Stalls - Power On and Power Off

Teaching and Learning Flying - Private Pilot, Single-Engine Airplane

Stalls - Power On and Power Off

DEFINITION

As the wing angle of attack (AOA) increases to or beyond the critical AOA (approximately 16-20°), smooth airflow over the wing is disrupted, resulting in great increase in drag and loss of lift: a stall

SAFETY FACTORS

A primary objective of stall training is to enhance safety by helping assure inadvertent stall avoidance or prompt stall recovery
Stall avoidance is promoted by understanding
- Flight situations where unintentional stalls may occur
- The relationship of various factors to stall speed (V_s)
- Recognition of the first indications of a stall
- Recovery technique
Practice stall entry:
- above 2,000 feet AGL to recover above 1,500 feet AGL
- lights on
- CLEAR area with 90° turns, left and right
- mix rich, prop high RPM
- check carb temp

TOLERANCES

Explain relevant aerodynamic factors, flight situations, recovery procedures, hazards of stalling uncoordinated
Select entry altitude allowing recovery above 1,500 feet AGL
Power-off stall
- Approach or landing configuration with throttle reduced or idle
- Straight glide or gliding turn with 30o, +10o bank
- Maintain attitude that will induce a full stall
- Promptly recover by decreasing AOA, leveling wings, and adjusting power as necessary to regain normal attitude
- Retract flaps and gear and establish SLF or climb
- Avoid secondary stall, excessive airspeed or altitude loss, spins, and flight below 1,500 feet AGL
Power-on stall
- Takeoff or normal climb configuration
- Establish takeoff or climb airspeed before power increase
- Straight or bank 20o, +10o and pitch to stall
- Recover as above

Explain aerodynamic factors related to stalls in various configurations and flight situations; effects of various factors on VS; recovery procedure
Allow recovery above 1,500 feet AGL
Stabilize airplane appropriately during entry
Maintain heading +10o straight or bank +10o turning
Pitch for imminent stall while maintaining coordinated flight
Recover promptly at first indication of stall
Recover with minimum altitude loss consistent with safety during power-on recoveries; recover to the glide airspeed, +10 kts, during power-off recoveries
Avoid full stalls, excessive pitch changes, spirals, spins, or flight below 1,500 feet AGL

OBJECTIVES

To familiarize the pilot with the conditions that produce stalls
To develop knowledge and skill in recognizing imminent and full stalls
To develop the habit of taking prompt preventive or corrective action
Power-on stall: to understand what could happen if the airplane were climbing at an excessively nose-high attitude immediately after takeoff or during a climbing turn
Power-off stall: to understand what could happen if controls are improperly used during a turn from the base leg to final approach or on final approach

PROCEDURES

Discuss definition, safety factors, tolerances, objectives, and other elements of stalls
Aerodynamics of stalls
- Lift of a wing is given by L = C_L(ρv²A)/2 where
- C_L increases with AOA to C_Lmax, where wing stalls
- Just before wing stalls, nose pitches down due to reduction in tail down force
- Most airplanes' wings stall progressively outward from the roots
- Rectangular wings have this "wash out" characteristic Wing "twist" (tips have smaller angles of incidence and attack than roots) helps assure wash out
- Allows aileron effectiveness at relatively high AOA
- In a stall, ailerons loose effectiveness; rudder should be used to maintain direction or level wings
Relationship of various factors to stall speed (V_s)
- Landing gear: 09T: no demonstrated effect on power-off V_s
- Flaps increase C_L, decrease V_s (09T: 1-4 kts)
- Increasing weight increases V_s
- Lift must be increased by increasing C_L by increasing AOA
- As CG moves forward, V_s increases
- Greater tail down force and thus greater total lift are required
- Aft CG decreases V_s, but aft of safe CG range, stall may be unrecoverable
- VS is proportional to the square root of the load factor
- Increasing bank increases V_s
- Turbulence can increase load factor and V_s
- Even small amounts of snow, frost, or ice increase V_s
Flight situations where unintentional stalls may occur
- Power-on
  - Takeoffs and departure climbs, esp. short fields with obstacles
  - Go-arounds
  - En-route best-angle climbs
- Power-off
  - Approach and landing
  - Turning base to final (may be crossed-control)
  - After engine failure
  - During glides; attempting to "stretch" a glide
Recognition of the first indications of a stall
- Vision: see relatively nose-high attitude and decreasing airspeed
- Hearing: quieter air flow, sounds of vibration, stall warning horn
- Best: kinesthesia: sense of change in direction or speed of motion; feeling of decrease in speed, settling or "mushing"
- Feeling of decreased effectiveness of controls
POWER-ON STALLS
- Performance of power-on stalls in climbing flight (straight or turning)
- Entry technique and minimum entry altitude
  - Enter above 2,000 feet AGL to recover above 1,500 feet AGL
  - Lights on, CLEAR area with 90° turns, left and right
  - During second clearing turn
    - Mix rich, prop in high RPM, carb temp check
    - Throttle back slow to V_R = 55 KIAS
    - + Gear down and flaps 20°
    - At 55 KIAS:
      - Throttle to 25" (or 30"), carb heat OFF
      - Pitch up slow (heading straight or 207deg; coordinated bank)
      - Maintain pitch up until airspeed slows to V_s
- Coordination of flight controls
  - Right rudder to counteract torque and P-factor
  - Maintain coordination even if controls are crossed (right turn)
  - Stall will break straight away from pilot if coordinated
  - Release right rudder as stall breaks
  - In uncoordinated stalls, the airplane usually yaws to the side with excess rudder (rolls or falls away from the ball)
- Recovery technique and minimum recovery altitude
  - Recover above 1,500 feet AGL
  - Technique:
  - Promptly release elevator back pressure
  - Lower nose to horizon, check power to 30" MP
  - Regain SLF coordinated
  - Safe altitude, accelerate to 90 kts, retract flaps and gear
POWER-OFF STALLS
- May be practiced in SLF, descending straight and turning flight
- To simulate landing approach stalls
  - gear down
  - flaps down
  - power reduced to idle
- Entry technique and minimum entry altitude
  - Enter above 2,000 feet AGL to recover above 1,500 feet AGL
  - Lights on, CLEAR area with 90° turns, left and right
  - During second clearing turn
    - Gear down <140 kts
    - Throttle back approximately 19", prop in high RPM, mix rich
    - Flaps down as airspeed slows
    - Carb temp check + carb heat on
    - Throttle back to idle
    - For level stall, hold nose up to maintain altitude until V_s
- Coordination of flight controls - as above
- Recovery technique and minimum recovery altitude
  - Recover above 1,500 feet AGL
  - Technique
    - Promptly release elevator back pressure
    - Throttle to 30 in. MP, carb heat OFF, flaps up to 20°
    - Level wings coordinated
    - Then either
      - Gear up, flaps up, resume SLF or
      - "Go-around": 70 KIAS climb, gear up, flaps up slow, 80 KIAS
- Demonstrate power-off stalls and recoveries with and without power
- Coach student practice of power-off stalls
- Demonstrate power-on stall
- Coach student practice of power-on stalls
- Critique student performance

COMMON ERRORS

Failure to establish the specified landing gear and flap configuration prior to entry
Improper pitch, heading, and bank control during straight ahead stalls
- Use outside and instrument references
- Right rudder in nose-high power-on condition; release at break
Improper pitch and bank control during turning stalls
Rough or uncoordinated control technique
Failure to recognize the first indications of a stall
Failure to achieve a stall
Improper torque correction
Poor stall recognition and delayed recovery
Excessive altitude loss or excessive airspeed during recovery
Secondary stall during recovery

Front Page

Top