Friday, May 1, 2009
Current Developments: Rotorcraft Evolve...Slowly
After decades of neglect, helicopter research and development are again gaining ground.
Helicopters — especially military helicopters — need to improve in a lot of ways. Most everyone in the business agrees on that, and after eight years of rotorcraft-intensive wars in Afghanistan and Iraq, the military and industry are focusing on new technologies for rotary-wing aviation with more urgency.
"There’s no question they’re paying increased attention to the need," said Rhett Flater, executive director of American Helicopter Society International. Government spending on rotorcraft technology, though, is "still very limited," Flater noted. Indeed, at about $100 million a year, it’s less than the price of a U.S. Air Force F-22 Raptor fighter jet.
Most experts agree that improvements in rotorcraft are long overdue, especially in those the military flies. Military helicopters aren’t a lot better today, fundamentally, than they were a half century ago. They’re faster but not by much, they’re safer but not safe enough, they’re far more vulnerable to enemy fire than today’s fixed-wing aircraft, they’re way too noisy, they burn too much fuel, and they have trouble landing in dust, sand or snow.
"Helicopters are pretty well limited to forward speeds of about 160 knots, they have limited radius of action, limited payloads," Flater said. Vertical lift aircraft need to "perform at speeds of 200 knots-plus, reduce specific fuel consumption by, say, as much as 30 percent" and "improve our record of safety and survivability," he added.
The military, immune to shareholder financial pressures commercial companies face and willing to take risks to gain advantages on the battlefield, has long been the primary source of cutting-edge technology in aviation. Those who share Flater’s views, though, enviously note that the military has spent billions on fixed-wing aircraft in recent decades while allowing rotorcraft technology to advance in baby steps by comparison.
Since the Vietnam War, the U.S. military has fielded several generations of fixed-wing jet fighters and improved versions of them. F-16s, AV-8Bs, F/A-18s, F-22s...the list is long and growing. The multiservice, multinational F-35 Joint Strike Fighter, now in flight test, is the latest fifth generation fighter underway.
With the exception of the V-22 Osprey tiltrotor, which the U.S. Marine Corps began flying in Iraq in 2007 and Air Force Special Operations Command declared ready for service in March 2009, the U.S. military hasn’t fielded a truly new rotary-wing aircraft since the 1970s. The U.S. Army cancelled its last one, the RAH-66 Comanche, in 2004.
The third of three Marine Corps squadrons that have flown the V-22 in Iraq since October 2007 is scheduled to return to New River Marine Corps Air Station, N.C., this month. The Marines have used the Osprey in Iraq to haul troops, supplies, and civilian passengers from point to point. They’ve also used them, less often, to search for insurgents. This coming summer, the squadron that originally took the Osprey to Iraq, VMM-263, is to deploy aboard an amphibious assault ship as part of a Marine Expeditionary Unit.
The wars in Afghanistan and Iraq are bringing home what the lack of investment in military rotorcraft is costing, not just in dollars but also lives. A 2008 study by defense consultants Whitney, Bradley and Brown Inc. reported that as of 2005 (the latest year figures were publicly available) the military had lost 212 helicopters in the Global War on Terrorism, compared to 13 fixed-wing aircraft. Those helicopter losses resulted in 371 fatalities, compared to combat losses of seven personnel in fixed-wing aircraft.
Congress isn’t likely to pour big money into new rotorcraft technology with the economy in crisis and the federal deficit and debt soaring. That may be especially true in the wake of embarrassing cost and schedule overruns of the sort that forced the Army last year to cancel and restart its Armed Reconnaissance Helicopter program and have some urging President Barack Obama to scrap the new VH-71 presidential helicopter. At the same time, political interest in rotorcraft seems to be growing.
Thanks to language put in last year’s annual defense bill by the four-year-old Congressional Rotorcraft Caucus, the Pentagon has a Future Vertical Lift Capabilities Based Assessment underway to determine what Vertical Take Off and Landing aircraft the armed services will need beyond those in use or on the drawing boards.
The armed services, meanwhile, and the Defense Advanced Research Projects Agency (DARPA) are working on a wide variety of programs to make rotorcraft sturdier, less vulnerable to enemy fire, more fuel efficient, quieter, and faster.
