AS350 Astar/Squirrel
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.
Join Date: Apr 2002
Location: UK
Posts: 593
Likes: 0
Received 0 Likes
on
0 Posts
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 ?
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
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.
Join Date: Jul 2002
Location: Denver, CO and the GOM
Age: 63
Posts: 515
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
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.
Join Date: Nov 2001
Location: Australia
Posts: 32
Likes: 0
Received 0 Likes
on
0 Posts
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!
Join Date: Mar 2003
Location: JAA land
Posts: 32
Likes: 0
Received 0 Likes
on
0 Posts
...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?
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
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?
Join Date: Jul 2002
Location: Denver, CO and the GOM
Age: 63
Posts: 515
Likes: 0
Received 0 Likes
on
0 Posts
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.
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
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.
Join Date: Jun 1999
Location: Norwich, CT USA
Posts: 146
Likes: 0
Received 0 Likes
on
0 Posts
Boy this one has become a bit of a contest. The 206 has some things about it that you just need to be aware of, one of the things that has kept me out of trouble, is the slow application of collective, no need to hank pitch, also I have found that just use enough power to do the task you need to do, Ie why pull in 100% when you can do it will 89% for example. A lot of this LTR stuff is to much pitch, to fast, the gov can't keep up, you then get a little rotor droop, and well you get the rotors slowing and you still have all that power pulled in, you get a yaw. Every time I got into one, mostly doing power assurance checks, the yaw would stop as soon as I reduced the power a little. Is the TR on the 206 little on the small side, yep, so you fly knowing that. As for the numbers well yea the 206 is going to be in more accidents and such, because there are a lot of them flying around, Bell sold something like 5000+ of them. All in all the 206 is not a bad helicopter, yes it has some quirks, but all and all if you take good care of it, and fly it well with in the limits rather that at the limit stops, and just don't push it. You could spend the next 20 years flying one and never raise a sweat. It also helps to keep the wind on the nose, but that would be true of any helicopter. Now from what I understand the UH-60 dose loose TR effectiveness ever now and again. Of course you have to have it shot off first.
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
BigMike,
I really do not know of any 206III LTE events, perhaps the redesign did help. It could be that it only covered the power/gross weight increases, however.
Please do not misread me on this, I have personally recommended the 206 to at least two folks who became operators, so I have no "agenda" with it. I do believe if you nurse it in the tight spots, it will work. But I am concerned that we decide it represents a good 21st century standard, which is not what I would envision handing to my son.
The situation is so bad that the FAA has approved 412's, 212's and 430's with NO pedal margin, and NO crosswind capability, using a Cat B, 9 passengers or less approval. They undertook this based on the success they had in teaching us to nurse our aircraft, and blame ourselves when our aircraft bit us while in its normal flight envelope. That concept truly concerns me, and is not where we want our industry to go, in the future.
Some lame poster above said I "screached" too much about this, but that is because he hasn't had his helicopter kick his ass, and then have some official with the correct rubber stamp and Advisory Circular tell him it was his fault.
I really do not know of any 206III LTE events, perhaps the redesign did help. It could be that it only covered the power/gross weight increases, however.
Please do not misread me on this, I have personally recommended the 206 to at least two folks who became operators, so I have no "agenda" with it. I do believe if you nurse it in the tight spots, it will work. But I am concerned that we decide it represents a good 21st century standard, which is not what I would envision handing to my son.
The situation is so bad that the FAA has approved 412's, 212's and 430's with NO pedal margin, and NO crosswind capability, using a Cat B, 9 passengers or less approval. They undertook this based on the success they had in teaching us to nurse our aircraft, and blame ourselves when our aircraft bit us while in its normal flight envelope. That concept truly concerns me, and is not where we want our industry to go, in the future.
Some lame poster above said I "screached" too much about this, but that is because he hasn't had his helicopter kick his ass, and then have some official with the correct rubber stamp and Advisory Circular tell him it was his fault.
Join Date: Jul 2002
Location: Denver, CO and the GOM
Age: 63
Posts: 515
Likes: 0
Received 0 Likes
on
0 Posts
To distill:
It's LTE if the helicopter is within its operating envelope, a yaw develops, you run out of pedal and can't stop the yaw.
It's LTA if the helicopter is outside of its operating envelope, a yaw develops, you run out of pedal and can't stop the yaw.
??
Perhaps this is why the FAA has elected to roll it all into the moniker "LTE" - while one is design induced and the other is pilot induced, the results are the same, as is recovery (full pedal, reduce power/torque, get airspeed, fly with the yaw).
It's LTE if the helicopter is within its operating envelope, a yaw develops, you run out of pedal and can't stop the yaw.
It's LTA if the helicopter is outside of its operating envelope, a yaw develops, you run out of pedal and can't stop the yaw.
??
Perhaps this is why the FAA has elected to roll it all into the moniker "LTE" - while one is design induced and the other is pilot induced, the results are the same, as is recovery (full pedal, reduce power/torque, get airspeed, fly with the yaw).
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
the difference is very important:
In a helo prone to LTE, the machine screws you
In a machine experiencing LTA, you screw the machine.
