The roll command path is scheduled wrt flight condition, mass, and store configuration. The maximum roll authority leaves enough control surface travel for maneuvering and stabilization. The roll input from the stick is scheduled with a linear + quadratic function for low sensitivity at small amplitudes, and high sensitivity at higher amplitudes. The command is filtered and rate-limited. Notch filters are placed on the sensor paths, this causes no phase lag except the actuator lag, decreasing PIO tendencies.
The roll command to aircraft roll rate is
$$\frac{p_e}{p_{eC}}(s)=\frac{h_{\dot{p_e}p_e}s+j_{\dot{p_e}p_e}}{(s-\sigma_{IR})(s-\sigma_R)}$$
Where \(\sigma_{IR}\) is the integral roll pole, and \(\sigma_R\) is the roll pole. You can select the direct link to cancel the integral roll pole.
$$h_{\dot{p_e}p_e}-\sigma_R$$
The roll constants (in seconds) were chosen by the dynamic pressure
$$0.25\leq\tau_{Reff}\leq0.5$$
Roll acceleration is limited to avoid roll ratchet.
Eurofighter Roll Axis Feedback Loops
[[F-18 Lateral Auto Flap Up]] – F-18 scheduled gains according to the dynamic pressure
Sources
- [1] “Realization of the Eurofighter 2000 Primary Lateral/Directional Flight Control Laws with Differential PI-Algorithm.” Accessed: Feb. 10, 2024. [Online]. Available: https://arc.aiaa.org/doi/epdf/10.2514/6.2004-4751
Backlinks:
[[Actuator Limits]]
[[Control Surface Rate Limits]]
Eurofighter Flight Control Laws
LQR Controller
[[Notch Filters for Flight Control Systems]]
Phase Lag
Pilot-Induced Oscillations