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LTE In the Hind


Denwagg
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It appears that after the newest beta the hind exhibits more LTE in ground effect. Could wind direction and speed have more adverse affect now?


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Did we even have confirmation that LTE has been implemented?

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It has been there since the beginning. It is dependent upon wind direction, particularly a headwind at 45 degrees off the nose or tail.

This wind condition causes the tail rotor to enter VRS  from the downwash of the main rotor. The tip vortices interfere with each other.

Takeoff, landing and hover in GE with a 45 degree headwind are the most likely conditions for this to happen.

The Yaw AP channel is there to stabilize the ship and prevent LTE from occurring.

You should always use the AP when taking off, landing or hovering in GE. That's what the engineers designed it for.

I strongly suggest mapping buttons to AP on and AP off for maximum overall control of the ship.

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I'd like to see a confirmation about this, tbh, from ED

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On 8/15/2021 at 7:42 PM, rayrayblues said:

It has been there since the beginning. It is dependent upon wind direction, particularly a headwind at 45 degrees off the nose or tail.

This wind condition causes the tail rotor to enter VRS  from the downwash of the main rotor. The tip vortices interfere with each other.

Takeoff, landing and hover in GE with a 45 degree headwind are the most likely conditions for this to happen.

The Yaw AP channel is there to stabilize the ship and prevent LTE from occurring.

You should always use the AP when taking off, landing or hovering in GE. That's what the engineers designed it for.

I strongly suggest mapping buttons to AP on and AP off for maximum overall control of the ship.


This is almost certainly not true. The latest official statement from ED was, ( I think in the Hind developer FAQ/Interview)  that LTE is presently

not modelled in any of the helicopter flight model in DCS, due to the complexity of the calculations involved to model it accurately.

 

Snappy

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29 minutes ago, Snappy said:


This is almost certainly not true. The latest official statement from ED was, ( I think in the Hind developer FAQ/Interview)  that LTE is presently

not modelled in any of the helicopter flight model in DCS, due to the complexity of the calculations involved to model it accurately.

 

Snappy

 

Then why is it happening?  If as you say, it is not modeled, then there is something  else going on.

 

If I try to do a vertical landing or takeoff without Yaw AP on, I will almost always enter a spin, depending on wind speed and direction as soon as I come to a hover.

There is not enough right anti-torque thrust available to recover.  There is lots of good info in this article:  LTE: the cliff edge | Flight Safety Australia

This applies to all helicopters. The Hind just happens to be more sensitive to LTE caused by tail rotor VRS.  (or at least the DCS version is.)

 

The best landing approach  (for me at least)  is to reset trims to center and turn AP off.  Line up on the LZ and then engage the Yaw AP.

I can then slow to a hover, without spinning and gently set her down;  even with a 45 degree wind.

 

 

 

 

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I think LTE is a very complex phenomenon, but what we’re experiencing is more a version of LTE that’s specifically the tail rotor experiencing independent VRS, and that only the Hind currently has a VRSing tail rotor 

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LTE (Definition) - occurs when the tail rotor of a helicopter is exposed to wind forces that prevent it from carrying out its function—that of cancelling the torque of the engine and transmission. Any low-airspeed high-power environment provides an opportunity for it to occur.

 

Factors which can lead to LTE are:

1. Main Rotor Disk Interference

2. Weathercock stability

3. Tail Rotor Vortex Ring state


Edited by Lurker
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There is the possibility that when you are heavy and attempting to hover or transition from hover to forward flight, that your main rotor rpm may drop, resulting in insufficient anti torque being available to correct any rotational tendencies.  
 

However, I do wish DCS could implement LTE in all helicopter modules.


Edited by Rabies
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It's not LTE that is spinning people  counter-clockwise on take off.  It's lack of available torque. Get your weight under 100% MGTOW and you will have plenty of right pedal/counter-torque for both IGE/OGE hover operations.

 

The fact that it doesn't happen at 100% MGTOW, and is easily reproducible with 0 wind mean that it's not LTE. 

 

Or take off heavy as hell, but do a rolling takeoff.


Edited by fargo007
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On 8/15/2021 at 10:42 AM, rayrayblues said:

.......

The Yaw AP channel is there to stabilize the ship and prevent LTE from occurring.

You should always use the AP when taking off, landing or hovering in GE. That's what the engineers designed it for.

