Ferranti Horizon Plane Gyroscope avionics test spinup teardown 24000 rpm - Page 1
Forum section: electronics / projects

author: oz2cpu
author_rank: Frequent Contributor
timestamp: June 05, 2022, 08:12:41 am
content: not so often i get avionics on my desk, but wow this one is cool hi end designof course i make it spin up :-)just had to construck a 115V 400Hz supply too so that took like 5 mins extra.see how simple that can be done, when it is a time to solution kind of task.https://youtu.be/BMEChfifRq8hope you like it

author: moffy
author_rank: Super Contributor
timestamp: June 05, 2022, 09:51:31 am
content: Hey I used to work in the PIG(Precision Instruments Group) at Ferranti, Silverknowes, Edinburgh Scotland. Worked on their Ring Laser Gyros but also had some exposure to the gymballed gyro/accelerometer setup. A blast from my past.

author: Stray Electron
author_rank: Super Contributor
timestamp: June 05, 2022, 02:46:03 pm
content: Quote from: moffy on June 05, 2022, 09:51:31 amI have a couple of Honeywell LRGs and a don't-remember-the-brand LRG from the LMCo F-35 prototype. Absolutely amazing devices! But I'm getting old enough now that I'm starting to wonder what to do with them. They're so specialized that few people outside of the .MIL even know what they are and I hate to see them get trashed after I'm gone.

author: Stray Electron
author_rank: Super Contributor
timestamp: June 05, 2022, 02:54:22 pm
content: Quote from: oz2cpu on June 05, 2022, 08:12:41 amThis is exactly why I've kept several Elgar AC Sources around. 1,2 or 3 phase, variable frequency and variable AC voltage output. :-) You can't beat them if you're working on avionics, even the cooling fans in the stuff that I used to work on were 3 phase 400 Hz!

author: moffy
author_rank: Super Contributor
timestamp: June 05, 2022, 03:39:58 pm
content: Quote from: Stray Electron on June 05, 2022, 02:46:03 pmI assume if they are the Honeywell LRG's then they are welded within a triangular Mu Metal case. They were the bees knees, everyone including Ferranti, Marconi etc were trying to duplicate what Honeywell was doing. The electronics, which I and others worked on, was pretty straight forward. The physics and the construction of the triangular zerodure lasers and especially the mirrors was something more akin to exotic art. Problem with the HeNe gas inside, is that the He will diffuse through solids and would degrade the laser over time. The Ne was also a special radioactive isotope of Ne, I guess to help with appropriate energy states and transisitions. Do they still lase?They are impressive devices for accuracy ours could easily resolve 1.57 arc seconds of angular rotation.There was a weekend where a number of gyros were on test for stability, and they all showed a particular anomoly at the same time. No one could explain it until the chief of the lab asked everyone to look for earthquakes around the world. Sure enough one was found in Pakistan, that including the propogation time coincided precisely with the measured anomaly.

author: mawyatt
author_rank: Super Contributor
timestamp: June 05, 2022, 04:36:10 pm
content: Spent 20 years of my career at Honeywell, although never did work on the RLG or ESG (Electrostatic Suspended Gyro) but did work on the FOG (Fiber Optic Gyro) and got a couple patents way back. Knew some folks that did work on these gyros and they said the ESG was even better in long term drift than the RLG!!They also had some of the best mathmaticians working on Kalman filters, my close friend's wife was a Fulbright Scholar in Math, and worked on the filters her entire career. Honeywell continued to pump large amounts of research funds into gyros and this kept them in the lead for a long time, Litton even tried to claim Honeywell had unfair business practices because they couldn't compete on performance/cost.Honeywell knew physics, material science, semiconductors, control theory, precision electronics and mathematics as good as anyone back then, but somehow lost their way and why we left in 99.Best,

author: moffy
author_rank: Super Contributor
timestamp: June 05, 2022, 04:51:24 pm
content: Quote from: mawyatt on June 05, 2022, 04:36:10 pmDidn't Litton once try a rectangular RLG? Smaller form factor but that extra mirror was a real killer.Never heard of the ESG, but fibre optic gyros were really interesting. Rather than a frequency shift didn't they produce a phase shift?Interesting story I was told while at Ferranti. For some bizarre reason Honeywell allowed a number of its competitors, Ferranti included, to tour their facilities in the USA. They were even provided with briefing notes including a number of technical secrets but were told they couldn't take any notes with them. So one of the more devious amongst the Ferranti delegation managed to take photocopies of all the Honeywell notes, on the Honeywell photocopiers, placed it all in a nice sealed bag, adressed it to himself and went to the Honeywell mail room and convinced them to mail it for him! The most bizarre piece of industrial espionage I have ever heard of. I never saw the documentation myself, but at the time there were quite a number of closed door meetings at the lab. To this day I shake my head at the incident.

