Trials and Errors

by Mike Brooke

  The Great Northern Tour, our last such visit of the year, ended the following day with a short flight from Edinburgh to Prestwick, on the west coast, to look over Scotland’s only aircraft manufacturer – Scottish Aviation Limited. This followed the usual pattern of warm welcome, coffee, several lectures, lunch and a tour of the factory where the workforce was turning out shiny new piston-engined Bulldog trainers and twin-turboprop Jetstream aircraft. The former was an indigenous design but the latter had been taken over from the Handley-Page aircraft company of Radlett, Hertfordshire, which had gone into liquidation in 1970. By the time that we made our visit the Jetstream was in service in both the RAF and the RN, as well as in its civilian guise around the world, notably in the USA.

  After lunch, as we winged our way homewards, we realised that we had been greatly privileged to have had the opportunity to see at first hand the full gamut of British aerospace expertise and capability. Despite some of the light-hearted attitudes we had taken, a lot of new and useful knowledge had actually sunk in. A fact not lost upon the folk who had hosted us. It was now early October. In two months’ time we would have just about finished our time at ETPS. The final exercise would be upon us – the McKenna Dinner. However, before that there were still test cards to prepare, data to analyse and reports to write. On, on!

  8 ROCKING AND ROLLING

  By the time we arrived at our third term of penance we had achieved a reasonable understanding of how aeroplanes flew and why, occasionally, some odd things happened. We had learnt how to seek out answers to questions that previously we had never even thought to ask. But just as things were becoming a little clearer we were introduced to lateral and directional (L&D) stability. In the first term our collective knowledge and use of mathematics and aerodynamics had been tested and extended through the ministrations of the Ground School staff’s teaching of longitudinal stability. We had learnt about such factors as the position of the aircraft’s CG, the size of the tailplane and its relationship to the airflow from the wing, the way that the elevator worked and how important all these things were to the stability and safety of flight. But that was only in one plane (if you’ll forgive the pun!) – the horizontal – that is in the sense of the aircraft’s nose moving up or down as viewed by the pilot. The relevant equations were complicated enough, as was the manipulation of the stability derivatives, but in the case of L&D stability the two were inextricably interlinked.

  So we were now dealing with a cat’s cradle of dimensions and inter-connectivity. So, after much study and chalkboard rolling, we were subjected to another examination to ensure that we had at least a moderate grasp of the theory. Then we were dispatched to prove that we knew what we were doing by completing the flight test exercises laid down in the syllabus. First we had to fly the VSS Basset so that we could learn the correct test techniques and explore the effects of some of the variables. The Basset’s clever analogue computer, which controlled the aircraft when it was flown from where we students sat, in the right-hand seat, provided most of the fun. The occupant of the other pilot’s seat was a tutor who fiddled knowledgeably with one or two of the computer controls on a panel between us. When he did so some factor in the aeroplane’s aerodynamic make-up, called a stability derivative, would be changed and the resulting variation in the handling of the Basset would quickly manifest itself. After each such selection a task would be flown and we had to see how difficult it had become. That meant that we had to come out with an opinion using the excellent Cooper–Harper rating scale, leading to a number. We were also encouraged to opine as to what the problem might be and how it might be fixed. The VSS Basset was an excellent tool for this but it did have one drawback. In order to protect the aeroplane from damage the automatic cut-out system, which warbled at you when the right-hand set of controls was automatically disconnected, was set a bit too far on the safe side. That meant that some of the more extreme modes were available for only a few seconds. Nevertheless we got the gist of it all.

  The three main test techniques that we applied in order to discover the aircraft’s L&D stability were steady heading sideslips, rolls on one control and something called Dutch rolls. I thought the latter the most interesting. The Dutch roll was ostensibly named after the rolling motion exhibited by the speed skaters of that flat land beyond the North Sea. In flight the motion was initiated by pushing the rudder bar in one direction until the nose had yawed off heading; a roll, normally in the same direction, accompanied that. As the motion got to its limit then the rudder bar was moved smoothly in the opposite sense and the nose and roll would reverse direction. After a couple of cycles the frequency of the aircraft’s natural response could be sensed and measured. However, an eye had to be kept on the sideslip gauge. If the limit was exceeded then structural damage could be caused, especially to the fin. A lot could be learned from this relatively simple test. Looking out towards the wingtips, the circular or ovoid path that showed the ratio between the yaw and the roll generated by the sideslip induced by the rudder deflections could be observed. If the wingtips were not in view then a mark on the canopy or side window would do the same job. Watching the heading change on the gyro-stabilised compass on the instrument panel meant that the yaw angle could be quantified. Of course with a fully instrumented prototype or development aeroplane then all of this stuff would be automatically recorded for post-flight analysis by the boffins. But for us it was very useful for those times when we would not have those luxuries on board.

