Nearly every control surface on your wing is engineered to increase lift - like vortex generators, slats and flaps. The one exception - spoilers.
Spoilers are found at both ends of the spectrum - they're standard equipment on gliders as well as airliners. Fast single-engine aircraft like the Cessna TTx feature them, too.
Destroying Lift Is Incredibly Versatile
What really makes spoilers amazing is how versatile they are - dumping lift can help you descend, roll and brake more effectively.
Dumping Lift To Slow Down And Lose Altitude
One of the most obvious reasons to dump lift is to increase your descent rate without increasing your airspeed. Gliders use spoilers to this effect during landing - allowing you control descent without dumping your nose and ballooning your airspeed. Without them, hitting an aiming spot on landing would be much more difficult.
Airliners and the Cessna TTx use spoilers to the same effect. And, on turbine aircraft, it can take time to regain power once you've pulled back the engines. Using spoilers lets you quickly achieve a desired descent rate without adjusting power.
Replacing Your Ailerons
Spoilers can also augment, or replace, your ailerons to control roll. In this case, you may hear them called "spoilerons," which is simply a spoiler with a different name.
By deploying spoilers on one wing, you drop the wing and bank the aircraft. Deploying spoilers on the other wing can roll the aircraft back to level.
What's the advantage here? High-speed aircraft may need flaps stretching much of the wingspan to achieve great slow-speed performance. However, it's pretty much impossible to mount ailerons on a flap. By using spoilers on the upper surface of the wing, you can use more of the trailing edge for your flaps.
Spoilers offer another advantage as well - this time at high speeds. When you have high speed airflow over your wings, your ailerons can generate so much force that they twist your wings - causing the airplane to bank in the opposite direction. Spoilers allow you to roll the aircraft without creating the twisting force.
You get a third added benefit, as well. When you use ailerons to roll an aircraft, the rising wing generates extra lift, which also creates extra drag. This adverse drag pulls the nose away from the turn, causing "adverse yaw." You use rudder into the turn to remain coordinated.
But, when you use spoilers to roll, they generate form drag on the lowering wing. This helps keep your nose in line with the turn and the aircraft coordinated - which means you don't need to use much rudder.
Spoilers do have a clear disadvantage - you only roll by dropping a wing. If you're close to the ground, dropping a wing to bank may not be a safe option.
That's why most fly-by-wire aircraft with spoilers also have ailerons at the wingtips. The spoilers alone are used for high speed flight, and the ailerons move with the spoilers during low-speed flight.
Putting Weight On The Wheels For Braking Effectiveness
As you roll out during landing, your wings still generate lift. That lift decreases the weight on your wheels and limits your braking effectiveness.
"Weight-on-wheels" sensors on large aircraft trigger your spoilers to fully deploy once you touch down, dumping all of your lift and putting your aircraft's full weight on the wheels. In addition, the spoilers generate form drag to slow you down. Some aircraft even have specific "ground spoilers" in addition to those used in-flight.
Design: Vertical or Hinged
Light aircraft like the Cessna TTx and a glider generally use vertical spoilers. They raise up from the wing in mid chord, stalling the aft portion of the wing.
However, vertical spoilers aren't effective as they first start to raise. If you're using spoilers to roll the aircraft, the controls will feel mushy at first and then suddenly become effective.
Hinged spoilers raise up from the wing like an upside down split-flap. They're more effective at small deflections, improving control response. You typically see these on large aircraft.
All These Benefits Out Of One Simple Design
Spoilers may be the most simple, and versatile, control on an airplane. A single control surface can help you roll, descend and stop - who knew killing lift could be so useful?
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