The Sikorsky-Boeing SB-1 Defiant compound helicopter completed its initial ground runs on 8 and 9 January and is being ground tested before its first flight which is anticipated for early 2019.

The demonstrator helicopter was supposed to have flown initially in 2017, but issues with the composite rotor blade manufacturing process and transmission gears delayed takeoff. Sikorsky and Boeing then thought it would lift off for the first time in 2018, but issues discovered by engineers in a powertrain system test bed delayed the flight again.

In a video released by Sikorsky and Boeing, the SB-1 is strapped down to the tarmac with cables, it powers up and rotates its stacked blades in opposite directions. The team needs to put at least 15h of testing time on the powertrain test bed before a flight safety committee will approve the SB-1's first flight. Sikorsky says the powertrain now has 18h of test time and it has resolved the system's problems, though it plans to continue to run tests in advance of a first flight.

The SB-1 is a coaxial compound helicopter with a pusher blade on its tail. It is a medium-sized demonstration helicopter for the US Army’s Joint Multi-Role Technology Demonstrator programme, a precursor to the service’s Future Vertical Lift programme. The aircraft is intended to replace the Sikorsky UH-60 Black Hawk and the Boeing AH-64 Apache.

Delays to the rotorcraft’s first flight come after its chief rival, the Bell V-280 Valor tiltrotor, has been flying for more than a year and on 25 January hit its speed goal of 280kt (518km/h).

Despite snags with SB-1, Sikorsky has demonstrated success with a smaller version of its compound helicopter technology, called the advancing blade concept, on its S-97 Raider. That helicopter has been flying for about 3.5 years and is a candidate for the US Army’s Future Attack Reconnaissance Aircraft competition.

Updated with responses from Sikorsky