The Barbers Pole

[Mr_Grubby]

Just been looking at some old pics of the HS-121 Trident cockpit.
I remember the Barbers Pole from when I did famil. flights, but what did it do ?????

Thanks.
Clint.

[BEagle]

The Smiths 'Para Visual Directors', of which there were 6 on each Trident flight deck, rotated to highlight attitude errors. The 'barbers pole' rotated until the error was corrected in a natural sense; the azimuth director was in front of each pilot and 'streamed' left or right until the correct roll input was made, the pitch directors (one on each side of each pilot) streamed forwards and backwards. This was a sort of wide area flight director and was part of the equipment fitted for the world's first operational 'blind landing' airliner.

[Mr_Grubby]

Thanks BEagle.
Answer in 21 mins.
Wow !!!

Clint.

[Mr_Grubby]

BEagle.

I’ve been thinking about your reply.
So were the Poles used on departure to keep the aircraft on the centreline ?
Were they used on a CAT 3B landing ?

I remember about 1970/1 LHR was closed due Fog/Smog for about 3 days.
I was on the radar. The only a/c that landed were BEA Tridents.
Great days !

Clint.

[BEagle]

Sorry - don't know. I was busy doing my Aero Eng degree at London University in 1970! (When I wasn't skiving off flying ULAS Chippies at White Waltham!)

[Preppy]

BEagle

the pitch directors (one on each side of each pilot) streamed forwards and backwards. This was a sort of wide area flight director

Err. Flew the "gripper" for 12 years and I never noticed these!

Only azimuth PVDs fitted, used for roll guidance and CAT 2/3 centreline guidance information (via ILS localiser).

The other interesting bit of kit was the GRM.

:):):)

[BEagle]

Thanks, I stand corrected - the information I had concerned the originally planned prototype PVD installation. The azimuth PVD was directly in front of each pilot; the pitch PVDs were intended to be sited on the pillar between each windscreen edge and front side window and on the centre panel top left and right edges.

[Engineer]

Was the Trident not a forerunner of the Cat III requirement. When I flew the Belfast everyone spoke about the smiths flight guidance system that was developed from the Trident

This is a question :D ? Sorry for hijacking thread hope you don't mind

[BEagle]

Preppy - having studied the Smiths Aircraft Industries' drawing of the prototype Trident flight deck, it clearly shows both azimuth and pitch PVDs (even labelling them as such). Yet, as you have kindly confirmed, pictures of BEA Trident 1,2 and 3 flight decks show only azimuth PVDs. It would be interesting to know why the pitch directors were never fitted to operational BEA aircraft....

Don't know about the Belfast, sorry.

Back to the Trident, what was the cruising speed? I've heard many tales about it being a very quick a/c when compared to current A320/B737 equipment.

Aviation was soooo much more interesting back then!

[Preppy]

BEagle

Seem to remember that the pitch directors didn't work very well, so they weren't installed. Not sure what they were meant to do! Those were the days when the computers onboard were all "analogue" in design. Incidentally a serviceable PVD was required for CAT 3a or 3b approaches, but not needed for CAT 2.

Cruise Mach Number? Originally M0.87, (audible warning at 0.885 Mind) reduced to M0.84 and finally to M0.80 in the early 1970's; speed reduced as fuel price increased due conflicts in the Middle East. In fact, without any cruise autothrottle, the most stable cruise Mach No was about M0.82.

Vmo ended up at 365 kts, with an audible warning at 375 kts. So descent speed was typically 360 kts, reducing if necessary in turbulence to 275kts/M0.80.

The Trident 1 GARPH, displayed at the Cosford museum, was I believe the first a/c to do a Cat 3 landing on a revenue flight.



P.S Who were your instructors at ULAS? :D

[BEagle]

ULAS? Jerry Brown, Pete Lane, Owen O'Mahony, Andy Whitaker (CFI), Keith Skinner, Chris Booth, Keith Bomber, Malcolm Swinhoe plus others whose names I forget!

The Trident was obviously pretty quick - not many a/c can cruise at M0.87 these days! On occasion we would cruised the VC10 at M0.88 (indicated - actually only M0.86 true MN) before the fun detectors stopped it - it was part of a trainee co-pilot's trip back from Keflavik to Brize to fly as high and as fast as the ac could achieve, as it was probably the only time they'd ever see it done. But I was still required to take the old ladies to over M0.9 on full air tests :D

[John Farley]

Seem to remember that the pitch directors didn't work very well, so they weren't installed. Not sure what they were meant to do!

Direct you in pitch? (should you not be focusing/concentrating on the attitude display at that moment)

It was a long time ago and I was only on the fringe of what BLEU and Smiths were up to with their PVDs but they did ask us to fit them to our TOD Vulcan. As I was happy with the head down director displays and could not see the case for looking out or generally around just after takeoff (unlike the landing case) I don't recall we thought much of them, although to be fair they could not be positioned ideally in the confines of the Vulcan.

On the more general case of were PVDs a good thing I never heard anybody argue against them for roll on the aproach. I did hear that for some reason they were fairly prone to being used in the wrong sense in PITCH but not in ROLL - especially if they were just creeping round at the threshold of nearly stabilsed.

Why pitch was more suceptable to being misinterpreted than roll I have no idea.