JOHN CECIL WIMPENNY
CEng FRAeS
1922-2015
It was an apprehensive John Wimpenny who reported for work at the de Havilland Aircraft Company on 4 October 1940. Straight out of Minchenden Grammar School at the age of 17, this was his first job and he wasn't sure what to expect - especially as the Hatfield factory had been bombed the previous day. What he didn’t expect was to be handed a pair of green kitchen scales by chief aerodynamicist Richard Clarkson and told to go and weigh a Mosquito fighter-bomber. Nothing more was said: he had to use his knowledge, resources - and the scales - to do the job.
As a Mosquito weighed in at around 14,000lb, this was rather beyond the capabilities of the kitchen scales, although he did use them for small components, and he learned very quickly about weight estimation methods and use of the weighbridge.
This was how Richard Clarkson judged the capabilities of his staff: he would assign them tasks which he thought they might - or possibly might not - be able to do, and then, with very little guidance or advice, let them get on with it.
From this humble beginning, John Wimpenny, who died aged 92 on 27 April 2015, went on to forge an illustrious career in the aviation industry. At the time of his retirement in 1984 he was Executive Director of Research for British Aerospace.
John’s interest in aviation started in his school days when he designed and built model aircraft, and his ambition at de Havilland was to work in aerodynamics. John was unfortunate to leave school in the only year that British universities did not accept undergraduates due to the war and so, at the behest of Richard Clarkson, he enrolled in evening classes at the de Havilland Technical School.
After two years as a weights engineer he transferred to aerodynamics design work in 1942 and became aerodynamics assistant on the Mosquito and the Tiger Moth. The following year he was at the sharp end as a flight test observer on the Mosquito. This was another baptism by fire, for the pilot was Geoffrey Raoul de Havilland, eldest son of the company’s founder. Geoffrey was a superb chief test pilot, and he could put an aircraft through its paces like no other, so an observer who was nervous, or who was being sick, was of no use to him, so he tested them first - and tested them to the limits.
John never forgot his first flight in the Mosquito. It started innocuously enough with Geoffrey saying they were simply going on a short flight, but he didn’t say what would happen on that flight, so John assumed there would be nothing dramatic. There wasn’t - at first. But Geoffrey had a girlfriend who lived on a nearby farm and, diving down, he hurtled over the buildings at about 100ft at full throttle before going into a series of fast, tight, high-g turns, almost reaching black-out point in very heavy turbulence. A battered Wimpenny wondered what was coming next and began to feel very sick - but the important thing was that he wasn’t sick, and had thus passed Geoffrey’s test without even realising he was being tested.
From 1942 until 1945 he was a flight test engineer engaged on aerodynamic flight tests on the Hornet and flight test analyses on the Vampire. The Hornet was a blisteringly powerful twin-engined single-seater and John had to crouch uncomfortably in the cramped bubble canopy while observing the behaviour of wing tufts, including on one occasion in 1948 during a full-power dive from 45,000ft piloted by John Derry.
From 1945 he became responsible for all stability and control design work on the wings of the Comet, which was the world’s first commercial jet airliner, as well as the Dove short-haul airliner, the Venom jet fighter, and the DH110 twin-jet swept-wing fighter, which later became the Sea Vixen.
These were the early and dangerous days of transonic flight at the very edge of the speed of sound, and de Havilland took advantage of Germany’s wartime experience with swept-back wings by designing the swept-wing tailless jet, the DH108 Swallow. Originally intended as a small-scale testbed for the Comet, the 108 had a prodigious performance due to its low drag and light weight, and it was the only aircraft in the country capable of exploring high Mach numbers.
In 1946, just after the first 108 flew, John co-authored a paper entitled ‘Sweep-back: the Key to High Speed Flight’, which was published in the ‘de Havilland Gazette’, discussing the many problems facing designers at both ends of the speed range.
By 1948 John was in charge of high Mach number research at de Havilland, and it was on 6 September that the 108 became the first British aircraft to exceed the speed of sound, in a wild and frightening dive piloted by John Derry.
During the early 1950s John’s responsibilities were broadened to cover the specialised functions of fluid motion, aero-elastics, aircraft systems, and the then new digital and analogue computers. In 1957 he was promoted to Deputy Chief Aerodynamicist and worked on the Trident airliner. He was also responsible for the overall aerodynamics design of the Hawker Siddeley HS125 executive jet.
John was always keen to broaden his interests and to help younger recruits working in adjacent areas. One such was Brian Clarkson (no relation to Richard Clarkson), who worked on structural vibration problems. An early example was when severe fuselage vibrations occurred at the onset of the stall in the first test flights of the new Comet 3 prototype. With John’s help it was established that eddies in the separated flow stream leaving the stalled wing were hitting the tailplane and exciting the fundamental mode of vibration of the fuselage. This resulted in a nodding of the extended fuselage and a very uncomfortable ride for Chief Test Pilot John Cunningham.
