Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Use of rudder during aircraft rotation

Tech Log The very best in practical technical discussion on the web

Use of rudder during aircraft rotation

Old 11th Dec 2006, 13:15
  #1 (permalink)  
Thread Starter
 
Join Date: Jan 2006
Location: France
Posts: 18
Likes: 0
Received 0 Likes on 0 Posts
Cool Use of rudder during aircraft rotation

Please your opinion on the following aircraft (Regional Jet) handling question.

Would you use rudder during aircraft rotation in crosswind conditions to push the nose into the wind? This in purpose to assure a correct drift angle to maintain runway track after lift-off.

Or...., wait until after lift-off and then bank slightly into the wind to maintain runway track.

I've a discussion with a collegue regarding the correct handling...

Feedback highly appreciated,

The Snake

Last edited by The Snake; 11th Dec 2006 at 14:49.
The Snake is offline  
Old 11th Dec 2006, 14:32
  #2 (permalink)  
Warning Toxic!
Disgusted of Tunbridge
 
Join Date: Jan 2005
Location: Hampshire, UK
Posts: 4,011
Likes: 0
Received 0 Likes on 0 Posts
Because of the crosswind element, as the aeroplane lifts off, it becomes in a slight yaw situation as the relative direction of the wind is not aligned with the runway direction, which is what the aeroplane is pointing in. This yaw situation results in the aeroplane naturally turning slightly into wind by itself. Only a small gesture is needed to complete the heading change you want to allow enough drift to maintain track. A small turn on the ailerons is all that is needed. I don't think you should use rudder- you are causing another yaw situation, and when you remove the rudder input, you are creating a reverse yaw situation in the other direction. It is probable that you will not end up with the aeroplane settled on the heading you want after all that yawing in either direction, so IMO just use a little aileron to turn where you want it and keep the aeroplane balanced. Anytime you try and use rudder as a turn aid, you create a roll element and it just becomes untidy.
Rainboe is offline  
Old 11th Dec 2006, 18:08
  #3 (permalink)  
 
Join Date: Jun 2002
Location: UK
Posts: 160
Likes: 0
Received 0 Likes on 0 Posts
If you are taking off in a crosswind, you will require a rudder defelction in the opposite direction to the wind direction (left crosswind requires right rudder) to maintain the runway centreline. There is therefore no need for an actual deflection of the rudder to yaw the aircraft into wind. On realeasing the rudder from the position you had it in to maintain the centreline, the aircraft will naturally yaw into wind itself.

I personally release the rudder to neutral as the aircraft gets airborne. This almost always results in the aircraft assuming the appropriate heading to maintain the runway track all by itself. However, once the rudder is centered you should use aileron only (assuming your aircraft has a yaw damper) to correct the aircraft track if need be, exactly as you would for any other turn.
captainpaddy is offline  
Old 11th Dec 2006, 18:33
  #4 (permalink)  
 
Join Date: May 2000
Location: Seattle
Posts: 3,195
Likes: 0
Received 0 Likes on 0 Posts
I don't know specifically about RJs, but in general the same control inputs (aileron & rudder) you need to maintain track just before rotation are a good start for rotation and liftoff. After you're airborne, level the wings and let go any rudder input to start your initial outbound track. The initial aileron and rudder inputs will likely set you up on a reasonable track with some crosswind correction. Fine tune it after the wheels are coming up.
Intruder is offline  
Old 11th Dec 2006, 19:28
  #5 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes on 0 Posts
Snake - Cpt Paddy and Intruder have the correct answer. It is so simple. 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 )
BOAC is offline  
Old 11th Dec 2006, 21:13
  #6 (permalink)  
Warning Toxic!
Disgusted of Tunbridge
 
Join Date: Jan 2005
Location: Hampshire, UK
Posts: 4,011
Likes: 0
Received 0 Likes on 0 Posts
But that hasn't answered the question! So where am I incorrect in my answer that I am excluded from your official stamp of approval (not that it's needed anyway!)?

