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Cut out taxying under power.

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Cut out taxying under power.

Old 27th Sep 2006, 20:49
  #21 (permalink)  
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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.
Indeed. Take LHR/EGLL: If we cut down the number of slots/flights each day, those arriving would hold for far less time and burn less fuel. If we had a third runway then incoming would not have to hold so long.

But, once we had a third runway, BAA would sell another 1,000 slots (or whatever it would be) and the Holds will be full once again!
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Old 27th Sep 2006, 21:43
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Originally Posted by JediDude View Post
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?
No Jedi, but good question.

The energy to move the plane at a given speed over a given distance is, as you suggest, exactly the same whether the plane is pushed by elephants or conventionally propelled by its engines.

The additional, think of it as parasitic, energy required to make the energy available to propel the plane, will vary vastly depending on the power source. The total energy price is Energy to Move the Plane + Energy Wasted (mostly as heat) To Make Available the Energy to Move The Plane.

Airplane engines are designed to be efficient at cruise speeds and levels and are decidedly inefficient on the ground at low speed. I expect that self-powering a jet to the runway burns a lot more total fuel than towing one.

So if the tug burns less fuel, perhaps its emissions are less. Doncha think?
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Old 27th Sep 2006, 21:49
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That makes sense. Cheers for the heads-up.
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Old 27th Sep 2006, 22:17
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I notice that nobody has mentioned the obvious issue - money. Smart businesses these days understand that pollution= waste = money.

The idea of operational towing is a case in point. Mr Automan suggests his company is burning 12000Kg per day in taxiing. The B747 burn is approximately 1.5 tonnes per hour. 12000 x 365 = 4.3 million kgs annually.

What is the current cost of Jet Fuel? Simply do the numbers for the projected fuel savings, cost of the tugs and associated maintenance and operational costs, plug them into a discounted cash flow spreadsheet and you will have your answer.
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Old 27th Sep 2006, 22:20
  #25 (permalink)  
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Originally Posted by kansasw View Post
The energy to move the plane at a given speed over a given distance is, as you suggest, exactly the same whether the plane is pushed by elephants or conventionally propelled by its engines.
Sorted! Elephants it is then! Doubt that gas-emissions would seriously compromise the ozone layer, and the other exhaust products could be recycled and even produce revenue.
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Old 27th Sep 2006, 22:38
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Picking LHR as an example.....

Do we really think BA will employ any more tug drivers? They don't employ enough dispatchers as it is, and it's getting worse (and how does the increased wage bill compare to the money saved?).

How does GMC cope with the fact that a/c (especially fully laden 747s) tow much slower than under their own power?

Who does GMC talk to? The cockpit? The tow crew? Both? That's just far too confusing!
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Old 27th Sep 2006, 22:47
  #27 (permalink)  
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There are other problems associated with a tug assisted taxi.
There will need to be a large start up area off one side of the taxi way as aircraft often have problems at start-up that necessitate a return to the gate. On the apron rarely a problem but if this all takes place near the threshold then an escape route for both aircraft and tug is required and many airfields simply don't have the space, just one aborted start-up and the ensuing log-jam will take a while to sort out.
Another consideration, how many ground engineers are you going to need, at JFK for example, to accompany each aircraft to the start-up point and then make their way back to the next aircraft on their list? Are you going to provide facilities at the start up area so that engineers can remain there for a shift to overcome this? If you do you have just doubled the engineering requirements, if you don't your engineers are going to spend an inordinate amount of time dedicated to one aircraft, to the detriment of others that may require them.
The list goes on, any system that requires tug, driver, handlers and engineers to be at the start up area at the threshold is going to double your workforce and tug requirement or, if not, it will halve productivity/take offs etc. and just think of the chatter on the ground frequency that will eminate from two dozen or more tugs all roaming the area!.
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Old 28th Sep 2006, 00:48
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Originally Posted by parabellum View Post
There are other problems associated with a tug assisted taxi.
There will need to be a large start up area off one side of the taxi way as aircraft often have problems at start-up that necessitate a return to the gate...
No different in principle to the delayed start of 1 or 2 engines often practiced by some operators. If you choose engines that start reliably when desired, it's not an issue.
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Old 28th Sep 2006, 00:48
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Sorry for the slight tangent but what size of engine do these tugs usually have? Is it just a highly geared small diesel or are we talking supercharged 9-litre V10s?
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Old 28th Sep 2006, 01:38
  #30 (permalink)  
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Have to disagree with you there Barit1, though I suspect your comment is tongue in cheek.

Most of my hours are on RR and P & W, two of the most reliable makers in the business and still there have been plenty of 'return to stand'

Then we have the case of the APU that fails en route to the start-up area, GPUs available there too? Dispatching with a u/s APU will require at least one engine started at the gate if no facilities at the start-up area so the savings are already being reduced as the initial costs may be prohibitive. Airlines shuttling their staff back and forth to the start-up area to suit their requirements? More vehicles on the ground frequency.

Don't see it happening.

M.Mouse I believe the USA system on companies controlling the apron is partly an insurance thing. The airlines lease the terminal space and apron from the airport authority, (think that is the N.Y. Port Authy. in the case of JFK), and the contract requires them to take full liability for all movements in that area, for which they require insurance cover and therefore need to control all movements. Everything from gate to threshold under one GMC would, I think, entail hours of either gate or remote area holding at places like JFK.
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Old 28th Sep 2006, 01:38
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Gov. S of California thinks this is a good idea...hmmm

well, I just read that too much testosterone, like if you take body building steroids, can kill brain cells.


