United States military aircraft designation systems

US Air Force FASTEST STRATEGIC AIRCRAFT ever the XB-70 Valkyrie

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• published: 14 Feb 2016
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A great idea for the us air force the XB 70 Valkyrie would have served the us air force very well. The North American Aviation XB-70 Valkyrie was the prototype of the B-70 nuclear-armed, deep-penetration strategic bomber for the Strategic Air Command of the U.S. Air Force. In the 1950s, the North American Aviation company designed the Valkyrie bomber as a large, six-engine aircraft capable of reaching Mach 3+ while flying at 70,000 feet (21,000 m), which velocity and altitude capabilities would allow the evasion of interceptor aircraft, then the only effective weapon against bomber aircraft. In 1961, improved, high-altitude surface-to-air missiles (SAMs), the U.S. Air Force's doctrinal change to low-level penetration bombing, the large development costs of the B-70 program, and the introduction of intercontinental ballistic missiles (ICBMs) to the U.S. nuclear arsenal, led to the cancellation of the B-70 program. As such, two prototype aircraft were built, and designated XB-70A; these aircraft were used for supersonic test-flights during 1964–69. In 1966, one prototype crashed after colliding in midair with a smaller jet aircraft; the remaining Valkyrie bomber is in the National Museum of the United States Air Force, in Ohio. Design[edit] The Valkyrie was designed to be a high-altitude Mach 3 bomber with six engines. Harrison Storms shaped the aircraft[68] with a canard surface and a delta wing, which was built largely of stainless steel, sandwiched honeycomb panels, and titanium. The XB-70 was designed to use supersonic technologies developed for the Mach 3 Navaho, as well as a modified form of the SM-64 Navaho's all-inertial guidance system.[69] The XB-70 used compression lift, which was generated from a prominent wedge at the center of the engine inlets that created a shock wave below the aircraft. The wing included inboard camber to more effectively use the higher pressure field behind the strong shock wave (the airflow at the XB-70 wing's leading edge was subsonic).[70] The compression lift increased the lift by five percent.[71] Unique among aircraft of its size, the outer portions of the wings were hinged, and could be pivoted downward by up to 65 degrees. This increased the aircraft's directional stability at supersonic speeds, shifted the center of lift to a more favorable position at high speeds, and strengthened the compression lift effect.[72] With the wingtips drooped downwards, the compression lift shock wave would be further trapped under the wings. The XB-70 was equipped with six General Electric YJ93-GE-3 turbojet engines, designed to use JP-6 jet fuel. The engine was stated to be in the "30,000-pound class", but actually produced 28,000 lbf (124.6 kN) with afterburner and 19,900 lbf (88 kN) without afterburner.[73][74] The Valkyrie used fuel for cooling; it was pumped through heat exchangers before reaching the engines.[25] To reduce the likelihood of autoignition, nitrogen was injected into the JP-6 during refueling, and the "fuel pressurization and inerting system" vaporized a 700 lb (320 kg) supply of liquid nitrogen to fill the fuel tank vent space and maintain tank pressure.[75] Development[edit] Background[edit] Main article: WS-110A As an offshoot of Boeing's MX-2145 manned boost-glide bomber project, Boeing partnered with RAND Corporation in January 1954 to explore what sort of aircraft would be needed to deliver the various nuclear weapons then under development. Providing for a long range and high payload were obvious requirements, but they also concluded that after release of nuclear bombs the bomber would need supersonic speed to escape the critical blast-radius. The aircraft also had to be large to carry a reasonable bomb load and a high fuel load for the unrefueled range required from the continental United States to the Soviet Union.[2] For some time the aviation industry had been examining this problem. From the mid-1940s, there was much interest in using nuclear-powered aircraft in the bomber role.[3][4][N 1] In a conventional jet engine, thrust is provided by accelerating air, which is accomplished by heating it with burning jet fuel. In a nuclear engine, heat is supplied by a reactor, although a small amount of jet fuel was carried for use during high-power portions of flight—take-off and high-speed dashes. Another possibility was the use of boron-enriched "zip fuels", which improved the energy density of the fuel by about 40 percent,[5] and could be used in versions of existing jet engine designs.[5] Zip fuels appeared to offer sufficient performance improvement to produce a strategic bomber with supersonic speed. The U.S. Air Force followed these developments closely, and in 1955 issued General Operational Requirement No. 38 for a new bomber with the payload and intercontinental range of the B-52 and the Mach 2 top speed of the Convair B-58 Hustler.[6] The new bomber was expected to enter service in 1963.[7][N 2]