A couple of stupid airliner questions...

[Quaint]

I found myself sitting in an over-wing exit row seat on a 737-400 this morning, and as we waited for take-off a couple of questions occurred to me. In the spirit of satisfying my idle curiosity, can anyone supply definitive answers to the following? No apologies for the idiotic nature of the questions. As I say, idle curiosity:

1) When taxi-ing, how do aircraft steer? I had always vaguely assumed they use the rudder, but it occurred to me that we were taxi-ing pretty slowly so I can't imagine the airflow over the tail was great enough for "steerage way". So - nosewheel? Throttling up the engine on one side? Magnets?...

2) Once an over-wing exit hatch has been used, can it be replaced? Or is the structure of the fuselage compromised in some way? Are airliners ever evacuated in situations where the airframe can be salvaged and repaired?

[B Oeuf]

Quaint said:

I found myself sitting in an over-wing exit row seat on a 737-400 this morning, and as we waited for take-off a couple of questions occurred to me. In the spirit of satisfying my idle curiosity, can anyone supply definitive answers to the following? No apologies for the idiotic nature of the questions. As I say, idle curiosity:

1) When taxi-ing, how do aircraft steer? I had always vaguely assumed they use the rudder, but it occurred to me that we were taxi-ing pretty slowly so I can't imagine the airflow over the tail was great enough for "steerage way". So - nosewheel? Throttling up the engine on one side? Magnets?...

2) Once an over-wing exit hatch has been used, can it be replaced? Or is the structure of the fuselage compromised in some way? Are airliners ever evacuated in situations where the airframe can be salvaged and repaired?

nosewheel steering using the rudder pedals or a seperate small wheel

they are just a hatch and can be replaced, they are removed on major servicing etc

[Quaint]

Marvellous - thank you!

[Eric Mc]

Aeroplanes are steered on the ground in a number of ways -

Nosewheel equipped aircraft (as mentioned above) will normally have nosewheel steering operated through a separate nosewheel "steering wheel" or using the rudder pedals (as in a kid's soap box cart).

Tailwheel equipped aircraft often have a free castoring wheel which is unsteerable. The aircraft is "pointed" by applying the mainwheel brakes differentially. Even aircraft as large as a Lancaster bomber were steered this way.

Older aircraft (pre 1930s usually) had a tailskid. In aircraft like the Tiger Moth the skid is fixed to the rudder post so applying the rudder pedals not only swings the rudder from side to side but also the tails skid allowing the aircraft to change direction on the ground.

World War 1 era aircraft tended to have fixed tail skids so they were pointed in the desired direction by a member of the ground crew running alongside and grabbing the wingtip.

[spitfire-ian]

Eric Mc said:

Tailwheel equipped aircraft often have a free castoring wheel which is unsteerable. The aircraft is "pointed" by applying the mainwheel brakes differentially. Even aircraft as large as a Lancaster bomber were steered this way.

Some nose wheel aircraft did/do this as well, certainly the EE Lightning did.

[cheadle hulme]

Larger airliners use the engines as well as the nosewheel when taxiing. Bit like using a bit of "oppo"!

Listen to the pilot of this bird struck 757 at 4'40'' state that he'll have trouble with tight turns on the one engine.

http://www.youtube.com/watch?v=_tLF-3d3PJk

[RizzoTheRat]

Eric Mc said:

Tailwheel equipped aircraft often have a free castoring wheel which is unsteerable. The aircraft is "pointed" by applying the mainwheel brakes differentially. Even aircraft as large as a Lancaster bomber were steered this way.

Having had a go at this in a Chipmonk, I'm pretty sure it's not actually possible and all pilots of such aircraft are skilled in the force and manouvre by telekenesis.
Want to go left, put a bit of left brake on, nothing happens, bit more left brake, nothing happens, eventually starts a slow turn to the left, come off the brake, continues to turn to the left, give it a bit of right brake, continues turning to the left, bit more right brake, left turn starts to slow, off the right brake, starts to turn to the right...etc...etc. After a couple of these oscilitions I was using the entire taxiway and the pilot had to take over

[Eric Mc]

RizzoTheRat said:

Eric Mc said:

Tailwheel equipped aircraft often have a free castoring wheel which is unsteerable. The aircraft is "pointed" by applying the mainwheel brakes differentially. Even aircraft as large as a Lancaster bomber were steered this way.

Having had a go at this in a Chipmonk, I'm pretty sure it's not actually possible and all pilots of such aircraft are skilled in the force and manouvre by telekenesis.
Want to go left, put a bit of left brake on, nothing happens, bit more left brake, nothing happens, eventually starts a slow turn to the left, come off the brake, continues to turn to the left, give it a bit of right brake, continues turning to the left, bit more right brake, left turn starts to slow, off the right brake, starts to turn to the right...etc...etc. After a couple of these oscilitions I was using the entire taxiway and the pilot had to take over

Imagine what it was like in a Lanc (or any of the other RAF four engined heavies).

[dr_gn]

The Tiger Moth has a steerable tail skid, which apparently only works (kind of) on grass. There have been many 'near misses' when taxying on tarmac or concrete, when the skid doesn't steer at all, and offers even less braking action than when used on grass.

[Eric Mc]

When the De Havilland DH88 Comet Racer G-ACSS was rebuilt in the 1980s, the original tailskid was replaced with a tailwheel for just that reason.

[dr_gn]

Eric Mc said:

RizzoTheRat said:

Eric Mc said:

Tailwheel equipped aircraft often have a free castoring wheel which is unsteerable. The aircraft is "pointed" by applying the mainwheel brakes differentially. Even aircraft as large as a Lancaster bomber were steered this way.

