There is a certain grace in the fall of a leaf. It floats and then it does not. It flies and then it ceases to fly and having spent all its kinetic energy, it falls inexorably to its fate by the pull of gravity. The falling leaf symbolizes the dance of nature. It is a slow graceful dance to behold. Plucked by the breeze drifting slowly, but filled with beauty. A portent of struggle, between the lift and the drag and also perhaps of unusual potential transfer from one force over to the other. It is a disorienting phenomenon filled with potential gifts of capacity, experience and facility and learning for a pilot.
The Falling Leaf maneuver is similar in every respect, except it is not meant to fall all the way down to the earth, but be held up in the air by the pilot. It is disorienting in nature but cannot be executed by an unfocused or untrained pilot.
CAUTION: DO NOT TRY THIS ON YOUR OWN WITHOUT AN EXPERIENCED INSTRUCTOR!
Let us look at a Stall first…
If you carefully fly into a slow coordinated flight and bring the aircraft to a stall, what happens? Most of you would say, that the aircraft first buffets a bit giving you a warning. In the big irons the “stick shaker” will be the corresponding alert. Once the shudder is past, the aircraft nose simply falls down. What exactly is happening there?
Noting that Lift is created as a consequence of the angle of the airfoil to the Relative Wind. It is a dance between the "pull" of the Lift being created by the wind over the upper surface of the cambered wing (Bernouille) and the "push" of the wind on the underside of the wing (Newton). The higher the angle of attack, the more the lift but equally with increasing AoA, the more the drag. That drag, is mostly a form drag that keeps increasing, ultimately exceeding the Lift when Stall occurs. There is separation of airflow from the upper surface of the wing starting from the trailing edge of the wing (airfoil) slowly migrating to the leading edge. Once the separation is complete, the drag takes over and gravity plays its part. Ok, so having figured the mechanics of that out, if one were to ask, how would you recover from a stall? The answer is simple, isn’t it? Put the nose down, let the wings gain lift and it will fly again. At low altitude added thrust (power) and the correct positive attitude with right rudder to counter the p-force etc. (per the aircraft being flown) is required. Remember the Center of Gravity or CG is forward of the Center of Lift or CL. As the Angle of Attack increase past the criticalAoA, the Lift decreases and the Gravity pitches the nose down (Aircraft designers are pretty smart - the CL initially becomes the fulcrum, so to speak). This nose down is further helped by the loss of the horizontal stabilizer efficacy, being buffeted by the high angle of attack. And with the nose down, the wing flies again. Remember, if it buffets accidentally (wind shear etc.) nose down and power up (i.e. if engine is running).
Quite simple, isn’t it? Next time, ask your instructor to demonstrate this to you. It will remove the demons that irritate and create unnecessary fear, off your shoulders.
Now assume you have mastered the Stall characteristics and the recovery mechanism (before you dare to go any further). Again, with a trained and able instructor by your side, who has experience in the maneuver, go fly up at a decent altitude say 4500 feet AGL and put the aircraft into a stall. Now instead of recovery keep the back pressure on the yoke.
What happens next? One or the other wing of the aircraft will fall away from level flight (usually the left one). When that happens, most pilots even with many thousands of hours will do the same thing...use the ailerons to level the wings. Here is the warning, Using the ailerons to level the wings, increases angle of attack and deepens the stall by increasing drag and lift loss and further aggravates the situation. The correct method is to use the opposite rudder to the low wing.
Let us look at it from a perspective of understanding. A falling leaf maneuver is a dance between multiple potential, imminent spins corrected by the judicious use of the rudder. You are not falling out of the sky, so to speak, just have less lift, more drag and you are controlling the loss of lift by coordinating the creating of the lift (as wings level momentarily) and losing it (when one wing drops and the other sustains the aircraft transiently) and doing the dance with expertise. The pitching and side to side motions can be abrupt and I don’t want it to sound gracefully benign but with expertise it can be made to look and feel comfortably benign.
No heavy lead feet needed in this maneuver. Just judicious anticipation and effective use of the opposite to the lower wing, rudder to keep the wings level (preventing a wing-over into an incipient spin is the key. Delay in opposite rudder input can deepen the roll). Remember there is grace in a falling leaf.
You might ask, “what is the benefit of putting myself through this ordeal?” Good question! The answer is quite simple, it helps understand that even during a stall the VSI stays at a 500+/- rate of descent, which means the aircraft is still flying, albeit poorly! It teaches the importance of the rudder use and gives you, the pilot, confidence. Or simply put, it teaches you to dance on the rudders with a deft touch when needed. It will also help you make expert, coordinated turns without skids and slips (which create drag and slow you down). So, learn to tap-dance gently on those rudders.
