The "SB-1" (or "SB>1") is a joint venture "compound helicopter" development between long-time helicopter-maker Sikorsky and defense powerhouse Boeing. The design is being fleshed out to satisfy the United States Army's "Future Vertical Lift" (FVL) program which has since taken over the "Joint Multi-Role" (JMR) requirement. The SB-1 technology demonstrator is in direct competition with the in-development V-280 "Valor" being offered by Bell Helicopters for the same high-speed, transport-minded Army requirement. To date (January 2019), the V-280 has been able to reach speeds near 320 mph and has been in active flight-testing for nearly a year.
The SB-1 is part of a next-generation of U.S. Army helicopters that encompasses a family of rotary-wing aircraft to undertake a variety of over-battlefield roles. These designs are intended to succeed the UH-60 Black Hawk,AH-64 Apache, OH-5 Kiowa, and CH-47 Chinook models in U.S. Army service. Commonality of parts between the new designs is also a strong suit of the family, lowering long-term maintenance and repair costs. In the end, it is hoped for a new, more mobile helicopter force to better aid elements on the ground. Sikorsky and Boeing have not teamed up on a military aircraft project since the cancellation of the RAH-66 Comanche stealth light-attack helicopter of the late-1990s / early-2000s.
At the heart of the SB-1, and other compound helicopters for that matter, is speed in a world where forward flight for helicopters is typically maxed under 200 miles-per-hour. The compound approach of the SB-1 promises twice that and doubles range in the process - this not only makes a speedier and rangier platform, it also augments general maneuverability and agility - useful for when the aircraft finds itself under fire or attempts to navigate the confined spaces of a mountainous or urban environment. One of the more notable American attempts at a frontline compound helicopter was the Lockheed AH-56 "Cheyenne" attack platform of the 1960s-1970s which was eventually cancelled after 10 units were completed. That helicopter is detailed elsewhere on this site.
The coaxial main rotor arrangement, already popular with many Russian Kamov-branded types (as in the Ka-50/Ka-52 "Black Shark" series, is used to provide the necessary lift properties while also aiding in general stability along the lateral axis. The tail propeller unit applies the required forward thrust - giving the aircraft a much improved operating speed for a helicopter. The use of a traditional main rotor blade coupled with a "pusher prop" gives such aircraft the name of "compound helicopter".
The prototype SB-1 was unveiled in December of 2018 at the Sikorsky West Palm Beach facility and ground-testing is set to follow during in 2019. A first-flight, which had been planned before the end of 2018, is also targeted for sometime in 2019 as there have been delays in bringing the SB-1 design to fruition. The product's design is influenced some from Sikorsky's previous work in the compound helicopter field - namely the "S-69" of the 1970s and the more modern "X2" (both detailed elsewhere on this site).
While the in-development Sikorsky S-97 "Raider" compound helicopter (detailed elsewhere on this site) shares an appearance and overall capabilities equal to the SB-1 Defiant, the S-97 is being developed by a separate design team at Sikorsky for a U.S. Army high-speed scout and light-attack platform requirement. The Defiant is intended to fulfill a multi, non-direct combat role closer to that of the UH-1 "Huey" or UH-60 Black Hawk series of medium-lift transports.
As with the S-97 Raider project, the SB-1 carries a fuselage similar in appearance to the Sikorsky UH-60 Black Hawk transport helicopter. This seats the two pilots at the front (behind a shallow nose cap) side-by-side in the cockpit. Aft of this position is the passenger/cargo cabin with sliding doors to either side of the fuselage. Above this compartment is the engine fitting encompassing 2 x Honeywell T55 turboshaft engines. Atop this installation is the double (coaxial) rigid main rotor arrangement made up of two independently rotating, four-bladed components with cranked tips. The fuselage then runs aft to house the pusher propeller unit. Under the tail is a ventral housing for the tail landing gear unit. The mass of the aircraft is supported through forward-set, single-wheeled landing gear near midships. The tail section also holds outboard vertical fins along wing stubs.