Videos of LTE?
 

Not wishing to re-open the debate. Just wondering if anyone has access to any videos of helicopters undergoing LTE?
Any model will do.

Here is one great video of waterboming Skycrane doing 360 just right before it dropped it's load taken from the ground under it. It was posted here before link

great stuff:ok:

That video is a fine illustration of what happens when you pull too much torque, reduce your rotor rpm and then lose yaw control. It is not LTE in any strict sense.

Shawn,

I even star in THIS ONE , I was flying the subject helicopter right before the camera ship started spinning. If you need it in higher resolution I can probably find the original.

Notice how they began spinning a lot higher than that 35 story building and they ended up almost all the way down. The spinning ship was a Bell 203 L3 which at this altitude when heavy has enough power to hover OGE but not enough tail rotor power to keep the helicopter from spinning.

By the way I got your book a couple of weeks ago and I haven't put it down since! Muuuuy Bueno.

Close Call.

The link does not work for me either - the other JPEGS on that directory though are simply stunning, some of the best heli pics i've ever seen - are they all on the Rotorheads around the world thread ?

http://www.helicopterservice.com.au/photos/Dawson/

Blender, what recovery action was taken in your video exactly ? Thanks.

PP,

The movie is in Quicktime format: do you have QT installed? If not, it won't download and display.

The directory is of photos taken by Neville Dawson, I hosted them for him when he didn't have his own ftp site, and left them as a courtesy to previous links that he set up. His current iteration is Ned-Air2Air (well, for the time being ;) :D :ok: )

So is it more correctly to say, the Air Crane was"out of left pedal"? not LTE?, but isn't correct though that the tail rotor was ineffective when it's rpm dropped, and the ship Lost Tailrotor Effectiveness :confused:

RR,

There's a difference between LTE (Loss of Tail Rotor Effectiveness - in it's simplist terms, the TR is not 'big' or effective enough to provide control within the entirety of the flight envelope) and LTA (Loss of Tail Rotor Authority - TR doesn't have enough RPM to maintain control due to mechanical problem or the pilot 'overcooking' things).

This has been covered in depth in previous threads.

The B206A was particularly prone to LTE whilst most helis can be subjected to LTA if the pilot allows the RRPM to droop too far.

Or at least this is my understanding of the situation.


HTH,

B73

Well put Bravo. Pretty much like the other issue of Vortex Ring State and Settling with Power... :}

Peachpilot. If you are already qualified you should be able to answer that one yourself. What do you think you would do instinctively? Foward airspeed is the key there...

Great Vid BP, I thought of you immediately after reading the thread title. I have your vid on my laptop and show it a lot in explaining the JR's foibles.

Concur with the Bravo.

Hi Shaun

No films of LTE but take a look at these other films.

http://www.rapp.org/archives/2004/09..._crash_videos/

This crash happened few days ago in Madrid.

No investigation report yet.

Thanks God, no fatalities.




Exterior View

Interior View

cfr,
That set of vids is really impressive! But in fairness, listen to the sound track carefully, you can hear the pilot exceed torque limits, pull the rotor rpm down very low, and then run out of pedal control.

This, like the Sky Crane, is actually "over pitching" and not LTE.

In LTE, and otherwise normal situation goes to worms purely because the tail rotor cannot deliver the control like Blenderpilot's film. In overpitching, the cause is the rpm loss, that symptom is the yaw control problem.

In Blenderpilot's case, he had lots of power, enough to swamp the tail rotor while at full rpm.

Could someone please explain what exactly happened?

The Machine was overgrossed, and therefore the pilot was pulling too much collective to get over the tribune.

Why did the machine start to spin?

hotzenplotz,

The aircraft was probably at or slightly above the OGE gross weight, which means that he couldn't takeoff with the engine power he had, at least not with the steep departure the scene required. When he got out of ground effect in the climb, the power to keep his departure going was more than the engine could provide, so the rotor decayed quite a bit (note the drooping sound especially in the interior video). This means the main and tail rotor are reducing rpm rapidly.

When the rpm goes down, the tail rotor produces less thrust, and more pedal is needed. The thrust is proportional to the square of the rpm, so even a 5% loss of rpm will yield a 10% loss of thrust; .95 x .95 = .9025 This means that if he is near tail rotor limits before the rotor rpm droop, he will run out of pedal during the droop. That is when the spin starts.

