Aerospace & Defence

Motors help aircraft make the most out of their fuel

19th May 2020
Alex Lynn

On December 17, 1903 in North Carolina, the Wright Flyer became the first powered, heavier-than-air machine to achieve sustained flight with a pilot aboard. The modern ambition for many aircraft designers is to achieve the opposite — aircraft that is lighter than air.

Here, Stewart Goulding, managing director at mechatronic drive system supplier EMS has explained how electric motors are helping aircraft make the most out of their fuel.

While the title of ‘lighter-than-air’ aircraft is held by airships such as Zeppelins and the Airlander, all aeronautic businesses are under pressure to make their planes lighter. A Boeing 747 uses approximately one gallon of fuel every second, burning around five gallons of fuel per mile. It’s not desirable for aircraft of any size to burn more fuel, and money, than necessary, so steps should be taken to make consumption as efficient as possible.

Lighten the load

Every day, 213,000 passengers land or depart from London’s Heathrow airport, with a plane either touching down or taking to the skies every 45 seconds. Our thirst for overseas travel isn’t going to decrease any time soon, but the need for more commercial flights runs parallel with increasing pressure to reduce our carbon footprint and make the industry more efficient.

In an attempt to reduce fuel consumption, airlines are cutting weight wherever they can — seats are getting thinner and lighter, pilots are carrying tablets in place of paper manuals and even the number of ice cubes in our drinks is decreasing.

Beyond warmer drinks and paperless documents, motors can also play an important role in reducing aircraft weight. As every gram on-board increases fuel consumption, cabin features such as reclining seats, motorised television screens and window blinds and even automated toilet seats to improve hygiene can all benefit from lightweight motors to deliver a luxury touch while reducing fuel consumption.

While the majority of motors are found in first class and business seats, motors can also be found in a number of safety-critical applications. For example, motors play a vital role in the locking mechanisms for cabin doors, emergency exits and the pilot’s seat, which must remain in a fixed position during take-off and landing. Motors are also used to adjust the valves that regulate pressure in the aircraft’s air-conditioning system.

With motors helping to enhance luxury and executive travel while also delivering a number of essential safety features, onboard operations simply wouldn’t be the same without them. In order to help reduce emissions and make travel more sustainable, aircraft engineers must make sure they are selecting motors that are lightweight and reliable.

Mixed, not stirred

Soaring away from the opulence of upper-class travel and large commercial flights, small and miniature aircraft also need to mind their fuel consumption. Also known as unmanned aerial vehicles (UAVs), smaller aircraft are vital transport methods for the military, emergency services and — increasingly — industry for reconnaissance flights and measurement.

To achieve extended flight times using minimal fuel quantities, these aircraft require reliable propulsion systems. Previously, the only way of achieving fuel delivery to the engine was done by a carburettor to provide a combustible mixture of fuel and air. However, a carburettor is unable to provide an optimum mix of fuel for all of the various phases of the flight.

In place of a carburettor, smaller aircraft manufacturers are increasingly beginning to consider electronic fuel injection (EFI) to provide the benefits of fuel injection to small UAVs. The system works by injecting fuel, which is under pressure in the system, into the intake manifold using special injectors and the fuel-to-air ratio is electronically controlled using a control unit. Sensors in the intake and exhaust system of the engine, feed data to an electric control unit, where it is then assessed, and the ideal amount of fuel required at a particular point is calculated.

The right balance of fuel and air in an engine is required for it to burn, so the sensors also help the system to fine-tune the mixture for the load and conditions at each precise moment of the flight.

Efficient fuel consumption is especially important in UAVs, where every gram of weight saved helps extend flight time or increase the usable load. Another issue with carburettors is the inconsistency of the fuel mixture they achieve. If the mixture is too rich at altitude, it’s perfect at sea level. Conversely, if it’s ideal at altitude, it is too weak on the ground. This compromise leads to reduced performance and increased fuel consumption.

The high pressure of EFI means that, even at high altitudes, the amount injected is continuously electronically calculated based on data such as temperature, air pressure and required performance. Because the pressure helps create an extremely fine vaporisation of fuel, it ensures a consistent mix of fuel and air. As a result, using an injection system is able to increase fuel consumption by as much as 30%.

Small planes, small motors

When designing an injection system for a small aircraft, everything needs to be minimised. The compact system consists of many components, including the injector, a fuel pump, ignition module and a fuel pressure accumulator. These mechanical components need to weigh just a few hundred grams and take up as little space as possible in order to save space and help keep the aircraft light.

A high-performance, low-weight DC micromotor, such as the FAULHABER range supplied by EMS, can fit compactly into an EFI system to help deliver consistent fuel pressure. The motor helps create the auxiliary energy required to build up the necessary pressure, which powers the fuel pump to deliver fuel and air into the system. Motors must be able to work tirelessly, with low rotor inertia for fast and reliable acceleration and braking. As FAULHABER motors are also characterised by their high power and low weight, they form part of this important fuel system without contributing to any unnecessary weight gain.

Just as the desire for light aircraft may have developed significantly since the Wright Brother’s invention, the need to economise fuel consumption won’t cease to grow in importance any time soon. From supplying a lightweight solution to highflying travellers, to helping smaller aircraft make the most out of their fuel, micromotors are key to helping developments in the aeronautical industry take off. 

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