Videos of LTE?
 

Not wishing to re-open the debate. Just wondering if anyone has access to any videos of helicopters undergoing LTE?
Any model will do.

Here is one great video of waterboming Skycrane doing 360 just right before it dropped it's load taken from the ground under it. It was posted here before link

great stuff:ok:

That video is a fine illustration of what happens when you pull too much torque, reduce your rotor rpm and then lose yaw control. It is not LTE in any strict sense.

Shawn,

I even star in THIS ONE , I was flying the subject helicopter right before the camera ship started spinning. If you need it in higher resolution I can probably find the original.

Notice how they began spinning a lot higher than that 35 story building and they ended up almost all the way down. The spinning ship was a Bell 203 L3 which at this altitude when heavy has enough power to hover OGE but not enough tail rotor power to keep the helicopter from spinning.

By the way I got your book a couple of weeks ago and I haven't put it down since! Muuuuy Bueno.

Close Call.

The link does not work for me either - the other JPEGS on that directory though are simply stunning, some of the best heli pics i've ever seen - are they all on the Rotorheads around the world thread ?

http://www.helicopterservice.com.au/photos/Dawson/

Blender, what recovery action was taken in your video exactly ? Thanks.

PP,

The movie is in Quicktime format: do you have QT installed? If not, it won't download and display.

The directory is of photos taken by Neville Dawson, I hosted them for him when he didn't have his own ftp site, and left them as a courtesy to previous links that he set up. His current iteration is Ned-Air2Air (well, for the time being ;) :D :ok: )

So is it more correctly to say, the Air Crane was"out of left pedal"? not LTE?, but isn't correct though that the tail rotor was ineffective when it's rpm dropped, and the ship Lost Tailrotor Effectiveness :confused:

RR,

There's a difference between LTE (Loss of Tail Rotor Effectiveness - in it's simplist terms, the TR is not 'big' or effective enough to provide control within the entirety of the flight envelope) and LTA (Loss of Tail Rotor Authority - TR doesn't have enough RPM to maintain control due to mechanical problem or the pilot 'overcooking' things).

This has been covered in depth in previous threads.

The B206A was particularly prone to LTE whilst most helis can be subjected to LTA if the pilot allows the RRPM to droop too far.

Or at least this is my understanding of the situation.


HTH,

B73

Well put Bravo. Pretty much like the other issue of Vortex Ring State and Settling with Power... :}

Peachpilot. If you are already qualified you should be able to answer that one yourself. What do you think you would do instinctively? Foward airspeed is the key there...

Great Vid BP, I thought of you immediately after reading the thread title. I have your vid on my laptop and show it a lot in explaining the JR's foibles.

Concur with the Bravo.

Hi Shaun

No films of LTE but take a look at these other films.

http://www.rapp.org/archives/2004/09..._crash_videos/

This crash happened few days ago in Madrid.

No investigation report yet.

Thanks God, no fatalities.




Exterior View

Interior View

cfr,
That set of vids is really impressive! But in fairness, listen to the sound track carefully, you can hear the pilot exceed torque limits, pull the rotor rpm down very low, and then run out of pedal control.

This, like the Sky Crane, is actually "over pitching" and not LTE.

In LTE, and otherwise normal situation goes to worms purely because the tail rotor cannot deliver the control like Blenderpilot's film. In overpitching, the cause is the rpm loss, that symptom is the yaw control problem.

In Blenderpilot's case, he had lots of power, enough to swamp the tail rotor while at full rpm.

Could someone please explain what exactly happened?

The Machine was overgrossed, and therefore the pilot was pulling too much collective to get over the tribune.

Why did the machine start to spin?

hotzenplotz,

The aircraft was probably at or slightly above the OGE gross weight, which means that he couldn't takeoff with the engine power he had, at least not with the steep departure the scene required. When he got out of ground effect in the climb, the power to keep his departure going was more than the engine could provide, so the rotor decayed quite a bit (note the drooping sound especially in the interior video). This means the main and tail rotor are reducing rpm rapidly.

