Wednesday, May 1, 2013
Future Vertical Lift: An Overview
Examining the contenders behind the U.S. Department of Defense’s Joint Multi-Role (JMR) Technology Demonstrator competition, the precursor to moving toward a Future Vertical Lift (FVL) decision for a new type of U.S. Army rotorcraft beyond 2030.
The U.S. Army’s rotorcraft fleet is wearing out at a much faster rate than was predicted thanks to a decade of operations in Afghanistan and Iraq. Department of Defense findings state: “The Operational Tempo (OPTEMPO) in Operation Iraqi Freedom (OIF) was, and Operation Enduring Freedom (OEF) is, five times that of peace time, and much higher than the design usage spectrum, further taxing the already aging fleet.”
The concept of Future Vertical Lift is to use new technology, materials and designs to deliver rotorcraft that are quicker, have further range, better payload, are more reliable, easier to maintain and operate, have lower operating costs, and can reduce the logistical footprint of “big Army.” So it’s a significant challenge to most original platform manufacturers whose trend of late has been to broaden their “families” of aircraft or provide remanufacture and Block upgrades of existing aircraft.
While FVL is expected to develop into a family of systems, the initial focus is on the medium lift because that is where the greatest number of helicopters to be replaced resides—around 4,000 or so.
The Joint Multi-Role technology demonstration is the first part of three “separate and distinct Science and Technology (S&T) acquisitions”, according to the Army’s synopsis. “The first acquisition was JMR TD Configuration Trades and Analysis; followed by Phase 1, Air Vehicle Development; and Phase 2, Mission Systems Development. In Phase 2, the Government intends to demonstrate advanced mission systems architectures.” JMR TD is only focused on the development of the aerial platform.
There are five main parties who have publically declared an interest in the JMR TD. These are: AVX Aircraft, Boeing/Sikorsky, Bell Helicopter, EADS North America and Piasecki—although the latter two have not been vocal about their bids (an extremely rare phenomenon in the case of EADS and its Eurocopter offering). So here are their bids (in alphabetical order).
AVX Aircraft, perhaps the company with the least known team and product, features a coaxial rotor aircraft, but with twin-ducted fans instead of the pusher prop of the Sikorsky/Boeing bid.
“As one of the four contractors for the CTA, over the last 18 months we have been working very closely with the U.S. Army, AATD and others,” said Ian Brown, director, program management. “They have been revising their requirements and the latest line in the sand is 230 knots and 30,000 lbs gross weight. That drove us to a higher power point. We were originally going to use the ITEP engines but now looking at the Advanced Affordable Turbine Engine (AATE), which is about 4800 hp, so all the extra power will give us our performance.”
Brown said that the AVX design would bring greater operational capability. “Our six-by-six-foot cabin is twice the interior of the Black Hawk cabin today. That not only allows us to meet the troop and crew loads but we also have two space seats.”
Brown added that 12 NATO litters could be fitted, or an auxiliary fuel system for self-deployment over distances. They also have plans to make the aircraft optionally manned.
“There are two different missions but the utility and attack version will have 90 percent commonality and will fly at the same speed. The O&S cost will be much reduced. Rotating components have a life but when our aircraft goes at full speed the rotor becomes like a wing. Forty percent of the lift is going to come from the fuselage and the canards, and the ducts that surround the fans which all serve to unload the rotor system,” he explained.
As the Army would like 360-degree cover fire they initially wanted to place a machine gun on the ramp door but were recommended to take it off as that would be the main exiting and entering point for troops, so the guns will be mounted on the side.
“This guy can lift 13,000 lbs under slung, with the internal payload at 8,000 lbs. We had to carry the 777 howitzer; so we could take over some of the Chinook loads,” stated Brown. “The coaxial or compound is going to give you the speed you need which is also a positive point for casualty evacuation.”
AVX proposes to build two aircraft for the JMR TD: one for the flight test and one that will go straight into the wind tunnel. Wind tunnel tests have already been run on one at three-quarters scale to validate the lift and drag of the fuselage, but not yet the rotor.
“We can use the GE T706 engines that are on the MH-60M Black Hawk—they are in production and in service so that is another huge risk reduction,” said Brown. He added that the AVX team is in place with such notables at Rockwell Collins, General Electric and BAE Systems declared onboard.
Bell Helicopter made public its JMR TD entry, the V-280 Valor, in April at the Army Aviation Association of America (Quad-A) annual gathering in Fort Worth. “This is our third-generation of tiltrotor which is based on over 55 years of experience,” began Keith Flail, Bell’s program director, FVL military programs.
“This is not going to be a product but a demonstration of capability for the buying agencies. You look at where we are with the great success of the V-22 with more than 170,000 combat hours and over 200 aircraft fielded. The DoD has already seen and what a tiltrotor can provide operationally compared to a conventional aircraft—particularly twice the speed and range. We have so many lessons learned and coming forward with new technologies to focus on what the Army needs.”
Having built tiltrotors that are smaller (Eagle Eye) and larger (V-22) than the JMR requirement, Bell’s FVL team considers that they are well positioned to deliver to the Army’s requirements—whatever they will emerge as. “The start point is to be able to hover out of ground effect at 6,000 feet, an optimized engine and transition to 280 knots with between one and two-thirds better fuel efficiency than with a conventional helicopter or a compound that wants to burn more gas to go faster,” stated Flail.
