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Aerodynamics

3-1 The four forces acting on an airplane in flight are

A - lift, weight, thrust, and drag
B - lift, weight, gravity, and thrust
C - lift, gravity, power, and friction

3-1 Answer A GFDPPM 3-2 (AFH) In normal (nonacrobatic) flight conditions, lift is the upward force created by airflow over
and under the wings. Weight, caused by the down ward pull of gravity, opposes lift. Thrust is the forward force which
prpels the airplane, and drag is the retarding force opposing thrust. Answer (B) does not include drag, and , while gravity
causes weight, it usually is not considered on tf the four forces. Answer(C) is also wrong because, while power and
friction affect thrust and drag, they are not aerodynamic forces.

3-2 When are the four forces that act on an airplane in equilibrium?
A - During unaccelerated flight. - Correct
B - When the aircraft is accelerating.
e - When the aircraft is at rest on the ground.
3-2. Answer A. GFDPPM 3-3 (AFH) In straight-and-Ievel, unaccelerated flight, the four forces are in equilibrium. Lift equals weight, and thrust equals drag. Answer (6) would require thrust to be greater than drag in order for the aircraft to accelerate.
Answer (C) is wrong because only weight is acting on the airplane. Lift, drag, and thrust are zero (assuming no wind).

3-3 (Refer to figure 1.) The acute angle A is the angle of

A - incidence.
B - attack. - Correct
C - dihedral.
3-3. Answer B. GFDPPM 3-5 (PHB) The angle between the chord line and the relative wind is the angle of attack. Answer (A) cannot be correct because the angle of incidence is the angle between the wing chord line and the longitudinal axis of the air- ~ plane. Answer (C) is wrong because dihedral is the upward angle of the wings in relation to the lateral axis of the airplane

3-4 The term "angle of attack" is defined as the angle

A - between the wing chord line and the relative wind. - Correct
B - between the airplane's climb angle and the horizon.
C - formed by the longitudinal axis of the airplane and the chord line of the wing.
3-4. Answer A. GFDPPM 3-4 (PHB) The angle of attack is the angle between the chord line and the relative wind. Answer (6) does not describe any aerodynamic term. Answer (C) describes the angle of incidence.


3-5 What is the relationship of lift, drag, thrust, and weight when the airplane is in straight-and-Level flight?

A - Lift equals weight and thrust equals drag. - Correct
B - Lift, drag, and weight equal thrust.
C - Lift and weight equal thrust and drag.

3-5. Answer A. GFDPPM 3-3 (AFH) Assuming the airplane is not accelerating, thrust equals drag, and lift equals weight. Answers (6) and (C) are wrong because all four forces do not have to be equal. Thrust must be equal to drag, and lift equal to weight.



3-6 One of the main functions of flaps during approach and landing is to

A - decrease the angle of descent without increasing the airspeed.
B - permit a touchdown at a higher indicated airspeed.
C - increase the angle of descent without increasing the airspeed.

3-6. Answer C. GFDPPM 3-12 (AFH) Because flaps increase lift, induced drag is also increased, thus allowing a steeper angle of descent without increasing airspeed. Answer (A) is wrong because the angle of descent can be increased.
Answer (B) is wrong since flaps increase lift, thereby allowing touchdown at a lower airspeed.


3-7 What is one purpose of wing flaps?

A - To enable the pilot to make steeper approaches to a landing without increasing the airspeed.
B - To relieve the pilot of maintaining continuous pressure on the controls.
C - To decrease wing area to vary the lift.
3-7. Answer A. GFDPPM 3-12 (AFH) Flaps increase both lift and induced drag, allowing a steeper descent without increasing airspeed. Answer (B) is wrong because flaps simply increase the cambe of the wing. Trim must still be applied to relieve control pressure. Answer (C) is not correct because most flap change the wing area very little. Some flaps will increase wing area, but none will decrease it.



3-8 The angle of attack at which an airplane wing stalls will

A - increase if the CG is moved forward.
B - change with an increase in gross weight.
C - remain the same regardless of gross weight.
3-8. Answer C. GFDPPM 3-6 (FTP) The critical angle of attack (angle of attack at which ar airplane stalls) is determined by the lift coefficient of a particular wing configuration. An airplane will stall when the critical angle of attack is exceeded, regardless of weight or airspeed. Answers (A) and (B) are wrong because the center of gravity (CG) and weight do not affect the critical angle of attack.


3-9 What is ground effect?

A - The result of the interference of the surface of the Earth with the airflow patterns about an airplane.
B - The result of an alteration in airflow patterns increasing induced drag about the wings of an airplane.
C - The result of the disruption of the airflow patterns about the wings of an airplane to the point where the wings will no longer support the airplane in flight.

