Fly-by-wire technology has long been credited for enabling military fighter jets to maneuver through the air. As the advanced computer controls continue to migrate into the commercial airliner and business jet fleets — and more importantly, come down in cost — the digital-only revolution is finally gaining some momentum in rotary-wing aircraft.
The Marine Corps in the coming years will replace the aging CH-53E Super Stallion with the next-generation CH-53K heavy lift helicopter — one of the first rotary-wing aircraft being bought by the Defense Department that will incorporate fly-by-wire into the cockpit. The technology displaces the pilot’s mechanical linkages to the flight control surfaces with wires, which will allow a digital signal to “drive” the helicopter.
The Army has yet to embrace fly-by-wire after two failed attempts to introduce it into its rotorcraft fleets — the first time on the RAH-66 Comanche, a light helicopter program that was canceled in 2004; the second time more recently on the UH-60M Black Hawk, the service’s workhorse utility aircraft.
But officials in January signaled that they would consider trying again.
The Army by year’s end will complete a testing program of two Black Hawk helicopters equipped with fly-by-wire controls. At that point, officials will consider whether to upgrade the UH-60M with the system.
“Fly-by-wire technology is better,” said Col. Neil Thurgood, project manager for utility helicopters. “We have 30 years of jet history that tells you that it’s better,” he told reporters at an Association of the United States Army conference in National Harbor, Md.
Analysts and aircraft developers say the technical challenges for integrating fly-by-wire aboard helicopters largely have been overcome. The remaining barriers are a matter of cost and corroborating claims of operational benefits.
Newer military helicopters like the UH-60M have digital advanced flight control systems, which are often confused with fly-by-wire technology. Digital flight controls involve layering computer hardware and software over the aircraft’s existing mechanical systems. Instead of the pilot directly moving the linkages — the control arms, push-pull tubes and the like — his stick-and-rudder inputs feed into electronics that communicate with those linkages to alter the corresponding control surfaces.
In a true fly-by-wire system, there are no mechanical linkages.
The Army several years ago was headed in that direction with the UH-60M upgrade program, which was leading Defense Department efforts to incorporate fly-by-wire technology onto helicopters. Officials tapped Sikorsky Corp., the manufacturer of the Black Hawk, to develop two fly-by-wire UH-60Ms. But instead of moving the variant into production, Army officials in 2008 opted to buy more baseline helicopters while continuing to test the prototypes.
The two aircraft are completing a 400-hour test program in West Palm Beach, Fla. Sikorsky officials said that both systems are performing well and that pilot feedback on practice flights suggests that fly-by-wire is lowering workloads inside the cockpit.
“This grand experiment we’re in should lead to significant data about the operational capability of the aircraft and eventually position us, if the customer desires, to productionize the system,” said Jim Kagdis, manager of advanced programs at Sikorsky Innovations, the company’s technology development organization.
Once the test program is completed, the Army will have to make some choices, Thurgood said. “Do I want to go from where I am on the M-models — a great aircraft — and cut in with fly-by-wire technology?” he said.
Officials could decide to insert the system into the current production run, or they may choose to wait for a future block upgrade. The Army this decade is buying about 75 to 85 UH-60Ms annually in order to maintain a fleet of 2,135 Black Hawks by 2015.
Analysts say the Army might want to think twice about breaking into the current production of the UH-60M to insert the technology.
“If you’ve only upgraded a third, or half, or a fourth of the fleet with the M-model, and then you take a break to develop something new, you don’t know how quickly you can get back on track, or whether the budget will be there,” cautioned Richard Aboulafia, vice president for analysis at Teal Group Corp. “If it requires a significant break in the production run, you have to be really careful in a budget environment like this,” he said.
Thurgood, who has flown the test aircraft, said that the biggest advantage of adding fly-by-wire to Black Hawks is that it increases aircraft handling capability. The pilot’s ability to control the helicopter in crosswinds is much improved and the aircraft itself is more responsive and stable, he noted.
“Those simple capabilities allow the pilot to keep his eyes and head up and out of the cockpit, and allow the aircraft to help the pilot fly,” he said.
When pilots are coming into a landing zone, they become occupied with numerous tasks in the final 200 meters. Not only are they trying to stay aware of potential enemy threats outside the aircraft, but they also have to focus their attention on safely touching down, Thurgood said.
Fly-by-wire controls simplify the process by allowing pilots to hit a button to coax the aircraft into a hover. It maintains position and then descends automatically once it determines that it is clear to land.
There are also secondary benefits. Fly-by-wire allows engineers to take about 484 pounds of mechanical systems out of the aircraft. That equates to approximately 372 parts that would no longer require repair or replacement, Thurgood pointed out.
On the commercial side, fuselage weight-savings benefits have been attained.
“The only thing I always guarantee a customer about a mechanical system is it will wear out,” said Bob Ellis, director of product and systems marketing for Rockwell Collins, a supplier of communications and avionics systems for civil and military aircraft. Fewer parts means fewer repairs, he said.
Because a fly-by-wire system would connect to many subcomponents, aircraft maintenance would also experience improvements.
