Missile test gear relies on shear force load cells

A Vishay Nobel product story
Edited by the Engineeringtalk editorial team Sep 22, 2000

Nobel KIS 3 shear force load cells and the E-1-WEI microprocessor controlled weight transmitter were chosen by Matra BAe Dynamics for a piece of test equipment for an air-to-air missile

A task facing engineers at Matra BAe Dynamics at Stevenage has been the design of a piece of test equipment to measure the mass and centre of gravity (c of g) of the Advanced Short Range Air/Air Missile (ASRAAM) currently under development.

It is critical to know these parameters for any airborne craft.

Obtaining them can often involve complicated and time consuming measurements.

The total mass and the c of g referenced to a datum on the missiles in the three axes - x, y, and z - was required to be known.

The design brief was such that the apparatus had to be accurate, fast and easy to use.

Discussing the task, Roger Harriss at Matra BAe Dynamics said "We considered using a number of systems from traditional mechanical balances and electronic scales to a variety of load cells or strain gauged flexures working in tension, compression or shear.

We considered the best solution was the Nobel KIS shear force load cell." Nobel KIS 3 shear force load cells and the E-1-WEI microprocessor controlled weight transmitter were chosen for three reasons.

The low combined error of the KIS (0.02% RO) was important as was the integration with the E-1-WEI weight transmitter to produce a weighing system with extremely high resolution - 0.001%F.S.

or 1gramme in 100kg.

The third reason was the serial communications interface ability of the E-1-WEI.

This allowed their use with a host PC computer and software developed by Matra BAe to control measurements, compute mass and c of g, record results, and compile a statistical database.

The weighing jig is cleverly designed using three KIS 3 1kN (100kg) shear force load cells to support the missile on precision bearings at three exactly defined points in the horizontal plane - two at the front and one in the centre at the rear.

The computed results from these three initial mass reaction measurements give the total mass and define the centre of gravity in the x and y planes for that orientation of the missile.

The missile is then rotated exactly 90 degrees in the jig and the mass at the three points is measured once more.

By looking at the change in mass at the three points for the 90 degrees rotation, the system can then compute the position of the centre of gravity of the missile with respect to its datum in all of the three x, y and z axes.

The weighing resolution is one gram in 300kg, which allows computation of the c of g to an excellent 0.01mm.

However, bearing in mind machine tolerances, the rig achieves accuracy of the order of 0.1mm.

The system, with its self-diagnostic and control software, is now in regular use and has been proved by Matra BAe Dynamics to be easy to operate.

Final results and records are printed out directly, and a permanent data base file of all results is retained.

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