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The Martin RB-57D Canberra was a specialized high-altitude strategic reconnaissance aircraft developed from the Martin B-57 Canberra tactical bomber, a licence-built version of the English Electric Canberra. It was used by the United States Air Force during the 1950s prior to operational use of the Lockheed U-2. ==Development== The RB-57D was built strictly as a high-altitude reconnaissance aircraft. It originated in a December 1952 USAF study funded by the Wright Air Development Center for a turbojet-powered special reconnaissance aircraft with a radius of that could operate at altitudes of . Subsonic performance was considered to be acceptable and it was felt that no defensive armament would be needed. The RB-57D was unique and set the stage for high-altitude reconnaissance operations in the rarefied air of the stratosphere. Preliminary specifications were prepared by the Air Force on 27 March 1953. The project was carried out in high secrecy. It was known as Weapon System MX-2147, and the code name was Bald Eagle.〔(USAF Factsheet Martin RB-57D Canberra )〕〔Mikesh, Robert C. (1995), Martin B-57 Canberra--The Complete Record, Schiffer Pub Ltd. ISBN 0-88740-661-0〕 The basic B-57 Canberra design was used as a starting point for the D model, but there were several significant changes incorporated. The most obvious was the greatly enlarged wing. The wingspan was lengthened by to overall. The chord (aeronautics) of the wing was also increased, which combined with the increased length gave the wing a very high lift capability.〔 The second major change to the RB-57D was the addition of Pratt & Whitney J57 engines in place of the Wright J65 engines used on all earlier B-57 models. The two J57 engines produced about total thrust, about more than the two J65 engines. Other changes in the D model included removal of all fuselage fuel tanks and the addition of "wet wing" fuel cells. All defensive armament was removed, and the bomb bay was also removed and replaced by avionics equipment. The horizontal stabilizer (aeronautics) was changed to the variable incidence or "all flying" type. Spoilers were added to the outboard wings to assist the ailerons in roll axis control.〔 Despite the very enlarged wing, an empty RB-57D weighed not much more than an empty B-57 due to the lightening measures taken. The most extreme measures were taken with the wings, which were thin metal honeycomb sections that formed a full wet wing (even in the leading edges). To avoid the weight of rivets, the wings were assembled with a special glue. The wing skin was waxed for aerodynamic smoothness. With a surface skin of only 0.010 inch thick, dropping a small tool on the wing could damage the skin. Even deicing fluid used on the aircraft could potentially cause the glue used to lose strength.〔 On takeoff, only 50% engine power was necessary for a takeoff ground roll of about . Climbing at 25-30 degrees, the RB-57Ds could reach in just 15 minutes. Maximum cruise altitude was and the pilots wore full pressure suits. With of fuel less than a stock B-57, the RB-57D had twice the duration, approximately seven hours compared to four hours for a B-57. Landing was challenging as the big wing would fly at very low speeds, and the small thrust the engines produced at idle made it difficult to reduce speed for touchdown. Even with the spoilers out and landing gear extended, the plane had a very low sink rate and pilots resorted to holding the RB-57Ds into a series of slight stalls to get the aircraft down to the runway.〔 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「Martin RB-57D Canberra」の詳細全文を読む スポンサード リンク
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