After a normal takeoff run and lift-off from runway 21 the pilot’s attention was momentarily distracted by rainwater which was falling on his shirt sleeve from the window channel. The distraction occurred as the landing gear was being retracted and inadvertent action by the pilot caused two propellers to strike the runway. The no. 4 prop and engine were damaged by metal pieces projected from the damaged no. 3 prop causing increasingly severe vibrations. As a right wing heaviness developed, a sudden excessive rise of EGT (exhaust gas temperature) of the no. 2 and no. 3 engine was noted and the pilot carried out an emergency wheels-up landing on a harvested wheat field. Touchdown was about 6930 feet beyond the end of the runway 21 and 21deg right of the extended centreline. PROBABLE CAUSE: “The captain’s diversion of his attention during takeoff which allowed the aircraft to settle to the runway striking the Nos. 2 and 3 propellers.”