Lift Augmentation Flashcards
Geometry Limited
Long A/C limit rotation angle therefore AOA
Trailing edge flaps - Plain flap
Increases peak suction on the upper surface of aerofoil - Increase in CL - Overall Lift increases
Lower critical AOA (reduce stalling angle - early seperation at boundary layer
Split Flap
Strip along the top and hinged below TE
Produces a greater CL max than a plain flap
Produces less turbulence than plain = higher stalling AOA
Has the worst L/D ratio so not used in CAT
Slotted Flap
Reenergise boundary layer
Keeps boundary flowing reducing the adverse pressure gradient
Increase in clmax and stalling angle
Variable camber leading edge flap
Peak suction increases towards original position
Additional lift without change in CP (no trim change needed)
Lift increases
Delays stall angle
Used in conjunction with TE FLAPS
Preserves stalling angle
Increases LE Radius to encourage airflow along upper surface delaying the separation point.
Droop nose
Leading edge flap designed by airbus involving moving the whole leading edge
Krueger flap
Leading edge flap that extends outwards and downwards
Increases camber but not leading edge radius
Used inboard to increase lift and ensure wings roots stall first
Fowler flap - Camber/Surface Area
Increase in camber and surface area of trailing edge
Addresses issues with peak suction and the increase in APG
Slotted to reenergise boundary layer
Used in most airliners
First stage extends outwards but not so far downwards - more lift for little drag
Slat - What does it do
A slot at the leading edge
Reduce size of suction peak (reenergise the flow)
Delayed separation greater stalling angle and greater clmax
Summary of all lift devices
TE FLAPS - Greatest CL increase
LE FLAPS - CL increases/no reduction in critical AOA
Slats - Increase the critical AOA
Extension of fowler TE FLAP initially on pitch
Nose down pitching moment
Cl increases for minimal drag due to outwards extension but not much downwards movement
Auto slat system
Extends automatically when a certain value of AOA is exceeded
Leading edge flaps effects on pressure
Peak suction increases without changing CP
Less adverse pressure gradient
Therefore high clmax
Trailing Edge and Leading Edge Flaps Working Together
TE provide most increase in CL
LE preserves the stalling angle
Slats - Peak Pressure modification
Reduces peak suction by spreading low pressure over upper surface to reduce adverse pressure gradient
Wing can reach greater stalling angle of attack and greater CLMAX
Why drag is good on final approach
Improves speed stability
Permit ac to run at higher rpm on approach for a go around
Drag created from high lift devices ranked from lowest drag to highest drag
Fowler Flaps - Lowest
Slotted
Plain
Split
Effect of flaps on tailplane
Increase in CL from lowering flaps increasing downwash on tailplane
EAOA increases on tailplane resulting in more downforce
Results in a pitch up moment
Effect of flaps on tip vortices
Flap extension creates more lift inboard away from tips
Inner part of wing working harder meaning decreased tip vortices
A/C Config for worst wake turbulence
Clean/slow heavy a/c
Vortex Generators
Thin fins on surface of wing generate small vortices to create turbulent boundary layer
Help keep airflow attached to upper surface for longer
Placed closed to wing tip to delay the stall
Flap asymmetrical extension will yaw where
Yaw to the wing with flaps deployed
Flaps asymmetry - uncommanded roll where
Roll towards the wing flaps retracted as flap extended wing generating more lift
Failure of the slats to extend will….
Affects stalling angle
Fly faster on approach
What flap setting would have the greatest affect on CL/CD ratio?
The higher the flap setting the affected CL/CD ratio
Slats and AOA
Slat requires a much increase angle of attack to give its CLMAX. Restricted in landing visibility for pilot
Asymmetric operation of a slat will lead to a
Yaw moment due to increase in drag
Flap asymmetry will lead to
Large rolling moment
