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

[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 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 donīt. 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 peopleīs knowledge and they wonīt ask, yet evidently donīt 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..

[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 donīt.

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?

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!! Argue with that statement.I miss her too.