The weather challenges of Concorde
IT hardly seems like 30 years ago. And yet it is. It was on March 2nd, 1969, that Concorde took to the air for the first time on a 20-minute testflight. Concorde 001, the French version of the supersonic aircraft, was the one that flew that day; its British counterpart, Concorde 002, flew a few weeks later, although it was to be several years before either of them began commercial operations.
The aircraft was a major milestone in aviation history, and its designers had to cope with many difficulties not encountered in subsonic flight. For example, although the air outside may be as much as 50 below zero, the friction of the atmosphere at cruising speed increases the temperature of its outer skin to well over 100 Celsius. With thermal expansion the aircraft increases significantly in length, and all pipes and cabling must be fitted with expansion joints or loops.
On the other hand, Concorde is less weather dependent than its subsonic cousins: it flies above the active weather zone, between 50,000 and 60,000 ft above the ground, with 90 per cent of the atmosphere below it. It did not present a major challenge to the meteorologists of 30 years ago.
In the first place conventional jets fly near the zone of maximum winds in the atmosphere. The winds encountered at, say, 35,000 ft may reach speeds which are up to 30 per cent of the airspeed of the aircraft itself, and can affect the duration of a long flight by up to an hour or more. Concorde, on the other hand, flies where the winds are significantly lighter, and cruises at three times the speed of a conventional aircraft; minor variations in wind strength have little impact on its flight-time.
At the cruising height of Concorde there are few unpleasant meteorological surprises. Turbulence, for example, because of the very light winds, is encountered only very rarely, and even then is very slight indeed. Accurate forecasts are still important in the ascent and descent phases - but that, after all, is familiar territory for the meteorologist.
The other major meteorological controversy about supersonic aircraft was the fear that emissions of nitrogen oxides from their engines would deplete the ozone layer. The fears were not without foundation, given that such aircraft were expected to increase in number as the years went by. But this did not happen, and in any event when an "ozone hole" was discovered over Antarctica a decade later, it became obvious that there was a much more immediate threat to parts of the ozone layer than any posed by a few Concordes.