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Pre-Solo Training Program Flight Briefing: Lesson 3 Slow Flight & Stalls In cooperation with Mid Island Air Service, Inc. Brookhaven, NY (Michael Bellenir, CFI)
Pre-Solo Training Program
Flight Briefing: Lesson 3Slow Flight & Stalls
In cooperation with Mid Island Air Service, Inc. Brookhaven, NY (Michael Bellenir, CFI)
Flight Briefing: Lesson 3
Lesson 3 Objectives
During this briefing, you will review normal and slow flight. You will learn the procedure for performing intentional stalls including stall aerodynamics, stall recognition, and stall recovery procedures.
Upon completion of this briefing, you will experience flight at various airspeeds, and practice intentional stall entry and recovery.
Flight Briefing: Lesson 3
Definition
In automotive parlance, a stall is an unintended stopping of the engine.
An aerodynamic stall is another matter altogether, and has nothing at all to do with the aircraft’s engine. In fact, gliders that have no engine can stall just the same as airplanes do.
In the context of aircraft, a stall is a maneuver that causes the wing to no longer develop lift.
Flight Briefing: Lesson 3
Rationale
You may have heard of accidents that occurred when the airplane stalled out of control, and may perceive stalls as an unsafe maneuver.
Some pilots think to avoid such accidents, by saying “I’ll just never let the airplane stall.”
But, unless the wing eventually stops developing lift, the plane can never land! So, think of controlled stall practice as preparation for learning how to land.
Flight Briefing: Lesson 3
Aerodynamics
To know how a stall occurs, we must first examine how a wing generates lift.
The wing’s shape causes air above the upper surface of the wing to accelerate. This accelerating air decreases in pressure. The pressure differential between the upper and lower surfaces of the wing cause the wing to rise. (Bernoulli’s Principle)
As the wing flies, it also deflects air downward. The resultant force is such that the air pushes up on the lower surface of the wing causing the wing to rise. (Newton’s Third Law)
Flight Briefing: Lesson 3
Aerodynamics-How the wing lifts
Bernoulli’s Principle:
As the velocity of a fluid increases, its pressure decreases. The accelerated air above the wing exerts less pressure on the wing than the un-accelerated air below it.
Flight Briefing: Lesson 3
Aerodynamics-How the wing lifts
Air flow over the wing creates downwash, the pushing of air down creates a lifting force.
The direct deflection of air downwards off of the lower surface of the wing also creates a resulting lifting force upward.
Flight Briefing: Lesson 3
Angle of Attack
The larger the angle at which a wing is presented to airflow, the more lift it generates. This is because a larger angle increases the effective curvature of the wing, as well as increasing the amount of air deflected downward off of the lower surface of the wing. This angle is called the “Angle of Attack.”
The definition of angle of attack is: The angle between the chord line and the relative wind.
Flight Briefing: Lesson 3
Angle of Attack
Flight Briefing: Lesson 3
Lift and Angle of Attack
As angle of attack increases, the amount of lift generated by the wing increases, until the airplane reaches the maximum coefficient of lift.
Flight Briefing: Lesson 3
Stalls
A stall occurs when the wing reaches its critical angle of attack.
At the critical angle of attack, the wing structure is presented at such a high angle to the relative wind that the airflow no longer stays in contact with the upper surface of the wing.
At the critical angle of attack, airflow separation from the wing occurs, causing the airflow over the wing to become turbulent.
Flight Briefing: Lesson 3
Stalling Aerodynamics
Flight Briefing: Lesson 3
Stalls
When airflow separates from the top of the wing, the amount of lift the wing produces is drastically decreased. The result is called an aerodynamic stall.
To recover from a stall, simply reduce the angle of attack. This can be done by either lowering the pitch, or by increasing speed. To recover the quickest with minimal altitude loss, lower the nose and add full power.
Flight Briefing: Lesson 3
Stalls
Remember that an airplane always stalls at the critical angle of attack. A stall can happen at any altitude, airspeed, or in any flight attitude.
Ailerons change the position of the trailing edge on the outboard sections of the wing. Therefore, changing the position of the ailerons will change each wing’s angle of attack. This makes it extremely important to keep the ailerons neutral during a stall, as different angles of attack on each wing will aggravate the stall condition.
Flight Briefing: Lesson 3
Stalls
Aileron deflection in the stall will cause one wing to have a higher angle of attack than the other, causing the wings to stall at different times. This will cause a rolling tendency toward the wing that stalls first.
If aileron pressure is applied away from the dropping wing (your natural instinct), the aileron on the dropping wing will deflect downward. This will increase the angle of attack on that side and deepen the stall; the dropping wing will continue to drop.
Make sure to keep the ailerons neutral during stalls.
Flight Briefing: Lesson 3
Stalls
Improper use of rudder can also aggravate a stall.
If the airplane is not coordinated properly, the wings will have slightly different relative airspeeds, and therefore different angles of attack.
Improper coordination will also cause one wing to stall before the other, causing it to drop first.
Flight Briefing: Lesson 3
Stalls
If one wing does stall before the other, the airplane will start to roll toward the stalled wing. To recover, keep the ailerons neutral and use rudder pressure away from the dropping wing to prevent any further rolling.
