When Cessna test pilots discovered a potential problem with its Citation jet anti-skid brake control system, they identified and addressed the issue by using MathWorks tools. First, they developed a software model of the aircraft and ran hardware-in-the-loop (HIL) tests that simulated system behavior under a variety of conditions.
While the aircraft continued to meet its certification requirements, on some landings the prototype’s brake control system applied and released the brakes more than necessary. Cessna engineers knew that certain combinations of runway and brake wear conditions played a role. Conducting hundreds of flights and landings while emulating the conditions would have been cost and time prohibitive.
Instead, the engineers developed HIL tests for the prototype’s brake control system using Simulink, Simulink Coder, and xPC Target. Using Simulink, they developed a model of the prototype. The model incorporated lift, drag, engine thrust, and the trailing link main landing gear. It also included parameters to simulate runway conditions – water, snow, ice, and grooved runways – as well as different brake wear conditions. They then used Simulink Coder to generate ANSI C code from the Simulink model. Using xPC Target, they ran the code and executed the model in real time on commercial off-the-shelf hardware connected to the aircraft’s brake control system.
In this testing environment, the engineers simulated hundreds of landing under different conditions until they could replicate the symptom consistently. During the simulations, the team gathered data on 20 different parameters at a sample rate of 2,000Hz. With each real time test lasting more than 20 seconds, more than a gigabyte of data was produced for each run.
Cessna used MATLAB to analyze the test data, plot various signal relationships, and identify the cause of the brake control issue: a dead band in the brake controller. After finding the dead band, the team developed a design that addressed the issue using additional parameters available from the aircraft controls and systems.