When the rpm goes down, the tail rotor produces less thrust, and more pedal is needed. The thrust is proportional to the square of the rpm, so even a 5% loss of rpm will yield a 10% loss of thrust; .95 x .95 = .9025 This means that if he is near tail rotor limits before the rotor rpm droop, he will run out of pedal during the droop. That is when the spin starts.

The scenario is doubly bad. When the rpm starts down, the torque goes up - even though the power is constant, because torque times rpm is power. Thus, reducing the rpm at constant engine power makes the main torque go up, which needs even more anti-torque! This means the tail rotor margin is being hurt by the torque rise, too, so the spin starts all the sooner!

It looks like the pilot reduced collective to recover rpm and stop the spin, and that caused the crash. It MIGHT have been better to let the aircraft spin slowly and hold altitude and accelerate, but that would take some pretty handy piloting (I did that once in a Cobra, it was like doing a ballet while my heart rate was 120+). Once translational speed is gained, the collective can be reduced and the situation recovered.

This is really not LTE because the spin is caused by a gross pilot error where the rpm is pulled down too low, because the aircraft is in a situation with too little power (and too little pilot planning.)

Thanks a lot for this detailed explanation! :ok:

On that spanish video, it would be interesting to say that on most Bell light helicopters in order to droop the RPM you REALLY have to exceed limits, for example on the 206 Jet Ranger, you have to probably reach at least 120% Torque before the RPM start to droop.

We had a pilot who hit a wire and had a "fight" with the wire that eventually broke and they flew away. The L model 206 had an Intellistart system that records all filght parameters when "events" take place, this guy had reached 130% torque and held it there for a while until the wire broke, if you look a the Intellistart graphs you can see that the NR had only drooped down to about 96 percent at first then started to recover to 100% even when he was appying almost 125% torque.

That guy in the video must have surely been at the redline or above when he began to transition to forward flight, it would have been wise to stop there and put it back down, he elected to continue and of course when he pushed the cyclic the helicopter tended to "dish out" and having the edge of the building in front of him he must have felt the urge to pull even more power with the known consequences. Believe it or not there are a lot of idiot pilots out there that make intentional use of the non-intentional torque limits during their day to day operations.

But of course maybe he just had a bad governor send one of his engines to idle or contaminated fuel or an air leak or a slipping freewheel, or . . . . . So many things could have happened.

One thing is for sure, on the video taken from the inside you can clearly hear the RPM start to droop as he transitions forward and towards the edge of the building, AND HE CONTINUES FORWARD, in my case if I have heard such a disconcerting noise at that point my inmediate reaction would have been to begin a silght backwards movement and make a right pedal turn back to the dirt, just from listening to the thing it was clear that he wasn't going to go far!

peachpilot,
Recovery technique? I think he just fought it all the way down, he made so many turns that I am sure that I am sure he didn't do what he should have done from the beginning, lower collective and push the nose down. I have flown the very same helicopter that spun, and I have had that nasty tail rotor bite me on several occasions, but when I knew that this could happen I was prepared, I mean that if I knew that I was heavy and this could happen, I would watch my wind and fly smoothly, then if I had to do anything that could cause LTE I didn't with plenty of room beneath me, but let me tell you, when the TR bites it does so quickly and you have to be ready to react in the correct sequence of movements with out delay, in this helicopter after the TR reaches its capability, you feel a quick jerk to the right which if you react properly by lowering collective and giving the cyclic a slight push should never go past 15 degrees, sure cameramen don't like it and get upset, but I don't even bother telling them what they just missed.

Blender pilot:
Thanks for the video and excellent discussion. and I hope you enjoy the jokes in the book as well.

Can we all agree that the situation described by Nick is as a result of overpitching and not LTA. Loss of Tail rotor Authority is generally taken to mean a reduction in the travel available in the TR control system due to damage to cables, rods, bellcranks etc or problems with ASE/ AFCS actuators giving a similar reduction in control authority. This is not the same as loss of TR control which would be total - LTA would be partial.

