As a former engineer at AlliedSignal Aerospace/Honeywell, I can say that you roughly have the concept correct but your model of the ring laser gyro is completely wrong. First off, it’s not a ring! The path is either a triangle or a square. Secondly, there are not two laser emitters, there’s only one that goes through a beam splitter. Third, there are not two detectors, there’s only one that senses the interference pattern.
Just fantastic. I have flown 737's for almost 8 thousand hours and never had the curiosity to understand better the IRS system. Very well explained. Thank you!
Nearly thirty years ago my wife's cousin described to me this amazing innovation being utilized in NATO Submarines, I had purchased my first LORAN at the time for my sailboat. It boggled my mind, but now I can comprehend how it works. Thank You!
The ring gyro was in fact developed for submarines. I worked with the inventor of the ring gyro. The project was sold to a company that used it in missiles. They had to call back the engineer who designed it because it failed in missiles. He understood the problem and was fascinated at how he found the fault
I wanted to really thank you for this video because I don't think I could break it down any easier. I was the sales and marketing manager for a company that designed and built the worlds most accurate multi axis test systems for ring laser gyros and earlier guidance systems all the way back before the Saturn program for NASA. As a matter of fact the test systems were so delicate back then they would hire ambulances to carry them all the way across the US in carefully built boxes so they wouldn't vibrate as much. I asked and they said they paid them a big fee and they charged for every mile and they had no idea what they were carrying other than it was for the US government and extremely delicate and was sworn to secrecy. True story. God Bless and stay safe.
Wow - what an amazing story! Who would imagine that this was the only means of safe transportation? Really an incredible part of history - thanks for sharing
At 12:55 it is not a frequency shift it is a PHASE shift. One laser is fired (pulsed) at a splitter and then into the input of each fiber optic cable. It is not one loop in each direction but precisely matched lengths to form several loops in each fiber optic cable - each looped in opposing directions. Because a single laser is fired and split into each fiber optic cable equally, the lights starts at the same phase in each cable. But if the Gryo rotates in one direction, the light will take a longer time to travel and arrive late at the far end (just a few pico seconds) in one cable. And the light will take a shorter time to travel and arrive early at the far end (just a few pico seconds) in the other cable. The two light beams are then combined as they exit the fiber optic cables. Because the two light sources are now slightly out of phase, they cancel each other out a tiny bit and thus the bightness is slighty dimmer (compared to as if it had not been rotated) and this dimming translates as to the rotation angle. The more it rotated, the more the result dims. The arrival times are also measured but not as accurately, they are just measured to see which arrived first to determine rotation direction. Ring Gyros are very quiet, compact, light weight, more rugged, have less procession and drift, and are more accurate than spinning Gyros. Even tiny Gryos can be made on Silicon. In that case, each path is just a circular series or traces in the Silicon that act similarly to fiber optic cables but use electrons rather than photons. These chips can be the size of your pinky fingernail and contain 3 Gyros, one for each axis. Adafruit has low cost ones that you can control with an Ardunio Nano to form a tiny Gyro system. I designed one into my Model Rocket Avionics Bay, along with an Altimeter and Temperature/Humidity sensor. It records these parameters, and when it senses the rocket has stopped gaining altitude and starts to tip over, it deploys the drouge parachute, and then the final landing parachutes at 300 meters from the ground.
When I was a teenager an Air Canada co-pilot explained this navigation system to me while I sat in the cockpit during a Toronto to Vancouver flight (pre 9-11 times). I never forgot his explanation and have always wondered about it ever since. This video confirms the missing pieces and details of the system I had naturally filled in from my imagination. I’m glad someone bothered to take the time to explain this sophisticated system to me. I’ve been interested in INS, GPS, GLANOSS, LORAN C, and ground based radar systems ever since.
Yes Sir, clear to the periphery, I have to read laser and understand why laser frequency and velocity is always constant irrespective of the velocity of the object on which it is fitted.
