Why do B737's taxi skew?
Thread Starter
Joined: Sep 2007
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From: Among camels and dunes
Why do B737's taxi skew?
I was following an SAS 737 the other day, close behind, possibly number 11 for departure, and the B737 had his nose wheel on the yellow line, and yet the aircraft was extremely skew all along the lengh of taxi. By measure of the distance between each of the main gear and yellow line, it was close to one third and two thirds difference between them, meaning the aircraft must be taxying as much as 10 degrees-12 degrees off centerline heading. Taxi way heading was 272 degrees (opposite of line up runway) and I would say this guy had a heading of 285, whilst tracking 272. Very clearly I thought the right main gear was not tracking straight, but rather tracking inboard. I have observed many other B737's and they all seem to taxi skew, however, on this occasion is was very obvious. Any idea's why they built the B737's like this?
Joined: Nov 2007
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From: Northampton
I was told that because the 737 autopilot does not have a rudder channel the main pintle bearing has certain amount of "play" to allow any drift to be absorbed during an autoland. This is then set until the next cycle. (or something like that)
Joined: Aug 2001
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From: A few miles from the airport
the angular displacement of the vertical axis is there for certification purposes. It allows the aircraft to land in an angle that is not fully aligned with the runway axis (crab/de crab technique during cross wind landings).
It has been discussed in this forum before. So for more info try the search function.
Happy landings.
It has been discussed in this forum before. So for more info try the search function.
Happy landings.
Joined: Sep 2004
Posts: 107
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From: Wetter ( Ruhr )
737 skew taxi
I beleive Boeing designed it for lazy or pilots who could not land In a x/wind. Many years ago I had to fly with a capt who could not land in x/wind on the type we were flying he had come of the 7373 fleet Frightning It was
Joined: Feb 2003
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From: Blue sky
t211, I believe you refer to landing in crab.
Boeing requires you NOT to decrab all the way above a certain crosswind value (I believe it is something around 17kts but someone should confirm this?) otherwise too much wing down will cause a CFM56 scraping the runway.
The CFM56 engine is simply slightly too big for the low wing, for that they needed to allow a slight crab during landing.
Boeing requires you NOT to decrab all the way above a certain crosswind value (I believe it is something around 17kts but someone should confirm this?) otherwise too much wing down will cause a CFM56 scraping the runway.
The CFM56 engine is simply slightly too big for the low wing, for that they needed to allow a slight crab during landing.
Joined: Mar 2007
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From: UK
I beleive Boeing designed it for lazy or pilots who could not land In a x/wind
I can't believe you wrote that!
Oh yes, I can just imagine the chief design engineer on the 737 many years ago sitting down with his fellow designers when that eureka moment struck them....
" Guys, how about this, they are a bunch of lazy gitz those pilots, lets design an aircraft that they can land in a x/wind without having to do anything!"
Last edited by CAT1 REVERSION; 22nd September 2008 at 10:25.
Joined: Jul 2008
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From: south pacific vagrant
Possibly something else that will accentuate what you can see is any slope (left or right) on the taxiway. Of course you will track the line with the nosewheel whilst the aircraft weight (mostly on the mains) will try to tend downhill one way or the other.
Taxi Skew
Joined: Jan 2002
Posts: 465
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From: UAE
The main gear can shimmy 7 degrees. Max autoland x-wind limit is 15kts I think.
Did an autoland yesterday but forgot already! Thank god for handy dandy's eh!
NG's taxi skew as well and more so when there's a cross wind pushing on the tail and winglets!
kempus
Did an autoland yesterday but forgot already! Thank god for handy dandy's eh!
NG's taxi skew as well and more so when there's a cross wind pushing on the tail and winglets!
kempus
Joined: Feb 2002
Aviation Qualifications: AME
Posts: 4,179
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From: UK
Get 'em bled.
Time to put it to bed then...
The main gear are fitted with hydraulic shimmy dampers. They need to be bled every now and again. A give away is the crabbing and lots of shoulder wear on the main gear wheels. The thing is that when you bleed them you have to select the gear up and down to cycle the shuttle valve. This allows fluid to flow through the damper. Not popular for those with a weak heart.
I think.... it's been a while since I worked a real aeroplane. It's all button pushing and resets these days.
The main gear are fitted with hydraulic shimmy dampers. They need to be bled every now and again. A give away is the crabbing and lots of shoulder wear on the main gear wheels. The thing is that when you bleed them you have to select the gear up and down to cycle the shuttle valve. This allows fluid to flow through the damper. Not popular for those with a weak heart.
I think.... it's been a while since I worked a real aeroplane. It's all button pushing and resets these days.
