Originally Posted by
777Supremecist
Speaking of which, a bit off topic, but how does Airbus's direct law work? In direct law, does the stick deflection actually use a blend of pitch and g rate (C*) or does it correspond directly to elevator deflection? If the case is the latter, isn't that a bit risky? As the pilot might overstress the airframe by pulling too hard at a higher speed etc/
I think maximum control deflection is limited if flaps are fully retracted, as a poor proxy for airspeed information.
For example, in a hydraulic aircraft, the aerodynamic effect that your input is going to have in the airplane, its not the movement of the yoke but the force on it which tells you whether you will over stress the airframe. At low speeds you will instinctively push or pull to obtain a given pitch rate, at higher speeds you will modulate stick forces to obtain a g load. The yoke will (naturally) be stiff and more sensitive at higher speeds, and vice versa for lower speeds.
The stick forces on hydraulic aircraft are generally entirely artificial. This is why the 737 has the extra pitot tube in the tail, to use airspeed to generate a stick force proportional to airspeed (Elevator Feel and Centring Unit). On more modern aircraft, I believe it's much like the A320: in normal conditions, stick forces are set based on airspeed (instead of elevator travel being set from airspeed). If there's data failures, fall back to a high speed/low speed regime based on flaps.
Rudder travel limiters are very similar I believe - there was an ATR runway excursion a while back where the automatic travel limiter stayed in the high-speed position due to electrical failure, and the crew lost directional control on rollout.