3-9. Answer A. GFDPPM 3-18 (AFH) When flying close to the ground, the airflow around an airplane is altered by interference with the surface of the earth. The resulting ground effect reduces the induced drag on the airplane. Answer (B) is wrong because the induced drag is reduced, not increased.
Answer (C) is wrong because the upwash and downwash of airflow on the wing is reduced, and the airplane can fly at lower speeds.



3-10 Floating caused by the phenomenon of ground effect will be most realized during an approach to land when at

A - less than the length of the wingspan above the surface.
B - twice the length of the wingspan above the surface.
C - a higher-than-normal angle of attack.


3-10. Answer A. GFDPPM 3-18 (AFH) Ground effect becomes noticeable when the height of the airplane above the ground is less than the length I the wingspan. Answer (B) is wrong because it states twice the length of the wingspan. Answer (C) is wrong because ground effect is not a result of angle of attacl and at a higher angle of attack, airspeed will be lower so that floating is decreased.



3·11 What must a pilot be aware of as a result of ground effect?

A - Wingtip vortices increase creating wake turbulence problems for arriving and departing aircraft.
B - Induced drag decreases; therefore, any excess speed at the point of flare may cause considerable floating.
C - A full stall landing will require less up elevator deflection than would a full stall when done free of ground effect.


3-11. Answer B. GFDPPM 3-18 (AFH) Since ground effect decreases induced drag, the air- _ plane tends to float while excess speed bleeds off.
Answer (A) is wrong because the reduction in induced drag causes wingtip vortices to decrease. Answer (C) is wrong because the wings produce more lift in ground effect than out of ground effect. Therefore, more up elevator deflection would be required.



3·12 Ground effect is most likely to result in which problem?

A - Settling to the surface abruptly during landing.
B - Becoming airborne before reaching recommended takeoff speed.
C - Inability to get airborne even though airspeed is sufficient for normal takeoff needs.

3-12. Answer B. GFDPPM 3-18 (AFH) The decreased induced drag while in ground effect allows the airplane to become airborne at a lower airspeed. This may fool you into thinking the airplane is capable of flying at the lower airspeed when you climb out of ground effect.
Answer (A) is wrong because ground effect tends to cause an airplane to float during landing, not settle abruptly. Answer (C) is wrong because ground effect allows an airplane to become airborne at a lower than normal airspeed.

3-12A Which statement relates to Bernoulli's principle?

A - For every action there is an equal and opposite reaction.
B - An additional upward force is generated as the lower surface of the wing deflects air downward.
C - Air traveling faster over the curved upper surface of an airfoil causes lower pressure on the top surface.

3-12A. Answer C. GFDPPM 3-4 Bernoulli's principle, from Swiss mathematician, Daniel Bernoulli, simply states that as the velocity of a fluid (including air), increases, its internal pressure decreases.

3-12B The angle between the chord line of an airfoil and the relative wind is known as the angle of

A -lift.
B - attack.
C - incidence.

3-12B. Answer B. GFDPPM 3-5 In addition to knowing the relationship of relative wind and angle of attack, remember that angle of attack is not an angle that is relative to the horizon or the aircraft's pitch in relationship to the ground. For example, the critical angle of attack, at which a wing will always stall, can occur in any flight attitude.

3-12C Changes in the center of pressure of a wing affect the aircraft's

A -lift/drag ratio.
B -lifting capacity.
C - aerodynamic balance and controllability.

Aerodynamic Principles

3-12C. Answer C. GFDPPM 3-4 (PH B) A wing's center of pressure moves forward and back with changing angles of attack (forward for high angles and back for lower). This movement changes the position of the air loads on the wing, which results in changes to an airplane's aerodynamic balance and controllability.


3-13 An airplane said to be inherently stable will

A - be difficult to stall.
B - require less effort to control.
C- not spin.

3-13. Answer B. GFDPPM 3-22 (PHS) An airplane that is inherently stable tends to return to its original attitude after it has been displaced, and is therefore easier to control. Answers (A) and (C) are wrong because stability does not prevent you from stalling or spinning an airplane.

3-14 What determines the longitudinal stability of an airplane?

A - The location of the CG with respect to the center of lift.
B - The effectiveness of the horizontal stabilizer, rudder, and rudder trim tab.
C - The relationship of thrust and lift to weight and drag.

3-14. Answer A. GFDPPM 3-26 (PHS) The longitudinal stability of an airplane is determined primarily by the location of the center of gravity (CG) in relation to the center of lift. Answer (B) is wrong because the rudder and rudder trim tab affect the directional stability. Answer (C) is wrong because this relationship affects acceleration, but not longitudinal stability.


3-15 What causes an airplane (except a T-tail) to pitch nosedown when power is reduced and controls are not adjusted?

