Ch 11 - Aircraft Drag Flashcards
Total Drag
Total Drag = Parasite Drag + Induced Drag
Parasite drag = Form Drag + Skin Friction Drag + Interference Drag
Profile Drag = Form Drag + Skin Friction
Form Drag
Impacted by Speed, Frontal Area, Shape and streamlining, Surface (smooth/dimpled)
To decrease form drag:
- Increase the distance aft of the point of max. thickness
Skin Friction Drag
Impacted by; Speed, surface area, boundary layer type and surface roughness
Interference Drag
All to do with how smooth the transition from air to flow around the object is.
Think of Fish
- Fillets and fairings all aimed to reduce interference drag
Parasite Drag
Proportional to:
- Airspeed squared
- Surface area of the aircraft
- Coefficient of parasite drag
Parasite drag is a factor of CAS/IAS and dynamic Pressure
Coefficient of Parasite Drag
Determined by;
- Form drag
- Skin Friction drag
- Interference drag
For a given config, Cdp does not vary with normal AoAs
Induced Drag
Cdi is inversely proportional to IAS squared
Weight makes the induced drag curve move up and to the left
- The heavier you are, the more lift you will need which means more induced drag
Cdi is inversely proportional to aspect ratio. So as aspect ratio increases, Cdi decreases as there is less downwash and less vortices
Reducing Tip Stalling Tendency
Vortilon - Creates vortex (barrier) to stop span wise flow
Wing Fence - Physical barrier to stop spanwise flow
Chine - Engine notch, at slow speeds, reduces root to tip flow on upper surface of wing
Notch - Create vortex (barrier) to help reduce spanwise flow
More commonly though:
- Washout at the tip
- Decreased camber at the tip
Cross Section on Stalling Angle
Sharpening the leading edge of the wing root will encourage the root to stall first
Some light aircraft have stall strips (Toblerone )
Wing Loading
=Aircraft Weight / Wing Area
High wing loading; increases the adverse pressure gradient, the flow energy is lost more quickly which encourages separation and an earlier stall onset
Aileron Reversal
When approaching the stall, you try to roll one way and in trying to increase the lift on the wing that you are trying to lift, cause it to stall which means that you actually roll the other way
Effect of mass on stalling speed
Increased mass = increased required lift (faster or increased AoA)
Which means the hat the stalling speed is Higher for Heavier aircraft
Flap Configuration on Stalling Speed
Flaps and slats will increase CLMAX which means the that flaps and slats decrease the stalling speed.
Can fly slower
VS1 = Stall speed at a specified configuration VS0 = Stall speed in landing configuration
Landing Gear on Stall Speed
Landing gear will create a pitch down moment which will increase the stall speed (normal orientation)
Propeller Thrust on Stalling Speed
Power-off Stall = Higher Stall Speed
Power-on Stall = Lower stall speed as you are gaining ‘free lift’
Jet Thrust on Stall Speed
Power-off Stall = Higher stall speed
Power-on Stall = Lower stall speed (pitch up moment created which is good for a stall)
CofG Positions on Stall Speed
CG Forward = Higher Stall Speed
Swept Wing on Stall Speed
Reduced CLMAX compared to a rectangular wing (much lower)
Which means a higher stalling angle of attack but a less defined stalling angle of attack
Altitude on Stall Speed
With altitude, the aerofoil loses energy at the leading edge which gives you less warning to when you are about to stall.
At high alt. stalling speed increases due to compressibility
At other alt. Ranges, the stalling speed is consistent
Contamination on Stalling Speed
Decreased stalling AoA
Decreased CLMAX
Increased stalling speed
Accelerated Stall
A manoeuvre that requires additional lift.
The wing has the same CLMAX, speed therefore has to increase
Stalling in the Turn
Load Factor = 1/cosThi
VSNEW = 3 step approach
Stall Speed in a Pitching Manoeuvre
Higher load factor which means the same as an accelerated stall
Stalling speed increases
To recover, reduce AoA
