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Aviation History
1951
1951 - 0355.PDF
FLIGHT, 25 February 1951 BACKGROUND TO THE AMBASSADOR Some Thoughts on Getting an Airliner off the Drawing-board and into the Air By Major HEREWARD de HAVILLAND, D.S.O. "\-. •,", '7.--.'.;-' THOSE of us who were in the industry when aircraft couldbe designed, built and put into production within twelvemonths of the initial conception may perhaps be forgiven if, momentarily,* we wonder what has changed during the pasttwenty years; but then we remember the performance and operational requirements of to-day's aircraft and compare themwith those of two decades ago and realize that, for better or worse, we are dealing with a very different and more complexset of conditions. It is not enough to make the obvious statement that speed,range and service-life requirements have gradually increased to three or more times the figures accepted in those days; the pointis that these increases—coupled with the stricter standards of safety and the effect of the equipment which has to be carriedto satisfy these standards—have brought in their train a host of new problems: so much so that the design and developmentman-hour total per pound of aircraft weight has increased out of all proportion. As many people know, intensive effort on the production-typeAmbassador—a development of the initial aircraft ordered by the Government during the later war years—started in the earlypart of 1948. Although the superficial appearance remains the same, this production Ambassador is really a very different air-craft and an outline of some of the work done in the intervening three years may help to give those readers who are not them-selves in the industry some idea of what is involved in the production of a modern civil aircraft. Starting with the broad requirements, the developed Ambassa-dor for British European Airways and other airline operators was planned with a payload considerably higher than thatoriginally envisaged. This, of course, involved a higher all-up weight which had already been agreed when investigations hadbeen made of the possible performance of the Ayrshire, a projected military version of the Ambassador. In order tocomply with the stringent engine-failure requirements of the post-war P.I.CA.O., a higher take-off power was then needed;and this, coupled with the decision to take full advantage of pressurization by cruising at higher levels, necessitated thedevelopment of new power-plants with two-speed blowers. In its train, the new all-up weight brought minor modifica-tions to the design of the undercarriage, a certain amount of stiffening of the original structure, increased braking power,and, indirectly, such changes as the introduction of automatic airscrew-pitch coarsening—to deal, in this instance, with thedifficult case of engine failure in which climb-away had to be possible during take-off without further action by the pilot.Pressurization for operation at 20,000ft also introduced many new problems, both in airframe and power-plant. De-icing,apart from the need to develop and test a thermal system from little-known first principles, involved a re-design of the elec-trical system in order to provide sufficient power for the cyclic heating of the airscrew blades. Meanwhile, work had to proceed, in parallel with production,on the construction of test specimens, including full-span wings, complete fuselages, an empennage, and a variety of castings,forgings and other items. Many of these specimens were tested in our own research laboratory and test house: others, whichwere too big, were sent elsewhere. The full-scale fuselage pres- sure test was carried out under water in Portsmouth dockyard,there being no test tank in England large enough to take it. The 115ft wing was sent to the R.A.E., Farnborough, and asecond full-scale fuselage went there also for torsion and bend- Milestone in 1947: towing the first Ambassador prototype from the Christckurcn experimental shop to the flight shed.
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