Motion Systems

Motion systems technology continues to evolve. MS&T’s Chuck Weirauch reports.

Although motion systems technology for aircraft simulators has not changed significantly since the introduction of electric motion platforms in 2006, the simulation industry has seen the recent introduction of second-generation systems that are designed to address the problems and issues experienced with the first-generation platforms. Another development in the marketplace is more emphasis on motion cueing technology to refine performance and increase the realistic simulation of actual aircraft motion and attitude.

Incremental Change

"One of the areas where we are seeing improvement for some of what I would call the first generation of electric systems is that they were fairly complicated, so we saw some early reliability issues of the system," said CAE's Senior Technical Fellow Nick Giannias. "Maintainability was a critical concern for customers."

Now what his company is seeing is that motion system manufacturers are learning from their systems in the field and incrementally improving the capability of their products, while increasing their reliability, maintainability and troubleshooting. Not exactly exciting work, but all a part of the maturing process for the technology and incredibly important to the simulation and training industry, Giannias pointed out.

James Takats, President of Opinicus, noted that there have been some ongoing advances in motion hardware, which relate largely to improvement to the motion legs with respect to maintenance, reliability, quality control and other factors. As electric motion system hardware has been fielded for about seven years now, feedback from the users' maintenance departments are being listened to by industry and improvements incorporated into the motion system hardware, Takats stated.

According to Ton Stam, International Account Manager for Netherlands-based E2M Technologies, innovative mechanical designs such as rotary actuators have made it possible to use full six-degree-of-freedom (6-DOF) motion systems in applications where limited space is available. He feels that this development is especially interesting for mobile military vehicle driving simulators or construction equipment simulators. As simulation technologies advance and become more affordable, there is a healthy growth in demand for military vehicle simulators, ranging from armored vehicle driving simulators to full mission helicopter simulators, Stam added.

According to Stam, in most simulators, the performance-limiting factor is not the motion system itself, but the structural integrity of the simulator as a whole, including the complete upper structure. Customers are therefore looking into more integrated designs that have sufficient rigidity to handle the dynamic behavior of the motion system and improve the overall performance by reducing weight and the center-of-gravity (CoG) height, he explained. .

In response, E2M has developed an innovative alternative for the traditional simulator construction, Stam continued. By integrating the customer base frame with the upper frame of the motion system, the company's customers now have a more rigid and lighter-weight mounting surface available to interface with their cabin or cockpit and visual system. This solution not only lowers the CoG of the total structure, but also lowers the eye reference point of the driver or pilot. As a result, a larger physical workspace is available, resulting in a more realistic simulation, Stam pointed out.

Moog will rollout its next-generation motion platform system this year, according to Charles Bartel, the company's Product Application Manager for Simulation. The new system features a redesigned cabinet that significantly reduces the number of fuses and replaces them with circuit breakers that are monitored through a control panel, Bartel explained.

"Now that electric motion technology has been widely accepted, we are making minor advances to improve performance," Bartel pointed out. "For example, in our next-generation system we are putting in technology that eliminates all of the secondary maintenance messages. This will reduce service time significantly, because now maintenance personnel won't have to trouble-shoot the whole system for faults. We are doing everything we can to improve maintainability and reduce the burden on maintenance personnel and reduce downtime."

Motion Cueing

One of the major goals of the industry has been to improve the fidelity of flight simulator performance to provide a more realistic and immersive training experience for pilots, including motion cueing. CAE has been focusing its performance improvements in the area of its vibration models in order to make the performance in their flight simulators as realistic as possible, Giannias said. That is because vibrations are a powerful cue to a pilot in order to understand what is happening to their aircraft, he explained.

"This is super-critical in helicopter simulators, because pilots experience more vibration in these airframes," Giannias said."This is a real challenge as helicopters become more sophisticated. We are improving our models to make sure that we accurately simulate current and new-generation aircraft."

To improve motion cueing in its products, Opinicus has developed motion cabinets to drive both legacy hydraulic motion systems as well as new electric motion systems, Takats said. This system is called REALCue. Opinicus is focusing its efforts on enhancements to the REALCue motion drive algorithms called oEMDS.

"Our latest generation of oEMDS provides for optimization of the available workspace, using specially-designed predictive software which provides for a continuous, real-time optimization of the motion system positioning in order to maximize the available workspace for upcoming maneuvers," Takats described. " This is particularly important during training scenarios such adverse weather conditions as windshear, microburst, approach to stall, stall and stall recovery training, in-flight refueling, and other mission-specific training events that are crucial for providing the best training and the best- prepared warfighters. REALCue is largely recognized by our users as the state-of-the-art in motion cueing."

G-Training Full-Flight Simulator?

