Robbies and LTE

[eagle5]

There's a new Robinson Safety Notice about UNANTICIPATED YAW. It mentiones that "Tail rotors on Robinson helicopters are designed to have more authority than many other helicopters and are unlikely to experience LTE."

 

From my limited experience I've seen that Robbies do have better tail rotor authority than some others (especially the Schweizer), but it seems rather boasty to claim that they're unlikely to experience LTE?

 

Thoughts?

[iChris]

There's a new Robinson Safety Notice about UNANTICIPATED YAW. It mentiones that "Tail rotors on Robinson helicopters are designed to have more authority than many other helicopters and are unlikely to experience LTE."

 

From my limited experience I've seen that Robbies do have better tail rotor authority than some others (especially the Schweizer), but it seems rather boasty to claim that they're unlikely to experience LTE?

 

Thoughts?

 

Safety Notice SN-42

 

Issued: May 2013

 

UNANTICIPATED YAW

 

A pilot’s failure to apply proper pedal inputs in response to strong or gusty winds during hover or low-speed flight may result in an unanticipated yaw. Some pilots mistakenly attribute this yaw to loss of tail rotor effectiveness (LTE), implying that the tail rotor stalled or was unable to provide adequate thrust. Tail rotors on Robinson helicopters are designed to have more authority than many other helicopters and are unlikely to experience LTE.

 

To avoid unanticipated yaw, pilots should be aware of conditions (a left crosswind, for example) that may require large or rapid pedal inputs. Practicing slow, steady-rate hovering pedal turns will help maintain proficiency in controlling yaw. Hover training with a qualified instructor in varying wind conditions may also be helpful.

 

 

 

No boast, they're just sick of hearing LTE, VRS, or SWP as the blame for pilot error caused accidents

Edited May 21, 2013 by iChris

[zippiesdrainage]

It's certainly better than the LTE you'll experience in the jet ranger. More or less the same rotor diameter as the 44 but the robinson has a significantly larger tail rotor.

Edited May 21, 2013 by zippiesdrainage

[Eric Hunt]

 

It's certainly better than the LTE you'll experience in the jet ranger.

 

And exactly what LTE have you experienced in a B206?? Real LTE, where the pedals are nowhere near the stops, but the tail snaps away.

 

After 7000 hrs on the 206 and a few thousand more on other Bell products, I have never seen anything like "LTE". Sure, I have used up almost all the left pedal available, but always fly away before hitting the stops.

 

The old chestnut of LTE gets trotted out any time somebody stuffs up and runs out of pedal. Go to the other site that sounds like PeaProon, search for comments by Nick Lappos, the chief Sikorsky test pilot (trained on B204, B205, Cobra) and he blows holes in the LTE myth that has been propagated. Bell even hired him a few years ago to fix the things that he had been so critical of.

 

95% of all documented real LTE cases were in the old B206 with the small tail rotor. If any of them are still around, chuck them out. But don't blame a stuff-up on LTE.

[Counterrotate]

I saw a video once of a guy in a 206 who got "LTE" and balled it up on the tarmac. Sure he had a quartering crosswind, but if you watch the video closely, you see the pilots feet frozen on the pedals in a neutral position. He did absolutely NOTHING to stop the yaw! Of course, when the FAA saw the tape, they faulted him. Loss of Tail-rotor Effectiveness my ass. More like Loss of PIlot Effectiveness. I'm not saying LTE isn't real. But usually, it's only a danger when flying in conditions that you shouldn't be flying in anyway. Regarding the R22, if you stick with the recommended wind limitations in the POH, you shouldn't* get LTE. They have tested the aircraft at those wind speeds and found the aircraft to have adequate controllability. If you go beyond that, you are rolling the dice.

 

Stay frosty on those pedals.

[Lindsey]

More like Loss of PIlot Effectiveness.

 

That is a good one. Gonna have to use that with my students. Thanks!

[Spike]

http://www.youtube.com/watch?v=T2ysuir6PnE

[Spike]

[Spike]

[Eric Hunt]

All that is shown on those videos is a heavy aircraft trying to fly without enough pedal AUTHORITY, not LTE. That Longranger on the top of the hill was moving left, then right, the relative wind was changing, but he kept on turning. If it was suffering from the dreaded LTE, once the relative wind shifted, the LTE would stop. Which part of LTE was he having? Tail rotor vortex ring? Vortex shed from main rotor?

