British Compass - Pattern 250 or 259
 

Today I was discussing early British aircraft compasses, Tabloid/Baby equipment in particular, and was referred that it my be something called a pattern 250 or 259 compass.

Does anyone have any information, drawings or references they can recommend?

Many thanks!
Russ

What would you like to know?
I think I have the orginal GA drawings of both of these. If not I have the orginal manual describing them with diagrams.

Hi Russ,
These are pics of a 259 that came up on ebay some years ago.

http://i231.photobucket.com/albums/e...e/a3_1_b-1.jpg

http://i231.photobucket.com/albums/e...npe/a2_1_b.jpg

http://i231.photobucket.com/albums/e...npe/db_1_b.jpg

Cheers, Nick

Thanks a lot guys !!

I'd be interested in photos of them mounted, and what time periods/planes they were used. I'm obviously snooping around '14 - '16 Sopwiths, and would be interested to know if these predated the 5/17 usage, and in what planes, Tab and Baby in particular.

Are the 250 and 259 similar?

Again, many thanks!!

From a RAF? document dated Sep 1918, "NOTES ON COMPASSES AND THEIR ADJUSTMENT", (S.S. 1035), the following comments are made:

The three types of aero-compasses now being fitted in British aeroplanes are:—
(i.) Type 5/17.
(ii.) R.A.F. Pilot's Compass Mark II.
(iii.) Pattern 253.

The following information is taken from what I believe is a RFC instrument repairman's course syllabus.

The patterns of liquid compasses now used are as follows:-

Pattern No. 200 (Very little used)
Pattern No. 250 (Very little used)
Pattern No. 251 (Very little used)
Pattern No. 252 (Used on large and slow machines)
Pattern No. 253 (Used on large and slow machines)
Pattern No. 255 (Obsolete)
Pattern No. 259 (Very little used)
Pattern R.A.F. Mark 2 (Generally used)
Pattern C.O. 5/17 (Widely used)

PATTERN NO. 250.
Similar to pattern No. 200. but with a wire lubber line extending in an arc of a circle from the edge of the card to the pivot support. This enables the pilot to read the card at all degrees of forward inclination. The pivot system is inverted to obviate spinning as far as possible. The cardinal and quadrantal points are marked with a radium compound for night flying. The position of the electric light is on top of the bowl instead of underneath. The glass cover is protected by means of a spring shield.

PATTERN NO. 259.
The bowl in this type is again circular but with a flat glass cover, and is in a vertical position. The expansion chamber is on the front of the glass. The lubber line is painted on the inside of the glass. It is thus aft of the card which, in view of this fact is numbered on the outside and anti-clockwise. Therefore, the red end of the magnets is adjacent to the South point of the card, making it necessary, for great care to be taken in adjusting.

The bowl is suspended in a circular metal ring and held in position with an arrangment of bolts and felt washers which absorb the vibration. The magnet box is placed directly over the center of the card on top of the outer metal ring and has two holes for the reception of correcting magnets.

I find I have a copy of the orginal GA drawings of Patt 251, 252 and the RAF MkII, so can not help you with an orginal dimensioned drawing for either of these 2 compasses.

I have a couple more books on the subject that may reveal more information on the subject.

Picture of Patt 259 compass
 

Here is a diagram of the Patt 259.

Patt 250 compass
 

In a book dated 1915, the Patt 250 compass is described as being:

Pattern 250. Radium Card Compass.

The new type of Service compass is a modification of the pattern 200 in which it has been possible to considerably reduce its weight and by an alteration in the method of pivoting the card to increase the angle of clearance between card and bowl from 15 degrees to at least 30 degrees and at the same time to add to its steadiness under vibration.
The figuring on the card is treated with radium compound which enables it to be clearly read in lens or prism at a distance of 3 feet; in this connection it should be noted that the full definition of the radium markings is not attained until the observer's eyes are accustomed to the darkness, a period of at least 10 minutes being necessary. An alternative system of electric lighting is arranged for and leads are provided for conveniently connecting to the instrument a lighting set or a dry cell in those machines in which the compass has to be placed at a greater distance than 3 feet.

The Patt 200 was placed in service in 1911.

This is clearly amazing information - many thanks - it's just incredible.

Now that it is clearer what the general layout, appearance and distribution are, I need to find some parts list or something tying one to early Sopwiths, elsewise may have to go with best option that I can find available.

Again, Many thanks!

Russ,
do you have the Tabloid drawings? I left my copy at Robert's. When I see you next week we can thumb through them to refine details...

Rob

Sop Baby
 

Hi Russ ..I think you will find that the Dash board drg for the Sopwith Baby shows a Patt. 200 compass mounted centrally atop the dash , just ahead , on the scuttle if I remember correctly ...( ? or perhaps it was a 250? ).
I bet JoeP has a drawing somewhere on his thread !
Can't help on the Tabloid I'm afraid :).

John M