NASHVILLE — The Boeing [BA]-Sikorsky built SB-1 Defiant technology demonstrator is set to undertake its third flight in the next 10 days to accomplish frequency sweeps and to check several other areas, including the aircraft’s active vibration control system and its hover out of ground effects profile.
“The plan is we’ll have another flight in a week and a half,” Bill Fell, the Sikorsky experimental test pilot for the SB-1, said Apr. 15 during a briefing at the Army Aviation Association of America’s annual conference here. Sikorsky is a business unit of Lockheed Martin [LMT].
The Defiant made its maiden flight March 21 and flew for a second time on April 5.
During these two initial flights, Fell and Boeing pilot Frank Conway “hit every test point and completed each data point we had planned to complete,” Sikorsky and Boeing said. “The team proved out the expected speed for these tests: 10 knots forward, left, right and rearward. It also proved out hover performance maneuverability, pedal turns, and a hover ladder from ground level up to 30 feet altitude. These tests are a first step in getting to the flight envelope we hope to achieve with this groundbreaking aircraft. Over the summer of 2019 we expect to expand the envelope in flight tests with additional speed and maneuverability and provide the U.S. Army with the necessary, robust, and relevant data in a timely manner that will enable them to make fully informed decisions as they pursue the Future Vertical Lift program.”
The Defiant’s coaxial, rigid-rotor design features eight rotor blades, four each on two counter-rotating main rotors and a rear eight-bladed pusher-propulsor — basically a backwards propeller — to provide forward thrust. The blades’ pitch is variable to maximize thrust and perform quietly at high speed.
Fell said Apr. 15 that the Defiant is “a 160-knot aircraft” with the propeller not turning. “With the propeller turning, it’s a 260 knot machine.”
An Apr. 4 Army request for information (RFI) from industry on the Future Long-Range Assault Aircraft (FLRAA) component of Future Vertical Lift lays out a desire for 280 knots maximum continuous cruise speed at max power.
Sikorsky and Boeing officials said that they will be able to meet such a goal through modifications, which would likely mean bigger engines and transmissions and a larger air frame and more horsepower going through the rear pusher prop, a higher horsepower generation that would mean higher drag and less efficiency.
The two most likely competitors for FLRAA are the Defiant and Bell’s V-280 Valor advanced tiltrotor. Both aircraft are participating in the Army’s ongoing Joint Multi-Role Technology Demonstration (JMR-TD) program. Bell is part of Textron [TXT].
Industry officials are awaiting the Army’s announcement of an acquisition strategy for Future Vertical Lift.
Like the Defiant, the Valor has seen some recent progress. Ryan Ehinger, the Bell program manager for the V-280, said on Apr. 15 that the Valor last week flew with the doors open for the first time and deployed a fast rope for the first time. Ehinger said Bell plans to fly an autonomous version of the aircraft late this year to demonstrate “significant new capabilities” and that the company is “heavily leveraging” the work it has done with the Bell Nexus eVTOL aircraft.
The Army has cut the budget for JMR-TD to just $10 million in its 2020 funding request to Congress, down from more than $140 million in the current fiscal year. Army budget documents, which realign all Future Vertical Lift development efforts under a single funding stream, state that the service considers JMR-TD effectively complete as of Oct. 1, though Defiant has only just flown.
With so much flight testing under Bell’s belt, company officials have suggested they will curtail further test and demonstration without future funding from the Army.
A contract for FLRAA should be awarded in late fiscal 2021 followed by a preliminary design review the following year and a critical design review in fiscal 2024. First flight is to occur in the second half of fiscal 2024, the Army’s published program schedule says.
Whichever aircraft the Army chooses should come in at no more than $43 million a copy in 2018 dollars, according to the Apr. 4 RFI.
FLRAA is structured as a multi-service program with the Army in the lead and Special Operations Command (SOCOM) and the Marine Corps acquisition programs following about two years later. The RFI lays out specific requirements both for SOCOM and the Marines.
For their part, the Marines want a maximum continuous cruise speed of 295 knots at 90 percent power and a sprint speed of 330 knots.