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Civil full flight simulators are mounted on top of a motion system. It is an expensive system, requires higher and therefore more costly buildings, and requires greater structural integrity of the simulator itself. A cost driver of considerable proportions.

Why do we have to have motion systems on simulators? We get motion information from our central and peripheral vision, right?

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    $\begingroup$ Your ears have more say over what your body perceives as "up" than you may think. $\endgroup$ – Ron Beyer May 9 '17 at 22:55
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    $\begingroup$ I'm not really sure what "cost effective" means here. Full motion simulators are required by regulation for certain types of flight training. If you want the training, you pay for the simulator. You could ask why the regulations exist, as opposed to allowing non-motion simulators, but that's a different question. $\endgroup$ – Zach Lipton May 10 '17 at 4:39
  • $\begingroup$ Some years ago there was a push from the industry to do away with motion systems due to the cost reasons in the OP. $\endgroup$ – Koyovis May 10 '17 at 22:44
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Here is what a lot of people experiences about simulator: they sit on a chair in front of a desk at home, run some PC flight simulator game with a yoke, and they can do pretty much anything - in the simulator. Many of these simulators are very real, especially with quality addons. Since they fly very good in the simulator, they should be good pilots too - after all, you just read the readings on the instruments then react to them! How hard can that be, huh?

It turns out, we are biologically wired to orient ourselves with our ears. It is the result of evolution, with us staying on the ground for the past million years or so. When we fly, the body sends "wrong" signals to the brain. These signals are interpreted as "instincts", and since we have trusted our body's sensation ever since we're born, they are very hard to fight against. Many new pilots faced trouble reacting to instrument readings, because their biological body is telling them the opposite of what the instrument is indicating, creating doubt.

Full-motion simulators solves this problem. The movement of the simulator itself is, obviously, restricted. However, it is designed with ear-balance in mind. For example, the simulator will slowly right itself to upright over time, but the rate of rotation is just under the detection threshold of the ear-balance mechanism. Therefore, the occupants will not feel the simulator platform resetting itself. This allows pilots to practice with the sensation associated with attitude changes, in a controlled environment, with a much lower risk (and much lower cost) than flying in a real airplane.

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  • $\begingroup$ Agree, asking if it is cost effective is the wrong question. It is an absolute necessity, and yes it is not cheap. $\endgroup$ – Koyovis May 12 '17 at 10:49
  • $\begingroup$ @Koyovis Asking if it's cost effective is precisely the right question. If there were something different to spend the same amount of money on that would do more to increase aviation safety, it would irresponsible to spend it on this rather than that. $\endgroup$ – Curt J. Sampson Mar 23 '18 at 15:18
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While a simulator with motion simulation is more expensive to own/operate than a simulator without motion simulation it is still cheap compared to a real airliner

So if the regs say a particular type of training can be done on either a real airliner or a full motion simulator then it is likely to be cost-effective to use the full-motion simulator.

And as a bonus you can run scenarios with a high level of realism that would be too dangerous to run on a real airliner. Emergency training in real aircraft has to strike a balance between training pilots to deal with adverse conditions and avoiding accidents during training.

Why do we have to have motion systems on simulators? We get motion information from our central and peripheral vision, right?

A pilot gets motion information from 3 different sources.

  1. His body
  2. His vision
  3. His instruments.

Unfortunately item 2 on that list is sometimes unavailable and item 1 has terrible medium to long term accuracy.

In normal life our brain uses a combination of our bodies motion sensitivity and our perhiperal vision to build up a picture of where we are. In the absense of visual information it will continue to try buliding up a picture of where we are but the accuracy of that picture will quickly degrade.

It's one thing for a pilot to be able to make correct decisions when his only source of motion information is his instruments. It's quite another to make correct decisions when his body and his instruments are apparently in conflict and he has no visual references.

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    $\begingroup$ +1 for the first sentence alone! Additionally, crashing in a simulator is far more cost effective than crashing in a real plane, both in monetary cost and in lives lost. $\endgroup$ – FreeMan May 10 '17 at 14:07
  • $\begingroup$ Indeed, which is why you can run scenarios that would be too risky to run or would require compromises to accuracy in the name of safety on the real thing. $\endgroup$ – Peter Green Mar 23 '18 at 15:00
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The fact that this is how flight simulators are built gives you the answer: yes, it is cost-effective.

It doesn't matter what the cost is, since they are built like that, the cost must be worth it.