  The two L&D exercises that I did were Asymmetric Flight in the Argosy and the L&D Assessment in the Lightning: chalk and cheese! I now had two new compatriots in our syndicate: Flt Lt Roger Searle and one of the Indian students, Flt Lt P.K. Yadav. As usual with the Argosy we were each given a different CG to fly, forward, mid and aft, and we would each fly as co-pilot and captain at least twice. From my seven years flying the twinjet Canberra I had plenty of experience of flying with thrust coming from only one side of the aeroplane, whereas Roger and PK, being single-jet pilots, had very little. On the quiet I was made aware that I would have to keep a bit of a supervisory eye on the other two; but I didn’t really have any fears about their ability. In the end everything went off safely and no undue excursions were made beyond the sideslip limits of the dear old Argosy.9

  As to the Lightning exercise we were allowed just two sorties, one subsonic and one supersonic. As usual, due to the Lightning’s enormous thirst for kerosene and its tiny fuel tanks, neither sortie lasted long enough; especially the second one. It was the Lightning’s highly swept wings that made it interesting, especially at the speeds around Mach 1. In fact, several Lightnings had been lost through pilots manoeuvring in the transonic regime. That was because the aircraft’s directional stability, reduced by the transonic shockwaves, then the application of large amounts of aileron, had generated much more sideslip than roll, so the aircraft had entered a spin. Which was something that was not easy to recover from in this particular fighter.

  Swept wings, along with wings that rise from the root, where they are joined to the fuselage, to their tips – known as dihedral – normally generate quite a lot of roll when sideslip occurs. Unsurprisingly this outcome is known as ‘dihedral effect’ and has its own stability derivative. It can be very important in some regimes of flight. For instance when landing an aeroplane with large dihedral effect in a crosswind. Because it is not good for the tyres it is highly desirable that the aeroplane’s wheels are in line with the runway when it lands. So when there is a wind blowing from the side of the runway, instead of the much-preferred direction of straight ahead, then something must be done to get the machine down in that direction – straight down the runway. One option is to allow the nose to point into the wind during the final approach; this will set up an angle known as drift and manifests itself as a crab-like approach. Then, just as the wheels are about to touch down, a judiciously judged boot-full of rudder is applied to bring the nose round to point at the other end of the runway. As in much of life, timing i
s crucial. Too early and the aircraft will start to drift sideways across the runway and perhaps be in danger of missing it altogether. Too late and the tyres will squeal in protest at being forced sideways onto the ground. Your popularity with any passengers, the ground crew and the logistics folk will also suffer.

  However, in an aeroplane with lots of dihedral effect, even if your timing is perfect, the amount of roll generated by the sideslip that the aforementioned boot-full of rudder produces may be too much to correct with the ailerons, especially at the low speeds that landing brings. In aircraft with low-mounted wings or underwing stores then, there may be a danger of those things hitting the ground. So another method had to be found. In the early days of swept-wing fighters, especially in the USA, pilots found that they could fly the aircraft straight down the runway centreline by using rudder and aileron in the opposite directions. This technique became known as the ‘wing down’ method and became widely adopted. Although a little more difficult to fly than the ‘crab’ technique, all the pilot has to do at touchdown is to put the crossed controls back to neutral. However, neither of these methods was safely successful for one large aeroplane – the USAF Boeing B-52 bomber. So an ingenious solution was engineered. The B-52’s main wheels are all housed in the fuselage and the clever folk at Boeing made it possible for them to be moved by the aircraft’s navigation system and set them to the correct drift angle. So all that a B-52 pilot had to do was fly a ‘crabbed’ approach all the way to touchdown in the knowledge that the wheels would stay in line with the runway. I’ve often wished that my flying machine had that facility on a dark and stormy night with the wind howling at some ridiculous angle across the runway!

  As a footnote to this chapter I cannot move on without a tribute to the man who was my tutor during that last term, although he was away for most of it. Walt Honour, the US Naval exchange tutor, was a man who possessed a wry sense of humour, a plethora of knowledge and great integrity. He was a hard but fair task master and I used to make fun of his American zpelling, in which he inzizted on uzing the final letter of the alphabet as the first, rather than the second, alternative; it was, in my opinion, all the fault of Webster’s dictionary and the US education system. A couple of weeks into that third term Walt was diagnosed with lymphatic cancer. He had first noticed a lump in his armpit while playing the unfamiliar game of cricket at the beginning of August and by mid September he was to be sent back stateside for treatment at the National Naval Medical Center [sic] in Bethesda, Maryland. In typical Walt fashion he threw a champagne party the evening before he and his wife, Lorraine, left us. We drank to his return, to both health and ETPS, hoping that would be before the McKenna Dinner. In the event it was not to be. However, Walt did go into remission and was able to return to Boscombe Down the following year. But tragedy was to strike again. Just after take-off the engine of the Hunter that he was flying exploded and he and his companion had to eject. They both landed safely with their parachutes, but perhaps the stress brought the cancer back into action. Walt died later that year. I believe that he still lives on in the minds of all of us fixed-wing student test pilots of 1975.

  Note

  9 The dangers were there. During the following year’s course an Italian student lost control during a two-engined asymmetric go-around and XR 105 crashed on the edge of the airfield. Both the student and the Air Engineer, Terry Colgan, lost their lives and the ETPS QFI, Mike Vickers, was very badly injured but survived, having been thrown from the cockpit as the Argosy crashed. The aircraft was totally destroyed.

