Stall Avoidance Training

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Stall avoidance training and pilot evaluations of approach to stall recovery procedures must develop essential habit formations that instill recognition and proper recovery from imminent and full stall situations. Using power as the primary control without a reduction in elevator backpressure while recovering from an approach to stall does not instill habit formation for effective stall avoidance and aircraft upset recovery.

Transcript of Stall Avoidance Training

  • 1.. AERODYNAMIC STALLS In-Flight Loss Of Control (ILOC) as a result of an aerodynamic stall has been one of the most significant causes of fatal Army Fixed-Wing aircraft accidents for many years. Loss of control usually occurs because the aircraft enters a flight regime which is outside its normal envelope, usually, but not always at a high rate, thereby introducing an element of surprise for the flight crew involved. 11/17/13DAC Clark J Wilson

2. Purpose Of Stall Avoidance Training Recognize the symptoms of an approaching stall (such as slow airspeed, sloppy controls and or maneuvering at more than 1G) and instinctively recover. Instill a habit formation so that a pilots reaction to an approaching wing stall is always timely reduction in the angle of attack.11/17/13DAC Clark J Wilson 3. Stall Avoidance A pilot should use all energy resources available, including altitude and power as appropriate to prevent or recover from an approaching stall condition.11/17/13DAC Clark J Wilson 4. Stall/Loss of Control Avoidance Training Aviators should be trained to instinctively recognize and recover from: Approach to stalls Fully developed stalls Stall situations that are unexpected Stall/Loss of Control Training should not emphasize initial stall recovery with a minimum loss of altitude and/or a target pitch attitude but an immediate reduction in the angle of attack. Stall/Loss of Control Training should not be associated the with the Go-Around maneuver . 11/17/13DAC Clark J Wilson 5. The Aerodynamic Stall STALL: AN ABRUPT, but not always abrupt, LOSS OF LIFT ANDINCREASE IN DRAG THAT OCCURS WHEN AN AIRFOIL EXCEEDS ITS CRITICAL ANGLE OF ATTACK (AOA) WHICH IS ABOUT 18 to 22 AOA.BASIC PRINCIPLES: BOUNDARY LAYER LAMINAR FLOW TRANSITION REGION TURBULENT LAYER SEPARATIONANGLE OF ATTACK (AOA) RELATIVE WIND CRITICAL AOAWING TWIST: 11/17/1318 ROOT TO TIP RELATIV E WIND STALL BUILDS INSIDE OUT ( MCA) MAINTAIN AILERON EFFECTIVENESS DAC Clark J Wilson 6. Airplane Wing Stall View: Airplane Stalls, King Video11/17/13DAC Clark J Wilson 7. Approach to Stall vs. Full Stall11/17/13DAC Clark J Wilson 8. An airplane wing can be stalled at Any: Airspeed Altitude Attitude (Pitch Attitude in relation to the horizon has no relationship to the aerodynamic stall) Given an airplane with the same weight, configuration and G loading, the Indicated Air Speed (IAS) at which a stalls occurs remains constant regardless of True Air Speed (effects of pressure altitude and temperature) 11/17/13DAC Clark J Wilson 9. Wing stalls typically occur following : Speed reduction Premature flap retraction Increased wing loading (G) Stalls can be aggravated by Ice contaminated wing surfaces.11/17/13DAC Clark J Wilson 10. Approach to Stall or Stall Recovery A Preventive actions must (ideally) be taken before the stall warning. An approach to a stall is a controlled flight condition. A fully developed stall is an out-of-control, but usually recoverable condition. The recovery procedure for both the approach to a stall and the fully developed stall should be an immediate reduction in angleof-attack. Most full stall and approach to stall incidents have occurred where there was sufficient altitude available for recovery. Stall incidents that progress into accidents occurred because the crew failed to make a positive recovery when the stall warning occurred resulting in a condition that progressed to a full stall.11/17/13DAC Clark J Wilson 11. Stall Recovery is the Priority. Altitude recovery is secondary to Stall Recovery The approach to stall recovery should not emphasize Powering Out of the approach to stall condition without also releasing back pressure on the elevator control. The Powering Out technique may be impracticable at altitude due to thrust available. At near stalled angle of attack, drag is high and available thrust for acceleration could be too slow to effect an optimum recovery. Do not increase back pressure unless ground contact is imminent. If a go-around maneuver is to be performed, accelerate until all stall warnings have ceased before pitching to a climb attitude. 