Question

What type of controller is used in an auto flare control?

(a) Proportional plus derivative

(b) Proportional plus integral

(c) Proportional plus integral plus derivative

(d) Proportional only

I got this question in examination.

My doubt stems from ILS/MLS Coupled Landing System and Automatic Landing topic in chapter Autopilots and Flight Management Systems of Avionics

Answer 1

Right option is (b) Proportional plus integral

To explain: The auto-flare loop is a high-order system; apart from the lags present in the filtered rad.alt. signals there are also the lags present in the response of the pitch attitude command loop. This loop controls and its response is significantly slower at the low speeds during the approach. A proportional plus integral control term is used in the auto-flare controller to ensure accuracy and some phase advance is generally provided to compensate for the lags in the loop and hence improve the loop stability and damping.