Nineteen years after the Westland Lynx achieved 400 kph. it still retains the world speed record for rotorcraft. A speed achieved by modifying the exhaust to take advantage of the extra available engine power.
It is unlikely that any future helicopter, which is equipped with only a single main rotor, will ever exceed this record. This is because future modifications to the profile, twist and tip of the blades cannot overcome the single-rotor's conflict between advancing tip compression and retreating blade stall.
There has been polite ridicule on this forum for my promotion of lateral symmetry for rotorcraft. However, with little humility, I would like to provocatively state that
'The above speed record will only be exceeded by VTOL craft that have lateral symmetry.'
All the V/STOL craft that are shown on
the American Helicopter Society's Wheel have lateral symmetry. Unfortunately, many of these craft are impractical and few have efficient hover capabilities.
The only laterally symmetrical 'pure rotorcraft' configurations are; the Tandem, the Coaxial, the Intermeshing, the Interleaved and the Side-by-side. It should be noted that only the last three have true lateral symmetry, with its inherent advantages.
For these 'pure rotorcraft' to achieve fast forward speeds some modifications must be made, such as;
~ Advancing Blade Concept, with its high rotor rigidity, dissymitry of lift and slowed rotor.
~ Active Blade Twist; including Reverse Velocity Utilization.
Simply and argumentatively put, if 'pure rotorcraft' are going to progress there must be
