Inflight loss of control (LOC), unintended departure of an aircraft from controlled flight, is regarded by the NTSB and the 25th Joseph T. Nall Report from the AOPA Air Safety Foundation as a significant flight safety issue. Over 40% of fixed-wing general aviation accidents occurred because pilots lost control of their airplanes. NTSB and AOPA Air Safety Foundation have determined that takeoff and climb, landing, and maneuvering are the deadliest phases of flight for LOC accidents. A precipitating factor of LOC accidents may be a pilot’s incorrect use of ailerons only to raise a lowered wing, rather than correctly applying top rudder pressure combined with appropriate aileron use. “Top rudder” may be defined as deflecting the rudder in the direction of the raised wing. For example, while banked 45˚ to the left, the right wing is raised or pointed upward; pressing the right/top rudder pedal deflects the rudder in the direction of the raised wing (Fig. 1).
In his seminal and insightful book Stick and Rudder, which should be required reading for all pilots, Wolfgang Langewiesche attributes improper usage of rudder as a contributing factor in accidents. He states, “In the typical fatal accident, which involves a stall and a spin, misuse of the rudder is almost always partly to blame—along with two other pilot errors… elevator pulled back too far in an attempt to keep the airplane up, and a possible ‘stumble’ over the ailerons.” That means a wing-tip stall leading to a spin due to improper use of ailerons.
In my experience as a flight instructor for many years, I’ve observed flight students, as well as certificated pilots, use ailerons only in an attempt to raise a lowered wing following takeoff, during climb-out, slow flight and stall training. In these situations, I’ve intervened by promptly applying top rudder and taught the importance of immediately applying this flight control input. Common to the aforementioned flight maneuvers are increased pitch-up attitude and angle of attack (AOA), low energy (low kinetic energy [airspeed] and potential energy [altitude]) and high induced drag (energy depleting condition). Attempting to raise a lowered wing under these conditions by using ailerons only is a potentially dangerous practice predisposing to an inadvertent aerodynamic stall-spin and LOC. It’s reasonable to speculate that this form of pilot error may have resulted in low-altitude, fatal stall-spin accidents.
Ailerons Change A Wing’s AOA
Lowering an aileron increases the wing’s AOA. Consider the following scenario—a Cessna 172 performing a short-field takeoff, pitched up at increased AOA 12° to 15° and at best angle of climb speed (Vx) while climbing over a 50-foot obstacle, like trees or high-voltage power lines. The airplane is in a low-energy and high-induced drag state where a pilot’s options are limited. Suddenly, the left wing lowers by 30˚ as a result of a wind gust, for example, and in an attempt to level the wings, the pilot incorrectly positions the yoke fully to the right, which lowers the aileron on the left (lowered) wing.
This control input may increase the left wing’s AOA to greater than the stalling AOA (for example, 17°), resulting in the left wing stalling, precipitating a spin to the left and LOC (Fig. 2A). Langewiesche refers to this as an aileron stall. Continuing to hold the yoke to the right in a futile attempt to raise the lowered wing simply aggravates and intensifies the spin leading to low-altitude, fatal stall/spin departure accident. Using ailerons only to raise the lowered wing while low and slow on departure or short final approach, an almost natural reaction, may kill you.
The correct flight control input in the above scenario is to immediately apply top (right) rudder pedal pressure to raise the left wing and to maintain this rudder pressure until the wings are level (Fig. 2B). As Langewiesche teaches, the rudder is very important in a stall: “Immediately prior to, and when stalled, the airplane becomes laterally unstable, causing it to capsize to the left or to the right.” Ailerons don’t work well on a stalled wing, and as stated above, inappropriate use of ailerons may contribute to a wing stall and spin. As long as the wings are nearly stalled, only the rudder will promote keeping the wings level or keep it from spinning.
Top Rudder Training Exercise
A rudder training exercise that teaches pilots to apply top rudder pedal pressure to roll the wings level rather than using ailerons has been described (B. Schiff, AOPA Pilot, November 2014 and M. Banner, Aviation Safety, October 2014). The exercise begins by flying at an appropriately high/safe altitude and maneuvering speed, and trimmed for level flight. Next, the pilot demonstrates improper use of rudder by applying a mild amount of rudder pedal pressure only (no ailerons) in the direction of a turn.
