Hughes Tailspin [Archive]

BlenderPilot

19th Dec 2002, 15:18

Captain Lai Hai,

It really upsets me when someone instead of helping makes such a naive statement to someone who is asking about a legitimate question

From CLH:
"If your'e talking about LTE then you should consider flying fixwing.
There is no excuse for LTE unless of course your military"

I flew 500's in Africa and I have no idea what this "tail spin" thing is, but if I can't help, at least I won't make dumb comments, I really don't know what kind of flying you do, but in the kind of work I have always done, even while trying to anticipate everything (incuding LTE) I have ran into it several times especially in 206's, we are all humans and we can make mistakes in judgement once in a while.

I have never gotten off a helicopter feeling there was nothing else I could have done to make things better or safer, there is always room for improvement.

And I would never "send" a fellow helicopter pilot to go fly stiff wing for only asking a question. I have been flying for a decent amount of time now and just until recently I truly understood Vortex Ring State thanks to the patience and careful explaining of one of my fellow helicopter pilots. (thanks by the way)

If you can't be positive then just . . . . . .

AND NOW CAN SOMEBODY PLEASE EXPLAIN THIS TAIL SPIN THING?

BMK

20th Dec 2002, 09:36

It's a real shame to read Captain Lai Hai's curt remarks when I'm only looking for constructive input, and I thank you BlenderPilot and Steve76 for yours. Visit Google and enter 'Hughes Tailspin' and you will find at least two specific references to the issue, one entitled 'A History Lesson' and the other 'A Tribute to a Great Aviator'. Oh and a message to CLH.......I have been (and still am) a fixed wing pilot for many years......however, five years ago I moved on (and some might even say up) to rotary and it's wonderful. :cool:

ATPMBA

20th Dec 2002, 12:41

BMK,

It sounds like you encountered Loss of Tail Rotor Effectiveness (LTE). I know of a fellow that this happened to in a H-500. I don’t have all the details but what I do know is that he was out on a mission on a hot summer day, hovering OGE, and all of the sudden the helicopter starts turning to the right. He thought he had a tail rotor failure, he entered an autorotation and landed with some minimal damage. The main thing about this incident is how surprisingly quickly it happened, one second he was fine and the next he was yawing to the right.

Tail Bloater

20th Dec 2002, 12:44

I know of two instances of this situation. That you have given so little data for us to unravel the problem, I can only tell of these two 'tail rotor spins'.

Both occurred on the same airframe and it would appear that the reason was as follows.
Approaching to the hover, little wind. too greater rate of descent building up as the craft closed with the hover point, large input of collective with no immediate pedal to compensate, heli yaws, pedal applied but too late, pilot thinks he has applied the wrong pedal, applies the opposite pedal, heli spins faster, pilot applies original pedal but too late and doesn't push hard enough or for long enough, first occurrance pilot recovered, second time heli splattered over ground, nobody hurt.
I believe it was too much collective too late without sufficient and coordinated pedal input.
It's odd that now that the Gazelle is in civilian hands this problem is happening and for no other reason than explained in the paragraph above.
If anything lead with the pedals!

PPRUNE FAN#1

20th Dec 2002, 14:42

We tend to think of the tail rotor having unlimited power-- if we think about it at all. We blindly assume that we can just push and push on the anti-torque pedal and it will always have enough "oomph" to counter the effects of engine torque, weathervaning tendencies...whatever.

Some helicopters have notoriously weak tail rotors. And it is a sickening experience to feel the clunk of the left pedal (CCW rotors) hitting the stop. Worse still is when the tail rotor gives up the ghost prior to getting to the pitch limit.

Smart helicopter pilots will always be aware of the amount of reserve thrust in their tail rotor. When we find ourselves in conditions of low airspeed, high power and a right-hand turn to the downwind (again, CCW rotor of course), it gives us goosebumps. Or it should. Because we must be ready for the yaw. Not only that, we must have a plan of action for when we do get it. Like, how to get out of it.

Flying helicopters is a "pro-active" and not a "reactive" activity. You cannot wait for the aircraft to do something before reacting to and correcting for it. Not to be harsh, but one cannot say, "I got into the dreaded Hughes tailspin!" without acknowledging that there were predictable circumstances that lead up to it......circumstances that the pilot should have noticed and been prepared for. That's like saying, "I got into dang ol' settling with power...it's the aircraft's fault!"

This is, I believe, what Captain Mai Tai was alluding to.

IHL

20th Dec 2002, 16:16

This is from Transport Canada's Safety Web Site.
Vortex is Canada's helicopter safety news letter.