The Army, which operates the lion’s share of U.S. military helicopters and has been flying the rotors off them in Afghanistan and Iraq, has an aviation priority list that focuses on better operational availability, mission reliability, and logistical support; safer operation in bad weather and terrain; new technologies to help air crews react to threats more quickly; new communications gear and new sensors to identify targets.
Better performance — more speed, more range, greater lift, longer endurance — are farther down the Army’s list. Completely new rotorcraft designs aren’t on it at all, with the exception of a program the Army and Air Force are working on to come up with a new heavy-lift transport for all the services.
That Joint Future Theater Lift project is in its earliest stages, and the services are still debating whether such an aircraft will have to be able to take off and land vertically. Bell Helicopter Textron Inc. of Fort Worth, Texas, and Boeing’s Rotorcraft Division in Ridley Park, Pa., that make the V-22 in a 50-50 partnership, are working on concepts for a big new tiltrotor, the configuration the Army has said it prefers, to do the job. So are Sikorsky Aircraft Corp. of Stamford, Conn., and Karem Aircraft of Lake Forest, Calif.
None of the armed services, meanwhile, is funding actual development of an "X" rotorcraft, an experimental new design.
Private industry, however, is focusing on overcoming the aerodynamic barriers that hold conventional helicopters to cruise speeds well below 200 knots: retreating blade stall and compressibility, in which rotor tip speed runs up against the sound barrier.
Sikorsky has begun flying its X2 Technology demonstrator, a compound helicopter that relies on two coaxial rotors turning in opposite directions and a pusher propeller to break the 200-knot barrier. As this issue of Rotor & Wing went to press, Sikorsky had hovered the X2, flown it up to 40 knots on the rotors and tested the pusher propeller on the ground.
Sikorsky plans to flight test the X2 more aggressively during the next year in West Palm Beach, Fla., where the company promises to expand its flight envelope to a cruise speed of 250 knots. The rigid coaxial rotors the X2 uses to defeat retreating blade stall also promise to reduce noise and vibration substantially while a fly-by-wire cockpit reduces pilot workload, said James Kagdis, manager of advanced programs at Sikorsky.
If the tests go as expected, Kagdis said, the company will start talking to potential military and commercial customers about what X2 Technology might do for them.
The X2’s advertised ability to hover and maneuver as conventional helicopters can at low speed could make it ideal for inserting special operations troops into hostile urban areas, Kagdis said. An X2 gunship, he added, would be able to escort the V-22 Osprey. The tiltrotor transport V-22, which can cruise at 250 knots or better, flies too fast for slower-moving helicopter gunships or faster-moving fighter jets to directly escort it.
Commercial jobs the X2 might do well include emergency medical services, executive transport and taking supplies and workers to offshore oil rigs, Kagdis suggested.
Another X-rotorcraft flying is Piasecki Aircraft Corp.’s X-49A Speedhawk, which adds a vectored thrust ducted propeller to the tail and a stubby, mid-fuselage wing to a Sikorsky SH-60 Seahawk to get past retreating blade stall. The Navy provided the aircraft and the Army has funded the program, though at levels largely mandated by Congress. The program’s congressional backers added $5 million to the $2.8 million the Army planned to spend on the program in fiscal 2009, which began October 1, 2008.
The Speedhawk, which uses a standard Seahawk rotor and engines, flew 86 hours in 79 test flights between June 2007 and October 2008 at Boeing Co.’s flight test center at New Castle Airport, Del. Using its pusher propeller, it hit a top speed of 180 knots — 47 percent faster than an unmodified Seahawk, said John Piasecki, the company’s president. Navy rules have barred the company from flying the Speedhawk faster so far, Piasecki said, but the company hopes to get permission to do so in the coming year or so.
Heliplane and DiscRotor
DARPA, whose mission is to push the cutting edge, is funding studies of other ideas for faster vertical lift aircraft. One DARPA program proposes to design, develop and flight test a futuristic "Heliplane" for combat search and rescue. The Heliplane would use a rotor to take off and land vertically but stop the rotor in mid-air while a jet engine propelled the aircraft to a cruise speed of 400 mph.
