An Examination of the available data on aircraft unreliability, whether on civil or military aircraft shows quite clearly that the systems engineering is more troublesome than the structural engineering.

The statistics show that landing gear, brakes, hydraulics, fuel and air conditioning systems are all at fault to approximately the same degree. In addition equipments for which the airframe manufacturer is not directly responsible, are a frequent cause of trouble.

The aircraft manufacturers’ contribution to improving reliability must come from three directions.

In a general survey of the Guided Weapon scene over the past twenty years, in the space available, it is not possible to be comprehensive, nor may it be desirable. It is necessary, however, in order to set the background, to go back to early work before the period under review.

I have been asked to contribute some reminiscences of the first two years of the 1914–1918 War to this Centenary number. Selection has proved difficult: I did not keep a diary and so must rely on memory alone for what I write. This may result in errors of detail and for any such mistakes I apologise in advance.

Early in February 1915 I received a telegram from the Admiralty as follows: “You have been appointed acting junior technical advisor to the Director of the Air Department and should present yourself for duty at the earliest possible moment”.

The title chosen identifies the period when flying was an adventure; when the design and construction of aeroplanes and attempts to become airborne on them, whether successful or not, created the pleasure and satisfaction that is felt by the “do it yourself” enthusiast who, with little previous experience to guide him, ventures more or less into the unknown; when every failure and disappointment is a spur, a stimulus and a positive urge to try again and do a little better next time. This period began seriously not much more than sixty years ago.

In this age when people are being whisked to the ends of the earth at speeds approaching Mach one and when tremendous efforts are going forward to propel them there two or three times faster than that, it is almost incredible that the progress which we have seen take place could have been possible in such a comparatively brief period.

Despite the fact that there have been few reported instances of the flutter of circular, cylindrical, iso-tropic shells, there still remains a challenge to the analyst to derive a theory which will correlate with the available experimental data.

“Learn to Test. Test to Learn.”which succinctly state the task of the student and the graduate test pilot, were selected in 1953 as the most suitable inscription to place under the Armorial Bearings of the Empire Test Pilots’ School. This small Unit, which was formed in 1943 at the Aeroplane and Armament Experimental Establishment, Boscombe Down, has, over the past 22 years, provided the formal training necessary to enable test pilots to meet the requirements of the Flight Test Establishments of the Ministries of Aircraft Production, Supply and Aviation. During this period the School has trained some 595 test pilots, 34 per cent of whom have come from 26 Commonwealth and Foreign Air Forces.

I returned to England in February 1919 to take over the duties of Assistant Director of Research and Development (Engines) under Brigadier-General Brooke-Popham, who was appointed Director of Research about the same date.

At that time it was anticipated (correctly) that there was no danger of another major war for at least ten years and the staffs of the Royal Air Force and the Air Ministry were cut down drastically to suit. The Engine Research and Development departments which had employed many hundreds during the war were reduced to about a dozen people. While this was being done the engine position as it existed was being examined. It soon became obvious that none of the engines which had been in production during the war were suitable for further development to meet the requirements of the 1920's.

A Vehicle Millemile is a 1000-mile unit of flight production. A big jet may cost in total £1500 to fly 1000 statute miles or 1 VMM.

If 6 tons of passengers (or 60 passengers and their free baggage) earn £200/Paxton Ton-Millemile x 6=£1200, and the revenue from 3 tons of cargo is £100/Load Ton-Millemile x 3=£300, it is simple economics to see that this “mix” will provide breakeven with 9 tons load on board and a total revenue mix of £1200 + £300=£1500/VMM or per 1000 miles. A big jet flying 1600 VMMs per annum at £1500/VMM costs £2.4m and the above passenger and cargo ton factors would provide sufficient revenue to break even.

In a few seconds, therefore, we have ascertained the composite “mix” of load and revenue needed to meet the cost of flying the aircraft 1000 miles, and the answers are far more enlightening than saying that an average 60 passengers are carried at 4.8 d/PM and 2721 kg of cargo are carried at 24 d/LTM.

The fact that many medium size or small airlines have route stagelengths of less than one Vehicle Millemile at 500 miles or 200 miles makes no difference to the validity of ease of application of VMM Economics, but its great value Jies in the study of intercontinental big jet operations, SST analysis, sub-orbital flight and even interplanetary flight costing.

Failure of electronic equipment represents a significant proportion of the overall defect rate for modern aircraft. While this is not entirely surprising in view of the quantity of electronic equipment installed, and the variety and multiplicity of functions performed, it remains a serious problem.

The specific reliability of electronic equipment, in terms of separate facilities, has tended to show marked and continuous improvement, but this has been overshadowed by the increasing number of functions performed, and by greater dependance on this equipment. Most electronic failures occur without warning, and many of the remainder need delicate and complex test procedures to obtain even a few hours warning of impending failure. In some instances, particularly where electronics is used because of its rapid reaction time, a fault can, unless special precautions are taken, be a serious risk to safety, or cause other serious consequences even before there is any warning that a fault condition exists.

Aviation in its early days was as beset as any new science with the ravages of that elusive creature the creeping error. They are rare today but a particularly daring one has crept into the Centenary review of the Fleet Air Arm (January, p. 208). We did not have catapults to launch our Sopwith Pups, Camels or Strutters from the turrets of battleships during the 1914-18 War. Catapults came later with the amphibians designed for service with cruisers.

This note deals with an extension of the basic fin theory, as found in refs. 1 and 2, suitably modified to estimate the heat dissipated by internal structure such as consoles, floors, bulkheads, and so on. It also outlines the electrical analogy method applied to complex structures.

A Comprehensive review of British contributions to aerodynamics would fill many volumes and take years to compile. For while some aspects of the science are embarrassingly well documented—every library possesses the monumental reports of the Aeronautical Research Council from 1909 onwards and the no less compendious Journals of the Society—other aspects are hardly illuminated at all.

Progress in aerodynamics has flowed in three main streams springing from the work of, first the research establishments and universities, second design offices and flight sections of the aircraft industry and third, the flying schools of the RAF.