Air Race E: Electric air racing looking to take flight

Those Magnificent Men in their Flying Machines used to be a television fixture on bank holidays in the UK, seemingly on rotation with The Great Escape and Chitty Chitty Bang Bang. With a huge cast of such 1960s stalwarts as Terry-Thomas, Robert Morley and Sarah Miles, it was an Edwardian-set madcap comedy depicting an air race between London and Paris with a fiendishly catchy theme song: They go up-tiddly-up-up, they go down-tiddly-down-down. It directly influenced the immortal cartoon character Dick Dastardly (who memorably took to the air himself in a never-ending and never-explained quest to stop a carrier pigeon. Cue another theme tune).

However, air races were no laughing matter in the early 20th century. They have a long tradition in aviation, and made important contributions to aerospace development. The Schneider Trophy, a prestigious competition for seaplanes, was a testing ground for the development of aerodynamics and aircraft engines, and its winners were the forerunners of such famous fighter aircraft as the British Spitfire (whose development from a seaplane was immortalised in another bank holiday favourite film, The First of the Few), the American Mustang and Italian Folgore. And air racing is still going now.

Today, the best-known air race event is probably the Red Bull Air Race World Championship, where small single-engine aircraft fly through a slalom course featuring sharp turns at high speed against the clock. However, the Formula One Air Racing series in fact predates this event, and was first proposed in 1936 with its first event in 1947. The biggest air race event in the world, the US National Championship Air Races in Reno, Nevada, attracts some 150,000 spectators annually.

In contrast to the Red Bull championship, Formula One events are full multi-entrant races, where eight aircraft compete virtually wingtip to wingtip around a 5.13km oval course at an altitude of about 10m. As with all motorsport, racing vehicles must comply with detailed entry criteria.

Aircraft must have a minimum wing area of 66ft² (6.1m²), a minimum empty weight of 500lbs (227kg) and a maximum engine displacement of 200in³ (3.28L). They can reach speeds above 200mph (322km/h) and the spectators are seated 150m from the course.

Formula One events comprise eight laps of the circuit.

Jeff Zaltman, chief executive of Air Race Events, which sponsors the Air Race 1 World Cup and is launching a new all-electric series, Air Race E, told The Engineer that electrification in aviation is 20 years behind automotive because it is focused on large aircraft that can carry a number of passengers. “For an air race, the situation is quite different. You’re only talking about small aircraft going a short distance over a short time, so you don’t have to worry about the limitations of battery size and weight balance which are so important for passenger airliners. But small aircraft like these are going to be very influential in the development of bigger ones, particularly in the testing and proving of the engine and energy management systems.”

Formula One Air Race forms the model for Air Race E, with the same course layout and eight-lap races, and the aircraft will be of similar size and envisaged as having comparable performance. The raison d’être of Air Race E is similar to that of the Formula E road motorsport series: to use the galvanising effect of a sporting competition to concentrate and accelerate development of electrical flight.

However, there will be differences, notably that Formula E is deliberately focused on development of a high-performance electric powertrain rather than car aerodynamics, unlike in Formula One where powertrain and aerodynamics are equally important to the Constructors’ Championship.

For aircraft, the challenge of installing an electrical propulsion system is very much more bound up with the design of the plane than it is with cars. So while the early Formula E series saw all the teams competing with essentially the same car, and teams have gradually been allowed to develop more of the powertrain themselves, for Air Race E, teams will be developing their own airframes from the beginning. Entrants will, of course, not be limited by gender, so it should be a case of those magnificent men and women in their flying machines. Initially, Zaltman plans to run Air Race E events as an ‘undercard’ to Formula One races, but he hopes the electric event will become more important than conventional fuelled races over time.

The open design regime is in keeping with the air racing culture, where the ‘maker community’ is heavily involved in designing and building aircraft. Some of the teams are made up of aeronautical engineering students, often representing their university. Others are archetypal ‘men in sheds’ (women can and do also have sheds): hobbyists who simply enjoy the challenge of making their own planes (sometimes, but by no means exclusively, from kits). In order to continue to fit in with this culture, entrants will have to conform with the specifications set down by the governing body (likely to include wing area, empty weight, maximum motor power rating and battery capacity and/or weight, closed cockpit, fixed undercarriage and propeller design), but will otherwise be free to build and fly their own designs.

