Reverse LTE?

[Nearly Retired]

As many of you know, I'm pretty strident in my views on LTE. In short, I don't believe that it is as big a problem as people worry about. Further, I don't believe that all of the accidents that get attributed to "LTE" actually are a result of that phenomenon. I think that once some uncommanded right yaw occurs, pilots either freeze, or they don't add enough left pedal and hold it for long enough (that is, until the spin stops) despite what they say afterwards.

 

A classic example of this was an ENG 206B that crashed in Van Nuys, California while the pilot was trying to put it on a dolly. He told the NTSB that it spun and that full left pedal didn't stop it. Trouble was, the cameraman in the back was filming at the time, and as the ship went around, just before it rolled onto its side the lens briefly caught a glimpse of the pilot's legs. You can see he's wearing shorts and sneakers. And he was clearly only holding neutral pedal, not full left. Oops! But the NTSB believed the pilot and the accident became part of the LTE folklore.

 

Here's a screenshot from the video:

 

 

Please understand that I've been flying these crazy things - and trying to understand *how* they fly for 40 years. My dad was a helicopter pilot and I started my rotary-wing primary training in 1976. In all of my 7,000 hours in 206's (and another 4,000 hours flying other things), I don't think I've *ever* hit the left pedal stop. Came close plenty of times. But I've never had an instance where I couldn't stop a right yaw with pedal. So my thinking is that...*generally*...LTE is a myth...an weasly excuse for crashing a perfectly good helicopter.

 

Keep in mind though that nearly all of my flying has been at sea level where the 206 has plenty...YES, I SAID PLENTY of tail rotor authority. You guys who fly them up in the mountains can probably tell me some pretty good LTE scare-stories. Still, I don't think there's ever a case in which the 206 tail rotor stops producing sufficient thrust without some warning - like having your left foot extended all the way out and not realizing it, and then not having enough oomph left when you get some right yaw.

 

I was explaining my views to some pilots not long ago. Yes, we were in a bar and yes, there was alcohol involved (hey, we're pilots, not Mormons). One instructor there let me get all the way through my diatribe before telling me that he got into LTE...get this...to the LEFT. That's right, to the left. I said something smartass (as I usually do) about calling Dr. Einstein, because what he just described violates the laws of physics as we know them. The instructor then called me a bad name and said I didn't know what I was talking about (he might have even implied that I was too stupid to hold a pilot's license and that my parents were brother and sister). His student nodded in agreement. The other pilots within earshot all got funny looks on their faces and quietly eased away as if someone just farted big time. Yep, both instructor and student insisted that their ship got into LTE to the left.

 

It's an American helicopter with a single main rotor and tail rotor configuration - the exact make/model doesn't matter. The story was that they were out practicing hovering when..."something"...happened and the ship started yawing to the left. Full right pedal would not stop the spin. They nearly crashed, but didn't.

 

Hmm.

 

My thinking on this event runs to two possibilities: 1) The tail rotor is horribly out of rig (which they swear it's not); or 2) They got into some weird weather micro-climate phenomenon...dust-devil, tornado...I don't know. However, where they were hovering was pretty dusty and you would *think* that they'd "see" a dust-devil coming at them unless it struck from the rear...which it could have, I suppose. It wasn't a particularly windy/gusty day - certainly well within the limits of student instruction.

 

One would think that while a dust-devil theoretically could cause some uncommanded yaw, it wouldn't make the helicopter go 'round and 'round uncontrollably to the LEFT. Torque to the main rotor sort of inhibits that. Take away the anti-torque thrust and pull some power and the left rotation *should* stop. But you never know.

 

I've thought and thought about this, and I've discussed it with people who know way more about how helicopters fly than I do. None of us can come up with a reasonable explanation for why an American helicopter would go into an uncontrolled spin to the *left*.

 

And so I'll throw it out there: Has anyone else ever experienced such a phenomenon where the helicopter yaws *into* the torque and right pedal wouldn't stop it? Or does anyone have any thoughts on this? Because it sure has baffled me.

[Hand_Grenade_Pilot]

The closest event I can recall, to what you're describing, was a situation where I reached full right pedal in a S300C. This was in a low IGE hover, at a very low DA, low weight and about 30kts of wind off the left side. Relatively low torque combined w/ a very strong weathervane tendency actually caused me to reach the right pedal stop. I compensated by increasing my hover height (to increase torque and bring the nose right). Certainly a very unusual situation.

