Crosswinds for Helicopter

[vagabondpiper]

Hy friends i am a new member over here . Brief introduction , i am military pilot , 800 hours on multi engine helicopter.

This morning someone asked me what wind ie from left or right , is gonna assist me during landing in case it's a crosswind ?.

Since my frist day in Aviation i have been taught in case of cross wind better keep it on power paddle. I am talking about MI 17 it has puller type tail rotor and right paddle being power paddle . So naturally my answer was wind from right but he said from left . He showed me service manual and it had mentioned in case takeoff is to be done in cross wind , preferable wind is from left . I somehow couldnt relate it with landing as in take off you are entering ETL and in landing you are getting out of ETL.

Now my question is can someone throw some light on this topic. What should be the ideal wind to land in case of cross wind . Does it have to do something with LTE and does puller and pusher type tail rotor makes difference ? thanks in advance .

[MALIK]

someone asked me the same question in the morning as wel,

[Nearly Retired]

Welcome Vagabond! We love the PA-15!

 

To answer your question: If I cannot land straight into the wind in an "American" helicopter (e.g. Bell), then I prefer a *LEFT* crosswind. I use the natural weathervaning tendency of the helicopter to minimize the amount of left pedal needed.

 

I know that some pilots will vigorously argue this point. They think that if you land with a left crosswind then you WILL get into LTE. It's true because they read it in a book! I even had one guy complain about the Bell 206B with its "weak-ass" tail rotor because he landed one day when he was heavy with a *right* crosswind and nearly ran out of left pedal.

 

Well...duh.

 

I only have 11,000 hours of total time, mostly in Bell 206's, and I have NEVER gotten into LTE with a left crosswind...

 

But what do I know?

[Gomer Pylot]

I agree. With a right crosswind, heavy, you run the risk of overtorquing if you have to put in a lot of left pedal. I've always preferred a left crosswind, and I only have a couple thousand hours more than Bob, but I've never seen LTE. Keep it slow, keep the rate of descent low, and you won't see it either. Cowboy it in, with a high rate of descent, hot, and you may see all sorts of bad things at the bottom. The 206 doesn't have a lot of TR margin to spare, but if you're smooth and careful you won't need any margin. I still have this discussion with check pilots, most of whom don't have enough experience to know what LTE really is, or what causes it. They've read the books, and answered the questions, but they don't really know how the aircraft reacts in many situations. I've had a few lately who had grey hair, but were still searching for a clue. Don't let the nose turn in the first place, and you can't get LTE. And it's easier to keep it from turning with the wind on the left.

 

MI-17, I have no idea. Never been close to one. But the principle should be the same. Pusher or puller makes no difference, ETL makes no difference. Keep the crosswind where it takes less power to keep the nose straight. That's my opinion, and I haven't changed it in 40+ years.

Edited May 19, 2014 by Gomer Pylot

[cburg]

Deleted comment

[iChris]

Hy friends i am a new member over here . Brief introduction , i am military pilot , 800 hours on multi engine helicopter.

This morning someone asked me what wind ie from left or right , is gonna assist me during landing in case it's a crosswind ?.

Since my frist day in Aviation i have been taught in case of cross wind better keep it on power paddle. I am talking about MI 17 it has puller type tail rotor and right paddle being power paddle . So naturally my answer was wind from right but he said from left . He showed me service manual and it had mentioned in case takeoff is to be done in cross wind , preferable wind is from left . I somehow couldnt relate it with landing as in take off you are entering ETL and in landing you are getting out of ETL.

Now my question is can someone throw some light on this topic. What should be the ideal wind to land in case of cross wind . Does it have to do something with LTE and does puller and pusher type tail rotor makes difference ? thanks in advance .

 

They’ve taught that there’s a good side and a bad side to be avoided. That’s a generalization and over simplification of the actual flight characteristics. Both left and right crosswinds present their own unique flight characteristics. Once you learn those characteristics you’ll see it’s sometimes a pick your own poison situation (left or right).

 

Learn the characteristics on both sides, left and right; however, don't forget the best wind is a head wind during takeoff/landing and hovering.

See the following prior post on this issue:

 

June 2013 Post: Myths and Crosswinds and Know-It-Alls

Edited May 19, 2014 by iChris

[Azhigher]

I always prefer a right crosswind (In an Astar) for no other reason than in a left crosswind I can only jam the cyclic into my left leg so hard before I run out of control movement. (Tall guy in an Astar problem)

[aeroscout]

There has been more than enough said by guys ahead of me about crosswind.