I had such hard time to understand INS till I watched your video. I’ve been following you on instagram for a long time and at first I was just curious about your pictures and now you’re an inspiration. The time spent watching your contents is never a dull
Good explaination! I used to work in the manufacturing of IRS systems based on RLG gyros. First job was with the F-T ADIRU. Basically it's the same sort of explaination I gave to alot of new techs and engineers. Have since moved onto MEMs based INS systems.
@@DeonMitton It was! Learned from alot of really smart folks. One thing I also generally added to help people understand was how rotation of the gyro caused destructive wave interference. The sensors then pick that up as pulses of light during rotation. Rate of pulses equals rate of rotations.
Would you mind answering a question please? I understand the basic principle for detecting rotation (I've read about laser interferometry because I like astronomy and it's used to great effect in LIGO). What I'm not sure I grasp is how the linear component of acceleration is measured. Is this also detectable based on interference patterns? I can't quite imagine how that would work.
@@macronencer The IMUs also have 3 accelerometers install as well. They are many styles used. MEMs based, vibrating beam, hinge and pendulum. All rely on inertia moving a structure to change either a resistance or capacitance reading. Calibrate that change to a know rate and you can build a model.
Thank you so much for the excellent explanation of ring laser gyros...it has helped me understand the IRS. Many years ago, I worked on INS on the USAF F-111A ( Litton AJQ-20) which had gyros in the stabilized platform unit (SPU). When ring lasers came out, I didn't understand how lasers could replace spinning gyros, but now I understand, thanks to you. You video was very helpful to me. Happy New Year!!!
Actually that was a good basic explanation of how it works. Obviously need some incredibly accurate computer system to be able to read it. But it's the first time I've had an idear how it works. Thank you.
I worked with the inventor of the laser ring gyro. It was never built for aviation use. The Ring gyro is over 40 yrs old. It has been adapted for use in aviation & missile systems since its development. The ring gyro was a triangle shape not a tubular fashion.
@@DeonMitton because a lot of it was company private I cant talk about a lot of thing as the company I worked for is a defense contractor. The company made submarine navigation systems, weapons control systems and the world leader in radar technology, developing doppler radar and phased array antenna panels, both military projects which are now used around the world. Dthe doppler was meant as a replacement for the EWR systems, but got cancelled due to satellites. The company sold the project to NOAA for tornado predictions as it was able to detect the tight radar echo in what as known now as the "hook" echo, detecting both inbound and outbound echos at the same time I can say that the ring gyro project was sold to another company that made missiles and at first they had major issues getting the ring gyro to work on a missile due to the huge g-force that were involved. I also know that the ring gyro was so sensitive that the optical bench that was used in my company could detect the earths wobble
Great video! I'm studying from home due to covid so it's hard to get basic questions answered. This helped me a lot in understanding my course content. Good explanation on ring laser gyros!
Essentially, the beams run in different, and opposite directions, they enter and exit the tubes at the exact same point, which enables an interferometer to measure the reassembled signal at the moment of the exit the tubes. When a ring laser gyro is in motion, the beams of light will travel different distances. In this system, difference in frequency is proportional to the rotation rate of the gyro (which is mounted inside the aircraft and therefore detects the roll rate of the aircraft in each of the axis where the laser is mounted). The frequency difference is detected and measured via an interference fringe pattern/ and which phasing contains the directional information. Hope that a bit more info about the fascinating science of using light beams to construct a gyro.
The IRS system still uses accelerometers as the ring lasers do not detect linear acceleration only rotation. There is 3 ring lasers one for each axis and accelerometers for each axis.
So you mentioned a difference in arrival time to the output detector is calculated with math. Well to some degree it is. The speed of light being 7.5 times around the earth in 1 second is hard to calculate speed differences in a enclosed 3 inch space. So it’s actually phase shift is what’s being calculated. The longer travel beam has a different phase than the shorter beam so the math is basically the Doppler Effect.