Loss of TR - it drops off or the driveshaft snaps

Loss of TR control - the cable/rod/pedal breaks

Loss of TR authority - blockage or damage or stab malfunction

Loss of TR effectiveness - you are flying a B206

Overpitching - asking too much of the engine and drooping the Nr, thus slowing the TR and reducing its thrust.

Does this seem fair?

Why don't we put to bed the expression Loss of tail rotor Effectiveness?
It stands to reason if the Tail rotor hasn't the grunt due to ancient design then there has been no loss of anything because it never had it to begin with!

Inneffective Tail Rotor would be a more correct term

W

We´ll NO, NO and again NO!

Read Blender pilot´s post carefully. He and I in another post have been trying to explain to you that a 206 with fully functioning engines will not "drop" Nr easily!

Just because Nick is convinced that everything bad in the world is beacuse of LTE in the 206 series then it does not mean that he´s always right.

The 206 series have a pretty powerful engine for it´s transmission (exception 206L ´straight´). The transmission rating in a L model is 500 hp and the C30 engine can produce 650 hp. The ´TwinRanger´ has two C20B engines 420 hp each so the pilot has potentially 840 hp available at ISA.

Even if you overtorque the transmission by 120-130% the rotor RPM will NOT decay because the engines are a long way from reaching their power limit.

On the other hand if he had some sort of power failure one could argue that he did overpitch the rotor for the power available and thus loose rpm both to the tail rotor and main rotor. But what was the guy to do? He is probably like me, does not have superhuman fast reflexes and able to analyze what the problem was in a split second and put the aircraft back in the ring! Sometimes it´s much easier to watch the video and after the incident sit back and tell the pilot what he did wrong.

But in my opinion the incident did not happen due to LTE in a fully functioning aircraft as a result of RPM decay!

Well this is starting to get interresting battle of opinions here :O

and for me, quite educational and very amusing discussion:ok:

where would we wannabe's be without you wise guys:E

I work for a company that has 2 L4T's. One is fitted with the "high-altitude" tail-rotor, and the other with the standard 206L type. The "high-Altitude" tail-rotor sucks alot of power and you must be on the ball as it is very easy to over Tq. From the guys here who have lots of experience on this type, Nr decay when too much power is pulled is not an issue in there experience. LTA is however. Regardless of the take-off profile, which was never ideal, he could have had Nr decay due to something else, ie not setting N2 correctly.

AEsir - if you read the posts, including mine, correctly - I and others have differentiated between low Nr as a result of overpitching reducing TR thrust and LTE (most cited as a problem with the 206) because the TR is not big enough for the job in the first place.

Big Mike - running out of pedal because you get to the end stops is a design problem or you are operating outside the Flight Manual - having an unexpected reduction in pedal travel due to blockage from a foreign object or an autopilot malfunction is LTA, they are different.

How about LTE = Lack of tail rotor effectiveness :}

Flingwing - I think Nick would certainly agree with you there.

Having watched the Spanish crash, low Nr certainly seems to be the pilots problem but whether it was due to a power loss or simply asking too much of the aircraft (hot, 3 pax, confined area needing HOGE performance) is impossible to tell.

If it was due to performance, he could have tried a vertical climb before transitioning so that he was above the level of the bull-ring. The way he transitioned meant that any form of power loss was going to mean a visit to the scenery and that his maximum power requirement was going to occur just before he got ETL - (about the edge of the bull ring).

We are discussing different cases, The Skycrane, The Spanish Light Twin, and the camera ship the is shown in the video spinning straight down for about 700 feet.

In the case of the Skycrane, I do believe it was not LTE, it was an RPM droop that caused the problem

In the case of the Light Twin, I do believe pulled power waaaaaaaay beyond limits and managed to droop the RPM, as impossible as it may seem due to the fact that he must have been pulling an obscene amount of power, as I have mentioned, the NR RPM in a 206 L model will probably stay close to 100% NR up to 120% Torque if you pull collective reasonably smoothy. It is amazing for me how he continued the takeoff when there was a very obvious RPM loss heard. I have caught the NR trim with my glove and trimmed it down accidentally in flight, just 2%, and I realized how quickly you react to any sound that shows NR drop, in a second I had lowered collective and scanned everything to see what was going on. I have no idea how he elected to continue the takeoff with such an obvious NR droop. Pilot should turn their ears into a NR tachometer and be able to detect any change.

