Pre-Solo Training Program Flight Briefing: Lesson 4 Slow Flight & Stalls In cooperation with Mid Island Air Service, Inc. Brookhaven, NY (Michael Bellenir, CFI)

Lesson 4 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.

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)

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.

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.

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.

Angle of Attack

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.

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.

Stalling Aerodynamics

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.

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.

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.

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.

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.

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.

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.

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).

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.

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 (full power) and decrease angle of attack (reduce pitch). Try to lose as little altitude as possible (very easy in this type of airplane) Return to straight and level flight

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.

Why We Do Stalls The point 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.

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!

Weight and Balance Several factors affect how an airplane will stall, especially weight and balance. If the center of gravity moves forward, the down force required by the tail is increased (airplane needs higher angle of attack). With a forward CG, the airplane will stall at a faster speed, but it will be more difficult to stall and easier to recover. Forward CG also gives the tail more leverage, and increased control effectiveness.

Weight and Balance Several factors affect how an airplane will stall, especially weight and balance. If the center of gravity moves back (aft), the down force required by the tail is decreased (airplane doesn’t need as much angle of attack). With an aft CG, the airplane will stall at a lower speed, but it will be more difficult to recover from the stall. Aft CG takes away some of the tail’s leverage, and reduces control effectiveness. A CG that is too far aft might make stall recovery very difficult or impossible.

Weight and Balance It is very important that the airplane be properly loaded, with the CG within the acceptable limits. To calculate where the CG is, use the information in the Pilot’s Operating Handbook (POH) or the Airplane Operating Instructions (AOI). The empty weight data must come from the documents specific to that airplane. These documents are required to be onboard the aircraft during all flights.

Computing Weight and Balance To find the CG location for your airplane: Find the empty weight and moment (in airplane) Compute the weights and moments for everything you are putting in the airplane (people, fuel, bags) To find the moment of something multiply the weight by its arm (location). W x A = M Add the total weights and the total moments Divide the total moments by the total weights. The answer is where the CG is located

Computing Weight and Balance Empty weight and balance data for N810EV: Empty weight = 738.6 lbs; Empty moment = 7704 in/lbs.

Computing Weight and Balance There is a computer spreadsheet available to help expedite the computation of weight and balance, but officially, this is how you determine the location of the CG.

Computing Weight and Balance Once you have determined the loaded weight and CG for the airplane, you will plot it on the Envelope graph to ensure the aircraft is loaded within safe and acceptable limits.

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: State the basic equation for weight and balance calculations. Write down your answers before continuing to next slide

Review Answers Define “angle of attack.” The angle between the chord line and the relative wind As a fluid’s velocity increases, pressure: decreases A stall occurs when the wing exceeds its: Critical angle of attack To recover from a stall with minimal altitude loss: Lower the nose and add full power Rolling in a stall should be controlled with: Rudder input and neutral ailerons State the basic equation for weight and balance calculations. Weight times Arm equals Moment Review any missed questions before continuing to today’s flight.

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.

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)