author: mawyatt
author_rank: Super Contributor
timestamp: June 05, 2022, 06:02:30 pm
content: Quote from: moffy on June 05, 2022, 04:51:24 pmYes Litton had a 4 corner RLG but didn't perform anywhere near as well as Honeywell RLG. The ESG were a thin hollow beryllium ball about the size of a golf ball suspended inside a beryllium oxide (yep the dangerous stuff) hollow cavity that had electrodes plated on the inside. An sealed optical window in the outer case allowed the ball to be monitored. The FOGs work on phase which is termed the Sagnac Function, whereas RLGs work on frequency difference between the counter rotating laser beams. The FOG we developed was closed loop in that the phase was forced to zero and since the Sine function is identically linear at zero the controlling function had a linear response. We used a technique from old microwave days which is called Serrodyne but applied as optical with a Lithium Niobate voltage controlled phase shifter. The phase shifter was "driven" by a linear ramp voltage to produce a linear phase shift with time, or ideal frequency shift without harmonics. The problem of ever increasing (or decreasing) linear phase shift was solved by precisely resetting the phase waveform at +-2*pi. This linear phase shift with time causes a delta frequency which forces the optically loop phase to be 2*pi*N , where N is an integer and thus effectively zero around the entire fiber loop (see patent 5339055).There were many attempts at intellectual property theft both industrial and defense, in those days Honeywell was a technology rich resource and a target for many. Recall a foreign agent was arrested across the street from one of our plants, he was working as a foreign auto mechanic and trying to glen information from Honeywell car customers. There were numerous others I can't comment about!!Best,

author: Stray Electron
author_rank: Super Contributor
timestamp: June 05, 2022, 06:32:29 pm
content: Quote from: moffy on June 05, 2022, 03:39:58 pmYes, it's a black painted round metal case about the size of a hockey puck and IIRC the top part of the case is triangular. The case was welded together but I pried one of them open and it has a triangle shaped laser tube in it. But amazingly small o.d., less then 3/16". Somewhere I have pictures, I'll try and find them and post a few of them here. Someone that I know got some of these back in the day and sold them on E-bay and got into a world of trouble for it and the company that let them out pretty much never got another MIL contract. Honeywell lowered the boom on them! So I've kept pretty quiet about them over the years. But I've had these for ~25 years so I can probably talk about them now.They have a IIRC 14 pin cable connector on the top and I don't have the pinout so I haven't been able to power them up. I just WISH that I had kept some of the documentation of the things that I used to work on. I had complete TDPs for just about everything.I think that by the time that these came out that most lasers were hard sealed and the life was much longer than the earlier soft sealed lasers.

author: james_s
author_rank: Super Contributor
timestamp: June 05, 2022, 08:33:24 pm
content: Quote from: Stray Electron on June 05, 2022, 02:46:03 pmI'm sure it won't be too hard to find someone who can appreciate them. I have a modest collection of gas lasers and would certainly find a LRG fascinating and I know I'm not the only one.

author: moffy
author_rank: Super Contributor
timestamp: June 06, 2022, 02:15:33 am
content: @mawyatt:Thanks for the info. Those ESG's sound exotic to say the least.Regarding the FOG's how did you deal with drift due to temperature? I would guess it was a significant issue.@Stray ElectronWould love to see photos of the devices! I can't wrap my head around a 3/16" OD. Our devices were huge by comparison, an equilateral triangle with each side a good 150-200mm long, and the Honeywell RLGs from the early 80s were a similar size.If your gyros are anything like what I know then they have:1. A HV cathode and two anodes that are current controlled.2. A tuning mirror/piezo drive that keeps the cavity in tune.3. A dither mechanism to vibrate the gyro back and forth to prevent lock in, also a piezo drive.4. An optical to logic output that provides a quadrature signal of the rotation rate.I was responsible for building the black box(literally it was black) that drove the RLGs when they were being tested. No digital electronics involved, all good old fashioned analogue.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: June 06, 2022, 09:47:19 am
content: is anyone able to help with the connector pinout ?preferred of the back side of my Ferrantior the round plane connector ?i have no idea what type of plane this was used in.my goal is to be able to see and test the auto level feature,also i am sure i feed only the motor spinup,since the bulbs dont light up,so a few extra signals / power / DC or AC inputs must be needed for the rest to work.thanks in advance

author: moffy
author_rank: Super Contributor
timestamp: June 06, 2022, 10:03:49 am
content: I was wondering if the auto level/initialisation uses some of those mercury switches to detect and level the gyro by driving the gymbal motors until every thing is level. It would then allow the gyro to spin up in that position.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: June 06, 2022, 12:02:20 pm
content: EXACTLY my idea Moffyjust need more info about how to wire up all the other missing signalsthen i am sure the auto level will work

author: moffy
author_rank: Super Contributor
timestamp: June 06, 2022, 12:23:22 pm
content: Those gyros were very expensive, just the gyro, in the 80's, I remember a figure of many thousands of pounds. Which makes me think maybe a military aircraft. The Tornados had a full INS(Inertial Navigation System), which I had some experience with, but I was told at the time of the Falklands, that the Harriers only had what you show in the video, an artificial horizon. Unfortunately, I have never seen one before, but the craftsmanship is beautiful, typical of the Ferranti instruments.P.S. Found an interesting picture of something similar mounted in a VC-10 cockpit:https://www.vc10.net/news_1718.htmlPerhaps the museum would have more info.

