Loss of T/R on the fulldown

[romanweel]

I have a hypothetical question. Suppose you've lost antitorque completely (tail's been chopped, I don't know), and you're performing your fulldown auto like you were taught in ground school. I know that during the glide, the M/R isn't producing any torque, and so you're alright (relatively speaking) without antitorque capability, but then you go into the flare. As the M/R RPM increases and you increase collective (keeping the throttle well into the detent), do you experience addition of torque as well? If so, what do you do? If not, why? I've heard it both ways and no satisfactory explanation. Can someone explain the aerodynamics of this to me?

[FlyNHighNFast]

No throttle, no torque.

[kodoz]

I have a hypothetical question. Suppose you've lost antitorque completely (tail's been chopped, I don't know), and you're performing your fulldown auto like you were taught in ground school. I know that during the glide, the M/R isn't producing any torque, and so you're alright (relatively speaking) without antitorque capability, but then you go into the flare. As the M/R RPM increases and you increase collective (keeping the throttle well into the detent), do you experience addition of torque as well? If so, what do you do? If not, why? I've heard it both ways and no satisfactory explanation. Can someone explain the aerodynamics of this to me?

 

Torque is the force produced by the engine that is opposite to the rotation of the blades. Without power from the engine, you don't produce torque.

 

Why do the blades turn then? In an auto, the driving region of the blade provides a horizontal force that drives the rotor--no torque is involved.

 

Also, loss of TR trumps loss of power...in the POH, the procedure for loss of tail rotor effectiveness is roll into the detent and conduct an autorotation as usual, making sure you stay in the detent during the flare and hover auto.

[Eric Hunt]

Loss of T/R power will give you some thrills at the bottom.

 

As you pull pitch, the transmission drag may pull the nose to the left, same direction as the blade rotation, but if any engine power is present, the torque will snap you off to the right. Expect to skid off the runway or landing area, and be unable to control it - unless you are in a wheeled helo, where you will have the brakes to give some control.

 

Just make sure the touchdown is fairly straight and not much faster than translational speed, and hope for the best.

[Sparker]

I vote for always flying with a tail rotor.

 

A book I read said that in an auto the torque was exact opposite of normal (but not as much force), because the momentum of the blades is pulling on the transmission and engine in stead of the engine pushing the blades.

[Gomer Pylot]

If you do an auto because of loss of tail rotor, you want to close the throttle completely and kill the engine, not just put it to the idle detent. You need to be completely power off. The friction from the transmission and drive train may pull the nose off a little, but most models will streamline sufficiently to not be a major problem. If you leave the engine at idle, though, you're going to get a big turn at the bottom, and very possibly roll over. It depends on the wind and your technique. Me, I'm going to try to get to a runway, or at least a clear highway, and when I go into the auto the engine is going to stop completely.

[beckwith]

I vote for always flying with a tail rotor.

 

I agree.

 

If it happens though. It seems like a little torque at the bottom is not as bad as hitting with out a flare and anyway there isn't anything you can do about the tourqe. So kill the engine, do your auto, and think as little about the torque as possible.

[Linc]

Don't forget a large forward shift in CG and a likely loss of aft cyclic authority in the T/R chopped off scenario, that will also make the termination sporty. I remember doing a "running landing" auto once during my initial training. It was totally by accident, I just forgot to decel and pulled collective to cushion the landing...at Mach 5 down the lane. I've always thought that is what a loss of T/R components auto would be like, with a lot of tumbling instead of sliding due to the fact that it won't conveniently occur at an airfield, lined up over the lane/runway/taxiway, at the "perfect" entry point, etc..

[Eric Hunt]

Linc, your story reminded me of an auto i did once in an AS350, WITHOUT ANY COLLECTIVE.

 

On the entry, when I put the lever to the floor, the collective lock managed to apply itself to the other set of dual controls (stupid French system!!). Did the auto, flared, went to apply a little collective before I levelled out, and found that it was locked down. Screamed at the other pilot to release the lock, but he had to push the lever hard against the floor to release it, and I was pulling up like crazy. I won.

 

All I could do was nose over early, while I still had some speed, and go for a running landing. We bounced with skids level, and managed to clear a raised taxiway ahead of us, and just missed a large stormwater drain as well, as we skidded to a halt in a cloud of dust and a hearty "Hiho Silver!"

 

One thing for those French, they build a sturdy set of crosstubes. No damage at all, other than having to replace the collective downlock after I tore it from the floor and threw it on the engineer's desk.

 

In the "chopped off" scenario, depending on the type, it might not be survivable. Back on 18 August 1981, one of my Hueys lost a T/R gearbox, and the resulting high-speed yaw and nose-down pitch caused a massive mast bump, rotor separation, and disaster for the three crew. I had been the last one to fly it, and was supposed to be on that flight, but fate decided that it wasn't my turn.

[spencer]

Linc, your story reminded me of an auto i did once in an AS350, WITHOUT ANY COLLECTIVE.

