Trials and Errors

by Mike Brooke

  ‘’Ow fast can eet fly?’ he asked the engineer and me. We told him what the maximum allowed airspeed was.

  ‘OK, give me ze power for zat,’ came the captain’s command.

  As we got closer to the airfield I told the control tower that we would join the landing pattern directly onto the downwind leg; he cleared us to do so. But when we arrived opposite the upwind end of the runway Gerard the Mirage driver was still going too fast to put the landing gear down. I apprised him of this fact.

  ‘No problem, mon petit copain,’ he said. ‘Zero thrust s’il vous plaît, engineer.’

  As the airspeed dropped below the limit speeds for undercarriage and the various stages of flap I selected them. Gerard had his head down now and turned onto the final approach as if he was still in his Mirage. I called ‘Finals to land, gear down and locked’ on the radio. The controller cleared us to land, but with a little uncertainty in his voice. He was obviously watching our high-speed arrival carefully. Gerard just pointed the big machine at the threshold and waited for the speed to drop. The power setting had not been touched since zero thrust had been set! As we crossed the big white stripes at the beginning of the runway the speed was just right. How did he do that? The landing was immaculate. It all went to prove that not all bad approaches end in a bad arrival!

  The test flying exercises during the first term were all related to longitudinal stability and control. In addition to those I have already described I flew two sorties in my dear old pal the Canberra T4. The aim of the exercise was to measure the elevator angles as the aircraft neared its maximum Mach number of around 0.84 at high altitude. Assessment of the aircraft’s handling and reporting on any limitations was also expected. There were no surprises for me; the Canberra did its usual thing of having a short period of longitudinal instability as it exceeded about 80 per cent of the speed of sound followed by a return of very strong stability with a nose up lurch at the maximum attainable speed.

  A memory of this period is one of a red-faced, ginger-haired George Ellis storming into the crew room after his first sortie in the Canberra, looking directly at me and saying, ‘That aircraft should have been put down at birth!’ He really was a Mad Dog that morning! The truth was that George was desperately disappointed because he’d always, from afar, admired the look of the Canberra and had long harboured a desire to fly it. However, the uncomfortable, un-ergonomic cockpit and poor view, plus the struggles with flying it on one engine had totally disabused him of his previous admiration. No amount of me extolling the later marks, like the B(I)8 and PR9, would change his mind! Unfortunately his perspective was upheld by unprintable comments from our US Naval aviator, Tom Morgenfeld, after his first trip. He was somewhat mollified when I told him that he had joined the ranks of a very special group of elite pilots – those that had flown the English Electric Canberra and survived!

  But the best was to be last. This time another longitudinal stability exercise, much like that we had done on the Canberra, but going through the ‘sound barrier’ in the Lightning. To do this we had to fly out to the southwest at around 36,000ft and get ourselves positioned at the south-west end of something called the ‘English Channel Supersonic Corridor’. A London Military Radar controller would watch us closely to make sure that we didn’t stray out of the corridor or fly out of the north-eastern end of it while still going supersonic. The usual eye-watering climb after take-off was followed by a cruise at 0.9 Mach until we were in position to turn into the corridor. Then it was full afterburner and hold the aircraft level to accelerate up to 1.3 Mach. That was a slightly harder task than I expected because as the speed increased, but with no change to the aircraft’s attitude, the altimeter steadily unwound until at 99 per cent of the speed of sound it had dropped by 1,500ft. Intuitively I knew that we were at the same height. This phenomenon was a huge, transient static pressure error caused by a shockwave passing down the long probe on the nose of the jet and over the little holes that measured the local static air pressure.