Aviation Safety Vortex 1/2002

LTE Accidents

Many of you have seen the literature on LTE before. Bell Helicopter and the United States Army have been aggressive in getting the message out for many years. Still, these accidents continue to occur, and many models are susceptible to this phenomenon (I’ve personally had it happen to me in a Hughes 500D, luckily without incident). Here’s a brief sample from the archives.—Ed.

May 1994
Hughes 300C

The helicopter was being used to search for a missing person. The pilot turned the helicopter abruptly downwind to search down a river bank and lost tail rotor effectiveness. The helicopter rotated through 3600 and descended rapidly toward a swamp. Despite the application of full power, the 300C landed heavily in swampy ground, breaking the skids.

July 1996 Bell 206B

As the 206 approached the pad at 7600 ft., it lost tail rotor effectiveness and spun through 3600, striking the pad heavily and damaging the skids, tail rotor and lower fin.

Oct. 1985 Hughes 269A

Tail rotor authority was lost and aircraft rotated into trees.

August 1988 Bell 206B

While looking for a remote site in mountainous terrain, a loss of tail rotor authority occurred. The helicopter struck the trees and came to rest about 6300 ft. ASL.

Sept. 1994 Bell 206B

The pilot had just released a sling load and was preparing to land when he lost tail rotor authority and the helicopter began to rotate. The helicopter struck the ground and rolled over on its side, suffering substantial damage.

July 1993 Enstrom 280

Just after liftoff the pilot lost tail rotor authority, and the helicopter began spinning. After numerous 3600 turns, the pilot rolled off the throttle and attempted a landing. On touchdown, the tail struck the ground and the tail rotor guard bent over, damaging the tail rotor and drive shaft.

Last updated: 2002-08-16 Important Notices

IHL

20th Dec 2002, 17:22

For more info on LTE check -out.

http://tcinfo/civilaviation/systemsafety/newsletters/tp202/1-02/V007.htm

Captain Lai Hai

21st Dec 2002, 09:25

BTW

Sincere apologies.

However I don't believe an experienced pilot should ever unintentionally get into LTE.

May I suggest to you that if for example you're on a photo job with the photograher and all his friends and their relatives as always happens hovering OGE say at a 1000' you have to expect you will be approaching the A/C's limitations and you will feel it without having to refer to the panel.

The collective position the amount of tail rotor you're using etc etc
Try using your collective as well as TR to control yaw.
You will be surprised how much more control over heading you can retain hovering in that spot with the wrong winds without losing any noticeble altitude.

Of course if your close to the ground you might want to consider keeping a bit of airspeed up and if you need to turn down wind climb a first to give you some margin to covert height into airspeed if required.

Steve 76 wrong assumption again

Seasons greetings to all and fly safe

Lu Zuckerman

21st Dec 2002, 20:03

On December 5, 2002, at 0900 central daylight time (cst), a Hughes OH-6, N353RK, operated by Freelance Air, Inc., lost tail rotor effectiveness during cruise flight and executed a sliding landing at the Omar N Bradley Airport (MBY), Moberly, Missouri. The helicopter was not damaged and the pilot was not injured. The 14 CFR Part 91 repositioning flight departed the Spirit of St. Louis Airport (SUS), St. Louis, Missouri, at 0810 cst, en route to Omaha, Nebraska. Visual meteorological conditions prevailed. No flight plan was filed.

:D

sycamore

27th Dec 2002, 22:43

Lu, in the case of the OH-6,this must have been a " loss of tail-rotor control", in that either the t/r fell off, the drive to the t/r failed ,or the t/r controls failed, or even a combination.
I can`t see how you can have LTE in the cruise,as it usually manifests itself at low speed,high power,a lot of yaw pedal input,,and combinations of high alt,or downwind approaches, or similar situations as you lift to the hover.
Nevertheless, it was obviously well handled and ended safely- the main criterion!!:)

Lu Zuckerman

28th Dec 2002, 00:12

To: Sycamore

Those are not my words above. It is a direct lift from the NTSB accident site.

