So how much weight would these electric motors, wiring, control system, strengthened undercarriage add?

And then, how much extra fuel would it take to carry this extra weight around the world between airports?

Flame icon for all that extra fuel burning...

"But this would involve much less wasted energy..."

Doubt it.

And what of the added weight penalty associated with the motors and fuel cell system?

"It's not clear at first sight how the Airbus wheel-motor scheme would avoid similar problems, but presumably Flourens knows what he's on about."

I would guess they'll power all of the landing gear, rather than just the nosewheel (which is what's used for towing)

Airbus builds planes: if they want it to be towable, they can make it towable. If Branson wants to make old planes towable, then he has to pay someone (like airbus, or boeing) who makes planes to make them towable.

I still think building runways at 50000 feet is the most rational fuel saving measure.

- Joel

"...but it was found that towing fully-loaded planes put unacceptable strains on their undercarriages, and the idea had to be abandoned.

It's not clear at first sight how the Airbus wheel-motor scheme would avoid similar problems..."

A tow would normally be attached only to the nose wheel part of the undercarriage - presumably this idea would be applied to all of the wheels (including the bigger ones under the wings), thus spreading out any forces.

Perhaps more useful if designed in from the start rather than added on.

If the plane was on a treadmill... never mind.

Or just power the wing wheels... gives tank like turning and should push the plane rather than pull it?

Other option is to get greenpeace activists to pull the planes around by long ropes. Gives them something to do and helps the environment, how could the refuse?

:)

"I still think building runways at 50000 feet is the most rational fuel saving measure."

Spectrum were a long way ahead of you in their constant battle with the Mysterons.

SIG!

Well, how much fuel won't be burnt? How much does that weigh? Electric motors are very goot at torque and it's not like you want your airbus taxiing round a hairpin at 40mph, is it.

I would be for this even if it didn't reduce overall emissions if only for the fact that there would be less jat fumes at the airport. y'know, that place with all them people (and the necessary lungs) sitting around.

Wheels have motors already. They are spun up before landing to the landing speed to minimise the strain on the undercarriage. So the weight is already the actual weight difference is between the current motors which are designed to spin up wheels to the equivalent revs for 200km/h+ and a motor that can move the plane on the ground. This in fact may end up requiring the same weight and the only difference is that the motor will have two different switching arrangements for low and high revs. In fact you can also use this for breaking as well which will eat some weight from the breaking system so overall this may end up weighting less than the current undercarriage assembly.

Come on we already have towing tugs at airports, just get them to tow the damn things to the end of the runway, no need to re invent the wheel, literally.

A couple of things.

Firstly, it occurs to me that having your engines run a bit, tested and warmed through before asking for full thrust on takeoff is almost certainly a good thing. Secondly, I've been on a couple that have refused to start on internal power and had to call for a trolley-ack to supplement the starting process (one of these tripped a breaker somewhere and plunged the cabin into darkness, causing some consternation among the more nervous passengers). Such an occurance could cause something of a problem with the thing marooned at the end of the runway.

Maybe they're only contemplating this approach for the taxi-in after landing? That would be more sensible.

As most of the damage caused by plane emissions is when they are airborne, it willmake little difference.

Bit like the pointless carrier bag debate (most can be recycled and many are biodegradable).

Make a tiny gesture to hide the real problems....

The only aircraft I know that has a system to spin-up wheels before landing is a Cessna Citation (I'de be interested to learn of others). Then it's only on the nosewheel as an option and uses compressed air to turn the wheels. There are plenty of patents for finned wheels to allow the aircraft's movement through the air to spin wheels, but I can't find examples in use.

I agree that electric motors could be used for regenerative braking, but the energy transferred from kinetic to electric must go somewhere. The aircraft's batteries seem the obvious choice for this, but the batteries must have sufficient capacity to store the energy from the electric braking. So the aircraft must land with partially/mostly discharged batteries. Friction brakes would still be required for landings or rejected take-offs with charged batteries.

All adds up to more weight. More weight == more fuel needed

Guess you missed this part?

"Colourful beardy biz kingpin Richard Branson has lately sought to use a somewhat similar idea with his Virgin fleet, in which the jets would have been towed to and from the runway by ground vehicles. This is sometimes done for various reasons with empty aircraft, but it was found that towing fully-loaded planes put unacceptable strains on their undercarriages, and the idea had to be abandoned."

Rubbish. About the only aircraft that has a system to spin up wheels before landing is the Cessna Citation business jet (and even then it is an option, not standard). It uses compressed bleed air from the engines to blow on vanes to spin up the nose wheels only, not the main undercarriage, and this is not to reduce tyre wear, but to reduce throwing up debris into the engines when landing on rough strips.

I was helping to chuck Phantoms of the front end of the Ark, we hooked the straps onto strong points on the fuselage.

