Stalls 2-3 Flashcards
Define the Boundary Layer.
The layer of airflow over a surface that demonstrates local airflow retardation due to viscosity.
*no more than 1mm thick(playing card) at the leading edge and grows in thickness at it moves aft over the surface
Laminar Flow & Turbulent Flow.
Describe the different types of Flow within the Boundary Layer.
Laminar Flow - Air moves smoothly along in streamlines, produces little friction but is easily separated from the surface.
Turbulent Flow - Streamlines break up and the flow is disorganized and irregular, produces higher friction drag than laminar Boundary layer, but adheres better to the upper surface of the airfoil, delaying BLS.
Describe Boundary Layer Separation.
Adverts Pressure Gradient: strongest at high lift conditions and high AOA; if BL does not have enough KE to overcome the APG lower levels of BL will stagnate. BLwill then separate from the surface and airflow along the surface aft of separation point will be reversed.
Define CL MAX AOA.
The AOA beyond which CofL begins to decrease.
Define Stall.
A condition of flight in which an increase in AOA results in a decrease in CofL.
Explain how a Stall occurs.
The Boundary layer does not have sufficient kinetic energy to overcome the adverse pressure gradient. Thus Separation point progresses forward as AOA increases, close to the leading edge, the net suction on the top of the airfoil will decrease and a decrease in CofL.
Identify the Aerodynamic Parameters causing a Stall.
Excessive AOA. Results in decreased L, increase Dt,and altitude Loss.
Compare Power-On and Power-Off Stalls.
Power-Off = engine at idle; Power-On stall speed will be less than P-Off because at High Pitch attitudes, part of the WT of the A/C is supported by Vertical Component of the Thrust Vector.
Describe the order of Losing Control Effectiveness approaching a Stall in the T6B.
Ailerons to Elevator to Rudder.
Explain the difference between True and Indicated Stall Speed.
Stall Speed (Vs) is the Min True Airspeed required to maintain Level flight at CofL Max AOA.
Substituting the Vs equation into the True A/S equation
**TAS increases with Altitude as IASs density is constant in Alt. Change.
Vs= (Square root) 2W / pSCofLmax ;
IASs = (SR) 2W /p(not)SCofLmax
Explain the effects of Gross Weight, Altitude, Load Factor and Maneuvering on Stall Speed.
As A/C WT decrease = Stall speed Decrease.
Altitude Increases = Stall Speed Increase.
Load factor and Maneuvering = Increase Stall Speed.
State the purpose of using High Lift Devices.
To reduce Takeoff and Landing speeds by reducing IASs and Stall Speeds by increase CofL at high AOA.
Describe how different High Lift Devices affect the values of CL, CL Max, and CL Max AOA.
Boundary Layer control Devices - airflow separation are delayed to a higher stalling AOA; CLMax and CLmax AOA increase.
Camber Change - Increase CLMax by increasing the Camber of the Airfoil. Increasing CL and Decreasing CLmax AOA
Describe devices used to control Boundary Layer Separation.
Slots - allow High Ps air beneath the wing to be accelerated and injected into the BL on the Upper Surface via a Nozzle to overcome APG. Fixed slots and Automatic slots(Slats)
Fixed Slots - gaps at the L/Edge to allow air to flow to the upper SFC
Slats - moveable L/Edge sections, deploy aerodynamically by High AOA
Vortex Generators - small vanes on upper surface to disturb BL to adhere
Describe devices used to change the Camber of an Airfoil.
Trailing Edge Flaps - Plain Flap a simple hing; Split Flap is a plate deflected from lower SFC; Slotted Flap - moves away from wing to open a slot for BLC; Fowler Flap extends and moves down.
Leading Edge Flap - change wing camber at Leading Edge operated manually or by Computer; Plain, Slotted are similar to TEflaps.
