The advanced control laws were developed by Boeing with a proprietary pictured-to-code tool. They also have some heritage with the RAH-66 Comanche. These control laws have a model-following architecture. These control laws are more effective at decoupling the aircraft responses. They also provide for a robust airspeed hold and turn coordination.
The model-following control systems have a feedforward element that includes the inverse dynamics of a plant, a command model, and feedback compensation. The inverse model can be represented by first or second-order representations as the low-frequency effects of trim, CG, and aerodynamics can be suppressed within the stabilization loop and the high-frequency effects of rotors and actuators are not feasible to suppress. The command model introduces the desired dynamic response as the principle inherent modes of the aircraft are cancelled. The control laws were implemented as first and second-order linear command models that produce first-order rate responses and second-order attitude responses.
For this system above 2.5 rad/s the lower-order inverse model can’t cancel the rotor lags and higher-order elements. The equivalent time delay at 10 rad/s is 0.157s.
Sources
- [1] C. Frost, W. Hindson, E. Moralez, G. Tucker, and J. Dryfoos, “Design and Testing of Flight Control Laws on the RASCAL Research Helicopter,” in AIAA Modeling and Simulation Technologies Conference and Exhibit, Monterey, California: American Institute of Aeronautics and Astronautics, Aug. 2002. doi: 10.2514/6.2002-4869.
Backlinks
[[Boeing]]
[[Doublet Step Response]]
Dynamic Inversion Control Law Structure
[[Equivalent System Time Delay]]
[[Feedforward Control
[[First-order Systems]]
[[Model-Following Control Systems]]
[[Pole-Zero Cancellation]]
[[RASCAL Aircraft]]
[[Second-Order Systems]]
[[Sine Sweep]]