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- Опубліковано 11 лип 2024
- This video presents the teardown of a vintage Ground Position Indicator which was used in Avro Vulcan aircrafts.
If someone knows something about this device please let me know, particularly the purpose of the various controls on the front panel.
00:00 - Intro
03:54 - Teardown
05:16 - Disc & Ball integrator
07:33 - Mileage computations
13:44 - Normal / Fix modes
15:16 - Synchronous motor
16:14 - Test with manual heading change
17:26 - Mileage simplified electro-mechanical diagram
Notes:
- At that time the goal of the third disk and ball integrator (on the bottom side) is unknown
Edit 07/03/24: according to @Pulsynetic the disk and ball integrator is used for a cosecant function which permits the correction of the meridians convergency to give the longitude.
- On the simplified electro-mechanical diagram the outputs of the disk and ball integrators are not the latitude nor longitude but the E-W and N-S mileages.
Mileages computation:
The mileages are computed using two disc and ball integrators. The disc of each integrator is linked to the same M-type stepper motor. The frequency of the signals which drive the motor must be proportional to the ground speed.
The input of the integrator (the displacement of the balls) is an image of the sine and the cosine of the heading. This is simply done using slides and levers linked to the heading shaft.
The angle of the output shaft is therefore an image of the integral of V(t)*sin(Theta(t)) and of V(t)*cos(Theta(t)), that is to say respectively the mileage on each axis.
Links:
Dead reckoning on Wikipedia:
en.wikipedia.org/wiki/Dead_re....
Disc and ball integrator on Wikipedia:
en.wikipedia.org/wiki/Ball-an...
on YT:
• Mechanical Computer (A...
Other navigation computers on my channel:
• LDM #313: Starfighter ...
• LDM #336: RAF Avro Vul...
• LDM #337: RAF Avro Vul...
Ball resolver:
• LDM #294: Navigation c...
THE V-FORCE : 1955 to 1966
www.blackmanbooks.co.uk/naviga...
Book Computing mechanisms and Linkages by ANTONÍN SVOBODA (1965)
www.randomwraith.com/document... - Наука та технологія
HI Michel,
Well done for the reverse engineering of the GPI MK.4, not an easy instrument to work out without any diagrams.
I have quite a bit of experience of the Ground Position Indicator Mark 4's. They are an evolution of the Air Position Indicator Mk.1, first flown in Lancaster Bombers. The API Mk.1 used compass input, corrected for variation, so true heading, and a rotational input equal to 24 revolutions per nautical mile of true air speed, measured by an Air Mileage Unit Mk.1 or Mk.2.. The resolved display of Latitude and Longitude didn't have correction for wind velocity, hence the name Air Position, as opposed to Ground Position. The navigator maintained an air plot on his chart from the data presented and had to add the wind effects on manually. The leap forward to the Ground Position Indicators came with the introduction of Doppler radar, that not only measured the true speed over the ground, but also the drift direction of the aircraft so the true track, as opposed to true heading could be used, in effect adding the wind velocity to the aircrafts velocity automatically. This allowed the instrument to calculate true Ground Position in several different display modes. The GPI Mk.4 has three data inputs, the first two are True Heading and Drift. By combining the two in the 'Azimuth Unit' on the rear of the indicator the aircrafts True track could be determined. The compass input is by M-type stepper input, 12 steps per sequence moves the compass pointer 6 degrees, so 0.5 degree resolution per step. The drift input was transmitted by Synchro data and represents the amount of drift, port or starboard, detected by the Doppler radar. External to the GPI Mk.4 and connected to it should be a small valve servo amplifier that runs the servo motor in the Azimuth Unit and nulls the track output to the combination of heading and drift. The compass display on the front of the indicator has two pointers. The single pointer is the aircrafts true heading from the compass, and the double arrow pointer is the heading plus drift angle, or true track. Only the track output is used in the two resolving gears to find the N-S and E-W mileages. The knob to the bottom left of the compass is to synchronise the GPI's heading display with the Aircrafts compass, press to engage the gears. If the compass was energised the knob would 'jump' the heading pointer around the compass rose in 6 degree steps.
The third input is Distance travelled over the ground. The large black motor you describe as a synchronous motor is not, its a big stepper motor. Again, it uses the Naval developed M-type transmission system, developed for Naval gunnery computers and has a twelve step sequence over the three wires. Its an odd system generated from a commutator type transmitter and connects each leg of the motor to either +24VDC, Ground or leaves it open circuit. Like the API it uses an input of 24 steps per nautical mile travelled. A conventional stepper motor driver cannot be used with it as the outputs don't support the disconnected step.
The four little DC motors internal to the unit have two functions. Two motors allow rapid drive to the counters for rapidly changing their values by large amounts. The setting knobs by the counters are normally held in to the panel. By turning the knob a quarter turn left or right the motors drive in either direction to rapidly change the counters. By pulling the knob out the knob can then be turned to mechanically set the position of the counters by hand. The other two motors are part of a storage mechanism. When the control knob is in the normal position locking pawls allow the resolved distance to be directed to the counters. When the knob is turned to the 'Fix' position the counters are locked and the distance is diverted to the storage units via the differentials. When the Knob is returned to 'Normal' the drive to the counters is resumed, and the stored mileage is driven out of the storage units by the motors and is added to the counters as well, back through the two differentials.
