A couple of things that didn't make it into the video: - 0:12 the F-18 crash is documented by the US Naval Aerospace Research Laboratory, see page 10-7: apps.dtic.mil/sti/tr/pdf/ADP013854.pdf - 6:57 notice how when the roll gets washed out back to neutral, it returns slower than the initial excitement. This makes sure that the pilots feel the initial roll (rate), but won't sense the platform going back to zero roll. - 13:04 the reason it's easier to compute aerodynamic and thrust forces is because these need to be calculated anyways to simulate and model the aircraft. For example, X-Plane has an option for directly outputting the aerodynamic/thrust forces along the aircraft's axes, which I could use as inputs for the animations. Computing gravity and acceleration would require determining angles and geometry, which makes the whole thing more convoluted. - 14:16 since we now have a solution for specific force in both directions (forward and side-ways), this means we can replicate specific force in the entire horizontal plane through a linear combination of both directions. However, in the vertical direction, it's only possible to replicate short, high-frequency movements, since the simulator can't be tilted to sustain long-term forces in the vertical direction (which is in-line with gravity). For sustained vertical g-force, some sort of centrifuge would be required, like in this simulator: desdemona.eu

"yumans" "hyumans" "newmans" what a journey

And here I was thinking this was going to be a clickbait video. Now I don't even trust gravity anymore. Thanks for that.

Einstein already said that you cannot distinguish between gravity and acceleration without a reference. Very well done!

I had worked for a simulation manufacturer in the late 80s and early 90s in Tampa Florida and we had some pretty cutting edge technology back then. This is next generation stuff here. Exceptional video.

This is the best piece I have ever seen on flight simulation. I have written software for flight simulators for 30+ years; both games and actual full flight simulators. Thank you for making a video that I can use to explain the rather obscure and mysterious magic behind pilot training.

The saddest part of the f18 pilot story is he did have visual cues for his attitude on the flight display. He just didn't trust his aircraft was telling him the truth, or failed to check his instruments in time.

It astonishes me that a pilot would take off at night, over the ocean, with everything pitch black, and not be fixated on the attitude indicator.

*watches video on airplanes* "In 2001" "ah shit, here we go again"

As someone who trains in sims regularly as a professional pilot, my experience is thus: usually the first time back in a sim after it's been awhile my brain knows "something" is wrong, and I tend to just be a little disoriented and maybe a bit queasy for the first 30 minutes. However, after a while my brain recalibrates and adapts to the sim and it becomes really cool how well it just "accepts" it. The motion is pretty well matched with the inputs and visuals. Especially that surge axis is perfect for quick jolts like turbulence or landings. Not for nothing too, having a perfectly replicated cockpit inside helps a lot, because you're leaning/reaching/turning your head in exactly the same way you would in the real airplane, and all of this motion is completely independent of the orientation of your body, so the illusion remains even when you're not sitting perfectly in the chair looking straight ahead.

I’m an ex pilot (H) and used to skate vert half pipes. Love how you made that connection and it made me realise something I’d never thought about as an adult. Cheers.

Motion base simulators are great for lower dynamic aircraft like passenger/cargo jets & bombers, but not great for high dynamic aircraft like fighters. Pilots can be taught that if they pull hard G's long enough, the G-force will eventually reduce - which is NOT correct. Back in the 1980s, we used an air-driven G-seat & G-suit in the simulator that would give the correct cues for a fighter pilot. We also used the visual system to give tunnel vision at very high Gs.

When I was a miltary pilot, we had two sims : one like this one, the other was a simple set just put on the ground. No moving parts, just a fake cockpit and some 3D rendering on a 180° screen. You know what, just watching the scenery move while you are simulating the flight gives your brain the sensation that the whole thing is moving. While we were tied to the ground, there was no hydraulic systems, no moving parts or whatever. Visual senses are really powerful to trick you in believing your're moving while you're not ^^

What an amazing comeback !!!!

I didn’t even know we had this simulator… And I’m a student at the faculty of aerospace engineering of the TU Delft haha 😅

FlyByMax: “If gravity and acceleration are in some sense the same…” Einstein: “Excuse me? In some sense?”

So when i'm in bed, i am actually accelerating forward with 1g. I'll keep that in mind next time someone calls me lazy ;-)

Wow, that was truly amazing. Having just recently flown in an A320 commercial sim, seeing this on my feed was perfect timing. I never really felt much motion as I flew the sim in a very realistic manner, but if I go again, I'll have them ramp up the turbulents or crosswind so I can feel more.. Thank you so much for making this clip and how great your narration and presentation is. Top class.

