An accompanying illustration shows a BO 105 fitted with a rear fuselage fairing, rotor head fairing and four small individual landing gear skids, under a high-speed research programme. Known as the BO 105HGH, this aircraft attained a speed of 372km/h in a shallow dive at max AUW in September 1973. Flight testing was rosumed in 1974 after tho addition of fixed wings, spanning 6.00m and with an NACA 230 section varying from 15% thickness/chord ratio at tho roots to 12% at the tips. Airbrakes are mounted above and below tho leading-edge of each wing, and a shorter-legged landing gear is fitted.

The HGH programme (Hochgeschwindigkeits Hubschrauber: High Speed Helicopter) ended on 4 March 1975 with a flight in which the aircraft attained a max speed of 404km/h; max blade tip speed was Mach 0.97. The BO 105HGH, which was converted from a pre-production BO 105 airframe, will continue in use as a rotor blade testbed.

Jane's All the World's Aircraft, 1975-76

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