The industrial drivers are also somewhat different. While the automotive industry is focused on producing electric cars that, although not single-seat racers, are not all that different from the Formula E vehicles, the aerospace industry is not interested in developing small single-seat aircraft, but larger passenger airliners to fly city-to-city routes. The environmental rationale is also different. Both automotive and aerospace industries want to reduce their fossil fuel burn and therefore their carbon emissions, but aerospace is also very concerned about the noise that aircraft make, and the desire behind the switch to electric propulsion is concerned with losing the jet engine scream. For both industries, the carbon emissions question is one of emissions in use: if the electricity to power the vehicles comes ultimately from fossil fuel power stations, then overall emissions are not reduced at all (although reducing emissions from large-point sources like power stations is simpler than reducing them from a large number of smaller sources, such as fossil-fuelled vehicles).

Both the land-based and air-based racing series are very much concerned with the development of battery technology – cramming more energy storage into as small and light a package as possible – and with the management of that battery system to ensure the most economical use of its stored power. For electric aircraft, the separation of energy production from propulsion (that is, removal of the need to actually burn fuel) has significance for design of the vehicle. “It’s not just a matter of replacing fuel tanks and batteries and an engine with an electric motor; the power electronics are also crucial, and new airframe configurations are possible even within the stipulations of the formula,” commented Glenn Llewellyn, general manager and chief technology officer of Airbus’s electrification programme.

“We are very interested in how competitors in Air Race E tackle that issue, and how they integrate batteries and motors into their designs. We think that might well give us some inspiration for how we might look at that in our larger aircraft. It really is an integration issue as much as it is an engineering design one.”

But Llewellyn stressed that because this project is within the context of a motorsport formula, the airframe innovations possible with electric aircraft will not be seen in Air Race E; Airbus is considering options such as tilt-rotors for vertical take-off urban mobility vehicles, and is likely to make use of hybrid technologies with an on-board generator for cruise flight, but Air Race E will be strictly all-electric, fixed-wing and front-engine.

Despite this, Zaltman said: “We are very much hoping the design freedom we are allowing in our competition will give rise to some interesting solutions to these kinds of problems. You probably wouldn’t see that variety of solutions if we were a single manufacturer series like Formula E was in its earlier years.”

Although the first race is currently scheduled for 2020, the series is still in its infancy technologically.

A prototype aircraft is being developed with Airbus’s help at the University of Nottingham, where hybrid propulsion systems research fellow Richard Glassock is converting a current Formula One aircraft by retrofitting an electric motorbike engine to power its propeller, and by replacing its fuel tanks with batteries. This prototype will be used to help set the specifications for future aircraft (particularly in terms of weight), and it is expected to make its maiden flight (probably at Cranfield) within the next couple of months.

“I’ve been working on electric and hybrid systems for aircraft propulsion for about 15 years and we can see now in the world that electric propulsion is really a growing industrial application, so this is a perfect fit,” Glassock said. As electric motors allow faster acceleration than kerosene-powered engines because of their instant torque, they are well-suited for racing aircraft.

The aircraft Glassock’s team is working on is a Cassutt III airframe which, he explains, is an older model but still popular in air racing. It has a welded tube steel fuselage with wooden wings which are fabric-covered with some composite fairings and nose cowling. The fuel tanks sits right behind the engine, so the substitution is direct: the batteries occupy the space where the fuel tanks were.

The original engine is a 0-200 4-cylinder piston design, the cylinders arranged in a horizontally opposing configuration. As electric motors are cylindrical, the characteristic “side cheeks” of the aircraft will disappear.

The major challenge in engineering terms, Glassock said, is concerned with weight and its distribution. “The electric motor has the potential for relatively high ‘power density’ or power-to-weight ratio compared to the original piston engine,” he explained. “The engines used in racing can be modified in some limited ways, and typically operate at much higher RPM than as certified, which enables considerably more than the standard power output.

