B737 35 knot Crosswind take off. Which wing drops on lift off?

[A37575]

Simulator conundrum. B737-Classic. Runway 36. Wind 270 at 35 knots (steady 90 degree crosswind component).
Considerable right rudder needed initially to track the centre-line but as speed approaches VR of 130 knots, less rudder pressure needed. As the main wheels leave the runway, I would expect the aircraft would weather-cock into the wind and this manifests itself by the left wing dropping slightly which is easily countered by appropriate aileron (plus minor spoiler deflection depending on amount of control wheel offset). In other words the momentary lowering of the left wing conveniently counters the drift angle and the aircraft tracks the extended centre-line albeit with a bit of wing wobbling until you settle on the correct amount of drift angle.

At least that is what I thought should happen and in fact I am sure I have seen this many times.

But what if it is the right wing that goes down at lift off, and a considerable change of heading into wind is needed to not only get back on to the extended centre-line but to accurately track the centre-line once drift angle is established?

Trouble is I am now momentarily confused as to which wing (left or right or if you prefer, upwind or downwind wing) one could expect to momentarily drop at the point of lift off? Could this right wing drop be a simulator fidelity defect? Or would you rightly expect the right wing to drop slightly and that anything else is simply finger trouble by the pilot? :hmm:

[BOAC]

Is this something you have seen in the sim? I would not expect either wing to 'drop' at the moment of lift-off providing appropriate aileron had been applied, but to commence thereafter with the yaw. The natural 'yaw' into wind at lift-off should produce a corresponding roll to the left (ie left wing 'drop'), both of which are 'good'. Any right-wing drop I suspect could possibly be the result of too much right rudder at lift-off causing yaw to the right as the wheels unstick? I assume the 'necessary' left aileron had also been applied whenever needed? Insufficient into-wind aileron, if not corrected as the wing rises, would cause the right wing to 'drop'.

Just remember that 'seat of the pants' is absent in the sim so inappropriate reactions could occur, and I was also very conscious of an evident 'yaw' with roll in all the 737 sims I flew, which was an 'unfaithfull' representation of the real.

[Admiral346]

Well Sir,
I have different experiences. I have noticed the plane would like to roll to the right in this case, as the wind hits the vertical stabilizers and "pushes" it. This will result in a left wing up momentum, wich has to be counteracted by aileron input.

Of course, with everything done right, there should be no wing dropping at all when leaving the ground.

Nic

[BOAC]

Admiral - in steady conditions this fin rolling moment is there from brakes off, so you should have countered that with aileron already? Quite how you are able to distinguish between upwind wing lifting and fin rolling I do not know!

[ray cosmic]

On the 747, you can say the required aileron input on rotation is twice what you had during the run. If while rotating you nicely increase aileron as well, no wing will drop. On the 737 it must be the same, only maybe a bit less pronounced.. And don't be afraid of the spoilers. I hung once out the window of a 737 while parked, and they came already up at 2.5 units. So you already quickly have the spoilers. You need that amount of aileron, so please disregard the spoiler deflection.

[Donalk]

'As the main wheels leave the runway, I would expect the aircraft would weather-cock into the wind'

I was always told that the tendency to weathercock is principally confined to ground movements. Therefore as weight is transferred from wheels to wings the amount of rudder deflection required to counteract will decline.

[frogone]

If you can track the centerline until liftoff with a certain amount rudder input, should any of it be removed in the rotation? My question is how can you have too much rudder input because if you had would you not loose the centerline before liftoff?

IR

[BOAC]

There are numerous threads on PPR about x-wind take-offs. Essentially you get airborne with 'crossed controls' - in this example, right rudder and left aileron. These controls are restored to neutral in a 'cordinated' smooth fashion at and after rotate. At lift-off the a/c starts to drift downwind, being no longer constrained by the runway surface, BUT it naturally 'weathercocks' into the relative 'wind' (slightly left of the nose) by yawing to the left and 'fine tuning' then takes place to track the centreline with no yaw or roll present. That's how it should be done - then, of course, there's my thrashing about of the controls:)

[frogone]

I have found with for example a crosswind from the left, with about 4 units on aileron into wind and tracking the centerline nicely once I get airborne that the left wing picks up. I am always asking myself is it too little aileron or too much rudder??

