DATE:20/05/10
SOURCE:Flight International
Sikorsky X2 breaks helicopter speed barrier
By John Croft
Sikorsky reports that its X2 advancing blade concept technology demonstrator has achieved 168kt (311km/h) forward speed, putting the dual counter-rotating pusher-prop compound beyond the typical maximum speed for traditional helicopters and outside the reach of the company's S-76 chase vehicle's 155kt capability.
A follow-on flight, expected the week of 24 May, is to see X2 test pilot Kevin Bredenbeck accelerate the LHTEC T800-powered fly-by-wire pusher to 180kt, completing the third of four planned envelope expansion test phases. Phase four, which could begin as soon as mid-June, includes the first attempts to slow the X2's main rotors while opening the speed envelope to 250kt or more.
The prototype is designed with no clutch between the main rotors and propulsor, which requires the pilot to increase forward speed through the variable pitch control on the six-bladed rear propeller. Once in the 180kt realm, the X2's computer will automatically slow the main rotors and increase collective pitch to prevent tip speeds from entering high-drag transonic region, with Bredenbeck correspondingly increasing propulsor pitch to increase the X2's speed as the propulsor also slows.
Ahsish Bagai/Sikorsky