The Electric Trend

Motion systems inject an invaluable level of fidelity into a flight crew’s simulator training experience. Dramatic advancements in performance, increased cost efficiencies and other developments have boosted the popularity of electric motion systems over their hydraulic cousins.
By Marty Kauchak

Electric motion systems have become services’ choice for aviation trainers.

Motion systems inject an invaluable level of fidelity into a flight crew’s simulator training experience. While current technology constraints prevent the use of motion systems in some fast-jet applications, these systems are widely used in the services’ rotary and other fixed wing trainers. Dramatic advancements in performance, increased cost efficiencies and other developments have boosted the popularity of electric motion systems over their hydraulic cousins.
The Need for Motion

A full-motion simulator provides feedback cues that the training audience interprets, knowingly or unknowingly, with their senses to control the “air vehicle.” “In fact, motion cues provide a quicker response feedback cue to your brain to sense that you are moving than does a visual cue of that same movement,” pointed out Dr. Joe Sheehan, human systems analyst, Naval Air Warfare Center-Training Systems Division (NAWC-TSD). The absence of motion feedback cues provides for a diminished simulation scenario. “This is due to the longer time it takes the pilot to process what he is seeing, making it more difficult to perform both routine and difficult maneuvers or control precise operations,” reasoned Sheehan, and added, “It may be easier to describe what we see than it is to describe what we feel, but the loss of motion cue feedback is no less dramatic than the loss of the visual scene. It would be like using your sense of touch and balance.”

Equally compelling reasons result in decisions to not use motion bases in flight simulators. The Navy and Marine Corps’ F-18 and AV-8B trainers do not have motion systems since their actual vehicle performance exceeds the acceleration capabilities of a motion platform. “Therefore, motion onset cues cannot be accurately simulated,” pointed out Anthony Maggio, aerospace engineer, NAWC-TSD.

A full motion system does not support the demand for some aviation trainers to be portable and expeditionary. A tradeoff was made to provide portability instead of motion systems when the CH-46E and CH-53E aircrew procedures trainers were delivered. The trainers operate inside an enclosed, heavy-duty, expandable trailer. “These enclosures are not large enough and rigid enough to house a motion system and withstand the reaction forces associated with movement of the training device,” said Maggio.

And at the end of the day, available resources also determine whether a flight simulator will have a motion system. “Some MH-60S and MH-60R tactical operational flight trainers don’t have motion systems primarily because of a budget constraint tradeoff to increase the number of training devices available. These devices provide tactical training but offer less flight fidelity than a full-motion simulator because of the lack of cueing available to your senses,” remarked Sheehan.
Electric Versus Hydraulic
Electric motion systems have become the product of choice for military flight simulators due to their lower life cycle costs, reduced oil leaks and other environmentally friendly attributes, and increased performance when compared to hydraulic systems.

These advantages aside, there is one reason for hydraulic systems’ popularity in training devices. “So far, the main issue has been payload,” pointed out Peter Jarvis, chief systems engineer, CAE. While hydraulic systems can support between a 38,000-to-40,000 pound (lb) (17,236 to 18,143 kilogram) payload, an electric system may support up to 32,000 lb. Indeed, Moog FCS also delivers electric motion systems that can support up to a 32,000 lb payload. “This is enough to carry the majority of all simulator payloads,” Michiel Post Van Der Molen, simulation market manager, Moog FCS, told MT2. However, industry is raising the bar for this standard, as CAE’s Jarvis reports that his company is “working on a solution with a pneumatic-assisted electric motion system that would support up to 40,000 lb payload”

Despite these advantages, Moog FCS and other providers continue to deliver hydraulic systems based on the requirements of their government customers. NAWC-TSD’s Maggio pointed to the performance of hydraulic systems with heavy payloads—in excess of 25,000 lb—noting “the superior ability of the hydraulic system to deliver performance in terms of acceleration, velocity, frequency response and other factors, while moving large payloads.”
But this advantage appears to be short lived.

“Let’s make a critical statement that the question of performance revolves around a pilot sitting in the seat of simulator,” said Charles Bartel, product application manager, Moog FCS. Bartel, an industry veteran with more than 35 years in motion system products, added, “The bottom line, as motion cueing has increased in fidelity and as more is expected from these systems, performance has to be such that unless you tell the pilot that he or she is sitting in a simulator with an electric motion base, they will not know the difference [from a hydraulic system].”

CAE’s Jarvis noted, “Electric motion is a step forward, not just in life cycle costs and being environmentally friendly, but in the quality of motion, too.” To solidify his opinion about gains in the quality of electric motion, he cited a cross-talk test conducted by CAE. The test evaluates an electric and hydraulic motion systems’ ability to not induce undesirable cues in other motion base axes during a command response to one axis. “The cross talk for electric motion using a 1-Hertz command is better than a CAE hydraulic motion by a factor of 10,” he recalled.

So, the debate of electric versus hydraulic is no longer performance-based, it’s the cost of ownership, asserted Bartel.

In one case the government-industry teams exceeded expectations with respect to energy savings when they used electric motion systems. An internal Moog FCS analysis from 2006, predicted cost savings of about 70 percent for electric systems compared to hydraulic systems. “In reality, the original equipment manufacturers are reporting energy savings up to 90 percent with electric systems,” reported Bartel.