It might be more useful to ask: Why are full-motion systems considered necessary to provide adequate simulation for pilot training?

One answer to that would be that only motion systems can provide a reasonable simulation of, for example, turbulence so violent that you can't even focus properly on the instruments.

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  • $\begingroup$ I do not see how this answers the question. It might fit better as a comment. You first offer an answer in the form of: It it is cost effective, it will be done; it is done, therefore it must be cost effective, which is a logical fallacy. You then go on to offer a legitimate reason why simulators are built and used, but one that does not address whether or not they are cost effective. $\endgroup$ – J Walters May 10 '17 at 3:24
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This question borders on opinion. Is it cost-effective, as in can a company make/save money by purchasing a full-motion machine to complete required flight training? Certainly it is for some.

But I think what you're really getting at is whether it's cost-effective in terms of reducing accidents. That is really hard to determine. Certainly the authorities think so or they wouldn't require it to fulfill some types of training.

Some might say its usefulness for helping the pilot learn how to use—or more importantly disregard—their vestibular senses is very limited.

The problem is that it is impossible to simulate many of the somatogyral illusions that get pilots in trouble when they lack visual cues. For instance the "leans." This happens in a banked turn. When the plane banks your inner ear feels your body rotate to the side, but in a coordinated turn the the overall feeling of "down" remains in the same direction. There is no way to simulate this. The simulator has to decide whether to tip to simulate the bank—in which case you feel yourself sitting at an angle—or to stay upright simulating the sum of forces. The only solution is to roll the sim to simulate the bank, then slowly roll it back upright hoping to approximate the feeling of gravity+centrifugal force. But that's not what actually happens in flight. Throughout the entire turn "down" never ceases to be perpendicular to the floor.

Lack of solid data can also be a problem. A motion sim is useless at training for unusual attitudes or situations. There is no data to inform the programming for things like high-speed, high-mach stalls or extreme angles of attack because gathering real-world data for these things would be too dangerous. Trying to guess at what it might feel like could be misleading.

On the other hand it can be useful in giving the pilot some practice in dealing with the possibly distracting motions experienced, for example, during a crosswind landing. When pitching or banking a pilot has to deal with the fact that he may not be sitting perfectly straight in his seat or there may be up and down or back and forth motions from turbulence. The pilot has to be sure not to transfer these motions to the controls, so the full-motion simulator can give them some practice at this.

So it really boils down to a subjective judgement call as to whether the expense of a full-motion sim is really justified in terms of accident avoidance.

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  • $\begingroup$ >>>There is no data to inform the programming for things like high-speed, high-mach stalls or extreme angles of attack because gathering real-world data for these things would be too dangerous. Trying to guess at what it might feel like could be misleading.<<< As of next year this exact training will be mandatory. Alaska Airlines has got a sim that is certified to recover from fully developed stalls. Data used is windtunnel data plus data from flight recorders of crashed aircraft (unfortunate, but keeping in the diligent tradition of trying to prevent a similar accident). $\endgroup$ – Koyovis May 10 '17 at 22:00
  • $\begingroup$ @Koyovis That is very good to hear. What types of aircraft are they designed for? I think Alaska flies 737s. $\endgroup$ – TomMcW May 10 '17 at 22:14
  • $\begingroup$ They go by category I believe, low wing low tail, low wing T-tail, high wing. Yes the certified sim is for a 737. It is really excellent news and it is tragic that such an important bit of training only gets added to the curriculum after two deadly accidents. Previously only stall prevention and stall onset were trained, not recovery from fully developed stall without ripping the wings off. $\endgroup$ – Koyovis May 10 '17 at 22:19
  • $\begingroup$ @Koyovis IMHO some simple practice hand flying in alternate law would have prevented the AF447 accident from happening. $\endgroup$ – TomMcW May 10 '17 at 22:38
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    $\begingroup$ Yes it may have prevented it. But once the aircraft was in a stall the pilots did not recognise it - had they been trained in it they would have recovered. Prevention is important, as is recuperation if the situation still occurs despite the prevention training. $\endgroup$ – Koyovis May 10 '17 at 22:43
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Is it cost effective to put a motion system underneath a Full Flight Simulator? Yes, because it is a requirement for being able to conduct recurring training, type rating etc. A necessary cost for civil aviation, generating a potential revenue stream.

Why is it a requirement to use a motion system at all? Because of what @kevin says. Without direct stimulation of our inner ear acceleration sensors, the whole "flight" experience is just an interactive wide screen cinema set-up.

