Thursday, 23 October 2014
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Electric nose wheel could reduce aircraft emissions

Commercial aircraft could cut their on-ground emissions by one quarter with a new hydrogen fuel-cell propulsion system, according to its creators.

Researchers at the German Aerospace Centre (DLR) supported by Airbus and Lufthansa have developed an electric nose wheel that could allow aircraft to move around airports without using their main engines.

For short-haul aircraft that often take off and land seven times a day, this could save between 200 and 400 litres of kerosene per day while reducing noise by around 95 per cent, without the use of towing vehicles.

The nose wheel drive system has already undergone successful tests in the laboratory, and comprises two highly efficient electric motors that are built into the rims of the aircraft’s nose wheel.

The nose wheel drive system has already undergone successful tests in the laboratory, and comprises two highly efficient electric motors that are built into the rims of the aircraft’s nose wheel

The system, designed for an Airbus A320, uses a low-temperature polymer electrolyte fuel cell driven by hydrogen and can provide ground propulsion for an aircraft weighing up to 70 tons.

It allows the pilot to turn off the main engines one minute after landing and not turn them on until three to five minutes before take-off, in order to heat them up. This means the engines could be used 1,200 hours less per year.

‘The weight of the propulsion system has to be as low as possible,’ DLR project manager Josef Kallo told The Engineer. ‘If you have a lot of weight in the nose wheel the hydraulics have to be changed.

‘It has to be very compact to fit into the rim of the nose wheel and has to have very high torque. Just to get to 3–5kph you have to work against something like 5,000–7,00NM.’

The DLR team took inspiration from electric cars to solve the power mass problem and looked to stationary applications and trains for the answer to the torque issue.

Kallo could not reveal how much hydrogen it consumed but said for a short-haul aircraft it would need refuelling every one or two days.

The team plan to trial the system in a Lufthansa test vehicle in Hamburg in April 2011.

They are also developing a fuel-cell unit for auxiliary power for the aircraft’s climate control and other electrical systems, which is currently provided by a turbine in the aircraft’s tail.


Readers' comments (15)

  • Hydrogen on board an airliner? Nein danke. With flammability ratios in air of between 4 & 94%, a small leak can rapidly cause a major fire. There is also the considerable extra weight of the pressurised containers and the fuel cell equipment. Which airports will provide the hydrogen? I will try to avoid them.
    I see that DLR give no figures for current requirements for the motor. While the electric nosewheel is an excellent idea, why can't it be powered by the existing APU, if necessary with a higher-output generator? There is already far too much flammable liquid on board most airliners. Jet fuel is relatively safe, the huge amounts of alcohol carried are not.

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  • An excellent idea! It just leaves me with one question. Is the power of the nose wheel motor adequate to achieve taxi speeds of at least 50-60 kph. At Schiphol taxiing after touch done at 180R takes about 15 minutes to the apron. So, 3-5 kph is too slow! Further, some taxi ways cross other roads which requires some bridge climbing. That will need quite some power with havy ones.

    Looking forward for further results!

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  • I would question the use of hydrogen fuel cells in aircraft, and the driving of the nose wheel as the sole power provider.

    Aircraft already have batteries on board to power their systems, surely it makes better sense to use these and omit the hydrogen all together.

    If we consider the low ground pressure on the nose wheel, and its small tread area, i see it slipping in many wet or icy conditions. Surely it would make more sense to use the main body wheels to drive it as these have much more weight on them.

    This would omit the need for carrying additional weight of the fuel cells, and provide a better solution. Planes are often connected to ground power units, or static electrical connections when on the ground so there would be no need for Hydrogen.

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  • If there's a generator running constantly while the aircraft is on the ground, would it not make more sense to use that to power the nose-wheel? Even if this were to require a generator upgrade as well as copious wiring, it would surely be more efficient than plugging in an entire new flammable-fuel power system in an area with many safety-critical moving parts. The effects of the hydrogen tanks on weight distribution and cargo space would also need to be taken into account, which again would be easier to do if only one ground-based power system needed to be taken into account.
    Caveat: I'm a chemist, not an aero engineer. Feel free to correct me if you know more about the subject.

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  • I think the concern about the hydrogen is probably minor given the hundreds of litres of aviation fuel and fumes already on board; It may be worth considering multiple smaller motors which could drive the aircraft, with power enough for some graceful degradation of the drive system. It would be nice if the motors also could “spin up” the wheels so as to reduce tyre wear on landing.

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  • Sorry folks - this has nothing to do with reducing emissions, that is a deliberate red-herring, in part to lend the device populist ‘green’ appeal, in part to avoid provoking union wrath over potential redundancies amongst airport tug operators.

    a) Emissions produced in the manufacture of hydrogen for the fuel cell, plus additional emissions produced as a result of transporting the propulsion unit for an entire trip, would more than negate the tiny emissions saving when reversing at departure (when main engines would, in any case, already be running in order to warm up to operating temperature).

    b) Planes do not taxi in at 3-5kph - they tax in at 25-100kph
    Planes do not taxi out at 3-5kph - they taxi out at 25-60kph.
    For both, they need to use their main engines, not an electric nosewheel that crawls along at 3-5kph.

    The primary objective of an electric nosewheel would be to eliminate dependence on airport tugs, especially when reversing from a docking station at departure, when any delay costs time and money - and could even cost a departure slot.

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  • A switched reluctance motor can be both a motor and a generator. Using these would generate a large amount of dc current from braking which can be stored in batteries inside the aircraft. The very short charge time is not optimal: perhaps super-capacitors would help and then they would be discharged shortly afterward when powering the motor. Why only use the nose wheel, what about the others?

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  • Further to Ken R's comments:
    I understand that Concord's wheels were spun up to near landing speed in order to save wear and tear on tyres and the shock loading of the undercarrage (which is subjected to a momentary rearward shock load/bending moment as the tyres speed up from rest to a periferal speed equal to the landing speed.
    I think the way to go would be to power one wheel each side on the main undercarriage which is nearer the C of G and so the weight would not be such a disturbance to balance and would be a smaller proportion of the total undercarriage mass. The pilot could then steer by braking and powering left and right sides.
    The power system would then be available to spin those wheels for landings.

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  • The wheel in the picture looks like it has a radius of 0.4m, so 6000Nm gives 2500N, at 1m/s, only needs 2.5KW.

    You could probably fit a Protean Electric hub motor and a reducing gear into that. This can produce over 50KW - it could drive the plane at 50km/hr.

    To power it I'd suggest a small petrol engine and generator, unless there's a small engine that can run on Kerosene.

    The few hundred kilos extra weight would be recovered from lower ground fuel needs.

    Unfortunately accelerating and braking a 100 ton plane needs on the order of 5MW, so the generator won't help much with regenerative braking.

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  • There is a far more efficient alternative: hydraulic motors are now much more powerful, lighter weight, and smaller in size. Consider the use of a hyraulic motor in the nose wheel for taxiing about, hydraulic pumps instead of friction brakes (these can also work as motors), and an accumulator system sized to deal with all braking issues. The energy stored in braking would be enough to move the aircraft well away from docking, do most or all of the taxiing to the departure strip, and if necessary the accumulator could be recharged from an auxilliary hydraulic pump powered off the jet engines. I leave the details of this in more capable hands than mine, but I recommend you consult with Ingo Valentin.

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