:cool:

spinningwings

28th Dec 2002, 11:37

Interesting thread this ...a good one for new chums to think over... The OH6 mentioned I hope had the metal T/R blades fitted....cos I can rember many many moons ago flying Hu 500As and Cs with the older Fibreglass T/R blades and they DEFINATELY would allow for the pedals to hit the stops and occassionally if one was not careful would STALL and cause LTE ...IT CAN happen to anybody. Anybody familier with the Bk117 flight manual ...the B1 & B2 versions have a torque limit imposed below 40kts IAS cos you "might" run out of T/R authority during slow speed ops! :eek: :eek:

Alien1950

29th Dec 2002, 21:42

Lots of input from knowledgeable people reporting other incidents of LTA.
But none explaining (or pointing to a source of explanation) the aerodynamics of this phenomena.
Vortex ring and settling with power get lots of coverage in training manuals and I have had them demonstrated by instructors. But never have I had a briefing on what nearly killed me in my H500 last summer (I was P2)
To find that the US army(go to www.google.com and put in 'hughes tailspin') knew of it with sufficent familiarity to name it "the Hughes Tailspin" means that it's covered somewhere, and others have died because of it.

Can someone tell me where, so that I can better understand it and avoid becoming another statistic?

tecpilot

29th Dec 2002, 22:53

@spinningwings

BK 117 B1 / B2 have a torque limit from 2 x 83 if the IAS is below Vy=65kt. That's 12% more than on higher speeds!!!
LTE on a BK 117 with the large fins and forward speed within the approved weights and altitudes, should be impossible. The torque could also be limited in line with construction and airframe problems. Think about the loss of the tail rotor on a BK 117 in the US and some equal crashes on other types.

Please don't mix several problems. The effectiveness of the tail rotor on all helicopters is limited.
It's public that some helos have more problems than others. It's a very complex problem with great parts from aerodynamics, kind of construction, design and used material. And some kinds of construction and design are still a compromise with other helicopter problems.
Tail rotor effectiveness depends from height of the tail rotor to the main rotor, turning direction, left or right hand on the helo, rounds per minute- blade profil - blade lenght - blade tip speed, bending of the blades, construction type (rigid, semi-rigid, fully...) and... and...

Sycamore is right "you can't have LTE in the cruise,as it usually manifests itself at low speed,high power,a lot of yaw pedal input,,and combinations of high alt,or downwind approaches, or similar situations as you lift to the hover"
Pilots must be carefully on such conditions.

PPRUNE FAN#1

29th Dec 2002, 22:55

Alien, it's not that hard to understand. First you must realize that "loss of tail rotor effectiveness" (LTE) does not happen in cruise flight. It does not happen on a normal approach, or even a steep approach at the altitudes that most of us fly (excepting, of course, a chap who owns his own ship in Nepal perhaps). It will generally not happen if you keep the wind on your nose instead of your tail.

It will always happen at very low airspeeds, close to ETL or below, when the streamlining tendency of the ship is also low, especially when operating with a quartering tailwind, (or at a high d.a.) and usually when you've got a lot of power pulled in (but not always on that last part).

There are three possibilities:

1. The tail rotor gets into a vortex ring state of its own, possibly due to interference from the wake or downwash of the main rotor. The tail of the ship "settles with power" sideways. This manifests itself as an uncommanded yaw rate.

2. Or maybe the wimpy tail rotor does not have enough thrust at maximum pitch (full pedal) to stop the aircraft from yawing at that particular airspeed, power and wind condition.

3. The vertical fin blanks off enough of the tail rotor that it momentarily can't get enough "bite" and you find yourself in #2.

The solution for all of the above examples is to avoid these conditions in every helicopter in the first place. Be aware of how much anti-torque pedal you have applied, and use caution when you're approaching an extreme.

That way, if it snaps around on you, you'll be ready for it. Then, keep FULL pedal applied, as the tail rotor is not "stalled"...at least, not the conventional way we think of an airplane's wing stalling from flying too slowly...at least, as long as you're not in a recip and you've allowed your MR rpms to get low.

However! There may be other things going on. You may be heavy, requiring a *lot* of power for the airspeed (or lack of it) you've got. The quartering tailwind may be strong enough to get you into LTE, but not strong enough to allow the ship to weathervane once it gets around and pointed into the wind, so momentum keeps it spinning. In these cases, you'll probably have to reduce the power/torque (i.e. lower the anti-torque demand) and maybe lower the nose to increase the airspeed to get some weathervaning tendency back.

Pilots in Viet Nam were surprised to find that the original OH-6A had a small, weak tail rotor compared to the aircraft it replaced, the Bell OH-13. The Army quickly recognized this not-so-improved feature of the new ship, and adapted to the limitation. But just about every small helicopter is susceptible to LTE. And if the LOH competition had been won by the Bell's entry, the OH-4A - at least, with its current fin as opposed to the little half-a-fin that the original design had - it would be known as the "dreaded Bell tailspin."