 

The crane was coming in downwind (see the trees?) and was heavy. Once he dumped the load he had enough authority back to fly away.

 

But those who have been indoctrinated into believing that LTE causes every flick/spin/die accident will never stop chanting their mantra. LTE...LTE...LTE...and never be to blame.

[ridethisbike]

That first one should have ended up like the third one.... As in flying out of it...

 

Also, this is something I never understood. I've heard plenty of people say "not enough authority blah blah blah." Here's what I see though. It wasn't LTE right? How do you figure? He put his tail in a position that it was no longer effective at its job. LTE. TR spins out of the LTE situation and then there's not enough authority. Got it. But what started the spin? LTE.

 

Point is... just because it was lack of authority after the initial spin, doesn't mean LTE wasn't a factor. I feel like someone of you write off LTE so rapidly that if you were writing the books, it would never get a mention.

 

For that matter, one could argue that lack of authority IS LTE as well. Got the pedal at the stop and you're still spinning the wrong way? Tail isn't being very effective at doing its job. LTE.

 

Just sayin...

 

 

Also... if you think about it, things like TR VRS can potentially be a self propagating problem... But I'm sure that's just not enough authority too, right?

[eagle5]

In the beginning I think its more about timing than just running out of pedal. If the pilot is late to respond to an abrupt yaw (caused by the changing wind direction or gusts) what happens next is LTE. In other words LTE the result not the cause!

 

What I think Robinson might be saying is that their tail rotors are so awesome that the only way a pilot could get into LTE is from a late response to sudden right yaw,...so get more training because its the pilot not the helicopter!?

 

Like what I think iChris was saying, LTE, VRS and/or SWP caused the crash, but the pilot caused the LTE, VRS, and/or SWP in the first place?

 

...but I'm just guessing?

[Spike]

All that is shown on those videos is a heavy aircraft trying to fly without enough pedal AUTHORITY, not LTE. That Longranger on the top of the hill was moving left, then right, the relative wind was changing, but he kept on turning. If it was suffering from the dreaded LTE, once the relative wind shifted, the LTE would stop. Which part of LTE was he having? Tail rotor vortex ring? Vortex shed from main rotor?

 

The crane was coming in downwind (see the trees?) and was heavy. Once he dumped the load he had enough authority back to fly away.

 

But those who have been indoctrinated into believing that LTE causes every flick/spin/die accident will never stop chanting their mantra. LTE...LTE...LTE...and never be to blame.

 

 

From Wikipedia:

Tail rotor failures which occur from either a mechanical malfunction of the tail rotor control system or a loss of tail rotor thrust authority, called Loss of Tail-rotor Effectiveness (LTE).

 

The FAA’s-H-8083-21A Helicopter Flying Handbook has a number of conditions which fall under a LTE event. Nowhere is there a mention of LTA (Loss of Tail Rotor Authority).

 

http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/helicopter_flying_handbook/media/hfh_ch11.pdf

 

Edited May 21, 2013 by Spike

[Eric Hunt]

Geez, Spike, you believe something written in Whacko-Pedia?

 

Lack of Tail Rotor EFFECTIVENESS is when it doesn't matter what you do with the pedals, the aircraft is doing its own thing. It is not effective.

 

It is different to just running out of pedal. Once the left pedal hits the stops, it is still effective (try putting in some right pedal and watch your eyeballs bounce off the window) but it does not have enough authority to do what you want it to. Caused by too much power being demanded, to hot/high/heavy, tailwind, rotor droop, etc.

 

But if you want to keep assigning all problems to LTE, fill your boots.

[Helipilot PTK]

Geez, Spike, you believe something written in Whacko-Pedia?

 

Lack of Tail Rotor EFFECTIVENESS is when it doesn't matter what you do with the pedals, the aircraft is doing its own thing. It is not effective.

 

It is different to just running out of pedal. Once the left pedal hits the stops, it is still effective (try putting in some right pedal and watch your eyeballs bounce off the window) but it does not have enough authority to do what you want it to. Caused by too much power being demanded, to hot/high/heavy, tailwind, rotor droop, etc.

