Performance & Limitations - A: Aerodynamics

Question 1

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

Answer 1

Lift—the upward acting force.
Gravity—or weight, the downward acting force.
Thrust—the forward acting force.
Drag—the backward acting force.

Question 2

What flight condition will result in the sum of the opposing forces being equal?

Answer 2

In steady-state, straight-and-level, unaccelerated flight, the sum of the opposing forces is equal to zero.

Question 3

What is an airfoil? State some examples.

Answer 3

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.

Question 4

What is the angle of incidence?

Answer 4

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.

Question 5

What is a relative wind?

Answer 5

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.

Question 6

What is the angle of attack?

Answer 6

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.

Question 7

What is Bernoulli’s Principle?

Answer 7

The pressure of a fluid (liquid or gas) decreases at points where the speed of the fluid increases.

Question 8

What are several factors which will affect both lift and drag?

Answer 8

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.

Question 9

What is torque effect?

Answer 9

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.

Question 10

What effect does torque reaction have on an airplane on the ground and in flight?

Answer 10

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.

Question 11

What are the four factors that contribute to torque effect?

Answer 11

Torque reaction of the engine and propeller.

Gyroscopic effect of the propeller.

Corkscrewing effect of the propeller slipstream.

Asymmetrical loading of the propeller (P-Factor).

Question 12

What is centrifugal force?

Answer 12

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.

Question 13

What is load factor?

Answer 13

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.

Question 14

For what two reasons is load factor important to pilots?

Answer 14

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.

Question 15

What situations may result in load factors reaching the maximum or being exceeded?

Answer 15

Turns—The load factor increases at a terrific rate after a bank has reached 45° or 50°. The load factor in a 60°-bank turn is 2 Gs. The load factor in a 80°-bank 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 that can be imposed upon the wing
depends on how fast the airplane is flying.

Question 16

What are the different operational categories for aircraft and within which category does your aircraft fall?

Answer 16

The maximum safe load factors (limit load factors) specified for
airplanes in the various categories are as follows:
Normal +3.8 to −1.52

Utility (mild aerobatics including spins) +4.4 to −1.76

Aerobatic +6.0 to −3.00

Question 17

What effect does an increase in load factor have on stalling speed?

Answer 17

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.

Question 18

Define the term maneuvering speed.

Answer 18

Maneuvering speed is the maximum speed at which the limit load can be imposed (either by gusts or full deflection of the control surfaces) without causing structural damage.

Question 19

Discuss the effect on maneuvering speed of an increase or decrease in weight.

Answer 19

Maneuvering speed increases with an increase in weight and decreases with a decrease in weight.

Question 20

Define loss-of-control-inflight (LOC-I) and describe several situations that might increase the risk of an LOC-I accident occurring.

Answer 20

LOC-I is defined as a significant deviation of an aircraft from the intended flight path and it often results from an airplane upset.

Question 21

What causes an airplane to stall?

Answer 21

The direct cause of every stall is an excessive angle of attack.

Question 22

What is a spin?

Answer 22

A spin in a small airplane or glider is a controlled (recoverable) or uncontrolled (possibly unrecoverable) 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. Spins result from aggravated stalls in either a slip or a skid. If a stall does not occur, a spin cannot occur.

Question 23

What causes a spin?

Answer 23

The primary cause of an inadvertent spin is exceeding the critical angle of attack while applying excessive or insufficient rudder, and to a lesser extent, aileron.

Question 24

When are spins most likely to occur?

Answer 24

A stall/spin situation can occur in any phase of flight but is most likely to occur in the following situations:

a. Engine failure on takeoff during climb-out
b. Crossed-control turn from base to final
c. Engine failure on approach to landing
d. Go-around with full nose-up trim
e. Go-around with improper flap retraction

Question 25

What procedure should be used to recover from an inadvertent spin?

Answer 25

Power—reduce to idle
Ailerons—position to neutral
Rudder—apply full opposite against rotation
Elevator—apply positive, forward of neutral, movement to break stall
Once the spin rotation stops, neutralize the rudder and begin applying back pressure to return to level flight.

Question 26

What causes adverse yaw?

Answer 26

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 less lift and less drag. This added drag attempts to pull or veer the airplane’s nose in the direction of the raised wing (right); that is, it tries to turn the airplane in the direction opposite to that desired. This undesired veering is referred to as adverse yaw.

Question 27

What is ground effect?

Answer 27

Ground effect is a condition of improved performance the airplane experiences when it is operating near the ground.

Question 28

What major problems can be caused by ground effect?

Answer 28

During landing, drag may be 40 percent less than when the airplane is operating out of ground effect. Therefore, any excess speed during the landing phase may result in a significant float distance. In such cases, if care is not exercised by the pilot, he/she may run out of runway and options at the same time.

During takeoff, due to the reduced drag in ground effect, the aircraft may
seem capable of takeoff well below the recommended speed. However,
as the airplane rises out of ground effect with a deficiency of speed, the
greater induced drag may result in very marginal climb performance, or
the inability of the airplane to fly at all.