The flexible lower wing skin on Sigma was one reason it was far draggier than the design spec. The gap between trailing edge and the extending section of the wing was up to 1/4 inch.
The wing section designer, Dr F.X. Wortmann was at Lasham during the initial performance trials. When aked what he thought about the aircraft, he replied enigmatically 'If I wanted to make a swiss watch I would not employ a blacksmith.'
The hydraulic mechanism to pump up an accumulator by pushing the rudder pedals agains a spring caused some amusement - the combination of seating position, strap arrangement, cushion material and ergonomics made it virtually certain that one's trousers would come down when the pump was operated, unles wearing stout braces.