by Donna J. Kelly
The U.S. Army’s Future Vertical Lift (FVL) program aims to replace legacy helicopters with new, improved vertical lift aircraft able to rapidly perform a wide range of missions across greater distances than ever before possible. As you read this, major defense contractors, including Bell, Boeing, Lockheed Martin, and Sikorsky, along with hundreds of other manufacturers and suppliers, are building demonstrators of these vastly superior aircraft.
The FVL program has set new standards that could only be reached by accessing new technologies and manufacturing techniques. These methods have enabled original equipment manufacturers (OEMs) to build modernized vertical lift aircraft that can meet the tough demands of the FVL initiatives, including faster speed and longer range. Reliability, serviceability, and reduced logistical support are other key factors of the FVL initiative.
Another concern is scalability, meaning that basic design is easily scaled up or down to produce lighter or heavier versions as needed for varying special applications. Airframes, propeller systems, engines, sensors, support systems, and more are all being radically improved to enable air superiority in any airspace or landing zone where U.S. military forces might operate.
It is interesting to note that while Sikorsky is now owned by Lockheed Martin, Lockheed Martin also has partnered with Bell in the FVL competition, which, at the time of this writing, was preparing to debut its new model. Boeing and Sikorsky also have been working together to demonstrate a full-scale prototype in early 2018.
Bell aircraft has been using a “digital thread” concept to streamline the entire process of building the Bell V-280 Valor, including the entire fuselage, the tiltrotor, and various parts and accessories. Bell Aircraft’s Director of Global Business Development for Advanced Tiltrotor Systems, Chris Gehler, explains, “We have been able to design the aircraft [and] collaborate with suppliers, engineers, and information technology teams in order to understand where interference might be and where changes need to be made. Pieces are snapping together, wires are going where they need to be, [and] the rework is significantly reduced.”
Using a digital design process also keeps costs low. Bell relates that it took 700 to 800 work hours to create the design drawings for the Bell-Boeing V-22 Osprey, but it took only 40 hours to design the V-280 Valor.
Specifications for the V-280 include a top speed of 280 knots (322 miles per hour, more than twice the speed of current helicopters), a range of 500 to 800 nautical miles (575 to 921 miles, also twice the range currently available), and a cargo load of up to 13,000 pounds. A team of four crew members can transport fourteen fully equipped troops, medical evacuees, equipment, or whatever is needed.
Features include cabin armor, fly-by-wire component redundancy, and state-of-the-art countermeasures. The tail-dragger landing configuration consists of two forward main landing gears and a large wheel on the aft fuselage — all of which are retractable. An internal bay holds four laser-guided bombs, and the outboard pylons are fitted with 19-shot laser-guided rockets.
Bell predicts that the advanced tiltrotor speed and range will provide operators with access to more places, as well as better in-flight control once the objective is reached. The V-280’s powerplant configuration offers situational advantages, because only the proprotor airflow is directed downward. The engines remain fixed in place horizontally, eliminating the hot exhaust problem that has led in the past — in the case of the V-22 Osprey, for example — to fires in the landing area. This change also “improves the pilot’s field of view, because much less machinery is blocking the view along the wings,” explains V-280 Build Team Manager Scott Allen.
Boeing and Sikorsky have teamed together to produce the SB>1 Defiant medium-size demonstrator. This new model features offset co-axial rotors that spin in opposite directions, eliminating the need for anti-torque systems and providing a significant weight savings. Co-axial systems also reduce the phenomenon of lift dissymmetry, because equal lift is generated on both sides. When one blade is advancing, the other is retreating.
The Defiant features an advanced drive with a rigid rotor system, a pusher prop with a clutch, and active vibration control. The pusher prop contributes forward thrust, effectively enabling higher speeds. Defiant’s top speed is anticipated to be over 250 knots, or 287 miles per hour. (By comparison, the UH-60 Black Hawk tops out at 183 miles per hour.)
