Principles of Flight

Define the following terms: Airfoil, Angle of attack, Angle of incidence, Camber, and Chord line

Airfoil - any surface designed to obtain reaction, such as lift, from the air through which it moves. Angle of attack - the angle between the chord line of the wing and the direction of the relative wind. Angle of incidence - the angle formed by the chord line of the wing and the longitudinal axis of the airplane. Camber - the curvature of the airfoil from the leading edge to the trailing edge. Chord line - an imaginary Straight line drawn from the leading edge to the trailing edge of a cross section of an airfoil. Wing planform the shape or form of a wing as viewed from above. It may be long and tapered, short and rectangular, or various other shapes.

What causes an airplane to turn?

An object at rest or moving in a straight line will remain at rest or continue to move in a straight line until acted upon by some other force. An airplane requires a sideward force to make it turn; in a normal turn, this is done by banking the airplane So that lift is exerted inward as well as upward. This force of lift is separated into two components: one that acts vertically and opposite to weight (gravity) is called the "vertical component of lift"; the other that acts horizontally, toward the center of the turn, is called the "horizontal component of lift" or centripetal force. The latter is the force that pulls the airplane from a straight flightpath to make it turn. Centrifugal force is the equal and opposite reaction" of the airplane to the change in direction and acts equal and opposite to the horizontal component of lift. This explains why, in a correctly executed turn, it is not rudder-supplied force that turns the airplane.

Explain the following terms as they relate to the production of lift (Bernoulli 's principle and Newton 's Third Law)

Bernoulli 's principle- -- states in part that the internal pressure of a fluid (liquid or gas) decreases at points where the speed of the fluid increases. In other words, high speed flow (above the wing) is associated with low pressure, and low speed flow (below the wing) with high pressure. Newton 's Third Law - since for every action there is an opposite and equal reaction, an additional upward force is generated as the lower surface of the wing deflects air down ward.

Explain the effect of wing downwash on longitudinal stability.

In level flight, there will be a down wash of air from the wings that strikes the top of the horizontal stabilizer and produces downward pressure, which at a certain speed will be just enough to balance the airplane 's nose-heaviness. The faster the airplane is flying, the greater the downwash and the greater the downward force on the horizontal stabilizer. If the airplane 's speed decreases, the speed of the airflow over the wing is decreased which reduces downwash, causing a lesser down ward force on the horizontal stabilizer. In turn, nose-heaviness is accentuated, causing the airplane's nose to pitch down more. With the airplane in a nose- low attitude, this lessens the wings' angle of attack and drag, and allows the airspeed to increase. As the airplane continues in the nose-low attitude and its speed increases, the downward force On the horizontal stabilizer is once again increased. Consequent the tail is again pushed downward and the nose rises into a Climbing attitude.

Explain the forces acting on an airplane when operating in straight-and-level unaccelerated flight.

In steady flight, the sum of lift, weight, thrust and drag is always zero. There can be no unbalanced forces in steady, straight flight based upon Newton's Third Law, which states that for every action or force there is an equal, but opposite, reaction or force. This is true whether flying level or when climbing or descending. It does not mean the four forces are equal but means the opposing forces are equal to, and thereby cancel, the effects of each other. In straight-and-level unaccelerated flight, lift equals weight and thrust equals drag; or said another way, the sum of all upward forces equals the sum of all downward forces and the sum of all forward forces equals the sum of all backward forces.

What are the four dynamic forces that act on airplane during all maneuvers?

Lift - the upward acting force Weight - or gravity, the down ward acting force Thrust - the forward acting force Drag - the backward acting force

Explain the relationship between the center of lift and the center of gravity.

Most aircraft are designed SO that the wing 's center of lift (CL) is to the rear of the center of gravity (CG). This makes the aircraft "nose heavy" and requires that there be a slight downward force on the horizontal stabilizer in order to balance the aircraft and keep the nose from continually pitching downward. Compensation for this nose heaviness is provided by setting the horizontal stabilizer at a slight negative angle of attack (AOA). The downward force this produces holds the tail down, counterbalancing the "heavy" nose.

Define the term "stability" and name the two basic types

Stability is the inherent characteristic designed into an airplane to correct for conditions that may disturb its equilibrium, and return or to continue on the original flightpath. The two types of stability are static stability, which is the initial tendency that the airplane displays after its equilibrium is disturbed, and dynamic stability, which is the overall tendency the airplane displays after its equilibrium is disturbed.

Explain the effects of speed on load factor.

The amount of excess load that can be imposed on the wing depends on how fast the airplane is flying. At slower speeds, the maximum allowable lifting force of the wing is only slightly greater than the amount necessary to support the weight of the airplane. Consequently, the load factor should not become excessive even if the controls are moved abruptly or the airplane encounters severe gusts. The reason for this is the airplane will stall before the load can become excessive. However, at high speeds, the lifting capacity of the wing is so great that a sudden movement of the elevator controls or a strong gust may increase the load factor beyond safe limits.

What are the four factors that contribute to torque effect?

a. Torque reaction of the engine and propeller: For every action there is an equal and opposite reaction. The rotation of the propeller (from the cockpit) to the right, tends to roll or bank the airplane to the left. b. Gyroscopic effect of the propeller: Gyroscopic precession applies here, the resultant action or deflection of a spining object when a force is applied to the outer rim of its rotational mass. If the axis of a propeller is tilted, the resulting force will be exerted 90 degrees ahead in the direction of rotation and in the same direction as the applied force. Most noticeable on takeoffs in taildraggers. C. corkscrewing effect of the propeller slipstream: High speed rotation of an airplane propeller results in a corkscrewing rotation to the slipstream as it moves rearward. Most notice- able at high propeller speeds and low forward speeds, (as in a takeoff), the slipstream strikes the vertical tail surface on the left side pushing the tail to the right and yawing the airplane to the left. d. Asymmetrical loading of the propeller (P-Factor): When an airplane is flying with a high angle of attack, the bite of the downward-moving propeller blade is greater than the bite of the upward moving blade. This is due to the downward -moving blade meeting the oncoming relative wind at a greater angle of attack than the upward-moving blade. Consequently there is greater thrust on the downward moving blade on the right side, and this forces the airplane to yaw to the left.