 

On the entry, when I put the lever to the floor, the collective lock managed to apply itself to the other set of dual controls (stupid French system!!). Did the auto, flared, went to apply a little collective before I levelled out, and found that it was locked down. Screamed at the other pilot to release the lock, but he had to push the lever hard against the floor to release it, and I was pulling up like crazy. I won.

 

All I could do was nose over early, while I still had some speed, and go for a running landing. We bounced with skids level, and managed to clear a raised taxiway ahead of us, and just missed a large stormwater drain as well, as we skidded to a halt in a cloud of dust and a hearty "Hiho Silver!"

 

One thing for those French, they build a sturdy set of crosstubes. No damage at all, other than having to replace the collective downlock after I tore it from the floor and threw it on the engineer's desk.

 

In the "chopped off" scenario, depending on the type, it might not be survivable. Back on 18 August 1981, one of my Hueys lost a T/R gearbox, and the resulting high-speed yaw and nose-down pitch caused a massive mast bump, rotor separation, and disaster for the three crew. I had been the last one to fly it, and was supposed to be on that flight, but fate decided that it wasn't my turn.

 

 

 

NTSB

 

 

The NTSB report above is of a bell 230 in my neck of the woods which lost the tail rotor gearbox. We all know that in the case of tail rotor thrust failure we would probably elect to do a autorotation. But with such a massive change in CG because of the weight of the gear box not being there any more, the pilot elected to do a running landing because the cyclic was in his gut and he didn't have enough aft cyclic authority to flare. This pilot also lost his job because the chief pilot said that he should have done a autorotation like the POH said. This makes me think about that chief pilot a little bit because the pilot saved the aircraft.

Edited November 25, 2007 by spencer

[500E]

Are we saying the = and opposite forces rule don't apply when in auto with no tail rotor\control or that there is enough weather vane effect to overcome the flare and collective under arm thingy, was told to do run on landing with enough speed to keep it straight, and engine OFF, this is not high on my want to do list.

Speccer

The pilot must have been real p***d loosing job

[Eric Hunt]

500E,

 

The weather vane effect only works with a fair bit of airspeed. The flare kills off the airspeed, and with it any weather vaning available. Round in circles you go. That's why they advocate keeping some airspeed on and running it on while still straight.

 

Once on the ground, ensure the engine is OFF, and hang on for the ride.

[Gomer Pylot]

The amount of weathervaning will depend a lot on the model. Some configurations naturally weathervane more, plus size matters, because larger fuselages have more inertia, and will tend to take more friction to turn them. About all I can suggest is to know the procedures in the POH, and if you don't follow them, have a very good excuse ready. Tail rotor failures are among the most variable emergencies you can have, because there are so many failure modes and what happens depends a lot on the failure mode. You can have everything from a fixed pitch setting to drive shaft failure to loss of components, and they're all different, to one extent or another.

[500E]

Eric & Gp

That is what I would expect & was saying, you have to run on if you hope to salvage anything.

kodoz talks about auto in normal way, I may have misunderstood his post but I auto with as little forward air speed as is practical at flair and set down, I quite like vertical autos, with tail rotor problem you have to be around a speed that will hopefully keep you straight when you flair, or fly (no flair) onto the ground with minimum speed to keep you straight, when training the run on landings were my worst nightmare, always looking for the hole that would trip me up, sliding along like a out of control skier was not my idea of fun.

Did a lot when training but not one for real hope it stays that way.

[Linc]

Linc, your story reminded me of an auto i did once in an AS350, WITHOUT ANY COLLECTIVE.

 

On the entry, when I put the lever to the floor, the collective lock managed to apply itself to the other set of dual controls (stupid French system!!). Did the auto, flared, went to apply a little collective before I levelled out, and found that it was locked down. Screamed at the other pilot to release the lock, but he had to push the lever hard against the floor to release it, and I was pulling up like crazy. I won.

 

All I could do was nose over early, while I still had some speed, and go for a running landing. We bounced with skids level, and managed to clear a raised taxiway ahead of us, and just missed a large stormwater drain as well, as we skidded to a halt in a cloud of dust and a hearty "Hiho Silver!"

 

One thing for those French, they build a sturdy set of crosstubes. No damage at all, other than having to replace the collective downlock after I tore it from the floor and threw it on the engineer's desk.

Eric,

 

Not a preferred method, I'm sure, but I'm gonna add that one to my bag of tricks. I did a lot of practice autos that taught me a bit about the autorotational flight envelope. Most were not quite intentional, but valuable for the lessons they taught, even if the results were ugly.

 

Which also brings to mind a flight with a young lieutenant who hadn't been up to fly in a couple weeks. We were flying NOE (30-50 feet...mostly, about 60 KIAS) and he asked me what we could do if the engine failed. I bottomed the collective and flared, and with the NR (RRPM) spooling up towards the high side, I set up for landing with whatever was in front of me. I don't think he was quite ready for it and having the engine running makes it a less than true picture, but I think he saw that there are options and time (albeit, not much) to affect your destiny towards the positive.