IR

[framer]

In this scenario start with a bit of aileron (left wing down) and as you rotate increase the input in order to keep wings level. You will need quite a bit of left wing down aileron at 35kts across.

[Rainboe]

The OP has it wrong. The upwind wing will lift, or right wing drop. It's an indication that not enough into-wind aileron was applied at the moment of lift off. You find there is not a great requirement for rudder at lift off speeds- it's aileron that is far more critical, and the vast majority of pilots never apply enough. I put on much more than most and find it far better. The ones that apply hardly any soon start learning why! I once did a 747 take-off with a copilot who applied none in a 25Kt+ crosswind from the left. I thought it would be the only way to get him to learn. The resulting right wing drop was really scary.

I am now operating 737 in a very windy place. I'd almost say you can't apply too much aileron. Put loads on and leave it there!

[framer]

Put loads on and leave it there!
I don't find that to be the best way of doing it.
I have a feeling you are a lot more experienced than me Rainbow so I am ready to learn something if need be. I find that the best way is to just put in a moderate amount on the roll and keep the nose straight with a a bit of rudder.....basically feels like you're sharing the job between the two....and as you rotate roll in that extra aileron that you know for sure is going to be needed to keep the wings level.
I agree that it is a lot of aileron during the rotation, I have heard people say that they double the cross wind and that will be the yoke angle ie 30kts then 60degrees of yoke angle.

[InSoMnIaC]

Farmer: In this scenario start with a bit of aileron (left wing down) and as you rotate increase the input in order to keep wings level. You will need quite a bit of left wing down aileron at 35kts across.

correct me if I am wrong here but shouldn't it be the other way around.

I mean at very low airspeed the aileron applied should be more and gradually reduced as you accelerate down the runway - ie as the effectiveness of the control surface increases.

I do agree with you about the comment on allowing both rudder and aileron to share the work. I find that if the aircraft is fighting my rudder input.. ie doesn't want to stay on the centreline even with quite a lot of rudder ... it's usually that there is not enough aileron.

[Rainboe]

I find that if the aircraft is fighting my rudder input.. ie doesn't want to stay on the centreline even with quite a lot of rudder ... it's usually that there is not enough aileron.

There really are some profound misconceptions about crosswind takeoffs in this thread! Understand the difficulty of keeping straight is unrelated to aileron. The crosswind is blowing the fin and weathercocking the aeroplane into wind. The only way to counter that is to hold the aeroplane on the centreline with rudder- aileron is ineffective at that. Consider the moment of lift off, the aeroplane's wheels leave the runway, and the aeroplane is then effectively in a yaw situation, with the wind blowing on one side and lifting the upwind wing, very powerfully. There is only one way to remain level. If you have applied not very much aileron, this is when you get a nasty surprise.

I won't repeat the previous stuff about how much aileron to apply. But if you want to keep life simple for yourself at a very busy difficult time, slap on a load of into-wind aileron at the start, and leave it there until after the wing drop. To assess how much you need, closely observe how much extra aileron you have to put on in a cross wind lift off. I have never heard or seen of too much in 38 years of jets, but you can so easily way underdo it.

[framer]

correct me if I am wrong here but shouldn't it be the other way around.

Stand corrected....you are wrong.

