Next-Gen Motion Technology Improving Performance

With the introduction of second-generation electric motion systems for full flight simulators and the further refining and improvement of FFS performance, training devices are becoming more capable of replicating actual aircraft performance. Chuck Weirauch writes.

A new means of evaluating motion performance could be the means to improve the fidelity of simulators to match that of the aircraft dynamics even more. According to Nidal Sammur, FlightSafety International's director of Engineering for Simulation, the company has been working extensively on its second generation of electric motion systems to make them easier to set up and operate. The redesign of some components includes improved diagnostics for maintenance and setup with fewer steps, along with an advanced communication infrastructure, all of which makes the second generation system more robust that the first one.

According to Mitesh Patel, L-3 UK's head of Product Line Management, one of the full flight simulator manufacturer's main areas of focus is on improving the diagnostics in the motion system. One of the reasons is because the company has seen a reduction in the experience and skills level of the technicians that maintain those simulators.

"In the past, we have had more experienced engineers working at our customers' facilities," said Patel. "What we have seen going forward is that technicians' skills are not as highly developed as they used to be in the past. These newer technicians rely more on diagnostics to tell what is going on, so we spent a lot of time developing a more robust diagnostics tool so those with limited experience can get our flight simulators back in operation if there is something wrong."

According to Jim Takats, president of Opinicus, there are some ongoing advances in the 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 are being incorporated into the motion system hardware.

"From a performance standpoint, 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 our efforts on enhancements to the REALCue motion drive algorithms called oEMDS, which execute at 2000Hz. Our latest generation of oEMDS provides for optimization of the available workspace, using specially designed predictive software which provide for a continuous, real-time optimization of the motion system positioning in order to maximize the available workspace for upcoming maneuvers. This is particularly important during training scenarios, such as those for adverse weather conditions such as windshear, microburst, approach to stall, stall and stall recovery training."

Motion platform provider Moog provided one example of how motion technology has improved by beginning the rollout of 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.

"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 troubleshoot the whole system for faults. We are doing everything we can to improve maintainability, reduce the burden on maintenance personnel and reduce downtime."

According to Ton Stam, International Account Manager for Netherlands-based E2M Technologies, his company is now seeing the introduction of the second generation of electric motion systems, featuring better reliability, motion quality, diagnostics and cueing. These improvements have been achieved by integrating newer and more COTS components into the motion systems, but also by continuing development which resulted in several innovations not found in earlier systems. Noticeably, these advances are new cueing algorithms for optimal workspace use and new joint designs to provide lighter, stiffer and lower simulators.

For its part, E2M has made extensive R&D efforts to maximize the smoothness of the electric motion system, Stam said. Together with advanced motion cueing software with the company's patented Direct Workspace Management wash-out algorithm, this leads to more fidelity in terms of motion quality and available workspace. In addition, the company's integrated upper frame solutions allow the construction of the lighter, more rigid simulators with a lowered center-of-gravity (CoG) height and eye reference point. These improvements result in improved performance of the motion system and a larger available workspace.

Establishing Standards So that flight training organizations can take advantage of the latest in motion technology, the training equipment providers interviewed by CAT 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 key thing in the commercial aviation world is to keep operating costs low, and L-3 UK is achieving that with lower power consumption required by its hybrid hydraulic/electric motion systems than with full electric systems. Patel said that the company is cutting costs by reducing the footprint of the equipment itself. Slimming down real estate requirements means that training centers don't need as much space for motion systems.

According to Bartel, Moog is working on a global software initiative which would have one graphical user interface (GUI) for all motion-based systems to have 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.

New Motion Cueing Test The simulation industry has long based the fine tuning of its motion systems on the subjective analysis of simulator motion performance by pilots. There are currently no standards for motion cueing, and up until now there has been no way to objectively test and measure the motion drive algorithm that drives the simulator's motion platform. That has now changed with the development of the OMCT.

The OMCT checks the relative gain and phase errors between the aircraft data and the simulator performance at specific frequencies. It looks at the motion drive algorithm, the motion hardware and implementation time delays, all in one. The combination of these elements should not be significantly out of phase with the airplane.