  In fact the most obvious sign that we had gone supersonic was the altimeter bouncing back up to the correct height. Then it was a case of carrying on to 1.3 Mach and letting the onboard test instrumentation do all the measuring. There was very little in the feel of the aircraft to tell me that we had passed the speed of sound. This really was a beautiful aircraft; but with one very important limitation. By now we were getting low on fuel, and we’d only been airborne fifteen minutes! In fact, as we had accelerated I could see the needles of the two fuel gauges slowly swinging towards zero! But we weren’t there yet. Now we just had to get back to Boscombe; about 60 miles away. The nice man at London Military Radar helped a lot and co-ordinated our hand-off back to Boscombe’s Approach radar controller, whom I informed that we would get to the runway using the Instrument Landing System (ILS).

  The ILS sent out radio signals from the ground and the receiver in the aircraft converted them into the displacement of a horizontal and a vertical bar on the Lightning’s large Artificial Horizon display, right in front of the pilot. This could be used to find the runway in bad weather with no need for any voice radio transmissions. But an even better scheme was to use the Lightning’s autopilot and autothrottle to help take all the effort out of the task. So, for practice, that’s what I did. I had used a very similar system in the Canberra PR9 before, so its operation was not new to me. What was new was the final approach speed of 165kt! It worked perfectly and at 200ft I disconnected both the autopilot and the autothrottle and landed the aircraft. The fuel gauges showed the minimum allowed fuel quantity for the day of 1,200lb and we had been airborne for all of thirty-five minutes!

  It was a great way to end my first three months at ETPS. We now had a week’s leave coming, so my wife and I hired a caravan on the south Dorset coast and set off on the Saturday morning for a well-deserved break. She was working for me as well: she typed all my reports. This was long before the days of PCs, tablets and laptops! The weather broke, in a good way, that weekend and it remained hot and sunny for the rest of the week. But it wasn’t all play and no work. I sat in the sun for several hours and analysed the in-flight recordings from my Lightning sortie, plotted strange-looking curves on graph paper and wrote my report about the results of that final exciting trip! The ten days from ‘flight-to-write’ was included in the week’s leave – a hard school with hard rules!

  5 OUT OF CONTROL

  It was now blazing June. We returned to school, like so many students had done for centuries, refreshed from our late spring break and ready to tackle the new mental and physical hurdles to be put in our way. This second term meant a change of syndicate, thus a change of tutor and fellow syndicate members. Our tutor was to be Sqn Ldr Duncan Cooke during this short but very busy nine weeks in which the main event would be that most exciting and potentially unpredictable mode of flight – spinning.

  A spin is sometimes called autorotation, and it is the aerodynamic result of flight beyond the point where the aircraft no longer responds normally to control inputs. In other words, the aeroplane is no longer flying where normal control is possible and exceptional steps must be taken to regain control. What does a spin look like? Well, the clue is in the name. A spin happens when the aircraft rotates around all three axes simultaneously and describes a spiral downward path, usually at a very high rate of descent.

  In the early days of flight, when there was a dearth of experience and understanding of stability, loss-of-control accidents were very common events. However, not all were fatal because, thankfully for some of those early aviators, their wood, wire and fabric contraptions flew at very low speeds, so the collision with terra firma was often a low energy impact. Many an early pilot, with his goggles, white silk scarf and flat cap on backwards climbed out of the ragged wreckage, dusted himself off and strolled away to find, or build, himself another flying machine. Hopefully a more stable one.

  By 1912, when aeroplanes were starting to become much more common, the spin had become notorious. The dyn
amics of the spin were still not fully understood and it was simply something that was to be avoided like the plague. However, in that year a Royal Naval Air Service officer called Parkes was the first pilot to be recorded as recovering successfully from the usually fatal ‘spiral dive’, as the spin was then known.

