Item Identification

[Wolfie116]

Hi people

First post please be kind.

I was hoping that one of you Navigator types may be able to provide information about an item i came across at a Car Boot sale.

It appears to be some sort of Radio Navigation Aid.
It is beige, metal and approx 5 inches square and flat.

On it's front it has the words "Loop Bearing Computer" "RAF Form 1288"

There are 2 movable discs one with an aircraft and another with arrows. Both can be rotated around the 360 degree background. There are instructions for it's use and on the back are 2 grids containing information around quadrantal corrections and how to use them.

It's obviously quite old but i cant find any info on google or wikipedia about how or where it was used. I have taken scans of the item and will upload them if this is possible or requested.


Any help or info appreciated :ok:

[foldingwings]

Piccie might help!

[hval]

You are correct that it is a radio navigation aid.

A book titled "Despatch on war operations, 23rd February, 1942, to 8th May, 1945" provides some basic information. It is by Sir Arthur Travers Harris. Appendix A (pages 63to 65) provides some information. Try Google Books for access. If interested further try looking up the basics on Radio Navigation with Lorenz and Loran as examples.

EDIT
I have just looked on Wikipedia (http://en.wikipedia.org/wiki/Radio_navigation)for a quick link.

Hval

[Wolfie116]

Is there an image uploader on the site?

I have the lmages on my desktop

Edit:

I have uploaded them to photo-bucket, links below



http://i1103.photobucket.com/albums/g470/wolfie1161/LBCFront.jpg

http://i1103.photobucket.com/albums/g470/wolfie1161/LBCBack.jpg

[henry crun]

Wolfie116: There are sticky threads on D&G, and on History & Nostalgia forums which will tell you how to post pics.

[Wolfie116]

HVAL,

thx for the info, I am trying to ascertain if this item was specific to a certain system (oboe, gee etc) or whether it was generic or just a one off.


I was surprised that a normal google search turned up nothing

[hval]

Wolfie116,

My apologies for not responding sooner.

The computer would normally be for a single system. The locations of the base stations and the wave lengths, as well as the design of the loop antenna/e effect the calculations.

[NutLoose]

Woofie also register in the historic forum on flypasts website, they are very very good at this sort of thing, you will probably get the Name of the Navs dog too ;)

Key Publishing Ltd Aviation Forums - Powered by vBulletin (http://forum.keypublishing.com/)

[Wolfie116]

Thanks for the replies gents,

You have given something to go on. I have joined that forum and will post up details as soon as my account gets activated

TVM :ok:

[TimL]

Woolfie

You may have got your answer from the other forum by now, but if not, this might help:

Your computer is clearly a gadget for calculating Conversion Angle in order to plot long-distance radio bearings on a Mercator projection chart. It would have been used with a radio compass, which provides the relative bearing of a ground station (typically a Non-Directional Beacon (NDB) or a broadcast station). Radio waves follow a great circle from transmitter to receiver, but great circles on a Mercator are curved and are impossible to plot. By calculating conversion angle you can plot the bearing as a straight line from the beacon on a Mercator and hence get a position line.

The value of conversion angle depends on the mid-latitude of the beacon and aircraft (lines of longitude converge towards the pole) and on the difference in longitude between them. Your computer does all these calculations - the front works out the true bearing from the relative one given by the radio compass and the back gives conversion angle - and provides the result as a rhumb line bearing from the beacon.

It's nearly 50 years since I learnt all this at Nav School, so anyone who has a better memory than me is welcome to correct me! I seem to remember that we had just a table to provide conversion angle but had to do the other calculations in our heads.

[tail wheel]

http://i1103.photobucket.com/albums/g470/wolfie1161/LBCFront.jpg

http://i1103.photobucket.com/albums/g470/wolfie1161/LBCBack.jpg