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737 Crosswind takeoff

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737 Crosswind takeoff

Old 9th Nov 2007, 20:00
  #21 (permalink)  
 
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Fair enough. I'll try it out.

Cheers
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Old 10th Nov 2007, 06:40
  #22 (permalink)  
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Originally Posted by Rainboe
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

FCTM, FCTM,,FCTM, repeat after me......
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Old 11th Nov 2007, 00:12
  #23 (permalink)  
 
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"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() 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.
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Old 11th Nov 2007, 01:18
  #24 (permalink)  
 
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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.
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Old 11th Nov 2007, 10:08
  #25 (permalink)  
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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.
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Old 11th Nov 2007, 12:07
  #26 (permalink)  
 
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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.
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Old 12th Nov 2007, 19:16
  #27 (permalink)  
 
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Cool

...or in other words, operate the aircraft according to the FCTM.

Why so much discussion to establish this?
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Old 12th Nov 2007, 19:22
  #28 (permalink)  
 
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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.
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Old 12th Nov 2007, 20:35
  #29 (permalink)  
 
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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
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