Pictured here in desert mode, it awaits a record opportunity in Nevada

Be sure to check out the video of the land craft in action

At speed in the desert.

Mk IV was built at CMI in Thailand in the summer of 2007 and had its first run on Lake lefroy in September. The first high speed run clocked 90mph in 20-25 mph winds. This was excellent performance from such a new and radical machine.

However, testing was stopped due to an unexpected control issue. The problem was that the pilot had no accurate control of the power at top speed. When the control inputs said zero power, the main wing was still pulling powerfully, creating a dangerous situation where a capsize would be enevitable at high speed. At the time, we were unsure why this was happening so decided to go back over the numbers and load tests to get to the root of the problem.

The problem turned out to be the main tail, which controls the angle of the main wing and hence the thrust from the sail. The pole that supports it was engineered and load tested to accept the force of an accidental full deflection of the tail at top speed, however, what we did not pay enough attention to was the flex under small forces. At cruise speed, the tail deflected 35mm to one side creating a change in angle compared to the centreline of the main wing. This discrepancy went undetected and caused the wing to pull powerfully when it should have been at zero lift. Luckily it is an easy fix, with a simple redesign of the tail mounting boom and control line. This will be implemented over the winter in time for the next weather window in August 2008.

The latest version, below, is the 'Greenbird'. See greenbird.co.uk for more details