HS Trident question for any former flightdeck crew.

[5025]

Can anyone tell me about the moving chart in the centre of the instrument panel. I believe it was called a Doppler Map, but what was it's function, when was it used etc?

[Trident Sim]

5025

It was indeed a Doppler Map display. A glorious piece of kit, occupying many pages in the flying manual and the undivided attention of some Route Check Captains. It provided hours of harmless entertainment and was, sad to say, almost completely useless.

The Doppler Map, a different one for each route, was a long roll of paper, wound round a portable spool, made up of pages and pages of airways maps covering what you hoped would be your route.

On arrival at the aircraft the map roll was fitted into the central map display, the chart angle and scale loaded into the controller, the indicator pen placed over the current aircraft position, the display initialised and a small prayer offered to the Navigation Gods.

Once airborne, above 400 feet, if it felt like working, the combination of the map scrolling (N-S) and the indicator pen moving (E-W) was alleged by those new on the aircraft to indicate the aircraft's present position. Provided you had just updated it, there was just a slim chance that it may even have been correct. It was loaded every flight and ignored nearly as frequently.

Among its more amusing faults was its ability to run backwards as well as forwards, or, if it thought you weren't paying enough attention, start running at double speed.

It took its feed from the Doppler Drift and Groundspeed Indicator, which was a useful and accurate instrument. The drift and groundspeed were obtained by using four aerials on the underside of the aircraft to transmit pulse energy along divergent paths every half second.

A receiver resolved the Doppler shift to calculate groundspeed, and compared the drift errors in each pair of beams to calculate drift angle.

If by chance anyone has any old map rolls they want to get rid of, I can ensure they are found a good home in the one remaining Trident 3B simulator.

[Lost_luggage34]

Trident Sim - many thanks for such an excellent post.

I found it extremely informative and amusing. Particularly having recently visited Brooklands and being an ex-employee of the major operator of said aircraft. 5025 - thanks for asking the question.

Regards

[5025]

Trident Sim, thanks for your reply to my post.

Now I know !!

[foghorn]

TS,

Was the Doppler Map kept working right up to the withdrawal of the Tridents from BA service in the eighties, or was it an early casualty for U/S stickers?

All the best,
foggy.

[Trident Sim]

foghorn

I'd left theTrident before the fleet finally disappeared, but the Doppler Map was still in use in the early/mid eighties.

Congratulations on the IR, but I shall now expect an even higher standard from you next time you fly De Havilland's finest! :D :D

Hope your IR renewal, which must be due around now, goes well.

Best Regards

Trident Sim

[mcdhu]

.................as opposed to the Decca roller map which was fitted to some ac in the 60s/70s which also required prodigous amounts of setting up and looking after for minimal navigational return. The maps themselves were hyperbolic, and thus one could be flying in a straight line, but the map could show the ac fizzing round a corner!! Decca was designed for maritime coastal nav where time is not often of the essence, however, much as Trident Sim says 'provided hours of harmless entertainment'. Sighs.....

Cheers
mcdhu