Essentially, the beams run in different, and opposite directions, they enter and exit the tubes at the exact same point, which enables an interferometer to measure the reassembled signal at the moment of the exit the tubes. When a ring laser gyro is in motion, the beams of light will travel different distances. In this system, difference in frequency is proportional to the rotation rate of the gyro (which is mounted inside the aircraft). The frequency difference is detected and measured via an interference fringe pattern/ and which phasing contains the directional information. Hope that a bit more info about the fascinating science of using light beams to construct a gyro.
With all due respect, the explanation of a RING LASER GYRO instrument is totally different. In a ring laser gyro, the cavity, usually 3 narrow tunnels, filled with the lasing gas (a mixture of helium and neon) IS the laser. (that is why it is called a RING laser) The edges have mirrors, such that the light travels in both directions in a precise triangular path. One mirror is semi- transparent, allowing light beams to exit in two directions with additional optics, these beams are brought together where they interfere with each other creating an interference pattern of waves that can be measured. At least one of the other mirrors is mounted on a piezzo-electric 'actuator' which moves the mirror about the distance of one light wavelength. Why? a gas laser operates only between mirrors when the path lenght is an integer multiple of the light wave lenght. The actuator holding the mirror is called the 'path lenght servo' and is controlled and moved to maximize the laser power. For the reasons that the presentor explained, the interference pattern will move in a direction that depends on the direction of the rotation rate component normal to the plane of the light triangle. By counting the interference waves, this rotation rate is measured with precision. There is one problem with ring laser gyros: When the rotation rate is small enough the counter rotating laser beams will 'lockin' and no interference pattern will be formed. One way to solve this problem is to mechanically 'dither' the instrument. Injecting an external laser light into a light guide pair is another but inaccurate way to measure rotation but it is NOT CALLED A RING LASER GYRO! It is called a fiber optic gyroscope
Beautiful location ! I thought you would start with Radio Direction Finding beacons as aircraft navigation aids. Not sure if you confused accelerometers (detecting accelerations, including gravity !) from gyroscopes (detecting angles of rotation). Yes navigation technology has undergone an amazing evolution over the last 50 years. From large mechanical systems, miniaturised, reliable laser/solid state, and now chips containing these devices with complex software providing complete navigation solutions (eg drone autopilots for $30).
There's much to say about the topic - and the purpose of this video is not as a technical classroom/lecture, but rather to create awareness to the interesting science at work, in the devices we take for granted today. I bring you these videos, in the spirit of raising curiosity about aviation and science in general. In that spirit, there are lots of other education center videos on the topic. My channel is purely for the enjoyment of aviation, and to inspire 1 x more person to take up aviation. If I achieve that, then I'll call it success.
I didn’t understand if we say the ring laser gyro is one solid-state one so when aircraft turning the whole item should turn so how does one light travels faster than the other, is it movable from inside or what. Thank you
@@DeonMitton You betcha! Thanks for the reply, it's a sweet hat. I bet you love your job, get to see great views constantly. Awesome video by the way, very informative and well presented.
There is no way that small difference in the two beams could be measured. If you study Walter Russel he said light has no speed so c is actually zero. They just use xyz accelerometers and the laser is just for show. I think JPL manufacture all the IRS units.
Think of it this way, a ring laser gyro is a delicate instrument. You should never drop, or subject the box to more than a few G's. The movements inside the box (The three ring laser gyros) one for pitch, one for roll and one for azimuth (Heading) are precision components. The ring movement is measured in thousands of an inch or fraction of a mm. The emitters and detectors project and receive laser light at the three apexes of an equilateral triangle simultaneously. Think of the three sides of each ring laser as A, B and C not a circle but a ring using a glass triangle. The glass is then surface coated like that of a microscope or telescope mirror. At each apex there is an opening where laser is emitted into and another for laser to exit and be detected for that side of the triangle. The three emitters and three detectors are calibrated to reference zero angle at a precise point. Any movement of the box in any direction results in the three ring lasers (When powered) results to give a precise output where the box has moved when bolted to the aircraft. The movements of the aircraft are measured in minuscule amounts instantaneously whether momentarily or, continuously. Theory being a mass remains in motion any change in the acceleration of that mass results in a change to the ring which is detected electronically by the lasers being reflected off the optical polished surfaces. The World moves around the ring laser gyro not the ring laser gyro moves around the World. This technology is only second generation inertial reference instrumentation. There are better instruments namely third and even fourth generation instruments which military uses for Nuclear defense and hyper-sonic aircraft.
