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Olendirk
8th Nov 2007, 14:24
Guys,

some questions:

1. How to do the proper takeoff? How much defelction and how much rudder? when do we release the crossed controls after airborne?

2.According flight director? can we follow the fd initially? the fd doesnt correct for crosswind right? so look through?

thanks for help!

od

BOAC
8th Nov 2007, 18:23
http://www.pprune.org/forums/showthread.php?t=255896&highlight=crosswind+aileron

http://www.pprune.org/forums/showthread.php?t=255798&highlight=crosswind+aileron

and other items from 'search'.

After take-off, the a/c should be pointed to correct for drift, so, until you can use 'heading' with the corrected heading or LNAV mode, 'look through' is correct.

RYR-738-JOCKEY
8th Nov 2007, 18:52
Rudder: Enough to keep you on the centre-line. Aileron: Initially, no more than 6', because that will raise the spoilers. Then at rotation, add aileron to keep wings level. Fd's: Don't follow the vertical bar, cause it commands heading. Just release rudder+aileron just after lift-off and follow your track on the ND.

Kit d'Rection KG
8th Nov 2007, 21:05
Errr, read the Flight Crew Training Manual. :ugh:

Regarding RYR's post above, the spoilers have practically no effect on the ground roll (when you say they should not be used) and a slight effect during the V2 plus a bit climb (where you say they may be used to keep the wings level). Rethink required perhaps? ;)

Rainboe
8th Nov 2007, 21:54
Quite right Kit! There is this myth that a little spoiler upfloat on the ground is 'a bad thing' Nonsense! Anybody who flies Boeings know that speedbrakes below 250 kts are pretty useless. A bit of spoiler upfloat provides negligible drag.

In a strong crosswind (>20 kts), you are likely to need about 4 or more of those divisions on the control boss. This is going to give you about 25 degrees or more of aileron. Put it there at the start of the roll and leave it there until after lift off! Don't take it off when you get airborne. I constantly see people remove it when airborne- as the crosswind hits them, the into wind wing rolls up, and back it comes on, twice the deflection. Just leave it on, let the aeroplane settle as it yaws, then just fly the aeroplane wings level. A good guide is what was used on the 747 and works well for the 737- set 1 division aileron per 5kts crosswind, and leave it. Try it.

Another self imposed myth that seems to be pervading our airline now amongst the copilots is 'we must slow to 250kts maximum below 10,000'!'. I ask why? Where did that come from? The response is 'because of birds!' I have to positively say 'to hell with the birds, we're late! There is no speed limit unless you have a broken windscreen! I'm up here, and my cold beer is down there- why are you keeping me from it?'

MrBernoulli
8th Nov 2007, 22:45
Initially, no more than 6', because that will raise the spoilers.

Wrong! Mr Boeing has taken the use of the spoilers into his performance calculations for takeoff. Use as much roll control as you need to keep the wings level during a crosswind takeoff. The 'negligible drag' comments are also red herrings - whilst there might be some drag the major factor being considered is actually the generation of lift! But as I said, this had already been accounted for in the aircraft's certification.

Artie Fufkin
8th Nov 2007, 23:05
Possibly hijacking the thread somewhat, but here goes;

As Rainboe says once airborne, the flight directors give "wings level" in the B737. Presumably in the airbus, you get something else as I remember last winter getting stuck at the holding point on 09R at LFPG and had to sit and watch about 8 heavys takeoff. All the airbuses took off and tracked the runway QFU and all the boeings started drifting off towards 09L.

The question is, how does this apparent difference affect parralel runway operations - I wouldn't personally have fancied going around off 09L in an airbus when a Boeing was taking off from 09R.

Or have I missed something?

Centaurus
8th Nov 2007, 23:31
Wrong! Mr Boeing has taken the use of the spoilers into his performance calculations for takeoff
It all depends how much spoiler is applied. The operation of spoilers creates drag. Drag increases as the square of the velocity. That is why there is a marked deceleration immediately on touch down as spoilers are automatically deployed. Same principle applies at higher speed during take off run. Nearing rotation speed spoiler operation drag is significant if too much applied. Boeing stated in an earlier edition of the FCTM that I have, that the take off distance increases with inappropriate use of aileron/spoiler use during a cross wind take off. This in turn makes V1 useless.

