Theory of Flight 6.07 Stalls References: FTGU pages 18, 35-38
Review 1. What are the two main types of drag? 2. Is it possible to eliminate induced drag? Why or why not? 3. What is one way to increase lift? 4. What are some ways to minimize drag?
6.07 Stalls MTPs: Laminar Flow Definition of a Stall Critical Angle of Attack Centre of Pressure Stalls Factors affecting stalls
Laminar Flow Boundary Layer The thin layer of airflow over the wing Laminar Layer Smooth portion of the boundary layer nearest the leading edge of the wing Transition/Separation Point Point on wing where the boundary layer becomes turbulent Turbulent layer Turbulent portion of the boundary layer at the trailing edge of the wing
Stall What is a stall? When a wing is no longer capable of producing enough lift to counteract the weight of the aircraft As a result, can no longer be maintained
Centre of Pressure Point on a wing where total aerodynamic pressure acts
Centre of Pressure Centre of pressure moves forward as angle of attack increases to the point of a stall After a stall the centre of pressure moves rapidly back The movement of the centre of pressure causes an aircraft to be unstable
Critical Angle of Attack Angle of attack above which air will cease to flow over the wings and a stall will occur
Critical Angle of Attack Most aircraft have a stall angle of positive 15 to 20 degrees
Centre of pressure and separation point move forward to point of stall and lift production is increased Angle of attack is increased beyond critical angle of attack Wing stops producing lift and stalls Centre of pressure moves rapidly backward Stall
Stall An aircraft can stall 1) When the critical angle of attack is exceeded 2) At any airspeed if the critical angle of attack is exceeded 3) At any altitude if the critical angle of attack is exceeded
Stall Symptoms of a Stall Buffeting
Factors affecting a Stall Centre of Gravity Weight Turbulence Turns (and load factor) Snow, Frost, Ice
Factors affecting a Stall Centre of Gravity (C of G) C of G too far forward Loading on the horizontal tail surfaces increase Overall weight of aircraft increases Stall speed increases C of G too far aft Decreased longitudinal stability Violent stall characteristics Poor stall recovery (very dangerous!) Stall speed decreases
Factors affecting a Stall Weight The more weight on an aircraft means that it must fly at a higher angle of attack Therefore the critical angle of attack will be reached at a higher airspeed Attitude to fly straight and level 2500 lbs, 90kts (closer to the critical A of A) 1000 lbs, 90 kts Start of a trip End of a trip
Factors affecting a Stall Turbulence Upward vertical currents cause the airplane to increase its angle of attack Could result in the aircraft stalling if flying near the stall speed
Turns As angle of bank increases the load factor also increases Therefore, an increased angle of attack is required to maintain level flight in the turn Subsequently, the stall speed in a turn increases Just like adding more weight to an aircraft Factors affecting a Stall
Turns and Stall Speeds
Factors affecting a Stall Snow, Frost, and Ice Accumulation of snow, frost, and ice affects a wing s ability to produce lift Increase in stall speed
Factors affecting a Stall Factors affecting a stall Increase stall speed Forward C of G More weight Turbulence Decrease in stall speed Aft C of G Greater angle of bank
Confirmation Check
Confirmation 1. Draw the movement of the C of P leading up to the stall. 2. What are some factors that increase the stall speed.
Confirmation 3. When can an aircraft stall? 4. What are the symptoms of a stall?
Stall Recovery