Electric systems also require less maintenance. “The preventive and corrective maintenance on an electric system is much, much less,” emphasized Post Van Der Molen. Hydraulic systems have oil filters, large pumps and other high-maintenance subsystems, and a requirement to drain, fill and resupply large oil reservoirs. Conversely, electric systems have minimal lubrication oil and other cost-saving design attributes. Legacy systems, that tend to be hydraulic, also have analogue control systems that are becoming very difficult to maintain. “Those are huge cost drivers for the simulator site,” added Post Van Der Molen.

Moog FCS’s other motion systems’ advancements include inserting more troubleshooting steps into the software at the maintenance-technician’s level. “A maintenance man can take our current software and push a button to play a recorded motion profile and automatically collect data. In about two minutes, you can compare the output of that test to a follow-on test and determine very quickly whether your system is degrading,” said Bartel. The recommended preventive maintenance for fielded systems is two-days in duration.

These and other developments are allowing electric motion systems to achieve almost near-perfect reliability rates.

The Army’s Flight School XXI training site near Fort Rucker, AL has an increasing number of high-fidelity, electric motion simulators supporting the TH-67, delivered by FlightSafety International, and other rotary aircraft. “In November of 2007, Flight School XXI celebrated 100,000 hours of training on the TH-67 simulators with every simulator and their sub-systems, including the motion systems, performing at an unprecedented 99.985 percent reliability rate,” reported Steve Phillips, director, communications, FlightSafety. Computer Sciences Corporation is the FSXXI prime contractor.
Motion System Providers

For its part, CAE continues to deliver hydraulic and electric motion platforms. Of note, almost all of the company’s flight simulators ordered by civilian airlines since 2007 include electric motion systems.

CAE’s standard hydraulic system has a 54-inch (in.) (1,372 millimeters) actuator stroke, whereas the company’s electric motion systems are delivered with 60-in. and 42-in. actuator strokes.

CAE’s electric motion systems are included in a number of recent bookings for military flight simulators. One contract provided two EADS CASA C-295 full-flight simulators, one for the Brazilian Air Force and a second for the EADS CASA C-295 training center in Seville, Spain. A second contract will provide for a 2009 delivery of a full-flight and mission simulator for the Royal Australian Air Force’s new A330 Multi-Role Tanker Transport aircraft.

FlightSafety International, another provider of fixed-wing and rotary aircraft training devices, has put into service more than 50 of its completely electric motion systems. The first delivery was made in May of 2005 on a C-17 weapon system trainer. “That system was the first electric motion platform ever produced that was rated for a payload of 32,000 lb and capable of achieving a Level-D qualification under Federal Aviation Administration (FAA) or European Joint Aviation Authority (JAA) Document JAR-STD [Helicopter Full flight Simulators],” recalled Steve Phillips, director, communications, FlightSafety. Since that time, FlightSafety has produced a steady stream of simulators equipped with actuation lengths of 60 inches as well as 36 inches.

“The FlightSafety International electric motion system was developed in close cooperation with actuation industry leader Moog FCS,” recalled Philips. FlightSafety provided some unique and proprietary design constraints to Moog FCS which produces the motion actuators. “This cooperation continues as the system enhancements are developed and implemented. The control of the electric motion is provided by FlightSafety’s own electric and control loading software, which gives the system the highest fidelity and maintainability in the industry,” added Philips.

Other simulated aircraft equipped with FlightSafety’s electric motion system include UH-60, CH-47, H-1, Bell 412 and more than a dozen civil aircraft qualified by FAA, the JAA/European Aviation Safety Agency and other regulatory organizations.

Moog is the provider of electric and hydraulic actuating systems for numerous military and civilian flight trainers. One of the company’s flagship programs provides 60-inch actuators and other electric-motion system subcomponents for FlightSafety International’s Flight School XXI’s TH-67 trainers described earlier.

The most recent FSXXI milestone in motion systems was announced in February 2008, when Flight School XXI subcontractor L-3 Communications’ Link Training and Simulation announced its two delivered OH-58 operational flight trainers (OFTs) entered service with the Army.

“Each OH-58D OFT high fidelity cockpit moves on a six degree-of-freedom electric motion system. A supplemental secondary motion system simulates vibration associated with helicopter flight. Kiowa Warrior aircrews view out-the-window computer-generated imagery, produced by a personal computer-based image generation system, through both wide field-of-view and chin window displays,” Lenny Genna, L-3 Link Simulation and Training’s vice president, Army programs, told MT2.
Forecasts

Electric motion systems will solidify their position as the system of choice in service simulators. “We think there is also an opportunity to improve the quality of motion cues—the motion cueing algorithms themselves and the aircraft dynamic models that feed the motion cues,” said Jarvis. “We think there is room to improve the fidelity of the experience. It’s my opinion, but electric motion gives us an opportunity to advance the fidelity of simulator cueing overall,” he added.

“What we see in simulation is in the new systems being built, 90 percent or more, have electric motion bases and that includes military and civil [applications],” said Moog FCS’s Post Van Der Molen.

For 2008, FlightSafety will deliver approximately 30 simulators equipped with electric motion, several additional systems that do not have full motion but incorporate electric control loading, and many more already slated for 2009. Aircraft to be supported by the electric motion systems already booked are the C-130, TH-1H, V-22 and C-17.
Industry’s Help Needed

The services have a number of suggestions for improving contemporary motion-capable simulators. Five items on NAWC-TSD’s short list included more freedom of movement, or excursion, capability; increased performance capability that would deliver higher accelerations, higher velocities, high frequency responses and other outcomes; smaller simulator footprint so more training devices may fit into an area; reduced power requirements that would further decrease life cycle costs; and investigating new ways to provide sustained motion (G) cues to pilots.