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How "full-motion" are simulators? Do they just simulate the major motions of the airplane in response to the flight controls, or do they also simulate the minor forces of the flight, such as the vibration from the engines?

(Bonus question: if they simulate engine vibration, do they simulate the severe vibration from an engine that's just thrown a fan blade?)

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    $\begingroup$ Some of them are realistic enough that they simulate the bumps/vibrations in the pavement while taxiing. $\endgroup$ – Ron Beyer Feb 7 at 2:49
  • $\begingroup$ Mark, the simple answer is yes , they include vibrations and other minor effects. $\endgroup$ – Fattie Feb 9 at 11:51
  • $\begingroup$ (I was trying to dig up a line of code that literally shows "add a bump" for a screenshot, but I can't find the repo! Heh) $\endgroup$ – Fattie Feb 9 at 11:58
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Full Motion is full in the sense that it can generate cues in all 6 Degrees Of Freedom: fwd/aft, left/right, up/down, pitch, roll, yaw. The term came in use to distinguish between 6-DOF systems and the earlier 3-DOF systems which only produced pitch, roll, heave cues.

Do they just simulate the major motions of the airplane in response to the flight controls...

They simulate the aircraft response by stimulating the sensations felt by the inner ear, making use of its limitations as also mentioned in this answer.

own photo

The two side-questions about reproduced vibrations boil down to the frequency response of the motion system: the ability of the system to reproduce commanded vibration signals, as measured at the upper platform with the payload installed. Older hydraulic systems, such as depicted above, had a very limited frequency response - the servo valve opens and oil flows through, creating dynamic flow effects and springiness from the compressibility of the column of oil supporting the payload. Yes, oil is compressible. Maximum perceptible cues up to 5 Hz.

Own photo

Electric systems have an electric motor at the bottom of the actuator. Electric field creation happens almost instantaneously when commanded and the connection to the upper platform is through the metal screwjacks inside the tubes: frequency response is almost an order of magnitude better than that of hydraulic systems. Maximum perceptible cues up to 30 Hz. Enough for engine vibration reproduction, severity depends on the magnitude of the amplitude.

The issues with reproducing severe vibrations at the motion upper platform are:

  • The cabin construction must be able to rigidly stay in one place and support the visual projectors without starting to wobble the image that the pilots are looking at - the rigidity of the upper construction must exceed the frequency response of the motion system. We've seen simulator cabins bobbing about like a gelatine pudding when subjected to serious amplitude/frequency combinations.
  • All instruments, electronics, cabling etc. are subjected to the alarming vibrations as well.

Both issues above are not an issue if the constructional design of the cabin etc. has incorporated the vibration inputs. The alarming vibrations are extremely effective training cues, and can be faithfully reproduced by an electric motion system plus suitable cabin construction.

Another way of producing severe high frequency vibrations are by means of a seat shaker or cabin shaker, used in the olden days of hydraulic motion, particularly with helicopter simulators for reproducing the main rotor vibrations. The seats would be mounted on up/down platforms with a stroke of several centimetres, actuated by a separate hydraulic small actuator.

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    $\begingroup$ Your "gelatine pudding" comment made me think of a secondary question. Surely someone has also investigated the question of which pattern of simulator motions will produce the most motion sickness in the most users in the fastest time? Either to simulate pilot incapacitation or to avoid any such motions for user comfort? $\endgroup$ – Jeff Y Feb 7 at 16:47
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    $\begingroup$ @JeffY There might have been research on motion sickness in the general public, I’m not aware of a project using motion bases for that purpose. Our inner ear organs get used to being shaken about, after some time people don’t get motion sick anymore. $\endgroup$ – Koyovis Feb 7 at 22:00
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    $\begingroup$ It’s crazy how that works. Both acclimatization and age have a lot to do with motion sickness. I know a pilot who started flying two years ago and got sick on every flight. After a year, he was over it enough to fly in mild turbulence. Now, he flies Caravans in Alaska. I, on the other hand, have gone from loving roller coasters and aerobatics, to having to watch what I eat if I plan to be inverted or pull negative Gs for too long. $\endgroup$ – Dean F. Feb 8 at 1:02
  • $\begingroup$ Very well documented explanation. $\endgroup$ – mins Mar 7 at 1:58
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The feel and graphics in a Level D FFS are pretty darn realistic. Even the feel of vibrations of the engine and the motion during taxiing is pretty well approximated. The entire gimbaled capsule shakes, vibrates and moves on electric jacks. One unit will seat 6-8 people. And, you had better use seatbelts. One unit will take up a room the size of a business jet hangar.

If you are in the Dallas area or in Florida, check out http://www.atopjets.com/index.html
They fly B737s and A320/330s.
Tell them Dean from the Dallas June class sent you.