The "falling leaf" maneuver is a series of full stall where you never release back pressure, but play the forces of the aerodynamic lift of the aircraft, relative wind, the angle of attack and form drag of the aircraft, all the while keeping the wings level. During the maneuver, your plane should look like a leaf gently rolling and falling but continue in its flight! Learning the Falling Leaf maneuver will help prevent you from making preventable mistake and inadvertently falling to the ground.
If you carefully fly into a slow coordinated flight and bring the aircraft to a stall, what happens? Most of you would say, that the aircraft first buffets a bit giving you a warning. In the big irons the “stick shaker” will be the corresponding alert. Once the shudder is past, the aircraft nose simply falls down. What exactly is happening there?
Noting that Lift is created as a consequence of the angle of the airfoil to the Relative Wind. It is a dance between the "pull" of the Lift being created by the wind over the upper surface of the cambered wing (Bernouille) and the "push" of the wind on the underside of the wing (Newton). The higher the angle of attack, the more the lift but equally with increasing AoA, the more the drag. That drag, is mostly a form drag that keeps increasing, ultimately exceeding the Lift when Stall occurs. There is separation of airflow from the upper surface of the wing starting from the trailing edge of the wing (airfoil) slowly migrating to the leading edge. Once the separation is complete, the drag takes over and gravity plays its part. Ok, so having figured the mechanics of that out, if one were to ask, how would you recover from a stall? The answer is simple, isn’t it? Put the nose down, let the wings gain lift and it will fly again. At low altitude added thrust (power) and the correct positive attitude with right rudder to counter the p-force etc. (per the aircraft being flown) is required. Remember the Center of Gravity or CG is forward of the Center of Lift or CL. As the Angle of Attack increase past the criticalAoA, the Lift decreases and the Gravity pitches the nose down (Aircraft designers are pretty smart - the CL initially becomes the fulcrum, so to speak). This nose down is further helped by the loss of the horizontal stabilizer efficacy, being buffeted by the high angle of attack. And with the nose down, the wing flies again. Remember, if it buffets accidentally (wind shear etc.) nose down and power up (i.e. if engine is running).
Quite simple, isn’t it? Next time, ask your instructor to demonstrate this to you. It will remove the demons that irritate and create unnecessary fear, off your shoulders.
Now assume you have mastered the Stall characteristics and the recovery mechanism (before you dare to go any further). Again, with a trained and able instructor by your side, who has experience in the maneuver, go fly up at a decent altitude say 4500 feet AGL and put the aircraft into a stall. Now instead of recovery keep the back pressure on the yoke.
What happens next? One or the other wing of the aircraft will fall away from level flight (usually the left one). When that happens, most pilots even with many thousands of hours will do the same thing...use the ailerons to level the wings. Here is the warning, Using the ailerons to level the wings, increases angle of attack and deepens the stall by increasing drag and lift loss and further aggravates the situation. The correct method is to use the opposite rudder to the low wing.
Let us look at it from a perspective of understanding. A falling leaf maneuver is a dance between multiple potential, imminent spins corrected by the judicious use of the rudder. You are not falling out of the sky, so to speak, just have less lift, more drag and you are controlling the loss of lift by coordinating the creating of the lift (as wings level momentarily) and losing it (when one wing drops and the other sustains the aircraft transiently) and doing the dance with expertise. The pitching and side to side motions can be abrupt and I don’t want it to sound gracefully benign but with expertise it can be made to look and feel comfortably benign.
No heavy lead feet needed in this maneuver. Just judicious anticipation and effective use of the opposite to the lower wing, rudder to keep the wings level (preventing a wing-over into an incipient spin is the key. Delay in opposite rudder input can deepen the roll). Remember there is grace in a falling leaf.
You might ask, “what is the benefit of putting myself through this ordeal?” Good question! The answer is quite simple, it helps understand that even during a stall the VSI stays at a 500+/- rate of descent, which means the aircraft is still flying, albeit poorly! It teaches the importance of the rudder use and gives you, the pilot, confidence. Or simply put, it teaches you to dance on the rudders with a deft touch when needed. It will also help you make expert, coordinated turns without skids and slips (which create drag and slow you down). So, learn to tap-dance gently on those rudders.
The "falling leaf" maneuver is a series of full stall where you never release back pressure, but play the forces of the aerodynamic lift of the aircraft, relative wind, the angle of attack and form drag of the aircraft, all the while keeping the wings level. During the maneuver, your plane should look like a leaf gently rolling and falling but continue in its flight! Learning the Falling Leaf maneuver will help prevent you from making preventable mistake and inadvertently falling to the ground.
CAUTION: DO NOT TRY THIS ON YOUR OWN WITHOUT AN EXPERIENCED INSTRUCTOR!
No comments:
Post a Comment