737 Landing Gear Swivel

[seacue]

I've read that the main landing gear of at least early 737s has some compliance and will swivel a few degrees if the plane is still crabbing at touchdown. This might only apply to planes with an early form of autoland.

Of course I don't mean that the change in gear direction is directly commanded by some means, just that there is more-than-usual complaince.

Thanks for any info.

.

[themoffster]

Hi, I'm not affiliated in any way with airlines/aviation, but I did have my work experience at Glasgow Airport's (in Scotland BTW) engineering dept. On the last few days we were on the Ramp (I don't know if that's what it is called, but the tarmac outside). Anyway, I was in a "tug" (I can't believe I forgot what they are called, the wee cars that push planes back from the gate) and the guy driving was telling me all about the potential energy in the landing gear. When they line the plane up they are meant to have it in a straight line with the metal arm, but he deliberatly didnt do this to show me a point. Once the metal arm was released the nose wheel automatically straightened itself. His words were along the lines of "if the metal arm (sorry, forgot it's name too) was disconnected from the tug the bar would be swung through the air like it was a drinking straw until it lines up straight".

So really, if I got what you are meaning - all passenger planes will have this turning ability of the nosewheel, probably by law.

[WhiskeyNovember]

A friend of mine who flys 737s described this to me once. He said that the first-generation 737s (-100, -200, -300, -400, -500) have main gear that can swivel a few degrees. This allows pilots to touch down in a slight crab without spilling too many drinks in back. If you are ever taxiing behind a first-gen 737 in a strong crosswind, you will see that it actually taxis in a crab, due to the swiveling main gear.

The next-generation 737s (-600, -700, -800, -900) apparently do not have this feature.

Perhaps some real 737 drivers can confirm my second-hand information.


-WN

[Sonny Hammond]

Yep your on the money, but I cant confirm if the reason why you gave is the technical one.

The gear does move about, and it weirds you out when your new on the airplane because as you T/O, they straighten out and the aircraft pivots on the gear creating the illusion that it is changing direction down the rwy, but it actually isnt! make sense?

Funny set up..

[Onan the Clumsy]

If you are ever taxiing behind a first-gen 737 in a strong crosswind, you will see that it actually taxis in a crab, due to the swiveling main gear.

...or them not being bolted on correctly :eek:

[eng1170]

Fantastic topic!!!! And interesting responses.

I am familiar with the 73-300/400/500, and will need to go and scrutinise the gear legs a bit more closly when I get back to the hangar.

I have experienced the whole "crabbing" thing while on the deck - I was ground running one of our -400's at Link G at GLA/EGPF and had one of our old -200's taxing towards on the p155!! It was distinctly on the squiff!! At the time my colleague and I assumed it was poorly rigged nosewheel steering at fault but from the responses above, maybe not.

I know that the fwd trunnion mount of the main leg is part of the main leg casting/assy and mounts into a "hole" in the wing rear spar. The rear trunnion however is connected to the top of the main leg casting via a link before mounting into a fitting on the landing gear support beam (large beam between wing rear spar and fuselage sta663"ish") I am sure the link is probably built in to ensure the gear lies in the correct orientation as it retracts inwards to lie in the wheel well as opposed to being to allow movement should the a/c touch down "crabbing". The link may inadvertantly allow this to happen but I would be surprised if it was a build feature, would it not complicate the retraction sequence? Heavy wear and tear, gear retracts while at wrong angle? I don't know.

The only other thought I had is that the 73 has hydraulic shimmy dampers on the main legs and should these be removed/replaced or serviced they will require rigging checks carried out. If one or both the dampers were not rigged correctly or not operating correctly then the aircraft may "crab" on the ground.

I do not know the correct answer here, but thought my comments may generate some conversation. I will endeavour though to find out whether this is indeed a build feature or not, and also have a closer look at this "birds" legs!!!!!!!

Eng.

[fruitloop]

Sounds to me that the shimmy Damper hasn't been bleed properly
(one of those dirty jobs)

[Tee White Nun]

I only have a little experience on the 737 (bout 200hrs)
But heres my guess (im not the man with the van, i jus fly em),

Our company procedures when on an autoland or landing on a slippery rwy is to use the crab technique down to touchdown up to max crosswind, which for us is 15kts on autoland and half that for slippy rwy!

My guess is that (especialy for the older planes) thru time subjected to this altho not constantly (and hey havent you ever landed and thought oops...maybe my big boot wasnt heavy enough!!! err cause i havent...honest!! :} ) they aint gonna stay
bang-on straight forever!!! Thats why i believe when ya taxi behind one, it looks like somebody screwed the mains on that day without their set square!!

Thats jus my idea, think prob only an eng on type could shed some true light on this one?

Tee

[eng1170]

Wear and tear may come into it, but will also cause other more noticeable symptoms such as vibration on take-off/landing roll, and after rotation while the gear is down.

I did hear of one aircraft (a 737) where there was a history of vibration when on take-off roll that got to the point that the it couldn't be traced to any one point of the gear legs, so a triple gear change was reqd! Apparently when engineers went with a crew to do some taxi tests at 80 knots it was nearly impossible to read the flight instruments due to the vibration!!

Wear and tear to the extent that the gears cause the aircraft to crab on the ground is very unlikely I would think, but I could be wrong. Routine lubrication and inspections helps to minimise wear and tear in the linkages and mechanisms if carried out correctly, if not lubed regularly, wear can be accelerated.

I have worked on 73's for 6 years now, doing major maintenance checks, and never come across this as a reported defect- yet!

[Dom Joly]

I was told that they had a small amount of caster. This as an earlier poster pointed out would allow you to autoland in poor vis with a 15kt Xwind without taking the drift off. Personally, I never liked the idea of doing this. Never fancied trying it. I'd be too worried something would break and as for the pax:eek: :eek: :eek: wouldnt have many coming back to fly with us again in a hurry.:O

However Boeing flying manual doesn't mention anything like this at all.

[tmusser]

Well, after all, Boeing built the B-52, with the ability to hydraulically turn all four mains to runway heading during a crab. Had a great big rotary knob on the center aisle stand - dial in the crosswind and feel the aircraft rotate to runway heading as the weight came onto the gear.

[Notso Fantastic]

It's not noticeable from the Flight Deck when it is happening to your own aeroplane, but when you are taxiing in a line behind other 737s, particularly 200s but also I think the 400 to a lesser extent, the taxi crab is very marked.