Motion ?

Regulatory bodies such as the Federal Aviation Administration (FAA) allow Level D Full Flight Simulators (FFS) to be used for pilot aircraft type conversion and periodic pilot recertification with a zero flight time requirement. Level D simulators are required to provide motion feedback to the crew, which is done through a motion platform on which the simulator cabin is mounted.

The motion platform must produce accelerations in all of the six degrees of freedom (6-DoF) that can be experienced by a body that is free to move in space. To maintain the proper view Out The Window (OTW), it follows that the display system must also be mounted on the motion platform, i.e., the motion platform is going to be moving large structures around with considerable force.

Until recently, the motion platforms used on these commercial simulators were driven by hydraulic actuators. Wikipedia has a neat little animated GIF that shown a Stewart platform being driven with 6 -DoF by 6 hydraulic actuators like the motion platform of a FFS might be.

It should be noted that the motion system does not actually mimic the airplanes attitude in a given scenario, rather, it is the acceleration forces on the body that are simulated. The motion system is designed to deliver an effect called acceleration onset cueing, the effect is more comprehensively described in the Wikipedia article, but in brief, the effect is achieved in three phases :

• The initial acceleration of the cockpit is reproduced by rapid movement of the platform which is detected by the occupant's inner ear balance mechanism
• Because the jacks have finite travel limits, the platform can only move over a short distance, so, after the initial acceleration force has been simulated, the platform motion is slowed at a rate low enough such that it is imperceptible to the occupant, before coming to a stop.
• The platform is then slowly reset to its neutral position, ready for the next motion event.

Operating in tandem with the visual system, the motion system is designed to give the impression of the movements and forces that the pilots would experience when performing the equivalent manoeuvre in a real aircraft. Although the absolute distances moved are relatively small, the motion platform needs to perform fast movement over sufficient distance to fool the body into thinking that is it moving.

The Canadian company CAE is a leading manufacturer of commercial full-flight simulators, their website has some great photos of their simulators that illustrates the size of these things - they are NOT small and neither are the buildings that they put them in! The actuators only move over relatively short distances, say 1-2m before imperceptibly moving back to the neutral point, but even so, considerable space is needed around the simulator cabin to achieve this.

Again, courtesy of Wikipedia, here's an example of a FFS used by Lufthansa that illustrates the space needed to install and operate one.

In addition to the motion features, the ability of FFS to generate realistic simulation of turbulence and other aircraft vibrations should not be forgotten either.

Do I want one? - Of course I do, but it's not realistic aspiration.

Full motion simulation is starting to come within the reach of the enthusiastic amateur though, there are now 6-DoF platforms driven by electric motors that are smaller and more affordable, for example, the system made by CKAS Mechatronics in Australia. They manufacture a range of motion platforms, including the 6-DoF "W" series shown below

This product has small stroke actuators with linear displacements in each axis of 150mm, but in the parked position, the platform still sits up to 1m from the floor. You'd then have to sit the cockpit and visual system on top, so the space requirements are still significant, as is the cost. A motion system of this type would still cost in the region of $50,000.

In my case, there would also be access issues, commercial simulators often have movable access platforms or gantries that can be retracted once the pilots have entered the cockpit, again, meaning more space is needed for the setup.

As well as the cost and space requirement of the hardware, there is also the question of software. If the motion sensation is at odds with the visuals, then this is likely to be a worse case than not having motion at all. I don't know the details, but I imagine that tuning a FFS to get the motion and visuals "in-sync" is not a trivial exercise and therefore is likely to incur significant cost in itself.

Another issue that comes to mind is the impact of movement on projector stability. As I noted earlier, the display or projectors/screen would also need to be mounted on the motion platform. For optimum results from a projected system, alignment of the projectors is critical and likely to be compromised by sudden and frequent movement of the supporting structure.

So, for a whole host of reasons, I won't be going for a full-motion simulator and, like the vast majority of home users, will be going for a "fixed base" simulator. Similar devices are used for training in the airline industry and are used to deliver cost-effective training in scenarios where FFD devices are not required, e.g., normal and abnormal procedures, ground operations and in-flight training, as well as general cockpit layout familiarisation and operation. They are often referred to as Flight Training Devices (FTD) or Fixed Base Procedural Trainers (FBPT).