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Moving maps displays - ancient mechanical!

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Moving maps displays - ancient mechanical!

Old 7th Aug 2009, 16:10
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Moving maps displays - ancient mechanical!

Folks,

As opposed to the slinky digitial GPS based moving maps of today, where could I find a good explanation of how the old paper (?) based types worked.

Seen a picture today of one in a Trident, and the display looked about a foot square...can't imagine how much map was available!
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Old 7th Aug 2009, 16:18
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and I have always wondered, how did you load them...like how did the map know where you were going?
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Old 7th Aug 2009, 17:06
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Is this what you meant?

Decca Navigator System - Wikipedia, the free encyclopedia

The picture shows the ship based display but there was a smaller aircraft version.

You just loaded the roll and off you went. It was as good as GPS (for its day it was fantastic). Helicopters used it for finding the oil rigs. I once was in a land rover that had a system installed.
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Old 7th Aug 2009, 17:21
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NWSRG,
Good question, now that you mention it...

I'll see what I can find out.
It wasn't paper, but some kind of backlit mylar film, IIRC.
For the mechanism, think those multiple advertising panels, where the posters are rolled up above and below the window.
The edges of the film maps would have been coded, so the display "knew" where it was.
If you wandered off the map sideways, it would go whirr-whizz to find the corresponding map on the roll.

By the time Concorde came along, they used a microfilm projector type device. Ferranti, I think. I witnessed a live demo in a LandRover around 1966, IIRC, and something like it was used in a James Bond film.
The Concorde one didn't last long..... who needs a map reader in the middle of the Atlantic?

SOPS,
I think you could get quite a lot of maps onto the thin Mylar film cassettes used, like most of Europe (Trident being somewhat short-range). They probably had cassettes for each route....
Same with the microfilm cassettes in the later projector-type displays.

Not too sure where the position data came from in those days without GPS.
Decca, possibly, for the Trident.. I don't think it already had an INS.

Ancient avionics engineer this end, not necessarily fully informed. But always curious. Anybody else for a trip down memory lane in the '60s?


PS A Trident survived almost complete... 'ZK.
And another forward fuselage survived, converted to a sim.
I'm sure the truth is out here....
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Old 7th Aug 2009, 17:47
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Old 7th Aug 2009, 17:49
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We used to have such a system in the Jaguar - since it's been retired from service now, you might get hold of a manual somewhere. (eBay?)

One of the peculiarities of it was that it put the aircraft in the centre of the map - just what you need when flying low level at 350+ knots (not that I ever got to sadly) - by and large it's what's in front that interests you and you spend approximately no time looking behind you!
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Old 7th Aug 2009, 20:41
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I know John Farley could tell you lots about the early Harrier moving map - a series of 35mm slides of 1/2 mill topo maps mounted on rollers and driven by rubber bands (literally). I cannot remember how the slides were mounted, but say 8 to a line, and when you 'went off the edge' of the end slide, a great whirring noise occurred and the whole assembly rotated to the next line at t'oher end. Being early INS it used to 'get lost' with montonous frequency and occasionally picked up its skirts and belted of hundreds of miles into East Germany at a great rate of knots.
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Old 8th Aug 2009, 02:17
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Decca Navigators were on trials at one California airline in the 1960's.
Decca set up the ground stations, and provided all the necessary hardware bits...and, is worked well, and was very accurate.
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Old 8th Aug 2009, 10:39
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The more advanced Decca moving map system was called Danac, which, iirc, used a map that bore some intuitive relationship to ground features. It was automatic in use - but you still had to load the right map rolls for the trip you were about to do and tell it where to start from. Sometimes on longer or triangular trips that ran off the map a new roll could be loaded in flight.
The basic Decca setup was a nightmare. The map was a closely packed mass of intersecting parabolic lines in three colours and frequently lost lock and had to be reset - a procedure that took some learning. This involved reference to the "Deccometers", three instruments reporting lane number in each colour, and one master instrument containing "spiders" and "cheeses" - wire crosses instead of needles that divided the instrument into 6 (?) sectors, and something that looked like a slice of cheese. Somehow, by base cunning and a great deal of luck one might sometimes be able to interepret the complex lane indicators and wildly gyrating spiders and cheeses and figure out which lane and fraction thereof you were on (in each colour) and then follow each coloured parabola to find where they all intersected on the map, by which time you'd flown a mile or three and weren't where you'd calculated any more, and had to start all over again. When it was working it was quite good - accuracy enough for non-precision approaches to 3-400ft, perhaps as good as 50m laterally if the lanes intersected closely and you weren't too far from the base stations, certainly not much worse than 100 - 150m over most of the UK and coastal waters. Accuracy dropped off as intersection angles of the lanes became more acute, and/or the lanes spread out at longer range but was useable up to maybe 600 miles from the base stations - I'd be guessing but accuracy of perhaps a mile or more out there. The real nasty gotcha was that when it "jumped" a lane (or more) it would carry on without a hiccup giving no indication that it was now lying like a cheap chinese watch, so had to be constantly monitored...a dreadful labour-intensive nightmare in a 2 crew cockpit at 500', 2 mile vis and blowing a gale as so often on the N Sea, with rigs lurking in the murk not far ahead. Still, some people seemed to be able to work it with ease. The Danac was fine.
(Fuzzy memory syndrome active here as it was in the mid '80s!)