  He was flying an Avro trainer and while turning towards the landing field he mishandled the controls so badly as to cause his aircraft to depart from controlled flight. It is said that he felt a strong side wind so applied full rudder to oppose it. At the same time he did something else that was totally non-intuitive: despite the ground coming up at him he moved the control stick forward. The Avro recovered and cleared the ground by not very much. Shaken and probably more than a bit stirred, Parkes climbed his aircraft away from the ground and then made a successful approach and landing. After a change of underwear Parkes analysed what he had done and it wasn’t long before the application of rudder to oppose the yaw and movement of the stick forward became known as the ‘Parkes Technique’ for recovering safely from a spin. However, it wasn’t until the advent of the First World War, with the consequent increase in the numbers of military aircraft and concomitant flying training, that intentional spinning became part of the syllabus. In 1917 a senior scientist at the Royal Aircraft Factory at Farnborough, Professor Frederick Lindemann, who, ironically, was a naturalised German, undertook a study of the physics and mathematics of the motion of the spin. He even flew some of the test sorties to prove his theories. A rare animal – a test pilot boffin!

  By the end of the 1920s the aerodynamics and the inertial forces on an aircraft in a spin were much better defined and understood, and designers were taking these factors into account, particularly in the design of fighters and trainers. All flying training now included intentional spinning so as to teach the correct method of recovery, as well as to dispel some of the fear of the spin’s rather disorientating, rotational aircraft motion. However, spins, especially those accidentally entered during combat or training, were still killing people and losing aircraft.

  One story from the test-flying world that I came across involved the US Air Force’s acquisition of the McDonnell F-4 Phantom. This formidable, supersonic, two-seat fighter had first flown in May 1958 and was initially acquired solely for the US Navy. It performed so well that, in the mid 1960s, the USAF decided that it too could usefully employ the Phantom. During the initial test programme, at Edwards AFB in California, the occupants of the appropriate ivory towers decreed that the F-4 should undergo a full spin test programme. These sorts of tests are always high-risk and the coalface guys at Edwards pointed out that the USN had already completed very comprehensive spin testing; why not use their results? This very sensible input was overruled and the general then in charge of the USAF aircraft procurement system was reported as having said, ‘If this spin programme saves just one USAF F-4 it will have been worthwhile.’ This wisdom was then translated into a banner, which was prominently displayed in the Ops Room of the F-4 test squadron at Edwards AFB.

  Some way into the programme the test aircraft was, once more, put into a spin and the required control inputs for that particular test point were applied. The spin very rapidly became much flatter, that is the nose rose from about 50° below the horizontal to only 15°. The rate of rotation increased and the Phantom was now in a classic flat spin; usually a very difficult spin mode to recover from. High definition cameras in the desert below were filming all this. It was a recording of this spin that we were shown at ETPS as part of the briefing before we started our spinning exercise. It was fascinating to watch. After more high-speed rotations the anti-spin chute, always fitted for these trials, was deployed. It simply fluttered like a large pocket-handkerchief above the Phantom’s spinning fuselage and so had no effect on the recovery. Then the brake parachute, normally used to help shorten the landing run, popped out and just as quickly fell away. The next event was the departure of the two crew using their ejection seats; back-seater first. The camera then continued to follow the stricken fighter all the way down to the desert floor and the inevitable impact and cloud of dust. This brought appreciative whoops from the audience in the ETPS classroom! I later learnt that the punchline came when the uninjured crew had been picked up and returned to their Ops Room. The first thing the pilot did was to walk over to the banner, get out his grease pencil, cross out ‘ONE’ and replace it with ‘TWO’.

  By 1975 there were still many military fighters, like the F-4 Phantom, that could be manoeuvred to a point beyond which a spin might be generated. As the twentieth century progressed into its latter quarter, computers were increasingly being used in the flight control systems of all classes of aircraft. The phrase ‘fly-by-wire’ was, even in the mid 1970s, becoming part of the language of flight control system design. As these specialised magic boxes became smaller and yet more powerful they could be programmed to protect pilots against losing control of their increasingly skittish steeds. A new phrase then appeared: ‘carefree handling’.

  However, that was, for us, somewhere in the future. The aim now was to get us to intentionally spin suitable aircraft, observe their characteristics while spinning, recover them safely, report on what we had seen and make recommendations. Sounds easy when you say it quickly! Apart from carrying out a couple of brief spins during our conversions to the Jet Provost earlier in the year, none of us had intentionally spun an aeroplane for many years. So we needed, literally, to be wound up before we tried to apply ourselves to the demands of this exercise.

