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Cut out taxying under power.

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Cut out taxying under power.

Old 27th Sep 2006, 17:20
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Cut out taxying under power.

Proposals by Governor of California Arnold Schwarzenegger and Virgin Atlantic's Richard Branson suggest that airliners should be TOWED to runway thresholds to avoid burning aviation fuel (often said to be up to and beyond an hour) whilst taxying from the stand.
This is aimed at reducing the 'global warming' effects of 'greenhouse gases emissions'.
The idea seems to have some merit, as taxying fuel allowances could be omitted (or reduced) and overall fuel loads reduced.
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Old 27th Sep 2006, 17:26
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And how does the tug get back to stand down the full up taxiway?

Diesel powered tug too. And how much burn off does a modern jet engine consume at ground idle compared to a long range flight?

It's an headline grabbing idea but the practicalities will need some thought.

How about all Virgin Atlantic engineers agreeing to use FEGP instead of GPUs and to turn off all the APU once all the pax have disembarked. Oh and only start them back up when needed for boarding.

And before any outraged Engs hit back, I used to tell a certain station eng about this weekly. Until I got a proper job

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Old 27th Sep 2006, 17:31
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Hmmm Interesting!

But, of course you would then need a lot of extra tugs and tow bars burning lots of extra diesel and extra tug drivers to staff them.

And then the aircraft would have to start and warm-up their engines for a certain period of time before take-off; before applying possibly full power for take-off.

I'm not sure it would be worth it really?

Last edited by Out Of Trim; 27th Sep 2006 at 18:37.
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Old 27th Sep 2006, 17:35
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I remember reading (some time ago) about a device that was going to address the huge fuel wastage caused by taxiing. If I recall correctly it was some kind of electrical motor which had an unbelievable amount of power, making it capable of pulling aircraft up to the size of 767s. I'm sure the designers were having difficulty creating a form that guaranteed the performance that airlines would demand, which would explain why it hasn't entered the market yet. Hopefully others can provide a link.


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Old 27th Sep 2006, 17:47
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And this electric motor would have negligible weight? Or would it drop-off on rotation?

A better idea would be a development of the steam catapult, whereby aircraft could engage their nosewheel into a slot, running from near the stands to each runway holding area. They could even incorporate a full catapult take-off assist.

I'm an Engineer . . .
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Old 27th Sep 2006, 18:26
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Couldn’t all LoCo aircraft or ‘Y’ class seats in other aircraft be fitted with bicycle type pedals to propel the planes to the runway? The purser could stand at the front of the aircraft and beat a drum to keep everyone in time, the rest of the cabin crew could walk up and down lashing out at those who are not making enough effort.

Hang on, I think I’ve already flown with this level of service, only the pedals were missing.

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Old 27th Sep 2006, 18:29
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haha.. how about the passengers push the aircraft to the resepctive runway and board at that point.
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Old 27th Sep 2006, 18:52
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Jest not!

Some pax once pushed back a Shorts at Glasgow due to lack of tug.

Yes, really...

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Old 27th Sep 2006, 19:17
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On the Today Programme this morning, Virgin top fellah supports it and GWL want to trial it.
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Old 27th Sep 2006, 19:27
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Wasn't the towbarless tug originaly designed for this by LH so they could save fuel for some of their ULH flts!
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Old 27th Sep 2006, 19:29
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Electric motors run on electricity, electricity comes from power stations, power stations burn fossil fuels (I like the idea of wind turbines, but ...).

Sooooooooo, net carbon saving equals?
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Old 27th Sep 2006, 19:33
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If you have a long taxi either way, why not taxi on one or two less than needed.

I regularly shut one down on the taxi in, it may save 50kg of fuel - not a lot but, it gives me a fuzzy feeling that I alone am saving the planet !
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Old 27th Sep 2006, 19:43
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Take a lesson from Ellen MacArthur, fit some sails. Ecologically friendly and gives the pax something to do (get them to sort out the rigging during extended taxiing).

Hmm, might get interesting on the upwind leg.
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Old 27th Sep 2006, 19:54
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The answer is actually far simpler. It is common at many airfields in the USA to call for start (which appears to be controlled by whichever company controls the apron, certainly not ATC), taxy out and find literally 35+ aeroplanes ahead of you in a long line (or several lines).

I know of no other airfields in the world who allow startup unless take off can be accomplished within a reasonable time.
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Old 27th Sep 2006, 19:55
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Originally Posted by TooL8 View Post
Electric motors run on electricity, electricity comes from power stations, power stations burn fossil fuels (I like the idea of wind turbines, but ...).