I have had LTE twice and was able to recover both times.

I have had full power pedal in on more than a few occasions.

I was either lucky to have an escape route, or skilled by pre planning one.

It helped me a lot to be able to weathervane into the wind and get back above ETL.

My addition to the crosswind discussion is crosswind converting into tailwind.

If in some of the above situations you keep the crosswind on your power pedal side, then you come to a hover, then turn your nose in the direction that would put your tail into the wind, be prepared for ETL backwards which can be an eye opener.

[vagabondpiper]

Welcome Vagabond! We love the PA-15!

 

To answer your question: If I cannot land straight into the wind in an "American" helicopter (e.g. Bell), then I prefer a *LEFT* crosswind. I use the natural weathervaning tendency of the helicopter to minimize the amount of left pedal needed.

 

I know that some pilots will vigorously argue this point. They think that if you land with a left crosswind then you WILL get into LTE. It's true because they read it in a book! I even had one guy complain about the Bell 206B with its "weak-ass" tail rotor because he landed one day when he was heavy with a *right* crosswind and nearly ran out of left pedal.

 

Well...duh.

 

I only have 11,000 hours of total time, mostly in Bell 206's, and I have NEVER gotten into LTE with a left crosswind...

 

But what do I know?

Sir thanks a lot for detailed reply , 11000 hours of experience cant be wrong .

[vagabondpiper]

I agree. With a right crosswind, heavy, you run the risk of overtorquing if you have to put in a lot of left pedal. I've always preferred a left crosswind, and I only have a couple thousand hours more than Bob, but I've never seen LTE. Keep it slow, keep the rate of descent low, and you won't see it either. Cowboy it in, with a high rate of descent, hot, and you may see all sorts of bad things at the bottom. The 206 doesn't have a lot of TR margin to spare, but if you're smooth and careful you won't need any margin. I still have this discussion with check pilots, most of whom don't have enough experience to know what LTE really is, or what causes it. They've read the books, and answered the questions, but they don't really know how the aircraft reacts in many situations. I've had a few lately who had grey hair, but were still searching for a clue. Don't let the nose turn in the first place, and you can't get LTE. And it's easier to keep it from turning with the wind on the left.

 

MI-17, I have no idea. Never been close to one. But the principle should be the same. Pusher or puller makes no difference, ETL makes no difference. Keep the crosswind where it takes less power to keep the nose straight. That's my opinion, and I haven't changed it in 40+ years.

Thanks for such an elaborate reply sir

[vagabondpiper]

I always prefer a right crosswind (In an Astar) for no other reason than in a left crosswind I can only jam the cyclic into my left leg so hard before I run out of control movement. (Tall guy in an Astar problem)

Astar is French machine and French machines have right paddle as power paddle , correct me if i am wrong .

[Azhigher]

Astar is French machine and French machines have right paddle as power paddle , correct me if i am wrong .

True, but it's more of an ergonomic problem than a power or LTE problem.

[Nearly Retired]

vagabondpiper says:

 

Sir thanks a lot for detailed reply , 11000 hours of experience cant be wrong .

 

Want to bet? *NO* pilot is so good that he cannot be wrong. *NO* pilot has so much experience that he never makes mistakes.

 

Don't even think that 11,000 hours of experience can't be wrong. I absolutely CAN be wrong. I may not prove it to myself on a daily basis, but I do so fairly regularly.

 

But here's what I *think*: LTE is an excuse that weak pilots use for crashing (or nearly crashing) a perfectly good helicopter due to bad technique on their part. Bell has done a lot of flight testing of the 206 over the years. The tail rotors of these aircraft do not spontaneously stop working or suddenly become ineffective.

[Astro]

I'm a little confused here. When I'm coming in and suddenly the tail gets a bit squirrelly and I look over at the wind sock to see a left crosswind, that's not LTE?

[Nearly Retired]

No.

[Jaybee]

I'm a little confused here. When I'm coming in and suddenly the tail gets a bit squirrelly and I look over at the wind sock to see a left crosswind, that's not LTE?

 

from AC 90-95

 

LTE is a critical; low-speed aerodynamic flight characteristic which can result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, can result in the loss of aircraft control.

You corrected it so - no, as NR said. The 'and' in the sentence means that all three things must happen to have it - uncommanded yaw, does not subside, loss of aircraft control.

[Wally]

I'm a little confused here. When I'm coming in and suddenly the tail gets a bit squirrelly and I look over at the wind sock to see a left crosswind, that's not LTE?

