![]() The air on the upper surface has a tendency to flow in toward, and the air on the underside tends to flow towards the tip of the wing. ![]() When an airfoil is flown at a positive AOA, a pressure differential exists between the upper and lower surfaces of the airfoil. The total drag of an aircraft is composed of many drag forces, but only three will be studied: parasitic drag, profile drag and induced drag. Examine the figure opposite, noting how the LC increases until the critical angle of attack is reached, then decreases rapidly with any further increase in the angle of attack. This is the critical angle of attack at stall, called the CL-MAX critical angle of attack. When the aircraft reaches the maximum angle of attack, the lift begins to decrease rapidly. The greater the angle of attack, the greater the lift (all other factors being equal). Each time the handle or handle is moved forward or backward, the angle of attack is changed. When lift is greater than weight, the aircraft gains altitude. If lift becomes less than weight, the aircraft loses altitude. In stabilized level flight, when the lift force is equal to the weight force, the aircraft is in a state of equilibrium and neither gains nor loses altitude. Lift is required to counteract the aircraft’s weight (which is caused by the force of gravity acting on the mass of the aircraft). Lift is the upward force on the wing acting perpendicular to the relative wind. This relationship is simple, but important in understanding the aerodynamics of flying. ![]() Weight has a definite relationship to lift. It will be noted that CG is of major importance in an aircraft, for its position has a great bearing upon stabilite. If the aircraft were supported at its exact CG, it would balance in any attitude. The CG may be considered as a point at which all the weight of the aircraft is concentrated. Weight - Gravity is the pulling force that tends to draw all bodies to the center of the earth. In level flight, lift opposes the downward force of weight Lift - is a force that is produced by the dynamic effect of the air acting on the airfoil, and acts perpendicular to the flight path through the center of lift (CL) and perpendicular to the lateral axis. As a general rule, drag opposes thrust and acts rearward parallel to the relative wind. Drag - a rearward, retarding force caused by disruption of airflow by the wing, rotor, fuselage, and other protruding objects. Several factors may change the rotor blade AOA and the pilot has little direct control over. The angle of attack (AOA) is an aerodynamic angle, not easy to measure. It is an aerodynamic angle and it can change without change to the blade pitch angle. As a general rule, it acts parallel to the longitudinal axis. The angle of attack (AOA) is the angle between the airfoil chord line and the relative airflow. It opposes or overcomes the force of drag. Thrust - the forward force produced by the powerplant/ propeller or rotor. The four forces acting on an aircraft in straight-and-level, unaccelerated flight are thrust, drag, lift, and weight. Understanding how these forces work and knowing how to control them with the use of power and flight controls are essential to flight. ![]() Yes, I know that without the effect of thermals or slope lift, "level" flight is really going slowly downward to the ground, so I'm calling that "level" for my question at this point.Thrust, drag, lift, and weight are forces that act upon all aircraft in flight. Or, is the wing generally flying with some angle-of-attack of the chord line relative to the airflow? To me, a true glider without a motor seems like it should'nt really be flying with an angle of attack in "level" flight which seems like it would just be shoving into the air and slowing down rapidly. If, for instance, you have a wing with an airfoil with a raised leading edge with "Philips Entry" sweeping back to the bottom spar, then flat on the bottom from the bottom spar to the trailing edge and a nice "standard"(I know, there isn't really a "standard") curved top (Selig 3010? I think), and if you draw a chord-line from the tip of the leading edge to the tip of the trailing edge, Is that wing generally flying through the air on "that" line during "level" flight? i.e.- Is forward travel of the wing through the air parallel to the chord-line? Just curious since I'm thinking about the incidence on the wing(and relative to the horiz stab)on my glider I'm building(Modified 2M Spirit) with a modified fusalage.
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