"We only regulate what we can measure, and all the rest is done subjectively," said Sunjoo Advani, president of International Development of Technology B.V. and the developer of the OMCT, along with Ruud Hosman, managing director of AMS Consult. "So there has been no yardstick by which to measure the cueing, and we could only measure the performance of the robotic platform. But that is not testing the cueing algorithms, which themselves introduce the biggest amount of phase, equating to significant time delays."

"When we test the drive algorithms, they may be different for every simulator," Advani continued. "This is because those performance values are currently defined through a subjective evaluation tool, which is the pilot evaluating the simulator performance. So there is a potential for significant differences in performance and perception, even between the same aircraft-type simulators produced by the same company. We don't tune the airplane to the pilot's liking, but we have been getting away with doing this in our simulators. Inconsistency is one of the reasons behind the motion/no motion debate."

To verify that assumption, the IWG Motion Task Team employed the OMCT to compare the overall performance of eight qualified simulators. What they found was a significant difference in performance between those devices. The differences stem from the fact that pilots were subjectively assessing simulator performance, and sometimes under different simulated conditions, Advani said.

"We have been tuning our systems based on what a pilot thinks subjectively, but many of these motion cues are very subtle," Advani reiterated. "The OMCT is a big step towards reducing the subjectivity of evaluation and helps us better tune our systems. We want to minimize the false cues, which is the top priority in motion cueing. We want to get the most out of the simulator system, and the way we do that is to try to get a good performance in the frequency range that matters to the pilot. We want to emphasize the good cues that help the pilot close the control loop and minimize the false cues that are not present in the aircraft and get rid of the false cues."

"At Opinicus, we believe if you are going to put motion on a simulator, then it needs to be good motion and it needs to enhance the pilot training," Takats said. "We believe motion is a very important cue for pilot training, particularly for high-gain tasks. However, we believe that no motion is better than 'bad' motion, so the industry needs to be very careful in order to make sure that motion systems that are being used are 'good'. And that is the purpose of the OMCT."

The simulation industry as a whole has now embraced the concept and practice of employing the OMCT to be used as a tool to improve simulator motion cueing performance. According to Advani, the industry agrees that it should serve as a new global standard. Patel said that L-3 UK has been taking a very active role in the IWC Motion Task Team to make sure that whatever motion cueing test is developed is understood by everyone in the industry and that the industry backs it as a whole, and that it adds value.

Since the OMCT has been shown to be a valid means of defining future motion system requirements, the formal acceptance of the OMCT process will be made official when it is published as Amendment 4 of ICAO Document 9625, the Manual of Criteria for the Qualification of Flight Simulators, scheduled for publication in 2014.

"Now we have a rigorous test that takes out much of the subjectivity," Advani pointed out. "Even though subjective tuning will continue to complement the OMCT, until a fully objective 'mathematical pilot' is someday accepted by industry, the yardstick is now in place to measure simulator motion performance. By providing the industry with an objective 'target', it is going to drive the industry to improve the quality of motion cueing, and we are starting to see this already, as some companies are already using it and seeing improvement in their devices."

FSI has also embraced the OMCT algorithm technology developed by the ICAO IWG. It is a good way to quantify motion cueing as bad or good motion, Sammur reported. With the OMCT, FSI can also look at the simulator with an overall system level approach to increase its performance. So far, improvements in the tuning of the motion cueing system based on objective test results rather than subjective pilot reports have been "really amazing," he said.

"Until now, the tuning of the motion cueing system has been done through subjective feedback from pilots," Sammur explained. "Now we have this OMCT technology. With this new technology, we can focus on comparing the motion base and what the pilot feels to the dynamics of the airplane to the simulator."

When John Van Maren, FSI's Vice President for Simulation, who is also a pilot, first experienced the motion system improvements based on the OMCT test data compared to the traditional subjective method, he was also quite impressed with the difference in simulator performance.

"My initial comment was 'wow', followed by how did we live with what the industry has done for so long," Van Maren said. "It's just a night and day difference in the cueing and the realism. You can close your eyes and actually visualize what is happening just from the motion cueing. It was really impressive."