Tail Rotor Problems

[Homer_Jay]

ShyTorque,

I see your point, no fin could equal disaster without the throttle off. I can only reiterate that a long discussion with an instructor about the type/s flown is the way to go. There is no simple "one size fits all" answer. Please see signature below.

Cheers.

[jellycopter]

To add my two-penneth regarding run-on speed and ROD; 1500fpm is about 15kts downward, 500fpm is about 5kts, 200fpm is about 2kts etc etc. Therefore, after the helicopter has broken its contract with you in such a major way, a relatively high RoD at touchdown is probably preferable to a high-speed run-on as the overall overall inertia, and therefore bone-breaking forces, will be less.

What about flaring to zero-speed? Not a recommendation; but a genuine question?

J

[the coyote]

jellycopter,

If I had to do an autorotation to maintain control and/or a powered run on landing was not possible, that's exactly what I would do, flare to zero touchdown speed.

It will yaw late in the flare, as you commence the collective application, but who cares? I would rather contact the ground with no speed and turning than roll it over at speed. The key is to make sure the power is off, lose all the speed completely and get it level prior to touchdown.

TheFlyingSquirrel,

As to your original question, what were you trained to do?

[Thomas coupling]

Silberfuchs: tell us what happened to you 10 yrs ago?

[Staticdroop]

I believe that one solution, as there are many ways to skin a cat, is to fly to an area where you will be happy to autorotate into, preferably an airfield as there is a runway and crash facilitys, otherwise best choice available. Let someone know, MAYDAY, dont delay to long there could be a lot of metal thrashing about back there and it could get worse shortly.
Enter Autotrotation close the throttle carry out Immediate Actions make sure the fire making stuff is shut off. As you approach the height specified in the a/c manual flare the a/c reducing speed to zero if possible and aim to come down the last 10 feet verticaly using the collective to cushion the impact. You will spin due to friction but that should be manageable, if you come down verticaly you will hopefully reduce the possibility of rollover associated with high speed run ons.
This may not be the perfect solution but it is the plan i have worked out for myself to give me something to work on come the day.
All comments welcome

[Gaseous]

Have a look in the POH. My Enstom POH details what to do for every concievable type of TR failure. The details may not be relevant to other types as Enstrom make a big issue of the fat tail boom helping get you out of trouble.

[Arm out the window]

A good start point for fixed-pitch type failures was taught in the RAAF for a long time, works well for helicopters with twist grip throttles like the B205, 206, and we had twist-grip mod squirrels.

In a nutshell, set up on a long low final for a good run-on area and slow the aircraft in 10 kt increments, stabilising level and unaccelerated to see what the yaw angle's doing.

If yawed left (rotor anticlockwise from above helicopters), keep slowing down in increments until you get 40 to 50 deg. left yaw. or 20 kt. Maintain the speed you're at until over the landing area, then smoothly slow to the hover. If it turns left, reduce your Nr in small increments with beep or throttle (yaw will initially speed up, then slow as the tail rotor slows down and you pull a bit of pitch to stay in the hover).
When the yaw's stopped, put it smoothly on the ground.

If yawed right, slow to a minimum of 20 kt or maximum 20 deg right yaw. Maintain that speed until over the run-on area, then take a 'bite' of throttle to swing the nose straight and conduct a fastish taxiing auto. Use any further throttle to 'steer' (the nose will go in the direction that the bottom of the throttle goes).

In the yawing left in the hover case above, if it starts to go right, again take a bite of throttle and do a hovering auto.

This set of techniques works really well, and has the advantage of being a bit 'scientific' and repeatable, ie gives you some procedures and limits to hang your hat on.

For more catastrophic things like loss of tail rotor components etc, I'm all for setting up for a zero-speed auto as some people above are advocating.

[slgrossman]

There are a few helicopters that, depending on the components lost and gross weight may achieve sufficient streamlining to continue powered flight to a more suitable landing area. Others can't be streamlined sufficiently no matter what the weight, and will spin until the torque is removed.

