2243. Mass Property Fixture Design for Missile Systems


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J Nabity, E Seeley, R Pritchard: 2243. Mass Property Fixture Design for Missile Systems. 1995.



Fixtures were designed and built to measure the center of gravity and mass moments of inertia (Ixx, Iyy, and Izz) of the Joint Stand-Off Weapon (JSOW). JSOW is a 1200-pound, 60-inch-long air-to-surface missile. One fixture supported the JSOW horizontally for measurement of center of gravity as well as yaw and pitch moments of inertia. This fixture design consisted of a roller plate assembly and required a set of rings to facilitate rotation of the missile. A separate fixture supported the JSOW vertically to measure the roll moment of inertia. It utilized portions of the yaw and pitch fixture, namely the strongback assembly, to minimize cost. This fixture was a gantry design with a yoke pivot, which allowed the JSOW to rotate to the vertical position after it was installed. Both fixtures were designed to mate with a Space Electronics Inc. KSR-5500 Mass Properties Instrument. The fixture designs were strongly influenced by safety considerations. The fixtures had to be easy to use, support an 1800-pound load, and satisfy ordnance handling equipment safety requirements. The other key issue in the fixture designs was to have a measurement uncertainty of less than one percent. Position and lean error are the major sources of fixture errors. Fixture design greatly influences the magnitude of these errors. Lean error is largely caused by poor design and was a major consideration in the design and fabrication of the gantry. ALGOR structural analysis software was used to refine the gantry fixture design and determine static and dynamic stiffness. Measured mass properties were compared to known values and agreed within the desired uncertainties.


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