HURST, Texas, 18 Feb. 2008. Engineers from Bell Helicopter Textron Inc. in Hurst, Texas, needed computer simulation tools to help them design the BA609 commercial tiltrotor aircraft.
They found their solution with the Control System Toolbox, Simulink, MATLAB Real-Time Workshop, and Control System Toolbox simulation tools from The MathWorks in Natick, Mass.
"As an aerospace engineer you rarely get to take an idea from a blank sheet of paper to a completed, flying aircraft," says Tom Brooks, principal engineer at Bell Helicopter Textron.
Starting with some basic assumptions, the team used Simulink to model and simulate high-level characteristics of the BA609 and its flight-control system (FCS). They then simulated the model to evaluate different aircraft configurations.
"To reach aircraft configuration decisions effectively, you must use an iterative approach," says David King, BA609 analytical integration leader at Bell Helicopter Textron. "The ability to make rapid changes and simulate them quickly using Simulink was a big advantage for this kind of rapid prototyping."
King and his colleagues performed complex analyses of structural components and control algorithms. In one case they evaluated the effect of turbulence on the BA609's barbell-like weight distribution.
Bell engineers built filters into the FCS feedback system to dampen oscillation and ensure a sufficient stability margin when the aircraft encountered turbulence. Using MATLAB and Control System Toolbox, they developed and implemented the filters and generated expected filter output for use in future verification tests.
Bell Helicopter provided their suppliers with working Simulink models to help them communicate requirements to suppliers while enabling the suppliers to test their software more effectively before delivering it to Bell.
Simulation played a key role in the system testing of the baseline FCS code. From the models they used for simulation, Bell engineers automatically generated FCS code using Real-Time Workshop. By comparing results from the automatically generated code with the code running on the flight control system hardware, they verified and validated system behavior before conducting flight tests.
The Simulink models will be part of the package that Bell submits to the U.S. Federal Aviation Administration for DO-178B level A certification of the BA609.
"To satisfy the DO-178B verification requirements for level A, we need an independent version of the flight control system that processes inputs and produces actuator commands," King explains. "The code we automatically generate using Real-Time Workshop gives us an independent version to meet that requirement."
The BA609 team used Simulink and Real-Time Workshop to create a hardware-in-the-loop (HIL) testing environment that incorporates a physical model of the BA609 called the "iron bird."
Pilots "fly" the iron bird to train on the system before flight tests by viewing simulated displays and operating real controls, including real stick and force-feel systems. Bell plans to use a similar system to provide training for civilian pilots.
For more information contact The MathWorks online at www.mathworks.com, or Bell Helicopter Textron at www.bellhelicopter.com.