Oh wait...the Bell design *did* become famous for that! ...Or "infamous" perhaps.

helmet fire

30th Dec 2002, 02:38

Another good example of terminology clouding the issues:D

"Tail Spin" is what stiff wingers do between Immelmann's and stall turns when showing off!

We fling wingers should call it one of the new fandangled name for it depending upon what you have experienced:

Loss of tail rotor control: You are not able to control the tail rotor pitch mechanism.

Loss of tail rotor thrust: Little spinning thing at the back stops spinning or falls off.

Loss of tail rotor effectiveness (LTE): "Newly" discovered and named in the 80's after many (in particular OH-58/B206) accidents. Although somewhat awkwardly named (as the tail rotor is still effectivly working and must be providing thrust) LTE refers to what is thought to be an injestion of main or tail rotor vorticey through the tail rotor which causes an onset of yaw in the direction induced by torque that cannot be overcome by the application of full "power pedal". The yaw rotation can build up quickly enough to fool most pilots into believing they have experienced a loss of tail rotor thrust. The concept has come under fire lately because of the early thoughts that the tail rotor enters vortex ring state being a little hard to proove. Oh - and then there is fenestron stall that possibly fits into this category too, although strongly denied as a possibility by the manufacturer whilst alledgedly being strongly experienced by the pilots!

Loss of Tail Rotor Authority(LTA): Also a new term to make the old Huey war story of "..and then I ran out of bloody left pedal and..." sound a little more sophisticated and technical. In this situation, the tail rotor does not produce enough thrust to counteract the torque/crosswind combination you require, your power pedal hits the stop, and around you go - though often quite gently when compared to LTE or loss of thrust. A lot of aircraft are susceptable to this, but the UH-1D/H Huey is famous for it - and many people have had the earth come up and smite them as a result. Someone mentioned the BK117 - it too is quite susceptible to LTA unless fitted with the C model tail rotor.

Thus BMK, you will need to give us a lot more info on your aircraft type/model, AUW, DA, manouevre you were attempting, wind strength and direction and IAS before we bull$hit artists can possibly hope to have a stab in the dark and argue around and around in circles about what caused it.:D

BlenderPilot

30th Dec 2002, 03:04

Over here at altitude 206L4's w/no High Alt. Kit will run out of left pedal a lot sooner than you will run out of power (TQ, TOT, N1), learning this has led many pilots around here to some nasty surprises. With the L3 if you watch your wind you'll run out about the same time you reach both limits.

I remember there was this really tall building I used to fly out of with a TV crew, and somedays the thing would hover IGE about 12 inches from the ground with 75% TQ, but the left pedal would be almost all the way in, any increase in power would start the nose going right and no pedal to stop it, so in order to clear the pad you had to start pulling pitch 180 deg. from the desired exit, the L4 would climb as it yawed right with the left pedal all the way in, then as I reached the desired heading being now 20-30 feet high, I would lower collective slightly to stop the yaw, and push CYCLIC forward until I had some airspeed, needless to say when the aircraft sank I now had plenty of altitude to clear my tail from the edge of the building.

Returning to the pad heavy was a completely different story, but I guess easier since it requires less power to land than to take off, but you had to have the wind help you.

My pics,

http://homepage.mac.com/helipilot/helicopterpictures/PhotoAlbum15.html

John Eacott

30th Dec 2002, 03:44

FWIW, here is my Ops Manual supplement on LTE for the B206. Any (constructive) criticism gratefully received, it was written 15 years ago, and could always do with updating!

D3.1 INTRODUCTION

D3.1.1 Unanticipated right yaw, or loss of tail rotor effectiveness (LTE) is when an uncommanded right yaw occurs which does not subside of its own accord, and which, if not controlled, can result in the loss of control of the helicopter.

D3.2 CONTRIBUTING FACTORS

D3.2.1 The following factors will contribute to the onset of LTE:

(a) High gross weight and high temperature.
(b) Tail wind component
(c) Low airspeed
(d) Loss of translational lift.

D3.3 SYMPTOMS

D3.3.1 The following symptoms may be experienced prior to the onset of LTE:

(a) In the event of an unanticipated right yaw, the tail rotor will have insufficient authority to control the yaw.

(b) The helicopter will commence a rapid right rotation, with a nose down attitude.

D3.4 RECOVERY TECHNIQUE

D3.4.1 The following recovery techniques should be employed:

(a) Simultaneously input full left pedal, and forward cyclic to increase airspeed.

(b) When recovery technique takes effect, control the helicopter to recover to normal flight.