SuperRanger
9th Nov 2007, 01:54
i dont know if the rest of you noticed this or not. for me, the 'correct' amount of ailerons would be just sufficient to offset the rudder input! i.e. if you have the correct amount of ailerons, you should require minimal rudder input!? at least that works for me.

and if you DO NOT hold the ailerons till airborne, your wings are bound to 'dip' just at liftoff. i guess, these will be more significant on the larger boeings.

SR

Rainboe
9th Nov 2007, 09:28
the 'correct' amount of ailerons would be just sufficient to offset the rudder input!
Don't agree with this at all. There are 2 factors affecting you on a crosswind take-off:
1- Lifting effect of the upwind wing
2- Weathercocking into wind effect of the side force on the fin.

Both quite independant. Rudder does not stop wing lifting.
You counter with:
1- into wind aileron
2- side force with rudder downwind

So you don't end up wrestling with controls whilst wheels are on the ground, I think you are best just leaving aileron fixed at your estmated setting, and keep tracking down the runway centreline with rudder. Whilst you are doing that, just feel for the upwind wing lifting, and hold it down with more aileron if need be. The lifting effect will probably reach its peak near rotate. When you lift off, you will instantaneously be in yaw in the air. You had better have your aileron on then, because that is when the wing will lift- and that is just when people tend to freak that they are airborne with all this aileron on! So off comes the aileron, the aeroplane tips downwind, then on comes up to double the aileron to get tyhe downwind wing back up. I see it all the time, then tell the copilot how much aileron he had to put on because he didn't listen to daddy!

Olendirk- try it, and report back. If you take that aileron off at take-off, try and see how much you then have to put on to level the wings. If it is not double what you would have had on the roll, I'd be surprised.

I think in threads like this, one should say what experience one has. 34 years on jets, nearly 20,000 hours. 18 years 747, 10 years 737, 6 years VC10.

(Heavens- we haven't even got into crosswind landings yet!)

RYR-738-JOCKEY
9th Nov 2007, 09:38
Uh...guys. The effect of raising the speedbrakes is that of changing your Vmcg, due to the yaw. The drag will be negligible.
I'm not talking about a 5 knot x-wind T/O, but a procedure that will keep you safe when taking off in max x-wind, V1 close to Vmcg, and then add an eng fail on top (critical engine, that is).
In our FCTM it says exactly that. Use a maximum of 6' aileron deflection during ground roll. Keep wings level during rotation.

PantLoad
9th Nov 2007, 12:21
I remember when I was wet behind the ears, flying with a crusty old captain who had more time in various aircraft than I had in a "T" shirt...(This is pushing 35 years ago.)...He told me, with regard to flying the 727 and the 737, 'It flies just like a Cub. Fly it just like a Cub.'

Hell, he was right...it's just an airplane...nothing magic about the aerodynamics...flies just like a cub.

As I gained more experience, and spent more time with my nose in the books (POH, FCTM, etc.), I discovered his over-simplistic advice coincided with the company SOP.

Amazing!!!!


PantLoad

RYR-738-JOCKEY
9th Nov 2007, 14:32
I see your point, but I beg to differ. A cub requires one pilot, a 737 requires two. That says something about the difference between them. I rest my case.

Syawriahsitirb
9th Nov 2007, 14:33
I have been flying the 737 for some time now and you can go on and on about crosswind takeoff techniques, but like 'PantLoad' mentioned, it's just an aeroplane. The techniques written in the manual are really for those just starting on the aircraft, but as you get more experience, it's a case of feel and react. Apply enough rudder to keep straight on the runway and a bit of aileron to keeps wings level as you rotate. You will prob find you need a little more of each as you lift off the ground, just keep everything straight and level and then about 200ft-400ft slowly start to release the rudder and aileron together. Simple as that. I don't know anything about units of aileron, as I'm not intelligent enough for that. I just fly the aicraft.

