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High Velocity Aircraft Rocket
The High Velocity Aircraft Rocket, or HVAR, also known by the nickname Holy Moses, was an American unguided rocket developed during World War II to attack targets on the ground from aircraft. It saw extensive use during both World War II and the Korean War.
==Design and development==
The HVAR was designed by engineers at Caltech during World War II as an improvement on the 5-Inch Forward Firing Aircraft Rocket (FFAR), which had a diameter warhead but an underpowered diameter rocket motor. The desire for improved accuracy from the flatter trajectory of a faster rocket spurred the rapid development. HVAR had a constant 5" diameter for both warhead and rocket motor, increasing propellant from of Ballistite. U.S. Ballistite propellant had a sea level specific impulse of over 200 seconds, compared with about 180 seconds for the British Cordite, German WASAG and Soviet PTP propellants. Hercules Powder Company was the principal U.S. supplier of high performance extruded Ballistite propellants: 51.5% nitrocellulose, 43% nitroglycerine, 3.25% diethyl phthalate, 1.25% potassium sulphate, 1% ethyl centralite, and 0.2% carbon black. The propellant in U.S. 3.25" and 5" rocket motors consisted of a single large X-shaped cross-section, "cruciform" Ballistite grain cavity. This went against the common practice of filling rocket motors with different numbers of smaller same-sized tubular charges with a round cavity, the number depending on motor diameter. The central hole in a tubular charge makes it more difficult to extrude, requiring a softer propellant blend that also yields somewhat lower performance. Rocket ∆V increased from 216 m/s for the 5" AR to for HVAR, giving the coveted flat trajectory. This was still somewhat slower than the German R4M World War II rocket's launch velocity of some , with a smaller calibre () and resultant weight of RDX explosive in the R4M ordnance.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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