 

But if you want to keep assigning all problems to LTE, fill your boots.

 

It just seems to me that if you run out of left peddle, and you are still spinning, you are in LTE. And if the pilots aren't breaking any limitations of the helicopter, shouldn't they be able to fly Hot/High/Heavy and have enough tail rotor power? And if they do run out of left peddle, and are still spinning, I don't see how you can say that it is not in LTE.

[eagle5]

It is different to just running out of pedal. Once the left pedal hits the stops, it is still effective (try putting in some right pedal and watch your eyeballs bounce off the window) but it does not have enough authority to do what you want it to. Caused by too much power being demanded, to hot/high/heavy, tailwind, rotor droop, etc.

 

But if you want to keep assigning all problems to LTE, fill your boots.

 

Too high of a power demand. That is mentioned as one of the things that leads to LTE in the FAA book linked above.

[iChris]

The videos Spike posted are perfect examples of what the safety notice stated; to avoid unanticipated yaw, pilots should be aware of conditions (a left crosswind, for example) that may require large or rapid pedal inputs.

 

The primary requirement for the tail rotor is that it must be able to generate enough thrust to balance main rotor torque in full power climbs with at least a 10% margin left over for directional control. It must also be able to provide adequate control in autorotation and low speed flight in any direction at any combination of gross weight and altitude in its design envelope. Therefore, the tail rotor has a finite amount of thrust it can produce within that envelope. In mountainous terrain the tail rotor often encounters complicated wind flows, especially during low speed flight and with winds from the left or turns with the tail moving clockwise (Counterclockwise rotors).

 

The first two videos are pilot induced accidents. These first two pilots when presented with an unanticipated yaw situation reacted with more collective and pedal. The first tries to pull straight up while trying to hold the left pedal. The second is low and slow off a ridgeline circling to the right and does the same things, more collective and pedal, as the ground gets closer and closer.

 

In both cases they continued to increase the power required as they fell further along the back side of the power curve to the point of rotor decay and subsequently a decay in tail rotor RPM; therefore, their tail rotor was producing less thrust. Note the sound of the rotor as it decays near the end.

 

In the last video you have a seasoned pilot (who I know) and at the beginning of that pass was aware there was a possible issue with the wind conditions. However, he left himself some room to play with (altitude) so when presented with an unanticipated yaw situation, he reacted by reducing the power required, maintained rotor RPM, and kept the helicopter moving forward into clean air. The results, he flies away and gets to fly another day.

 

Recognize what you’ve gotten into and ease off the collective, forward cyclic, and get the helicopter moving forward into clean air.

 

Those first two were operating at low airspeed, out of ground effect more than likely near gross weight with very little extra power available above the power required to hover. They were unaware of the situation they were entering and didn’t react in time or didn’t have the experience to handle the situation when it hit. We can’t blame it all on LTE.

 

The figure shows tail rotor pitch required in sideward flight or at a hover with wind at the same speed and from the same direction.

[superstallion6113]

The basic way I understand it is, LTE is the tail rotor losing thrust because of aerodynamics. If wind/aerodynamics caused the tail rotor to lose thrust, I'd call it LTE. I wouldn't call a mechanical limitation/design limitation of the tail rotor or yaw channel of the flight control system LTE.

 

If the pedal is hitting the yaw stop, the tail rotor is still effective, as in producing thrust. You have just reached the maximum amount of thrust the tail rotor can produce, and since the torque the main rotor is producing is now exceeding the torque the tail rotor can by design produce, an uncommanded yaw will occur. It seems like Frank Robinson designed his tail rotor so that it is much more difficult to get into the tail rotor thrust required > thrust able to be produced scenario, running out of pedal.

 

I'm just a newbie pilot, but that's my take on it.