Last edited by Rainboe; 11th Dec 2006 at 21:31.
Rainboe is offline  
Old 11th Dec 2006, 21:53
  #7 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes on 0 Posts
As I said, posts 3 and 4 answered it, did they not?
BOAC is offline  
Old 11th Dec 2006, 22:05
  #8 (permalink)  
 
Join Date: Oct 2001
Location: Australia.
Posts: 308
Received 0 Likes on 0 Posts
Originally Posted by The Snake
Please your opinion on the following aircraft (Regional Jet) handling question.

Would you use rudder during aircraft rotation in crosswind conditions to push the nose into the wind?
Perhaps the question cannot be answered because it includes incorrect assertions in the first place.

Yes you would use rudder deflection during rotation in crosswind conditions, but it would not be to
push the nose into the wind
but rather to keep the nose parallel to the runway during rotation. Once airbourne, you gently reduce your leg pressure on the rudder pedals. The pedals subsequently move back to the centre and the aircraft naturally "weather vanes" into the direction of the wind and subsequently continues to track the runway centreline. Meanwhile use the ailerons to keep the wings level. As the amount of rudder input reduces, so too does the aileron input.
Blip is offline  
Old 13th Dec 2006, 00:19
  #9 (permalink)  
 
Join Date: May 2000
Location: Seattle
Posts: 3,195
Likes: 0
Received 0 Likes on 0 Posts
but rather to keep the nose parallel to the runway during rotation.
Not quite...

Rudder (and nosewheel steering, when available prior to nosewheel liftoff) is used to maintain track down the runway centerline. Depending on the airplane and the crosswind component, the airplane may not be aligned with the runway while tracking the centerline.

After the airplane is airborne, rudder pressure is unneeded on most airliners, because the roll spoilers and yaw dampers provide yaw control in turns. So, once the wings are leveled after liftoff, rudder input should no longer be needed. Use aileron input to adjust heading/track outbound.
Intruder is offline  
Old 13th Dec 2006, 05:27
  #10 (permalink)  
 
Join Date: Jan 2000
Location: South Africa
Posts: 510
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Intruder
After the airplane is airborne, rudder pressure is unneeded on most airliners, because the roll spoilers and yaw dampers provide yaw control in turns. So, once the wings are leveled after liftoff, rudder input should no longer be needed. Use aileron input to adjust heading/track outbound.
On the CRJ you can feel unbalanced flight immediately. You also need rudder during low speed turns to keep the a/c balanced - if balanced flight is important to you obviously. It seems more and more of the newer pilots don't care.

I think you are making this too technical. After lift-off, maintain balanced flight (first) and runway track (second) using whatever control inputs are necessary.
nugpot is offline  
Old 14th Dec 2006, 13:37
  #11 (permalink)  
Thread Starter
 
Join Date: Jan 2006
Location: France
Posts: 18
Likes: 0
Received 0 Likes on 0 Posts
Thanks to all for the reply's.

Good point Blip noted. It's indeed a false assumption to use the word 'push the rudder', while reducing (smootly) pressure on the pedals close to Vr and thereafter to maintain track is what you actually do.

Sometimes I lost a bit the picture of rudder use during crosswind take-offs . But everything is much more clear now.

Luckily the past few days were windy in the UK and Ireland, so I could practice your advises in real life...

Happy take-offs!

The Snake
The Snake is offline  
Old 14th Dec 2006, 16:04
  #12 (permalink)  
 
Join Date: Aug 2000
Posts: 192
Likes: 0
Received 0 Likes on 0 Posts
"if balanced flight is important to you obviously. It seems more and more of the newer pilots don't care."

And a lot of older ones, too. A few years back a co-pilot said to me that I must have done some gliding. Why do you say that, I asked. Because you're the only captain (moderate size company) I've come across who keeps the ' ball in the middle'.

