sentences:  Since shortly after World War II training has always been done in two-seat dual control gliders, but high performance two-seaters are also used to share the workload and the enjoyment of long flights.Originally skids were used for landing, but the majority now land on wheels, often retractable.Some gliders, known as motor gliders, are designed for unpowered flight, but can deploy piston, rotary, jet or electric engines.