SubscribeThe U.S. Air Force and the Swedish FMV recently sponsored a program to develop an Automated Aircraft Collision Avoidance System (ACAS).
The objective of the project was to develop a generic automated collision avoidance algorithm for both piloted and unpiloted applications. Unlike other collision warning or traffic advisory system already in use today, this system will automatically take control of the vehicles and perform the necessary last-moment evasive maneuver to avoid an impending mid-air collision.
Because the development effort included the extensive involvement of various contractors (SAAB, Boeing, Lockheed Martin) in addition to the government entities, a capable, yet flexible, common simulation platform was needed for the development and testing of the ACAS algorithm. At the outset of the program, D-Six was selected as the common simulation environment for the development team.
D-Six performed a wide variety of crucial simulation tasks for this program; as the primary simulation platform for the development and testing of the ACAS algorithm using the D-SixNet high performance network for multi-vehicle simulation, as well as the platform for man in the loop evaluation of the algorithm with D-Six integrated into comprehensive manned simulation hardware in the Saab, Lockheed Fort Worth and the Air Force Research Lab simulation labs. Perhaps the most unique and groundbreaking application of D-Six in this program was the first successful deployment of a simulated vehicle fully integrated as a multi vehicle element in a manned vehicle flight test program.
D-Six Ground Station for ACAS Flight Test:
After the ACAS algorithm had matured following detailed sim analysis and manned evaluation, a flight test was planned using two F-16’s as the test vehicles. As a risk-mitigation measure, the D-Six Ground Station was cooperatively developed with Lockheed Martin incorporating a Bihrle-supplied high-fidelity F-16 flight model. The purpose of the ground station was to provide a virtual target for the airborne F-16 at the initial stages of the flight test to verify safe system integration and perform various algorithm checkouts before attempting high-risk two-ship collision flights to demonstrate the ACAS’s effectiveness.
The D-Six Ground Station consisted of several primary components as illustrated. The Garmin GPS receiver provided UTC time to the Ground Station’s ACAS system just as the aircraft navigation computer provided UTC time stamps to the ACAS algorithm onboard the airborne F-16 test vehicle.
The 1553 PCMCIA MUX card sent and received encoded ACAS link messages to the SADL radio to communicate with the F-16 aircraft’s onboard SADL radio. With this approach, a virtual target was generated by the ground station, directly stimulating the ACAS algorithm hosted in the airborne F-16’s flight control computer. The implementation of ACAS algorithm and other supporting subsystems could be rigorously evaluated without risking two manned aircraft.
Additionally, the use of the D-Six Ground Station’s “relative IC” (relative initial conditions) feature allowed very efficient flight test conduct since new collision geometry was easily recomputed by the ground station without the need to synchronize and repositioning the manned aircraft before each test run.
Prior to the flight test, additional hardware-in-the-loop simulation was performed at Lockheed Martin’s Fort Worth HQ simulation facility. The D-Six ground station was once again used extensively to provide collision scenarios against the flight hardware-in-the-loop HQ sim for debugging and to verify satisfactory system integration.
Because of D-Six’s unique hardware independent model “project” format, the propagation of the various flight models, algorithms and sim applications to the various program participants was seamless, allowing truly collaborative program evolution. Further, D-Six provided a single coherent and integral simulation tool that easily supported initial concept exploration, detailed ACAS algorithm development, piloted simulation demonstration and finally, flight test risk mitigation and demonstration.
