The Sikorsky UH-60 Black Hawk has been in service since being selected in 1976 to replace the venerable UH-1 Iroquois “Huey”, an icon of the Vietnam War. The Army has chosen a new aircraft to replace the Black Hawk, the Bell Textron V-280 Valor tiltrotor. (The Army has a long tradition of naming its helicopters after Native American tribes — the tiltrotor name is a break from that.) This is the long-awaited decision on the Future Long Range Assault Aircraft (FLRAA) competition.
The tiltrotor concept is similar to that of the Bell-Boeing V-22 Osprey; the engines tilt up to provide vertical lift for landing and takeoff.
The V-280 Valor is different from the Osprey in that it has a V-tail, and instead of pivoting the entire engine nacelles, only the forward propellor mounts pivot. It also has a tail wheel versus tricycle gear.
Why a tiltrotor? The problem with a helicopter is that its top forward speed is limited by aerodynamics. The blades rotate in a horizontal plane all the time. As it moves forward, the blades spin. On one side of their rotation, the advancing blades are moving forward in the same direction as the helicopter, “into the wind” — but much faster. That generates more lift.
On the opposite side of their rotation, the retreating blades are moving in the opposite direction to the helicopter, effectively slower than the helicopter. Less lift on that side of their rotation. As forward speed increases, the disparity also increases. (This would be true if the helicopter was flying in any direction — but it’s forward flight where this really matters for practical purposes.)
This is called dissymmetry of lift; helicopters compensate by shifting the way blades are tilted to generate lift as they rotate, plus a certain amount of flexibility/flapping. This requires all kinds of mechanical complexity to pull off, which is why helicopters are demanding birds to maintain and fly.
This short video shows how it works.
It’s roughly comparable to the problem of a tracked vehicle like a tank — the tank treads get slapped down on the ground and don’t move as the tank rolls on them. They get picked up at the back and are run forward at twice the speed of the tank so they can be slapped down in front of it again.
The competing aircraft from Sikorsky Boeing, the SB-1 Defiant X, attempted to meet this challenge with a coaxial rotor design — two rotors, one above the other spinning in opposite directions to compensate for dissymmetry of lift and remove need for a tail rotor, and a pusher propellor for higher forward speed.
The advantage of a helicopter is that it can operate out of any open space large enough to accommodate its rotors; ditto for a tiltrotor design. The ability to hover, to do without runways, is what makes vertical lift capability so important. While the reasons for the Army’s choice of a tiltrotor over a helicopter are probably complex, my guess is that they decided the V-280 will be easier to maintain and will offer greater speed while operating like an airplane.
Some numbers:
“Bell’s V-280 Valor tiltrotor first flew in December 2017; it accrued 214 flight hours and demonstrated a maximum speed of 305 kt (565 km) before it was retired in 2021. The coaxial-compound Sikorsky-Boeing SB>1 Defiant made its first flight in March 2019 and hit 247 kt (457 km/h) in October 2021.”
UH-1 Huey
- Maximum speed: 127 mph (204 km/h, 110 kn) (at maximum takeoff weight; also Vne at this weight)
- Cruise speed: 127 mph (204 km/h, 110 kn) (at 5,700 ft (1,700 m) at maximum takeoff weight)
- Range: 318 mi (511 km, 276 nmi) (with maximum fuel, no reserves, at sea level)
UH-60 Black Hawk
- Maximum speed: 159 kn (183 mph, 294 km/h)
- Cruise speed: 152 kn (175 mph, 282 km/h)
- Never exceed speed: 193 kn (222 mph, 357 km/h)
- Combat range: 320 nmi (370 mi, 590 km)
- Ferry range: 1,199 nmi (1,380 mi, 2,221 km) with ESSS stub wings and external tanks[211]
V-22 Osprey
- Maximum speed: 275 kn (316 mph, 509 km/h) [266]
305 kn (565 km/h; 351 mph) at 15,000 ft (4,600 m)[267]
- Stall speed: 110 kn (130 mph, 200 km/h) [74]
- Range: 879 nmi (1,012 mi, 1,628 km)
- Combat range: 390 nmi (450 mi, 720 km)
- Ferry range: 2,230 nmi (2,570 mi, 4,130 km)
Trade offs are that it’s going to be a different kind of transition for pilots moving over from helicopters. There’s also the difference in handling and maneuverability in vertical flight mode compared with a helicopter.
A report by Meredith Roaten at National Defense Magazine gets into some of the details:
...Over the next 19 months, an initial obligation of $232 million will fund Bell’s preliminary design and development of a virtual prototype that the Army will then use to proceed with the acquisition, Army Brig. Gen. Robert Barrie, program executive officer for aviation, told reporters at a media roundtable.
...The total award amount for the FLRAA contract including engineering manufacturing and development phase and the first lot of low-rate initial production is $7.1 billion, Barrie added.
“There's a larger number on the order of $70 billion of potential, depending on how many aircraft the Army procured over the long term to include potential foreign military sales,” he said. “So that's both near term and long term.”
...Army Maj. Gen. Walter Rugen, director of future vertical lift’s cross functional team, added the service is confident about the ability of the platform to perform in degraded visual environments, which are increasingly becoming more common on the battlefield.
“We are very concerned about the loss of visual reference in vertical lift systems, and the cognitive offloading that we want to attain in our future systems,” he said at the reporter's roundtable. “So with a digital cockpit and full authority, digital fly-by-wire capabilities, we certainly see an ability to protect our crews in the future.”
...The first Army unit is slated to be equipped with FLRAA by fiscal year 2030. The initial prototype will be delivered to the Army by 2025, according to the service.
Sikorsky-Boeing may protest the decision; it remains to be seen whether the other service branches will go with the Valor, or opt for the Defiant — although the Army decision could be the big factor assuming the virtual prototype evaluation proves out.
There’s also the lessons currently coming out of Ukraine about the survivability of any aircraft in the modern battle space given the advancing rate of anti-air systems development, and the expanding role of drones.
Mike Hirschberg at the Vertical Flight Society weighs in with the importance of the FLRAA decision, concluding:
The conflicts over the past two decades have highlighted the need to move beyond today’s enduring fleet of helicopters conceived in the 1960s and 1970s. The mountainous terrain and vast distances of Afghanistan, coupled with China’s increasingly bellicose postering in the Pacific, have highlighted this need for new capabilities. And Russia’s invasion of Ukraine has underscored the need for strengthened defenses in Europe and elsewhere, particularly for longer range and higher speed.
The Defiant and Valor technology demonstrators have proven the potential for next-generation rotorcraft to leap far beyond current Army helicopters, and far beyond anything else available in the world.
FVL aircraft or their derivatives could fulfill the needs of NATO countries and other allies, just as the Black Hawk and its derivatives nearly a half-century ago. Commercial derivatives or civil variants are also a possibility. The FLRAA decision could also have a major impact in solidifying or reshaping the existing US rotorcraft industrial base, with significant implications for the civil business as well.
Thus, the FLRAA decision is a turning point — immediately for the two competing teams and, longer term, for the US rotorcraft industry, the US Army and global market.
Helicopters are going to be around for a while yet, but vertical flight has gotten some new options.