(c) Collective pitch reduction will assist the reduction of yaw, but should be used with caution in view of the resulting increased rate of descent.

(d) Should loss of tail rotor effectiveness occur at low altitude (below 1000 ft agl) and reduced collective be used to assist recover, the increased collective pitch subsequently required to reduce the rate of descent may lead to increased yaw rate and reduce rotor RPM.

(e) Should uncontrollable yaw continue to low altitude, the pilot should consider a full autorotation to the ground. Full left pedal should be maintained until the spin stops, then adjusted to keep heading into wind for landing.

D3.4.2 Recovery actions as laid down in the appropriate Flight Manual will take precedence at all times.

D3.5 AVOIDANCE

(a) Operations at low or hovering airspeeds OGE should be avoided in a relative wind that has a tailwind component.

(b) For low speed operations, eg orbiting a ground feature during aerial filming, close attention should be paid to the airspeed in order to avoid loss of translational lift. Constant airspeed must be flown, not constant groundspeed.

D3.6 BELL 206B/206L FLIGHT MANUALS

D3.6.1 The performance section of these manuals deal with "Critical Wind Azimuth Area", and its effect on helicopter performance is shown in the HIGE and HOGE graphs.

D3.7 CLOCKWISE ROTATION ROTOR SYSTEMS

(a) Loss of tail rotor effectiveness will result in LEFT yaw in helicopters with clockwise rotor systems, eg AS350B.

(b) In this case, recovery is as described for right pedal demand instead of left pedal.

D3.8 REFERENCE READING

(a) Bell Helicopter Textron "Rotor Breeze" July/Aug 1984

(b) Bell Operational Safety Notice OSN 206-83-10 Oct 1983

(c) Bell Information Letter 206-84-41/206L-84-27 Jul 1984

(d) Department of Aviation Central Office Paper Apr 1983

(e) Air Safety Digest 128/86 Autumn 1986

Nick Lappos

31st Dec 2002, 03:13

As a general rule, true LTE is very hard to induce in most helicopters. It is certainly not endemic in all single rotor helicopters, in spite of the FAA/Bell publications that try to insinuate that any helo has a propensity to lose tail effectiveness.

The factors that get you close are generally not laxity on the pedals, they are more likely cause by using using too much main rotor power/collective pitch, especially at the bottom of an approach. If the approach is made with too much speed and rate of descent, arresting the descent at the bottom will take an armful of collective. The extra torque, above that needed for the hover after all the approach transcients have settled, is all a problem for marginal tail rotors. Most LTE accidents occur in the termination of an approach, sometimes downwind, or in a cross wind. Most LTE accidents also occur in only one or two types of helicopters.

In a study I did a few years back, surveying all reported helicopter accidents for a 2 year period, some interesting facts about LTE came out:

1) 90% of all LTE accidents occurred to Bell 206 and Bell 205 helicopters, the other 10% were spread across a great number of types.
2) None occurred in modern helicopters designed to higher yaw control standards, such as those that the Black Hawk, Apache and OH-58D had to meet. Pertinent to this thread, no LTE accidents occurred to Hughes/McD helos (in that study)].
3) For all helicopters LTE was a small accident contributer (less than 2%) but for the Bell 206, it was the cause of more than 10% of all accidents.
4) A high percentage of LTE accidents caused major damage, but few resulted in loss of life (low altitude, low rate of descent).

spinningwings

31st Dec 2002, 12:23

Tecpilot
....thanks for your input ...I do however stand by my post...the Bk Torque restriction is I believe <40kts IAS but having said that it has been a year since I read the manual !!!
and I do believe (?) that the restriction goes away if the "C" model T/R is fitted.....
and if the Bk crash due loss of tailboom pylon is the accident you are refering too ( the Colgate aircraft), then if you investigate it you will find that it was due to a maintenance fault due to use of incorrect rivets used on doublers to repair frame cracking ....which was probably caused by vibration. ...

cheers all the best for the New Year everyone

:D

Shawn Coyle

2nd Jan 2003, 17:32

We live in an imperfect world.
Loss of Tail Rotor Effectiveness is one of those imperfect things. It can happen in just about any helicopter if the conditions are right. The Gazelle had it, and the UK military had plenty of examples of it happening. I know, as I was at Boscombe Down when the first reported loss due to this happened. It has been widely reported on the OH-58/206 series - in fact Bell Helicopter deserves tons of thanks from the helo community for delving into the problem - one of their test pilots won the Test Pilot of the Year award for this work.
Aerodynamics at the tail rotor are very complex, and have more variables than we probably know.
I've had LTE in a couple of strange places, but at least had been prepared for something like this and could fly away.
Like everything else- preparation and a prior plan will keep you out of trouble in the long run.
High power settings, or large power changes, wind not right on the nose, slow to put in a pedal input are all things that contribute. My recommendation is to always turn left (if you have to do turns at slow speed) in CCW main rotor helicopters - this means if you're doing photowork, put the photographer in the left side; make sure you always approach into wind, and know what to do if you get the loss of tail rotor effectiveness. The consistent advice seems to be add full left pedal, forward cyclic and get airspeed across the vertical stab.
For what it's worth.

