What’s ground effect?
Ref Ch5 Ans: air cushion phenomenon The reason of ground effect is that the air that is trapped between the wing and the landing surface, as if there were an air cushion. When the plane is very close to the surface (say just before touchdown), it would suddenly feel like the plane did not want
Strategy to avoid wake turbulence?
Ref Ch5 Ans: 飛緊 : avoid similar flight path with 1000 ft vertical separation T/O : rotate before the point at which preceding acft rotated LAND : approach above preceding acft’s flight path LAND : touch down after the point where other’s wheel contact If doubt, 用 3 mins margin time (rule of thumb) For
When the wingtip vortices are greatest?
Ref Ch5 Ans: heavy, clean, slow Vortices 正比 Weight Vortices 反比 Wingspan Vortices 反比 Speed 所以大機, 無落FLAPS, TAKE OFF/APPROACH 果陣最勁~ 因為大機重, 無FLAPS 要產生升力, AOA 自然大, INDUCED DRAG as well as Wingtip vortices 就當然大 Reference: https://aviation.stackexchange.com/questions/52762/how-can-larger-wingspan-decrease-the-strength-of-wingtip-vortices
點解vortices 係 wingtip ? The formation of wingtip vortices~
Ref Ch5 Ans: pressure differential (between upper and lower surfaces of wing) air always moves from high pressure toward low pressure bottom : span-wise movement of air (outward from fuselage to and around tips) upper surface : span-wise movement (flow in toward fuselage and off the trailing edge) fuselage limits the inward flow –
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Induced Drag 成因?
Ref Chapter 5 Ans: air tends to flow from the high pressure area to low pressure area higher pressure at the bottom of airfoil vortices is created (at wing tip) – wingtip vortices vortices roll off, and create a downwash downwash points the relative wind downward lift is tilted the more the tilted lift, the
What’s Induced Drag?
Ref Chapter 5 Ans: inherent drag due to lift production. Induced drag is inherent whenever an airfoil is producing lift and, in fact, this type of drag is inseparable from the production of lift. Consequently, it is always present if lift is produced. AOA increases, induced drag increases proportionally When view from the tail
What’s boundary layer?
Ref Chapter 5 Ans: the layer of air between the wing and free-stream velocity level The area between the wing and the free-stream velocity level is about as wide as a playing card and is called the boundary layer.
Free-stream velocity?
Ref Chapter 5 Ans: the speed at which molecules are moving at the velocity that same as the air moving around the aircraft. Each layer of molecules above the surface moves slightly faster until the molecules are moving at the velocity of the air moving around the aircraft. This speed is called the free-stream
Skin friction Drag?
Ref Chapter 5 成因: contact of moving air with the surface of an aircraft 解決／緩解方法： flush mount rivets remove any irregularities that may protrude above the wing surface smooth and glossy finish remove dust and dirt no matter how apparently smooth, has a rough, ragged surface when viewed under a microscope
Interference Drag?
Ref Chapter 5 成因: intersection of airstreams （that creates eddy currents, turbulence, or restricts smooth airflow） 解決／緩解方法： Fairings most interference drag is observed when two surfaces meet at perpendicular angles （e.g wing and wing root)
Form Drag?
Ref Chapter 5 成因: shape and airflow around the airfoil (aircraft) 解決／緩解方法： streamline (as many of the parts as possible) When the air has to separate to move around a moving aircraft and its components, it eventually rejoins
Parasite Drag?
Ref Chapter 5 Three sub-type of parasite drag Form Drag Interference Drag Skin Friction Drag not associated with the production of lift Types of Drag?
Air Density , 3H?
Ref Chapter 5 Ans: Air Density drop (air becomes less dense) when High altitude (高度) High temperature （溫度） High humidity (濕度)
What’s stalling AoA? What’s CL-max Critical AoA?
Ref Chapter 5 Ans: the AoA at which after that the acft will stall! Remember: aircraft (airfoil) always stalls at the same AOA! When the aircraft reaches the maximum AOA, lift begins to diminish rapidly. This is the stalling AOA, known as CL‑MAX critical AOA. Notes: generally, 20° AOA is the critical angle
Relationship between Speed and AoA?
Ref Chapter 5 Ans: Speed decrease, AoA need to be increased (and vice versa) Reason is simply, refer to the lift formula, to generate same amount of lift, one factor drop, then another factor must be increased. Lift formula
Lift formula
Ref Chapter 5 Ans: Lift = 1/2 * CL * p * V2 * S where CL : coefficient of lift –> related to AoA p : Air Density V: Airspeed S : Wing Surface What’s 4 forces?
What’s AoA – Angle of Attack?
Ref Chapter 5 Ans: angle between chord line and the direction of the relative wind