And while I'm at it, centre-line tracking post take-off is also becoming something to be filed under 'can't be bothered about'. I frequently line up, stiff crosswind, and watch the aircraft departing ahead drift further and further from the extended centreline - no apparent effort whatsoever to maintain it. What are they teaching at flight schools nowadays?
MaxReheat is offline  
Old 14th Dec 2006, 16:05
  #13 (permalink)  
 
Join Date: Dec 2006
Location: europe
Age: 49
Posts: 16
Likes: 0
Received 0 Likes on 0 Posts
Im lost....are we in the training forum or in a QUALIFIED AIRLINE PILOT one?
If one doesnt know the basics of a crosswind take/off (and not talking about perfect crosswind t/os), what is this person doing flying passengers around??


Best Regards to all who take their time to actually explain such method...
CNTDSCT is offline  
Old 14th Dec 2006, 17:34
  #14 (permalink)  
Anotherflapoperator
Guest
 
Posts: n/a
I've also found a lot of older high hour Jet pilots, well the ones I fly with who are ex 707 and the like NEVER touch the rudder except in the last instant of a crosswind landing. They will also always trim out using the rudder trim and never the aileron trim as well.

Our old 146-100 is exceptionally bent, I suspect the flaps are a degree or so out as it flies straight as a die with the ailerons offset by about 2-3"! Some roll moment going on there. Very few other pilots at my base will ever adjust the aileron trimmer, and I find a full turn will balance it right at cruise speed. We need a quarter turn of rudder trim but this is power related whereas the aileron trim is speed related.

Two of them, like me, apply rudder on crosswind takeoffs, keeping it applied as they rotate and gently feeding it off to allow the a/c to centre.

I suppose as we have the short one, it does lack much stability, and can't be dispatched without the yaw dampers working as well.

Now I'm no test pilot, but most of the experienced guys keep their feet up and out of the way most of the time. What do I know anyway? Perhaps my fiddling is totally unneccessary.
 
Old 14th Dec 2006, 17:56
  #15 (permalink)  
 
Join Date: Feb 2006
Location: London
Posts: 25
Likes: 0
Received 0 Likes on 0 Posts
A quick point regarding Blip's post (sorry if I have misunderstood you). An aircraft only "weather vanes" when on the ground. As soon as it is airbourne the aircraft no longer has a tendancy to turn into wind.
Q400 Pilot is offline  
Old 14th Dec 2006, 18:06
  #16 (permalink)  
Gender Faculty Specialist
 
Join Date: Mar 2002
Location: Stop being so stupid, it's Sean's turn
Posts: 1,872
Received 4 Likes on 3 Posts
Yes it does! It's called drift.
Chesty Morgan is online now  
Old 14th Dec 2006, 18:15
  #17 (permalink)  
 
Join Date: Feb 2006
Location: London
Posts: 25
Likes: 0
Received 0 Likes on 0 Posts
Not the same thing at all. An aircraft will maintain heading wherever the wind is coming from when airbourne (assuming it is trimmed). An aircraft drifts downwind, it doesn't turn into it.
Q400 Pilot is offline  
Old 14th Dec 2006, 18:22
  #18 (permalink)  
Gender Faculty Specialist
 
Join Date: Mar 2002
Location: Stop being so stupid, it's Sean's turn
Posts: 1,872
Received 4 Likes on 3 Posts
It will maintain a heading if that's what you or the autopilot are trying to fly, but the track will change. If however, you are trying to maintain a track, such as the runway centreline, then it wont. Try landing the Q400 without a yaw damper in a gusting cross wind. With low speed the slipstream effect is reduced and the old girl swings around. Yes it was trimmed.
Chesty Morgan is online now  
Old 14th Dec 2006, 18:38
  #19 (permalink)  
 
Join Date: Feb 2006
Location: London
Posts: 25
Likes: 0
Received 0 Likes on 0 Posts
Fair enough, if you speak from experience. Maybe we can discuss it further when we next fly together.
Q400 Pilot is offline  
Old 14th Dec 2006, 20:05
  #20 (permalink)  
 
Join Date: Nov 2002
Location: the pub
Age: 56
Posts: 149
Likes: 0
Received 0 Likes on 0 Posts
What did Rainboe say that was so incorrect? Seemed like a perfectly reasonable course of action.
one dot right is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.