author: mawyatt
author_rank: Super Contributor
timestamp: June 06, 2022, 12:54:32 pm
content: Quote from: moffy on June 06, 2022, 02:15:33 amRecall there was a unique fiber winding technique which twisted the fiber as it was wound on the core and the fiber core was made of some different materials and all this was for temperature compensation of the fiber sensor, but don't remember any of the details for electronic temperature compensation. I do remember these FOGs challenged the RLGs in performance in many ways, which didn't make the older RLG diehards happy!!One fundamental advantage FOGs had over RLGs was the RLG can only lase over a certain path length range which scribes out a sensor "area", whereas the ROG can have varying lengths, core diameters and number of turns. The RLG sensor can only experience an input exposure "area" over a small range and effective single "turn" vs. the FOG which can cover a much larger "area" and have multiple "turns" thus the exposure of the FOG is better that the RLG for the input stimulus. However, the effective "Q" of the HeNe laser in the RLG is much higher than the laser diode utilized in the FOG, so pros and cons on both techniques.Best,

author: moffy
author_rank: Super Contributor
timestamp: June 06, 2022, 01:35:15 pm
content: Quote from: mawyatt on June 06, 2022, 12:54:32 pmYeah, with the FOG you could have kms of length all wound into a nice coil increasing its sensitivity while as you put it the RLG was single turn. But the RLG gave a rate vs phase output and had the higher Q. But then the RLG suffered from the lockin phenomena because of minute amounts of backscatter energy from the mirrors locking the counter rotating beams together at low rates or frequency differences. Hence the need for a dither mechanism and all the complexities it added. Signal to noise ratio must have been more important for the FOG as you had to resolve the angular displacement of the sine interferance pattern as RLGs tended to only resolve full pulses, but there was certainly more resolution available in the RLGs but it was never used. Interesting instruments both of them.

author: LaserSteve
author_rank: Super Contributor
timestamp: June 06, 2022, 02:40:17 pm
content: Neon 22 is not radioactive. It has a higher single pass gain then the natural isotopic mix. One isotope also makes for a highly desirable narrower gain bandwidth in the laser amplifier.Steve

author: moffy
author_rank: Super Contributor
timestamp: June 06, 2022, 03:03:49 pm
content: Quote from: LaserSteve on June 06, 2022, 02:40:17 pmThanks, I should have just said isotope.

author: james_s
author_rank: Super Contributor
timestamp: June 06, 2022, 07:45:18 pm
content: Quote from: moffy on June 06, 2022, 12:23:22 pmVirtually every certified aircraft had something similar, avionics have always been crazy expensive. I've seen videos of similar systems for Boeing airliners where the gyro is a separate much larger assembly that mounts in the avionics bay. Even small planes like Cessnas have something similar to the self contained unit that is the topic of this thread.

author: moffy
author_rank: Super Contributor
timestamp: June 07, 2022, 12:26:20 am
content: Quote from: james_s on June 06, 2022, 07:45:18 pmI was aware that pretty much all aircraft require a virtual horizon, but I was thinking that Ferranti instruments were like Rolls Royce and there might have been cheaper, relative, Ford virtual horizons available for non military aircraft. It is pure speculation on my part, I have no direct knowledge.

author: james_s
author_rank: Super Contributor
timestamp: June 07, 2022, 02:24:03 am
content: Quote from: moffy on June 07, 2022, 12:26:20 amCould be, I don't really know, I've never tried to price out anything like that. I just know that the similar units I saw from Boeing airliners were larger and looked much more expensive, with the gyro unit in a separate cabinet and remote displays. Regardless, these are very impressive instruments, I love that sort of sexy electromechanical precision, you just don't see that much anymore. I don't think I could ever get used to modern glass cockpits, a panel covered with rows of mechanical dials just looks the way an aircraft should IMO.

author: moffy
author_rank: Super Contributor
timestamp: June 07, 2022, 03:58:41 am
content: Quote from: james_s on June 07, 2022, 02:24:03 amYeah, the beauty of an almost completely mechanical solution is something else. How they managed to pack so much functionality into such a small package is real engineering. I love the fact that even the slip rings after 50 years are still fully functional. I am lucky if my DMM selector switch lasts more than 5 years, a given, you get what you pay for.

author: ivaylo
author_rank: Frequent Contributor
timestamp: June 07, 2022, 05:25:12 am
content: Yes, these are fun to play with! Three out of the standard “six pack” steam gauges of the general aviation planes usually contain gyros (art. horizon, turn indicator/coordinator and gyro compass). It’s interesting to see how they are used differently in the different instruments. Some are tiny too. I like the 14 or 28V DC ones, no need to muck with 400Hz or whatever (although I liked your solution), most are vacuum driven though.

author: peter-h
author_rank: Super Contributor
timestamp: June 07, 2022, 12:42:38 pm
content: Haha yes I fly behind a vacuum driven KI256 which (a 1982 design) is quite similar to the one above, although the one above is really old - my estimate is 50-60 years.These artificial horizons are being replaced with AHRS (3 yaw sensors and 3 accelerometers, and some software) but there are issues unless you have a separate electrical source (a second alternator for example).