A - The CG shifts forward when thrust and drag are reduced.
B - The downwash on the elevators from the propeller slipstream is reduced and elevator effectiveness is reduced.
C - When thrust is reduced to less than weight, lift is also reduced and the wings can no longer support the weight.

3-15. Answer B. GFDPPM 3-30 (PHB) At higher power settings, in airplanes other than Hail designs, the propeller slipstream causes a greater downward force on the horizontal stabilizer. When power is reduced, this downward force on the tail is also reduced, and the nose pitches down. Answer (A) is wrong because CG is determined by how an airplane is built and loaded, and is not affected by changes in thrust and drag. Answer (C) is also wrong because most airplanes can fly with thrust less than the weight.

3-16 Not Used

3-17 An airplane has been loaded in such a manner that the CG is located aft of the aft CG limit. One undesirable flight characteristic a pilot might experience with this airplane would be

A - a longer takeoff run.
B - difficulty in recovering from a stalled condition.
C - stalling at higher-than-normal airspeed.

3-17. Answer B. GFDPPM 3-28 (AFH) With a CG aft of the rear CG limit, the airplane becomes tail heavy and unstable in pitch because the horizontal stabilizer is less effective. This condition makes it difficult, if not impossible, to recover from a stall or spin. Answer (A) is wrong because an aft CG tends to shorten the takeoff run, and it may cause the airplane to pitch up and lift off early at a lower than normal airspeed. Answer (C) is wrong because an airplane with an aft CG requires less downward force on the tail. The airplane can fly at a lower angle of attack and will stall at a lower airspeed.

3-18 Loading an airplane to the most aft CG will cause the airplane to be

A -less stable at all speeds.
B -less stable at slow speeds, but more stable at high speeds.
C - less stable at high speeds, but more stable at low speeds.

3-18. Answer A. GFDPPM 3-28 (AFH) In an airplane loaded to the aft CG limit, the horizontal stabilizer is less effective, causing the airplane to be less stable at all speeds. Answers (B) and (C) are wrong because an aft-loaded airplane is less stable at all speeds.

3-19 In what flight condition must an aircraft be placed in order to spin?

A - Partially stalled with one wing low
B - In a steep diving spiral
C- Stalled


3-19. Answer C. GFDPPM 3-39 (AFH) An airplane must be stalled before a spin can develop.
Answer (A) is wrong because a spin occurs when both wings are in a stalled condition, with one wing more completely stalled than the other. Answer (B) is wrong because an airplane may be put into a steep diving spiral without being stalled.


3-20 During a spin to the left, which wing(s) is/are stalled?



A - Both wings are stalled.
B - Neither wing is stalled.
C - Only the left wing is stalled.

3-20. Answer A. GFDPPM 3-39 (AFH) In a spin, both wings are stalled. Answers (B) and (C) are wrong because both wings must be stalled for a spin to develop, although the outside wing may be less fully stalled than the inside wing.


3-21 In what flight condition is torque effect the greatest in a single-engine airplane?

A - Low airspeed, high power, high angle of attack.
B - Low airspeed, low power, low angle of attack.
C - High airspeed, high power, high angle of attack.

3-21. Answer A. GFDPPM 3-47 (PHS) Torque effect is greatest at low airspeeds, high power settings, and high angles of attack. Answer (8) is wrong because these conditions produce the least amount of torque effect. Answer (C) is also wrong because it includes high airspeed.

3-22 The left turning tendency of an airplane caused by Pfactor is the result of the

A - clockwise rotation of the engine and the propeller turning the airplane counter-clockwise.
B - propeller blade descending on the right, producing more thrust than the ascending blade on the left.
C - gyroscopic forces applied to the rotating propeller blades acting 90° in advance of the point the force was applied.

3-22. Answer B. GFDPPM 3-49 (PHB) P-factor, or asymmetric propeller loading, normally occurs at a high angle of attack. The descending propeller blade on the right side takes a larger "bite" of the air, and produces more thrust than the ascending blade on the left. The result is a left turning tendency of the airplane. Answer (A) describes torque reaction, not P-factor. Answer (C) describes gyroscopic precession, not P-factor.


3-23 When does P-factor cause the airplane to yaw to the left?

A - When at low angles of attack.
B - When at high angles of attack.
C - When at high airspeeds.

3-23. Answer B. GFDPPM 3-49 (PHB) P-factor is most pronounced at high angles of attack, which cause the descending propeller blade to produce more thrust. Answer (A) is wrong because at low angles of attack, thrust produced by the ascending and descending propeller blades is almost equalized.
Answer (C) is wrong because at high airspeeds, the angle of attack is lower, thus reducing the P-factor.

3-24 (Refer to figure 2 on page 3-10.) If an airplane weighs 2,300 pounds, what approximate weight would the airplane structure be required to support during a 60° banked turn while maintaining altitude?