11/17/13DAC Clark J Wilson 12. Altitude Loss During Stall Recovery There are many variables which could affect the amount of altitude loss encountered in a smooth recovery from an approach to stall. These variables may include, but are not limited to: Entry Altitude Bank Angle Aircraft Weight Aircraft Configuration Density AltitudeThe reduction of angle of attack required to initiate recovery will most likely result in altitude loss. The amount of altitude loss will be affected by the operational environment. Training programs and evaluation standards should not mandate a predetermined value for altitude loss for stall recovery. Proper evaluation criteria should consider the multitude of external and internal variables which affect the recovery altitude. The aircraft manufacturers recommended stall recovery techniques and procedures take precedence and should be followed.11/17/13DAC Clark J Wilson 13. The only recovery procedure that is valid for the approach to stall and full stall is to release the back pressure on the control column and simultaneously apply power until a safe airspeed is attained. If stall warnings are still indicated, continue pitching below the level pitch attitude until all stall warnings cease. 11/17/13DAC Clark J Wilson 14. Stall Speed Is Increased When Flaps Are Retracted Retracting the flaps prematurely in the RC-12 will reduce lift and increase the indicated stall speed: Selecting flaps from Full Flaps (100%) to Approach Flaps (40%) Effects about a 10 Knots increase in stall speed Selecting flaps from Full Flaps (100%) to Approach Flaps (40%) Effects about a 10 Knots increase in stall speed Any sudden retraction of flaps at slow speed or during an approach to stall recovery may result in a possible fully developed stall and loss of aircraft control. 11/17/13DAC Clark J Wilson 15. FULL STALLS The successful recovery from a fully developed stall involves a very different technique compared to the recovery from the approach to stall. Recovery from a full stall without reducing pitch attitude is impossible and will certainly require a significant loss of altitude. 11/17/13DAC Clark J Wilson 16. ACCELERATED STALLS The accelerated stall occurs when an aircraft experiences a load factor (G) higher than 1G, for example while turning or pulling up from a dive. An aircraft can theoretically be stalled at any speed. An aircraft experiencing a load factor greater than 1G will stall at a higher indicated airspeed speed compared to its wings level, un-accelerated stall speed. 11/17/13DAC Clark J Wilson 17. Accelerated Stall In A Turn The higher wing loading in a turn due to the higher centrifugal force causes the aircraft to stall at higher speeds compared to the straight and level stall speed.View: Accelerated stall Video 11/17/13DAC Clark J Wilson 18. Deep Stalls Due to the T-Tail design, C-12 and RC-12 aircraft may not manifest the buffeting, pitching and rolling characteristics that typically indicate a stall condition in other fixed-wing aircraft. A deep wing stall develops when the angle of attack increases well beyond the wings critical stall point, aggravated by the T-tail configuration. Initially, the T-Tail aircrafts elevator remains effective even after the wing has stalled because the T-Tail remains above the wings wake. 11/17/13DAC Clark J Wilson 19. T-TAIL Deep Stall The elevator remaining effective after the wing has stalled could cause the pilot to inadvertently pitch-up to an even greater Angle of Attack (AOA) and into a deep stall. In a fully developed deep stall the horizontal tail surfaces becomes buried in the wings wake and the elevator may then lose all effectiveness, making it impossible to reduce pitch attitude and break the stall. In the deep stall regime the enormous increase in drag at low speeds can cause an increasingly descending flight path with no change in pitch attitude which further increases the AOA. Once the deep stall is fully developed there is no guarantee that recovery may be affected by down-elevator movement and it may be impossible to affect a nose-down pitch attitude to increase airspeed. . 11/17/13 DAC Clark J Wilson 20. DEEP STALL RECOVERY The Deep stall is characterized by a level pitch attitude, however, the actual flight path may exceed 45 degrees down and a sink rate of up to 8500 feet per minute. Deep Stall recovery requires a 10 15 degrees nosedown pitch change to brake the stall. Allow airspeed to increase to at least 25 KIAS above stall speed. 11/17/13DAC Clark J Wilson 21. Ice Contamination On Wings Any ice (including frost) adhering to the wing surfaces of an aircraft willsignificantly increase drag and its stall speed. Ice forming aft of the de-ice boot is especially dangerous. The Stall Warning System in the C-12 (Stall Horn) normally activates about 5-10 Knots above a stall, but with ice on the wings, the Stall Warning System may not activate before a full stall develops. With an ice contaminated wing, an abrupt full stall may occur without the typical pre-stall warning, i.e. buffet, pitchdown. A brisk reduction in pitch attitude is required to recover. When landing with any ice adhering to the wings, as a rule of thumb, VREF should be increase by 10 Knots IAS.11/17/13DAC Clark J Wilson 22. APPROACH TO STALL RECOVERY At the first sign an approaching wing stall (Stall Warning Horn, pre-stall airframe buffet, loss of control effectiveness and/or nose pitch-down): 1. Decrease angle of attack by simultaneously: Reducing Pitch Attitude to a measured amount depending upon proximity to the ground and Simultaneously Adding Power 2. Maintain coordinated flight. 3. Roll wings level. An airplane in a turn has higher wing loading which increases the stall speed. 4. Increase airspeed well above the stall warning airspeed before retracting flaps. 5. After the