For example, apply left rudder pedal pressure to yaw and slightly skid the airplane to the left for about 10 seconds. This motion about the vertical axis results from a greater relative velocity acting on the wing outside the turn and reduced velocity on the inside wing. Because lift force is dependent on velocity, more lift force is generated on the outside wing, and less lift on the inside wing, causing the airplane to roll into the turn. Following this, the pilot continues to apply a small amount of additional left rudder pedal pressure in the direction of the turn (bottom rudder) to increase the rate of turn rate, which also increases the bank angle to the left. The nose eventually begins to slide down and the airplane descends while airspeed increases.
Continuing to hold bottom (left) rudder pedal pressure would eventually result in a spiral dive, not an objective of the exercise. So, after losing approximately 100 to 200 feet, the pilot properly uses the rudder by applying an appropriate amount of top/right rudder pedal pressure. In this example, apply just enough top (right) rudder pressure to level the wings while maintaining coordinated flight and slowly recover from the turn. Deflecting the rudder (as shown in Figure 2B) yaws the airplane and provides differential wing lift, resulting in a yaw-induced roll moment. By employing top rudder to raise the lowered wing, the nose of the airplane comes up to a normal wings-level attitude; lost altitude is restored; and airspeed recovers to about where it was before the maneuver began.
Upon returning to a wings-level condition, stop applying top rudder pedal pressure and assure the rudder returns to the neutral position with the slip-skid indicator centered. The rudder exercise reviews improper use of rudder, but more importantly, it teaches to properly use top rudder to raise a lowered wing. By practicing this exercise, it makes it more likely that a pilot will instinctively use rudder, not ailerons, to roll the wings level.
Flight Safety–Proper Rudder Skills
For flight safety, proper rudder usage is a requisite pilot skill. Not only useful for coordinating turns, the rudder is a primary flight control having numerous uses, for example, raising a lowered wing caused by wind shear while in turbulent flight conditions or wake vortex penetration resulting in an unusual bank attitude (for example, 60° bank) during climb-out, following takeoff or on short final approach; performing a sideslip for a crosswind landing; performing a forward slip to deplete potential energy (altitude) without increasing kinetic energy (airspeed); stopping autorotation of an airplane during a spin; and following an engine failure with a twin-engine airplane, yawing the airplane in the direction of the operating engine (as well as banking with ailerons in the direction of the operating engine).
The rudder may be the most underused, improperly used and misunderstood primary flight control. For pilots with poor rudder skills and desiring improvement, two types of airplanes to consider flying with an appropriately experienced flight instructor are a tailwheel airplane, like an American Champion Citabria, or a sailplane/glider, like a Schleicher ASK 21. Both types of airplanes are intolerant of improper rudder usage, especially when turning base to final during landings in a glider, forcing the pilot to learn to use the rudder properly.
To turn an airplane, I’ve observed many pilots move ailerons only, like a two-axis autopilot. Many don’t realize all three primary flight controls—rudder, ailerons and elevator—are needed when turning an airplane, nor do they understand the proper order for moving these flight controls. Start or lead the turn by applying appropriate rudder pedal pressure in the direction of the turn, immediately followed by aileron pressure and slight back pressure on the stick/yoke to appropriately deflect up elevator to prevent altitude loss.
How much rudder pedal pressure should be applied? Some airplanes fly differently than others. Just enough rudder pedal pressure should be applied to remain coordinated with no adverse yaw. Pilots shouldn’t have to stare at the slip-skid indicator to make coordinated turns. Assuming the flight is in visual meteorological conditions (VMC), the pilot should look outside at the horizon and feel for cues in the “seat of his/her pants” that a coordinated turn is being made.
Top Rudder: If You Think You Might Die, Then Step On The “Sky”
Incorrect application of ailerons only to raise a lowered wing following takeoff under conditions of low airspeed and high AOA rather than correctly applying top rudder pedal pressure is a flight safety issue that heretofore hasn’t been described in aviation training textbooks or aviation journals. This may be an unrecognized, and thus undocumented, causal factor in LOC stall-spin departure accidents. Timely/immediate application of top rudder in the above situation is a potentially life-saving maneuver. Pilots need to be aware of the potentially fatal practice of using ailerons only and consider obtaining additional flight training, preferably from a qualified aerobatic flight instructor, in understanding the aerodynamic effects and use of top rudder.
Dr. Banner is a flight instructor at University Air Center, Gainesville Regional Airport (GNV), Gainesville, FL, professor at the University of Florida in Gainesville, and instructor pilot in the U.S. Air Force Auxiliary/Civil Air Patrol. A CFII, MEI, he has 5,000 hours flight time and owns a GCBC Citabria.