It is such a dynamic event from zero knots on the ground to 170 airborne with all the factors/forces changing with every knot increase in speed and every gust of wind.
But if you want to keep life simple for yourself at a very busy difficult time, slap on a load of into-wind aileron at the start, and leave it there until after the wing drop.
I can definately see your point there Rainbow. The way I look at it is that there is definately a prerfect amount of aileron for any snapshot in the roll. That amount will be just enough to stop the wing lifting and not so much as to create an extra "weight" on that side of the aircraft. If for example you take it to the extreme and used full left airleron in this scenario, then as the speed built and the aileron/spoiler had more effect, effectively extra weight would be felt on the left main gear/extra drag on left side of aircraft, and the a/c would want to turn slightly in that direction, the reaction to this, of the pilot, is to put in more right rudder to hold the center-line. So the pilot needed x units of aileron and x units of rudder but ended up using x+1 of both just to hold the centerline. A training captain I had once demonstrated an interesting technique to me aimed at getting the correct amounts of aileron and rudder and it results in a nice roll and lift-off. Basically he starts with fwd pressure and no aileron, as he rolls and needs rudder to keep it straight he feeds in aileron, just a little, if he needs more rudder he feeds in a little more airleron, baiscally like they are connected. You find that a requirement for rudder arrises, and as a little more aileron goes in the requirement for rudder reduces a fraction. It's a bit hard to explain here but in real life it seems to work very well. The result is that even in 30kts across you don't need a heck of a lot of either.....until rotation that is. I am pretty sure that a lot of guys I watch take-off are needing so much rudder because they have so much aileron.
I know I open myself up to getting shot down when putting opinions like that out there. Thats all good, might learn something :ok:

[InSoMnIaC]

Farmer: Stand corrected....you are wrong.

It is such a dynamic event from zero knots on the ground to 170 airborne with all the factors/forces changing with every knot increase in speed and every gust of wind.

again.. I could be wrong with the previous statement about amount of aileron however I fail to see how your statement has "corrected" me.

I thought we were talking about a constant crosswind here..

rainboe: you are right . i was actually referring to the fact that the upwind wing could be jumping up and down along the runway (due not enought aileron) hence making the centerline keeping kind of wobbly.

[Rainboe]

If for example you take it to the extreme and used full left airleron in this scenario, then as the speed built and the aileron/spoiler had more effect, effectively extra weight would be felt on the left main gear/extra drag on left side of aircraft, and the a/c would want to turn slightly in that direction, the reaction to this, of the pilot, is to put in more right rudder to hold the center-line.

My head is starting to ache here! Let´s deconstruct what you say. As the speed builds up, the upwind wing lifting effect gets stronger. The reason you are putting aileron on in the first place is to reduce lift on that wing to counter the upwind lifting effect. Who knows what extra drag or alleged wheel drag there is? You have no way of knowing, you just have to keep the thing balanced and straight into the air. Forget 'spoiler drag´, it´s a complete nonentity for spoilers slightly cracked open below 150kts. Hell, the things are hardly effective up to 250kts fully open.

You bang on aileron to stop the wing lifting (be generous- it´s never enough at liftoff), you put downwind rudder on to keep straight (you will find that requirement reduces as speed builds up and the rudder becomes more effective). There is no such thing as asymmetric thrust to keep straight. Keep it simple like that and forget about other complications. My qualification is about 15,000 hours of 737, 747, 757. They are all the same and behave just the same way. I am now flying in possibly the most notoriously heavy wind place in the world, with frequent 35 kt crosswinds. It works. Don´t come up with manufactured problems or theories that are not factors. Keep it simple requiring minimum brain effort and you have more capacity for deciding which crew meal you are going to have and which of the lovelies may strike lucky.

[BOAC]

Something you may not have noticed in your flying, RB - and you need that rare down the runway KEF wind to try it - but you CAN steer with aileron on the ground, as Framer is saying. Try it one day (after your crew meal and before you 'strike lucky', of course). It was demonstrated to me years ago in Aunty Betty's flying club and it works.

[Dit]

Just to interrupt with something taken from my 738 FCTM:

"Large control wheel inputs can have an adverse effect on directional control near V1(MCG) due to the additional drag of the extended spoilers."

and

"Excessive control wheel displacement during rotation and liftoff increases spoiler deployment.... drag increases and lift is reduced.... results in reduced tail clearance..."

[Rainboe]

Yes, we know about that! Define 'large control wheel inputs'as seen by Boeing? Over 45 degrees? I would say something up to about 35 degrees maximum would not be considered 'large'. 45 degrees or more would be more than required up to limiting crosswind.Boeing make no attempt to define 'large'

I think it is one of those statements meant to absolve the authors of any blame in a subsequent accident enquiry, like in rear-view mirrors: 'caution, objects are closer than they appear in the mirror!' Boeing have the opportunity for a known crosswind to specify a maximum control wheel deflection- they haven't done anything apart from a wishy-washy statement that means little and is no real guide.

