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Author Topic: spitfire compass (P.8)  (Read 12543 times)
jan.vallenduuk
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« on: June 13, 2010, 11:46:23 AM »

Hi
I am a newbie to this forum.
I have compass in my possion with the markings:
a small copper plate with written on it: a crown, A M and ref no. 6A/726
on top: type P.8 and No 18845 B
Is there anybody who can give me more info?
I would like to know where it comes from etc.
I actually picked it up on a scrapheap in Hermanus, South Africa.
The glass was cracked, so there is no more liquid in it.
I have also taken off the vials of radium from the "spider"and cleaned
and repainted the inside to get rid of the possible radiating paint.
I would like to know what liquid to use in the compass (could i use modern silicon based liquid or just alcohol ?)
I have some experience working with compasses. (used to work at a magnetic observatory in SA)
I now live in Alkmaar, Nederland.
A lot of the brass screws are missing and I would like to now where to find some(It looks like that small size is not readily available)
What kind of wood was the case made of? I have no wooden case and would like to restore the compass completely

Regards

Jan Vallenduuk
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Spits
Jr. Member
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Posts: 58


« Reply #1 on: June 14, 2010, 06:08:41 AM »

The P8 compass was pretty universal with midwar British aircraft.Alcahol is best for filling the compass up.Brass screws are all BA type and thread.The box is depending on Airforce it flew with.Have a pic here somewhere.
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Edgar Brooks
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« Reply #2 on: June 14, 2010, 09:55:29 AM »

The P8 was superceded by the P10-P12 compasses, which can still be obtained from Sirs, who are based in Kent.  The tubes, on the spider, were not filled with radium paint, but radium powder, so should be handled with extreme caution, since inhaling it, from a broken tube, would be very injurious to health.  Post-war, the powder was replaced by "fluo" powder, which reacted to fluorescent light, rather than simply glowing in the dark.  The interior paint (black for a/c compasses, white for landing compasses) is a special alcohol-proof type, which can be removed by cellulose thinners.  The tubes were attached to the spider with small blobs of the paint; there should also be a small tube attached to a pointer somewhere on the edge of the bowl (which was aligned with the cetre-line of the a/c.)
From your description, I can't tell if you have the whole thing, since the P compasses consist of a bowl, which sits on cone-shaped brass springs inside a metal casing, and has a rotating circular bezel set on top of the whole thing.  The bezel is marked with the full 360 degrees of the compass, with N, E, W, S, engraved into squares, at their relevant positions.  A pair of wires (four on later versions) are laid E-W under the glass of the bezel.  The wires, over some of their length, and the bezel's cardinal points were painted with radium paint, which, by now, is probably turning to dust, and could also be very dangerous to your lungs.
The liquid is Industrial Methylated Spirit (IMS)99, aka known simply as "alcohol," which is now used neat, but usually had about 10% water added, during wartime.  Having been splashed with the stuff, I can reassure you that it tastes foul, and is poisonous, so no attempt, to drink it, should be made.  The glass has a chamfered edge, and should have a surrounding O ring, made of 1/8" (3mm, these days) rubber, held in place, and squeezed by the outer brass ring (secured by 6BA countersunk brass screws.)  The bung, in the filler neck, should have a fibre washer fitted to it; normally, the whole item is immersed in a quantity of alcohol, and de-aerated at the same time as the alcohol inside the bowl.  The spider should have a pivot fitted in its centre, which sits on a sapphire "jewel" in the vertical post set in the middle of the bowl.  Balance of the spider, in the fluid, is achived by judicious bending of the "spare" four arms of the spider, and application of quantities of paint where necessary.  The handling difficulties are made worse by the paint's propensity to flake off, if, once soaked with alcohol, it's allowed to dry out, so speed is essential.  The compass was designed for use anywhere in the world, so could cope with any angle of dip induced by the Poles (around a maximum of 13 degrees, if memory serves.)  This means that the further North, or South, you go, the lower one edge of the spider would go; this means that, here in the U.K., the compass has to have a 7 degree (or thereabouts) Northern dip built-in.
A.M. = Air Ministry, and the crown signifies military (Crown Property.)  6A/726 is the stores reference; some postwar landing compasses were 6B/34, 6C/2024 & 6C/2027, for example.  18845 is the serial no., but I don't know the significance of the "B."  Carrying boxes were normally wood, using a mixture of glue, and brass screws; in the base would be a false "floor," with three cut-outs to accept the three lugs which were used for fitting the compass to the a/c.  The hinged lid would normally have a couple of pieces of wood, with felt attached, which would just lightly bear down on the rotating ring.
Hope that helps a little.
Edgar
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BillKnox
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« Reply #3 on: May 30, 2011, 01:38:00 PM »

Hi

I am also a newie to this forum.
Regarding the P* compass, I was under the impression that the P8 was replaced by the P11 towards the end of the war and was only used in fighters.
The P10 was was used in heavy bombers, ie, Lancs, Manchester, Mosquito and many others.
The fluid according to another forum, is alchohol with distilled water added to get a specific gravity of .81 using a hydrometer.
The letter at the end of the serial number I was told relates to the name of the manufacturer, but I have not been able to get this verified anywhere, can anyone help here?

Regards

BillKnox
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