Joining Westland Helicopters Ltd. in 1975 as a researcher in aerodynamics and eventual Head of Future Projects, Dr. Ron Smith talks about faster helicopters and the future of rotorcraft in an interview with alternative aviation news site, Husk-Kit.
When asked about which effort to produce faster helicopters seems most promising, Smith thinks that it would be between Sikorsky’s designs and the tilt-rotor designs such as the AW609, or the Bell V-280 Valor. Smith explains that Sikorsky has, since the XH59A achieved max speeds of 274 mph in 1973, followed the ABC or Advancing Blade Concept which uses two contra-rotating rotors to maintain balance and auxiliary propulsion to achieve high speeds. Sikorsky found further success in 2008 when the X2 reached speeds of 290 mph, and in 2015 with the S-97 Raider, which boasts cruising speeds of 253 mph.
When asked about why helicopters seem to be limited at 200 mph, Smith explains that for safety and noise control, manufacturers tend to restrict the flight envelope to around 200 mph or less. Helicopter rotation is usually around 650-700ft/sec, and on the retreating side, local speeds get reduced and ultimately lead to blade stall and stall flutter, which can cause fatigue damage to the key helicopter rotors system components. While doing things such as adding an auxiliary wing and thrust devices can push the flight envelope to 250 mph, this creates a different configuration known as a compound helicopter.
And when asked about the future of tilt-rotors, Smith answers, the problem is not in the design or the success of tilt-rotors, but in whether they can be financed. Smith points out that the V-22 Osprey, a tilt-rotor with Congressional backing and sufficient funds, still took 18 years between first flight and operational deployment.