Edited December 2, 2007 by Linc

[romanweel]

Thanks everybody; this is exactly the discussion I was looking for (especially the forward shift in CG, pretty obvious but I sure hadn't thought of it). Anyone have any more stories to share?

[chamerican]

My training was entirely in 206's and each and every auto was done to a run on landing. Yes it may be true that you may not have the luxury of a runway or a road but as Gomer said, but the reasoning behind this is that it gives you that much extra cushioning/rotor RPM remaining to accomplish the task with as little damage (if any) to the aircraft. For the nose to drift with collective application you can't argue with physics. I'm curious as to why it would be necessary to cut the engines if the engine is decoupled from the rotor. Equal and opposite reaction- Is the induced drag enough to pull the nose to the left? I find that hard to believe. As far as that guy losing his job, I completely agree that he was right in every way. Gomer was also correct in saying that tail rotor malfunctions/loss of thrust are the most variable emergency procedure you will face. I have the luxury of hopping in a full motion sim which can duplicate just about every one you can think of. I spent a complete period (2hrs) on tail rotor EP's and have yet to master them all. At low airspeeds, reaction time is critical since the yaw rate can build and will be unrecoverable. I was given a loss of tail rotor thrust at low airspeed and at climb-out power and the aircraft spun like a top before I had the time to pull the engines back to idle and enter an auto. Gomer also talked about the weather vaning of various aircraft. For example, the UH-60 with give you trimmed flight at or above 110Kts An AH-64 here recently completely lost his tail rotor and rather than enter an auto (into bag guy land) elected to determine what airspeed gave him trimmed flight. He ended up doing a run on landing somwhere between 80-100kts- granted he does have tires. Point being that the POH may dictate specific procedures but the situation may warrant otherwise. My POH gives the PC the authority to deviate from it if the situation dictates. If I have a loss of TR thrust/components and I can still maintain trimmed flight, why elect to autorotate to a field when I could continue to a road or landing strip?

[K-38]

Thanks to everyone for contributing to this discussion. This represents VR at its best.

[Eric Hunt]

Chamerican says, "If I have a loss of TR thrust/components and I can still maintain trimmed flight, why elect to autorotate to a field when I could continue to a road or landing strip?"

 

Cham, you don't know what is happening behind you. If you have lost a part of the machinery, you might also have a T/R drive shaft thrashing itself to death. It can emerge from the tail boom and take part or all of a rotor blade. The damaged tail boom can depart too, and that will be terminal. A thrashing drive shaft can damage the gearbox of your engine. In an R-22/44, a drive shaft bearing collapse or loss of a shaft piece will make the clutch useless and down you go anyway.

 

But, if an immediate auto means a really messy finish, whereas a couple of minutes of ugly yawing flight means a less messy piece of dirt to plop onto, give it a try. What have you got to lose? Everything....

[chamerican]

Chamerican says, "If I have a loss of TR thrust/components and I can still maintain trimmed flight, why elect to autorotate to a field when I could continue to a road or landing strip?"

 

Cham, you don't know what is happening behind you. If you have lost a part of the machinery, you might also have a T/R drive shaft thrashing itself to death. It can emerge from the tail boom and take part or all of a rotor blade. The damaged tail boom can depart too, and that will be terminal. A thrashing drive shaft can damage the gearbox of your engine. In an R-22/44, a drive shaft bearing collapse or loss of a shaft piece will make the clutch useless and down you go anyway.

 

But, if an immediate auto means a really messy finish, whereas a couple of minutes of ugly yawing flight means a less messy piece of dirt to plop onto, give it a try. What have you got to lose? Everything....

 

Good point Hunt- I agree. I should have been more specific when I said "continue" and said for a very short distance. Yes that extra 5 seconds might still mean a messy landing but so is a auto into a patch of trees- especially with those tiny 44's. Yes you could have a part getting ready to separate but if you do it would happen very close to the time of initial material failure. In any case you do have a slight idea of what's going on back there by changes in engine noise, vibrations/feedback in the flight controls, and/or change in CG. During my 206 training at Mother Rucker another crew had a TR component failure IMC at 4000'. According to the instructor the failure was almost instantaneous. A portion of the drive shaft failed and separated from the aircraft followed by another- if I remember correctly. They auto'd and broke out at about 400ft. I agree with you. I'm going to auto as a first choice but if my landing is going to be messy and I determine I can- why not take the extra 5-10 sec find that better place? At the speed those components are turning, a failure (for the most part) in the system will not be gradual. I guess my point is that the POH isn't necessarily the end all be all and there are always many variables to consider in a TR emergency. I know most of you out there don't have to consider this but some of of us have little guys here that don't like helicopters and would love to kill each and every one of us when we come back to earth- let alone auto right into there backyard.

Edited December 5, 2007 by chamerican