[Dit]

Very true, though you could also read it as inferring that any spoiler deployment would be a "large" input.

[Kiltie]

Without wishing to interrupt the physics of aerodynamic theory, worthy as it is and ever-informative to my simple mind, has anyone mentioned the oft-forgotten technique during crosswind take-offs of .........looking out of the window??? As the mainwheels have left the ground I have relaxed all pressure from the rudder pedals I had required for the take-off roll, allowing the required weathercocking, and (not forgetting the glance at the PFD during rotation) am watching intently over the glareshield for my lateral clues as to how much control wheel movement of aileron is required to be maintained or even increased. And I concur with Rainboe; it's usually a LOT in the first fifty feet which surprises those who have not experienced it that often.

[john_tullamarine]

A37575 (http://www.pprune.org/members/110826-a37575) Harking back to another life you and I enjoyed some years ago, that box was a bit average with respect to rudder fidelity until an upgrade occurred prior to its going O/S. I have a suspicion that your symptoms here might be a fidelity issue .. have you flown a strong X/W departure in the particular box yourself rather than just observing ?

[Rainboe]

has anyone mentioned the oft-forgotten technique during crosswind take-offs of .........looking out of the window???
Not to be relied on. When you see a blowing 30kt fog (Shetlands speciality) or visibility is pretty greyed out, you would be up a gum tree relying on visuals at that moment. Essential to have a robust handling technique that applies in all weathers, and know what you are doing.

When a crosswind is significant and the copilot is handling, I always ask tham if they know exactly what they are going to do and do they understand it. I find very often it becomes embarrassingly apparent they don´t. When I was refining the technique on 747s, I was not afraid to ask the Captain to explain it fully from first principles, and those lessons are 100% applied now. There seems to be a reluctance to admit there are holes in some people´s knowledge and they won´t ask, yet evidently don´t understand. You cannot approach crosswind landings in a jet thinking you can 'hash' it as you go along.

[A37575]

I always ask tham if they know exactly what they are going to do and do they understand it.

A courageous question Prime Minister. Few would admit to their captain that they haven't a clue...while some might know - but are tactful enough to pretend to seek the advice of the all-knowing in the left seat. They are the first officers who will go far..:ok:

[framer]

Insomniac, sorry mate, I knew as I was writing it that it could come across as very condescending but it was meant to be a bit theatrical...the old sergeant major saying " stand corrected son, you're out of line" kinda thing and was a response to you asking to be corrected if you were wrong in your previous post. No harm meant. You're right, I didn't really correct you, just informed you you were wrong. Basically the wing drop on the 73 in a cross wind take-off is quite pronounced if you do nothing, it is more that the upwind wing lifts quite markedly and you need to increase the aileron you have in quite a bit as the rotation progresses and through to maybe 100feet.
Rainbow, you have nearly three times the jet experience that I do so my comments are made with all due respect.
Your de-construction didn't really bring me any closer to seeing your point other than that your method is simple.
When you hold into wind aileron you are trying to counter the upwind lifting effect.
If you do that too much you achieve this and then start exerting a downward force.
That force requires a slight opposite rudder input to counter. Yes or no?
All I'm saying is that I think some people use too much aileron which in turn causes them to need extra rudder.
I'm not suggesting it can be done perfectly or anything silly like that and I am a big fan of keeping it simple in practice.....but I do like to break things down to their elements when I have the time to think about it, like in the cruise with a coffee.
If you were rolling on a calm day and at 100kts put ten degrees of aileron in do you think you would need rudder to keep the centerline?
Cheers mate, Framer.

[Kiltie]

Thanks Rainboe, been to Shetland 348 times last time I checked the logbook; I'm not foolish enough to try to rely on visual cues when there is nothing to see; I thought everyone would take that as read.

I increase the upwind aileron input as the rotation begins; works for me.

