Aerial refueling craft was eventually modified by Airspeed to Cobham's specification, for a non-stop flight from London to India, using in-flight refueling to extend the plane's flight duration. Meanwhile, in 1929, a group of U.S. Army Air Corps fliers, led by then Major Carl Spaatz, set an endurance record of over 150 hours with the "Question Mark" over Los Angeles. Between June 11 and July 4, 1930, the brothers John, Kenneth, Albert, and Walter Hunter set a new record of 553 hours 40 minutes over Chicago using two Stinson SM-1 Detroiters as refueler and receiver. Aerial refueling remained a very dangerous process
The Airplane Factory Sling 2 endurance at standard cruise of approximately 24 hours. The aircraft cruised at 89 knots Indicated airspeed (IAS) (98 knots True airspeed (TAS)) with almost full fuel. When more nearly empty, it would cruise at 96 knots IAS (105 knots TAS). With full fuel, fully loaded with crew the Sling weighed approximately 1,984 Lbs (900 kg), or about 600 pounds overweight. At sea level the aircraft would climb slowly, at a rate of 350 feet per minute. The Airplane Factory Sling 2 The Airplane Factory Sling 2 is a South African two-seater light aircraft designed and produced by The Airplane Factory