Through the 1950s various studies on supersonic transports (SSTs) suggested that the economics of such designs were far too poor to be practical. Lift is generated in different ways at supersonic speeds and achieving reasonable lift-to-drag ratios requires the wings to have a very short span. This works well at supersonic speeds, but offers very little lift at low speed. In order to make a design that is able to take off and land on existing runways, either the aircraft would have to use wider wings and lose supersonic cruise economy, have enormous engine power, or be extremely large.