recalls flight test
instrumentation of the 1950s…..
Automatic observer panels (AOPs) were the obvious answer to augment the pilot’s kneepad jottings. These were the forerunners of the proverbial many and varied ‘black boxes’ leading to today’s flight and crash recorders which became bright orange boxes to make them more easily identifiable in the event of a mishap. Hawker’s first foray into the task of collecting data was achieved on a very limited scale, mainly because space was at a premium in our small fighter aircraft. Some usable space was found by the simple expedient of removing one of the two VHF transmitter/receivers that were fitted for communication between the aircraft, the ground and other aircraft.
A box to fit in place of the VHF set was made and at
one end inside this box a panel was fitted which contained only four or
five instruments. Nestling between these and fixed to the panel was a
small clockwork Pathe ‘H’ 9.5mm cine camera. The camera looked through
the panel away from the instruments towards a mirror at the far end of
the box. The mirror enabled the camera to be focused on the
instruments. Lighting was provided in the form of a number of small
12-volt bulbs mounted round the instruments. A sheet metal screen was
positioned an inch or so away from the panel with cut-outs to ensure
that the camera could see the faces of the instruments but not the
bulbs. The camera was started and stopped electrically by the pilot for
either single shot or cine.
One of the instruments on the panel of the AOP was a clock. This would be synchronised with another in the cockpit so that the times noted by the pilot and those recorded on film could be correlated.
After flight the developed film would be read by a Flight Development engineer using a light box and magnifying lens and the instrument readings noted. The readings would be corrected using the instrument calibrations and then correlated with the pilot’s comments from his debriefing and kneepad notes. This was a time consuming task.
As time went on the AOPs became bigger and better and were not always confined to ‘black boxes’. Because of the greater number of instruments it would have been unnecessarily complicated to use a masking screen with so many holes. We therefore made our own individual Bakelite bulb holders, complete with removable aluminium covers, to use on our AOPs, doing away with the screen.
The AOP in the Sea Hawk prototypes was a large panel containing twenty or more instruments. As this aircraft had a bifurcated jet pipe the panel was placed across the comparatively roomy inside of the rear fuselage aft of the ventral access panel. With no box or mirror necessary in this application a much larger camera was positioned forward of the access hole looking aft. To work on this installation it was necessary to duck under the aircraft and stand up through the access hole. This was fine if the aircraft was jacked up off its wheels.
Editor’s note. I joined Flight Development in 1961. Hunters and P.1127s were still using AOPs although the paper trace recorder was the primary recording system. In another article Roy will tell us about these.