“As the pilot runs pre-flight checks, we can detect more issues and isolate them early,” said Igor Cherepinsky, Black Hawk flight components lead for Sikorsky. The system also can interpret the operator’s intent at the controls. It could shape the commands that are transmitting to the control surfaces in such a way as to increase component lives dramatically, he added.
“We can design wider airframes because of this, because we’re taking advantage of life-cycle improvement controls,” he said. “We can make airframes lighter and also reduce pilot workload, which is not possible with the current generation of mechanical systems.”
Aviation experts said that helicopters are destined to follow in the wake of their fixed-wing cousins.
“We are definitely moving ahead with fly-by-wire. We don’t foresee building another aircraft with mechanical flight controls at this point,” said Cherepinsky.
Still, there are concerns over having a computer at the wheel.
“There continues to be controversy about the safety of fly-by-wire, or computer-controlled airplanes,” said Hans Weber, president of Tecop International Inc., an aviation consultancy based in San Diego.
Of most concern is when aircraft encounter unusual flight conditions such as turbulence or poor weather on a landing approach. The computer can act erratically and contrary to pilots’ intentions.
“They end up fighting each other,” said Weber. “It’s an ongoing problem.”
Another issue is that it can be difficult to train pilots to concentrate on flying the aircraft during emergencies as opposed to troubleshooting the computer, he said.
When Korean Air experienced a number of fatal crashes involving its fly-by-wire jet aircraft, officials noted a trend in how their pilots responded to in-flight computer difficulties. Whenever they encountered technical problems, the pilots would push buttons rather than focusing on keeping the plane airborne.
Despite those initial hitches, the benefits of fly-by-wire are outpacing its problems, proponents said.
Weber said, “When the pilot is not fighting the computer, the workload is lightened. That continues to be an important consideration ever since we went from a three-crew cockpit down to a two-crew cockpit. That’s a safety implication by itself.”
Moreover, fly-by-wire systems can be programmed to protect aircraft in the event of incorrect control inputs from the pilot.
“The pilot cannot inadvertently break the airplane,” said Weber. Similarly, the controls can be calibrated for fuel economy and other flight characteristics.
In the fixed-wing market, the technical challenges of integrating fly-by-wire onto aircraft have been mastered, said Rockwell Collins’ Ellis. Costs continue to decline as the system is being developed and certified on smaller and smaller airplanes, he added.
Those factors are driving the helicopter market toward making a similar transition. “The technology is there,” said Weber. “I think it really boils down to the cost-benefit equation, whether the benefits that the technology will provide are big enough to justify the costs.”
Fly-by-wire aboard military helicopters has lagged largely because development and design of new rotary-wing aircraft has not occurred in tandem to capitalize on the advancement.
“The opportunity just hasn’t come along,” said Ellis. “We understand helicopter control technology. We understand computing technology. Industry has a good track record now on integration. I don’t think there’s a technical barrier.”
But convincing fly-by-wire’s toughest critics — the helicopter pilots themselves — could be the largest hurdle to overcome.
Veteran pilots worry they will lose the mechanical feedback from the aircraft if the controls migrate to all-digital controls. Flying rotary wing aircraft is a very hands-on process, they say. Not having the rotor, motor and rudder “feel” in the stick, collective and pedals, respectively, could result in more mishaps, they say.
That fly-by-wire controls eradicate tactile feedback from the aircraft is a common misperception.
“That’s an area of significant confusion in the market,” Ellis said. Contrary to popular belief, it is possible to give pilots the physical cues of flight in fly-by-wire controls.
“We believe in giving the pilot controls and the ability to override the system, yet while providing him with full information on the aircraft state and what’s going on,” said Cherepinsky.
On the fly-by-wire Black Hawk, developers have incorporated active controls with force-feedback motors, he said.
“We can actively program the tactile feel of the [mechanical] controls,” he said. “That allows the pilot to concentrate on the mission by just holding the controls.”
Engineers can give pilots additional cues, such as shaking the stick, to indicate that they are nearing a threshold. For example, the collective will shake if the pilot throttles the engine beyond a certain range of torque.
Fly-by-wire could potentially help with training pilots to fly different models of the same aircraft, said Ellis. Pilot interaction with the airplane can be “tuned” across the range so that how one flies the variants is exactly the same. Even if the aircraft are physically different, the pilot cannot tell the difference from a handling perspective, because the computer translates the control inputs, Ellis said.
“That’s a good thing when you have crews that are equipped to fly multiple models,” he said.
Training on the fly-by-wire Black Hawk prototype has shown that a non-aviator can jump into the flight simulator and fly a resupply mission after 15 minutes of familiarization. “The next generation of pilots will appreciate this,” said Cherepinsky. “Training costs will come down.”
Fly-by-wire also permits easier integration of new systems into the aircraft. If Army program officials wanted to add onto today’s Black Hawk the Sandblaster, an obstacle avoidance system that peers into landing zones, engineers would have to hardwire another screen into the cockpit.
The Army is also interested in pursuing an optionally piloted Black Hawk, meaning that the helicopter could fly autonomously.
Cherepinsky said that the fly-by-wire Black Hawk prototypes are production-ready. The software is more than 95 percent complete.