LTE question

[thecontroller]

can someone explain this diagram?

http://helicopterflight.net/critical_wind.htm

it seems to contradict the usual LTE wind azimuth angles as seen here:

http://helicopterflight.net/figures.htm

[[email protected]]

Not sure why they have the quadrant extending from 180 to 210 degrees in the first diagram but the rest of it is correct since any wind from the right will require more left pedal to hold the heading and, if you are already yawing right, a lot more left pedal to stop the rotation.

The advice not to raise the collective is only valid if you are either a. already at max power and to do so would droop the Nr and worsen the problem or b. flying a Jetranger which doesn't have a big enough tail rotor for its flight envelope.

[imabell]

under the first diagram it should have read that care should be taken as the wind up the tail pipe could raise tot temps, that is how it is put in the original longranger manual.

now it also includes the myth of lte, a pilot induced phenomena.

[SEL]

The first diagram is to do with some tail rotor issues. On a helicopter with counter clockwise rotation, viewed from above (basically speaking, not French or Russian), the tail rotor thrusts to the right by forcing air to the left. Thus, wind from the right is the same as putting the tail rotor into a climb condition. Whilst wind from the left is akin to a descent. With the wind from 'back and left', the tail rotor is effectively in an oblique descent. The wind is pushing against the rotor flow and with the oblique angle, leads to a few other aerodynamic nasties. Both cases lead to differing rotor effectiveness and power requirements.

The second link is looking just at the stability of the tail surface (and the flat plate effect of the tail rotor) which is stable with wind from the front i.e. keeps the nose into wind. Whilst wind from the back has the same effect of trying to swing the nose into wind which may not be where you want it to be!

Thing with these kind of sites and some text books is that its all given separately, whereas in reality all of the effects are occuring at the same time. Which one is 'dominant' will depend on a large number of factors.

Helicopters, you've got to love 'em!

[gwelo shamwari]

My two cents on what I was told it had to do. Someone else would probably know the best.

“Quoting from notes taken in a recent class”

The "critical wind azimuth" has to do with the amount of tail rotor power/authority available to maintain directional control and TOT limits (TOT - wind blowing exhaust gas back up the pipe making it hotter).

Aircraft are certified to have demonstrated adequate yaw control in certain conditions - POH.

When winds are encountered from the given "critical wind azimuth", they exert a force upon the aircraft fuselage and tail section. The larger the more force applied.

If the tail rotor has very little or no additional power left in reserve (Area B of the hover performance charts e.g. full left pedal, high power setting, max gross, a nice hot day (not for those in the UK :} ) at altitude below ETL) the force will cause the aircraft to yaw.

With no or very little power available to the tail rotor, one is unable to stop the yaw allowing it to accelerate, resulting in LTE.

This was a real problem with the early 206's (this is where the image comes from), hence it being mentioned in the POH in the hover performance graphs- awareness, along with upgraded tail rotor blades - improving tail rotor authority, and change of tail rotor rigging for more left pedal - again improved tail rotor authority.


Now, this is what I was told and makes sense to me with out going it to crazy mathematical calculations of where the wind is 3” from the root of the blade at the 6 o’clock position on a overcast but pleasant morning, or
what ever.

It may be completely wrong, but who knows.

Please do not shoot me....:sad:

TGZ

Editied for my poor spelling

[Shawn Coyle]

The diagram is taken out of context. It's from the Bell 206 Flight Manual and is used with the hover performance charts.
The manual explains it all quite nicely, if I remember correctly.

[topendtorque]

now it also includes the myth of lte, a pilot induced phenomena.


or phobis perhaps?? All of which including technicalities was covered in a recent thread on the subject.

However it is coincidental that this LTE subject has been again raised.

Point 1)
Fairly recently I overheard a story from the far north of oz.
Seems an instructor operating in a remote location with several hill billy students returned a helicopter (R22) to its owners with some damage.
To wit; a broken bracket on the T/R pedal console assy and a bent support at the aft end of the T/R control rod at the rear of the cabin.
This feat apparently bemused all of the locals and it was put down to the simple pucker factor that is encountered as the ground approaches at initial auto training with a very strong and heavy footed student.

The answer to the irate owners question of what the f*** happened here were all batted of in the style of ‘Manuel’ from ‘FaultyTowers’ with, “I know nuththing!”

Point 2)
More recently there was a story about the same instructor, himself a very heavy chappie, doing what was described as an LTE exercise from the hover which went like this;
Left pedal is slammed forward to the stops and the student is to recover by rolling off the throttle and landing.
Yep that is right re-read that, that is how I heard it!! The story goes that the left pedal application was always violent.

Now perhaps the damage may be as the result of landing stresses from suggested LTE exercise, or heavy footed pedal slamming or who knows what.

One thing for sure if the chappie (who is rumoured to come from Perth) ever tried it with me it would be the end of him for sure. Can anyone make sense out of it???

I doubt that any of the students involved will comment here owing to the remoteness of their location. You know, right - out – in – the – sticks – like – they - reckon. And yer c’n say that again slowly.

One of the students learnt so much from the school where he did his PHL and also on the way past his Fixed wing BFR that he, is rumoured to have later;

a) forced landed onto a highway on the way home in such fierce rain conditions that he tore most of the wing leading edge paint off (a cross hired C172 mind you), then tried to pass it off as a bad paint job, and

b) later again with a brand new second hand F/W of his own whilst conducting mustering operations in a commercial sense as a PPL managed to write off said F/W as a result of the fuel tanks being contaminated with too much fresh air.

Strange that.
cheers tet

[remote hook]

Thanks Nick, as usual.

I thought the TOT rise was attributed to the engine ingesting warm exhaust air, thus causing the TOT to elevate, not blowing exhaust back up the tailpipe?

RH

[imabell]

thanks again nick, very much. and very much only a bell problem, i have not seen another type with any mention of lte in the flight manual, i could also be wrong as i have not flown many types.

remote hook, i guess that argument is a cosideration.

we were told that the breeze up the tailpipe was the main offender but i guess reingestion of wam air should be considered as a valid point.

[topendtorque]

I’ll also say thanks Nick. I remember twenty or more years ago (1982) defending my position from a DCA (then) examiner who said that we had to do LTE exercises in our ‘47s.

I can tell you that I felt like shag on a rock, I wish I had your paper then to refer to. This gent was an author of another paper professing to spell out doom and gloom and disaster if we all didn’t practice it. Well the easiest way for silence was to challenge him to take me up, demonstrate it and every time he managed to get it happening then I bet him I will recover so quickly to prove that it is not a problem. I think the only type that he had ever flown up till then was the fabled ‘bad one.’ (kiowa)

Hence my use of the word PHOBIA, it is utter baloney as you say, and not a reason for kids to be frightened witless by mindless know it alls around beer fridges.

Enough of that, the problem that I refer to is probably also a hot exhaust problem with a confused tailpipe direction, I mean how could a qualified instructor call up an LTE exercise (in a R22) then apply LEFT pedal to initiate it, and then expect the student to roll OFF power to land as the recovery from the hover.

Maybe someone in Perth (read Jandakot) from where this instructor must hail will be able to enlighten us. There are two big schools there and some correspondents on these forums from there as well. C’mon you sandgropers let us know the giff.

When you get bit by the big bad rotor torque means rotating the other way doesn’t it? Then a quarter of a turn later when the T/R zooms into fresh air with full opposite pedal you get bit by the sudden stop in rotation – read violence - and its all over in a tad.
Maybe they have LTE over there when they are in auto????