The GENIUS of Inertial Navigation Systems Explained

[Music] what you're currently looking at is a moving platform inertial navigation system it was developed in the 60s for the f-104 starfighter to help it navigate towards targets on a mission and in this video we're going to learn what makes this device such an incredible solution to a problem that humanity has been facing for hundreds of years and not only does it solve the problem it does this in such a genius and clever way that makes this device one of my favorite examples of aerospace engineering so what makes them look so complicated how do they work and why is the military interested in using them this system has won a very important goal and that is to figure out the position of the vehicle that it's attached to by calculating the vehicle's location inertial navigation systems can not only be used to guide aircraft along a route but also missiles towards a target and even a rocket into space now the mysterious thing about these contraptions is that they work independently from the outside world meaning that they do not rely on things like satellites or radio signals this makes them unique because traditionally aircraft use all sorts of connections with ground stations to help figure out where they are inertial navigation on the other hand is kind of like a stubborn teenager who refuses any help from the outside world whatsoever [Music] the fact that these systems can operate all on their own also makes them very attractive to the military since a satellite or a radio station could always be destroyed by someone who does not have your best interests in mind but if you're like me this may feel a little bit weird i mean how is it possible to determine where you are if you're not using your surroundings it's like dropping a person without a map in the middle of an unknown forest and just expecting them to somehow know the way [Music] some of the first people to try and figure out this problem were european explorers in the middle ages the main instrument sailors used was a magnetic compass but a compass alone does not tell you what your location is this is a genuinely tough problem to solve and one of the ways that sailors navigated the vast oceans at the time was through a method called dead reckoning [Music] so imagine you're a dutch sailor out at sea trying to find a new route across the atlantic ocean as your ship leaves amsterdam you locate yourself on the map by simply looking for well amsterdam thereafter you decide to embark on your long and treacherous journey by heading west and following your compass to the americas since we know where both north and amsterdam are on our map we can draw a line heading west from our initial point of departure now in real life the chances of you following this line perfectly are of course almost zero but let's just take this as an example for a second if we're following our compass perfectly and we neglect things like ocean currents then we know that we must be somewhere on this line since we started off at a known location you can imagine that over time we're probably going to be further and further away from amsterdam depending on how fast our ship is sailing so if we know something about the velocity of our ship and the amount of time that has passed since we initially left the harbour then we can calculate where we are on this line by simply multiplying time and speed and funnily enough the way sailors measured their speed was by throwing a piece of rope with knots overboard and timing how long it would take until a certain number of knots were pulled into the water behind the ship this is why almost every plane on the planet to this day still uses knots to measure airspeed although it's unlikely that you'll see your captain throwing a piece of rope out of the cockpit anytime soon okay but how does all of this relate to inertial navigation systems [Music] the type of system that you can see on screen right now is one example of a moving platform ins the center platform is supported by three gimbals which allows it to rotate in all three directions the outer wonders roll the middle one does pitch and the inner circle does your notice that even though the outer gimbal is attached to the frame of the aircraft the inner platform always maintains a constant orientation relative to the horizon this is important for later on the same way a sailor has a compass and a rope with knots the ins also has five main instruments consisting of three accelerometers and two gyroscopes which you can see here the three accelerometers are basically doing the same thing as a sailor who is measuring the speed of a ship with a rope except this time we're not measuring speed but we're measuring how the speed changes over time this is really useful since aircraft are of course a lot more maneuverable than big and heavy ships imagine that you're sitting in the back of a parked car blindfolded as the car starts moving you suddenly feel pushed into the back of your seat which leads your brain to conclude that the car is accelerating forward even though you can't see anything moments later you suddenly feel the weight of your body shift to the right which gives you the impression that you're in a left-hand turn so even though you haven't been able to see which direction the car has been going in you already have an intuitive sense of what your root looks like and all of this is only possible because your body has a certain amount of weight and inertia this is why these navigation systems are called inertial it's because inertia is what allows us to sense movement even when we cannot see what's going on outside of our bodies and that's exactly what's going on with our three accelerometers which are continuously providing new data to update our location the same way a sailor keeps track of his position and root this is also the reason why inertial navigation systems are sometimes referred to as modern dead reckoning because they're essentially doing the same thing as our ancestors did except way more accurately so now we know why the accelerometers are on this platform why does the platform itself need to tilt let's go back to the example of a blindfolded car passenger if the car is parked on an uphill slope you will of course feel as if you're being pushed into your seat and you may be thinking well surely i could tell the difference between a car that is accelerating and a car that is parked on an uphill slope but here's the thing if your eyes are closed and you have no other reference aside from the force of your seat then there is simply no possible way for you to tell which of these situations applies to you and this isn't just a limitation of your body or your perception this is a limitation of the physics of our universe which means it also applies to our accelerometers so coming back to our pitching aircraft we now have to face a similar problem if we attach our accelerometers to the frame of the aircraft as soon as we start pitching upwards the accelerometer will feel as if it is being pulled backwards this is because a portion of gravity is now pulling in the backwards direction and this is a big problem because if we take a look at what the accelerometer is telling us there is no way to know if it can be trusted or not since gravity is now also playing a role in our measurement so one of the solutions to this tilting problem is to always align the accelerometers with the horizon because that way gravity will never interfere with our measurements we do this by placing all our instruments on a moving platform which is the reason we need all these gimbals we can then use gyroscopes to tilt the platform such that it always stays level regardless of how the aircraft is moving around it gyroscopes are essentially spinning wheels which always wants to keep their orientation fixed no matter what is happening outside of them this makes them the perfect instrument for our platform given that we want to keep it fixed relative to the horizon inside a rotating aircraft although gyroscopes are great at correcting for the rotation of the aircraft they're actually too good if you were to fly from the equator to the north pole holding a gyroscope from your perspective it would seem as if the gyro was drifting or wandering this is due to two reasons firstly due to the rotation of the earth the gyro will seem as if it is building up an error whereas actually it's doing exactly what it was supposed to by keeping itself at a constant orientation relative to where it started off from and secondly due to the curvature of the earth if we fly from a to b the gyro will again keep itself aligned with whatever its original orientation was but in both cases this means that the platform will no longer be aligned with the horizon which unfortunately for us is exactly the issue we've been trying to solve the entire time and in our frustration this is where the magic happens so to compensate for these rotations we use the accelerometers to give us our position and velocity in real time this then allows us to continuously correct the gyroscopes literally on the fly to make sure that they're following the rotation of the earth and keeping the platform aligned with the horizon at all times and because we're now keeping the platform level in turn this means that the accelerometers can do their job properly without accidentally measuring gravity as we saw earlier and the incredible thing is that the feedback between the accelerometers the gyros the gimbals and the platform are what allows the ins to continuously correct itself during flight with its own live data the constant cooperation between all these instruments is what allows inertial navigation systems to navigate independently and it's a beautiful example of what humans can do if we set our mind to it huge thanks to olaf for letting me use his videos thank you very much for watching and i hope to see you again soon [Music]

Channel: FlyByMax

Views: 1,840,693

Keywords: X-Plane, X-Plane 12, XP12, XP11, X-Plane 11, Threshold, X-Plane threshold, Microsoft Flight Simulator, MSFS, MSFS2020, FSX, moving platform ins, ins, inertial navigation system, ln-3 inertial navigation system, navigation system gyroscopes, navigation system gyros, gyros navigation system, transport wander, apparent drift, ln-3 ins, ln3 ins, ln3 inertial navigation system, inertial navigation

Id: Pq_PDaYclAw

Length: 11min 5sec (665 seconds)

Published: Sun Jun 26 2022