Well explained!!! Without cutting any corners. I tip my hat off to that.

I took a free online intro aeronautics course from TU Delft some years back, and it was incredibly fascinating. It did require a fair amount of math.

Best explanation I’ve seen in my 28 year flying career. Well done!

I love the detailed explanation. Too many channels give the basic idea and leave out the detail.

In fact the one of the most important discoveries that helped Einstein develop the law of general relativity was the principle of equivalence, which says that gravity is an acceleration, not a force, in such a way that if you subject a person (in a vacuum) ) at an acceleration of 9.8 m/s^2 you will feel the same as if you were on Earth under the effects of gravity

So glad to see one of the best aviation channels I've ever seen back. Excellent video!

I was blown away as a kid when I felt the acceleration in a simulator..I asked my dad how it worked and he said they blow air in your face while tipping you back, but you're still "looking forward" ... genuis

I had the opportunity to 'play' in a jet fighter simulator that can flip upside down. I was VERY impressed by the sensations. I have always wondered about how a simulator can fool you into thinking you are climbing. This video was great - thanks. . . . As a side note - I am a glider pilot - I once climbed into a cloud with an instructor (and only VFR instruments). We wanted to test my ability to sense the g-forces when visual cues are removed. I thought we were flying straight and level, but when we popped out the side of the cloud we were actually in a relatively steep descent with one wing down. Wow what a sensation; the power and importance of the visual horizon. . Last year I flew in France. We took off in a valley and I suddenly found myself desperately looking around between the mountains to get a glimpse of the horizon just to orientate myself.

The simulator is much more complex than I initially thought. Great video showing the engineering difficulty.

The one part you missed was braking on the runway, why presumably needs the simulator to tip downwards with a very brief upward movement of the scenery to simulate the nose dip when brakes are applied. Otherwise I'm very happy to say that all this works in exactly the way I was expecting it to. I'm an electronics engineer so instead of washout filters, I would simply say AC coupling so the steady state does not make it through the system. The turnover frequency of the coupling gives the time needed for the system to return to centre after the load is applied.

This helped me to imagine what flying in space with a rocket pack could feel like. In space, you'll feel like you're in constant freefall, because no forces will be acting on you. If you start to accelerate in one direction, you'll start feeling a force that could be felt as down. As you accelerate faster, that force increases and rotates.

I finally understand why flight simulator doesn't need that large of range of motion, I never understand why they can trick human, but without actual visual reference, gravity can do the job. Maybe only thing it isn't capable of simulating is continuous freefall. It might be the reason deep stall situation get pilot into so much stress, as they can't really experience it in simulator.

In my experience the most realistic part of the sim is straight and level flight through turbulence, or the feel of turbulence with spoilers deployed and the vibrations from hitting stuff with the nose wheel. The biggest inaccuracy is due to the sim’s inability to simulate g forces accurately in the vertical plane.

One thing to note about mimicking linear acceleration with tilting the seat in the simulator, it would actually be somewhat noticeable because while the horizontal component of gravity would match the acceleration, the vertical component would be reduced making the seat feel like it is pushing you up less. This method of miming the acceleration could also only simulate up to 1 g of force by only rotating and would feel less and less like what it is mimicking as it approaches that max force.

The fidelity of Level D simulators is so good that in the US, pilots can receive a type rating without actually flying the aircraft. For many airline pilots, the first time they ever fly the actual airplane with passengers aboard may be the first time they have ever actually flown the aircraft. They will have a check airman with them, but its still pretty amazing to think they have never actually flown the aircraft before.

I played VTOL VR and the visual cues alone can trick you into feeling you are actually flying. Can't imagine how coupling that with an actual simulator that throws your body around.

I already knew this stuff, but it's fun to see such a great visual representation of the physics and math behind it.

Superb Max! Having worked there, it means even a whole lot more!

Since this simulator is for research purposes, you could add BCIs to the mix to measure brain activity and get a more complete picture of what's going on.

Yes, there are two independant factors here, what jacks do and what the display does. This example integrates it. Amazing.

I find the somatographic effect so interesting, and the better understanding of it and how it is applied to both sim flight training and the human factors of a number of aircraft crashes (like the F/A-18 catapult crash mentioned in the beginning).

I was actually thinking about that stuff several times. Thanks for the video :)

Acceleration & gravity feeling the same is why sometimes we cannot accurately feel what the aircraft is doing. That's why we learn to read and trust our basic flight instruments.

