First look at ultra-fast Sikorsky/Boeing SB>1 Defiant dual-rotor helicopter

Sikorsky and Boeing have been working on this high-speed, long-range, ultra-maneuverable military helicopter design for some time, and now they've released the first photos of what is expected to become a highly effective US Army utility helicopter sometime in the 2030s.

The SB>1 Defiant is a joint multi-role medium-class Future Vertical Lift technology demonstrator built around Sikorsky's X2 platform, which uses two counter-rotating rigid blades on the top of the aircraft to eliminate the retreating blade stall problem that puts a ~150 mph (~240 kmh) speed limit on helicopters with a single top rotor.

Putting it simply, at a stable hover with no ambient wind, a helicopter's top blade generates an equal amount of lift throughout its whole rotation around the central axis. But when you start moving forward through the air, the blade starts developing extra lift on the side where the blades are rushing forward into the wind, and less lift on the opposite side where the blades are going backwards with the wind. This can get so unbalanced that it threatens to tip the helicopter over altogether if you don't stay beneath a defined maximum airspeed.

Sikorsky's technology puts two main rotors on top of each other, rotating in opposite directions, which balances out the lift profile on either side and allows the craft to fly much faster – up to twice the airspeed of a regular helicopter – while maintaining excellent handling and agility.

It also negates the need for a regular tail rotor, as yaw can be managed using just the top rotors. The SB>1 Defiant uses a pusher prop at the rear, along with active rudders and elevators. At takeoff, this means the aircraft can lift off and move away quickly without needing to tilt forward. At higher speeds, the rear prop provides extra drive and the rudders and elevators help with high speed maneuvering.

The Defiant will have retractable landing gear, reducing drag to allow higher speeds at greater efficiencies, leading to longer range. Its twin rotor system will minimize downwash as you get on and off, and Sikorsky also claims a "dramatically reduced acoustic signature." On the ground, the top rotors can be folded back, allowing it to be stored and transported easily.

When it enters service, the Defiant will carry a crew of four and a cabin equipped for up to 12 combat-ready troops or eight medevac litters. That's in an assault configuration; there will also be an attack variant that shares a common fly-by-wire drivetrain and many other systems, but has a different composite fuselage and is much more heavily armed.

Take a look at the concept video below, or click through for a larger look at the photos released today.

Source: Sikorsky/Boeing