Then in the case of the video of the spinning camera ship, I do believe it was LTE, the engine had enough power to turn the Main and Tail rotors at their designated speeds, and the pilot applied full control inputs to the pedals but the aircraft still turned because the Tail Rotor was insufficiently effective to counter torque under the circumstances.

(Please forgive my spelling mistakes, my main language is Spanish)

There are - and I think people do not realize this - two separate types of "206 LTE." In the first, the t/r simply does not have enough oomph to counter the massive torque to the main rotor. A right yaw rate is allowed to develop which quickly escalates into a worsening situation whereby 'round and 'round you go with your left Gucci loafer pinned firmly to the pedal stop.

But there is another form of LTE that many a OH-58 pilot will describe for you. And that is being at low speed with perhaps a tailwind component and suddenly finding yourself spinning like a top even though the left pedal is not at the limit.

206's have big vertical fins that blank off much of the inflow to the tail rotor. Now put the wind back there at 170 degrees or so, which really aggravates the weathervaning tendency and makes the nose of the ship want to yaw to the right. Throw in some good old-fashioned t/r VRS and you've got a recipe for a nice little surprise. The "break" is so sharp that you might be forgiven for thinking that the t/r has just stalled like the wing of a plank. Happened to me in a 206L-1, and that is what I thought. It felt like a tail rotor failure.

However, Bell's attitude is that the tail rotor is not in fact "stalled" and is still producing thrust - just not enough of it at the moment. Their suggestion is to push and hold full left pedal, reduce power/torque, increase airspeed and "fly out of it." To us old-timers, this is "classic" LTE. Most of us don't have much experience with other types of LTE (especially when the wind is off our left) because we're good about not letting yaw rates develop in the first place. But that LTE-when-the-wind-is-up-your-bum...oh boy, that can bite without warning!

pprunefan #1,

thanks for relaying how Bell would explain this, but I am not buying it. That explanation is interesting for two reasons:

1) If the aircraft spins around and the pilot is not using full pedal, we call that "pilot error" because that is why we put the controls in the aircraft. To call it a type of LTE is silly, because you must use the controls for them to work, at least until we invent FBH (Fly By Hope, where the pilot's Hopes are turned into control inputs.)

2) Absent obvious power/rpm abuse, if the control is on the stops and the aircraft still spins the opposite way, we call that a design problem, because again those controls are simply supposed to work. It is a testament to Bell's ability to sell this as "possible with all single rotor helicopters" and "due to pilot actions" and the like instead of placing the blame squarely where it belongs. The US Military knows that, they insist that it be fixed on new models, and they had a whole new tail rotor put on the OH-58D because it failed their tests and had "LTE" until corrected, in spite of Bell's insistence that the TR was fine and dandy.

When people blame the manufacturer for the problem, and stop buying the bad actors, the manufacturer will stop making them and the problem goes away. Later today I will post the accident study I did several years ago that shows how rare "LTE" is unless you fly older Bells.

Crab, "running out of pedal because you get to the end stops is a design problem or you are operating outside the Flight Manual" ? Who said anything about running out of pedal? and then you suggest we are operating outside the Flight Manual? Do you know anything at all about this type or are you just guessing? The people I have flown with here are some of the most professional pilots I have seen, and have been operating this type for quite a while. It's pretty arrogant to suggest they are operating outside the limits.

I don't fly this machine other than a couple of hours in it, and it does have it's little "quirks" The other pilots here have alot of time in them and after showing them the 2 videos again they concur with BP, you could droop the Nr by pulling in too much power, but boy it would have to be a massive over Tq.