Still others fall somewhere in the middle and the outcome depends on airspeed and other factors.

In any case, while it may be possible to run the aircraft on, the better choice seems to me to be zero-airspeed autorotation, which greatly reduces the kinetic energy that needs to be dissipated at touchdown.

-Stan-

[VeeAny]

You guys may find this interesting reading, its a CAA paper on tail rotor failures, and the procedures highlighted in a number of flight manuals. A bit long, but interesting if you like that kind of thing.

http://www.caa.co.uk/docs/33/CAPAP2003_01.PDF

Cheers

V.

[McHover]

I was a pax on board an Alouette III recently and experienced loss of tail rotor command first hand. The solution to getting us to the ground safely seemed to be a combination of a few of the last posts.

Immediately the problem occured (just after take off from a clearing amongst some cocnut palms) the pilot elected to head back towards the nearest airfield (a virtually unmanned third world scrape in the jungle), a journey which took an agonising 40 minutes.

His approach was long and low, progressively easing off the speed as we got closer to the field, allowing him time to assess the degree of control. We had the benefit of about a 20kt head wind which meant that he was then able to bring us almost into the hover.

So as the yaw started to kick in and the outside world started to rotate he executed what one might term a "positive" landing. The Alouette was equipped with wheels but the pilot chose to land in the long grass off the runway which seemed to help in absorbing the impact of our landing. The outcome however was that we all emerged unscathed (and the a/c was easily repairable).

Hats off to our pilot, he handled it extremely calmly and I really hope that I get the chance to fly with him again. Unfortunately we had to abandon the heli and switch to fixed wing to complete our task. And the cause..., a failure of the t/r command cable.

[McHover]

It was a clean break of the control cable just forward of the helix drum around which it wraps in the tail rotor assembly.

Please bear in mind that I am not qualified in the engineering department however as far as I could see there seemed to be no signs of wear and tear, and the operator informed me that it was only six months old. The break was so clean that it looked like it had been cut.

I have a picture of it if you're interested.

McHover

[JerryG]

I’m grateful to this thread for sending me back to the notes I made the day after suffering a complete T/R drive shaft shear in a 109 some years back. (I caution when reading this that the 109 of course has a very big fin). Part of those notes read:……..

According to both the previous tail rotor failures on 109s the aircraft doesn’t yaw with a failure in forward flight above 120 kts since the tail rotor is completely unloaded and the fin is taking the entire anti-torque load. However in both these cases the entire tail rotor assembly had departed the aircraft. Mine was attached and sometimes windmilling, sometimes not. (I had a chase S76 join me to take a look).

There was a definite and violent yaw to starboard and there was no way it was ever going to fly in the direction it was pointing, or even within 40 degrees of the heading. Although that was uncomfortable it would happily fly at a good range of power settings and between 60 – 100 kts, leaning heavily left “wing” low. The envelope is undoubtedly much wider but I wasn’t brave enough to explore it!

I flew dummy approaches to two out of wind runways in the hope of gaining some help with the heading but the whole thing felt very unnatural and there was no conspicuous advantage to be gained.

I trained the camera man in the left seat (we were returning from a job together) to chop the overhead throttles on my shout. The into wind runway was chosen and I entered a 60 kt constant attitude auto with the engines running (and without intending to flare). The nose stayed 20 degrees to the right of the centreline. At about 20 feet we chopped the engines. It felt very late at the time but was actually a bit early as I was amazed how quickly the nose yawed to port whilst I was pulling in a bit of pitch. I was hard pressed to get onto the ground before the nose swung through the centreline.

In retrospect I would not do an auto next time. I think I would go for a flat approach at 60 kts and accept the increased yaw to starboard (probably as much as 45 degrees). I would then try to gently arrest the descent and then the speed down the centreline at about 5 –10 feet before chopping the throttles, giving more time to worry solely about timing the touchdown to coincide with runway heading. This assumes somebody available in the other seat to look after the throttles.