[Nearly Retired]

That chart posted by iChris confuses me. It indicates that in left-sideward flight (i.e. a left crosswind) you would need four degrees *more* left pedal than in a hover. Hmm. This seems counterintuitive and contrary to my experience. Anyone who's ever flown a 206 (for example) knows that a 10-15 knot *left* crosswind will result in a demand for *LESS* left pedal, not more. See, there's this thing called weathervaning tendency...has to do with the fact that there is more fuselage behind the mast than in front of it. Maybe those figures were derived in a wind tunnel or some place that did not take into account weathervaning tendency. In any case, I do not believe them. Try hovering an FH1100 in a 10-15 knot left-crosswind and you will just about be on the *right* pedal stop because the ship wants to yaw to the left so strongly (visualize it).

 

I know that a lot of pilots look at the LTE chart and assume that winds from the left or left-front can cause "LTE" due to interference between the main rotor wake and the tail rotor. Some must jump to the conclusion that a left-crosswind will cause you to spin like a top as the tail rotor suddenly loses effectiveness!

 

In reality, the effects are only transitory and not permanent. *IF* the MR wake interacts with the TR in such a way that the TR loses some thrust, it will only happen for a moment. AS SOON as the fuselage starts to yaw that interaction between the two rotors changes due to the different angle of all the wind vectors. So hovering in a left-crosswind will mean that your feet will be "busier" because the tail rotor's thrust will vary. However it never stops producing thrust!

 

Hovering a Bo105 in a right-crosswind is serene because the TR is up in nice clean air. However you'll need a lot of left pedal. Hovering the 105 in a left-crosswind can be intense, with your feet dancing on the pedals as the wakes interact, but the total amount of left pedal required will still be less than trying to hover in the same wind with the wind off the right.

 

Plus, we all know that the huge vertical fin of the 206 can blank off some of the inflow to the tail rotor, causing some reduction in thrust (witness the slimmed-down "fast fin" on the 205/212 - when will they come out with one for the 206??). This, combined with the aforementioned weathervaning tendency can cause a 206 to want to swap ends real quick (but not necessary spin around and around). Ergo, a 206 pilot hovering with a rear or slightly right-rear wind must be hyper-aware of that wind and be on the ball.

 

The trick is to be on the lookout for *any* uncommanded yaw rate to the right AND STOP IT before it builds up. If it takes full left pedal, PUSH IT. I've seen the video that Counterrotate referred to above. It was an ENG helicopter and the cameraman was filming from the back seat as the pilot hovered around to his landing platform. The wind got behind them, the helicopter started rotating to the right, and the pilot (as the video evidence clearly showed) had his feet together, pedals in the hover position when that left pedal needed to be fully extended.

 

"LTE" has become this monster that is awfully convenient to blame when a pilot screws up and crashes an otherwise airworthy helicopter.

 

In the video of the LongRanger departure above, the pilot evidently had a lot of power as we see from that vertical takeoff. We can infer that he probably had plenty of left pedal available as well. His rate of rotation to the right is not horribly high at first, and probably could have been overcome with a reduction of torque combined with FULL left pedal pushed and held. And at times he *almost* got it stopped. But for some reason (lack of pilot skill?) he allowed the rotation to continue until things got so out of hand that he rolled the throttle off in desperation/panic. That situation was, in my opinion, salvageable before ending up in a crash. I kept yelling, "NOSE DOWN, STUPID! FLY OUT OF IT!!" But hey, not every pilot is Chuck Yeager. Lucky that guy wasn't hovering over downtown Honolulu when that happened.

 

And that's the thing: Fly the damn aircraft! At all times be cognizant of the wind and how it will affect your helicopter. DO NOT let the wind get behind you in a hover; keep the relative wind from the front. Be ready, willing and able to push FULL left pedal and hold it as long as necessary, even if it causes an overtorque. And don't crash the f*cking helicopter.

[Rogue]

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.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/aba9e26c4d43dfab862569e7007463bf/$FILE/ac90-95.pdf

 

[Counterrotate]

I have to agree with NR on this. Also, the above post is spot on. IN MY PERSONAL EXPERIENCE it is difficult if not impossible to get into a situation where you are spinning uncontrollably without first putting yourself in a position where you failed to immediately correct an uncommanded yaw. If you get an uncommanded yaw (and yes, it happens, in fact, it can happen a lot on windy days), push opposite pedal. Do it immediately and with authority. The few situations where you might actually run out of pedal before you are able to stop a turn, you probably are outside the edge of the performance envelope anyway and shouldn't be there. I've gone a full 360 before (with a student) but it was because he locked up on the pedals when we encountered an uncommanded yaw. He immediately blamed LTE. I blamed his frozen feet. He was so locked up, I couldn't override him. The human leg is the strongest part of our body. After all, we walk around on them all day long. We argued about it for a bit, and then it happened again, but this time I was able to immediately put in left pedal. Guess what? It stopped the yaw. It's what I call maintaining positive control of the aircraft.