I got to fly a B1-B simulator at Dyess AFB about 20 years ago, and when the sim operator relented and turned on the motion base, it got WORLDS easier to control, it just felt right. In the sim we dropped a massive boom on Abilene and then cruised 50 miles north to see the location of the sim op's fishing shack on Lake Stamford. Flying supersonic at 300 feet even if only in a sim is AWESOME.

We need a home version of this with VR headsets.

Videos like this make me appreciate KZfaq even more. Great work!

Awesome video once again! Great to see you back.

I feel like I've reached a new level of nerd, all these science videos with 'it's not what you think' are exactly like I thought they were gonna be

when you used to fly VFR for a long time, then took the instrument course, the first time you find yourself flying at night with only instrument to guide you is scary as hell.

This stuff with the washout is what causes CFIT (Controlled Flight Into Terrain). It happens in the dark or clouds. If the plane starts to slowly roll and the pilot doesn't notice on the instruments they wont feel it. Then when they do notice they try to fix it, but it feels like they're turning in the opposite direction. They can't merge the feeling in their ear to the gauges. Pilots that have CFIT will believe their ears and not the plane. They end up turning tighter and tighter, not understanding what is going on, and lose altitude because the lift component keeps shrinking. Pulling up only makes the turn tighter, making the problem worse. The whole event doesn't take that long. And all because of slow roll rates not being registered by the inner ear. Cool for a simulator, deadly in the real deal.

Outstanding material! Thanks and keep up the good work!

For non pilots, just a minor addition on how strong and fatal this disorientation can be when you lack visual cues and only rely on your "lying inner ear": As per FAA and NTSB studies from years ago, pilots who do not have an instrument rating, but end up flying into clouds, have a life expectancy of about 97 seconds. One and a half minutes, before your disorientation takes you into a so-called graveyard spiral and you crash. It's that bad! Which is why instrument training drills trusting your instruments and ignore all other cues. It would be interesting to find out why this Navy pilot didn't do that. EDIT: reading the linked Navy report now and see that it makes reference to that.

Thanks for the video! Interesting how those mistakes happen even with HUD information.

This channel deserves a lot more subscribers

This was very well made, adressing a very specific niche but really intriguing

Really great presentation! Aircraft maneuvering is generally described with the following terms: Aircraft Movements are dynamic and are Pitch (Elevator), Roll (Aileron) and Yaw (Rudder). Aircraft Attitudes are static and are Banked, Climb, Descent, Cruise and Slip/Skid. Aircraft Movements are in relation to the aircraft axes. Aircraft Attitudes are in relation to the Horizon. The Pilot Pitches the nose up to Climb, down to Descend, level to Cruise. The Pilot Rolls the aircraft into a Banked Attitude to turn. The Pilot uses Rudder and opposite Aileron inputs to Yaw and Roll the aircraft into a Slip Attitude or too much rudder for the amount of aileron to put the aircraft in a Skid Attitude. Slip and Skid are indicated on the Aircraft Turn Coordinator. Attitudes are displayed on the Attitude Indicator (aka Artificial Horizon) and also by looking out the front window at the natural horizon in VFR weather.

It makes sense that gravity and acceleration would be dealt with the same way, gravity is measured as an acceleration, the units for both are the same.

This is amazing… this is literally what I graduated on AT the TU Delft, with the Simona Simulator. Motion cuing fidelity for a B747. Modelling the semi circular canals and the otoliths of the operator. Good times

That's pretty much what my DIY Stewart platform does. I have the outside world obscured by a VR headset. It can replicate a sustained longitudinal acceleration and deceleration up to 0.5G. It feels pretty convincing. I was inspired to build it after experiencing the motion platform at the RAF museum in Hendon about 10 years ago.

This doesn't really explain how a trained navy pilot could decide to ignore his instruments entirely when flying in the dark with cloud cover.

I was able to guess every trick while watching, but it's so pleasant to see such amazing content. Kudos for the clarity of your explanations and the impeccable visuals, this is high quality educational material ❤

Very interesting. I have to admit I had not thought about this concept very deeply but it all makes good sense. I wonder though in a roll for example, in order to zero the force out the simulator needs to return from the roll position to level, but what prevents that roll back to level applying an unrealistic force to the pilot? In the real world when entering a roll, the forces are the initial roll force in that direction then neutral assuming a properly coordinated turn. But the simulator has no alternative but to apply roll in that direction, then roll in the opposite direction then neutral. I assume it must do it in such a subtle way that the unwanted effect is minimal.

