Stalling Flashcards
What happens to the separation point at the critical AoA?
Moves well forward and causing large increase in turbulence over the wing
At what point does the separation point move well forward and causing large increase in turbulence over the wing?
Critical AoA
What effect does not encourage the formation of low static pressure areas above a wing?
Turbulent flow
How does turbulent flow disrupt lift generation?
It prevents the formation of low static pressure above a wing
At what point does a stall occur?
Critical AoA
At the critical AoA, what does the Centre of Pressure do?
Moves rearwards rapidly
The stalling of an aerofoil is what?
Significant breakdown for streamline flow into turbulence over a wing
What causes a buffet in a stall?
Turbulent flow over the tailplane
What causes the nose to drop in a stall?
Rearwards movement in the centre of pressure
The centre of pressure’s rearward movement in a stall has what marked effect?
Nose will drop
Despite the ability of a stall to occur at various attitudes, airspeeds etc., what flight factor is generally constant in a stall?
A specific AoA
What lift factor affects stalling speed?
Square-root of lift
That IAS at the stall depends on the square root of the lift means that…
Anything that requires the generation of extra lift will increase the indicated stalling speed
Load factor and stalling speed relationship
If load factor increases, so will the stalling speed
How would you work out a new stalling speed from an increased load factor?
The square root of the increase in load factor
What CG change has the same effect as an increase in weight?
CG moves forward
Why does CG moving forward have the same effect as an increase in weight?
Down force is required from the tailplane
What CG change has the same effect as a decrease in weight?
CG moves aft
How does wing loading affect stall speed?
Low wing loading means a lower stall speed
Does stalling IAS vary with altitude?
No
How does stalling IAS vary with altitude?
It doesn’t vaary - it remains constant
Why will an altitude variation not affect stalling IAS?
Altitude variations do not affect C-Lift Max (which is a function of the stalling speed)
How does power affect stalling speed?
It is less in a power-on stall
How does power reduce stalling speed?
High nose attitude (nearing the stall) allows thrust to have a vertical component and off-load the wings so less lift is required
How does thrust off-load wings in an approaching stall?
The aircraft will have a high nose attitude so the thrust will have a vertical component and thus reduce the lift required from the wings
How does power-on affect the stalling of the wing?
Slipstream will generate lift from inner wing, so outer wing may stall first
Why might the outer wing stall first in a particular kind of stall?
Power-on stall means inner wings generate lift from slipsttream and outer wings do not
Why is it more preferable for inner wings to stall first before outer wings?
Inner wing has a shorter moment arm thaan the outer so a lesser rolling moment is produced
How may an aircraft be designed so that its inner wings stall before its outer wings?
A wing washout will mean greater AoA at the wingroot will create a stall before the lower AoA at the wingtip
In what two ways does ice increase stalling speed?
Ice-accretion on the wings prevents lift generation at lower AoA
Ice increases weight
Where is the stagnation point of a wing at positives AoA?
Loweer surface of the leading edge (not visible from some cockpits)
What is the blanking of an elevator?
Poor elevator control due to turbuence over the tailplane
How are stalls with flaps extended quite sudden and rapid?
Flaps have increased drag so any speed loss will be rapid
How is yaw prevented in a stall with flaps?
Using rudder, not ailerons
Why should ailerons not be used in a stall with flaps?
Ailerons will deepen the stall on the wing with the downgoing aileron
Why do swept-wing aircraft enter a deep stall?
Their wingtips are aft of the CG and will stall first, thus creating a nose-up moment which further increases the AoA
Relation of wingtips and CG on a swept-wing aircraft?
Wingtips sit aft of the CG
What happens to the wings entering a spin?
Outer wing speeds up, more lift, rises, AoA decreases
Inner wing slows down, less lift, fallls, AoA increases and stalls
What stage comes between a stall and a fullly-developed spin?
Autorotation
What are the stages of an autorotation?
Roll, sideslip, nose drop and rotation rate increases
What occurs to instrumentation in a spin?
The coordination ball will settle in the bottom left corner irrespective of spin direction