Do we need our inner ear to experience motion sensation? Yes and no. Give our brain a moment, and our steady state motion sensation is distilled quite accurately from our peripheral vision. Not from our central vision, where the instruments are.

But any changes in motion are immediately conveyed by our inner ear. That's why we have the sensors there: immediate, direct perception of acceleration. Not of velocity or position, which are integrated signals with the associated 90/180º phase lag, and undefined state of constants.

So our inventory of sensors for position and motion awareness is:

  • Central, stereoscopic vision for detailed perception of relative position. But stereoscopic vision is not applicable when reading flight instruments.

  • Peripheral vision for constant velocity detection (central vision is not very good at this, other than from stereoscopic distance perception).

  • Inner ear acceleration sensors for being alerted to instant changes of velocity.

Motion systems can do a pretty good job at reproducing direct accelerations, until the actuator stroke runs out of course. So for short term accelerations - sustained accelerations require a whole country as stroke. Gravity can be used to a limited extent for simulating sustained acceleration, with some pretty decent effects such as take-off push. An approach flown in a simulator with motion creates much more accurate results, even in the hands of an expert pilot, because the inner ear aids the interpretation from flight instrument data.

For controlling a helicopter in a hover, motion is absolutely essential. Trying to maintain an unstable equilibrium, like standing on top of a large inflatable ball, depends almost exclusively upon inner ear acceleration sensing.

What motion cannot do is reproduce increased load factors such as occurring in co-ordinated turns. Fighter simulators have g-seats and g-suits to do this. And for fighter simulators, it is not considered cost effective to use motion systems, because of the different focus in training tasks. The G-seats recreate the secondary effects from sustained load factor: the pilot is pressed into his seat, so the whole seat is lowered and the seat cushion pumped up. And the G-suit pumps air pressure to the pilots legs, what he experiences in the real aircraft to prevent the blood from being drained from the head.

Motion is pretty awesome, especially the modern electrical systems which are way faster than the old type hydraulic ones. Hydraulics are good for high static forces, but struggle to pump enough oil through the servo valves for fast actuator extensions. Brushless DC electric motors can exert high forces as well, produce instant accelerations, and at 4000 RPM have no problem with high actuator velocities.

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  • $\begingroup$ Your answer contradicts Kevin's answer: you say the inner ear helps pilots, while this is not generally the case (e.g., loss of spatial awareness in IMC). Another note: a good state estimator (like the brain) does not necessarily have a 90° or 180° phase lag normally associated with a simple integrator; the real problem is that just an accelerometer is not enough to recover the pilot's orientation (or 'undefined state of constants' as you call it). $\endgroup$ – Sanchises May 14 '17 at 13:44
  • $\begingroup$ Yes the inner ear can confuse pilots and get them into a spin or make it difficult to recover from one , however it usually provides a very helpful sense of what is up. An integrator introduces 90º phase lag. Yes an accelerometer cannot provide orientation (position) information, we agree on that. The brain is a good state estimator, and it uses 1st and 2nd derivative signals to get a rapid sense of change. $\endgroup$ – Koyovis May 14 '17 at 18:51
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Complicated question.

A lot have been said about how the human body is receiving these information of motion and they are most of them true and acceptable. But why using Full Flight Simulator with motion. To give the most realistic feedback. Why doing it for small aircraft sometimes less expensive than the simulator. Because the simulator can give you way more possibilities of training, especially on EBT(Evidence Based Training).

But do we really need a FFS for every minutes of Type Rating training. The answer is no. EASA authorize 50% of the time outside a FFS but on a Fixed Based simulator qualified at level FTD 2. (For furthermore explanation go look to the CS-FSTD(A) regulation) Question is why? Because a lot of the training is just about procedures and doesn't require a full flight to understand how to enter a flight plan or to execute a normal take-off or a normal landing.

So the question is not about do we need motion or not, but what the simulator can let you do in term of training. FFS is mostly used for EBT and other devices are used for procedures learning. That is the real question about the use of a simulator.

I hope it answer the question!

Sources:

EASA CS-FSTD(A): https://www.easa.europa.eu/sites/default/files/dfu/CS-FSTD%28A%29%20Initial%20Issue.pdf

ICAO EBT GUIDE: https://www.icao.int/SAM/Documents/2014-AQP/EBT%20ICAO%20Manual%20Doc%209995.en.pdf

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