Electric taxiing - landing gear

Electric nose wheel – innovative taxiing

Tim Takeoff
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4 minutes

From the very outset, aviation has provided a massive playground in which innovations could evolve. People were always trying to flesh out the detail on rough ideas. However, many ideas look better on the drawing board than they actually are in practice. This may well be the case with the idea of taxiing using an electric nose wheel on commercial aircraft.

Some years ago, the German Aerospace Centre (DLR) carried out corresponding tests. Working in conjunction with Lufthansa Technik, a modified nose wheel was fitted to the “ATRA” research aircraft, an A320 belonging to the German Aerospace Centre. A fuel cell provided the necessary power to supply two electric motors in the nose wheel assembly. The tests were successful and the aircraft was able to taxi at walking speed.G

At first glance, this naturally seemed to offer improbable benefits. It meant that the engine operating time on the ground, together with all associated noise, fuel and CO2 emissions could be reduced. And due to their significantly lower wear, the maintenance cost of the engines alone could be reduced accordingly.

It was also a desirable development from the viewpoint of the personnel in the cockpit. At some of the world’s major airports, taxiing and waiting for clearance for take-off with a “queue” of aircraft waiting can take 30 minutes or even longer. Initially, passing this time without engine power naturally seemed a bright idea. “Smart” links to air traffic controllers could also be considered, who could then electrically clear the aircraft on the ground or even stop them. Naturally these scenarios are technically absolutely feasible today.

Unfortunately this overlooks an aircraft’s ‘Achilles heel’: the engines themselves.

In the past, these huge turbines were somewhat simpler. Today these high-tech assemblies are becoming increasingly complex and more delicate as they are improved. A jet engine is a component made up of the most diverse materials and therefore has the same properties as, say, a car engine. As soon as the engine heats up, the different metals need to expand depending on their properties.

This leads to every manufacturer specifying a certain time for their engines to allow the turbines to thermally stabilise, meaning that a “warm-up phase” is always required. This is also understandable when you consider that massive forces are produced when starting take-off and, in the worst case, at full thrust. No one wants to be dragged from their sleep and forced into action in winter in icy temperatures.

And similarly, it is equally unhelpful to immediately shut down a warm engine as soon as it has landed, without giving it time to cool down. The engine is also powered up again when reverse thrust is used for landing and braking.

A striking example of this is currently demonstrated by the Airbus A320 neo on which the Pratt & Whitney engines have suffered problems (German article) since they were introduced, as they need a longer warm-up time than other models.

Compromises needed

Jets need to be monitored much more closely in these processes as they can seriously suffer from these problems in the short or long term. This needs to be weighed up against the benefits of the electric nose wheel, quite apart from the safety aspect. As a pilot, you will want to make sure that the engine runs reliably for a few minutes before placing it under serious load.

Regrettably factoring in a warm-up phase just before take-off is just as impracticable, as that would not allow the required number of take-offs and landings at a major airport to be maintained. Those in the cockpit never know precisely at what point they are going to receive clearance for take-off. It would have a massive knock-on effect on the air traffic controllers’ well-oiled processes if an aircraft takes a little too long to start up its engine and the pilot then advises the tower that the aircraft needs to “warm up” for a few minutes.

It is therefore in the hands of the manufacturers to negotiate and jointly seek a compromise for these current problems. Obviously it is not expedient to create new or even bigger conflicts when solving a problem.

And until then, we will continue to taxi up to the runway, as usual, with a comfortably warm engine. 

Title image © Tim Sirok

by Tim Takeoff

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