  9 BEAVERING ABOUT

  By the middle of October autumnal tints were appearing on the trees outside our house and lining the long walk that I was still making down the hill to the Ground School building. Those warm colours were the first harbinger of winter, which we hoped would see us graduate from ETPS and move on. But before that we had the final hurdle to successfully put behind us: ‘the Preview’. This was the ultimate and most extensive test flying exercise of the course. We would each be put into a team of two or three and then undertake a comprehensive assessment of a current in-service aircraft against a set of requirements. The worst bit was we then had to report our findings in the by now familiar manner. This exercise would draw together all the test techniques that we had learnt and practised throughout the previous nine months, and it would be done using an aircraft type on which we had no previous flying experience.

  However, this sort of ‘testing to learn’ was not going to be completely new to us. In mid September we had each to complete a lesser version of the Preview, when we flew an unfamiliar but simpler type of aeroplane in order to assess its suitability for its role; this mini-Preview was called the Pilot’s Assessment. Again it was done in teams of two or three. Svend Hjort and I were allocated the de Havilland DHC2 Beaver. The exercise took place at the ‘Beavers’ Lodge’ – The British Army Air Corps (AAC) airfield and HQ at Middle Wallop, Hampshire, not more than a thirty-minute drive from Boscombe Down. We had each been given a copy of the Pilot’s Notes a few days beforehand, along with a role description and some basic requirements. That gave us time to work out what tests we should prioritise, as we would be allowed no more than an hour and a quarter to complete them. Although we were in teams the reports were to be written individually.

  The Beaver was a late 1940s product of the Canadian arm of de Havilland Aviation and was designed to be a rugged, all-metal aeroplane with a Short Take-off and Landing (STOL) capability. It had a high wing, fixed landing gear with a tailwheel and was powered by a single 450hp (340kw) Pratt & Whitney Wasp radial engine. Like the animal it was named after it was a relatively rare sight in the circles in which I had moved. The DHC AL Mk 1 Beaver was adopted by the AAC in the 1950s for the light transport and observation roles. So I thought that its prime characteristics should be good longitudinal stability and control, a decent field of view from the cockpit and vice-free low-speed handling, with clear, unambiguous warning of an impending stall. It should also possess high-quality manoeuvrability for the observation role and for positioning during approaches to short and possibly semi-concealed landing strips.

  I wrote up the test cards to take into account the normal sequence of a general handling flight. So field of view and ground manoeuvrability would be assessed before take-off. Then engine handling, take-off handling and performance, trimmability in the climb and the rate of climb would be the first airborne tests. The aircraft’s control characteristics, longitudinal stability, both static and dynamic, and stalling would be next. After that turns up to the normal G-limit, roll-rates and L&D control and stability would be on the menu. I was aware that if I was not careful to fly the tests quickly and accurately I could reach the time limit while I was still miles away from Middle Wallop. However if I did manage the time for each test properly I should still be able to look at the glide performance for the engine failure case, before having time to do at least a couple of landings on the grass runway back at Middle Wallop.

  When the day dawned Svend and I were sitting in the ETPS crew room waiting for our supervising tutor, Pete Sedgwick, to take us up the road for our day with the Army. ‘Transport for all going to Centre Thump,’ he announced cheerily as he appeared in the doorway. Svend gave me a questioning look. ‘Centre Thump?’ he intoned.

  ‘Yes. It’s Sedgwick’s attempt at wordplay – Middle Wallop – Centre Thump. See?’

  ‘Not really,’ replied my exasperated Danish friend.

  An hour later we had arrived, found our way to the appropriate hangar and were guided to the Ops Room. After introductions were made I met the poor soul who was going to sit next to me and suffer my pitiable imitation of a test pilot! He was a mature, grey-haired chap called Mr Mackenzie; most, if not all, of the instructors on the Beaver Flight at Middle Wallop seemed to be civilians of an older persuasion. After I had briefed Mr Mac about what I wanted to do he told me what I would be allowed to do. Fortunately the two were not irrevocably different. He then sent me to the Officers’ Mess
for lunch and asked me to be back in time to walk out to our steed by 1.30 p.m. Steed was a good description because, having observed the way that things had been done during the latter part of the morning, it seemed that the Beavers were treated a bit like horses in the cavalry. They were stabled overnight, groomed and fed with fuel in the morning and then just topped up between flights. I supposed that at the end of the day someone was going to give them an encouraging pat and a sugar lump.

  We walked around the green and matt-black beast together while my mentor was checking that all the required bits were still attached. The next task was to mount. It was a bit of a climb up the side and in through the car-style entrance door. Once inside there was a definite retro ambience, but the seat was comfortable and most of the required knobs and levers fell readily to hand. As with radial-engined aeroplanes starting the motor was a bit of a lottery and required a fairly high level of ambidextrousness. After priming it with extra fuel, the starter flywheel was spun up electrically until the noise it made reached around treble C, then the switch was moved to the engage position, ignition switches selected ‘on’ and the throttle opened slightly. The propeller spun up, encouraging pops and bangs emanated from the exhaust pipe, along with a good deal of oily smoke, and then the engine started to run more smoothly. Such machines are much more fun to get going than jets!