Understanding the basic aerodynamics of how an airplane’s control surfaces work is a major part of safely commanding it both on the ground and in the air. When you have a good grasp of these principles, both abstractly as well as while acting as pilot in command, you are better equipped to make sound decisions and predict how the aircraft will respond, both to control inputs as well as the environment outside the cockpit. You will learn these basics in ground school if you are a student pilot. It’s important to do further research or ask for clarification from an instructor if you’re having trouble grasping these ideas, as they are foundational to the understanding of flight. Knowing what lift, weight, thrust, and drag are, as well as how they affect control surfaces, are all part of understanding the craft under your command.
What Are Control Surfaces?
Control surfaces are the parts of an airplane the pilot uses to operate it—to taxi, aviate, bank, accelerate, decelerate, and land. By forcing differences in air pressure, these parts of the aircraft use the air surrounding it (air pressure) to take whatever action the pilot wishes. Manipulation of these parts of the aircraft is what makes flight possible. Aeronautical engineers spend a great amount of time pondering these concepts and the safest, most efficient ways to maximize them. The beneficiaries are pilots and their passengers, who control and enjoy the benefits of harnessed air power.
While control surfaces may vary greatly depending on an airplane and its type—and even kind of aircraft—the basic principles of aerodynamics remain the same. These might look as different from a blimp to a fighter jet and large airliner. However, all of these have control surfaces, and they all contribute to keeping the object aloft for its intended purpose. Sometimes this can vary for durations and specific missions. The space shuttle, for example, took off like a rocket, flew like a spacecraft, and landed like a glider. That all of these tasks were undertaken by a single vehicle was a tremendous feat of engineering and a testament to modern man’s understanding of the manipulation of control surfaces. These realities, however, can be contemplated with a basic training airplane, even the simplest paper airplane.
The Tail As a Control Surface
The tail of an airplane isn’t what most people think of when contemplating what makes flight possible. That honor usually goes to the wings. However, without the tail, an aircraft could not remain stable for long. The tail of an airplane allows it to recover quickly after it has been “pushed against” by any kind of wind.
The aircraft’s vertical stabilizer— also known as the “tail fin”— is what permits a pilot to continue in his or her desired course through the air. If an airplane is in level flight and the pilot does not wish to bank or turn to the right or left, the air pressure on either side of the vertical stabilizer pushes equally on either side of its plane, and the aircraft is then assisted in the act of flying straight and level. However, if the pilot is ready to turn, this control surface will enable this possibility. By manipulating the vertical stabilizer, the air pressure is suddenly increased on one side and decreased by the same amount of the opposite side. The result is movement in the desired direction.
A horizontal stabilizer also plays a role in “balancing” the airplane in steady, stable flight. As is the case with vertical stabilizers, the equal air pressure on both sides of a horizontal stabilizer assist in this goal. However, if the pilot wishes to ascend or descent, the horizontal stabilizer comes into play. When the pilot decreases the air pressure on one side, the plane will ascend. If it is increased on the other, descent will take place. Learning how to control these motions make for safe takeoffs and landings. Newton’s Third Law of Motion (“for every action, there is an equal and opposite reaction”) is what is at work here.
Rudders As a Control Surface
The rudders of an airplane are instrumental in its directional control. While the rudder is attached to the vertical stabilizer, its role is important enough to be discussed on its own. Rudders directly affect the airflow around the airplane. It can be moved to the right or left, depending on which direction the pilot wishes to take. By using a sideways angle of attack, the airplane is now able to yaw either to the right or to the left. Depending on how much airflow is surrounding the rudder, this control surface can bring tremendous assistance to the pilot. Rudders are particularly useful to aircraft, which are operating at a high rate of speed—think about fighter jets or racing airplanes.
Rudders are what enable such craft to move quickly and with precision. Since airplanes weren’t operating at blinding speeds until the latter half of the twentieth century, rudders weren’t developed until more recently. Rudders are also important when it comes to efficient takeoffs, as pilots employ them in conjunction with the airplane’s tailwheel and nosewheel. Most engineers install pedals in the cockpit to control the rudders.
Wings As a Control Surface
Just as with the tail of the airplane, the wings play a vital role in getting and staying aloft, then landing at the proper time. An airplane’s ailerons control the “rolling” motion of an aircraft around its center of gravity. These are small hinged areas on the wing, and when the pilot actives them in opposition to one another, banking occurs. The airplane will turn to the right or left accordingly.
Where speed is concerned, a pilot will pay attention to the flaps of an airplane. Extending the flaps decreases the stall speed of an airplane; drag is increased. The wing is now creating more lift, and the airplane is assisted in the act of taking off. Wing design varies greatly with the mission of the aircraft.
Mr. Matthew A. Johnston has over 23 years of experience serving various roles in education and is currently serving as the President of California Aeronautical University. He maintains memberships and is a supporting participant with several aviation promoting and advocacy associations including University Aviation Association (UAA), Regional Airline Association (RAA), AOPA, NBAA, and EAA with the Young Eagles program. He is proud of his collaboration with airlines, aviation businesses and individual aviation professionals who are working with him to develop California Aeronautical University as a leader in educating aviation professionals.