“Some racers claim around 150kW from their piston engines (originally certificated at 75kW rating), and the weight is around 110kg. A good presently available technology electric motor installation should give the same power at about half this weight, when the necessary ancillaries (mainly cooling system, heat exchangers, pumps fluid, etc) and power electronics are included. Whereas the old internal combustion engine in this case was pretty well at the limit of power to weight, the electric propulsion systems still have a lot of development potential.”

A bigger problem is the batteries. For presently available battery technology, the energy required at 150kW may require batteries that “imply excessive weight for the Formula One-type aircraft in current use”, Glassock said. “This will be an interesting problem for the overall design. It may be necessary to increase the wing area, or introduce high lift devices (flaps, spats, etc) to enable higher gross weights. Alternately it may be better to use lower power and therefore less energy, if the overall speed can be made competitive.”

“It’s not just replacing fuel tanks and batteries and an engine with an electric motor; the power electronics are crucial”

Glenn Llewellyn, Airbus

These are typical aircraft engineering, racing and strategy design problems, he added. “Also, the battery technology will improve over time along with motor and power electronics so that it is likely within some years that the 150kW Air Race E platform will be of similar gross weight to the present-day units.”

The electric motors are commercially sourced, although at least one model being considered was designed and built at the University of Nottingham. These racing motors are rated at “continuous” and “peak” power, Glassock explained. “The e-bike motors are in the order of 200kW peak and 120kW continuous rated, however the motorcycle race duty cycle is much different from the air race conditions. Also, the motor power is of course limited by the ratings and operational conditions for the power electronics and battery.”

In many types of aircraft, fuel tanks are located in the wings. Racing aircraft tend to locate them in the nose, and the retrofit project will follow suit with batteries behind the motor, to ensure that the centre of gravity is in the right place. If future designs locate them in the wings instead, some mechanical reinforcement would be needed, Glassock speculated, as the batteries and associated equipment weigh some 100kg.

Glassock’s project has two phases. “The first phase is to retrofit the aircraft with mostly commercially available components and replicate the original performance as far as possible,” he said. “The second phase will be to design a bespoke propulsion system including custom-built power electronics, motor and integration systems. The aircraft we are using was fitted with a relatively standard engine. We believe it would have been developing approximately 80kW and so we are aiming at replicating this for Phase 1. We would like to keep the gross weight as close as possible to the original aircraft too, and so we expect equivalent performance, handling and manoeuvrability.”

In the second phase, things may change. The goal of this part of the project will be to optimise the aircraft and its systems. “This will involve the motor and power electronics design primarily, but as with all aircraft design, and racing in general, the whole system including the airframe, propulsions system and the environment have to be considered.”

In the future, as teams develop their own aircraft, Glassock believes that the noses might become longer and thinner, with differences in the cooling requirements of the motor leading to differing approaches to aerodynamics.

Glassock believes that the Air Race E project will be very significant for development of commercial electric aircraft. The main reason for this, he says, is that the 150kW power level needed in racing aircraft is the same as the engine rating that will be needed commercially.

“Electric motors are suitable for relatively easy ‘stacking’, so that multiple motors can easily drive a single load, propeller or fan,” he said. “These properties make the technical development of Air Race E propulsion systems highly relevant to broader commercial use such as in eVTOL, PAV and even regional and sub-regional transport.

“I can see this racing becoming very exciting, both in terms of the flight environment but also in the technical design and operations. And the human potential, social interaction and innovation environment can be spectacular. We want to encourage younger generations to positively embrace the ambition at all levels too. I think these factors align with the sort of future thinking and spirit necessary to solve many complex problems facing the aerospace industry, transport and environmental issues and within educational, commercial and industrial engagement.”

So, while some harbour doubts about the transfer of technology from Formula E to commercial road cars, there seems to be agreement that the world of air racing will be of definite influence to the coming generation of electrically powered commercial aircraft.

And although problems still remain to be cracked, such as low-carbon energy to charge the aircraft’s batteries, and the batteries themselves (although the imminent launch of 1kWh per kilogram batteries may well change this, as we will see in coming issues of The Engineer), it seems certain that the way we fly – for short distances at least – is on the verge of a significant change.

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