Far, far better - infinitely better, was the Loran (or maybe a VLF/Omega) that one of our machines had. Looked and acted like an early GPS, ran automatically off gound stations on the other side of the world and was nearly as accurate as Decca. Why didn't everyone use that? And why did Britain persist with the antedelluvian Decca?

Decca Navigator - Airborne Receivers and Indicators

The systems I've tried to describe are, I think, the Mk8 and the Mk15 with DANAC which are well depicted at the site above. The Mk19 section also shows good pics of a DANAC chart reader.

http://www.jproc.ca/hyperbolic/decca...ice_map_b1.jpg

This map is a great deal less cluttered than the ones actually used, for a start it only shows two colours but gives the general idea.

Decca Navigator - System Overview

Chapter and verse here.

Last edited by Agaricus bisporus; 8th Aug 2009 at 11:26.
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Old 10th Aug 2009, 08:04
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The Trident had a Doppler navigator. It may have been made by Decca but I don't think it used Decca navigation. You got a scroll for your route and fed that in at the beginning of the trip. I flew briefly on the Trident and nobody took any notice of the Doppler, but had it running all the same.

In case you are unfamiliar with this, the Doppler gives you speed over the ground and drift angle. If you combine this with your heading you can move the motors on the display appropriately to keep the map correctly under a stylus that indicates where you must now be on the map. As I recall, the stylus drew a line so you could see your track (so far).

A bloke called Andy Mattock did have a pukka BA Trident simulator down near Gatwick but from what I can remember the Doppler Map had been replaced by something else, but I can't swear to it.

Last edited by twistedenginestarter; 10th Aug 2009 at 08:15.
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Old 10th Aug 2009, 14:12
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Decca navigator

The Trident did have a moving map. Your position was where the pen nib was.

The map moved up and the pointer (pen nib) moved side to side. Initally the pen had ink in it so you could see where you had been, but, having used it the map was then unusable, so very quickly the ink was not replaced.

I think thouge the first Decca Navigator was fitted to the Viscount. This worked in the same way but the vertical portion of the map was only about a third of the size of the one on the Trident.

When the Russians (Aeroflot) started flying in to London in the early 1960`s they had a couple of TU104`s fitted with the equiptment. They refused to rent them from Decca, the same as everybody else who used them did, but actually bought two complete systems. As a result they normally could only use those two aircraft into the UK.
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Old 10th Aug 2009, 21:48
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I know John Farley could tell you lots about the early Harrier moving map - a series of 35mm slides of 1/2 mill topo maps mounted on rollers and driven by rubber bands (literally). I cannot remember how the slides were mounted, but say 8 to a line, and when you 'went off the edge' of the end slide, a great whirring noise occurred and the whole assembly rotated to the next line at t'oher end. Being early INS it used to 'get lost' with montonous frequency and occasionally picked up its skirts and belted of hundreds of miles into East Germany at a great rate of knots.
I still have one of the later Harrier map displays, from aeromart anorakism days. I think the same model was also fitted to the Tornado. They were built by Ferranti as iirc, part of the FE540 ins system.

Internally, a pair of 35 mm film spools are mounted on a circular platform which is rotated by servo / gearhead assemblies, presumably from ins / compass heading data. Within the platform, the map is scrollable and there are effectively servoed x/y stages to index to the map point of interest. A map film is several tens of feet long and typically covers the whole of Northern Europe. It’s projected at selectable intensities by a halogen lamp in the rear of the case to a very directional fresnel lens on the front of the case. The front panel has various controls, including a zoom function.

Whatever the faults, these units are a work of art in mechanical engineering terms and a tribute to the ingenuity of their designers. Considering the technology of the time, the whole ins must have stretched the capabilities to the ragged edge. I had plans at one stage to get the unit running from standard gps nmea output, via a bit of microcontrollery, but too many other projects and lack of system info means that it’s still on the back burner.

Have all the AP reference numbers for the system, but though obsolete, it’s still 30 year rule, so no help from the usual sources. Any ideas ?…

Last edited by syseng68k; 10th Aug 2009 at 22:12.
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Old 10th Aug 2009, 23:31
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Originally Posted by syseng68k
I still have one of the later Harrier map displays...
Considering the technology of the time, the whole ins must have stretched the capabilities to the ragged edge.
Not necessarily.... 't were all clockwork those days....
I had plans at one stage to get the unit running from standard gps nmea output, via a bit of microcontrollery, but too many other projects and lack of system info means that it’s still on the back burner.
Have all the AP reference numbers for the system, but though obsolete, it’s still 30 year rule, so no help from the usual sources.
Infuriating, what?
Civil is usually some kind of ARINC standard.
Friend of mine got several bits and pieces running (ADI, HSI, INS CDU, clock), simply by cross-referencing from the Concorde documentation, even though none of his bits and pieces were originally Concorde.
I can understand your frustration.... especially since it CAN be done given the system info.
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