Electric cars and speed are not closely associated in most people’s minds. But tomorrow at Elvington airfield in Yorkshire a team will attempt to break the British land speed record for electric vehicles, which stands at 106mph. If successful the next target will be the world record of 215mph, set last October by Eric Luebben of the US in Lightning Rod.
Fittingly, in the centenary year of land speed records, the car will be driven by Donald Wales, grandson of pioneer record-breaker Sir Malcolm Campbell and nephew of Donald Campbell. And, in the tradition they established, it will be called Bluebird.
Though the sleek shape evokes Donald Campbell’s Bluebird car of the 1960s, underneath Bluebird Electric is radically different, bringing together some of the latest electric traction and control technology.
The drivetrain has been designed by the machines and drives research group at Sheffield University’s electronic and electrical engineering department. Its involvement in Bluebird stems from work the group was doing on an electric Formula 3000 racing car.
‘We got the racing car to a stage that we could demonstrate it,’ says research associate Tim Allen. ‘It was featured on Tomorrow’s World Live and the Bluebird team saw it on TV.’ They immediately beat a path to Sheffield to see for themselves. ‘We developed the drivetrain further to fit into Bluebird,’ says Allen.
The essential features of the racing car drivetrain have been retained. It uses brushless DC motors that can reach 20,000rpm, and which can be made much smaller than a conventional motor for a given power output small enough, in this case, to fit in an integrated wheel hub/suspension upright assembly.
A hub-mounted epicyclic reduction gearbox transmits the power to the wheel. As with the racing car, the two rear wheels are driven. Allen says all four wheels could be driven in a future evolution of the vehicle to get more power or speed.
Use of brushless DC motors has been made possible by advances in control technology, notably integrated gate bipolar transistors. These are large power transistors which can be turned on and off at high frequencies by a low-voltage signal with low losses.
‘The control electronics for Bluebird Electric fit into a box the size of a suitcase,’ says Allen. ‘Five years ago you would have needed something the size of a filing cabinet.’
For the land speed attempt the car has to cover a mile in both directions with an hour to turn round in between, and the average speed is taken.
Bluebird is therefore designed to go fast in a straight line. This means limiting aerodynamic drag, which is the dominant way in which power is dissipated above 50mph.
The car has a small cross-sectional area. The shape was designed by independent GT race car consultant Chris Humberstone and refined by wind tunnel tests at MIRA. In profile, it approximates to a half-teardrop, with a long, tapering tail. This is the most efficient shape, provided airflow under the car can be eliminated as far as possible, to prevent lift and downforce.
These are both undesirable because they dissipate energy which could otherwise be used to drive the car forward. Bluebird is designed to have a slight nose-down attitude, so that the space underneath tapers, creating suction towards the rear which has the effect of sucking out air from underneath. A drag coefficient of 0.17 has been achieved.
Chassis design was led by motorsport designer Martin Bryant and his consultancy Podium Designs. The car runs on bespoke tyres produced by sponsor Michelin.
In theory, as cornering ability is not a prime consideration, Bluebird should need very thin tyres to minimise rolling resistance. In fact they are wider than would be expected, at 250mm, to allow running on sand: future record attempts are expected to take place on Pendine Sands in south Wales, where the last world land speed record achieved on British soil was set by Sir Malcolm Campbell 70 years ago.
Surprisingly, Bluebird runs on lead-acid batteries, provided by sponsor Hawker Energy, rather than any of the new battery technologies already on the market or under development.
But these are no ordinary lead-acid units. ‘Hawker produces sealed lead-acid aircraft starter batteries which have a very high power-to-weight ratio,’ says Allen. ‘They are well able to do the job.’ Nevertheless, the batteries still make up more than half the weight of the car. ‘NiCad cells would do the job with less weight,’ Allen says, ‘but for a lot more money.’
So far the car has been developed for £250,000.
The Bluebird team stresses that the record attempt is not being made for its own sake, but to demonstrate the potential of electric vehicles. Much of the technology could be incorporated in ‘ordinary’ electric cars, it claims.
Allen believes unfavourable public perceptions of electric vehicles can be overcome. Given that most car trips are less than 16km, the limited range of electric cars is much less of a problem than has been suggested, he argues. If charging stations were available at workplaces and supermarkets, range and battery lifetime could be extended considerably by short ‘opportunity charges’.
‘Electric cars are too expensive, because there’s no demand, because the image is wrong,’ says Allen. Bluebird Electric’s biggest achievement could be to change that image.