# What happens if the pilot tries to do a loop in a full-motion simulator?

I know that full-motion simulators, typically used to train pilots on commercial aircraft, have limits to how much they can tilt. They can't go upside down, for example. What happens if the pilot goes outside those limits, by doing a loop for instance? Does the simulation continue with the loop and the just the physical tilt effect gets ignored, or does the whole simulation shutdown and reset?

• during a full loop the perceived gravity is still in "pilot's down" direction: the pilot is still siting on the seat rather hanging by the harness. In this case, gravity is actually doing you a favor to simulate centrifugal force. The tough case is when the plane is flying upside down and that should be the scenario in question. – user3528438 Oct 29 '17 at 15:37
• @user3528438: To achieve a nice, round loop it is helpful to push at the highest point, so the pitch rate is reduced and negative gs are quite likely. When I did my first flight in a Boeing Stearman, I did just that, which resulted in urgent "pull, pull" shouts from the instructor in the back seat. It turned out he hadn't secured his pockets and was starting to loose their content in the open cockpit. Given the low g limits on airliners, looping them will certainly involve negative gs at the top. – Peter Kämpf Oct 29 '17 at 23:22

The motion systems in simulators do NOT mimic the airplane's attitude. Whether the airplane is right-way-up, upside-down or inside-out has no effect on the motion system.

The motion system is used to move local gravity around to mimic the accelerations felt while flying. eg. To mimic the braking during landing, the cab tilts forward, moving local gravity forward relative to the cab, making it feel like you're hanging in the straps due to the braking. Note that when you are braking during landing, the cockpit is level, and yet you are still propelled forward.

• You're right in that gravity is used for simulating sustained accelerations by tilting the platform. Onset linear accelerations are reproduced like in the real vehicle, it's just that that has the whole world to move around in and the motion system has only a metre or so. You're also absolutely correct in that the motion system reproduces accelerations. We're geared to feel those, and get sick when we expect them and cannot detect them. – Koyovis Oct 30 '17 at 10:18

No they cannot do loops. During a loop, the pilot feels an increase in effective gravity (n). A motion system can only increase Z-forces by going up, but has to stop this when the travel stops are reached. It then goes imperceptibly back to neutral position, while the manoeuvre continues without the motion system being able to contribute to it.

So the motion system will tilt and heave during the initiation manoeuvre for the loop, will then heave some more until actuator stroke runs out, and them slowly return to neutral.

Motion systems are great for commercial airliners, which cannot do loops. For fully aerobatic aircraft such as military jets, G-suits and G-seats are used that simulate secondary g-force effects:

• A G-seat lowers the seat pan slightly and loosens shoulder straps when pulling g.
• A G-suit pumps up air chambers around the trouser legs, so that the pilot feels the blood flow restriction that reduces blood being drained from the brain, thereby delaying unconsciousness.

G-suits are used in the actual jets, pilots wear them inside the simulator as well.

• I am interested in what happens in actual flight simulators. (Also, BTW some commercial airliners are capable of doing loops. The ULF for Boeing 737, for example, is about +3.75g which is the same needed to do a loop.) – Tyler Durden Oct 29 '17 at 15:49
• Actual flight simulators for military jets often have no motion systems. In a simulator with a motion system, it just returns to neutral during a loop. – Koyovis Oct 29 '17 at 15:56

At Flight Safety in a Class D simulator, the aircraft I have flown there will do aerobatic maneuvers, such as spins, loops and barrel rolls, but they will not provide realistic motion feedback. However the simulator visual display and instruments will emulate the aircraft, as the dynamic requirements exceed the design limits of the motion simulation.

• I think the curious point of the question is, what exact will it do? We know it will not provide realistic feedback, but will it like, bounce around or shake or ? – kevin Oct 30 '17 at 22:50
• It provides motion feedback until the excursion limits are exceeded then it will resume the axis exceeded after about 100 msec. One time I had a the DG tumble so many aspects of the sim are realistic. The programming changes periodically on the sims. On one recurrent ride the sim was smoother entering a flat spin than on a previous ride. I had the same instructor and he commented that they made SW changes as a military customer who bought training in that aircraft had made some requests. – mongo Oct 31 '17 at 4:14