Recovery from LTA involves reducing power (torque) down to normal, thus generally reducing from a climb to level, with ground strike as much less probable. Aircraft that experience LTA almost never crash due to it.
Recovering from LTE involves reducing the power from normal to descent, thus almost always assuring that you and the ground can become one. Aircraft that experience LTE often crash because of it.
that being said, if you find yourself spinning to the right, put in full left pedal, carefuly reduce torque, and try to accelerate out of the mess you are in, no matter if you call it LTA, LTE, MTA or FTA (SASless, tell them what FTA means!)
One thing I learned from this thread: there are pilots out there who would allow their helo to spin out of control without putting in full opposite pedal. For what reason would one allow loss of control without fighting the situation with all the tools at your disposal?
In a helo prone to LTE, the machine screws you
In a machine experiencing LTA, you screw the machine.
Recovery from LTA involves reducing power (torque) down to normal, thus generally reducing from a climb to level, with ground strike as much less probable. Aircraft that experience LTA almost never crash due to it.
Recovering from LTE involves reducing the power from normal to descent, thus almost always assuring that you and the ground can become one. Aircraft that experience LTE often crash because of it.
that being said, if you find yourself spinning to the right, put in full left pedal, carefuly reduce torque, and try to accelerate out of the mess you are in, no matter if you call it LTA, LTE, MTA or FTA (SASless, tell them what FTA means!)
One thing I learned from this thread: there are pilots out there who would allow their helo to spin out of control without putting in full opposite pedal. For what reason would one allow loss of control without fighting the situation with all the tools at your disposal?
Join Date: Jul 2002
Location: mostly in the jungle...
Age: 59
Posts: 502
Received 0 Likes
on
0 Posts
I like Nicks definition about pilots screwing machines and machines screwing pilots!!
Didn't have the privilege to get my hands on a Blackhawk (or any derivative) yet, but I am still hoping!
When I started to fly the 206 I had about 1400 hrs on the Bell-47 and about 2000 on the R-44.
Generally I am slow to get used to a new machine, but after about 35 hrs I started to explore the limits of the machine ( or rather MY limits in the machine!)
It took me about 500 hrs to get to the edge in the R-44.
It took about 5 hrs to find the limits in the 206. Still I liked to fly it, until part of the compressor let go - down it went, it flew again 2 weeks later, but I prefer the EC120 hands down.
Back on track - LTE:
Nick talks about the upper edge (economically) of good TRs.
Let me give you a sample of the lower edge:
I don't know wether it still gets demonstrated, but at my first Robinson Safety Course the instructor would demonstrate
(albeit light wind, half fuel, 2 persons on board) a 1 foot hover at 75% RRPM!! This was not to show how a R-44 still stays aloft when RRPM is 29% below nominal ( R's fly at 104% RRPM), but to demonstrate the TE (Tailrotor Efficiency). He still could do a complete pedal turn either side!
He never demoed it at 70%, but would confess, that it gets hard to control there and he would run out of pedal at times!
The same demo in a R-22 is done at 80% - well it is a little more sensitive!
Now when I loose a little MRRPM a times when external cargo is heavy and Density Altitude is high - LTE is no concern EVER!!
If you can't afford a Sikorsky, go for the Robinson - LTE is NOT in the Robinson Vocabulary!
3top
Didn't have the privilege to get my hands on a Blackhawk (or any derivative) yet, but I am still hoping!
When I started to fly the 206 I had about 1400 hrs on the Bell-47 and about 2000 on the R-44.
Generally I am slow to get used to a new machine, but after about 35 hrs I started to explore the limits of the machine ( or rather MY limits in the machine!)
It took me about 500 hrs to get to the edge in the R-44.
It took about 5 hrs to find the limits in the 206. Still I liked to fly it, until part of the compressor let go - down it went, it flew again 2 weeks later, but I prefer the EC120 hands down.
Back on track - LTE:
Nick talks about the upper edge (economically) of good TRs.
Let me give you a sample of the lower edge:
I don't know wether it still gets demonstrated, but at my first Robinson Safety Course the instructor would demonstrate
(albeit light wind, half fuel, 2 persons on board) a 1 foot hover at 75% RRPM!! This was not to show how a R-44 still stays aloft when RRPM is 29% below nominal ( R's fly at 104% RRPM), but to demonstrate the TE (Tailrotor Efficiency). He still could do a complete pedal turn either side!
He never demoed it at 70%, but would confess, that it gets hard to control there and he would run out of pedal at times!
The same demo in a R-22 is done at 80% - well it is a little more sensitive!
Now when I loose a little MRRPM a times when external cargo is heavy and Density Altitude is high - LTE is no concern EVER!!
If you can't afford a Sikorsky, go for the Robinson - LTE is NOT in the Robinson Vocabulary!
3top
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
good story, 3top!
the maximum rotor thrust drops by the square of the rotor rpm, so that at 70% rotor, the max thrust is about half what it is at 100% (0.70 x0.70 = 0.49).
the maximum rotor thrust drops by the square of the rotor rpm, so that at 70% rotor, the max thrust is about half what it is at 100% (0.70 x0.70 = 0.49).