I found one of the hardest aspects was keeping my feet on the floor instead of constantly trying to pedal a control that wasn’t there.

…………Now don’t ask me for more details, it was a long time ago, but those notes were made the very next day. I’m certain they are very specific to the 109.

I do very clearly remember being astonished at how the brain speeded up with adrenalin and could remember comprehensive details of stuff I’d read or been told about T/R failures from long before. I couldn’t have remembered it all the day before and probably not the day after, but it was all in there somewhere when needed at the critical moment.

JerryG

[TheFlyingSquirrel]

McHover's failed cable....

[topendtorque]

T/R failure in forward flight

Interesting notes, pitch controil fails or drive shaft fails. simple, play with your throttle, wind it off just before you touch down at very slow forward speed. don't stuff up the aproach.

If drive shaft fails in the hover, man that's scary, after the second rotation one's self preservation usually remembers training, wind the throttle off idiot, they don't stop, only slow down a bit.

What not to do is don't wind it off, check out the story from Sydney Australia many moons ago when this happened in a tele-news 47 after the old leightweight style T/R thru bolt let go, very messy and all on camera.

If the G/Box is gonna fall off, do your CofG, then work out how you might kiss your posteria goodbye!

But refer to the recent seaking crash on the after deck of travelling ship, many cowboys reckon that T/R fails, no-one noticed the rapid quick flex down and up of the M/R when it unloaded in a typical vortex ring state, of course the T/R parted company with the rear end of flight path when it also got fouled up air.
Maybe no one has ever seen a cowboy film when the wagon wheel goes into slow flicker motion when in synch with and at right angles to the camera?? T/R was still going ok when it went past the cam close up and also when it smashed with high power into the deck and disappeared to the port side of the vessel.

[CareBear]

A technique that works in the Huey Simulator (or AB205 etc) following a loss of drive to the tail rotor:

1. Enter auto and roll throttle off to reduce tendency to spin to a minimum
2. Establish fairly fast auto to get some benefit from the fin
3. During auto gently re apply throttle
4. during the flare as the speed reduces and you start to pitch pull, the aircraft will begin to yaw due to frictional torque produced - at that stage start rolling off the throttle and that will help to keep straight.

Don't know if this is a "works for all" technique but it works on the Huey so my guess is it might work on 206 and other Bells.

Any one have use of a 206 sim to give it a go? Please let us know the results.

[SASless]

While a very new US Army pilot...in a land far-a-way....bummed a ride to H-3 Heliport in Saigon...sat in the front seat. Normal flight to H-3 with one stop in Di An for fuel....then to H-3. Arrived at H-3 to the hover....brief discussion about where to park...still at a hover....I point left ...the pilot looked left...and the aircraft turned right. Me being quick witted assumed the guy was doing a clearing turn or something. As the nose passed what had been the original 12 o'clock position we continued to turn right but at an ever increasing rate or rotation. The first turn felt almost normal in rate but did speed up as it progressed. As the nose passed the 12 o'clock position for the second time....and the rate of rotation was becoming interesting....being really quick witted...I asked the pilot what he was doing. As the nose passed the 12 o'clock position for the third time in a blurring eyeballs against my Aviator Ray-Bans.....again being quick witted I ascertained the pedals were full left, the world was still spinning left, and that my now deaf and dumb pilot.....was not reacting in as correct a fashion as I desired.

I asked him politely, in my slow measured southern drawl, to reduce throttle.....sounded kinda like an excited Geordie SgtMajor calling drill commands....."Chopthethrottleforchrissakesyouidiotwhatareyou tryingtodokilluschopthethrottlechopthethrottlepleasechopthet hrottleplease!