 

Ignore the dumb-ass narrator. Watch carefully when the camera pans to the pilots feet just before impact.

[Spike]

Geez, Spike, you believe something written in Whacko-Pedia?

 

Lack of Tail Rotor EFFECTIVENESS is when it doesn't matter what you do with the pedals, the aircraft is doing its own thing. It is not effective.

 

It is different to just running out of pedal. Once the left pedal hits the stops, it is still effective (try putting in some right pedal and watch your eyeballs bounce off the window) but it does not have enough authority to do what you want it to. Caused by too much power being demanded, to hot/high/heavy, tailwind, rotor droop, etc.

 

But if you want to keep assigning all problems to LTE, fill your boots.

 

You know what I believe? It doesn’t matter what I believe. That’s what I believe……

 

It appears once pilots get some experience under their belts (somewhere in the realm of 100 hours) they often read into or interpret information in their own way, regardless of what is written (published). That is, information published by organizations whose job it is, is to publish facts…..

 

LTE is what it is, regardless of how it happens i.e. tail rotor failing to counteract torque. With that said, yes, I’ve reach the pedal stops in different types of machines just as many working pilots have. If a pilot hasn’t, he will. Furthermore, I work of a company that actually trains in the recognition and recovery form LTE events. This training is done by hovering OGE, downwind, sometimes even flying backwards to induce LTE. Good fun…..

 

Call it what you want. Funny enough, I call it TRF for Tail Rotor Flatulence because of the sound it makes during LTE. However, that’s not a published term either…….

 

IMHO, by Robinson stating the obvious, that LTE is a result of pilot error, and that their tail rotors have more authority will create a false sense of security. Meaning; the pilots moving into machines with less authority will no doubt be behind the curve……

 

Edited May 22, 2013 by Spike

[pilot#476398]

I have to agree with NR on this. Also, the above post is spot on. IN MY PERSONAL EXPERIENCE it is difficult if not impossible to get into a situation where you are spinning uncontrollably without first putting yourself in a position where you failed to immediately correct an uncommanded yaw. If you get an uncommanded yaw (and yes, it happens, in fact, it can happen a lot on windy days), push opposite pedal. Do it immediately and with authority. The few situations where you might actually run out of pedal before you are able to stop a turn, you probably are outside the edge of the performance envelope anyway and shouldn't be there. I've gone a full 360 before (with a student) but it was because he locked up on the pedals when we encountered an uncommanded yaw. He immediately blamed LTE. I blamed his frozen feet. He was so locked up, I couldn't override him. The human leg is the strongest part of our body. After all, we walk around on them all day long. We argued about it for a bit, and then it happened again, but this time I was able to immediately put in left pedal. Guess what? It stopped the yaw. It's what I call maintaining positive control of the aircraft.

 

Ignore the dumb-ass narrator. Watch carefully when the camera pans to the pilots feet just before impact.

 

If these reporters were worth a damn (and thus knew ANYTHING about on what they were reporting), he would have said, "As you can see the pilot's feet were obviously asleep, its no wonder he crashed!"

[Nearly Retired]

That incident Counterrotate posted the video of occurred in September of 1996 at Van Nuys Airport in California. If you watch the video you see the pilot smoothly approaching the dolly. Then it starts to go around, ending in a horrible-sounding crash. For a couple of brief seconds you can see the pilots legs. Here's a screen-shot from the video mere moments from impact:

 

 

And here is the pilot's description as told to the federales:

 

"The pilot reported to FAA inspectors that he was approaching the helipad for landing on a heading of 160 degrees. The pilot brought the helicopter to a stationary hover about 5 feet agl. The wind was 140 degrees at 10 knots. The pilot decided to do a pedal turn to the right to a heading of 250 degrees. Once the right turn was initiated, the pilot could not stop the turn with full left pedal. The pilot attempted to fly out of it into the wind without success. He then reduced power and attempted a landing while rotating to the right. The helicopter landed hard on the left skid and rolled over."