I have not experienced a simulated uncontained engine failure. But, hard landings are pretty realistic.

In contrast, a Redbird full-motion AATD still uses Plane-X 11 software. The graphics and motion are realistic for a video game. It compares to a VR arcade or Disney World ride. The Redbird can spin 360°. But, it has limited up and down motion. The entire system can fit in the master bedroom of your house or apartment.

For full-motion FTD rental, check out
https://inthepattern.com/
Or
https://www.thrustflight.com/

The main difference between the AATD/FTD and the FFS would be the force feedback of the controls and the tactile feel of the avionics.

Here are a couple of YouTube videos of the American Airlines Full-motion Flight Simulator Level D.

The ATOP course is taught by longtime airline pilot and AOPA Flight Training Magazine writer/contributor Wayne Phillips.

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    $\begingroup$ Dean, appreciate your experience, but be careful making recommendations/referrals. You'll want to make sure you clearly disclose any affiliation (or lack thereof) as we don't want spam. $\endgroup$ – fooot Feb 9 at 0:47
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    $\begingroup$ No affiliation. I just give praise where praise is due. I’m the sort of person to call an organization’s home office when I get exceptional service. Wayne, the owner/operator at ATOPS did a great job. Shout outs to him. American Airlines was also very warm and welcoming at their training center. Great experience over all. $\endgroup$ – Dean F. Feb 9 at 3:08
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    $\begingroup$ I rent from Sherman Gardner at In the Pattern and from Nathan Rausch’s group up at Thrust Flight. Both great organizations. They host free FAAST seminars and an occasional cook out on the ramp. KADS is also a great venue for July fireworks. Other than that, I am not affiliated with them, neither. $\endgroup$ – Dean F. Feb 9 at 3:19
  • $\begingroup$ I believe the RedBird Full-Motion Simulators are running a highly-customized version of Lockheed Martin's Prepar3d software, not X-Plane 11. I was unable to find it mentioned in the spec, but the entry-level (non-full-motion) simulators list it in the specifications: simulators.redbirdflight.com/products/…. I think it's been so customized for their full-motion sims that it's just a part of their "Red Bird Navigator" software. I don't think calling it " X-Plane 11" is doing it justice, as great as X-Plane is. $\endgroup$ – Canuk Feb 11 at 9:10
  • $\begingroup$ You may be right. I have no citations on the type of software used. In the simulator that I used, it’s graphics looked very similar, no better than X-plane. $\endgroup$ – Dean F. Feb 11 at 11:07
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The Shuttle Mission Simulator's (SMS) Motion Base simulator sat on a standard hexapod motion base so it had the usual three translational / three rotational axes.

Unusually though it had an additional degree of freedom: the cabin could tilt upwards almost 90 degrees to simulate launches. It used an additional hydraulic actuator (highlighted) for this. This degree of freedom was also used to simulate g-loading.

enter image description here

(Picture from old Link newsletter the Link Log, personal copy).

I worked on the motion software some; it was art as well as science. We simulated random vibration from the solid rocket boosters, transitioning abruptly to the smooth liquid-fueled ride on the main engines at solid rocket booster separation.Checking some old notes, we also simulated vibration/buffet due to the following reasons: passing Mach 1, reaction control jet firings, flat tires, and "runway rumble".

We were left in the dust though by the amazing Vertical Motion Simulator at Ames, which was the cockpit on a hexapod, mounted on a trolley which moved longitudinally along a beam, which beam could move vertically! Kind of like an x-y plotter stood vertically. That was one amazing facility, and I treasure the memory of visiting it. But then the crew would come back and say, we want the SMS to feel like that...

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A "6 degrees of freedom" motion base still has to cheat, to emulate real-world motion.

For example, it can't do several consecutive rotations about one axis, like an aerobatic airplane flying rolls. I haven't heard of one that can even do a half roll (or half loop) into steady inverted flight.

Translational motion also has its limits. To simulate sustained forward acceleration as with a long takeoff roll, instead of shoving the cab through the wall and across the street, it must eventually pitch the cab nose-up to push you back against your seat. As the forward acceleration eases off, the cab slowly pitches level again. Minimizing the felt effects of this "slosh" (faking translation with rotation) is tricky.

But for conventional within-the-envelope maneuvers, it's good enough that lessons learned in it transfer well to the real world. That matters more than raw physical fidelity.

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    $\begingroup$ Yes you’re absolutely right. The real ride has the whole world to create motion effects, a simulator must limit itself to being in a building. $\endgroup$ – Koyovis Feb 7 at 22:01
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Left-right, up-down, roll, yaw, and accelerate/decelerate. Faking engine vibration, and more violent yawing from engine failure is pretty standard capability.

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