John became Chief Research Engineer in 1964 and was engaged increasingly on future project and research work, including co-operation with Southampton University, where Brian Clarkson was by now a professor and director of the Institute of Sound and Vibration Research (ISVR.) This led to fruitful research into STOL and V/STOL designs, including collaborative work with Dornier in Germany on the Do31 military transport aircraft. This was later followed with work on several specific design studies of aspects of the DH/HS146 short take-off and landing aircraft.
But John also found the opportunity to revisit his early love of model aircraft – although this time on a rather larger scale. He was founder and chairman of the Hatfield Man-Powered Aircraft Club, so as well as working on wings for supersonic flight he was also designing an aircraft with an 84ft span built of balsa wood to fly at the speed of a push-bike. The project was a critical combination of lightness, strength, and a drive system that would transmit enough pedal power to the pusher propeller. There were complex design considerations involved: for example, aero-elasticity, more usually associated with high speeds, had to be considered – even though the maximum speed would be no more than about 20mph.
The outcome was the 'Puffin', designed by a team headed by John and built by de Havilland volunteers, which John pedalled through the air for 993 yards to set a record on 2 May 1962 that remained unbeaten for ten years. This historic flight, which lasted two minutes, won him the princely sum of £50, the first award ever to be given for man-powered flight by the Royal Aeronautical Society. There was no special training programme for this flight, his only preparation being to cycle to work from his home in St Albans for several weeks.
John's record-breaking flight in the ‘Puffin’ was reported in all of the main national broadsheets as well as in major newspapers abroad. His achievement caught the public imagination, and in several of these publications it was the lead story on the front page. This in turn led to extensive coverage of his accomplishments on both national and international television.
In the decade following the ‘Puffin’ flight, following initial wing design and wind-tunnel testing of the Airbus in 1971, John was appointed Executive Director of Research for Hawker Siddeley Aviation with responsibility for overall research co-ordination on all HSA aircraft. The most important subjects were carbon fibre, supercritical wing design and the exploitation of avionics. In 1978 this research responsibility was extended to the newly-formed British Aerospace Aircraft Group, and as Executive Director of Research for British Aerospace (Aircraft Group) John’s expertise covered computational fluid dynamics, the application of composite materials and fly-by-wire technology.
John also oversaw a number of special investigations, including an STOL review, the European wind tunnel at Cologne and information technology as well as the development of quantitative techniques for assessing research priorities. He retired in 1984.
In his long career, John held many other appointments. He was chairman of the Society of British Aircraft Constructors (SBAC) Committee on Research (1978-83), Chairman of the BAe Aircraft Research Group Committee (1978 onwards), and Chairman of the Aircraft Research Association (1980-83).
He was a member of the Industrial Committee Imperial College(1962-70), the Joint Research Committee of the MoD (1976 onwards), the Aeronautical Research Council (1977-80), the Scientific Advisory Committee (1978-83) and the SBAC Technical Board (1983 onwards). A Fellow of the Royal Aeronautical Society, he won their Hodgson Prize in 1976 for his paper on ‘Costs and Decision-making’, the RAeS Silver Medal in 1978, and again the Hodgson Prize in 1983 for his paper ‘Aircraft R and D in Europe - a Perspective View’ which was presented at the seventh European Pioneers Day in Toulouse.
He delivered two RAeS lectures – ‘Stability and Control in Aircraft Design’ (1953) and ‘The Scope for Aerodynamic Development in Aircraft of the 1990s’ (1981).
From 1990 until 1999 he was Visiting Professor for undergraduate research projects at City University, and was Vice-Chairman of the RAeS Human Powered Aircraft Group from 1995 until his death.
John’s colleagues, friends and acquaintances remember him as a man with an innovative mind and a natural flair for aerodynamics. He is also remembered with fondness and respect for his kind, reasonable manner and his collaborative approach to problem-solving.
John married Angela Mary Hemmings in 1957 after the couple met in an amateur orchestra, and they had three sons - Francis, Gerard and Benedict.
Music was one of his many interests, and after his retirement he had the opportunity to pursue them more than had previously been possible. These interests included work on a steam-powered model railway in his back garden that he had first built in the late 1960s, dinghy-sailing and yachting and extensive travel with Angela, taking in trips to Australia, Alaska, Hawaii, the USA and Svalbard.
Ingenious and inventive throughout his life, his garden was also the centre of other engineering projects, including a towing tank for dinghy hydrofoil research, and several wind-powered generators.
Even when failing health curtailed his activities, John maintained his enthusiasm and interest in aviation until the end of his life.

Brian Rivas


14 August 2015