In desparation, fearing this guy was going to be like my Commanding Officer trying to decide what kind of marks to give me on my annual evaluation, and that I had other more pressing business to attend to.....I politely without saying anything to him...snapped the throttle off from my side. Not that I was aggressive with it...but the leather covering on the throttle came off in my hand as I recall with weird clarity.....and the rotation immediately slowed to an almost sedate pace....the world was only partially blurred. We landed with a good thump, sounds of paperwork being generated, and the aircraft took a decided list to port and settled by the stern. I opened my door, stepped up to the ground and tipped my hat to the pilot and headed for Saigon to visit the Christian Serviceman's Reading Center for a Kool Aid and cookies.

It is amazing how quickly the rotation slows or stops with the reduction of torque in a loss of thrust situation.

[ppng]

Anyone notice that the 'big guns' haven't pitched in so far? Probably it's because there is no single answer to this. React today in a certain way and you might get away with it - do exactly the same thing in the same machine tomorrow and we might all die (different weight, alt, temp, TAS, etc). Try it in a different machine (whichever way the blades go) and everone is toast every time. Trust the simulator if you're brave enough, but remember the way it responds is just a guess.
ANSWER (assuming control failure):
1. Don't panic.
2. Fly what you have left.
3. Don't panic.
4. Consider the wind direction for landing (having already thought about this on the ground one foggy day in advance!)
5. Don't panic.
6. Do everything slowly.
7. Don't panic.
8. Don't hit anything while not panicking!
9. Don't panic.
10. Good luck!

[the coyote]

I did one in a Robbo once as a demonstration for a student. I set the pedals to a pre determined position that gave neutral TR pitch (almost full right pedal). Rolled off the throttle and entered auto. At the bottom at the end of the flare it started to yaw left quite slowly and then more as the collective pitch pull came in. We touched down about 90 deg left of the original heading, so the key is to make sure you lose all ground speed. Either that or run it on at about max touchdown speed of 35 KT before it starts to yaw.

CareBear,

As per your scenario, I have used a very similar technique in the B206. Once established in the auto at speed, roll the throttle back on. Use only enough collective in the descent to prevent an Nr overspeed. During the flare and pitch pull, as it starts to yaw under torque, roll off the throttle to keep it straight and touchdown. Very controllable.

I think a genuine drive failure would be noticeably different to a simulated one though, due to the tail rotor still providing some stability even if it didn't have any pitch applied.

[John Eacott]

I guess the original question "in forward flight" has morphed into a general TR failure discussion. Whenever possible, practice, practice, and if you can, practice. Two I've had were both my fault, and instinctive reaction got us out in one (relative) piece on both occassions.

Low level filming in a 206L, I got distracted and hooked a wire under the toe of the left skid. The Mayday was instinctive, the decision to pull power to break the wire was the only solution (we were hanging nose down in our straps by then, with full aft cyclic), and I have no recollection of rolling off the throttle when the wire broke and I cut the tail off with the rotors. But it must have been instinctive, because we didn't spin

We were lucky enough to come down upright, but I snapped the collective trying for that last degree of blade pitch, and the back does still hurt now and then





The other was in the BK117, at night, backed into a tree in a high hover. The decision to dump the collective was done without thinking, and got us out with a slightly spread set of crosstubes, rather than rolled up in a ball.

No obvious training is going to account for every eventuality, but lots of practise (or mental preparation) will go a long way to making the right move "in extremis", the correct move

[NickLappos]

ppng said, "Anyone notice that the 'big guns' haven't pitched in so far? Probably it's because there is no single answer to this. "

Right on!

The idea of a "failure" consumes paragraphs describing what tail rotor thrust is left - lots, too much, cruise power, almost none. full right?

Then we deal with individual models of helo, and then with varying flight conditions, and then with experience levels, whew!

I'd rather answer, "Honey, do I look fat in these slacks?"

Boiled down to a short, accurate helpful answer, I like ppng's checklist just fine!