Aero · Flight Controls · Demo
One stick, two aircraft — the mechanical one obeys and stalls, the computed one refuses.
One stick, two aircraft
Both aircraft receive exactly the same command. Pull past ~55% and the commanded angle of attack crosses the stall — one aircraft obeys, one refuses.
Readout
Lift is read off the same live lift curve for both aircraft — watch the two dots on the plot.
In plain terms
In a mechanical aircraft the stick is connected to the elevator by cables — so it honours any command, including one past the stall angle, where the wing stops flying. Hold the stick back and the nose drops, the wing recovers, the held stick pulls it back through the break, and the aircraft porpoises.
In the A320 the stick talks to computers instead. They measure what the aircraft is doing many times a second, move the same elevator harder and earlier than a human could — which is why the pink aircraft settles faster — cancel most of a gust before it develops, and simply refuse to cross α-max. Full aft stick delivers maximum lift, held safely at the edge of the stall.
The loop above is why the two aircraft differ. Direct linkage is open-loop: the elevator angle is fixed by the stick, and the response unfolds at the airframe’s natural pace. Fly-by-wire closes the loop: measured angle of attack, pitch rate and load factor come back to the computers, which continuously re-command the elevator — higher effective bandwidth and damping from identical hardware, the same way ABS out-brakes a driver pumping the pedal.
The seven computers come in two dissimilar designs, written by separate teams, cross-checking each other; a computer that disagrees is outvoted. If enough fail, the aircraft steps down from normal law (full protections, what this demo shows) through alternate law to direct law — degraded but always flyable. In this demo the direct aircraft answers with a ~0.45 s time constant, the fly-by-wire one ~0.22 s with ~78% of the gust cancelled.