Boeing Co. is doing design studies on a similar concept called DiscRotor under a $7.3 million DARPA contract awarded January 30. DARPA describes the DiscRotor as a fixed-wing jet with rotor blades that would retract after vertical takeoff into a circular aerodynamic housing mounted over the fuselage. Retracting the blades into this disc would reduce drag, theoretically allowing the aircraft to fly at 400 knots or more at up to 30,000 feet yet, by extending its rotor blades, hover and maneuver at low speed like a helicopter.
Other new rotorcraft technologies in the works are less exotic, and include several aimed at immediate payoffs. The Army, the service primarily responsible for military rotorcraft research, "is trying very hard — doing a pretty darn good job — of balancing their investment for the near-term and the long-term fight," said Col. Steve Kihara, commander of the service’s Aviation Applied Technology Directorate at Fort Eustis, Va.
One priority is to come up with technologies to allow safe landings in brownout and whiteout, when rotor downwash kicks up clouds of sand or dust or snow that make it hard or impossible for pilots to see the landing zone. Brownout landings have caused many of the military’s helicopter losses in Iraq and Afghanistan.
Two systems that combine multiple technologies show promise as ways to overcome brownout, military and industry officials say.
Sikorsky recently finished an 18-month demonstration for DARPA of a system called Sandblaster that combines automated flight controls, a 94GHz radar that can scan a landing zone through brownout, a digital-map database, and an electronic cockpit display. Combined, those devices give the pilot a 3D representation of the landing zone overlaid with symbology that shows not only where the aircraft is but where it’s going. Sikorsky is partnered with Honeywell International and Sierra Nevada Corp. on the project.
Three Army guest pilots flew demonstrations of Sandblaster in January for the Army Aeroflightdynamics Directorate at Moffett Field, Calif., with the system mounted in Sikorsky’s RASCAL JUH-60 Black Hawk research helicopter. The tests went well, said Brad Kronauer, Sikorsky’s program manager for Sandblaster, and DARPA and the companies are discussing with the Army what to do with the technology next.
"I think the jury’s still out on where it exactly goes next," Barry Lakinsmith, acting director of the Aeroflightdynamics Directorate, said of Sandblaster. "There are lots of people working on this (brownout) problem with lots of other approaches."
One alternative is LandSafe, a system devised by Optical Air Data Systems of Manassas, Va., and licensed to Rockwell Collins of Cedar Rapids, Iowa, for production. Tested once so far by the Marine Corps on a Sikorsky CH-53E at Creech Air Force Base, Nev., LandSafe uses LIDAR, a laser range-finding sensor, to measure altitude above the ground, ground speed, airspeed down to zero, direction and relative and natural wind. A computerized display lets the pilot see the helicopter’s motion relative to the ground in real time as it approaches the landing zone and set the helicopter down safely.
Lakinsmith said the Army is waiting for such technologies to mature before choosing one. As always in aviation, a major issue is how much weight such a system would add to an aircraft. For that reason, the Army wants any such sensor package "to address not just brownout but all degraded visual operations," Lakinsmith said. "It’s a tough sell to put a single-purpose sensor" on an Army rotorcraft, he noted.
Another major rotorcraft issue for the Army is hovering power. The sprawling country’s lack of roads and the risk of improvised explosive devices on those that exist make rotorcaft pivotal in moving, supplying and covering troops there. Flying and fighting in mountain valleys puts a premium on being able to hover out of ground effect at higher altitudes.
The Army wants its UH-60 Black Hawks and AH-64 Apache attack helicopters to be able to HOGE at 6,000 feet on a 95-degree day, a big jump from the old standard of 4,000 feet. The service is working on the problem in a couple of ways.
Under its Advanced Affordable Turbine Engine program, the Army has awarded contracts to GE Aviation, a unit of General Electric Co., and ATEC, a joint venture that teams Honeywell and Pratt & Whitney, to demonstrate engines that can generate 3,000 shaft horsepower. Among other things, the new engine is provide a 65 percent increase in the power-to-weight ratio of the Black Hawk’s current T700-GE-701D engine and a 25 percent cut in its specific fuel consumption — how many pounds of fuel an engine burns per hour to produce a given amount of horsepower.
