Performance & Limitations - A: Aerodynamics Flashcards
What are the four dynamic forces that act on an airplane during all maneuvers?
Lift—the upward acting force.
Gravity—or weight, the downward acting force.
Thrust—the forward acting force.
Drag—the backward acting force.
What flight condition will result in the sum of the opposing forces being equal?
In steady-state, straight-and-level, unaccelerated flight, the sum of the opposing forces is equal to zero.
What is an airfoil? State some examples.
An airfoil is a device which gets a useful reaction from air moving over its surface, namely LIFT. Wings, horizontal tail surfaces, vertical tail surfaces, and propellers are examples of airfoils.
What is the angle of incidence?
The angle of incidence is the angle formed by the longitudinal axis of the airplane and the chord of the wing. It is measured by the angle at which the wing is attached to the fuselage. The angle of incidence is fixed and cannot be changed by the pilot.
What is a relative wind?
The relative wind is the direction of the airflow with respect to the wing. When a wing is moving forward and downward the relative wind moves backward and upward. The flight path and relative wind are always parallel but travel in opposite directions.
What is the angle of attack?
The angle of attack is the angle between the wing chord line and the direction of the relative wind; it can be changed by the pilot.
What is Bernoulli’s Principle?
The pressure of a fluid (liquid or gas) decreases at points where the speed of the fluid increases.
What are several factors which will affect both lift and drag?
- Wing area—Lift and drag acting on a wing are roughly proportional to the wing area. A pilot can change wing area by using certain types of flaps (i.e., Fowler flaps).
- Shape of the airfoil—As the upper curvature of an airfoil is increased (up to a certain point) the lift produced increases. Lowering an aileron or flap device can accomplish this. Also, ice or frost on a wing can disturb normal airflow, changing its camber, and disrupting its lifting capability.
- Angle of attack—As angle of attack is increased, both lift and drag are increased, up to a certain point.
- Velocity of the air—An increase in velocity of air passing over the wing increases lift and drag.
- Air density—Lift and drag vary directly with the density of the air. As air density increases, lift and drag increase. As air density decreases, lift and drag decrease. Air density is affected by these factors: pressure,
temperature, and humidity.
What is torque effect?
The torque effect experienced in helicopters and single propeller-powered aircraft is an example of Isaac Newton’s third law of motion, that “for every action, there is an equal and opposite reaction.”
In a single-propeller plane, the torque effect causes the plane to turn upwards and left in response to the propeller turning the plane in the opposite direction of the propeller’s clockwise spin.
What effect does torque reaction have on an airplane on the ground and in flight?
In flight—torque reaction is acting around the longitudinal axis, tending to make the airplane roll.
On the ground—during the takeoff roll, an additional turning moment around the vertical axis is induced by torque reaction. As the left side of the airplane is being forced down by torque reaction, more weight is being placed on the left main landing gear.
What are the four factors that contribute to torque effect?
Torque reaction of the engine and propeller.
Gyroscopic effect of the propeller (Precession).
Corkscrewing effect of the propeller slipstream.
Asymmetric thrust (P-Factor).
What is centrifugal force?
Centrifugal force is the “equal and opposite reaction” of the airplane to the change in direction, and it acts “equal and opposite” to the horizontal component of lift.
What is load factor?
What is the formula?
Load factor is the ratio of the total load supported by the airplane’s wing to the actual weight of the airplane and its contents.
The formula is the actual load supported by the wings divided by the total weight of the airplane.
For what two reasons is load factor important to pilots?
a. Because of the obviously dangerous overload that it is possible for a pilot to impose on the aircraft structure.
b. Because an increased load factor increases the stalling speed and makes stalls possible at seemingly safe flight speeds.
What situations may result in load factors reaching the maximum or being exceeded?
Turns— a 60° turn is 2 Gs. An 80° turn is 5.76 Gs.
Turbulence—Severe vertical gusts cause a sudden increase in angle of attack, resulting in large loads which are resisted by the inertia of the airplane.
Speed—The amount of excess load imposed on the wing is proportionate to how fast the airplane is flying.