Nick Lappos

3rd Jan 2003, 10:19

Shawn may be technically correct in that LTE "can happen to any helicopter" but in fact, it does not. If the helicopter is designed right, the probability of incurring LTE is nil. LTE is actually a misnomer, the tail rotor never looses effectiveness in LTE accidents, it is merely too small to do the job when it is swamped by events. The poorer the tail rotor, the more easily those events can be arranged.

Only some helos regularly experience LTE, and those are demonstrably poor in anti-torque control margin. LTE is actually been eliminated by modern military design rules that require more powerful tail rotor designs by specifying more rigerous yaw maneuver capabilities. Unfortunately, the civil regulatory folks have actually allowed LTE to continue in new designs by blaming pilots for LTE, and by allowing explanations such as these to stand in the place of a demand for proper yaw control capability.

The award that was mentioned above for the team that promulgated the training words about LTE was also un-earned (in my opinion) because that same group fought any improvements in yaw control regulations, thus assuring LTE would be around for years more in newly approved helicopters. In fact, there are newly approved helos that have no yaw control power when loaded fully. Beware of those machines that are approved for " Cat B, 9 passengers or less," and that require the wind to be only from the nose during hover. Those are code words for helicopters whose tail rotors are so poor that no yaw capability exists, and LTE is one inch away.

I actually fought a move to include the LTE words in ALL single rotor helicopter flight manuals, because we saw the real handwriting on the wall, where if we allow the blame to be placed on the pilot, we don't have to worry about fixing the aircraft. See my above post for the actual statistics on LTE. LTE is not a pervasive single rotor helicopter problem, LTE can be cured by modern design rules, and LTE is not something we as pilots must accept forever.

Shawn Coyle

3rd Jan 2003, 15:19

Nick:
You are, of course, correct - LTE cannot happen in some helicopters that have been designed to meet military requirements. Sorry for the slip up.
It is interesting to note that the design standards only call for sufficient tail rotor authority to handle winds of at least 17 knots from any quadrant, at maximum weight, and typically 7,000' density altitude. If the helicopter is not using maximum power in these conditions, then what is the pilot to do who wants to takeoff and climb vertically (and has enough power to do this)? He will probably run out of tail rotor authority, because there is no certification requirement for this!
But what do we do about the examples given for the 206L series that appears to run out of tail rotor well before the certification requirements? Was it overloaded for the density altitude? Should an incident report have been sent to the FAA about the lack of tail rotor authority?
Interesting discussion.

Nick Lappos

3rd Jan 2003, 18:33

Shawn,

It is worse than you think. The FAA has approved a bunch of aircraft for weights at which there is NO side flight capability, using a change to 27/29 that allows them to abrogate the 17 knot demonstration. They retain just the ability to hover and approach/depart with nose into the wind. Look at:

http://www.bellhelicopter.textron.com/products/commercialHelicopters/430/

page 22, step 2 shows how to calculate the weight at which you have no sideflight capability, whic is the weight for Cat B, 9 pax or less operations. They have similar charts for the 412 family and ohers. They have proposed these weights for Saudi mountain rescue operations in the 412!

Check out page B101 of AC 29-2C:

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/1ab39b4ed563b08985256a35006d56af/107c87959e896f13862569cf00737a9d/$FILE/Chap2_pgB46-B124.pdf

IHL

3rd Jan 2003, 20:46

Hi Nick:

Has there ever been any LTE incidents with the S76?

Shawn Coyle

3rd Jan 2003, 21:09

Nick:
I would be slightly happier with this state of affairs if we had a good low airspeed sensing / indicating system for helicopters, but sadly that is not the case.
I guess we just need more educated users and procurement people so we don't get snookered by this sort of thing in the future.

helmet fire

3rd Jan 2003, 23:26

John Eacott, that is a great Ops manual explanation. A couple of points from a different perspective:

It does not distinguished LTE from loss of tail rotor thrust in the opening explanation.

