Spoiler alert…

Spoilers are often used on jet transports to aid the ailerons. These hydraulically operated hinged panels rise from the top of the lowering wing to decrease lift (plus add some drag which helps fight adverse yaw). They are typically located on the aft half of the surface just in front of the flaps and rise as a function of how much roll is applied to the yoke. The spoilers only deploy on the inside wing as the airplane is rolled (they rise with the rising aileron). One airliner has the spoilers start to rise after about 10° of yoke movement. You don’t start a crosswind takeoff with a lot of aileron into the wind due to their drag, which not only hurts takeoff performance but increases weathervaning tendency.

Spoilers are also used as speedbrakes to increase descent rate without picking up airspeed. In this case, all of the flight spoilers rise symmetrically based on how far the pilot moves the speed brake handle. Fully extending the flight spoilers can give some pretty good buffeting, so just less than full extension might be the best combination of sink and smoothness.

The flight spoilers are used on landing, either automatically or manually, to add drag and kill lift (more weight on the wheels for better braking effectiveness). Often there will be ground spoiler panels adjacent to the flight spoilers panels. These only deploy on the ground because they either cause too much buffeting inflight or are located in front of rear-mounted engines and might cause compressor stall at high power settings.

Automatic spoiler extension on the ground can be triggered on landing by things like landing gear strut compression or wheel spin-up. A safety feature might be related to the radio altimeter, so they can’t deploy until the aircraft is just a few feet above the ground.

The Fokker 100 used only ailerons for roll control, but had a full set of spoilers for the ground. The lift-dumpers (no, really, they were called “lift-dumpers” and dump lift they did) would deploy automatically if armed but would also rise with reverse thrust. On a rejected take-off (abort), closing the throttles and raising the reverse levers would raise the lift dumpers. The speedbrake on this great little airplane was a clam-shell tailcone that would open for drag. Since this didn’t affect lift, the airplane could be landed with the speedbrake extended. It would automatically retract when the TOGA buttons were pushed, the throttles full-forward (firewalled) or the landing gear retracted.

Even with all of these lift killing devices, the ailerons can still be quite effective just after touchdown. Too enthusiastic rolling of full aileron into the wind on a crosswind landing just after touchdown (say, after an all-night trans-Atlantic 777 flight into London) might actually lift the downwind wing momentarily, or, uh, so I’ve been told. (Control effectiveness = deflection x KCAS). Remember, airmanship is critical, no matter what you’re flying or how many hours you have.