 

Come again? I didn't see any "stationary hover," and I didn't see any "full left pedal" applied. Looks like you just froze on the controls there, bub. But hey, it happens!

 

Some of the commenters on the YouTube video appear to be pilots. And one in particular appears to have it really, really wrong. DMFK1981 says:

 

 

 

It's called "Tail Rotor Vortex Ring State". When the pilot made the final turn, it caused the wind to be at a critical angle(between 210°-330°) for TRVRS. As he lost command of the tail rotor thrust, and yawed to the right, the helicopter entered into "Weathercock Stability". Which, in simple terms, forces the tail around in the direction of the yaw at a high rate of speed.

BTW, this pilot had 1570 hours total time.

 

Wow, he gets it *all* wrong! And DMFK clearly misunderstands weathercock stability. All that does is make the ship want to point into the wind. Good if you're already headed into the wind; bad if the wind is up your butt.

 

And then in response to a since-deleted comment, DMFK says...

 

 

 

But why land accepting a left crosswind in a bell that is known for having an underrated tail rotor?

 

Umm, ever actually flown a helicopter, son? Again with the misconceptions! Having a *left* crosswind in a Bell will mean you'll have to use LESS left pedal upon termination because of the aforementioned weathercock stability.

 

But see how pilots get these crazy ideas in their heads from reading books and seeing charts they really don't understand? I hold the FAA partically responsible for this, because they tend to complicate every issue to the point of gobbledygook.

 

But the real point of this "War And Peace" post is to point out that what pilots say AFTER the accident is sometimes a little...um, different...than what actually happened. In the above video, the pilot SWORE to the NTSB that, by God, he had *full* left pedal applied and it didn't stop the spin! "I tried, yer Honor, I really did! It just kept a-spinning and a-spinning and there was nothing I could do to stop it! It was the damn weak-ass Bell tail rotor, I tell you!"

 

And maybe the dumb FAA guys took him at his word and/or didn't immediately see the video of the crash. Or maybe they saw it and didn't know what they were looking at like we armchair experts do. Maybe they just didn't care since nobody got hurt.

 

Either way, pilots freeze up and later state that they did everything by the book, cool as a cucumber, yesiree. And hey, as long as nobody dies who are we to say they did not? Who are we to criticize? Sure, this 206 ended up on its side, but what the hell, both people walked away from it, right? So I guess it counts as a successful landing and we should call that pilot a HERO! Why, if I ever meet him I'll buy him a beer!

[Hand_Grenade_Pilot]

This has more or less been said by multiple posters, but I'll say it again anyways.

 

Helicopters are naturally unstable, especially at very low airspeeds. Unless the aircraft is directly streamlined with the wind, the pilot's workload on the pedals will increase. The specific wind azimuth, as well as specific design features of the aircraft, determine 'how hard' the pilot has to work to maintain precise yaw control.

 

An uncontrolled spin in the opposite direction of the main rotor is 100% pilot error (assuming there is no mechanical failure). The FAA Helicopter handbook describes 3 wind azimuths that can cause increased instability. Each azimuth creates instability in a unique way and each requires different inputs from the pilot to maintain control.

 

Specifics aside, total control is possible if the pilot knows what they are doing.

 

If you are operating near max gross, at high DA and hovering in a critical wind azimuth and succumb to an uncontrollable spin, that is your fault. Not the tail rotor, not the vertical stabilizer, not the manufacturer and certainly not Mother Nature.

 

If you are hovering under those conditions, it is your responsibility to consciously manage torque and rotor rpm, and if an uncommanded yaw starts to develop with full anti-torque applied it is your responsibility to further reduce torque (reduce power, increase forward airspeed, dump the load, etc.)

 

Unfortunately, it easy to toss up an accident to things like LTE, Vortex Ring State and Settling with Power. But at the end of the day, assuming no mechanical failure has occurred, the true cause is operator error.