 

I'd really like to see some kind of technical reference to this. I am a retired helicopter pilot and spent the last 29 of my 45 year career flying heavy lift helicopters equiped with various types of Automatic Flight Control Systems and never once in all of that time have I ever heard any kind of reference to the yaw channel of the AFCS contributing to the avoidance of LTE, either intended or accidental. While I can easily believe that you have experienced this in the DCS World of helicopter flying, I can assure you that no such thing exists in the real world. At least not in human controlled helicopters anyway. I can't speak to digitally controlled helicopter drones (with conventional rotor systems).

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Could those who experience the presumed LTE post a track with an LTE event?

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On 8/15/2021 at 3:48 PM, Whisper said:

I'd like to see a confirmation about this, tbh, from ED

Dude, all you gotta do is just jump on in, pull collective to max pitch and you'll swing and spin around like a chandelier in an earthquake. Its implemented.

On 8/23/2021 at 12:00 PM, fargo007 said:

It's not LTE that is spinning people  counter-clockwise on take off.  It's lack of available torque. Get your weight under 100% MGTOW and you will have plenty of right pedal/counter-torque for both IGE/OGE hover operations.

 

The fact that it doesn't happen at 100% MGTOW, and is easily reproducible with 0 wind mean that it's not LTE. 

 

Or take off heavy as hell, but do a rolling takeoff.

 

 


Edited by Hammer1-1

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LTE is aerodynamic phenomenon. What you are talking here is not LTE, it is overloading your tailrotor. Early Bell 206, and I think 212, had the same issue. Tailrotor was just not powerful enough to keep heading in hot/high and heavy conditions.

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15 hours ago, Hammer1-1 said:

Dude, all you gotta do is just jump on in, pull collective to max pitch and you'll swing and spin around like a chandelier in an earthquake. Its implemented.

 

 

If this is all that is needed, then it's not LTE

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16 hours ago, Hammer1-1 said:

Dude, all you gotta do is just jump on in, pull collective to max pitch and you'll swing and spin around like a chandelier in an earthquake. Its implemented.

 

Although the DCS Mi-24P models torque and weather cocking, and it is possible to run out of pedal authority, AFAIK it does NOT model LTE due main rotor vortices or tail rotor VRS due to crosswinds etc. 

 

This is an abridged version, for further detail check out page 147 - FAA-H-8083-21A, Helicopter Flying Handbook 2012

 

 

jELT3Eg.png

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1 hour ago, Whisper said:
17 hours ago, Hammer1-1 said:

Dude, all you gotta do is just jump on in, pull collective to max pitch and you'll swing and spin around like a chandelier in an earthquake. Its implemented.

 

 

If this is all that is needed, then it's not LTE

 

Spot on.

 

It also cannot be LTE if it's reproducible with zero wind. And it is. 

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5 hours ago, Avimimus said:

Something is going on though:

 

 

Oh there is... 

 

What's the weight at takeoff?

 

Reduce the weight to less than 100% in the rearm display and try again.  

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If I can get the main rotor to overpower the tail rotor while maintaining forward velocity, then I can safely say theres wind involved. Yes, the tail rotor loses effectiveness at above 13 degrees of blade angle at just about any speed. Thats what I have observed consistently.

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9 hours ago, Hammer1-1 said:

If I can get the main rotor to overpower the tail rotor while maintaining forward velocity, then I can safely say theres wind involved. Yes, the tail rotor loses effectiveness at above 13 degrees of blade angle at just about any speed. Thats what I have observed consistently.

Watch RRPM. If you lose RRPM, because of gearing, you will lose more TRRPM, hence you lose authority.

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Loss of tail-rotor effectiveness (LTE) occurs when the tail rotor of a helicopter is exposed to wind forces that prevent it from carrying out its function—that of cancelling the torque of the engine and transmission. Any low-airspeed high-power environment provides an opportunity for it to occur.

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37 minutes ago, Denwagg said:

Loss of tail-rotor effectiveness (LTE) occurs when the tail rotor of a helicopter is exposed to wind forces that prevent it from carrying out its function—that of cancelling the torque of the engine and transmission. Any low-airspeed high-power environment provides an opportunity for it to occur.

As quoted above, which aptly describes what I see when I add too much power and my aircraft starts to yaw in the opposing direction of the rotation of the disc, which incidentally eventually disappears when the weathervane effect helps to start straightening the aircraft out in fwd flight.

Screenshot 2021-08-28 114702.jpg


Edited by Hammer1-1

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On 8/27/2021 at 3:19 AM, admiki said:

Watch RRPM. If you lose RRPM  because of gearing, you will lose more TRRPM, hence you lose authority.

So what you're saying is that its easy to overpower the tail rotor with the main rotor. That by itself is LTE by the definition highlighted for the most part...albeit a mechanical shortcoming.  My bad...


Edited by Hammer1-1

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