 

That's not LTE anymore than the jiggle you get driving over a highway expansion strip is a loss of control skid.

The TR in most helos located where a lot of changes happen quickly- main rotor wash and associated turbulence, ground effect, and the vertical stab. I attribute most of those small quick yaw variations to those effects. It could develop into LTE...

 

I'm not as comfortable as some in saying that 206 LTE is ultimately poor pilot technique. The plan that allows adequate reaction requires that you prepare for it. The 206 TR is relatively weak and I've been on the left pedal stop on occasion.

[Astro]

So its not considered LTE until after my feet fail to respond properly and I lose control?

[cburg]

There's a saying "lose it to the right..goodnight".

[cburg]

LTE AC Excerpt:

 

5. UNDERSTANDING LTE PHENOMENA.

 

To understand LTE, the pilot must first understand the

function of the anti-torque system.

On U.S. manufactured single rotor helicopters,

the main rotor rotates counterclockwise as

viewed from above. The torque produced by the

main rotor causest he fuselageo f the aircraft to rotate

in the opposite direction (nose right). The anti-torque

system provides thrust which counteracts this torque

and provides directional control while hovering.

 

c. Tail rotor thrust is the result of the application

of anti-torque pedal by the pilot. If the tail rotor

generates more thrust than is required to counter the

main rotor torque, the helicopter will yaw or turn

to the left about the vertical axis. If less tail rotor

thrust is generated, the helicopter will yaw or turn

to the right. By varying the thrust generated by the

tail rotor, the pilot controls the heading when hovering.

 

d. In a no-wind condition, for a given main rotor

torque setting, there is an exact amount of tail rotor

thrust required to prevent the helicopter from yawing

either left or right. This is known as tail rotor trim

thrust. In order to maintain a constant heading while

hovering, the pilot should maintain tail rotor thrust

equal to trim thrust.

 

e. The environment in which helicopters jly,

however, is not controlled. Helicopters are subjected

to constantly changing wind direction and velocity.

The required tail rotor thrust in actual flight is modified

by the effects of the wind. If an uncommanded

right yaw occurs in flight, it may be because the

wind reduced the tail rotor effective thrust.

 

e. The wind can also add to the anti-torque system

thrust. In this case, the helicopter will react with

an uncommanded left yaw. The wind can and will

cause anti-torque system thrust variations to occur.

Certain relative wind directions are more likely to

cause tail rotor thrust variations than others. These

relative wind directions or regions form an LTE

conducive environment.

 

6. CONDITIONS UNDER WHICH LTE MAY OCCUR.

 

a Any maneuver which requires the pilot to

operate in a high-power, low-airspeed environment

with a left crosswind or tailwind creates an environment

where unanticipated right yaw may occur.

 

b. There is greater susceptibility for LTE in

right turns. This is especially true during flight at

low airspeed since the pilot may not be able to stop

rotation. The helicopter will attempt to yaw to the

right. Correct and timely pilot response to an

uncommanded right yaw is critical. The yaw is usually

correctable if additional left pedal is applied

immediately. If the response is incorrect or slow,

the yaw rate may rapidly increase to a point where

recovery is not possible.

 

c. Computer simulation has shown that if the

pilot delays in reversing the pedal control position

when proceeding from a left crosswind situation

(where a lot of right pedal is required due to the

sideslip) to downwind, control would be lost, and

the aircraft would rotate more than 360’ before stopping

.

d. The pilot must anticipate these variations,

concentrate on flying the aircraft, and not allow a

yaw rate to build. Caution should be exercised when

executing right turns under conditions conducive to the aircraft would rotate more than 360’ before stopping

 

OTHER FACTORS. The following factors can

significantly influence the severity of the onset of

LTE.

 

a. Gross Weight and Density Altitude. An

increase in either of these factors will decrease the

power margin between the maximum power available

and the power required to hover. The pilot

should conduct low-level, low-airspeed maneuvers

with minimum weight.

 

b. Low Indicated Airspeed. At airspeeds below

translational lift, the tail rotor is required to produce

nearly 100 percent of the directional control. If the

required amount of tail rotor thrust is not available

for any reason, the aircraft will yaw to the right.

 

c. Power Droop. A rapid power application may

cause a transient power droop to occur. Any decrease

in main rotor rpm will cause a corresponding

decreasein tail rotor thrust. The pilot must anticipate

this and apply additional left pedal to counter the

main rotor torque. All power demands should be

made as smoothly as possible to minimize the effect

of the power droop