Just a quickie - I am little concerned about your comment Rainboe in regards to your frustration at co-pilots slowing to 250kts below 10,000ft. I have flown with guys who just love to kiss the barbers pole in the descent and I have indeed flown like this myself, but have you actually looked at what it saves you. In the time you spend flying around below 10,000ft, whether you're at 250kts or 320kts, it really makes no difference. Your comment of, "to hell with the birds, we're late," suggests you're putting pressure on the first officer to fly faster than perhaps he/she is comfortable with. This is completely and utterly wrong. It makes almost no different in time at all. Have a look at the FMC ETA when you change the descent speeds. If you delete the 250kts below 10,000ft constraint, on more or less every occasion, the ETA will not change. So rather than pressuring your FO's into doing things they're not comfortable with, just sit back in the knowledge that as they gain more experience, perhaps they might just start flying that little bit faster. Plus, is it not a rule now that we must fly 250kts below 10,000ft in the London TMA?

P.S. Are you one of those drivers who drives up the ar** of other drivers? :p

misd-agin
9th Nov 2007, 14:46
Wish that I had saved the email from a Boeing test pilot that had answered this exact question.

He said Boeing's policy was to use as much aileron as necessary to keep the wing level during the takeoff roll.

Aileron input prior to takeoff roll or during inital takeoff roll? Hmmm, how much aileron input due you need to keep the wings level? None.

RYR-738-JOCKEY
9th Nov 2007, 17:01
misd-agin: Try no aileron in max crosswind.
Not very pleasant. My first lesson in a C-172 taught me the opposite. In addition it contradicts everybody else in here.

And britishairwayS:
I'm talking about X-WIND T/O here. F.ex. rwy 18, W/V 225/33G46. Using "abit of aileron" will flip you over in no time. You need probably 10 units/45 degrees/half deflection on the yoke to have control. During rotation, that is.

BOAC
9th Nov 2007, 17:26
Ho hum - obviously no-one has looked at the links to previous threads and this keeps on coming up over and over again.:ugh:

This from the Boeing 737 Training Manual, but good for all:

Maintain wings level throughout the takeoff roll by applying control wheel displacement into the wind. During rotation continue to apply control wheel in the displaced position to keep the wings level during liftoff. The airplane is in a sideslip with crossed controls at this point. A slow, smooth recovery from this sideslip is accomplished after liftoff by slowly neutralizing the control wheel and rudder pedals.


It's simple; it works - do not get drawn into making it more complicated! Think of it as:-


1) Keep the wings level ( a good idea)
2) Gently remove the rudder pressure (it gets tiring:) )

Maintain wings level throughout the takeoff roll by applying control wheel displacement into the wind. - that means 'as required', not needed at the start of the roll unless you are in a Tiger Moth

A slow, smooth recovery from this sideslip is accomplished after liftoff by slowly neutralizing the control wheel and rudder pedals. - this, of course, omits 'remove aileron input in a co-ordinated manner as you remove the rudder input' - well, that's how you fly, isn't it?

I shudder when I see 10 units go on before brakes off and stay there, unchanged:sad:

Rainboe
9th Nov 2007, 17:43
Aileron input prior to takeoff roll or during inital takeoff roll? Hmmm, how much aileron input due you need to keep the wings level? None.
The aim is to set and forget. You cannot 'fly' the aileron on in the early roll, so just set and leave and concentrate on holding the centreline. You will need it more>100kts when it will be set already, not giving you a rising wing to suddenly remember to counter.

I don't like home made, self imposed speed restrictions.....reason? .... 'for birds'. 'The birds' should not be in a control area. There is no such official speed restriction on the aeroplane. One hesitates to do it at London, but most of flying occurs elsewhere where skies are not so congested, and I do hustle for it.

This one is a regular Pprune item. Search should bring up several discussions on this topic, with all the old chestnuts regurgitated and spewed out!

Rateofdescent
9th Nov 2007, 18:59
1/ Crosswinds T/O are NOT the same in a CUB and a 737. On a CUB you should decrease input during T/O roll on the B737 you have to increase control input during the roll.
The only correct answer is in the FCTM, only the part 'as needed' is something you learn with experience. (indeed on a B737, speed=0, control wheel and rudder input needed=0)
Set and forget? Tell me how do you know the exact amount to be set before you started the T/O roll.
2/ 250Kts below 10.000. Check airspace class qualifications (by the way,the non-busy clear skies are often lower than class C). And yes, the reason is NOT birds.
(Anyway, most birds are now informed not to fly in controlled airspace without clc and Tx)
The ETA does change one or two minutes, that is if you also delete all other speed restrictions on the arrival, which occur sometimes above 10.000feet.