  So it was back into the dear old JP. However, this was ETPS; it was to be for only one sortie, with my tutor in charge, which would function as both a re-familiarisation on operating and handling the JP and a demonstration of the required test techniques. One hour was all I would get before I went off and did a whole series of spins on my own. That trip happened about one week later, during which I had to perform about a dozen spins and gather all sorts of information, without the benefit of automatic data recording equipment. I would have a voice recorder and a kneepad holding a handful of neatly drawn up test cards. However, the voice recorders that we used were notoriously unreliable and it was very easy to lose track of the test cards while doing all the things necessary to fly safely around England’s busy southern skies!

  The day of 12 June 1975 was a fine one for flying, so I had no excuses for not getting airborne. Once I had climbed Jet Provost XS 230 to 20,000ft, which took about ten minutes, I set up for the first spin. I looked all around, particularly below, made sure that my straps were tight and that there were no loose bits in the cockpit with me. All was well so I told the radar controller, who was keeping a friendly eye on me, that I was about to enter the first spin. I closed the throttle and held level flight until the speed had dropped to about 100kt. Then I simultaneously pulled the stick fully back and pushed the rudder bar as far as it would go with my left leg. This meant that the little JP’s wings stalled but the yaw to the left caused by the application of full rudder started the autorotation that was essential for a spin to develop. All the time that this was happening I had to make sure that the stick was held fully back and central, so that I would not be applying any roll control input. The aircraft pitched up and then performed a tight barrel roll to the left as the nose dropped quickly below the horizon.

  To imitate a real spin test programme, but much abbreviated into one flight, the first two spins were very short because my test schedule was first to check that the recommended immediate recovery action of simply centralising all three controls would stop the spin. If this was done before the end of the first full rotation then the aircraft should recover. In fact this was an essential requirement for a training aircraft, which the JP was. I had to check this result for a spin in both directions, left and right. Sure enough it worked. But it wasn’t enough to come back with one’s white silk scarf flying in the breeze and say, ‘It’s fine chaps, don’t change a thing!’

  No, the designer and engineer chappies need to know all sorts
of esoteric information, like the rates of pitch, roll and yaw; angles of attack; time from application of the recovery controls to the time that the aeroplane stops gyrating; how much height was lost until normal, safe flight was re-established. And lots more! Once those so-called incipient spin recoveries had been done, all the while with me chatting away to myself and, hopefully, the tape recorder, I had to move on to the fully developed spins. These also had to be completed in both directions and the same sort of data recorded in my increasingly illegible handwriting. Recovery from the fully developed spins would be taken after at least three full rotations had passed. The entry method was exactly the same: throttle closed, full rudder and stick fully and centrally to the backstop. Once settled into the spin the JP was rotating through 360° in about four seconds and losing about 2,000ft while it did so. The recovery action was to check that the throttle was closed, then look at the turn indicator on the instrument panel to confirm in which direction the aircraft was yawing.5 After that the rudder bar had to be pushed fully in the opposite direction to the yaw. This was followed by a short pause before the stick was moved progressively and centrally forward, only stopping once the spin had stopped. There were other tests required, such as applying the recovery actions in the wrong order, to see whether the aircraft would still recover (again a mandatory requirement for a trainer). Then there were different entry conditions to check, such as during turns in each direction.

  After an hour I had done a dozen spins and was very ready to go home. I had used the few minutes between each spin, while climbing back to a safe height, to make notes and talk to my voice recorder. How I would make sense of it all was a challenge that I would face later. But that would be in our spare bedroom, in the quiet of the long evenings that I was used to spending there. The JP spinning exercise was just the beginning of a period in which rotation in a variety of forms would fill my summer days. The next step was the Hunter spinning assignment.