PIGGYBACKS & PARASITES

One good aeroplane deserves another.

- PETER GARRISON

THE first aeroplane to cross the Atlantic was a war surplus Vickers Vimy bomber with a wingspan of 21 metres.

The Spirit of St. Louis had a 14-metre wing. In 1975 I made the 3,200-kilometre trip from Gander, Newfoundland to Shannon, Ireland, by then a commonplace for single-engine planes with optimistic pilots, in a homebuilt of 7-metre span. In 1998 a pilotless aeroplane of 3-metre span did it, only to be surpassed in smallness, a few years later, by The Spirit of Butts' Farm, a model plane of 2-metre span that arrived in Ireland with 40 grams of fuel remaining.

It is an unexpected fact of aeronautics that the range of an aeroplane is unaffected by its size. For all practical purposes, only three factors govern range. They are, first, aerodynamic efficiency, represented by the lift-drag ratio and governed, mainly, by streamlining and wingspan; second, propulsive efficiency, the product of the amount of fuel the engines require to produce their power and their effectiveness in converting that power into thrust; and, finally, the fuel fraction, or how much of the takeoff weight consists of fuel. An aeroplane of ordinary efficiency requires a fuel fraction of around one third to cross the Atlantic.

Unfortunately, there's a catch. An aeroplane with a sufficiently heavy fuel load might be able to fly a great distance once airborne, but it might be unable to get off the ground or out of ground effect.