[Bruce Waddington]

Hi All,

Years a go I was taught that when starting a crosswind take-off you needed no aileron into wind. As the speed increased and you got a feel for how much rudder was needed to keep on the centerline you would then start to put in some upwind aileron. The point being that if you needed a small amount of rudder you needed a small amount of upwind aileron and if you needed a large amount of rudder you needed a large amount of upwind aileron.

This, explained the wise old Captain, would stop me from doing three things;

1. Having too much aileron selected as the airspeed increases which will actually cause the aircraft to turn into wind even more than the crosswind tries to make it and therefore will require more rudder than is really required to keep staight on the runway. The correction for this overcontrol can make for some interesting moments during the take-off run and just after lift off.

2. Having too much spoiler deployment for the conditions which can also cause the aircraft to turn into wind even more than the crosswind tries to make it with the same issue as above.

3. Having not enough aileron selected which will allow the upwind wing to start rising around 100 kts and also create some interesting moments during the correction process.

There is no 'preset formula' for aileron displacement during a crosswind take-off. Too much is just as bad as not enough. See how much rudder you need to keep straight and then, early in the take-off run, put in enough aileron to keep the wings level. Adjust as required if the wind changes or gusts.

regards,

Bruce Waddington

[Rainboe]

When you hold into wind aileron you are trying to counter the upwind lifting effect.
If you do that too much you achieve this and then start exerting a downward force.
That force requires a slight opposite rudder input to counter. Yes or no?

How we make things complicated! Into wind aileron is ineffective at slow speeds. The effect builds up, just as asymetric wing lift builds up, therefore hold constant aileron on. The technique taught on the 747 was 1 division on the control boss for each 5 kts crosswind. Some people apply more.

I'm mystified why a downward force requires opposite rudder. In a fresh to strong crosswind, are you really going to notice? As you speed up, rudder requirement actually reduces, even in a strong crosswind. I believe in set and forget aileron, rather than try and fiddle with it as you speed up. People amazingly either forget to increase it, or actually, as one pilot did this week, apply downwind aileron. Keep it simple, and don't look for complications. In a strong crosswind, you won't find them- you will be concentrating of flying.

It's all there. If you know better, good on you. I know the way I was taught and works, and I am applying it every week up near the Arctic Circle. It works.

[framer]

Geeeez rainbow.....you're really hard to be polite to sometimes do you know that?
How we make things complicated!
In a conversation like this, away from the aircraft, it doesn't hurt to think about things and try and figure out exactly what forces are having which effect.
I always ask tham if they know exactly what they are going to do and do they understand it. I find very often it becomes embarrassingly apparent they don´t. I remember a captain who used to ask questions like that, often when I was half way through a flow or quietly concentrating on something else, normally he'd ask with about ten seconds of spare time before we had to roll or do something else. It was a real pain in the butt. Often I would be wondering "exactly what is this guy asking?" when he would seize the oportunity to display his amazing wealth of knowledge. The same type will often ask you to go and get an ATIS or something similar just as you have begun another task.Basically unaware of their mates activities, hope that wasn't you Rainbow?
If you know better, good on you. I know the way I was taught and works, and I am applying it every week up near the Arctic Circle. It works. You don't have to defend your method Rainbow,it's not a competition, rather a chance to learn what others think. I'm sure the way you were taught is great, once again, I agree that keeping it simple is smart. ....but surely we can discuss the forces at play without getting defensive?
I'm mystified why a downward force requires opposite rudder.Well here is an excellent chance to think, learn, and discuss then.
Answer this,
If you were rolling on a calm day and at 100kts put ten degrees of aileron in do you think you would need rudder to keep the centerline?
what do you think? Because if the answer is yes then obviously it is possible to put in so much aileron that you counter the wing lifting and go further. Therefore needing excess rudder.
Once again, my position is that many use too much aileron. I would like to hear what you really think about this rather than just defending your tried and tested and valid technique.
I'm glad you are flying into the Arctic circle it must be fun, I'll keep the bottom half of the globe under control into Wellington and Queenstown every week aye? With the two of us on the job everything should be ok. Cheers, Framer

[BOAC]

If you were rolling on a calm day and at 100kts put ten degrees of aileron in do you think you would need rudder to keep the centerline?- several of us here know the answer to that, framer - in fact at #18 I invited RB to try it. I doubt he will. Best left alone, I feel.