By applying rudder pressure, you will speed up the dropping wing and slow down the rising wing. Rudder pressure will help restore the wings to the same angles of attack and stop the rolling.
Flight Briefing: Lesson 3
Stalls
If a stall is entered without aileron input and with proper coordination, the airplane will not roll at all. Instead, it will simply pitch down slightly as the wings lose lift.
Flight Briefing: Lesson 3
Flying into the Stall (Intentional Stalls)
This airplane is inherently stable and will have gentle stalling characteristics.
As the airplane slows down, you will notice that the nose of the airplane will pitch down; this is the tendency of the airplane to resist going into a stall (it’s trying to recover before the stall even happens).
If you want the airplane to stall, you’ll have to apply back pressure on the stick to hold the nose up.
As the airplane approaches the stall, you’ll feel a slight shaking, or buffeting in the airframe. This is an indication that the airflow is starting to separate from the top of the wings, causing turbulence on top of parts of the wing.
Flight Briefing: Lesson 3
Stall Progression
The stall starts at the wing root near the trailing edge, and progresses outward as the stall develops. When the wing loses enough lift, the nose will drop. Wings are designed to stall this way in training aircraft so that the ailerons will remain effective as long as possible (but remember that using ailerons can aggravate the stall more).
Flight Briefing: Lesson 3
How To Enter a Stall
To stall, we have to increase the angle of attack to the critical angle of attack.
Remember that as we slow down, the angle of attack has to increase to maintain a constant amount of lift.
We will slow down with the power reduced, and hold altitude as long as possible. This will cause the angle of attack to increase.
Flight Briefing: Lesson 3
How To Recover From a Stall
When the airplane stalls, the nose drops. To recover from the stall, we simply reduce
the angle of attack. Increase airspeed (reduce pitch) to decrease
angle of attack, add full power to recover lost altitude, and climb out at best climb speed.
Try to lose as little altitude as possible (very easy in this type of airplane)
Return to straight and level flight
Flight Briefing: Lesson 3
Different Types of Stalls
Remember, the airplane can be stalled at any airspeed, attitude, configuration, or power setting.
You’ll practice basic stalls with the flaps at different settings and at different power levels.
When practicing stalls with power applied, remember that the engine and propeller create left turning tendencies, thus requiring the use of more right rudder.
Flight Briefing: Lesson 3
Why We Do Stalls
One purpose of this training is to recognize when the airplane is approaching a stall, so that you don’t stall accidentally.
Pay close attention to what the airplane feels like as it approaches the stall. You’ll notice that the controls become significantly less effective, that the airplane tries to pitch down, and that you can feel the aerodynamic buffet of airflow separation from the wings.
Flight Briefing: Lesson 3
Don’t Be Afraid! (Easier said than done)
It’s normal to have some apprehension of stalls (you should keep some of this fear; unintentional stalls at the wrong time or handled improperly can cause pilots to lose control!)
Don’t worry. When done properly, there’s really not much that can go wrong in this type of training.
Generally, the worst thing that can happen is that because of improper use of the controls, one wing will stall slightly before the other.
Keep the stick neutral, and control direction in the stall with rudder.
Your instructor won’t let you get into too much trouble!
Flight Briefing: Lesson 3
Weight and Balance
Stall speed increases as the weight of the aircraft is increased. An LSA must meet a 45 KCAS stall speed limit, flaps up, at its maximum gross weight.
It is very important that the airplane be properly loaded, with the CG within the acceptable limits, in order to recover properly from a stall.
To calculate where the CG is, use the information in the Pilot’s Operating Handbook (POH) or the Airplane Operating Instructions (AOI). This will be covered in detail in a later lesson.
Flight Briefing: Lesson 3
Review Questions
Define “angle of attack.”
As a fluid’s velocity increases, pressure:
A stall occurs when the wing exceeds its:
To recover from a stall with minimal altitude loss:
Rolling in a stall should be controlled with:
What happens to stall speed as the aircraft’s weight increases?
Write down your answers before continuing to next slide
Flight Briefing: Lesson 3
Review Answers
Review any missed questions before continuing to today’s flight.
Define “angle of attack.”– The angle between the chord line and the relative wind
As a fluid’s velocity increases, pressure:– Decreases according to Bernoulli’s Principle
A stall occurs when the wing exceeds its:– Critical angle of attack
To recover from a stall with minimal altitude loss:– Lower the nose, steer with your feet, and add full power
Rolling in a stall should be controlled with:– Rudder input and neutral ailerons
What happens to stall speed as the aircraft’s weight increases?– It goes up.
Flight Briefing: Lesson 3
On Today’s Flight
We’ll practice flying the airplane at different speeds, including slow flight.
We’ll approach stalls in different configurations (flaps up/down; power on/off).
We’ll practice recognizing the beginning of a stall, and recovering to normal flight.
Flight Briefing: Lesson 3
In the Traffic Pattern
Pay attention to how the airplane feels on approach to landing, don’t let it stall before getting to the ground!
Thanks to Mid Island Air Service, Inc. Brookhaven, NY (Michael Bellenir, CFI)
