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BRABAZON AND ON (Part V)
Stick Force per g. One of the most important assessments relating to the handling qualities of an aeroplane is the “feel” of the flying controls and the harmonisation of these in all axes. |
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The achievement of this is simplified in modern powered-flying control systems because the feel is entirely artificially provided anyway. The Brigand flying controls were manually operated via square tubes and the measurement of the pilot effort required in the elevator circuit during various manoeuvres was known as “stick force per g.” tests. Aircraft VS 860 was used for this, the relevant instrumentation comprising a force-recording control-column to measure the pilot’s input effort and VG recorder mounted in the rear fuselage. The latter struck me as being a fairly rudimentary device, being connected to the pilot system and containing an accelerometer. The trace from each separate test was scratched by a stylus onto a small glass slide which had been coated in candle or lamp black. This had to be changed before each manoeuvre. The first flight did not start too auspiciously. Just before lift-off with Mr. A.J. Pegg at the controls, a tremendous bang rocked the aircraft. The pilot made an emergency stop, informed the tower, and turned on the runway to check if we had struck an obstacle. At the same time he racked his seat to its highest position to survey the front of the aircraft and instructed me to check the rear. Nothing untoward could be seen so a second take-off attempt was made and again at about the same time a massive shudder was felt. I was instructed to check the rear hatch for security and we then returned to allow the ground crew to make a more thorough inspection. Again nothing was found and although on the third take-off a further shudder was felt we were soon safely airborne. I never heard any satisfactory explanation for this phenomenon but many years later I learned from a Concord Flight-Engineer of the “oil-can effect” which was being experienced on one of the prototypes. This apparently occurred several times during climb-out when a part of the fuselage structure behind his panel would suddenly “re-arrange” itself, with a startling effect on the crew. Perhaps this is what had occurred on VS 860 all those years before. Now I suspect the public image of test pilots is that they are all “Dan Dare” types oblivious of all danger and always pushing themselves and their aircraft to the very limit. Nothing could be further from the truth. However these particular tests were shared by a number of pilots to obtain the widest possible evaluation and I thought I noticed just a little bit of professional rivalry creeping in for the honour of pulling the most “g”. The highest level I recorded was something over 4g, peanuts of course by today’s standards, but at the time probably approaching the design limits of the aircraft. As it was necessary for me to stand by the Automatic Observer Panel to operate the camera I was sometimes forced to my knees and would finish up grovelling on the floor of the aircraft. At the end of each flight it was common to find the rivets had popped and slight skin wrinkles had developed but the structure was basically strong. During the Farnborough Air Show the Brigand was rolled at low-level with a torpedo slung, allegedly by a French pilot, but quickly emulated by Walter Gibb. A further “hiccup” occurred on a later flight. The pilot this time was Johnnie Howman, a most friendly and relaxed character, who sadly recently made his last take-off to the great beyond after having completed a second career as an Air Traffic Controller. I should explain that to keep the pilots effort within acceptable limits the elevator controls incorporated a “follow-up” tab. This was operated by way of a spring-pot in the elevator control line which “broke-out” at a predetermined load causing the tab to assist the pilot. On this flight it was decided to inhibit this tab by removing the spring from the pot and substituting a piece of solid mild steel bar. The tests had gone smoothly over the South coast and, rather unusually, we had been cleared by ATC to return at low level over Salisbury Plain – a pleasant novelty. The pilot was relaxed, as usual, and singing his favourite tune “Steamboat Bill –steaming up the…..” as we roared along scattering the sheep and the soaring birds. The “greenhouse” type cockpit provided a magnificent 360 degree view. Suddenly the steamboat stopped in mid-bar and I froze as I heard on the intercom “Stand-by – I think the elevator is coming loose.” Followed shortly afterwards by “You’ve been monkeying about with this elevator, what actually have you done to it?” I explained briefly about the change to the spring-pot and confirmed that I had actually witnessed it being securely wire-locked after reassembly. After some tense minutes, a few “switch-backs and a bit more grumbling things seemed to return to normal and soon I was relieved to hear the sound of Steamboat Bill again! On landing I was greeted as usual by the amiable Ron Burchell the senior ground crew-man “Did you have a good flight?” “Yes thanks, quite exciting.” “It would have been a damned-sight more exciting if you had had to jump out,” he smiled, pointing to my parachute pack still in the back of the duty truck! I had worn the harness only! I never did that again and I’m not too sure that I would do “stick force per g” tests for five bob an hour again. Many years later I was on my way to Toulouse in our wonderful HAS 125 communications aircraft. We were being rocked a bit by turbulence over the Massif Central. I noticed my colleague, a senior engineer with a very explorative mind, was gazing intently though the window at the aileron. After a lengthy silence he remarked “You know a bit about follow-up tabs. I’m sure that one has either become disconnected or has been connected the wrong way round.” I had to admit it wasn’t working in such a way as to assist the pilot and, like a shot, he was off up to the cockpit. Shortly afterwards he came back all smiles having been given a run-down by the pilot on the flying-control system. Apparently it was an “anti-tab”, to de-sensitise the over-responsive ailerons, something which we old-timers had never found necessary! The late Tony Wilkey |
