The horizontal stabilizer is part of the aircraft's tail section, working in tandem with the vertical stabilizer to keep the aircraft balanced in the air. Located at the tail, it is a small lifting surface that generates aerodynamic forces counteracting pitch tendencies and maintaining longitudinal equilibrium. While fixed or adjustable, it functions as an airfoil whose effective shape the elevators alter to command pitch, confirming that the horizontal stabilizer is an aerodynamic wing surface providing stability and longitudinal balance in flight.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is a horizontal stabilizer airfoil?
A horizontal stabilizer airfoil is the specific cross-sectional shape of the horizontal stabilizer, a fixed or adjustable surface located at the tail of an aircraft, which is comparable to an airfoil. This airfoil profile is a lifting surface that provides reactive force when in motion relative to the surrounding air, generating aerodynamic forces that counteract the aircraft's pitch tendencies. The design of this airfoil is pivotal as it must maintain longitudinal stability and equilibrium during flight by exerting a vertical force at a distance, assuring that the summation of pitch moments about the centre of gravity is zero. The profile is typically set at a slight angle of attack, often between 12 to 15 degrees, to the airstream to produce the necessary downward force that balances the aircraft's natural nose-heavy tendency. This downward pressure, boosted by the downwash from the wings striking the top of the stabilizer, increases with aircraft speed, providing the required stability.
The aircraft manufacturer sets the stabilizer at an angle that provides the best stability during flight at design cruising speed and power setting. While the horizontal stabilizer itself is the larger, usually fixed part of the tail that provides base stability, its airfoil section must be carefully engineered to work in conjunction with the elevator, a hinged aft surface attached to the back of the stabilizer. The elevator deflection changes the effective shape of the airfoil, altering the lift generated and allowing pitch control. Thus, the horizontal stabilizer airfoil is not merely a flat surface that is fixed, but an aerodynamic element whose profile and integration with the overall tail assembly - including structural support and load distribution throughout the airframe - are vital for preventing pitch motion and maintaining controlled flight.
Is the horizontal stabilizer airfoil fitted upside-down?
No,the horizontal tailplane is not fitted upside-down. The airfoil itself is simply attached at a negative angle of attack so that it generates negative lift. The lift vector is illustrated upward because that is the chosen positive direction, even though the value of lift on the horizontal stabilizer is usually negative.
Nose-heavy airplanes - like WWII fighters - require this downward force to keep the nose from continually pitching downward. The manufacturer sets the stabilizer angle, and the resulting negative lift holds the tail down, making the summation of pitch moments about the center of gravity zero. Downwash from the main wing strikes the top of the stabilizer and adds to the downward pressure, but the airfoil is not inverted but merely operates in the negative-lift regime.
What are the best airfoils for a horizontal stabilizer?
A simple symmetrical airfoil like a NACA 0012 or 0009 is a good choice for any horizontal tailplane. Symmetrical or virtually symmetrical airfoils with 9% to 12% relative thickness are chosen for horizontal tailplanes. Because tail surfaces produce lift only with deflection of control surfaces, and symmetric sections at angle of attack do not produce lift or lift-induced drag, the main requirement is low drag and predictable moment characteristics. Thus, thin and symmetrical airfoils like NACA 0012 are most affected by turbulent air yet remain the standard.
The choice of an airfoil for a horizontal tail is distinct from that for a wing. I regard symmetric airfoils as the best choice because their form makes pitching moment near 0 and pitching moment does not alter significantly with the angle of attack. This feature gives steady handling characteristics.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