Sooooooooo, net carbon saving equals?
The electricity could be stored in batteries which are recharged in flight.
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Old 27th Sep 2006, 19:55
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I think that at 95% of the worlds major airports it wouldn't be worth it. At some, such as LHR, LAX, JFK etc it may be .... but as others have said, there are infrastructure implications, such as escape routes for tugs, ATC giving accurate take off times so that engines could be started to comply with warm up requirements. And even then, the fuel savings only really mount up for the B747 types which burn about 1.5 tonnes per hour at idle on 4 - an approved taxi-out-on-3 procedure would have a quicker benefit here.

However, 1.5 tonnes per hour ground holding compare as to nothing to about 8 tonnes per hour airborne holding for a 747-400. If we could more effectively reduce airborne holding by the use of predictive EAT's we would do much more to reduce oil consumption and emissions.
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Old 27th Sep 2006, 20:15
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Correct me If I'm wrong but surely a tug towing an aircraft and an aircraft powering itself are going to use exactly the same amount of energy over the same distance? Surely the emmisions saved from burning aviation fuel is going to be offset by the increased emmisions from the tugs?
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Old 27th Sep 2006, 20:15
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Knowing that operational towing has been looked at for several years now, I initially brushed off the idea when it came up again in our company.
However, with rising fuel cost AND *possibly more stringent environmental laws* in the future, the idea definitely needs to be reviewed.
I agree that it may make no sense at most airports due to short taxi times (just covering heat up period for the engines) - but looking at taxi times of more than 2hrs in JFK, I think it would make sense there.

One thing that we need to look at from the engineering point of view for current designs: In what way will op. towing affect the nuts and bolts, in particular the NLG support structure? Keep in mind that you´ll tow airplanes around MTOW longer, faster and more often than today...

Oh, BTW: Any flight crew having (legal) objections against a tractor driver towing them around the planet...?

J. V.
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Old 27th Sep 2006, 20:27
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Here ya go;
Flight International, 17-05-2005

Electric taxi concept gets test-drive on Boeing 767

Demonstration to show airliners could manoeuvre on ground without engine power
An advanced electric-drive system that will enable crews to taxi and manoeuvre aircraft without using engines will be tested by Boeing on a 767 later this month.
The proof-of-concept on-board electric-drive device is being developed by Chorus Motor, an electric-drive technology specialist and subsidiary of Borealis Exploration, under a Boeing Phantom Works-led programme. Chorus, a "virtual" company based in Gibraltar, is providing a version of its Meshcon system.
The demonstration is being conducted on a 767 to prove the electric-drive system is powerful enough to handle large aircraft. "It could just as easily go on a 777 or a 747 because the technology is adequate to deal with any size of aircraft," says aerospace applications programme manager Robert Carman.
To get more torque out of an electric motor, it is necessary to increase the current handling capabilities of the inverter. However, this usually requires a larger, more expensive inverter, not all the capacity of which is usable because of limits on the total power available. The Meshcon system gets round this by regulating the voltage required by the inverter at various speeds, allowing the inverter to deliver all its power at reduced motor speeds.
Carman says the Meshcon system has been developed specifically for traction and increased low-speed torque loads, and applications for which starting torque requirements are higher than the continual torque requirements. The system uses multi-phase motors in which the windings are connecting several inverter terminals to each other, and not the ground. The different connectors act like different gear rates, and the motor can electronically change "gears" by operating the inverter at the harmonics of the drive frequency.
The system therefore uses harmonic drive to essentially fool the drive electronics into thinking they are operating at a higher speed. The net benefit is that the motor drive can achieve five times the torque speed of a similarly sized machine and is therefore much smaller and lighter.
"We believe the ability to integrate it into a weight-sensitive application is totally feasible," adds Carman. The demonstration is not representative of a flight-worthy system, suggesting that the drive system is being temporarily integrated into the nose gear bay and undercarriage leg rather than into the fuselage. The concept dovetails with Boeing's move to a more-electric aircraft philosophy, as is being pursued with the 787.
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Old 27th Sep 2006, 20:38
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I'm not sure if the battery idea was 'tongue in cheek' or not.

If not then I some really light batteries would need to be invented as such batteries would now burn up to 4% per hour of their mass in fuel just for the privilege of being flown around. (As well as the electric motors) In addition kerosene would be burnt in supplying the charge to the batteries.

Any extra mass would also reduce the available payload on a limiting sector which would be a difficult one to sell to the A380 engineers just now.

Just my thoughts.

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