Two points I see in the vid that I think worthy of note

1/ That ship is heavy and has a fwd CofG , note the way it is peeled off the deck yawing to the right as it does so but also lifting from the rear of the skids first.

From the inside vid we have two pax in the middle seats plus two maybe three in the rear. Not clear if there is anyone in the front left. That poor lady does not look comfortable BTW.

2/ From the soundtrack amazed that the engines appear to be happily running whilst the wreckage is on it's ear, although I'd imagine he would have two oil PX captions (amongst others) on his CWP.

W

Big Mike - I am not suggesting for a moment that you or any of your crews are operating outside the RFM - you used the term LTA when I think you meant LTE.

My point, if you accept my definition of LTA, is that you only reach the maximum travel of yaw pedal on a well designed helicopter in extreme conditions, one of which is operating outside the limits set by the manufacturer. LTE on the other hand is waiting to bite you if the manufacturer hasn't made the TR powerful enough (insufficient control margins) within the normal flight envelope.

The sensitivity to a downwind component (PF1's post) is something you can experience in many helicopters especially in turbulent conditions like mountain flying and comes down to an awareness of relative wind, lever position, airspeed etc and if this bites you it is usually because you lacked one of the above and failed to anticipate/feel the aircraft's desire to yaw. If you compound this by flying an aircraft that has poor yaw control margins in the first place then you get a lot of pilots being spun round when they didn't expect it. The problem with the prescribed recovery (ie full pedal and hold it) is that few pilots are willing to do it because it feels so different to the norm that 'it can't be right' and they let the rate of yaw increase.

Nick Lappos:You know, Nick, for a guy who disparages one particular helicopter model so much, you obviously have very little if any time in a 206. (Then again, I've never had cancer, but I know it's bad.) When a 206 pilot encounters what I call "classic" LTE, no amount of pedal-jabbing will immediately stop the yaw. It literally spins like a t/r failure until that prop in the back can get a "bite" again. If you wish to call this "pilot error" that is, of course your choice.

Conversely, if the pilot has his left pedal depressed all the way and persists in whatever he's trying to accomplish, he should be rapped soundly on the wrists and be made aware that he is now being paid as a test pilot. If he then allows the nose to yaw without an immediate reduction in torque, and further allows the yaw to wind up into a spin, then that is indeed pilot error.

Yes, the early 206 tail rotors were probably not as powerful as they "should" have been. But it's that dang fin- extending both above and below the t/r hub. It just blocks too much of the inflow, I guess, especially when the t/r needs it the most. Not surprising, is it, that Agusta drastically reduced the size of their fin and even Sikorsky "trimmed" the fin on the vaunted S-76B? Or was it because Big S decided that the '76 really didn't need all the "extra," superfluous, more-than-necessary yaw stability provided by that big, fat fin?

So PF1, we come to the conclusion that the 206 was a very poorly designed aircraft since it had such poor directional stability (both in powered flight and in auto) that it needed a big fin top and bottom that then blanked the TR in certain wind conditions. What were the FAA thinking when they certified it? Or is it just that the TR is too small?

pprunefan#1,

Don't blame the fin, blame the aircraft! The aircraft has to be controlled, not just part of it ("The tail rotor is big enough, but the fin robs power, don't blame the tail rotor....")

As far as how and why all this is done, I was the pilot who trimmed the fin on the S-76B and also on the A, and I know this stuff a little!

Regarding the spinning in your first case, I assumed when you said the pilot doesn't use full pedal, that you were advocating that he left some control unused. Now you are saying that there really is pedal travel but no more control. Which is it? If he leaves control unused and loses control, its his fault. If the yaw has no more power, and the aircraft spins, it is the aircraft's fault.

I think you have all kinds of interesting issues spinning in your head but one I really disagree with is simple - if your helicopter is inside its envelope and it goes out of control, do not call it pilot error, call it crappy helicopter. To make excuses for poor helicopters is foolish in any case, unless you want to lose your job and your life, or unless you think blenderpilot and I are stupid, since both of us have more time on the pedal stops that we care to admit.

