SLATS AND SLOTS –
Slats are auxiliary airfoils attached to the Leading edge of the wing. They increase Stalling Angle and decreases Stalling Speed.
When extended, Slats appears to have a gap between the wing and the slat, which is called SLOT.
It causes Transition Point to move backwards and therefore re-activates the Boundary Layer.
When air passes through this gap it accelerates because it is Convergent in shape, gap at the beginning is more and later it is less.
The transition point moves backwards and therefore, boundary layer is re-activated.
The low pressure area is uniformly distributed over the wing and a greater part of it (wing) is used to produce lift. Therefore, they increasing the CL max, or we can increase the angle of attack to increase CL max.
Slats and Slots increases stalling angle and decreases stalling speed.
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FIXED SLATS – At lower Airspeeds it gives more Lift and at higher Airspeeds it gives more Drag.
AUTOMATIC SLATS – Slat automatically moves out with increase in AOA.
CONTROLLED SLATS – Slats are controlled by Pilot manually.
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FLAPS
Flaps are auxiliary aerofoil, attached to the trailing edge of the wing generally.
Flaps are auxiliary airfoils, which when extended increases Coefficient of Lift.
On giving flaps CL increases, With flaps you get more lift without increasing angle of attack.
Flaps give more lift without increasing angle of attack unlike slats and slots.
All Trailing edge Flaps decreases stalling angle.
Lowering of flaps increases the downwash of the wing.
With Flaps-
CL increases.
Use of flaps increases effective camber of the wing.
Extension of Flaps increases the Downwash of the wing, increasing Coefficient of Lift as well as the effective Camber of the Wing.
PLAIN FLAPS: Trailing edge goes down.
SLOTTED FLAPS: On extension a gap appears between the Wing and the Flap.
SPLIT FLAPS: Bottom of Flap Splits into Two.
Split Flaps cause Minimum Pitching Moment.
FOWLER FLAP: On extension the Flap first goes back and than goes down thereby it also increases the Wing Area.
Fowler Flaps give Maximum increase in Coefficient of Lift with Minimum increase in the Drag.
KRUEGGER FLAPS (Leading Edge Flaps) On extension they give more Lift
at a higher AOA.
They also increasing Stalling Angle.
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” FLAPS increases Lift and also increases Drag but increase in Drag is much more than Lift. Therefore Lift / Drag Ratio decreases, therefore flaps give a Steeper Gliding Angle without increasing Airspeed.
” FLAPS decreases Stalling Speed, thereby giving a lower Takeoff speed, resulting in lower Takeoff Run.
” FLAPS give lower Approach and Landing Speed
” FLAP decreases Float Period, therefore decreasing Landing Run.
” Flaps give more Control Effectiveness at low Airspeeds.
Rudder and Elevators are more effective, due to Slipstream effect because Flaps give more Drag. To counteract this Drag We increase Power, creating a Slip Stream effect.
Ailerons are not affected due to this Slip Stream effect, because aileron are located outboard of the Wing, which is out of the Slips Stream Effect.
“Flaps increases Forward Visibility during Approach and Landing.
” IF flaps are extended at a higher Airspeed, than there is a large increase in Coefficient of Lift, which can cause the Wing to Twist, therefore Flaps are not operated above a Specified Speed.
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BOUNDARY LAYERS CONTROL DEVICES
SUCTION DEVICES – are located at the Trailing edge on top of the wing, and it sucks the Boundary Layer that is breaking off.
Not used in Commercial Aircraft due to large Power required for usage.
BLOWING JETS – are jets that are blown backward at high speeds on the Trailing Edge, it attracts the Boundary Layer that is breaking off.
Not used in Commercial A/C due to large Power required for usage.
VORTEX GENERATORS – are Longitudinally fitted towards Leading Edge. They are 4″-5 “long and 1”-2 “high, they push the Boundary Layer back on to the wing.
It inducts air of high Kinetic Energy into the Boundary Layer and therefore re-activates it. It is widely used in commercial Aircrafts.
All Boundary Layer control devices decreases Stalling Angle as well as decreases Stalling Speed.