Review of Captive Trajectory Testing Techniques
In the past two decades captive trajectory testing has been performed using hardware dictated by the current state-of-the-art in computer technology and the type of wind tunnel in which testing was conducted. Some of the earlier systems were installed in blowdown tunnels, and it was imperative that these systems used for trajectory generation be relatively fast. These systems used an analog computer as the trajectory generation computer since it afforded an easy solution to the store model equations of motion and, with the proper time scaling, could easily generate store trajectories within the 30 to 45 sec during which the desired test conditions were prevalent.
The outputs from the analog computer to the store model positioning rig were the store component velocities in some cases and store position in others. In the latter case, the positions were continually being updated and, to an outside observer, the model movement would appear as velocity-based control.
The balance force and moment signals obtained during the trajectory were digitized and stored on magnetic tape for off-line analysis. From the digitized data a "digital trajectory" was computed to determine the trajectory that should have been generated by the store model in response to the recorded forces and moments. The "digital trajectory" was then compared to the "analog trajectory" for verification of the controlsystem operation during on-line trajectory generation. The basic disadvantages associated with the analog computer method were the long initial setup and checkout time, typically 20 to 40 hr, and electronic drifts.