Great video and explanation. Modern simulation feels just like the aircraft, at least for Jet transports. Just one additional thought about somatogravic illusion is not only do you lower the nose to compensate for the perception of over pitching, with a takeoff thrust setting, the lowering of the nose further exacerbates the illusion by increasing the acceleration. Unfortunately I knew a couple of people killed by this phenomenon taking off from a dark remote airfield at night in a high powered piston aircraft. This is the typical scenario, dark night, high acceleration. Any night takeoff, even after 30+ years of flying is still locking onto the attitude indicator, the sensations still make you feel uncomfortable.

Why does this vid only have 2k views, this needs at least 50k! Great work man

I’ll never forget being on break at flight school, I asked one of the other pairs of students if their instructor let them go in motion. They answered with an affirmative ‘yes’. I was surprised, mine didn’t. Their instructor poked his head out of his office and said ‘no we weren’t’. The visuals tricked their bodies into thinking their simulators were on motion!

Excellent explanation and graphics! Best video ever on this topic.

Well made video demonstrating and explaining spatial disorientation... Tho you made me upgrade my gaming setup, yet again. 😮‍💨

Amazing video as always!!!

Einstein had a thought experiment that sheds light on the acceleration vs gravity idea. He proposed that if you were inside a closed elevator, there wouldn't be any device that could tell the difference between the elevator moving upwards rapidly or just sitting in a gravitational field. Same goes for our vestibular system.

Thank you for this really interesting video!

Incredible high quality video, well done

Thanks a lot for this video ! I always wondered how those clearly limited range actuator could give a realistic immersion for pilots that should clearly know the real deal already. Now I know, the explication is passionating, and it gives an even better and deeper comprehension of the gravitation/acceleration equivalence ! Great work !

Amazing Video, animations look super cool!!!

Excellent video :) If i understand it right in summary its all about the force experienced by the pilot. In a real aircraft the force vector will shift with acceleration (either in translation or orientation). However in the simulator the force vector is static (gravity), so instead the orientation of the horizontal plane is manipulated. Simplified what the simulator does is it matches the angle between the force vector and horizontal plane experienced in the real aircraft by offsetting the perceived horizontal plane in relation to it's static force vector. As the aircraft accelerates the force vector is shifted backwards at an angle and so the simulator pitches up to match the angle of the "horizontal" plane to the static force vector. As the plane stops accelerating the force vector is again straight down so the simulator pitches back down to level.

Many questions answered. Thanks!!

Excellent video! I am an engineer who helps design high-fidelity fights simulators. It's a lot of fun flying them.

The acceleration feeling by tilt will be overcome the instant outside (simulated ) view is removed. In other words someone in a simulator and not watching the screen will correctly feel the tilt of the platform, even to the point of understanding approximately how much tilt is in effect.

Omg the Video make so Sense and the end just make this all Even bettttter

Great video - may I suggest a part 2 that focuses on the complexities of the visuals and the collimated display? Having seen it I can tell you this is one of the biggest changes you'll see between professional and nin-professional sims...

Assuming the pilot's instruments (particularly the HUD) were functioning correctly he/she made the mistake of not trusting them. All pilots training for flying in poor/zero visibility will be told "Trust your instruments!" for this reason - you cannot trust your senses to differentiate between gravity and acceleration.

I noticed how simulators used to work and figured this problem had to exist. Its good that we're coming up with solutions, may it help our pilots keep the skies safe ✌

I once had the chance to experience such a full flight sim and can attest how incredibly convincing the motion system tricks you to realistically feel the forces. I can recommend to anyone, if you got the chance to sit in a FFS

Really interesting. Presumably it's conceivably possible for the pilot to put in a series of inputs that the simulator controller cannot achieve all of them and still have time to 'washout' back to a neutral position allowing 'spare' hydraulic travel... how often does that happen and how does the controller decide what to prioritise?

Hey Max. Great video!

Brilliant video. Thanks for sharing your insights.

