Design and Development
The HVAR was designed by engineers at Caltech as an improvement on the 5 AR (Aircraft Rocket) which had a 5 inch diameter warhead but an underpowered 3.25 inch 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 8.5 lb to 23.9 lb 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% diethylphthalate, 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 “cruciform” Ballistite grain. This went against the common practice of filling rocket motors with different numbers of smaller same-sized tubular charges, 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 710 ft/sec for the 5” AR to 1375 ft/sec for HVAR, giving the coveted flat trajectory.
Read more about this topic: High Velocity Aircraft Rocket
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