The reason for the Store/ Fix function is, the unit is still a 'dead reckoning' computer. From a known starting position, say a carefully surveyed LAT and Long at the centre of the runway being departed,, the unit will accumulate small errors in position as time runs on. From time to time the navigator had to perform a 'Fix' to determine his actual position and if the GPI was off the displayed position had to be corrected. The fix was found by either flying over a known location, Radio Direction Finding (RDF) on beacons, GEE or Loran, TACAN, Decca Navigator etc, or even celestial fixing via a sextant. As some of the position calculations could take some time, 15-20 mins in the case of a star fix, the displays were halted so the correction could be calculated and the displays corrected. All the time the fix is being calculated the plane is still flying along. Hence the need to store the mileage during the fix phase, then add it back on to the counters once they were reset.
The storage system is very sensitive to damage. You have to be very careful to connect the 24VDC supply voltage correctly, otherwise the motors can run away backwards and damage the control contacts. The storage units have an emergency operation mode whereby any stored mileage could be cranked out by hand in the event of a motor failing. Be very careful about cranking these controls, as again damage can be done to the storage mechanism if they are wound the wrong way or against the end stops. On a newly serviced unit the crank and the input drives would have been lock-wired in place so that any tampering was evident.
P.S. I have the RAF AP's for the GPI Mk.4s. If you want a copy PM me, though it kills the fun of reverse engineering the units if all the answers are put on a plate.
Cheers, Ian
The disk and ball integrator you show at 5.30 in the video is the cosecant calculator. The output from the two N-S and E-W resolvers on the top are in nautical miles. In order to display the result as Latitude and Longitude the Longitude display has to be divided by the cosecant of the latitude. This accounts for the effect that lines of longitude are only equal to one nautical Mile per minute of angle at the equator, Latitude 0. As the lines of longitude converge towards the poles a given mileage flown parallel to the equator would cross an ever increasing number of lines of Longitude, reaching infinity at the poles. This also places a maximum Latitude on the GPI Mk.4 of + or - 70 deg. Latitude, after which there is a risk that the cosecant gear stars to slip.
This is UA-cam.
Please use smaller paragraphs for readability. Thanks.
Thank you very much for these detailed explanations!
There is three modes of operation. The modes cannot be changed in flight without having to reset the whole instrument, hence the high speed setting motors. Grid, the displays are in nautical miles travelled and was supposed to be useful for navigating a search and rescue grid, or locating things like submarines. Lat/Long, speaks for itself, displays re-geared to indicate change in degrees and minutes, with the cosecant gear brought in to use. A/A, or Along and Across, is an oddity one. In A/A mode the desired Track the aircraft is to fly is dialled in on the little window and knob on the bottom right of the indicator. The displays then show how many miles have been flown along the track, and how many miles you may have drifted L, Left or R, Right. There is a mechanical interlock between A/A mode and the Track setting indicator, and your unit appears to be locked in A/A. The track indicator must be returned to 0 degrees, the four legged pointer behind the knob must have its longest leg vertically up. Once in this position the mode lever should be able to move freely between all modes. sometimes you have to rock the knob slightly to get the interlock to release.
@@pulsynetic Very reassuring, the sounds of Understanding and Experience. Bravo!
Wow that’s a nice piece of analog computing!
Somehow not surprised to see you here! Cheers!
dire que tout ceci a été étudier et dessiné en 2D, sans ordinateur, respect les concepteurs !
j'ai pensé la même chose, on ne se doute pas de la complexité, jusqu'au moment où l'on retire le capot, impressionnant!
Hello. I am an ex RAF navigator and used this equipment back in the day. The GPI Mk 4 was also in some Canberra aircraft and most likely the Victor and similar vintage aircraft. I was a navigation instructor too and the Dominie T Mk1A had the GPI Mk4 in the second navigator's position, although it had fallen out of use in the early-mid 90s.. If you have any questions of how it was used please get in touch.
Absolutely fascinating and as always superb analysis. What a massive undertaking it must have been to design a device like this and the many others you have evaluated. Merci Michel.
toujours des merveilles , je ne m'en lasse pas, et toujours épater par la facilité que vous avez a vous balader la dedans chapeau !!! , un grand merci pour le partage c'est a chaque fois un réel plaisir.
Very interesting part, thanks a lot 🙂
(Also, cudos to you for going through the effort of manually turning the gears)
The Vulcans were always flying over my house as a kid. I lived near RAF Waddington. Very loud. :)
Check this book: Computing Mechanisms and Linkages by Antonin Svoboda
It was written before computers were available as a design guide for navy engineers to design mechanical autotargeting systems. Much of the internal workings reminds me of bits and graphs of the mechanical examples given for different methods, visually.
Thank you for that, very interesting book. I have found the pdf version, I have placed the link in the description.
Fascinating!
When it comes to weaponry, there's really no limit on the spending...
Old school, COOL!
é muita engrenagem motores elétricos eixos rolamentos e muito mais
Maquina incrível
Bro casually has military equipment.
It’s available if you know where took and if your willing to spend a lot
eBay is your friend.. sometimes you can find it on the country too, you have to find who sells them..
I think this was constructed by engineers who had previously constructed naval targeting systems for ship's guns.
Wonderful video. I bet these units cost a fortune when built!
👍👍
Dang those grey gears look like technics Lego gears
Is paint on the scales radioactive?
When I catch myself thinking "I could've designed this" I remember how much harder it would've been to design with just a slide-rule!
I love this kind of tech, it makes me think about all of those mechanical systems to make operations, that's a big one porpouse calculator and the fact that probably nowdays this can be made with an arduino 🤣🤯
"Use 250VDC Megger only"...well, that rules out mine since it only works at 500V.
Si un jour on rentre en guerre on compte sur toi michel 😂👍
sine and cosine drive