A major change between the V-280 and other tiltrotors is the fixed non-rotating engine for the air assault mission. “There are six foot wide doors for troops to rapidly egress on the LZ, crew chiefs can lay down suppressive fire, so there is no concern about running or firing into the rotors or tail rotor. There are both operational reasons and technical advantages for this particular application as we look at where turbine engines are going in the future. There will be higher exhaust gas temperatures, which would become a factor if we rotated the engine in this application. At the moment you get more lift power through this in the V-22 but as we go to the next generation with less thrust to provide lift, there is no benefit in rotating the engine.”
Talking strategically, Flail noted that due to the restrictions of the defense budget “we are going to end up with a smaller force structure so in the V-280 you can go twice as far, twice as fast, and your ability to project combat power around the battlefield is immensely improved. Force projection and force protection is what it is all about.
“The fly-by-wire allowed us to use different configurations and we have evaluated those; we wanted to keep the size down and maintain the performance,” said Flair. “We looked at T-tail and H-tail, but selected the V-tail (butterfly). This also offers alternative positions for antennas and defensive aid systems.”
As everything in the TD is currently focused on the utility rather than the attack version, Bell is still considering how it can maximize the attack platform: “we would have stores that could fold out and back into the aircraft so you still have the aerodynamic efficiency that you need at the high cruise airspeeds. We want to bring the same principles in commonality that we have applied to the H1 Yankee and Zulu helicopters for the Marine Corps for the U.S. Army.”
On January 13, Boeing made a fundamental and deliberate leap away from developing the next generation of tiltrotor technology (it is still committed to the V-22 program) in leaving its partner Bell Helicopter Textron for new joint venture partner Sikorsky.
Douglas Shidler, Sikorsky’s director of the JMR TD program, said that the Army needed to start its FVL approach with the Armed Aerial Scout requirement.
“Start on your small fleet, go for your Armed Aerial Scout, if you don’t do something your industrial base is going to lose its capability to develop a future platform. We did the X2 to ensure we had continuity throughout our engineers, those who started young on the X2 have now matured and are working on the S-97 Raider,” which is Sikorsky’s own AAS offering.
Shidler said that the aim was for the first AAS unit to be equipped by 2025-27. The first unit equipped with FVL will be in the 2035-38 timeframe. “If the Army buys 100 aircraft a year, how long will it take to replace those thousands of medium lift helicopters,” he questioned, underlining the need for precise timing of the FVL program.
The Boeing/Sikorsky JMR TD is an X2-based configuration, which will demonstrate technologies to allow the Army to establish its definitive requirements for future vertical lift.
“Some people say we are offering a new, never-been-done-before platform. But it could arguably be our fourth platform that began with the XH-59A/S-69 helicopter advancing blade concept (that reached over 204 knots), which we brought to a close at the end of the 1980s, with X2 being the second, S-97 the third and finally the JMR. X2 and Raider are rapidly prototyping platforms—using existing technology.”
He added that this was Sikorsky’s sixth fly-by-wire platform (the CH-53K, S-92, UH-60, etc.), with vibration control systems on multiple platforms, composite technology and rigid rotors: “What we are doing now is blending those together.”
Boeing’s involvement comes from its experience (and dominance) of the attack market while Sikorsky offers the same in its range of UH-60 platforms. Added Shidler: “In the tech demonstrator phase there is a cost share and a fair amount of money is needed—so the resources of both companies can be brought into play. The scale of the TD has not been announced yet, only that it will be in an X2 configuration.” There has been no decision on the powerplant and the conceptual design is being done jointly, with Boeing people co-located in Connecticut.
Steve Weiner is Sikorsky’s director of engineering sciences, as well as the chief designer of the X2 technology demonstrator. He told Rotor & Wing that Sikorsky had conducted a series of internal studies into the concept of the future of the helicopter, looking at all technologies. He said they understood the need to expand the operational range of the helicopter, particularly speed and maneuver.
“Every system is a compromise,” he said. “The co-axial rotor maintains pitch and yaw. There is a clutched propeller so that when the aircraft needs to hover that is turned off. The Raider will provide hot and high performance and at speeds of up to 220 knots.”
When the propeller is turned off, he continued, “the aircraft behaves like a regular helicopter with speed up to 160 knots. We use the main rotor to provide lift at speed. To brake, we can reverse the prop to quickly slow in a short distance,” he said, adding that “fly-by-wire is our standard work now and we are way along the learning curve.”
When the Army’s Aviation Applied Technology Directorate (AATD) awarded four contracts for JMR configuration and trades analysis studies in 2011, Sikorsky was one of the beneficiaries alongside Boeing, the Bell-Boeing partnership and AVX Aircraft. Said Weiner: “the CTA study meant that we could look across many options, from single rotor aircraft to compounds, as well as different types of tiltrotor. During multiple studies 2004-05 looking at multiple configurations—then there wasn’t AAS or FVL—we were looking at speed. We selected the X2 to retain the attributes of a helicopter and we wanted to go fast without reconfiguring. The reason for that, if you have a problem in flight you don’t want to have to reconfigure the aircraft. With the S-97 you can autorotate like any other helicopter, without having to reconfigure the platform. We also wanted to make sure it has a comparable rotor downwash for SAR and disaster relief.”
EADS North America
This offering is a complete unknown. A derivative of Eurocopter’s X3 aircraft is perhaps to be expected for the EADS North America bid. The company describes the X3 as a hybrid technology demonstrator that has attained a speed of 180 knots that various company spokesmen continue to affirm is well within its limits.
Its tour of North America was used to showcase it to military aviators, among others. This could well have laid the groundwork for what is to come—whenever it comes!
This well-known research organization has entered its PA61-4 Advanced Winged Compound (AWC) into the JMR arena. It has a vectored thrust ducted propeller (VTDP) as seen on its X-49 aircraft. The long wing not only provides lift but also anti-torque and pivots in flight.