 

My best guess is that the CFI is referencing a time where they were hovering w/ a large gust spread. A sudden increase in wind speed from the left could cause the nose to weathervane sharply. The pilot would simply compensate by decreasing anti-torque (reducing left pedal). I would hardly classify that as LTE though.

 

And I'll second that rant. One of my biggest pet peeves is pilots who insist that the LTE boogeyman screwed them over. Simply a scapegoat for incompetency; failing to understand basic aerodynamics and the correlation between wind direction, torque and DA.

 

 

[Wally]

If the TR pitch can reach 'negative' the possibility would exist of an LTE type situation when you required that torque assisted boost to yaw rate. I can't imagine how it would persist beyond the initial onset.

Why would it persist? The initial yaw would change the circulation that caused the LTE, in my mind I see it resolving at the 180 to the initial onset- if the pilot maintained the control application.If you go all blank with a WTF? control inputs can get pretty random. Also, the conservative pilot action would seem to be an increase in vertical thrust (lift) for clearance, which would assist stopping the spin???

Edited March 18, 2016 by Wally

[Eric Hunt]

A very experienced test pilot, who learned on Bells, flew them in a jungle hot zone, was chief test pilot for Sikorsky and then Bell, has summed it up fairly simply, and I will try to remember the bones of it:

The original B206 in army format had a small tail rotor, and was a bit unforgiving. In the initial stages of acceptance to service, this model had a lot of accidents where the crew ran out of left pedal and crashed. The army questioned the manufacturer, who came back with the whole LTE spiel, and basically said that any helicopter with that layout would suffer LTE and it is not the aircraft's fault, or the pilot's fault, and you will never suffer LTE if you never fly the aircraft with a tailwind, a wind from the left, or a wind from the right. And keep the weight low.

 

And the spin machine worked so well that even the FAA believes it, and every text book in creation has the same pictures in it. But funnily enough, in 90-something percent of TR crashes, it was this model with the small tail rotor - not Astars, not Enstroms, and certainly not Robinsons.

 

Like Nearly Retired, I have over 7000 hrs on the B206 and similar amount on 10 other types, and have never run out of pedal. Always know where my feet are, how fast that left foot is moving forward, and when to poke the nose over and fly away.

 

LTE to the left?? Only if LTE stands for "Lack of Training and Experience."

[r22butters]

 

Like Nearly Retired, I have over 7000 hrs on the B206 and similar amount on 10 other types,...

 

 

So you've got like what, 70,000 hours?,...damn!

 

I fly a Robby, so all I've ever gotten was 4G LTE

[Astro]

Flew with a CFI not long ago who was so fearful of LTE that while lined up with a very nicely lighted runway at a very dark non-towered airport, he INSISTED that I alter my approach to the other (very dark) runway to the left because a mighty 7 kts wind was coming from the left!

[WolftalonID]

A mighty wind...of what?!?

 

Nearly retired, was that cfi and his student in an inverted negative 4 G dive when that left spin occured?

[Gomer Pylot]

Strong and gusty winds can make you work very hard, and if you're a little lazy on the pedals, can spin you to the left pretty quickly. But once the nose gets into the wind the turn should stop. You can call it LTE if you want, but that's just weathervaning, and it happens in every model, some more than others. If you're paying attention as you should be, you'll stop the turn before it goes more than a few degrees. It does take paying attention and some finesse. But those should be the rule, not the exception. The good thing about the wind being from the left is that the rapid application of right pedal shouldn't result in an overtorque. It can happen with the wind from the right, and has, with the aircraft at max gross weight and the pilot a little behind. But LTE to the left at a hover? I have to doubt the veracity of the reporter, to put it politely. With in the neighborhood of 14,000 hours, I've never seen LTE. I've had examiners tell me that making an approach with the wind from the left in a 206 is dangerous and should never be done, but that's the way I've always preferred it, because it takes less power. Just never let the nose move, never let an uncommanded yaw start, and you'll never see LTE, wherever the wind is from.

[Nearly Retired]

I'm not quite sure why there is such paranoia within the CFI community about LTE with wind off the left. Because if anyone has actually flown a helicopter when the wind is blowing they would know that a left wind is most advantageous in nearly any case. But *someone* (Bell?) put out that stupid diagram that says a direct-left crosswind might cause the t/r to go into "sideways" LTE and ba-da-BING! nobody wants to fly with a left crosswind anymore. Silly instructors, get some experience!

 

Then again... Some helicopters have stronger weathercock stability than others. The stupid FH1100 (of which I have more than a passing acquaintance) would not hold a hover in a strong direct left crosswind - you'd run out of right pedal!