Rainboe
9th Nov 2007, 20:01
Set and forget? Tell me how do you know the exact amount to be set before you started the T/O roll.
What worked for me 18 years on the 747 also works on the 737. On top of the control wheel are marked divisions in units, what you use to check control wheel central. At the start of the roll, set 1 division into wind per 5kts crosswind component, and leave it there. Later on at high speed, you don't even have to remember which way to put it on, or cope with a wing lifting. It will hold the wing down until you get airborne. Do not take aileron off after lift-off, just leave it. The aeroplane will weathercock into wind, and then you will know when to relax it- once all yaw has washed out. You will find you gently start rolling aileron central, with no wing drop at all. The masters in the BA training section drummed it in long ago on the 747, and it works so well there is no other way.

I see it again and again. As pilots get airborne, off comes the aileron immediately, horrible wing drop followed by reapplication of double the amount of aileron (with a gasp). When the wheels lift off, the aeroplane is in instantaneous yaw, and all they can think is 'I'm airborne- I can't need this aileron!'. They do. All I can say is try it- you will find it works a treat.

Rateofdescent
9th Nov 2007, 21:00
Fair enough. I'll try it out.

Cheers

BOAC
10th Nov 2007, 07:40
Search should bring up several discussions on this topic, with all the old chestnuts regurgitated and spewed out! - indeed, and even a search of THIS THREAD will do the same:ugh:

FCTM, FCTM,,FCTM, repeat after me......:confused:

misd-agin
11th Nov 2007, 01:12
"misd-agin: Try no aileron in max crosswind."

I have. At zero airspeed the ailerons are useless. At speed they're vital.

Next time you're sitting on the tarmac(:confused:) doing your flight control checks notice the rolling motion they create. Nothing happens. Therefore the controls are doing nothing at low speed.

I guess the Boeing boys were wrong. I'll ask them to retest their aircraft.

And to compare the handling of a C-172 or Cub with our aircraft is silly. 40 kts gusts don't flip over commercial jets. Piper Cub's become bowling pins taxiing downwind in 40 kt winds if handled improperly.

fireflybob
11th Nov 2007, 02:18
Also heard all these different arguements before!

On the B707 I recall we were taught about 1 unit per 5kts of crosswind component (and it was VERY important to keep the wings level on rotate due to potential pod scrape on the outer engine!!).

That said I think the really important thing is to maintain the into wind aileron (and rudder) DURING the rotation for take off and then once you are safely airborne to smoothly centralise the controls for balanced flight. Ok there may be an arguement that you dont need into wind aileron during the early part of the take off roll but having to change the aileron input during the roll takes a lot more thinking about (well for simple folks like me that believe in the KISS approach).

On a (re) conversion course onto the B737-800 a very experienced training pilot was of the opinion that when taking off in max crosswinds FULL (yes FULL) aileron should be briefly applied during rotation. Having done about 4,500 hours on B737 variants I feel somewhat uncomfortable with this technique and it is not what I use but I would be interested to hear any comments from others!

That said I believe we should be following the advice of the Boeing FCTM.

Rainboe
11th Nov 2007, 11:08
The Boeing FCTM is remarkably vague about any precise instructions during the take-off roll. It appears to allow a degree of indicidual preference.

I don't see what the problem is with putting aileron on at the start. What drag are you going to get below 100kts from spoilers cracked slightly open? Put it there and leave it- you don't have to do any more or even think about it- just keep on the centre line. If full speedbrake at even 250 kts gave me the drag I wanted, I might be worried about the drag at 140 kts airborne, but it's negligible. Look at it this way- if it gave you drag to be concerned about, why, when you wind on a lot of aileron after take-off because you have let the wing rise, do you not yaw. Not a bit. There is no perceptible drag from the spoilers after take-off. So during the roll there is nothing, so why not just leave it set all the take-off? It works for the 747- you don't feel that wing start lifting early.

I was once surprised to see a copilot not use any aileron during roll on a heavy 747 in a strong crosswind. I thought I would not say anything until afterwards and explain. The moment we lifted off, up came the wing, almost full aileron then to lower it- it was awful. I found myself thinking we came close to scraping a pod. People are either lazy on crosswind takeoffs or they've never had it fully explained and don't understand, but all the unpleasant movements I've had on crosswind takeoffs have all had one cause- too little aileron, never too much.

fireflybob
11th Nov 2007, 13:07
all the unpleasant movements I've had on crosswind takeoffs have all had one cause- too little aileron, never too much.

