What’s Induced Drag?
February 22, 2024
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?
February 22, 2024
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?
February 22, 2024
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?
February 22, 2024
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?
February 22, 2024
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?
February 22, 2024
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?
February 22, 2024
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?
February 21, 2024
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?
February 21, 2024
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?
February 21, 2024
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
February 21, 2024
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?
February 20, 2024
Ref Chapter 5 Ans: angle between chord line and the direction of the relative wind
4 forces in steady flight?
February 20, 2024
Ref Chapter 5 Ans: sum of 4 forces is always zero, provided that it is a steady flight! Steady flight? -i.e unaccelerated status! Based on Newton’s 3rd law (every action or force there is an equal, but opposite, reactionor force.) However, amount (magnitude) of 4 forces not exactly same! Weight cancel out by Lift
What’s 4 forces?
February 20, 2024
Ref Chapter 5 Ans: Lift, Drag, Thrust, Weight Thrust— forward force produced by the powerplant/propeller or rotor opposes force of drag. act parallel to longitudinal axis (in general but not must) Drag— rearward, retarding force caused by disruption of airflow by the wing, rotor, fuselage, and other protruding objects drag opposes thrust (in