 

Now granted, the tail rotor rigging on that type was kind of vague, and the total amount of pitch change could vary a degree or two either side of what was desired. So you might end up with a degree more left pedal than the book called out for (which was good)...but that meant you also had a degree *less* right pedal (which could be bad).

 

The test for correct rigging was to take the ship up, initiate an autorotative descent at 50 knots and see if you could yaw the nose 45 degrees to the right. If you could, good-to-go! LIke I said, not absolutely precise.

 

But I digress...

 

In the event I cited that started this thread, I guess my real problem is that the pilot(s) insisted on calling what they got into, "LTE to the left." Not saying that what they described can't or didn't happen, but calling it LTE is maybe a stretch.

 

I am genuinely curious about how these things fly. In fact I've made a lifetime study of it. So things like this are a puzzle. Gomer, I'm inclined to agree with your assessment. But before we chalk it up to confused pilots, I'd like to find out if such a thing has happened to anyone else.

[Dragbrace]

As another old timer I have to agree with most of the comments concerning LTE.When I learned to fly the term LTE didn't exist. It was called running out of pedal and was considered pilot error by the guys that pioneered the industry back in the late 40's. I had it drummed into my thick head from the beginning that if I had to use excessive pedal inputs I was to fly out of that situation and approach from a different angle.

 

Looking back I think it was as much of a power issue as it was a control issue. The Bell 47 that I learned to fly in still had the 178hp Franklin engine, irreversible controls and wooden main & tail rotor blades. The mechanics used to tell me that it took at least 25hp to operate the tail rotor @ full left pedal. If you subtract 25 from 178 and you were at full gross and low airspeed you were most likely in deep trouble from that point on.

 

My Instructor was the 28th licensed helicopter pilot in the U.S. and he put situatioal awareness at the top of the list when teaching a new student. I credit his attitude in keeping my butt out of the mud for the 50 plus years of my flying career.

 

I think that in today's world we have lost the art of teaching situation awareness & common sense to our new students.

[r22butters]

...I think that in today's world we have lost the art of teaching situation awareness & common sense to our new students.

"Common sense" killed himself in a murder/suicide with "good judgement" after seeing their friend "freedom of speech" nearly beaten to death by the pc police back in the early 90's.

 

I heard "situational awareness" is in a safe house somewhere in the mid-west, hiding out after receiving threats on his life from LTE, SWP, FTS, IIMC, and CFIT.

[kona4breakfast]

I'm not too current on my aerodynamics, but I'd imagine "LTE" has a lot more to do with airframe/rotor downwash interactions with the tail rotor than purely "upwind" through the tail rotor. In order for a tail rotor to get into VRS, you'd either need a pretty gnarly crosswind (the tail rotor on a 206 has approximately the same disc loading as the UH-60's main rotor, according to my sticky note calculations), or, more likely, odd airframe/rotor interactions. All of this is generally sorted out during initial flight testing. The gearbox flip on the Huey improved T/R authority even though it went on the "wrong" side because the tail rotor blade was going up through the M/R downwash instead of down, so sometimes things can change afterwards. You'd be surprised a tailboom strake could do as much as it does as well.

 

You can lose tail rotor effectiveness if your RPM decays, but the tail rotor isn't the problem there.

 

I have trouble believing LTE can happen on most machines, if the pilot makes adequate yaw corrections to mitigate yaw excursions, simply because you hardly ever hear of settling with power incidents with large machines, and the disc loading is similar. On the small machines, if you elect to take a 20 knot crosswind or land in the vicinity of large structures with high winds, that's not loss of tail rotor effectiveness, that's loss of pilot judgement.

 

Unless you're a test pilot, just fly the machine, comply with the limitations in the manual and exercise good judgement and you shouldn't ever have to worry about LTE.

 

Reverse LTE is only possible when the driveshaft to the engine breaks and the one to the tail rotor doesn't, but the tail rotor isn't the problem there, either.

[iChris]

Strong and gusty winds can make you work very hard, and if you're a little lazy on the pedals, can spin you to the left pretty quickly.

 

But once the nose gets into the wind the turn should stop. You can call it LTE if you want, but that's just weathervaning, and it happens in every model, some more than others.

 

If you're paying attention as you should be, you'll stop the turn before it goes more than a few degrees. It does take paying attention and some finesse.

 

 

You have it right, that's likely what happened. That gust of wind caught them by surprise and the flight instructor and student fighting each other on the pedals. They may have done a loop around before they got it under control, that's about it.

 

No reverse LTE, sounds like another “Sea Story”, as we called it in the Navy

Edited March 27, 2016 by iChris