SB>1 Defiant reaches new top speed of 205 kt in flight

The Sikorsky-Boeing SB>1 Defiant coaxial helicopter on 9 June reached a new top speed of 205 kt in flight while using less than 50% of the installed propeller power.

Defiant test pilot Bill Fell told reporters on 16 June that the industry team hopes to exceed 250 kt in a few months. The Defiant is designed to achieve a minimum of 230 kt in flight. Sikorsky and Boeing are developing the Defiant for the US Army’s Future Long-Range Assault Aircraft (FLRAA) programme, where they are competing against the Bell V-280 Valor tiltrotor and an AVX-L3 Technologies compound coaxial helicopter.

Sikorsky-Boeing will be able to ramp up speed testing when it has the propeller torque qualified on the test stand. Fell said that the Defiant team will qualify the propeller torque in 10% increments until it reaches 100%. Sikorsky-Boeing generally aims for envelope expansion in 20 kt increments, but this depends on how much extra propeller torque Sikorsky and Boeing can clear on the test stand, he added.

Fell said Sikorsky and Boeing have to perform some engineering work on the propulsion system test bed (PSTB) to keep the loads in check as the loads on the test bed are significantly higher than in flight, where the aircraft uses airflow to help hit higher speeds. Fell told Janes after the event that there were no known mechanical challenges to prevent the Defiant from reaching faster speeds.