Researchers from the German Aerospace Center (DLR) Institute of Technical Thermodynamics have begun ground testing a new technology that, if successful, could eliminate much of the fuel burn and noise generated by airport taxiing.

The invention is an emission-free, fuel cell powered, electric nose wheel for the Airbus A320, which scientists estimate could save up to 400 liters (150 gal.) of kerosene during an aircraft’s daily schedule. An A320 usually undergoes five to seven runway turnarounds per day, repositioned by tugs that typically are diesel powered. During taxiing, the aircraft’s main engine runs at a lower efficiency than it would during flight. The new, electric nose wheel can power the A320 both forward and backward without requiring power from the aircraft's main engine. In addition to the energy savings, the electric nose wheel completely eliminates engine noise during taxi maneuvers.

This innovation should reduce aircraft emissions by about 27% during taxiing because main engine power is no longer necessary. On average, an A320 main engine runs for about 3.5 hours per day during taxi processes alone, says Dr. Josef Kallo, project manager for the electric nose wheel. The testing could reduce main engines’ operating time by 1,200 hr. per year.

DLR has been working with Airbus Deutschland GmbH to test the nose wheel for the past three years, and Lufthansa Technik oversaw the construction of the nose wheel from start to finish. In February, the institute received the green light to start rolling tests of the invention on its Airbus A320 Advanced Testing and Research Aircraft. DLR has scheduled tests this month in Hamburg to see how the innovation performs on the runway.

The nose wheel drive is powered by a fuel cell system that converts electrochemical energy and produces electricity from hydrogen and oxygen. The advantage of using this method to power the motor instead of a combustion engine and generator is that the fuel cells can run more efficiently at lower loads. Kallo says the fuel cells are about 40-50% efficient, compared to a good combustion engine that may be only 33% efficient.

The key to making an electric nose wheel work is maximizing the torque of the engine inside the nose wheel rim to be able to power a 70-ton aircraft. The electric nose wheel consists of two motor units that fit inside the nose wheel’s rims. The outside diameter of the A320 electric nose wheel is the same as the traditional component, but engineers have redesigned the inside of the rim to fit the motors and planetary gear, minimizing the size of the parts and maximizing the mechanical torque of the motors.

Kallo says that testing the torque of tugs was necessary to determine how powerful the motors inside the nose wheel needed to be.

“We moved a lot of planes around with a diesel tug and measurement bar and saw that a torque of around 4,500-7,000 Newton-meters was enough to accelerate most airplanes,” he says.

The maximum torque that can be applied on the electric nose wheel is 11,000 Newton-meters, and the current certification for the electric nose wheel can support up to 120 tons.

The original axle of the A320 nose wheel drive stays the same, so technicians only have to make minor changes to the nose wheel to fit the motors inside. Kallo says that DLR has designed the electric nose wheel with new-production aircraft in mind, but retrofits would be very easy to achieve because technicians have to add little more than a torque clamp and four connection points to make the new nose wheel drive system work.

Kallo acknowledges that the Airbus A320 was the first candidate for the electric nose wheel because of its convenience—DLR has one on hand at its facility. But, he says, the A320 is also a great candidate for the electric nose wheel because it spends so much time taxiing between shorter flights. With that utilization pattern in mind, it makes sense to further develop a model for similar aircraft, such as the Boeing 737 series.

The need for the electric nose wheel for a larger aircraft making transatlantic flights may not be as immediate, but Kallo says that an opportunity to install the fuel cell on the main gear of a larger aircraft may be a good idea in the long run.

“A good thing with the main landing gear is that the diameter of the rims is bigger,” says Kallo. “With bigger diameters, the torque of the motor can be much higher. It’s going to be better, if you compare the motor to the weight of the plane, the bigger it gets.”

Kallo says to expect an announcement from a launch customer using the electric nose wheel “very shortly,” and indicates that both original equipment manufacturers and airlines are interested in purchasing the technology.