A wind-tunnel test programme aimed at producing new, hi-tech rotor blades for helicopters has finished. The trials, which used blades fitted with trailing-edge flaps like those seen on aeroplane wings, reportedly offer the prospect of much-enhanced copters in future – in particular, the long-heralded "whisper mode" for covert (or domestic) urban operations may be on the horizon.
The just-completed flapcopter push was a joint effort between famous whirlycraft company Sikorsky and the Aviation Applied Technology Directorate of the US Army (AATD – the US Army is a much bigger operator of helicopters than the US Air Force).
"We have validated the concept of properly controlled, high authority flaps to favourably impact external rotor noise, and vibration," says Sikorsky bigcheese Jim Kagdis. "Our test results show reductions in vibration, rotor hub and controls loading, and a reduced acoustic emission."
Present-day helicopter rotors themselves are fairly unsophisticated, though their materials have changed since the early days of whirlybirds. Though they are spun and controlled by a highly complicated hub assembly, the actual blades have long lagged behind their aircraft-wing cousins in terms of technology: aircraft wings can nowadays change shape radically, with various benefits.
In large part because of this, helicopters themselves still have most of the limitations and problems they started out with – in particular the related issues of noise and vibration, which severely limit where and when they can be used and drive up costs disastrously.
Back in the 1950s, it was commonly thought that helicopters would soon replace cars as the main means of personal transport: and on the face of it this might have seemed reasonable enough. Nonetheless the deafening racket that helicopters make and the expense and difficulty involved in preventing them from shaking themselves to pieces meant that this never happened. (Along with other issues, of course, such as the fact that until quite recently helicopters remained very difficult to fly – especially in bad weather.)
Various US military research efforts have been kicked off in recent years aiming to make a serious step change in helicopter technology: while many modernisations and improvements have occurred, the US military choppers flying today are still recognisably the same basic designs that went into service in the 1960s.
Sikorsky and its Army partners feel that their flaprotor tech is a definite step towards something new – if not yet, perhaps, the telescoping-blade morphcopters aspired to by Pentagon crazy-prof bureau DARPA.
"The completion of this wind tunnel testing provides valuable data to guide future programs such as AATD's Reconfigurable Rotor and DARPA's Mission Adaptable Rotor (MAR) programs," contends Sikorsky veep Mark Miller.
Sikorsky has also, of course, recently built and demonstrated its vision for next-gen helicopters – the X2, which uses stacked contra-rotating rotor discs and a pusher prop to achieve speeds well beyond 200 knots and is much simpler than the tilt-rotor V-22 Osprey, the only other aircraft which can both achieve vertical takeoffs and fly at such speeds*.
However an ordinary helicopter – or perhaps a gyrocopter/autogyro – which was quiet, low-maintenance and cheaper to run would be quite exciting in itself, and not just for the established aviation biz and the military. Helicopters no longer need to be difficult to fly, regardless of weather – in fact they can fly themselves. So if they were quiet as well and not too costly, the 1950s dream of a helicopter in every garage might soon come true at last.
All that said, however, the US government seems unwilling to make a major effort here: and even Sikorsky, though quite adventurous with its own money as major aerospace firms go, may feel unable to take much of a punt on its own. ®
*Jump jets such as the Harrier and the forthcoming F-35B aren't generally designed for vertical liftoff. They can take off straight up, but only if stripped of most of their payload and fuel. Normally a short takeoff roll, often assisted by a ski-jump ramp, is preferred.