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''Blue Bird K4'' was a powerboat commissioned in 1939 by Sir Malcolm Campbell, to rival the Americans' efforts in the fight for the world water speed record. The name "K4" was derived from its Lloyd's unlimited rating, and was carried in a prominent circular badge on the forward hull. K4 was built by Vosper & Company as a replacement to the Blue Bird K3, which had set three other water speed records for Malcolm Campbell before the K4 was built. It also used the same Rolls-Royce R engine. K4 was a three point hydroplane. Conventional planing powerboats, such as Miss England or Blue Bird K3, have a single keel, with an indent or "step" projecting from the bottom of the hull. At speed, the force on this step is enough to lift the bow upward, reducing the wetted surface area of the hull and thus also the frictional drag. A "three pointer" has a two distinctly separate floats fitted to the front, and a third point at the rear of the hull. When the boat increases in speed, most of the hull lifts out of the water and planes on these three contact points alone. These points being even smaller in area than the planing hull of a monohull hydroplane, have even less drag. Having a broad spacing between the front planing points, the three-pointer is less susceptible to instability caused by small disturbances than is a monohull. However if the bow lifts beyond its safety margin, the ''aerodynamic'' forces (not the hydrodynamic forces of the water) on the broad forward area of the hull will cause it to "kite" upwards, leading to a somersault and crash. This is what happened to both Slo-mo-shun and Bluebird K7. K4 set one world water speed record on 19 August 1939 on Coniston Water, Cumbria, England. == Jet engine trials == After World War II, Sir Malcolm unsuccessfully re-engined K4 with a de Havilland Goblin turbojet engine. He didn't gain any records, but the new superstructure did gain the nickname '' 'The Coniston Slipper' ''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Blue Bird K4」の詳細全文を読む スポンサード リンク
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