Cue onset is critical. (Get the perception started) Cue conflict is critical (especially the visual vs vestibular) Selective cue disruption can actually complement the perception.( my own theory. Flying close engagement fighter maneuvers with lots of rapid turns climbs, dives, vertical loops; the 6 degree of motion platform can not fully replicate but the immersive display (270 degrees horizontal 8 collimated display panels of a dodecahedron) is the compelling orientation cue. A G-seat which pushes you around in the cockpit seat is supposed to provide a gravity cue by making you sink into the seat during high g manuevers or lift you upon the seat during zero G, but it mainly disrupts your “seat of the pants” sense of gravity. By disrupting your sense of gravity direction in the simulator, it disrupts the cue conflict between actual gravity and acceleration vector forces being simulated thereby eliminating the cue conflict.) In the heat of intense excitement and intense focus of attention on the dogfight, the 6 DOF motion system provided little benefit. The fully immersive collimated display was the overwhelming cue especially when the g seat disrupted the “seat of pants” sense of orientation. At one point the motion platform system shut down in the middle of a simulated dogfight when a moog valve limit switch was triggered. The jolt of the platform when it settled to its resting position was a momentary distraction but the lack of motion was not even noticed until later. (Total visual immersion in a display that looks infinitely far away plus the G seat disrupting the sense of gravity plus intense focus of attention on the training task made a compelling simulation. The 6 Degree Of Freedom motion does help sometimes like initially establishing reliance on immersive visual cues and not noticing a cue conflict of visual vs sense of gravity, when nose down in idle with speed brakes out while following an aircraft in a vertical dive but careful not to end up in front of the other aircraft, the 6 DOF motion does make you feel like you’re falling forward out of your seat & held in by your seat belt harness, sense of acceleration when kicking into afterburners, roll rate changes when rolling 30 degrees to look down underneath the aircraft, Real time training Simulation provides two benefits, 1… realism which equates to better transfer of training skills learned in the simulation to real world 2… cues necessary to perform the training task

Great video, really cool!

acceleration vs velocity is another weird sensation. Try this in a car with a manual gear box: Get the car traveling backwards at a decent speed - now, shift into first and by just feathering the clutch and gas (no brake), get the car to slow down, stop, and start traveling forward. If you are smooth enough, and your passengers close their eyes - they will have no idea when they have stopped going backwards and started to move forward! They will be unable to feel the change in direction or the brief / instantaneous moment of zero speed/being stopped.

Fascinating stuff

In my opinion, using the tilts to simulate acceleration are easy to understand. The fascinating part is how the simulator decides to wash out the signal in order to maintain the same position. The sim can't reproduce forces exactly due to these restraints, so it's cool to see how it compromises accuracy with practicality.

Amazing. Amazingly explained. Thanks.

An interesting watch, but I have to say much of this was figured out even before I started working at Singer Link Miles back in the 1980s. I think what's really improved since then isn't the kinematics but the vision systems. The computer just for that took up an entire room full of 19" racks.

This is a great video. Was thinking a lot about this kind of trickery in terms of VR motion sickness cure. It could be a platform that simulates acceleration by simple tilting

it was an awesome video thanks for making it!

Excellent video. I have a couple of scenarios which I think may be related to this that I’ve never understood. Worth knowing that I am actually completely blind. 1. When on a train, I can not always tell if we are going forward our backwards. I assume this is due to me not being able to look out of the window and the force of the seat would either be very low when the train first sets off in a forward motion or non-existent if the train moves backwards . 2. When on a plane taking off, at first you can feel the upward motion, but when they reduce the engines from max power, you get a sensation of falling even though the plane is still climbing or levelling off

Physically speaking, fully experiencing gravity is feeling no force as freefall is an inertial reference frame. When gravity is acting unhindered upon us, we are experiencing no acceleration. When we "feel" gravity we are feeling the acceleration force counteracting gravity from some part (air or ground) pushing us up to stop us from falling. Ergo we only ever feel acceleration and it wouldnt make sense for us to understand the difference in feeling gravity vs feeling acceleration.

15:40 pilot bro apparently has the memory of a goldfish, not remembering that he was launched pretty much completely level off of an aircraft carrier less than 5 seconds prior, and that there's no way he could be rotated at such a drastic angle. Also I feel like even if you were completely blind, as long as you knew you were in a high-speed aircraft and had just taken off, it would be very hard to mistake the forces you're feeling for gravity. I feel like in most scenarios your eyes do play a role in determining if the specific force is gravity or acceleration, but I feel like in this scenario you have enough context that I think the human brain would not make that mistake, even on instinct, as in you would know it was acceleration and wouldn't have to think twice about it. But here we are so I guess I'm wrong.

Thank you! I have been trying to wrap my brain around that translation. You explained it very clearly. I have a loose project in mind for a racing sim and was wondering how that works. Some of them actually tighten your shoulder belts to add to the feeling of hard braking. (how about pulling on your helmet with about 35 lbs. for turns?)

Super interesting! If only I wasn't damaged by stress I might want to work in this field...

Great video! Well explained.

Can it simulate the force of the seat pushing the pilot into the controls?

I absolutely agree with all settings. I‘m also proud, that may settings are the same. 😅