Ever since the attempts to provide a 6-DOF full-flight simulator for advanced jet fighters proved unfeasible back in the 1970s, flight simulation manufacturers and the world's military have largely relied on fixed-base jet fighter flight simulators like the Lockheed Martin F-35 Full Mission Trainer (FMS). The FMS does not feature a G-cueing motion seat but rather relies on the Rockwell Collins Griffin Dome, which provides high- resolution visuals and a 360-degree field of view to visually impart motion cueing for pilots.

The US Air Force and other military services around the world require G-training in centrifuges for their advanced jet fighter pilots and other aircrew, and some require G-cueing motion seats in their fixed-based trainers. But Ken Ginader, retired U.S. Navy Captain and a highly qualified Naval Flight Officer, says that such training is not adequate for future potential combat scenarios that involve more sophisticated air defense systems than those experienced over Iraq and Afghanistan and demand high-G maneuvers. Ginader is the Director of Business Development for ETC Tactical Flight Training Systems, which provides high performance motion systems (centrifuge-based) for all stages of flight training, including G training.

"I compare the fixed-motion simulator to flying the airplane in the hangar at zero knots and one G, and that's not the way you fly the airplane," Ginader said."If you are only training in an FMS, you won't be prepared for real combat environments."

ETC's answer to this problem is the Authentic Tactical Fighting System (ATFS-400) that can be reconfigured to be essentially a high-performance motion system that combines the capabilities of a full-flight simulator and a centrifuge. ETC has shipped the final main motion system components of the ATFS 400 Model 31 to the US Air Force's 711th Human Performance Wing’s new complex at Wright Patterson Air Force Base in Dayton, OH.

The ETC simulator will be used by the USAF to support aircrew high-G training, acceleration research, as well as a variety of other training and research initiatives. According to Ginader, the current Air Force contract does not include the components that would allow the ATFS 400 to be configured as a high-G full-flight simulator, such as a high-fidelity cockpit, but he hopes that the service will add this capability as an upgrade which can be provided by ETC sometime in the future.

"Now with motion technology getting to a level that it has never been before, it has provided another opportunity to look at the flight training continuum," Ginader summed up. "And now that more flight training has to go into simulation, doesn't it make sense that some of that training has the same motion as the aircraft? I think that intuitively that does makes sense."

Lowering Cost, Establishing Standards

So that flight training organizations can take advantage of the latest in motion technology, the training equipment providers interviewed by MS&T are working to lower the costs of integrating such technology into training programs. For example, according to Takats, Opinicus is working with motion hardware vendors to lower the cost of electric motion system hardware. One item that is being explored is simplifying the actuator design and maintenance. The initial cost of motion is important, but the overall life-cycle cost is what needs to be considered, he emphasized.

The company is also standardizing its motion systems, as well as the installation procedures and manufacturing techniques employed in an effort to lower costs, Takats added. Stam said that at E2M, motion systems, and specially the smaller ones, are regarded as a commodity rather than a project. This means that the company builds its systems in large batches to reduce costs and delivery times, leading to significant cost savings for its customers, he explained.

According to Bartel, Moog is working on a global software initiative that would have one graphical user interface (GUI) for all motion-based systems and the same control infrastructure in order to reduce maintenance costs. Takats is working with the Royal Aeronautical Society (RAeS), the International Civil Aviation Organization (ICAO) and the International Working Group (IWG). As Chairman of the IWG Motion Task Team, he is leading the effort to develop a set of Objective Motion Cueing Tests (OMCT) in order to help develop an objective means to determine between "good and bad motion cueing", as he described it.

Lower-cost Motion Platforms

Advancements in motion cueing technology are also now being applied for lower-cost flight training devices as well. At the 2013 Interservice /Industry Training, Simulation and Education Conference (I/ITSEC), show attendees can check out one example, Precision Flight Control's DCX Max Promotion FAA and Transport Canada-approved Advanced Aviation Training Device (AATD). This device features a D-BOX 3 Degree-of-Freedom (3-DOF) motion cueing system, and will be located within the joint D-BOX and Precision Flight Control exhibit area.

The D-BOX motion base is designed with four electric actuators and coupled with software for accurate replication of aircraft pitch, roll and yaw. The actuators are in the four corners of the base so that the system parallels the motion of much more expensive motion bases, said Mike Altman, Precision's CEO and President.

"The most important factors for us is that the D-BOX offers seat-of-the-pants feel throughout the full flight regimen, offering roll, pitch, yaw, heave, stall buffet and turbulence," Altman explained. "These cues provide pilots with a realistic training atmosphere with common distractions found when flying a real aircraft. We meet a much higher standard than is required, since motion is not required at this level of flight training device. Half of our customers prefer motion over non-motion."