293. A Low-Cost, Practical Approach to the Actual Measurement of the Horizontal and Vertical Center of Gravity of a Small Missile

Paper

Abstract

This paper was presented at the Twentieth National Conference of the Society of Aeronautical Weight Engineers at Akron, Ohio, May 15 – 18, 1961. Actual measurement of an aircraft’s horizontal center of gravity has for years been a standard practice. However, center of gravity location in the vertical reference system has not been a critical parameter and therefore, the standard practice in this respect has been to rely on calculated values.
This approach is entirely inadequate when confronted with high angular thrust values under ballistic conditions that have appeared on a current project at Columbus Division of North American Aviation, Inc. In July 1960, the Army Rocket and Guided Missile Agency, through the Cleveland Ordnance District, awarded a development contract for the Roadrunner Target Missile System.
The basic configuration of the North American designed Roadrunner Target Missile pointed out the necessity for knowing the exact vertical as well as the horizontal location of the missile center of gravity. The sustaining power source for climb and cruise is a ramjet engine, mounted high on the rear of the missile. For propelling the Target Missile to a speed at which this ramjet will produce thrust, a solid propellant booster with a fixed cant angle nozzle is mounted below the missile body. The Roadrunner Target Missile is zero-length launch and behaves according to ballistic laws for approximately the first three seconds after boost ignition. At this time, aerodynamic surfaces are effective to a point where missile attitude may be controlled. From the conditions that exist, it can readily be seen that the booster thrust must be directed through the total center of gravity. Otherwise, within three seconds the missile will have pitched or yawed out of control causing structural damage, tumbled gyros, and it may not even reach engine light off speed. More serious misalignment of booster thrust could easily pitch the missile into the ground in front of the launcher, or in the other direction, drive the missile into a loop, impacting behind the launch pad.