Boeing-Sikorsky SB-1 DEFIANT

SB>1 DEFIANT is a modern, fully-integrated vertical lift aircraft being developed by Boeing and Sikorsky for the US Army’s joint multi-role (JMR) technology demonstration of the Future Vertical Lift (FVL) programme.

The aircraft will meet the attack and assault needs of the US Army, along with the long-range transportation, infiltration and resupply needs of the US Marine Corps.

The Sikorsky X2-coaxial Advancing Blade Concept (ABC) was originally proven on the S-69/XH-59, own between 1973 and 1981. It demonstrated 263 kt (487 km/hr) in a shallow dive. (US Army photo)

SB>1 DEFIANT will be capable of performing tight assault formations, close proximity landing, unique hovering, high-speed and low-speed flights due to its large angular rates and precision attitude control capabilities.

Sikorsky S-100 registration confirmed as SB-1 Defiant

The news of the registration — for N-number N100FV, serial number 0001 — was first reported by Helihub. A spokesperson for Sikorsky parent company Lockheed Martin confirmed to Vertical that the registration is for the compound helicopter that Sikorsky and Boeing are developing for the U.S. Army’s Joint Multi-Role Technology Demonstrator (JMR TD) program, a precursor to the Future Vertical Lift (FVL) program that aims to modernize the Army’s rotorcraft fleet.

“Yes, the registry application for S-100 is referring to the Sikorsky-Boeing SB>1 Defiant,” the spokesperson said. “Our team is following the FAA’s process for how they formally designate experimental aircraft; however, we will continue to use SB>1 Defiant when describing our aircraft asset.” Source


Lockheed Martin


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SB>1 DEFIANT design and features

The next-generation aircraft will meet the future demands of the military, offering an optimal combination of speed, lift and range, with better agility and greater manoeuvrability. It will be built with 85% commonality between attack and assault aircraft.

The fuselage of Defiant will be made of composite materials for achieving superior strength and weight reductions. It will integrate a retractable type landing gear for less drag during flight.

SB>1 DEFIANT will be equipped with X2 rigid co-axial rotor system technology, which was tested aboard the X2 and S-97 Raider aircraft. Each rotor of the twin co-axial rotor system will revolve in opposite direction and will reduce the net torque of the other rotor in real-time.

Twin rigid co-axial counter-rotating main rotors / Mike H

Its rotor blades will be made from composite material, which will reduce vibrations and minimise wear of the components, while providing greater life and reduced maintenance costs. The aircraft will also be equipped with the active vibrator control technology to dampen the vibrations from the rotors and deliver smooth lift and manoeuvrability.

The rear fuselage will integrate a pusher propulsor with the clutch, enabling the aircraft to attain approximately twice the speed of a conventional rotorcraft. The pusher configuration will also allow the aircraft to cover longer distances during the long-range missions, while advanced drive system will ensure minimal transmission losses.

The manually foldable blades will reduce the space requirements during parking, picketing, and transport. The aircraft will fit in the footprint of a folded AH-1 when folded for shipboard stowage.



SB>1 DEFIANT will feature a rotorcraft equipped with a fly-by-wire system, which can control the rotors, pusher propulsor, rudders, and elevators. Each rotor blade actuator will be connected to the fly-by-wire technology to avoid any potential mechanical losses.

The active rudder and elevator controls can change the flight path of the aircraft with greater agility and ease. The aircraft will also have options to employ weapons during all modes of flight.

Cabin details of SB>1 DEFIANT

SB>1 DEFIANT can accommodate 12 fully combat-equipped troops and four crew members. It will also offer sufficient space for medical evacuation (MEDIVAC) operations.

SB>1 DEFIANT performance

The aircraft will be capable of flying at a maximum speed of 250ktas (463km/h) and hover out of ground effect (HOGE) at an altitude of 6,000ft.

It will have greater expeditionary range and endurance and will have the capability to carry heavier payloads compared to the present generation rotorcraft.

The forward thrust offered by the pusher propulsor will enable the aircraft to rapidly displace itself from the flight path in high-threat environments.

