Thursday, 9 July 2015

Missing data: planes

It's Boy Engineer time! The Wellington bomber was an engineering marvel for its time.  It was constructed from a monocoque geodesic frame-work of duralumin. Some definitions are in order for that last sentence:
  • Monocoque from the French for single hull is a method for supporting loads by an external structural shell rather than internal trusses. Buy an egg recently? - that's monocoque, as are the exoskeletons of beetles are other arthropods. We do our engineering internally with a bony skeleton made up of weight-efficient cylinders, although the rib-cage has elements of monocoquicity.  Monocoque is handy because it gives a clear unencumbered interior which can be wholly given over to pilot, co-pilot, and load.
  • geodesic is a mathematical concept derived from the measurement of the earth which gave us the definition of the metre as well as the concepts of latitude and longitude.  These practical ideas were generalised into the idea of parallel 'straight' lines enclosing curved spaces. The mathematical ideas served as the inspiration for engineers to design structures that were extremely efficient w.r.t load/weight ratios. Initially employed to construct hydrogen-filled lighter-than-air air-ships by Barnes "bouncing bomb" Wallis and other aeronautical engineers.
  • duralumin is an alloy of ultra-light aluminium with about 4% copper that, having been cast, cures over several days into a crystalline structure that is much stronger but scarcely heavier than pure aluminium.
The Wellington was designed by Vickers-Armstrong's chief engineer Rex Pierson and was an enormously successful multi-purpose work-horse: initially designed as a bomber, it saw service in anti-submarine work and as a troop-carrier. More that 10,000 were built between 1936 and 1953. In a LibertyShip-like construction speed trial in 1943, the Vicker's shop floor built a Wellington in less than 24 hours and had it in the air an hour later.  The geodesic frame was covered with a skin made of finest Irish linen <huzzah!> slathered with 'dope': a lacquer made of highly flammable nitrocellulose or cellulose-acetate.  The picture [top R] shows the remarkable robustness of this design even when the entire skins of the tail has been burned off the Wellington was still capable to returning to base.

There was a lot of concern about the Wellingtons that didn't come back and it was known that most of these were downed by enemy action rather than metal-fatigue or pilot-error. The boffins were instructed to decide where to apply some judicious armour to maximise the number of round-trips.  If you re-specified the Wellington troop-carrier to hold only 16 soldiers instead of 18, that would free up 200kg of pay-load that could be installed as steel-plate. An inspection tour was organised and it seemed obvious to everyone that they should protect the nose and the tail because these were clearly riddled with holes.  One of the party, Abraham Wald, a Hungarian refugee and smarter than the collective, demurred. Let's not look at the planes that returned, he said, let's look at the planes that never came back. Of course, nobody could do that, but they could look at the areas with comparatively little damage of the plane that returned  [R].  They then did what they could to armour-up the cockpit. A good pilot can fly a plane with a missing wing-tip but a wing-tip can't fly a plane with a missing pilot. Wald and his wife were killed in a plane-crash in India after the war. It was a combination of fog, hillside and "pilot error" rather than bullets.

Previous missing data in The Blob: policular homicide; Limerick students; wisdom teeth; Irish abortions; [black] work experience;

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