Because of the Sled kite's simplicity it captured the attention of many kite designers. The original design by William M. Allison many claim had a tendency to collapse with wind change and 'wobble' as the air flow left the trailing edge.
Frank Scott added a triangular vent to the lower half of the sail and made the kite more stable. Ed. Grauel introduced two trapezoidal vents to the lower half of the sail which improved the kites performance.
Guy Aydlett turned his attention to the Sled's tendency to collapse and introduced a curved leading edge instead of the straight edge of other designs. Air is equalized over the curved leading edge and improved stability.
This kite is known as the Hornbeam and has no vented sail.
The original design by William M. Allison had three (3) spars which prevented the leading edge from collapsing, further designs removed the centre spar which gave the leading edge a tendency to collapse as the air flow left the leading edge.
The Hornbeam was a result of improving the two (2) spar design.