Towing aircraft in a similar way would obliviate the 'excess stresses' on the nose wheel strut. Though, considering the stresses that the landing gear goes through I wonder whether the nose wheel would notice it.

The idea of having wheel motors which would actually be powerful enough to move a fully fuelled & loaded aircraft and light enough for the aircraft to actually take off, together with a power source sufficient to drive these motors, is laughable. Perhaps in 20 or 50 years the technology would be available, now - no.

Icon; 'cos that's what would happen if you tried to fly with wheel motors fitted.

No pilot of any sort of plane will accept the idea of only turning the engine on at the end of the runway, and immediately taking off. Power checks are needed first to give you confidence they aren't going to fail at the worst possible time, which is immediately after take off. In commercial jets this is done on the taxi out, smaller planes stop at the hold points, in either case it involves burning as much fuel as a good few minutes taxiing.

Finally the idea of putting electric motors on the landing gear powerful enough to taxi the plane, even slowly, is fraught with difficulties. The gear is designed to be very light otherwise you need even more powerful hydraulic gear to retract it. Also under emergency gravity assisted deployment if it is too heavy it might rip itself off. It is enough of a challenge to compensate for the aerodynamic changes while deploying the gear without factoring in further weight and balance instability.

Lastly by far the most important consideration is fuel efficiency in the air where the plane spends more of its time, and any excess aircraft weight is a non starter. Its just another hair brained idea by the carbon cultists, which ends up causing more problems that it solves, and will have no effect on climate change.

@Peter Depledge

"I agree that electric motors could be used for regenerative braking, but the energy transferred from kinetic to electric must go somewhere."

Yeah, it can be transferred in to heat. You put a hefty resistor bank on board and, once the batteries are full, just burn off the speed (literally - almost).

@TeeCee

If this idea was adopted...

Firstly, the aircraft would taxi to holding point CLOSE to the end of the runway and then go through the engine warm up procedure. This is what Branson was planning.

Secondly, there would be backup power available at the parking lot surely? Airlines are not that dumb - cheap but not dumb.

@Peter Fielden-Weston

Isn't it the main gear that takes the vast majority of the stress on a commercial jet? The nose wheel is mainly there for steering... and stopping the horrible scraping sound of the aircraft frame on tarmac.

And for those bitching that taxiing isn't the problem, well it was a big enough problem for Branson to bother trying to tow his heffalumps. Taxiing is horrendously inefficient; those engines are designed to run fast and high. For an airline manufacturer to propose this solution they obviously think that there is an operational saving to be made (although this IS Airbus...).

UMMM yes I missed that, never mind, thank god I am not in charge of a plane.... I would never have the skill to dodge in and out of all those tugs and luggage trolley's racing up and down the runway.

I must get another bar of chocolate now excuse me

Delta, Northwest, American all - I believe - require pilots to only start one engine at the gate for taxi and start the second (third, fourth, etc.) engine(s) when they reach the end of their taxi prior to take-off. The reverse is done on landing: only one engine is left on once the aircraft is on the taxiway.

The reason for this - and, at least Delta, has been doing this for well over 8 years - is, as Jim points out above, taxiing IS horrendously expensive in a limited sort of way. Delta started this procedure back in the late '90's to reduce the amount of fuel used. Even a few minutes of jet operation adds up over hundreds of aircraft each day.

The extra weight won't help. Rather use an external tractor to drag the aircraft around. The weight stays on the ground and there are no compormises of size/weight etc that need to be made. An electric ground tractor can be more efficient than anything they can put in the plane itself.

It's all just PR bollocks for an industry falling over itself to greenwash itself.

...am I suddenly reminded of that little bit in "Man vs Animal" special a few years ago? Especially about the one with the elephant vs. a gaggle of midgets. All hitched to one or the other of two airplanes.

Personally tho, the dwarf horde would be a *great* towing service. Anything to keep down The Great Midget Rebellion. They'd be too tired to uprise against us tallists after an 8-hour shift of shifting planes.

If you look at the gear, all the available space is already used by the hubs, the brake packs and the brake cooling.

The only way I can see you'd get motors in there is to ditch some of the brakes (not really practical - it's all needed, and nothing is likely to outperform the existing carbon/carbon packs so you can't make them any smaller), or make the wheels/gear larger to make the space for the motors (again impractical as there isn't room).

There's also the minor problems of finding a motor capable of surviving an environment where it will go rapidly from a coldsoak of -50C or worse, up to living in close proximity to 600C brakes.

Plus you'd need a motor which could survive the mechnical inputs it'd see during landing.

I also suspect that even if you could build it and make it work that the weight penalty might increase fuel consumption to the point where it would outweigh any benefits on the ground.

I personally suspect things like electric engine start and other design changes on B787 and A350 will be much more beneficial and have the advantage of actually being possible & practical to implement

...get a REVERSE gear?

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