an approach, so that the torque is somewhat above hover torque at the bottom, LTE can occur. The best way to make LTE occur is to make the approach too fast, so that you make a quick stop at the bottom, and suck in a lot of collective to stop the descent. That is precisely where most LTE's occur.
LTE occurs when a marginal helicopter runs out of yaw control while inside its envelope, LTA occurs when a proper helicopter is pushed outside its envelope. Both have run out of yaw control, but the LTE bird is in far worse shape, because there is nowhere to fix it. The LTA bird asks that we lower the collective, stop pulling too much power (stop climbing, usually) reduce the engine power, and all gets right.
Last edited by NickLappos; 7th Oct 2005 at 19:21.