Ornithopter Carried cover, Great Britain

An ornithopter (from Greek ornithos "bird" and pteron "wing") is an aircraft that flies by flapping its wings. Designers seek to imitate the flapping-wing flight of birds, bats, and insects. Though machines may differ in form, they are usually built on the same scale as these flying creatures. Manned ornithopters have also been built, and some have been successful. The machines are of two general types: those with engines, and those powered by the muscles of the pilot. 2nd October 1971, 'Birdman' Bert Hansell of Kent takes off in an attempt to fly like a bird across the 50 yard wide river Nene in Peterborough, after just 5 seconds airborne his home made 'Ornithopter' plunged into the river.  The above cover in my collection is one of the covers carried and signed by him.