Flashcards in Aerodynamics Deck (26)
What are the four dynamic forces that act on an airplane during all maneuvers?
Lift, gravity, thrust, drag
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?
An airfoil is a device which get s a useful reaction from air moving over its surface, namely lift. Wings, horizontal tail surfaces, vertical tail surfaces, and propellers.
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.
What is relative wind?
The relative wind is the direction of airflow with respect to the wing. The flight path and relative wind are always parallel but travel in opposite directions.
What is 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/gas) decreases at points where the speed of the fluid increases. In the case of airflow, high speed airflow is associated with low pressure and low speed flow with high pressure.
The airfoil of an aircraft is designed to increase the velocity of the airflow above its surface, thereby decreasing pressure above the airfoil. Simultaneously, the impact of air on the lower surface of the airfoil increases the pressure below. This combination of pressure decrease above and increase below produced lift.
What are several factors which will affect both life an drag?
a) Wing area - life and drag on a wing are roughly proportional to the wing area.
b) Shape of airfoil - as the upper curvature of the airfoil is increased the lift produced increases. Flaps, etc
c) Angle of attack - as the angle of attack is increased, both lift and drag are increased, up to a certain point.
d) Velocity of air - an increase in velocity of air passing over the wing, increases lift and drag.
e) Air density - Life and drag vary directly with the density of the air. As air density increases, life and drag increase. As air density decreases, life and drag decrease. Air density is affected by these factors: pressure, temp, and humidity.
What is torque effect?
Torque effect involves Newton's Third Law of Physics - for every action there is an equal and opposite reaction. This means that as the internal engine parts and prop are revolving in one direction, an equal force is trying to rotate the airplane in the opposite direction.
It is greatest when at low airspeed with high power settings and high angle of attack.
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. To compensate, some of the older airplanes are rigged in a manner to create more lift on the wing that is being forced downward.
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 the torque reaction, more weight is being placed on the left main landing gear.
What are the four factors that contribute to torque effect?
a) Torque reaction of the engine and prop. For every action there is an opposite reaction. The rotation of the propeller to the right, tends to roll or bank the aircraft to the left.
b) Gyroscopic effect of the propeller. Gyroscopic precession applies here. The resultant action of a spinning object when a force is applied to the outer rim of its rotational mass.
c) Corkscrewing effect of the propeller slipstream. At high prop speeds and low forward speeds (on 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 prop (P-factor) - When the airplane is flying at high angle of attack, the bite of the downward moving propeller blade is greater than the bite of the upward moving blade. There is greater thrust on the downward moving blade on the right side, and this forces the airplane to yaw to the left.
What is "centrifugal force"?
Centrifugal force is the "equal and opposite reaction" of the airplane to change the direction, and it acts "equal and opposite" to the horizontal component of lift.
What is "load factor"?
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. In other words, it is the actual load supported by the wings divided by the total weight of the airplane.
Why is load factor important to pilots?
a) dangerous overload to the aircraft structure
b) an increased load factor increases the stall speed and makes stalls possible at seemingly safe flight speeds.
What situations may result in load factors reaching the maximum or being exceeded?
a) Load factor increases tremendously after a bank has reached 45/50 degrees.
c) Speed. The amount of excess load that can be imposed upon the wing depends on how fast the airplane is flying.
What effect does an increase in load factor have on stalling speed?
As load factor increases, stalling speed increases. Any airplane can be stalled at any airspeed within the limits of its structure and the strength of the pilot. There is a direct relationship between the load factor imposed upon the wing and its stalling characteristics.
Define the term maneuvering speed?
Maneuvering speed is the maximum speed at which the limit load can be imposed w/o causing structural damage tot he aircraft.
Discuss the effect on maneuvering speed of an increase or decreases in weight.
Maneuvering speed increases with an increase in weight and decreases with a decrease in weight.
What causes an airplane to stall?
The direct cause of every stall is an excessive angle of attack. Each airplane has a particular angle of attack where the airflow separates from the upper surface of the wing and the stall occurs. An airplane can stall at any speed, weight, load or density altitude.
What is a spin?
A spin is a controlled or uncontrolled maneuver in which the airplane or glider descends in a helical path while flying at an angle of attack greater than the critical angle of attack. If a stall does not occur, a spin cannot occur.
What causes a spin?
The primary cause of an inadvertent spin is exceeding the critical angle of attack while applying excessive or insufficient rudder.
When are spins most likely to occur?
a) Engine failure during takeoff climb out - pilot tries to stretch the glide to landing area by increasing back pressure or makes an uncoordinated turn back to departure runway at a low airspeed
b) Crossed-control turn from base to final (slipping/skidding turn) - pilot overshoots final and makes an uncoordinated turn at low airspeed.
c) Engine failure on approach to landing - pilot tries to stretch glide to runway by increasing back pressure
d) Go-around with full nose-up trim - pilot applies power with full flaps and nose-up trim combined with uncoordinated use of rudder.
e) Go-around with improper flap retraction - pilot applies power and retracts flaps rapidly resulting in a rapid sink rate followed by an instinctive increase in back pressure.
What procedure should be used to recover from an inadvertent spin?
a) Close the throttle
b) Neutralize the ailerons
c) Apply full opposite rudder
d) Briskly move the elevator control forward
e) Once the stall is broken the spinning will stop. Neutralize the rudder
f) When the rudder is neutralized, gradually apply enough pressure aft elevator pressure to return to level flight
PARE - Power (reduce to idle) Ailerons (position to neutral Rudder (Apply full opposite rudder against rotation Elevator (apply positive, forward of neutral, movement to break stall)
What causes adverse yaw?
When turning an airplane to the left for example, the downward deflected aileron on the right produces more lift on the right wing. Since the downward deflected right aileron produces more lift, it also produces more drag, while the opposite left aileron has left lift and less drag.
What is ground effect?
A condition of improved performance the airplane experiences when its operating near the ground. The three dimensional flow pattern around the airplane, around the wing, is restricted by the ground surface.