Aircraft taxiing
Discussion
Can't answer for the civvies, but we certainly do (mil fast jet). Obviously we taxy out with everything working (otherwise there'd be no point leaving the engineers and trade support), but once we have landed we'll shut an engine down if on a suitable surface (due to fuel venting when you shut an engine) and taxy in on one.
adsvx220 said:
Why don't jet passenger aircraft only taxi with 1 engine? You often see turbo props making movements with 1 prop spinning? Whilst the other is not. Is there a reason??
When have you seen them taxi on two? At MAN most of the turbo props are Q800s (Flybe et al) and they always taxi on the RH engine - saves fuel vs using both. They use the RH for safety, because the doors are on the left.otherman said:
When have you seen them taxi on two? At MAN most of the turbo props are Q800s (Flybe et al) and they always taxi on the RH engine - saves fuel vs using both. They use the RH for safety, because the doors are on the left.
That what I mean. You always see props taxiing on 1 engine but the airliners always run both. 747 for example, after landing why don't they shut off 2 engines to taxi to save fuel (or do they?) same as twin engine jets why don't the switch off 1 engine?? I understand with the props that it's safety but it's also to save fuel. Surely if every aircraft shut an engine down you will also lower sound pollution no??
Single engine taxi is very common on twin jets too - must be a pain when trying to make turns in the wrong direction. You'll often notice a barking dog sound on Airbus 320s during taxi, which is a hydraulic pump compensating for one engine being shut down. Quads will often shut two down also.
adsvx220 said:
That what I mean. You always see props taxiing on 1 engine but the airliners always run both. 747 for example, after landing why don't they shut off 2 engines to taxi to save fuel (or do they?) same as twin engine jets why don't the switch off 1 engine??
I understand with the props that it's safety but it's also to save fuel. Surely if every aircraft shut an engine down you will also lower sound pollution no??
I'm no expert but I understand it's normal practice to shut down the inboard engines on a 747 during landing taxi:I understand with the props that it's safety but it's also to save fuel. Surely if every aircraft shut an engine down you will also lower sound pollution no??
a) to save fuel
b) the use of 4 engines would involve further heating the brakes to keep the speed down. Idle thrust on 2 is more than adequate.
I would imagine all 4 engine jets would do this
adsvx220 said:
Why don't jet passenger aircraft only taxi with 1 engine? You often see turbo props making movements with 1 prop spinning? Whilst the other is not. Is there a reason??
Going electric soon: http://www.greentaxiing.com/Pretty sure the last time I was at Heathrow, one of the engines got stopped pretty much as soon as we were off the runway & stayed off till we got to the terminal. They taxied out to the runway with both running though. I always assumed that was so you didn't have a problem of one of them failing to start when you were at the head of the takeoff queue & miles away from a fitter.
On the 747 we shut down one engine after three minutes at idle after landing.
We cannot shut down any more, nor taxi out with less than all four running.
The twins I used to fly could taxi out on one, so long as you had two minutes warm up prior to take-off once the start sequence had completed.
We cannot shut down any more, nor taxi out with less than all four running.
The twins I used to fly could taxi out on one, so long as you had two minutes warm up prior to take-off once the start sequence had completed.
On the triple we taxi in single engine once the relevant engine cool down period has elapsed for that engine type. Before we do so we take into account taxi distance, slope, apron congestion, surface conditions and even direction of turn onto stand.
Its purely a fuel saving exercise and the GE90 copes with 251 tons no problem at all with one of the donks shut down. Most 4 engine aircraft have 4 engines due to their size and shutting down 2 engines would normally mean they wouldn't have enough power on the other 2 to taxi without advancing the thrust to a level that would result in another engine cycle.
In saying that there's always that embarrassing moment on our RR powered triples when its an up slope onto a stand and the aircraft slowly grinds to a halt 15m before the stand. Requires a fair bit of oomph to get it moving again at the determent to another engine single and anything that may get damaged in the resulting jet blast.
Its purely a fuel saving exercise and the GE90 copes with 251 tons no problem at all with one of the donks shut down. Most 4 engine aircraft have 4 engines due to their size and shutting down 2 engines would normally mean they wouldn't have enough power on the other 2 to taxi without advancing the thrust to a level that would result in another engine cycle.
In saying that there's always that embarrassing moment on our RR powered triples when its an up slope onto a stand and the aircraft slowly grinds to a halt 15m before the stand. Requires a fair bit of oomph to get it moving again at the determent to another engine single and anything that may get damaged in the resulting jet blast.
5150 said:
On the 747 we shut down one engine after three minutes at idle after landing.
We cannot shut down any more, nor taxi out with less than all four running.
The twins I used to fly could taxi out on one, so long as you had two minutes warm up prior to take-off once the start sequence had completed.
And always no 3, yes? We cannot shut down any more, nor taxi out with less than all four running.
The twins I used to fly could taxi out on one, so long as you had two minutes warm up prior to take-off once the start sequence had completed.
Ginetta G15 Girl said:
You don't use rudder at taxy speeds, you use either nosewheel steering or diff braking.
When the USAF were flying various Migs for dissimilar training out at Tonopah the pilots found the steering system a bit, well, crap! So they started to taxy at 60-70+ knots and used the rudder instead.Simpo Two said:
Ginetta G15 Girl said:
You don't use rudder at taxy speeds, you use either nosewheel steering or diff braking.
I'm sure I've seen piston-engined fighters use bootfuls of rudder during taxying - but I agree that's not a modern situation.DeuxCentCinq said:
Simpo Two said:
Ginetta G15 Girl said:
You don't use rudder at taxy speeds, you use either nosewheel steering or diff braking.
I'm sure I've seen piston-engined fighters use bootfuls of rudder during taxying - but I agree that's not a modern situation.Gassing Station | Boats, Planes & Trains | Top of Page | What's New | My Stuff