To replicate a falling leaf, the pilot applies and holds maximum up elevator to keep the aircraft in a stalled attitude. With the nose pitched up and the aircraft stalled, one wing or the other should begin to drop. Holding the ailerons in their neutral position, the student uses rudder inputs to lift the dropping wing and to try and keep the wings level throughout the maneuver. It's difficult to maintain a wings-level attitude and to predict which wing might begin to drop next. This means the student must always be ready to apply the corrective rudder input. This is why the falling leaf stall is one of the great training exercises.
The falling leaf stall does more than mimic Mother Nature. It teaches students about a forgotten primary flight control - the rudder.
Compared to taildraggers, tricycle gear airplanes are docile. Because their center of gravity is between the nose and main wheels, they are easier to direct and are less susceptible to crosswinds on the ground. Offset engines and rudders, and Frise-type ailerons tamed torque, P-factor, and adverse yaw. The result? Most tricycle gear trainers can be flown just fine without ever touching the rudder pedals. But that doesn't mean the rudder is no longer important.
And that's where a problem lies. A student must be able to see the effects of not using the rudder before he (or she) can be expected to learn to use it. That's why tail draggers make such good trainers. They don't forgive poor rudder technique as easily as tricycle airplanes do. Typically, the first time a student discovers he needs to use the rudder in a tricycle trainer is in a stiff crosswind. At that point, after many hours of getting along fine without really using the rudder, it's like learning a new control.
The falling leaf stall is a great exercise to teach rudder awareness, control, and usage. Besides, instructors can introduce it early in training, with other types of stalls, to help students get a handle on rudder use before they start learning to land. The falling leaf stall builds student confidence, especially in the slow flight and stall regimes, where the controls become sluggish and lose effectiveness.
Nearing the stall, the ailerons are the first flight controls to become sluggish and less effective because the airflow over the wing is disturbed. The elevator is next because it's in the wing's turbulent wake, and the resulting buffet is a natural stall warning indication.
But the rudder, riding above the wing's wake, remains effective. Rudder inputs can lift a wing easily whereas a downward deflected aileron may actually induce a stall. (When the aileron deflects downward, its trailing edge moves downward as well, increasing its angle of attack.) Before practicing stalls, falling leaf or otherwise, you should explain stall regime aerodynamics on the ground before flight. Students who understand these concepts are primed for falling leaf stall practice.
How to Teach It
To practice falling leaf stalls, first climb at least 1,000 feet above a minimum safe altitude and clear the area. Establish a long glide with partial or idle power and flaps extended. This will lower the pitch attitude and give students a better view over the nose. Enter a power off stall, but don't recover immediately. Hold the elevator aft to maintain the stalled condition. Try not to make any aileron inputs - they should be neutral. When a wing rolls off, apply enough opposite rudder to "lift the wing" and maintain wings-level flight.
Let your student figure out how long to hold the rudder correction. He should soon see that holding the correction until the wings are level is an over-correction because the wings will pass through level to a roll in the opposite direction. How much rudder correction an airplane needs depends on the airplane, so let your student experiment to learn what works best. Not only does this teach the use of the rudder, but it also can build confidence because your student is a "test pilot" learning more about the airplanes he flies.
When your student can keep the wings level, have him repeat falling leaf stalls with the flaps up. Have him note the higher pitch attitude and different handling characteristics. During the preflight briefing tell your student that some trainers buck like a bronco in this condition (you should practice - and master - the maneuver yourself before flying with a student), but it's nothing to be alarmed about. It's the airplane's way of telling the pilot it is trying to recover on its own. It takes a lot of work to keep an aircraft in a falling leaf stall.
Regardless of flap position, to recover from a falling leaf stall, just lower the nose to reduce the angle of attack, add power to minimize altitude loss, and retract the flaps if necessary. Naturally, you must plan the maneuver to recover from the exercise at or above the minimum safe altitude.
One common problem students have while practicing falling leaf stalls is that they don't hold enough back pressure on the yoke to maintain the stall. The purpose of this exercise is to teach your student how to keep the aircraft's wings level in a stall, so have him keep the yoke all the way back, if necessary.
Make sure your student doesn't make any aileron inputs. If he tries to lift a wing by turning the yoke in the opposite direction (left wing down, right aileron), try holding the yoke yourself and telling him to concentrate on working the rudder. If he still tries to use the ailerons even while you hold the yoke rigid, it could mean he doesn't completely understand the aerodynamics of stalled flight - something that calls for more ground instruction.
Sometimes a student doesn't recognize soon enough that a wing is beginning to drop and, therefore, makes his rudder inputs late. Usually this means he isn't looking outside at the horizon to compare its position to the airplane's nose. With flaps extended, the view over the nose should be more than adequate. Without flaps, the nose is higher, and he might have to use his peripheral vision to see the aircraft's bank angle.
On rare occasions a student tries to correct by pushing the rudder pedal on the same side as the dropping wing (left wing dropping, left rudder correction), rather than the opposite rudder. More often than not, students don't make their rudder inputs soon enough or they underestimate the amount of rudder deflection necessary to make the correction. It's not uncommon to make full and abrupt rudder inputs during this exercise. This is exactly what we instructors want to see. A student may not realize that flight controls can and should be used aggressively, depending on the situation. The unappealing alternative is to have the aircraft fly the student.
The PTS does not mandate the falling leaf stall, but it's something all instructors should know about. The falling leaf stall helps students combat rudder neglect. Practicing falling leaf stalls will build your student's confidence in the aircraft, slow flight, and stalls. And it's a great way for you to teach the aerodynamics of stalls and spins during pre-solo maneuvers. Of course, the best part of this challenging stall is that it gives your students the freedom to practice "dancing on the rudders."