The scenario is doubly bad. When the rpm starts down, the torque goes up - even though the power is constant, because torque times rpm is power. Thus, reducing the rpm at constant engine power makes the main torque go up, which needs even more anti-torque! This means the tail rotor margin is being hurt by the torque rise, too, so the spin starts all the sooner!

It looks like the pilot reduced collective to recover rpm and stop the spin, and that caused the crash. It MIGHT have been better to let the aircraft spin slowly and hold altitude and accelerate, but that would take some pretty handy piloting (I did that once in a Cobra, it was like doing a ballet while my heart rate was 120+). Once translational speed is gained, the collective can be reduced and the situation recovered.

This is really not LTE because the spin is caused by a gross pilot error where the rpm is pulled down too low, because the aircraft is in a situation with too little power (and too little pilot planning.)

Thanks a lot for this detailed explanation! :ok:

On that spanish video, it would be interesting to say that on most Bell light helicopters in order to droop the RPM you REALLY have to exceed limits, for example on the 206 Jet Ranger, you have to probably reach at least 120% Torque before the RPM start to droop.

We had a pilot who hit a wire and had a "fight" with the wire that eventually broke and they flew away. The L model 206 had an Intellistart system that records all filght parameters when "events" take place, this guy had reached 130% torque and held it there for a while until the wire broke, if you look a the Intellistart graphs you can see that the NR had only drooped down to about 96 percent at first then started to recover to 100% even when he was appying almost 125% torque.

That guy in the video must have surely been at the redline or above when he began to transition to forward flight, it would have been wise to stop there and put it back down, he elected to continue and of course when he pushed the cyclic the helicopter tended to "dish out" and having the edge of the building in front of him he must have felt the urge to pull even more power with the known consequences. Believe it or not there are a lot of idiot pilots out there that make intentional use of the non-intentional torque limits during their day to day operations.

But of course maybe he just had a bad governor send one of his engines to idle or contaminated fuel or an air leak or a slipping freewheel, or . . . . . So many things could have happened.

One thing is for sure, on the video taken from the inside you can clearly hear the RPM start to droop as he transitions forward and towards the edge of the building, AND HE CONTINUES FORWARD, in my case if I have heard such a disconcerting noise at that point my inmediate reaction would have been to begin a silght backwards movement and make a right pedal turn back to the dirt, just from listening to the thing it was clear that he wasn't going to go far!

peachpilot,
Recovery technique? I think he just fought it all the way down, he made so many turns that I am sure that I am sure he didn't do what he should have done from the beginning, lower collective and push the nose down. I have flown the very same helicopter that spun, and I have had that nasty tail rotor bite me on several occasions, but when I knew that this could happen I was prepared, I mean that if I knew that I was heavy and this could happen, I would watch my wind and fly smoothly, then if I had to do anything that could cause LTE I didn't with plenty of room beneath me, but let me tell you, when the TR bites it does so quickly and you have to be ready to react in the correct sequence of movements with out delay, in this helicopter after the TR reaches its capability, you feel a quick jerk to the right which if you react properly by lowering collective and giving the cyclic a slight push should never go past 15 degrees, sure cameramen don't like it and get upset, but I don't even bother telling them what they just missed.

Blender pilot:
Thanks for the video and excellent discussion. and I hope you enjoy the jokes in the book as well.

Can we all agree that the situation described by Nick is as a result of overpitching and not LTA. Loss of Tail rotor Authority is generally taken to mean a reduction in the travel available in the TR control system due to damage to cables, rods, bellcranks etc or problems with ASE/ AFCS actuators giving a similar reduction in control authority. This is not the same as loss of TR control which would be total - LTA would be partial.

Loss of TR - it drops off or the driveshaft snaps

Loss of TR control - the cable/rod/pedal breaks

Loss of TR authority - blockage or damage or stab malfunction

Loss of TR effectiveness - you are flying a B206

Overpitching - asking too much of the engine and drooping the Nr, thus slowing the TR and reducing its thrust.

Does this seem fair?

Why don't we put to bed the expression Loss of tail rotor Effectiveness?
It stands to reason if the Tail rotor hasn't the grunt due to ancient design then there has been no loss of anything because it never had it to begin with!

Inneffective Tail Rotor would be a more correct term

W