Having had a go at this in a Chipmonk, I'm pretty sure it's not actually possible and all pilots of such aircraft are skilled in the force and manouvre by telekenesis.
Want to go left, put a bit of left brake on, nothing happens, bit more left brake, nothing happens, eventually starts a slow turn to the left, come off the brake, continues to turn to the left, give it a bit of right brake, continues turning to the left, bit more right brake, left turn starts to slow, off the right brake, starts to turn to the right...etc...etc. After a couple of these oscilitions I was using the entire taxiway and the pilot had to take over

Imagine what it was like in a Lanc (or any of the other RAF four engined heavies).

Probably significantly easier, since there is a huge moment arm between the braked wheel and the thrust lines of the opposite wing's engines (which could also be throttled up if necessary). With a Chipmunk, with its single central engine, there is far less moment arm and therefore likely to be less easier to control.

[Eric Mc]

The Battle of Britain Memorial Flight keeps a couple of Chipmunks on strength in order to give new pilots to the flight some initial tailwheel practice.

[Caruso]

RizzoTheRat said:

Having had a go at this in a Chipmonk, I'm pretty sure it's not actually possible and all pilots of such aircraft are skilled in the force and manouvre by telekenesis.
Want to go left, put a bit of left brake on, nothing happens, bit more left brake, nothing happens, eventually starts a slow turn to the left, come off the brake, continues to turn to the left, give it a bit of right brake, continues turning to the left, bit more right brake, left turn starts to slow, off the right brake, starts to turn to the right...etc...etc. After a couple of these oscilitions I was using the entire taxiway and the pilot had to take over

When I learnt on Chipmonks swerving down the taxiway was SOP as it was the only way to be able to see where you were going. The engine prevented a direct view forward.

[Eric Mc]

Caruso said:

RizzoTheRat said:

Having had a go at this in a Chipmonk, I'm pretty sure it's not actually possible and all pilots of such aircraft are skilled in the force and manouvre by telekenesis.
Want to go left, put a bit of left brake on, nothing happens, bit more left brake, nothing happens, eventually starts a slow turn to the left, come off the brake, continues to turn to the left, give it a bit of right brake, continues turning to the left, bit more right brake, left turn starts to slow, off the right brake, starts to turn to the right...etc...etc. After a couple of these oscilitions I was using the entire taxiway and the pilot had to take over

When I learnt on Chipmonks swerving down the taxiway was SOP as it was the only way to be able to see where you were going. The engine prevented a direct view forward.

Another inherent problem with many tailwheel types. Sometimes, it was common practice to have a member of groundcrew sit on the wing to provide the pilot with steering instructions.

[eharding]

spitfire-ian said:

Eric Mc said:

Tailwheel equipped aircraft often have a free castoring wheel which is unsteerable. The aircraft is "pointed" by applying the mainwheel brakes differentially. Even aircraft as large as a Lancaster bomber were steered this way.

Some nose wheel aircraft did/do this as well, certainly the EE Lightning did.

The Yak-52 being another example - woe betide you if you manage to get the nosewheel fully canted to one side - the only options being to either select a stupidly high power setting (and run the risk of blowing debris, Tiger Moths, small children etc into the next county) to try and force it straight, or shut down and perform the comedy bouncing procedure using the grab-handle provided under the tail.

The zig-zag taxying procedure in tail-draggers quickly becomes second nature, and I always found the Pitts to be far more agile in ground-handling than anything with a nose-wheel (the mid-wing Extra 300, however, a least for relatively stumpy gits like me, is a nightmare - you really can see the square-root of sod-all of anything closer than about 20 metres in front of you from the back seat - and the things you hit tend to be immediately in front of you)

[Dr Jekyll]

B Oeuf said:

Quaint said:

I found myself sitting in an over-wing exit row seat on a 737-400 this morning, and as we waited for take-off a couple of questions occurred to me. In the spirit of satisfying my idle curiosity, can anyone supply definitive answers to the following? No apologies for the idiotic nature of the questions. As I say, idle curiosity:

1) When taxi-ing, how do aircraft steer? I had always vaguely assumed they use the rudder, but it occurred to me that we were taxi-ing pretty slowly so I can't imagine the airflow over the tail was great enough for "steerage way". So - nosewheel? Throttling up the engine on one side? Magnets?...

2) Once an over-wing exit hatch has been used, can it be replaced? Or is the structure of the fuselage compromised in some way? Are airliners ever evacuated in situations where the airframe can be salvaged and repaired?

nosewheel steering using the rudder pedals or a seperate small wheel

they are just a hatch and can be replaced, they are removed on major servicing etc

Harrier pilots have been known to get into awkward situations. Going too slowly for the rudder to have any effect, but still 100ft in the air.

[eccles]

spitfire-ian said:

Eric Mc said:

Tailwheel equipped aircraft often have a free castoring wheel which is unsteerable. The aircraft is "pointed" by applying the mainwheel brakes differentially. Even aircraft as large as a Lancaster bomber were steered this way.

Some nose wheel aircraft did/do this as well, certainly the EE Lightning did.

The Hawk also has a fully castoring nose wheel and steering is by differential braking.

[Ginetta G15 Girl]

On C130's we would often practice 'nosewheel steering failure' and taxi using differential power - which was fun...

Of course, we could (and regularly did) taxi backwards and even do 3-point turns.

[eccles]

Ginetta G15 Girl said:

On C130's we would often practice 'nosewheel steering failure' and taxi using differential power - which was fun...

Of course, we could (and regularly did) taxi backwards and even do 3-point turns.

Not an easy thing to do on a C-130 as there is almost no castoring built into the nose leg.

[Ginetta G15 Girl]

Hence the ellipsis!