Para D3.3 does not explain the symptoms "prior" to LTE, rather it details symptoms of developed LTE.

Para D3.4 (c) and (d) say the same thing. For para (e), this recovery technique came in for critisim afetr an Australian Army B206 suffered from LTE in a fifty odd foot hover and the (low time) pilot correctly carried out checklist actions: Lower collective - if insuffcient height remains to enable the collective to be lowered: conduct autorotation. Further investigation of the accident concluded that the checklist could be ammended to reflect a revised approach to an LTE situation which was to maintain collective (where low altitude prevented lowering it) and use cyclic to fly out of the spin with forward and out of turn cyclic application. Obviously, such action requires the pilot to be full conversant with the difference between LTE and loss of tail rotor thrust - hence my first point.

As an aside, and quite disappointingly, the fact that the pilot correctly carried out the checklist actions in the above accident did not seem to help him fight critisim of his actions by more senior pilots. :(

Para D3.5 (b) (probably unitentionally) implies a limitation on your aerial filming operations to be conducted above translational lift regardless of helicopter type or conditions. This may indeed be prudent in B206 Ops with low time pilots, but I think it is not appropriate in AS350 or BK117 ops.

:cool:

the wizard of auz

4th Jan 2003, 08:20

I was studying my aerodye stuff the other day and came up with this very question......can you get a "settling with power" effect on the tail rotor?. then I read this bit on this thread

1. The tail rotor gets into a vortex ring state of its own, possibly due to interference from the wake or downwash of the main rotor. The tail of the ship "settles with power" sideways. This manifests itself as an uncommanded yaw rate.

I really hope this is the way things happen because it was about how I was thinking......other wise its back to study to get the right answer to my own question. (god I hate wanting to know everything, all it does is continually raise more questions)
What would the right recovery actions be? lower collective and cyclic forward? would a slight decrease in power help? how does this effect machines that decrease power when lowering the collective? (governer/corrilator?)
Has anyone had this problem with the R22? I would expect the machine would be in the worst sorts of conditions all the time whilst mustering in the north bit of oz.

Lu Zuckerman

4th Jan 2003, 15:48

To: Shawn Coyle

I would be slightly happier with this state of affairs if we had a good low airspeed sensing / indicating system for helicopters, but sadly that is not the case.

I believe such a system was developed by a firm called J Tech. It was originally designed to be used in underwater operations to detect water currents. It worked just as well in air. It operated on the principle of vortex shedding with the vortex frequency being detected by an ultrasonic detector. The individual units were coupled to provide airspeed in four directions

Another system is employed on the Apache and the USCG HH-65 but I believe in the case of the Apache, it is used to detect wind direction with this information being fed into the main computer to calculate windage for the chain gun. On the HH-65 I believe it is used to detect wind direction to correct for drift when in a hover. At least that is what I believe to be the reason for the systems.

:cool:

GLSNightPilot

4th Jan 2003, 22:06

Nick, you may believe that modern helicopters designed to military standards cannot experience loss of tail rotor authority, but I don't. I think any helicopter can experience it, with enough gross weight & altitude. The UH60 that crashed & rolled down the mountain under the gaze of CNN experienced it. Certainly some models have more margin than others, but I don't believe it's impossible in any model.

helmet fire

4th Jan 2003, 22:30

GLS:

I would draw a distinction (see my earlier post) between LTE and LTA, and the UH60 most certainly did not have LTE.

As for LTA, I think that most helicopters would experience it at such extreme DA's when attempting to operate the aircraft outside it's maximum performance envelope. I still do not know what happened in that accident, but it simply looks like they ran out of power (whether by low side failure or simply hitting the limiter). Losing main rotor RPM costs you exponentially more loss of lift from your tail rotor due to loss of tail rotor RPM (because of V is squared in the lift equation). Thus the tail rotor is no longer able to provide the lift you require even though you are at full pedal, and around you go - just like the UH60. Just like any single rotor helicopter at such extreme DA's with a main rotor that is bleeding off. No certification is required for helicopters to maintain tail rotor authority at extreme DA's with out of limits decayed RRPM.

The difference between these "modern" designs and say the UH-1H is that the poor old Huey runs out of left pedal at high DA's before you even get to the bleed. In fact I think there is a warning about this in the FM for DA's above (now I am stretching the memory) 4000 ft and weights above 8300 lbs (9500lbs is MGTOW - reduced from 10500 in the original design).

In other words, Nick is quite correct and the UH60 accident does not contradict him at all.