Essentially, the beams run in different, and opposite directions, they enter and exit the tubes at the exact same point, which enables an interferometer to measure the reassembled signal at the moment of the exit the tubes. When a ring laser gyro is in motion, the beams of light will travel different distances. In this system, difference in frequency is proportional to the rotation rate of the gyro (which is mounted inside the aircraft). The frequency difference is detected and measured via an interference fringe pattern/ and which phasing contains the directional information. Hope that a bit more info about the fascinating science of using light beams to construct a gyro.
@@DeonMitton they way you describe the change in frequency points to the Doppler effect. I think that is what's going on here. Thanks for your explanation!
@@ThomasHaberkorn checkout the Sagnac-effect : en.wikipedia.org/wiki/Sagnac_effect - I might be mis-guiding by using Frequency - but I believe the interferometer to detect phase shift also
Close... IRS is an inertial platform that can detect and measure accelerations along 3 axis, as well as rotational acceleration. Therefore calculate displacement from a known position. I.e. it can be used for Navigation as well as provide attitude and heading reference. AHARS will only give attitude and heading reference and requires another sensor to provide navigation such as a GPS system.
Accelerometers are not the same as gyros -- accelerometers detect acceleration and using math can be used to determine speeds and translations. That get's you only 3 axis of information. The other 3 axis are the rotations about those 3 axis and that is provided by gyros. I know you know this and am mentioning this because you are inconsistent in usage. A small error can be ignored, but this is major and you should have redone that portion of the video.
Deon, very interesting; what about wind drift.? Does INS/IRS account for this or would pilots have used another method without the aid of external radio signals? Cheers
For wind vector, we need heading, drift ,groundspeed, True air Speed,we have heading ,drift ,groundspeed through INS/IRS,for True Airspeed ,INS/IRS gets its True air speed through Air Data Computer,thus obtaining the wind vector..
The video is cool. How accurate would INS be for a 4-hour flight? How much would he deviate going from airport A to airport B after 4 hours of flight? Would it be like drifting 1Nm for every hour of flight?
It's used on airliners, like inertial navigation, and is usually used to supplement other navigation systems, for long flights. You can probably find the performance specs online - so I won't elaborate here. Suffice to say, the predecessor, INS/IMU was used to land man on the moon (IRS is a FAR superior system) - I think that flight exceeded 4 hrs
All the comments saying “great explanation!” Got me to stick around. But you tools 10 minutes to finally get to the point and even then you did a terrible job explaining the ring laser. It is a SINGLE laser beam which is split, sent down two separate paths, then recombined at a SINGLE sensor. You have no idea what you’re talking about.
Dude you crazy doing here drawings in sand and using algea and stones. I get it but inoy because i am familiar with this. Serisoly you want to talk about beach do this, bur yiu wona talk a subject line ring lasers pls do yourself and others a favour and use at least a f pen and paper if yiu do t knoe to use power point or anomations. Serisly man...
EACH LASER WOULD NEED TO BE STATIONARY, WITH THE DETECTORS BEING MOVEABLE, TO DETECT ANGULAR/LATERAL MOMENTUM. WITHOUT BRINGING THE 'Z' ACIS INTO THE SETTING, AS ELEVATION CHANGE IS NOT DIRECTIONAL CHANGE. PITCH AND YAW RATE MIGHT HAVE SOME EFFECT HERE, BUT NOT CERTAIN.
Detection of rotational acceleration, is actually accomplished by means of measuring the interference of the 2 x waves. When a ring laser gyro is in motion, the beams of light will travel different distances. In this system, difference in frequency is proportional to the rotation rate of the gyro (which is mounted inside the aircraft). The frequency difference is detected and measured via an interference fringe pattern/ and which phasing contains the directional information.