Kihara said the additional horsepower, up from the 2,000 SHP produced by the T700-GE-701D, is to get the Black Hawk "to the high/hot areas that it usually can’t get to right now."
The Army also plans to boost the AH-64D Apache Longbow’s hoverability by installing a new split-torque face gear transmission Boeing has developed for its Block III upgrade to the gunship, scheduled for a Pentagon decision on production this summer. The new transmission is to let the Apache use more of its engine power without adding weight to the aircraft.
Much of the research being done on how to improve helicopters is focused on rotors — especially on ways to change their shape as they fly to improve aerodynamics. Success could mean big payoffs in speed, payload, maneuverability, noise and vibration.
One of the first major tests done in the 40x80x120-foot wind tunnel at Ames Research Center last year after the Air Force re-opened the facility, which NASA had shut down in 2003 to save money, was on a rotor with trailing edge flaps on its blades that are controlled by piezoelectric actuators. Piezoelectric materials flex in response to electrical charges.
The Defense Advanced Research Projects Agency (DARPA), NASA, the Army, the Air Force and Boeing are studying the technology as a way to improve performance and dramatically reduce noise and vibration. Known as SMART (Smart Materials Actuated Rotor Technology), the program is to receive AHS’s 2009 Howard Hughes Award for the year’s outstanding improvement in fundamental helicopter technology at the society’s 65 Annual Forum May 27-29 in Grapevine, Texas.
DARPA is also in the earliest stages of a new program called Mission Adaptive Rotor, which is soliciting industry ideas on how to produce rotors that can morph on-the-fly. Rotor blades that could become longer or shorter, wider or narrower, or change their twist or other characteristics depending on flight conditions might offer dramatic increases in payload and range and even larger decreases in noise and vibration, DARPA calculates.
Industry is at work on less comprehensive ways to improve rotors. Karem Aircraft, for example, has developed an Optimum Speed Rotor whose revolutions per minute can be adjusted for maximum efficiency at different altitudes and cruise speeds. Conventional rotors turn in a narrow range of RPMs, which isn’t the most efficient method in all stages of flight but avoids a variety of complex technological challenges.
Karem’s OSR is being used on the A160 Hummingbird, a 35-foot experimental unmanned rotorcraft Boeing is testing under a DARPA/Army contract. Using a two-speed transmission to compensate for the increase in engine torque when a rotor is slowed, the Hummingbird’s operator can vary its single rotor’s tip speed from 100 percent down to 65 percent RPM. The 2,500-poundUAV stayed aloft nearly 19 hours in a May 2008 test, setting a world endurance record for an unmanned vehicle in its weight class.
The Army is interested in such programs but its near-term rotor research is focused on finding ways to make blades more durable. Erosion caused by the sands of Iraq and Afghanistan and the difficulty of powering de-icing systems through slip rings — notoriously unreliable devices used to transmit electricity and electrical signals from the fuselage to rotor blades as they spin — are priority problems.
Sikorsky and Boeing are working on solutions under shared-investment contracts the Army awarded them last year under its Rotor Durability program, whose goals are to come up with a reliable way to predict rotor blade erosion and then find a permanent solution to the problem. Under the same program, the companies are studying "active rotor blade" technologies to reduce vibration and noise.
Pat Donnelly, director of Boeing Advanced Rotorcraft Systems, said his company also is using the contract to work on its Unloaded Lift Offset Rotor, a project to mount a slightly swept fixed-wing above each of the tandem rotors on its CH-47 Chinook. In theory, the wing could reduce noise and vibration and increase forward speed by making it possible to feather the rotors in the retreating portion of their rotation.
Sikorsky is using its Army Rotor Durability contract to investigate active leading edge slats that could delay retreating blade stall. The slats would extend on a blade’s retreating side and retract on its advancing side each revolution. On its own money, the company also is studying active flaps for rotor blades and, with a German partner, a technology called Individual Blade Control.
Industry, said AHS Director Flater, "is doing its part" but the "high risk stuff, at least for the American companies, has got to come from a shared investment by government and industry. Without a significant increase in science and technology investment, the technology barriers that limit performance will remain."