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HeliTorque :: View topic - Loss of T/R effectiveness
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HeliTorque Forum Index » Flight Dynamics

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Loss of T/R effectiveness
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bug
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PostPosted: Sat Mar 17, 2007 4:22 pm    Post subject: Loss of T/R effectiveness Reply with quote

I was thinking the other day that ....if indeed I ever experienced this almost always fatal phenomenon...that altitude would be a better friend to me and allow me to gain...with a vertical fin 40 knots or so...just a thought for you. I am not a pilot nor am I an engineer.
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PostPosted: Sat Mar 17, 2007 10:50 pm    Post subject: Reply with quote

Bug, you are way off the mark with "almost always fatal".

It ain't.

But it is "almost always" the best excuse for a stuff-up where the pilot simply demanded more from the T/R than it can provide, and with a look of horrified surprise, he conducts some ever-decreasing circles and disappears up his own fundamental orifice.

Know your machine, don't ask too much of it, and don't believe the Bell propaganda.
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PostPosted: Sun Mar 18, 2007 2:31 am    Post subject: Reply with quote

The trick with LTE is to be aware of the possibility, ALWAYS be smooth on the controls and to react IMMEDIATELY you see the nose moving to the right - this means not being asleep at the wheel! I am convinced that almost all of the occurrences are pilot induced - if you move the controls too quickly, you will get all of the drag without the lift while the induced flow builds up a split second later, and the same goes for the tail rotor.

In 3500+ hours on the 206, never had a sniff of it. And yes, to answer your question, altitude is best, but it is not necessarily fatal even at low level, as Charlie says.

Phil
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Heloplt
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PostPosted: Sun Mar 18, 2007 2:48 am    Post subject: Reply with quote

I have to agree that this isn't almost always fatal.

Quote:
Know your machine, don't ask too much of it


Thats the key. If you fly something with little excess T/R authority (like our OH-6's) its not something to play around with. Like my mechanic said, "she'll usually tell you when she is not feeling well." If you are hovering and you are dancing on the pedals to keep her pointed straight, she's warning you that she's thinking about coming around. At altitude its just disconcerting, at a 3 foot hover you had better be quick about getting that throttle rolled down. I had it happen in one of our OH-6's at a 600 foot OGE hover. It was hot and we were trying to spot something for the fire department over a brush fire. The winds were coming in from all over the place because of the heat off of the fire. The helicopter came around 180 degrees very rapidly and I lowered the collective and pointed the nose slightly down. The turning stopped about 270 degrees beyond my initial heading and I flew out of it after losing about 75-100 feet. Not a big deal because I had some altitude. Without that altitude it would have been a very big deal. Just be aware any time you are in a high torque hover or close to a hover you are a candidate for LTE. Of course mechanical failure could put you there anytime, but the mechanical failure is more likely to happen when you are in that high torque region because of all the stress on the drivetrain with the high power settings.

Not sure about the "Bell" stuff, I just finished the CFI refresher clinic at HAI and the Bell instructor (Randy Rowles) covered LTE in depth and he sure didn't imply his products wouldn't get into it (although our 407's have A LOT more tail rotor authority than our OH-6's). Hopefully the other Bell folks out there aren't painting a rosy picture about the Bell's ability to avoid LTE.

Jeff
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PostPosted: Wed Oct 24, 2007 8:17 am    Post subject: Reply with quote

i personally think its more important what you are doing at altitude the only time i have seen loss of tail rotor authority was at about 5000 ft asl and an h-60 was coming in for a cal fully loaded with relief supplies the high gross weight combined with the altitude and high torque demand of the steep approach the pilot pulled collective at about feet lost tail rotor autority spun about 70 degrees and clipped a power line while this was going on the pilot bottomed colective and landed very hard but probably saved the lives of him and his crew
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PostPosted: Fri Dec 07, 2007 3:47 pm    Post subject: Reply with quote

Quote:
Hopefully the other Bell folks out there aren't painting a rosy picture about the Bell's ability to avoid LTE.



As a relative newbie to helos (but with 40+ years of airplane experience) I have been working hard to understand as fully as possible the "gotchas" associated with the helos I fly. I have found much authoritative opinion on LTE in the online forums to the effect that LTE results primarily from helicopter designs with marginal tail rotor authority, and that around 95% of documented LTE events in light turbine helos occur in the Bell 206 series, due to the limited tail rotor authority of this design.