A - 2,300 pounds.
B - 3,400 pounds.
C - 4,600 pounds.

3-24. Answer C. GFDPPM 3-60 (PHB) At 60 degrees of bank, 2 G's are required to maintain level flight. This means that the airplane's wing structure must support twice the airplane's weight, or 2,300 x 2 = 4,600 pounds. Answer (A) reflects 1 G, or straight-and-Ievel flight. Answer (8) is correct only if 1.48 G's (approximately 50° bank) are applied.

3-25 (Refer to figure 2 on page 3-10.) If an airplane weighs 3,300 pounds, what approximate weight would the airplane structure be required to support during a 30° banked turn while maintaining altitude?

A -1,200 pounds.
B - 3,100 pounds.
C - 3,960 pounds.

3-25. Answer C. GFDPPM 3-60 (PH B) The load factor for 30 degrees of bank is 1.154, or about 1.2. The airplane weight (3,300) multiplied by the load factor (1.2) is 3,960 pounds which the wing structure must support. Answers (A) and (8) are both wrong because the weights are less than the airplane weight.

3-26 (Refer to figure 2 on page 3-10.) If an airplane weighs 4,500 pounds, what approximate weight would the airplane structure be required to support during a 45° banked turn while maintaining altitude?

A - 4,500 pounds.
B - 6,750 pounds.
C - 7,200 pounds.

3-26. Answer B. GFDPPM 3-60 (PHB) At 45 degrees of bank the load factor is 1 .414, or approximately 1.5, the wing loading would be 4,500 x 1.5, or 6,750 pounds. Answer (A) reflects only 1 G, and is therefore incorrect. Answer (C) is wrong because 1.6 G's are required to produce a load of 7,200 pounds.
Therefore, (8) is the closest correct answer.



3-27 The amount of excess load that can be imposed on the wing of an airplane depends upon the

A - position of the CG.
B - speed of the airplane.
C - abruptness at which the load is applied.

3-27. Answer B. GFDPPM 3-64 (PHS) The amount of excess load that can be imposed on an airplane depends on its speed. If abrupt control movements or strong gusts are applied at low airspeeds, the airplane will stall before the load becomes excessive. At higher airspeeds, the increased airflow causes a greater lifting capacity. A sudden control input or gust at a high airspeed may result in an excessive load factor beyond safe limits. Answer (A) is wrong because position of the CG does not affect the load factor on the wings. Answer (C) is wrong because the amount of excess load depends on both the speed and total load. Although abruptness does affect the total load on the airplane, the determining factor is airspeed.

3-28 Which basic flight maneuver increases the load factor on an airplane as compared to straight-and-level flight?

A- Climbs.
B -Turns.
C - Stalls.

3-28. Answer B. GFDPPM 3-60 (PHS) In a level turn, lift must be increased to compensate for the loss of vertical lift as well as overcome centrifugal force. Since the wings must support not only the airplane's weight, but also the load imposed by centrifugal force, the load factor is greater than 1 G. Answer (A) is wrong because once established in a climb, there is no additional load factor imposed on the airplane. Answer (C) is wrong because when an airplane is in a stalled condition, it is producing insufficient lift, and the load factor decreases below 1 G.

3-29 What force makes an airplane turn?

A - The horizontal component of lift.
B - The vertical component of lift.
C - Centrifugal force.

3-29. Answer A. GFDPPM 3-56 (PHB) In a turn, lift has both a vertical and a horizontal component. The horizontal component of lift, which is also referred to as centripetal force, opposes centrifugal force and causes the airplane to turn. Answer (B) is wrong because the vertical component of lift opposes weight. Answer (C) is wrong because centrifugal force acts outward from the turn and opposes the horizontal component of lift.

3-30 During an approach to a stall, an increased load factor will cause the airplane to

A - stall at a higher airspeed.
B - have a tendency to spin.
C - be more difficult to control.

3-30. Answer A. GFDPPM 3-61 (PHB) Stall speed increases in proportion to load factor. Added G-forces cause an airplane to stall at an airspeed higher than the normal 1 G airspeed. Answer (B) is wrong because load factor normally does not affect an airplane's tendency to spin. Answer (C) is wrong because load factor does not affect controllability. Rather, this is a function of the airplane's stability.

3-31 Reserved

3-32 Select the four flight fundamentals involved in maneuvering an aircraft.

A -Aircraft power, pitch, bank, and trim.
B -Starting, taxiing, takeoff, and landing.
C -Straight-and-level flight, turns, climbs, and descents.

3-32. Answer C. (AFH) All controlled flight consists of one of the four fundamental maneuvers or some combination of them.
 

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Last modified: 06/17/09