View Full Version : Sim Motion Platforms
13th Mar 2004, 22:29
Hi all, just a quick question.
I am having to write an essay regarding the use of motion platforms in flight simulation. I know the subject is a well trodden path but I could do with some of your personal opinions;
Do you feel having the motion cues aids your training?
How realistic are the motion forces?
Any tales to tell to illustrate the subject?
Thanks a lot for your time
18th Mar 2004, 19:18
Yep I find the motion cues are essential to aviation simulator training, more so with the higher quality visuals.
The motion forces are realistic, more so when combined with seat motion simulation.
No tales really, but although one knows that the last flight was a simulation, with todays higher spec sims it sometimes seems amazingly real.
Some Pilots have suffered from the "leans" at sometime in their careers, I've suffered in both the real aircraft and the sim, which I suppose would illustrate their realism of motion forces.
22nd Mar 2004, 20:47
Thanks for your input. Your views back up a lot of the research thats been done over the years. It's nice to know that they have a basis in reality!
The reports in for marking now so fingers crossed it comes back ok :uhoh:
23rd Mar 2004, 10:02
It may (or may not!) interest you to realise that the motion platform of simulators is used primarily to replicate acceleration not attitude. Thus, in a regime of ,say, heavy braking, the box will be tilted fully forward. Likewise under acceleration on takeoff, the platform will tilt fully back. (Compare this to the somatogravic effect or 'pitch up' illusion which was believed to have contributed to so many accidents).
Further, as the flight regime being duplicated assumes a 'steady state', ie un-accelerated, the simulator will return to its neutral position at a rate below your detection threshold to leave the full range available for the next manoeuvre.
Thus, the attitude of the box when viewed from outside will probably bear no relation to the flying attitude of the aircraft. The only obvious exception I know of is in the case of a helicopter landing either on sloping ground or a ship.
Most students, in the presence of a complete 'out of the window' view ( ie, less so when IMC) are a) unable to detect the difference between motion on and off, and b) quite certain that the opposite is true! This demo. proves utterly conclusively to even the most sceptical that around 80% of their situational awareness (including the part that they interprete as 'motion' cues) actually comes through their eyes.
The fact that so many (experienced) aircrew suffer from some form of vertigo in sims is due almost completely to the limitations of visual modelling and the tiny inaccuracies between what they have learned to expect and what the sim presents them with. This is borne out by the fact that ab-initio students almost never have the problem.
'The Leans', which is not a simulator effect, is due to a mismatch between the information coming from your semicircular canals (ie. due to acceleration again) and that presented by your instruments. The effect can be very unpleasant and extremely compelling but it's not really to with simulators. (except, perhaps, to prove that they actually replicate th eoutside world really rather well).
Boffin stuff ends.
23rd Mar 2004, 11:17
Ta fokker, all input is welcome on this subject.
5 months ago I too was one of the sceptics untill 2 crucial events turned me into a believer!
1) I got thrown around in a Jetstream with no visual reference and asked "what do you think is going on?". Post landing analysis showed that I was soooo wrong. Very scary when you are totally convinced you know which way up you are!
2) I was VERY luck as a non pilot to get a session in a 777 sim with 6 degree of freedom motion platform. I've had experience in fixed base sims but that thing was unreal. I was very impressed with the motion sensations.....and then they turned the motion platform on!! Following the "flight" I observed one of the sims from the outside and its interesting to see what actually goes on to provide the false acceleration references. Those things can get pretty violent, especially when you let me land one!
Never really thought about Helli sims but you raise an interesting point. Are the visual field requirements on those things greater than the fixed wing types? Do they use conventional motion platforms and do they have a greter need for acceleration cues in the normal axis?
Not that anybody is really that interested but the essay revolved around the requirement for motion platforms in simulation. A tiny title for a very complex argument!
Thanks for all the help
23rd Mar 2004, 12:27
Not quite "on topic" but you may find it relevant, the RAF had a number of devices which were used to produce disorientation effects in a classroom setting. One of these was a small cabin on an arm, a bit like a mini centrifuge. The subject was placed in the cabin facing the centre of rotation and closed up (no visual reference). The system was capable of very smooth acceleration at precise rates. The machine was then started and the subject asked to say when he was moving. Sitting outside you watched the machine start to rotate and accelerate to quite a high rate of roatation - but at a sub threhold level. The subject inside would still be reporting that they were stationary, until the machine was slowed at an above threhold level when they would of course report that they had started to move. A number of other interesting little demos could be carried out with that particular machine.
The last time I saw the machine was at the RAF Aero Medical Training Centre at North Luffenham in the early '80s. It might be worth your while to contact the successor organisation to AMTC (no longer at North Luffenham - don't know where it is now) if you want more info.
As far as motion systems on sims go, good ones are great but some of the early ones were just a distraction
23rd Mar 2004, 12:39
Completely agree with fokker, and your own experience in the 777, that most subjects, at all levels of experience, are completely unable to detect whether the motion is on or off. This applies to the large 6-axis sims I have worked with in the past, to the rather rudimentary helo sim I'm using now.
On helo sim specifics, many modern ones have the extra visuals required to give "chin window" views, which are very necessary for landing on decks, etc. Windscreen field of view is the same as FW sims. Motion platforms the same, but acceleration is mostly lower than FW, even vertically, so nothing special required.
In all this it should be remembered that it depends what sort of training is being done. IF procedures require little in the way of visual or motion, visual procedures need more.
23rd Mar 2004, 14:52
Yellow Sun - Never come across that, deserves a bit of investigation I think, ta :ok:
keithl - thanks for the specifics, must be quite impressive sitting infront of all those visuals! :cool:
fully agree with you regards training, quite a few studies show that although pilot performance in the sim may shoot up with motion the transfer of training isn't quite as impressive. Obviously it's all context specific and motion might still have it's place (say in military sims?) but I think the general concensus of opinion is that in commercial sims we've gone as far as were going. Be a shame to loose it though, its good fun to whack the turbulence up to full and enjoy the ride :yuk:
24th Mar 2004, 04:31
LF: The six degres-of-freedom of a modern simulator are - Roll/Pitch/Yaw/Heave/Slip/Sway, and provide ACCELERATION cues along and around the three axes of flight,i.e. Roll/Pitch/Yaw.
A realistic maximum acheivable in terms of 'G'-forces is up to 3g initial change of acceleration. By this time, the jacks will have almost reached the physical limit of travel, at which point you will soon realise it! There are normally three acceleration cues, Onset, Sustained and Washout. Onset is the initial change of acceleration in any plane, followed immediately by the Sustained cue, to provide the "feel" of attitude change, e.g. climb after t/o. The Washout cue is active when the motion platform is returning to the orthogonal at a rate lower then the sensibility of the vestibular system, ready for the next Onset cue.
It is a curious anomaly that the "motion sickness" sometimes experienced by crews is achievable only with a perfectly-operating vestibular system. Personally, I found the worst case was if using the sim off motion, with only the visual cues to stimulate the senses, never in all my time as a sim tech was I nauseous on motion. I came close to it when in the RAF, on Harrier and Jaguar sims, but the civvie world was much more sedate! One exception to this is a "wheels-up" landing on motion, just make sure you are strapped in tightly!!
Hope this was of interest, if you have any more queries I'll be delighted to try to help.
25th Mar 2004, 08:54
Cheers Mr Owl, it's all a lot clearer in my head now :8
Suppose the simulator sickness would probably have a fairly large negative impact on pilot performance in the sim. I'm no expert but I guess it's hard to fly whilst hurling?!