491. Precise Booster Thrust Alignment in an Asymmetric Application

Paper

Abstract

The Redhead/Roadrunner Target Missile (MQM-42A) is a Mach 1.25 to 1.35 cruise, 350 foot altitude, highly maneuverable and recoverable target, soon to be operational in the U.S. Army Hawk Crew Training and Annual Qualification Program.
The Redhead/Roadrunner was designed, manufactured and flown by North American Aviation, Inc., Columbus Division, to fulfill the mission requirements defined by the Target Missile Branch, Development Division, DR&D, U.S. Army Missile Command, Redstone Arsenal, Huntsville, Alabama.
SAWE Technical Paper No. 293, presented at the 1961 Annual Conference, described the development of a special tool used to locate the Horizontal and Vertical Center of Gravity of the Redhead/Roadrunner. The original tool is still in use today and has contributed significantly to the overall program success.
The paper describes the follow-up stage of aligning the booster thrust with the Launch C.G. The Redhead/Roadrunner configuration, which mounts the ramjet sustainer motor above the missile body and depends on an underslung, canted nozzle, solid propellant booster to provide ground launch power from lift-off through sustainer motor ignition to a speed of Mach 1.4, is similar to the well know missiles, Regulus, Matador, Mace, and others including zero-launch aircraft. The problem of the booster thrust alignment on this type of configuration is a difficult one. The complexity of the problem on the Redhead/Roadrunner is magnified considerably due to the missile’s small physical size, the high specific impulse of the booster and the fact that there is zero thrust produced by a ramjet when ground launched until lit-off speed is reached. Try to imagine the difficulty in pushing a broom handle through the air with the point of a pencil, from underneath! This is the situation encountered when ground launching the Redhead/Roadrunner.
The evolution of a set of tools and a working procedure, the combination of which affords maximum assurance that an acceptable thrust alignment has been accomplished, is described herein, pointing out the significance of measurement relative to mission success. The reader will easily follow the five stage evolution of procedures and tools from Phase I, which relied mainly on faith, through the precise but prohibitively time consuming Phase II, through the optically inferior Phase III, to the highly refined system used during Phases IV and V. The present system has demonstrated a consistent ability to direct the booster thrust well within an area of 0.20 square inches from a point 40 inches away; its accuracy will allow for the variable effects of crosswinds at launch, the inherent errors of estimating launch conditions based on Weight Empty actual measurements and the normal lack of repeatability associated with the ability of a random group of people to perform the same precise task.
Within the text and figures, the restrictive acceptable alignment zone boundaries are defined, description and sketches of the various tools included, documented actual misalignment figures are plotted and chart describing performance task versus hours to accomplish will be found.