The essence of air transport is speed, and speed is unfortunately one of the most expensive commodities in the world, principally because of the disproportionate amount of the power required to achieve high speed and to lift loads thousands of feet into the air. This is strikingly illustrated by the fact that while an average cargo ship, freight train and transport aeroplane are each equipped with engines totalling about 2,500 H.P., the ship can carry a load of about 7,000 tons, the train 800 tons and the plane only two and a half tons.
