Answers for your flight control law questions and the role of in-flight simulations for testing flight control law design can be found in the book "In-Flight Simulators and Fly-by-Wire/Light Demonstrators", ISBN 978-3-319-53996-6 ISBN 978-3-319-53997-3 (eBook).

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Peter

[1] The “brain” of any flight control system, the flight control laws, is defined as a software (embedded in digital systems) composed of a set of logic and algorithms that translate the system’s operator commands to electrical demands to the system’s actuators (effectors in the most general sense) using the measurements of the system states provided by a suite of sensors.

The flight control laws are designed to fulfill three key objectives:

1. To ensure the proper stabilization of the controlled system for every possible operational condition.

2. To improve the dynamic response of the resulting augmented system.

3. To enhance the system’s rejection capability to exogenous perturbations.

In a model-based design approach, engineers use mathematical models that emulate the system’s dynamics to obtain the best candidate control architecture, along with the optimal value of the flight control laws’ internal parameters.

[2] In the launchers and satellites field, the flight control laws are "renamed" by Attitude and Orbit Control (AOC) Laws.

[3] The Differential PI architecture developed for the EF2000 uses a very simple hack, the first derivate, apply the scheduled gains to the derivative of the feedback, and then integrate. It has several advantages w.r.t. a standard PI controller, the most relevant one is that transient perturbations induced by fast gain scheduling variations can be minimized (imagine a gain scheduled with AoA in a turbulent environment or a discrete change of gain values due to a change of the external store configuration).

This type of PI controller is used in many other military platforms, but as always, there's not much public information out there.

[4] The key point of in-flight simulation is that you test your controller against a similar plant. You might wonder, how the heck an F-16 could have similar dynamics to those of the LCA. One more time, the answer is the flight control laws. In a nutshell, you can "augment or modify" the F-16's dynamics by designing a specific controller that makes it fly like a LCA (at least with similar linear dynamics as those of the LCA models). It provides a safe way to flight test experimental flight control laws in a controlled environment. It's also useful to check hardware implementation.

I hope this helps!

1) Control laws (or controllers) can be applied to any plant (aircraft, vehicle, spacecraft, missile, etc.).

2) The term of flight control law applies to all air vehicles.

3) The flight control law design concept is diverse. Each control concept has advantages and disadvantages. While the differential PI control you asked about has some advantages, it has the disadvantage of being susceptible to noise due to differential effects. And while the NDI (Nonlinear Dynamic Inversion) control applied to the F-35 is sensitive to model uncertainty, if the model is accurate, it has the advantage that it can be commonly applied to A, B, and C versions with one control structure. This is because only OBM (On-Board Model) needs to be replaced. In addition, sensor-based INDI (Incremental NDI) is a method that is quite robust to model uncertainty, but it is difficult to obtain the measured angular acceleration, and the use of a filter that minimizes noise is essential when the angular velocity is differentiated from the IMU sensor. is. And although it has the characteristic of reducing the stability margin of the system (especially the phase margin), the stability margin is quite robust against uncertainty. Hybrid INDI, which takes advantage of these two control methods, is sometimes used.

4) IFS (In Flight Simulator) is a method that can be safely verified with an aircraft platform that has already been tested when developing a flight control computer or a new flight control rule. In other words, new functions can be efficiently verified while ensuring flight safety by using the already verified flight control system for take-off and landing and verifying the function with the newly developed flight control rule in a specific flight condition.