While the new model’s range was unspecified at the time of this time writing, the aircraft is expected to perform well at high altitudes, one of the main deficiencies of today’s helicopters. “The only reason that we’re not meeting the range requirement at this time is that we are using a pair of T-55 engines from Honeywell, and their fuel consumption is bigger than the projected fuel consumption for FVL,” explains Pat Donnelly, Defiant Program Manager at Boeing. A new engine in development will be coming online soon.
Defiant is a fly-by-wire aircraft with retractable landing gear. It will carry a crew of four, with a passenger complement of twelve combat-equipped troops or eight casualty evacuation stretchers. A gun mounted on the nose and winglet launcher racks for missiles and rockets make the aircraft combat-ready. The developing team also states that the SB>1 boasts a “dramatically reduced acoustical signature,” allowing for stealthier entrances and exits — a key advantage in certain missions.
Improved Engines to Give Extended Life
Billed as the U.S. Army aviation’s “top modernization priority program,” the Improved Turbine Engine Program (ITEP) forms the second major component of FVL. ITEP will provide new powerplants to improve the performance and capabilities of the Army’s existing fleet of Sikorsky UH-60M Black Hawks and Boeing 64E Apaches.
Operations in the hot temperatures and high altitudes of Afghanistan and Iraq have revealed significant shortfalls in the capabilities of the GE Aviation T700 engine currently installed on both types of aircraft. In addition, extra weight and drag have been added to the airframes throughout the years, as technology has progressed and mission requirements have changed.
Richard Kretzschmar, Project Manager of both the FVL and ITEP initiatives, estimates, “It would take 30 years to replace all the Black Hawks in the fleet. In the meantime, those Black Hawks and Apaches are going to need the ITEP engines, designed to fit into the existing airframe spaces, and capable of producing an increase the shaft horsepower (hp) from the current 2,000 hp to 3,000 hp.”
The ITEP program seeks to: 1) provide 50 percent more power at the same weight, 2) achieve a 20 percent longer engine life, 3) realize a 25 percent improvement in specific fuel consumption, and 4) reduce operations and support costs over the lifetime of the engine.
Currently, the ITEP program has two main contenders. GE Aviation, of Evendale, Ohio, received a development contract for $102 million. Advanced Turbine Engine Co. (ATEC), of Huntsville, Alabama, a 50–50 joint venture formed by Pratt & Whitney and Honeywell, received a contract for $154 million.
One fundamental difference between the two engines in development is that GE Aviation’s T901 engine is a single-spool core, while the ATEC engine has a dual-spool core. In a single-spool core, all rotating components in the compressor and the gas generator are on one shaft and rotate at the same speed. A dual-spool core splits the compressor into two independently spinning rotors, with each being powered by a separate gas generator/ turbine on concentric shafts. The advantage of having two compressors is that they can run at different speeds for engine optimization.
Proponents of single-spool engines state that this configuration is less weighty and complicated, making it easier to fix in the field. Advocates of the dual-spool variety assert that it delivers better dependability and greater fuel efficiency.
GE Aviation has had four decades of success with its single-spool T700 engine, and this knowledge was used in the design of the new T901 powerplant. The availabilities of new technologies, such as advanced ceramic matrix composites, 3D aerodynamic modeling, and additive manufacturing have enabled GE to go far beyond what was possible with the T700. Reportedly, the 901 also will be less expensive to manufacture and have a 35 percent lower acquisition cost, while delivering as much as 65 percent higher power to weight than its predecessor.
ATEC’s T900 dual-spool engine boasts 10 percent more power growth capability than comparable single-spool offerings. In addition, according to the manufacturer, the T900 will provide a 3 to 4 percent specific fuel consumption advantage over single-spool alternatives.
The dual-spool engine design uses computerized systems to distribute load between the two compressors and adjust engine load to enhance performance. The result is a potentially cooler engine with reduced wear and tear. For instance, if a helicopter was operating in sandy conditions, the dual-spool engine could allow the rear compressor to turn faster and the front compressor to turn more slowly, potentially improving performance while helping the front compressor take less of a beating from sand ingestion.