The SB-1 will initially be powered by a pair of Honeywell T-55 engines but will later be upgraded to the winner of the Future Affordable Turbine Engine (FATE) competition. The aircraft is expected to have a cruising speed of 250 knots.  Source

The Transmission System Test Bed will run in 2016 at West Palm Beach. (Sikorsky graphic)

Sikorsky Defiant chief engineer Steve Weiner observed, “The basic features of X2 technology continue to be the same — fly-by-wire, active vibration control, integrated propeller, high lift-to-drag rotor, increased operational envelope, low pilot workload. All those features have been incorporated into De ant, just like previous X2 designs. To date, the De ant has all the performance with a lower weight empty fraction than previous X2 designs.”

Weiner expected the Defiant weight fraction would approach that of the Black Hawk and added, “We’re coming in where we expected to be when we first proposed these demonstrator aircraft. ”The SB>1 benefits from composite lessons learned in the CH- 53K and other structures programs. “The Defiant airframe combines a primarily composite structure with metallic components in an engineered structure that minimizes weight. This general construction is similar to the Raider, but the different requirements for De ant result in a different structure. There are also payload differences.”

Defiant leverages work done on the X2 and Raider rotor systems. “Overall rotor performance, from both figure-of-merit and lift-to-drag ratio is as good or better than Raider,” summarized Shidler. “The Defiant blades are similar to those on Raider as far as general planform and airfoil choice. However, the De ant rotor diameter is larger due to greater payload requirements, and some of the performance goals of De ant are different than Raider, requiring other minor differences. De ant also includes manual blade fold, which is not a feature of the current Raider design. The incorporation of the fold feature, in combination with a different hub to blade interface has resulted in a different airfoil distribution than Raider.”

Lockheed Martin

Deviant blades approximate those of the UH-60M in size and those of the Raider in design. Weiner summarized, “As the basic requirements change, things like chord and diameter will change. They’re certainly not identical, but they’re not very far o either.”

The XH-59A exercised differential pitch on its coaxial rotors to make snap turns, and coaxial rotors lowered disk loading to reduce turn radius dynamically. The X2, Raider and Deviant all share an auxiliary tail thruster integrated with the main rotors via fly-by-wire flight controls to provide forward and reverse thrust as needed. Source

2 x Honeywell T-55 engines

The T55-714A features a seven-stage axial compressor, a two-stage free power turbine, a two-stage gas producer turbine, centrifugal compressor, and a reverse-flow atomizing combustor. All models can be configured with a Full Authority Digital Electronic Control (FADEC) system. / Mike H

Upgrade kits are currently available from Honeywell for the T55 Family of engines. These will update the engine with latest technology standards. Compared to older T55 engines, the T55-714A upgrade provides a 22% power increase, a 7% improvement in fuel efficiency and a significant enhancement of reliability and maintainability. Altogether, the upgrade results in a 25% reduction in operation and support costs. Also, the time between engine overhauls will increase to 3,000 hours. The goal is to go to on-condition maintenance in the future.

Honeywell‘s next generation T55-L-71X engines will offer the flexibility of even more power with improved SFC.

Manufacturer: Honeywell International, Inc.
(originally produced by Lycoming Engines – Textron)
Power: Continous: 4,168 shp; Max: 4,867 shp
Overall Pressure Ratio at Maximum Power: 9.32
Compressor: Axial flow/centrifugal
Compressor Stages: 7-stage axial/1-stage centrifugal
Turbine: 2 HP + 2 PT
Engine Control: FADEC
Length: 47.1 in (1.2 m)
Diameter: 24.3 in (61.6 cm)
Dry Weight: 830 lbs (376 kg)
Platforms: CH-47 Chinook; MH-47 Special Forces Chinook
Price/Unit Cost: $1.06 million (in 2016)
Introduced: 1950s (first T55 model)
First Run: 1950s (first T55 model)
First Flight: September 21, 1961


Main material source

Images are from public domain unless otherwise stated

Updated Sep 12, 2021

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