Aircraft Instruments

I have always been interested in the technology used in aircraft instruments. In many ways they reach the pinnacle of what can be achieved in displaying and sometimes calculating information mechanically.  Items such as moving maps, horizontal situation indicators and bomb sight computers being particularly advanced. I will expand this page over time to cover various aspects of these devices.

British Blind Flying Panel Replica

Blind Flying Panel

 

Whilst I have gathered up odd instruments from a variety of sources over the years, I haven't had a good way of displaying them.

This project kicked off when I was lucky enough to find a job lot of instruments on ebay for a bargain price, and I therefore had a good proportion of the instruments to put a blind flying panel together, even if they aren't exactly the right items to be representative of any particular aircraft type.

The blind flying panel was a succesful attempt by the RAF/ Air Ministry in World War Two to standardise the layout of the essential instruments for flight across the cockpits of many planes. Whilst there remains a range of differences between aircraft as diverese as a Spitfire and a Lancaster in areas such as the scaling on the airspeed indicator, a very high degree of commonality was acheived. Pilots were able to reap the benefits of this approach in training and ease of movement between aircraft types.

The general principle lives on to today, with many light aircraft maintaining the layout first developed over 80 years ago.

It is possible to find genuine panels available for sale, but at upwards of 200, this wasn't going to be economic. There are also several suppliers of replica panels, but whilst they aren't unreasonable prices, they cost more than I paid for all the instruments combined, so as I have a well equipped home workshop, I decided to make a panel myself.

Despite extensive searching, I failed to find a good, comprehensive drawing for the panel, so based mine on a number of key dimensions found around the web as well as scaling from images. The most useful was a basic drawing posted by Qldspitty on the Key Aero forum(1). Supplementing this with mounting drawings for the individual instruments and dimensions from the instruments themselves, I was able to put a 'close enough' drawing together.

I found a piece of suitable 3mm aluminium in my scrap pile and put together the panel, bandsawing the outline, cutting the large mounting holes with a trepanning cutter and then drilling off the remainder of the holes.

Blind Flying Panel
BFP

Panel in Build

Instruments are mounted with BA & UN screws as necessary. I turned up some 1/2" & 7/8" long 2BA brass clearance spacers for the 3 instruments that need them on the lathe.

I put together a plinth to mount the instruments on, made from some oak from a salvaged bookcase.

The panel is populated with the following instruments:

 

Altimeter      6A/1538
Direction IndicatorAN5735-1
Artificial HorizonMKII CIVIL
Air Speed indicator- Knots      6A/422
Turn and Slip Indicator MKIA  6A/675
Vertical Speed Indicator6A/942

 6A/422 Air Speed Indicator

6A/422 Air Speed Indicator (Knots)

6A/675 Turn & Slip
6A/675 Turn and Slip Indicator MKIA

6A/942 VSI

6A/942 Vertical Speed Indicator

6A/1538 Altimeter

6A/1538 Altimeter

AN5735-1 Direction Indicator

AN5735-1 Direction Indicator

MKII Artifical Horizon

MKII Civil Artifical Horizon

Illumination 

At the time of WW2, instruments were not generally illuminated by internal means, relying on external illumination. Indeed external illumination has lasted in a large proportion of cases right up until recent times as mechanical instruments are phased out. One chief advantage of this is that bulbs are easy to replace, and so there are quite a range of ways of providing external illumination.

For WW2 era instruments the dials and pointers were normally painted in one of two ways, a white paint that flouresces under UV illumination, introduced around 1944, and a luminous finish that glows without external lighting.

The two can be easily identified as the luminous finish loses it's glow with time and ages to a  browny yellow colour

The luminous finish contains Radium and is therefore a radiological hazard. Whilst the radiation levels are low, it is wise not to store these instruments in places where there is easy access to them, and to handle carefully. It is also wise not to disassemble or handle instruments with broken glass. There are a number of guides relating to this I would recommend you read.

Horizontal Situation Indicator

I was lucky eough to find this instrument at a scrapyard- As it was damaged, I felt that it would be good to open up and leave it this way to see the internal details. Hopefully the photos will be of interest to the fascinating mechatronics used.

Horizon Situation Indicator

HSI2

HSI

HSI

HSI

HSIHSI

Sources & Further Info

(1). https://www.key.aero/forum/historic-aviation/136922-dimensional-drawing-for-blind-flying-panel

Aeroplane Maintenance and Operation Series Volume 2: Aeroplane Instruments (Part I)
E Molloy
George Newnes Limited 

Aeroplane Maintenance and Operation Volume IV
E.W. Knott
George Newnes Limited

An illustrated guide to British Aircraft Equipment 1939-1945: Volume 1 Aircraft Instruments
Alan Hulme 2003

Aircraft Development and Production
M.M. Williamson
Third Edition 1948
Paul Elek Publishers

Aircraft Instruments
George Ellis Irvin
Second Edition 1944
McGraw Hill Book Company

Aircraft Instruments
Their Construction and Maintenance Fully Illustrated
J. Riley

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BFP Built Sept 2023
(C) M.Pantrey 2023