The Future of Un-Piloted Vertical Lift
According to the Defense Advanced Research Projects Agency (DARPA), combat outposts require on average 100,000 pounds of materials each week to remain operational. However, forward bases and outposts are commonly difficult to reach, due to rugged terrain, the danger of improvised explosive devices (IEDs), and other enemy threats. Thus, vertical lift aircraft often are the best option for resupplying, conducting tactical insertion and extraction, and evacuation of wounded personnel.
In 2009, DARPA created the Transformer (TX) Program to build un-piloted vertical lift systems to serve as resupply vehicles. The goal was to provide flexible, terrain-independent transportation for logistics, personnel transport, and tactical support for small ground units.
In 2013, DARPA selected the Aerial Reconfigurable Embedded Systems (ARES) design concept, which consists of a new type of vertical take-off and landing (VTOL) aircraft. Lockheed Martin’s Skunk Works of Palmdale, California, is building the aircraft, in conjunction with Piasecki Aircraft of Essington, Pennsylvania, in a $77 million DARPA contract.
ARES is a 41-foot span, tiltrotor-configured drone, with two ducted proprotors, each approximately 8 feet in diameter. These swiveling proprotors are embedded in a short fuselage, enabling ARES to take off like a helicopter; when the proprotors are tilted forward, it flies like an airplane. Cargo “plug-and-play’ modules have been designed for the quick on- and off-loading of specific types of cargo.
Powering the lift of the 7,000-pound maximum take-off weight will be two non-tilting Honeywell Aerospace HTS900 helicopter engines, each with 989 horsepower, allowing a top speed of 195 miles per hour. The earliest demonstrators will have a roundtrip mission range of 175 miles and fly as high as 20,000 feet.
ARES aircraft pose a very different future for the re-supply of forward areas. At present, large aircraft are often used to drop 10,000 pounds of supplies to a small unit. The problem is that having such a large amount of supplies makes the receiving unit much less mobile. Some part of it must be immobilized to secure the supplies.
ARES drops would be smaller, more flexible, and more frequent, facilitating the ability of the whole unit to move when necessary. Plus, units could direct flight modules using mobile phones or ruggedized tablets. As we went to press, ARES was currently in its third and final development phase, and was about to make its first test flights.
A Bright Future
The future of vertical lift is indeed bright: a sky filled with ingenious designs of vertical lift aircraft performing missions that once would have been impossible. So much has come, and will come, from ongoing research and development. As vertical lift aircraft become faster and quieter, can go longer, and operate more efficiently, the hard work of the FVL program will pay off for both the military and civilian sectors.
Image #1 – The Future Vertical Lift (FVL) program is meant to develop replacements for the U/S Army’s UH-60 Black Hawk, AH-64 Apache, CH-47 Chinook, and OH-58 Kiowa helicopters. Four different sizes of aircraft are to be developed and will share common hardware, such as sensors, avionics, engines, and countermeasures. Each class of aircraft will have the potential for service-unique or mission-specific variants. (Photo courtesy of the U.S Army)
Image #2 -The Bell V-280 Valor provides warfighters strategic options, operational reach, tactical agility, and overmatch at the point of decision. (Photo and caption courtesy of Bell Helicopters)
Image #3 – The Sikorsky/Boeing SB>1 Defiant is one of the contenders for the U.S. Military’s Joint Multi-Role program. (Photo courtesy of Sikorsky-Boeing)
Image #4 -Photo courtesy of Army.mil
Image #5 – Photo courtesy of Lockheed Martin
Image #6 – ARES is a vertical takeoff and landing (VTOL) flight module designed to operate as an unmanned platform capable of transporting various payloads. The ARES VTOL flight module has its own power system, digital flight controls, and remote command-and-control interfaces. Twin tilting ducted fans provide efficient hovering and landing capabilities in a compact configuration, with rapid conversion to high-speed cruise flight. Missions for ARES might include cargo resupply, evacuation of casualties, and intelligence, surveillance, and reconnaissance. (Photo courtesy of DARPA.mil)