Rainboe, I agree - better to have slightly more aileron into wind rather than not enough.

Kit d'Rection KG
12th Nov 2007, 20:16
...or in other words, operate the aircraft according to the FCTM. :bored:

Why so much discussion to establish this? :uhoh:

RAT 5
12th Nov 2007, 20:22
X-wind takeoff and the a/c wants to weathercock into wind. Downwind rudder is applied to keep on centreline. Into wind aileron is applied as has been said. B737 rotate and it wants to roll off the wind. Keep wings level with even more aileron. But hang on a minute; guess where the rudder is; encouraging the a/c to roll off the wind. The B737 has a roll off tendancy anyway; keeping the downwind rudder on during rotation increases this tendancy. Thus, why not slowly release the rudder during rotation so that it is off at lift off, allow the into wind aileron to cock the nose into wind - which is what you want to do to hold the centreline - and use the aileron to keep wings level all the time. Holding track for centreline in HDG SEL will depend on what HDG is set on takeoff. Some airlines demand RWY HDG (zero drift), some airlines allow pilot discretion to pre-set a drift HDG. As you lift off in the former case the a/c should be tracking the centreline, so why not 'gear up match HDG'? The F.D is then correct and Bob or Hairy Dick is your uncle.

Trying to make it too scientific and exact is not perhaps what piloting is all about. Feel and intuition are also part of the game. Making it less difficult is also up there.

Pilot Pete
12th Nov 2007, 21:35
This from the B737 FCTM, not sure which ones others have in their companies, but mention is made to excessive aileron inputs in a few places.

Directional Control
Initial runway alignment and smooth symmetrical thrust application result in good crosswind control capability during takeoff. Light forward pressure on the control column during the initial phase of takeoff roll (below approximately 80 knots) increases nose wheel steering effectiveness. Any deviation from the centerline during thrust application should be countered with immediate smooth and positive control inputs. Smooth rudder control inputs combined with small control wheel inputs result in a normal takeoff with no overcontrolling. Large control wheel inputs can have an adverse effect on directional control near V1(MCG) due to the additional drag of the extended spoilers.

Note: With wet or slippery runway conditions, the PM should give special attention to ensuring the engines have symmetrically balanced thrust indications.

Rotation and Takeoff
Maintain wings level during the takeoff roll by applying control wheel displacement into the wind. During rotation continue to apply control wheel in the displaced position to keep the wings level during liftoff. The airplane is in a
sideslip with crossed controls at this point. A slow, smooth recovery from this
sideslip is accomplished after liftoff by slowly neutralizing the control wheel and rudder pedals.

Gusty Wind and Strong Crosswind Conditions
For takeoff in gusty or strong crosswind conditions, use of a higher thrust setting than the minimum required is recommended. When the prevailing wind is at or near 90 to the runway, the possibility of wind shifts resulting in gusty tailwind components during rotation or liftoff increases. During this condition, consider the use of thrust settings close to or at maximum takeoff thrust. The use of a higher takeoff thrust setting reduces the required runway length and minimizes the airplane exposure to gusty conditions during rotation, liftoff, and initial climb.

Takeoff and Initial Climb
Avoid rotation during a gust. If a gust is experienced near VR, as indicated by
stagnant airspeed or rapid airspeed acceleration, momentarily delay rotation. This slight delay allows the airplane additional time to accelerate through the gust and the resulting additional airspeed improves the tail clearance margin. Do not rotate early or use a higher than normal rotation rate in an attempt to clear the ground and reduce the gust effect because this reduces tail clearance margins. Limit control wheel input to that required to keep the wings level. Use of excessive control wheel may cause spoilers to rise which has the effect of reducing tail clearance. All of these factors provide maximum energy to accelerate through gusts while maintaining tail clearance margins at liftoff. The airplane is in a sideslip with crossed controls at this point. A slow, smooth recovery from this sideslip is accomplished after liftoff by slowly neutralizing the control wheel and rudder pedals.


Hope this helps.
PP