GPI Mk7
 

I'll put this here, and hope.

During NAV / OBS training in the RAAF HS748s, we used to use the Ground Position Indicator Mk7 (GPI Mk7). Going down memory lane, I wanted to collect some information on it but so far have come up empty handed.

The best I have found is a reference that it may have also been used on RAF Valiants.

Does anyone know of any web-based sources for pictures and / or technical data on the GPI Mk7?

I imagine you'll shortly get bombarded with replies from ex-V crews and nav inst techs. I don't know too much about the workings of the kit as I was primarily a radar/NBS tech (on Vulcans), but what I'm pretty sure about is that the Vulcan had the GPI mark 6. I would therefore imagine the rest of the V-fleet had the same GPI. If I'm wrong, I expect Pontius Navigator will correct me.

Try this for a little bit of info on the GPI6 http://john-dillon.co.uk/V-Force/nav_kit.html

MSJ

They used a spherical resolver (metalic cricket ball on a flat disc) to computate travel and position, and because most of the SAN navex routes departed Sale via Mt Livingstone (60 miles north east?), over time, they developed a small groove where the metal sphere travelled on the plate. This meant that no matter where you departed to (in a northerly direction) the GPI ALWAYS went to Mt Livingstone. Good start for a trainee nav cadet who was lost shortly after take-off. It took three to four '20 minute' nav cycles to get the 'plot' back, by which time you had erroneously entered Sydney Control airspace somewhere east of Parkes on your way to St George.

If they were fitted to Vulcans, how the bloody thing got them to Stanley is beyond me.

The answer was to install Twin Carousel INSs, robbed from ex British Airways VC10's.

IIRC the Victor had the GPI Mk 4 fitted, it certainly looked like that on ASI in '82.

For us it was always 50nm ES. From memory, you could always get a reliable TACAN fix there - as well as a reminder you were leaving ESL airspace.

Ah yes, the old ESL 50 tacan fix - just before DSPT....and just around the TOPOC fix.

Just to get in a quick dit before the navs take over... IIRC the Vulcan usually had a GPI6A in my time. The only real difference was that if you were lucky enough to cross the International date line with a GPI6A it would automatically switch from West of Greenwich to East,without a lot of manual knob winding and cursing.
Worked for me in Sep 74:)

I think that's a bit misleading. Yes Carousel were fitted, but without DME update, the allowable error rate was 3+2t NM, where t is time of flight in hours. I think there was a lot more to it than just placing faith in a couple of INUs.

S_H

This thread is an excuse to bring a brilliantly mad lady to the fore - :ok:

http://www.tatjavanvark.nl/tvve/dduck0.html

Blimey! A one woman vintage electro-mechanical collector cum mad professor type. Have the Vulcan team asked her to re-wire the cockpit yet? All strength to her.:D

OMG, that takes me back a few years! I remember having to tell the easily-amused FLMs off for leaning on the scanner once it was stabilised - they thought it was fun to hear the amplidyne speed up as it tried to counteract their force to keep the scanner level (and it did a pretty good job too but the FLMs didn't have to change it once they succeeded in burning it out). And the Calc 5 - us fairies had a chit from OC Eng. authorising us to disconnect/reconnect starboard nosewheel door jacks in order to get a u/s one out and a serviceable one in. Getting the split pin through the castellated nut and bending the legs over was a real b@sta@rd of a job for those of us with delicate hands!

I wonder what motivates someone to put something like that together. Truly amazing!

MSJ

MSJ,
Likewise, a trip down memory lane for me also. All credit to the lady . She even made up tools for all those Plessey Mk4 connectors! I wonder if it is possible to visit the rig?

Edit: As a result of looking at that site, I have just delved into a cabinet to extract a RAF Form 619A, which contains amonst other things , my own youthful scribblings on items such as ADRIS, GPI Mk4, Autopilot Mk 10, Periscopic Sextant Mk2, G4B & G4F Compass, GM Mk7ACompass, all complete with references to AP3280, I think I'll go and lie down in a darkened room.......

I'm sorry if this affects evilroy's quest for GPI info - but this has to be seen!

What does this woman do in her spare time.:eek: I've e-mailed her web man for a contact; her garage would definitely be worth a visit!

http://www.tatjavanvark.nl/tvva/harm0.html

Forget, all of those bits actually look like they were inside the GPI - and LOTs of them. They must have been trained in a Swiss watch factory.

Bl**dy hell. that brings back memories. I can feel the heat coming from all that kit coming from my computer screen!

On of our navs had worked out that the NBS (size of a small family car) had the computing power of about 1kb. To think all of that could be fitted into a digital watch these days!

That is one incredible lady.

CAPT Pugwash, I was also starting to think about the B6 driftmeter with all the gear you mentioned....

At least the Driftmeter on the Draggie did not lie, unlike the other hi tech nav kit.

Safety Helmut
 

Sorry you thought my comment about the Twin Carousels was misleading, I must admit as a past user of a single Platform Ferranti INAS I would have just about given my right arm for 3+2t.

Given the kit was in "Nav" mode, or whatever it was called on Carousel for around 8 hours without DME update your 3 + 2t gives an error of 19 miles, does it not? More than enough to find the Islands, but obviously not enough to bomb by. That was solved by a pop up to radar check the position with around 50 miles to run, and of course the bombs themselveswere dropped on radar, so the INS was irrelevant to the bombrun, AFAIK.

Sure, you need to have aligned the kit with TLC, and and you need some luck in hoping 3 +2t "applies" on the night and that one of the platforms hasn't raced off to New York, Flamborough head or somewhere more exotic... but don't you always need a little good fortune war? FWIW White's book claims the position at pop up was around 1 mile out from the mid-position of the two platforms.

Wiggy,

Was the IN stand-alone or integrated?

Just to clarify the importance of an accurate heading reference for radar bombing, whether using the HRS or IN, most radar attacks would be using an offset technique.

The radar is 'fixed' on a radar significant feature some distance from the real target. In the case of a target surrounded by water features a headland gives a well defined aiming point. The bombing computer is then offset back to the real target.

The accuracy of his technique is dependent on 3 things, the ease of identifcation of the aiming point, the accuracy of the calculation of the offset distance and most importantly the accuracy of the heading reference sysetm used by the computer.

As a ball park, a one degree heading error with an aiming point 10000 yards from the target would give an error on the ground of 174 yards.

For a runway target the usual close-in aiming pont would be a hangar. This is a cultural feature and susceptible to deception so the distance aiming point would ideally be a physical feature. Also, in the case of a runway, it may be possible to breakout the runway from the surrounding terrain. This is particularly true of an airfield with parallel runway/taxyway and well vut grass.