On the morning of 26th March 2009 at Ivanpah Dry Lake on the California/Nevada border, USA, the Ecotricity Greenbird broke the world land speed record for wind-powered vehicles. Greenbird recorded a top speed of 126.4mph (203.4km/h), and sustained a speed of 126.2mph (203.1km/h) for the required time of three seconds, beating the previous, American held, record of 116mph (186.7km/h), set by Bob Schumacher in the Iron Duck in March 1999 at the same location.
The Greenbird project is a partnership between Ecotricity (which describes itself as the UK’s first and largest independent ‘green’ electricity company) and engineer Richard Jenkins. It builds on Jenkins work as founder of the Windjet project, which he started in 1999 while studying mechanical engineering at Imperial College, London. All-British, the Greenbird team is independent, passionate and committed to a vision of a zero-carbon transportation future.
Vehicle design
As well as being elegant, sophisticated and futuristic, Greenbird is nevertheless based on familiar principles borrowed from aeronautical, sailing and wind technologies. In conventional vehicles, more power almost always equates to more speed. With land sailing, however, more wind does not necessarily mean more speed. Instead a design is required in which aerofoil lift (translated to forward thrust in a land-based craft) is maximised but, more importantly, drag is minimised. Greenbird tackles this problem by combining racing yacht, aeroplane and Formula 1 racing car concepts and technologies.
The main structure of the vehicle is made from carbon-fibre composite materials that have the high stiffness and strength required to transfer the wind loads on the Greenbird’s ‘sail’ (actually a rigid vertical wing) into traction forces on the ground. And the structure really does have to be extremely strong, with the vehicle taking huge forces when travelling at high speeds: Greenbird only weighs 600kg but at high speeds it is transferring up to one tonne of side force into the ground.
Greenbird’s vertical wing generates thrust in the same manner that an aeroplane wing generates lift. The pressure differential over the wing creates forces that are translated into forward thrust. To prevent the craft from tipping over, a horizontal wing uses the effects of aerodynamics and weight to keep the Greenbird firmly on the ground.
Evolution
The Greenbird is an evolution of Jenkins’ WindjetMkIV, which recorded speeds of 90mph (145km/h) in winds of 20-25mph (32-40km/h) in 2007. These test runs suggested key modifications that have been incorporated into the Greenbird design. For example, the main tail was redesigned to control power and acceleration more accurately, and the steering position has been moved from the rear cockpit position to the front cockpit position to give better visibility.
Future developments
With the land-speed record broken, the team now has its sights on new challenges. Plans are in place for an assault on the ice speed record in the winter with a Greenbird ice craft equipped with blades instead of wheels. There is still some debate within the team over whether ice or land will be faster.