I am presently completing a Commercial certificate and Instrument Rating in the Enstrom 480B, and have been looking for info relating to LTE susceptibility in this helo. My instructor (20,000+ hours in Bells and Enstroms, and a helo accident investigator for insurance companies) says he has never heard of an LTE event in an Enstrom, and attributes this to substanial "excess" tail rotor authority in this design. He recently conducted a demonstration for me in which he wound Nr down to about 80% and proceeded to turn and hover downwind in winds of 15G22 with no trouble at all. I have read all the NTSB accident reports on Enstroms and can find no accidents attributed to LTE. Anyone have any informed view on LTE in the E480B?

Thanks,
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PostPosted: Fri Dec 07, 2007 10:45 pm    Post subject: Reply with quote

Not LTE, but in this 1980s accident in Australia, the Enstrom pilot demanded too much of the tail rotor and then didn't know how to get out of it. He was on a photo flight, reports said the machine hovered at altitude over several areas, facing in several directions, then was next sighted spinning and sinking until it fatally hit the ground. My brother actually saw it falling down.

No fault found with the machine, very junior pilot.
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PostPosted: Fri Feb 22, 2008 4:00 pm    Post subject: Reply with quote

LTE is not the fatal scenario most think. It does however require calm action and smoothness on the controls. What you do depends soley on WHY the LTE exists. Was there a complete loss of the tailrotor itself, or ineffective pedal inputs. Lets address the more severe.....TR separation. or loss of TR thrust. The most common method is to reduce collective and throttle so as to lessen the torque effect, reduce to autorotation speed and gradually descent to an altitude from which an autorotation is normally made.
Streamlining due to airflow over the fuselage will keep the ship fairly straight but some right yaw is expected.
IF yaw exceeds or approaches 90 degrees without any sign of stabilization, enter the auto immediately.
Loss of pedal effectiveness is hardly a problem Ship will fly almost normally due to the wind streamlining.
Use a shallow approach with runon landing, throttle to control direction, and reduce the collective to brake.
Flying helicopters when things go wrong can certainly be a nerve shattering experience, but it does not have to be a metal bending incident, or worse.

Fly safe and remember.....
BUMBLE BEES DO FLY!
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PostPosted: Fri Feb 22, 2008 4:33 pm    Post subject: Reply with quote

EN48 and Ascend Charlie,

May I comment on your post. Firstly, the Enstrom helicopter has always been noted for it's reliability, and yes...there are comparatively fewer Enstrom incidents then with other ships, but mechanical devices are just that. Push them too far and they break, or left to their own devices, will break on their own.
However, I cringe when I hear the term "excess authority". The Engstrom due to its' more powerful engine, needs more authority with the left pedal. This is by design. The larger tailrotor adds to its overall effectiveness.
It's all relative to the helicopters engine output, and TR airfoil design. A helicopter is seldom designed with "more" than what you need, but simply that which you might need in the normal operation of it.

Anyway, in reading over the Australia incident, Could it be possible that the crash was more the result of the pilot allowing the ship to enter a "settling with power situation". LTE will normally cause a yawing and rotation, but not rapid sinking. It would appear that the pilot was attempting to set the ship down, as we all would, but entered the ships own turbulent air cone. At low altitude, there is little time to "fly" out of it, especially with no tailrotor thrust.

Helicopters are wonderful flying machines, but the pilots who fly them need to "go back to basics" once in awhile and practice emergency procedures. In the normal course of our flying, do we usually go about doing low altitude autorotations, or hover autos? Periodic recurrent training will keep the "edge" on our side.

Safe flying!
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PostPosted: Sun May 18, 2008 9:18 am    Post subject: LTE Reply with quote

Go and have a look at www.sha-safetyofficer.ch and click the international button and you'll find something about LTE
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PostPosted: Thu Aug 13, 2009 8:20 pm    Post subject: Reply with quote

I was trying some slope landings with my instructor last week with my nose in a N direction and the wind at 240/8kts I found keeping the left skid on the slope very tricky and I didnt seem to have enough tail rotor authority when the wind was gusting. My instructor didnt mention it in the de brief, could it be the onset of vortex ring in the tail rotor or was it perhaps my lack of experience and knowledge of the situation. I have 15 hrs in the 22. Anyone out there experienced the same thing?
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PostPosted: Fri Aug 14, 2009 8:26 am    Post subject: Reply with quote

Have a look at this document regarding LTE.

In your case, the wind was probably a bit too far back on your tail to really be related. However, if it was gusting, was it also changing direction? Watch out for 10 o'clock winds!


(I'm sure there's a joke in there, about a 9 o'clock curry, or something...)
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PostPosted: Fri Aug 14, 2009 9:47 am    Post subject: Reply with quote

http://www.helicoptersafety.org/genericaccident.asp?keyword=LTE

Some of this may help , not all the videos are LTE but all are tail rotor related.
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