The right idea is "flow control" and engine start to wheels up of about 6 minutes...my company also says on first flight of day, engines are to be run 5 minutes prior to takeoff power, not to be confused with take off power.


this same stupid concept of taxiing out and waiting for takeoff AFTER being deiced/anti iced, is partly responsible for deadly accidents.



kudos to flow control...and to branson and the big S...wake up!

anyway, pilots won't stand for it as we get paid from doors closed and OIL pressure on engines.

and you would still have to run the APU for air and electrics.
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Old 28th Sep 2006, 02:39
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Is it time to restart the conveyor belt thread?
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Old 28th Sep 2006, 03:24
  #33 (permalink)  
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Think laterally. Bring the runway to the stand.
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Old 28th Sep 2006, 08:10
  #34 (permalink)  
 
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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?
Quote from Tesla motors FAQ..

http://www.teslamotors.com/index.php?js_enabled=1

Qon't electric vehicles actually just move pollution to another location? And therefore don't EVs still use oil?

A:No. Electric power generation in the USA does not use oil. Coal, hydro, nuclear, solar, and natural gas are typical sources for generating electricity. Power generation plants, even coal burning ones, are inherently more efficient and less polluting than vehicles due to economies of scale and the ability to more efficiently remove pollutants from a smaller number of much larger fixed locations.

Also, an electric car is far more efficient than a gasoline car, so the amount of pollution generated by producing the electricity to drive an EV a given distance is much less than the pollution from the gasoline to drive an internal combustion car the same distance.
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Old 28th Sep 2006, 08:17
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A neat trick would be to use the energy released by a landing plane to power the taxi system. Bit impractical to implement. Would need arrestor wires or something similar to recover the energy.... but it would also save fuel used on reverse thrust etc. Once captured by a cable system it could be towed to the stand. Way too expensive to impliment though.
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Old 28th Sep 2006, 08:23
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Originally Posted by JediDude View Post
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?
In fact I believe turbine engines are more efficient than many other gas engines. They have been considered for use in hybrid cars...

http://www.eere.energy.gov/cleanciti..._gas_turb.html

However I'm not sure if they are more or less efficient in this application.
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Old 28th Sep 2006, 09:39
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Lightbulb

If the Boeing electric taxi trials are a success, then it's only a short step to regenerative braking. The downside is that you'll need some sort of battery/ultracapacitor which will add mass and decrease the efficiency of the rest of the flight, although if you're not carrying taxi fuel then that is quite a saving...

After a little research, I found a tractor unit capable of pushing/towing a 747. It has a 400hp diesel engine so not that different in power to many lorries. I think the fuel savings at major hubs (LHR, JFK, etc.) would be considerable, given that the tug uses gallons per hour and the aircraft, tons!

Whether after the necessary changes in infrastructure (paved tug return paths), buying the tugs and paying the tug drivers it still proves economic I don't know. I'm pretty certain that there would be a huge saving from not using even a small percentage of the fuel required for taxi at LHR...
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Old 28th Sep 2006, 09:49
  #38 (permalink)  
 
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cwatters - if you read the last couple of paragraphs on that very good website you quoted, you'll read that a
gas turbine is less suitable for low-power applications - At partial throttle conditions, the efficiency of the gas turbine decreases.
That's why tugs are very much more efficient than aircraft engines when it comes to taxiing.

There is a tug out there that's designed to move an aircraft using a MLG, with the cockpit supplying steering input in the usual way. It's remote control, and designed to fit under a B737 wing. I wonder if pilots could do their own remote control tug taxiing...
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Old 28th Sep 2006, 12:41
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I think the answer is to give up this namby pamby idea of building flat airfields!!!

Build them on the side of a hill!!!! Take off runways can always be downhill, downhill taxi and no takeoff penalty, can roll out with no donks. Landing runways can always be uphill, cut the throttles and the masters, less braking and you get to roll downhill to the stand!!! (note to self, make sure there are enough turn-offs and an extra strong TDZ!)

Who cares about the wind, it's never bothered Zurich ATC much has it (Rwy 14!!!!)

Cracked it, off to the patents office....... Bwaaaaah!
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Old 28th Sep 2006, 13:37
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or eliminate airports

with a bit of air to air refuelling and parchutes, I reckon just quit landing and discharging passengers. Just drop off them off over the aerodrome via parachute, with their bags tied to them! Sure to cut down on how much stuff people drag around with them.

For "boarding" then try the USAF method of tieing a balloon to yourself and waiting for the plane with a pickup claw to pass overhead. terminal roofs are ideal for this scenario... again, it's all "carry on" so the natural tendency would be carry less. A380's would be interesting to watch! And any boozed up passengers will be stone cold sober by the time they get to their seat, guaranteed!

And for loco's there won't be seats, just stay hanging under the plane all the way to drop off. Shame if the Alps are in the way...

Just have one big aerodrome for the UK so planes can stop once a week for assorted maintenance... put it somewhere isolated like.. Scotland...

BAA could make a fortune putting houses on the no longer needed runway's across the South of England

S
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