As an IP on Cobras which are notorious for their LTE, and with at least 20 LTE events under my belt, I can assure you crappy helicopters will bite you, and making excuses for them is a good way to perpetuate their existance.

Good Lord, Nick, are you this obtuse and arrogant in real life, or just online? Or is it that you're just daft? Hard or reading? Your fixed-wing job evidently does not take up much of your time, considering how much of it you spend trolling this board. Do your bosses know? Or is it that they give you so little to do?

In my experience...listen closely...IN MY EXPERIENCE, when "classic" 206 LTE bites it does so without warning. The ship suddenly swaps ends. No pilot I know (including me, and I'm pretty damn good, but maybe you're that quick, Mr. Hero Test Pilot) can jab the pedal in quickly enough to stop the turn. It goes around. How far will depend on how quickly you do a couple of things, including stuffing in the rest of the pedal and reducing the collective. And this is what "got" all those Scout pilots back before Bell came out and "explained" LTE to us and made their problem everyone's problem.

Is this an aircraft problem? Yes! Is it a fatal flaw? Obviously not, as the 206 made it through CAR 6 certification and the FAA has not since seen to revoke it's Airworthiness Certificate (much to your dismay, I'm sure) or even look further into it like they did the MU-2 or Piper Malibu. As with AVRS in a tiltrotor, education and training can alleviate this handling "peculiarity." I.E. "Don't fly with the left pedal fully depressed unless you're an moron," and "Don't hover hover at high power settings with the wind up your butt."

Now as to your other point, personally, I am a professional pilot and whether in fixed-wing or helicopters, I do not continue a maneuvre with any control on the stops unless there is a very good reason (like someone is shooting at me). If you and Mr. Blender feel that this is a safe way to conduct flight operations, more power to ya! (More t/r power, that is.) I have reached control stop limits in various aircraft and I do not like it. Then again, I'm no Hero Test Pilot and I'm not one of these "anything-to-get-the-mission-done" guys.

You want a ship with a weak tail rotor? Ever fly an early OH-6? Or maybe "pre-flopped" Enstrom? Good grief! But we learnt to fly them within their (meager) limits, and didn't blame the aircraft's design or the mothers of it's designers when we got ourselves into a crash situation because we were such a dumbass.

'if your helicopter is inside its envelope and it goes out of control, do not call it pilot error, call it crappy helicopter.'

... or maybe the flight envelope has not been carefully designed.

ATN

pprune fan #1,
You are entitled to your opinion, but not the silly personal attacks. You say this fine helicopter has bitten you several times (your vast experience says so) and that when it does no pilot on earth can see it coming or correct it. But the helicopter is just fine thank you.

If you actually read and believe what you posted, you must have had a few beers today. Sober up read what you wrote later on. I hope you have NOTHING to do with the safety operations of the poor fools who pay you to fly.

As far as your opinion of me, it really lands right where your opinion of ****ty helicopters is, in the dumpster.


AESIR,
I just found your post about the probability of power loss, and you are quite right it is a possibility. The sounds and behavior of the aircraft don't seem to support it very much, but the investigators should first run there, because pilot error should only be wheeled out when the airplane is found to be fully healthy. I would expect the aircraft to lurch a bit, settle vertically and even yaw left at the power loss, none of that seems apparent. Nonetheless, it is quite possible. Even if he perhaps had an engine power problem, he overpitched, lost control and spun because of the rpm loss, and landed hard. Frankly, if it was an engne power loss, he did a fine job, spin or no spin. If there was no power loss, he is one sorry guy.

PF#1

You have never really had LTE have you?

"Jabbing" the pedal will not stop it, that's why it's called LTE in the first place, we are not talking about slow reflex pilots who use pedals late. LTE is all about using the pedals and them not working, maybe that is where you are confused!?

May I suggest that the accident at Madrid was instigated by "recirculation" as the aircraft passed close to the concave wall and parapet thus leading to overpitching etc.?!!

An aircraft does not have to be overweight for "recirculation" to occur.

Glad to see that no one appeared the worse for wear after their ordeal.