FJVee

5th Jan 2003, 08:50

BMK, check out http://www.lighthorseaircav.com/s-a-history-lesson.html for a similair incident during the SEA era. Regards.

BMK,

Quite a long article , as on my last , here it is pasted to save time:

In D Troop, 3rd Squadron, 5th Cavalry, the Scouts, call sign "War Wagons", carried their gunner/observers in only the left front seat with the pilot in the right. With the rear of the ship nearly empty there was always room for picking up a crew that had been shot down. Each aircraft had a 7.62mm mini-gun mounted on the left side. The gunner had an M60 machine gun and we only made left-hand turns. Left hand turns required a little more power but the possibility of encountering "Hughes tailspin" was minimized. The tailspin arose during slow right turns at high power settings, finally resulting in loss of tailrotor effectiveness and the helicopter would spin out of control. Not a good condition when flying very close to the ground!

Regards.

LordGrumpy

5th Jan 2003, 10:25

Following on from John Eacott's informative post.
Can this situatiion always be flown away from, provided the helicopter has enough altitude and room for manouvre.

John Eacott

6th Jan 2003, 00:04

Helmet,

Thanks for the comments, I'll see what I can amend to cover some of them. Point taken about low level ops being restricted if applied to other aircraft, but this is specifically the Bell 206 supplement. I'd hoped that Para D3.4 (c) and (d) were dealing with separate issues, but I see how they can be read to be the same, and I'll research the issue of para E. It was all written a few years ago....

Lord G,

I'd venture to suggest that it is in the lap of the Gods whether it can always be flown away from. Given a trained and capable pilot, and as you say suffient altitude and airspace, it should be recoverable, BUT it happens extremely quickly, and will consume heaps of altitude before all stops whizzing around ;) Those I know who have encountered LTE and recovered could not stress enough how sudden and sever the onset is, often with little or no warning.

Skycop9

6th Jan 2003, 02:47

I have over 1200 hours in the OH6A and fly for a police department. The OH6A has numerous references in the Operators manual (-10) which cautions about right hand turns when you are close to the ground and at a slow speed.

In the OH6a, (500C) the V tail can develope lift and force the nose of the helicopter down and to the right when you have a right quartering tail wind. This is not loss of tail rotor authority. It is the wind exerting a force on the LARGE stabalizers. If you do not have enough altitude you may not be able to correct the attitude without ground contact.

I have experienced this on a number of occassions but because of altitude been able recover. Other unpleasant things can happen at High gross weight, Density altitude, slow airspeed, etc.

What type of a "tail spin" are you refering to? Is it the nose being force down during slow flight or LTE? Provide some more information and possibly I can provide you with more information.

If you would like like can email me.

[email protected]

:cool: :cool:

Nick Lappos

6th Jan 2003, 13:50

GLSNightPilot,
That is the problem with imprecise lables that cover several points. The available yaw control power in a Black Hawk, Apache, S-76 or OH-58D make LTE very difficult to find, and easy to get out. To teach and advocate that "any helicopter" can get LTE is to blur the real causes and prevent the real solution. No Black Hawk has had true LTE, even though you think so.

The HH-60 that crashed at Mt. Hood had been drooped down to very low Nr because it was hovered beyond its capabilities. At very low rpm the pedal reached the stops.

The truth is that LTE is not a prevelent accident cause for most helicopters, and it is a big problem for a few. You don't have to believe that, I guess.

If we want to stop LTE accidents, we should all understand their cause, and fight for helos with big enough tail rotors so that LTE is not a problem. Continue to say that LTE is purely a pilot problem and you blur the real message, you make it entirely possible to sell dozens more marginal helos.

Shawn Coyle

7th Jan 2003, 16:14

To Lu:
We have a low airspeed sensing system on our UH-1N, courtesy of the Canadian Forces who left it on when we purchased it from them.
I have used this system for performance testing, and also used the HH-65 system. both work well.
They just need to be understood and a more robust system made for everyday use.

GLSNightPilot

8th Jan 2003, 00:56

Nick, I agree that some helicopters are more susceptible to LTA, LTE, or whatever you want to call it, than others. My only point was that none of them are totally immune under all conditions. Get high enough, let the Nr droop under adverse wind conditions, & most any helicopter can lose tail rotor authority & turn without control.

To summarize, perhaps unfairly, some of your previous posts, everything about helicopter design is a compromise. The marketplace decides which compromises are acceptable & which aren't. Unfortunately, pilots have less say in this than they should have. Like you, I'd take Cat A performance under all conditons, unlimited range, & all the rest if I could get them, but my employer decides which aircraft he will buy & I will fly.