[411A]

This, explained the wise old Captain, would stop me from doing three things;

1. Having too much aileron selected as the airspeed increases which will actually cause the aircraft to turn into wind even more than the crosswind tries to make it and therefore will require more rudder than is really required to keep staight on the runway. The correction for this overcontrol can make for some interesting moments during the take-off run and just after lift off.

2. Having too much spoiler deployment for the conditions which can also cause the aircraft to turn into wind even more than the crosswind tries to make it with the same issue as above.

3. Having not enough aileron selected which will allow the upwind wing to start rising around 100 kts and also create some interesting moments during the correction process.

There is no 'preset formula' for aileron displacement during a crosswind take-off. Too much is just as bad as not enough. See how much rudder you need to keep straight and then, early in the take-off run, put in enough aileron to keep the wings level. Adjust as required if the wind changes or gusts.



Yup.

Now, it would indeed be interesting to have a few of our younger First Officers here (and a few of the younger Captains as well), strap themselves into an oldie such as a B707 intercontinental model with straight pipe engines and a parallel yaw damper which had to be switched OFF for takeoff and landing.
Throw in a very gusty crosswind, and watch the 'fun' with these folks wondering WTHIH?:E

More than likely, they would be just as surprised as I would be in their present glass paneled wonderbusses.:}

[RAT 5]

Well known fact for years, and I don't know why, nor can I analyse it: a B737 rolls off the wind on rotation. i.e. when rotating you need to increase aileron into the wind. Nothing to do with rudder, just a fact of doing it for years.

On takeoff roll you have some rudder down wind and will have some aileron into wind near Vr. On rotation, because of this 'roll off' tendancy you need to increase into-wind aileron to keep wings level. This increases the cross control configuration. The natural roll-off is aided by the down-wind rudder. This is where I have a hesitation in agreeing with the FCTM, even if that is blasphemy. It says smoothly neutalise controls once airborne. The down wind rudder is counteracting the weather cock factor ON the Ground. Ideally you want the a/c to head INTO the wind on liftoff to maintain Rwy track. The roll-off and rudder are countering this. If you slowly release the rudder at rotation the amount of extra into wind aileron needed is less. This leads to less spoiler delection etc, etc. and results in a less drag confuration at liftoff. It also means you are not cross controlled at actual liftoff.
It's just what I've found works on real a/c.
KISS.

[BOAC]

Indeed R5 - my technique too - remove the rudder first and the roll into wind pretty well sorts out the tracking problem.

[rubik101]

Bruce has it 100% correct. Read the Flight Crew training Manual; that is exactly as he describes it. More than 2.5 units of aileron lifts the spoilers and that is a big no-no on take-off.

[rubik101]

Over 24 hours and no response from rainboe? To those of you new to this forum, lots of hours and lots of posts does not make you right.
Some, who really should know better, seem to think that Training Manuals are written for the Insurance company's benefit and can be safely ignored in 'the real world'. Pilots who write their own manuals are a danger to the rest of those of you who are trying to learn from the experience of others. Be wary.....
Take with a large pinch of salt and a ladle of scepticism most of what you read from anyone who includes in their many and varied posts the fact that they have been flying for 25 plus years and have 20.000 plus hours. Including me!
The book was written, and constantly updated, by those who do know how to fly an aeroplane correctly.
If anyone wants a copy of a recently updated Boeing Flight Crew Training Manual, please PM me.

[40&80]

Yes Boeing update their training manuals....based on errors and ommisions and online operational incidents, accidents and experiances.
So do Airbus.....
All this talk about how badly pilots are trained to do crosswind takeoffs on a particular type....reminds me of the other question about the amount of aileron to be used on a max manual xwind landing...for a good guide of how much or little aileron should be used....see it done in the simulator on a maz xwind autoland.
I found I soon learnt about keeping on the centre line in xwinds and steering if required with aileron drag and useing rudder on the C46 and DC3.
Best aircraft in a huge crosswind for me was the L100 tristar...there you go 411A!!:ok: Argue with that statement.I miss her too.