Cessna 172N Aerodynamics — PPL Oral Exam Questions

DPE oral questions · aerodynamics

10 questions a DPE may ask in this section

1. Question 1 · PA.I.G.K1

   What is angle of attack, and what is the critical angle of attack?

   What a DPE expects to hear

   • Angle of attack (AoA): the angle between the chord line and the relative wind
   • NOT the pitch attitude relative to the horizon
   • Every wing has a critical angle of attack — typically 15-18 degrees for most general aviation aircraft
   • At or beyond critical AoA, the wing stalls regardless of airspeed, pitch attitude, or power setting
   • A stall can occur at any airspeed, any attitude

   SourcePHAK FAA-H-8083-25C Chapter 5

2. Question 2 · PA.I.G.K2

   Explain load factor and how it relates to stall speed in turns.

   What a DPE expects to hear

   • Load factor (G): total lift / aircraft weight
   • In level coordinated turn: load factor increases
   • At 60° bank: load factor is 2G
   • Stall speed increases with load factor: stall speed in turn = normal stall speed × √G
   • At 60° bank: stall speed = 1.41 × Vs1

   SourcePHAK FAA-H-8083-25C Chapter 5

3. Question 3 · PA.I.G.K2

   What is Va (maneuvering speed) and what does it protect against?

   What a DPE expects to hear

   • Va is maneuvering speed — the maximum speed at which full or abrupt control deflection can be applied without exceeding structural load limits
   • At or below Va, the aircraft will stall before structural damage occurs from full control input
   • Va decreases as aircraft weight decreases (lighter aircraft is more susceptible)
   • Found in POH and is weight-dependent
   • Does NOT protect against repeated full control inputs or simultaneous multiple inputs

   SourcePHAK FAA-H-8083-25C Chapter 5; Aircraft POH

4. Question 4 · PA.I.G.K2

   Explain what causes torque effect and left-turning tendencies. Name all four.

   What a DPE expects to hear

   • Torque reaction: engine rotates clockwise, airframe tends to roll left
   • Spiraling slipstream: propwash hits the left side of the vertical stabilizer, yawing left
   • P-factor (asymmetrical thrust): in a high angle of attack, descending blade (right side) has a greater bite — more thrust on right, yaws left
   • Gyroscopic precession: propeller acts as a gyroscope; any pitch or yaw input creates a 90° lagged precession reaction

   SourcePHAK FAA-H-8083-25C Chapter 5

5. Question 5 · PA.I.G.K3

   What is ground effect and how does it affect takeoff and landing performance?

   What a DPE expects to hear

   • Ground effect occurs within approximately one wingspan of the ground
   • Reduces induced drag due to disruption of wingtip vortices
   • Takeoff: aircraft may lift off in ground effect at a speed insufficient to fly out of it — can sink back to runway or settle into obstacles
   • Landing: aircraft may float in ground effect past intended touchdown point
   • Pilots should not rotate too early and must ensure aircraft can climb out of ground effect before obstacle clearance

   SourcePHAK FAA-H-8083-25C Chapter 5; AFH FAA-H-8083-3C

6. Question 6 · PA.I.G

   What is maneuvering speed for our flight today, and why does that number change if I bring my heavy cousin?

   What a DPE expects to hear

   • Va = speed at which aircraft stalls before exceeding limit load factor
   • Decreases as weight decreases — lighter aircraft more easily accelerated by gust

   SourcePHAK Chapter 5; POH Section 2

7. Question 7 · PA.I.G

   Point to the flaps. Point to the ailerons. Explain the difference in primary function.

   What a DPE expects to hear

   • Flaps inboard — increase lift AND drag for takeoff/landing
   • Ailerons outboard — control roll by moving opposite directions

   SourcePHAK Chapter 6; ACS Task IV.A

8. Question 8 · PA.I.G

   Can you enter a spin without stalling first? What causes the aircraft to actually start spinning?

   What a DPE expects to hear

   • No — stall must occur first
   • Spin caused by uncoordinated stall — one wing more deeply stalled than the other due to yaw during stall

   SourcePHAK Chapter 5; ACS Task VII.D

9. Question 9 · PA.I.G

   During soft-field takeoff, why do we stay level just above the surface before climbing?

   What a DPE expects to hear

   • Remain in ground effect to allow acceleration to safe climb speed while eliminating high drag of soft surface
   • Ground effect reduces induced drag — aircraft can fly below normal climb speed which would be dangerous if you climbed immediately

   SourceACS Task IV.C; PHAK Chapter 5

10. Question 10 · PA.I.G

    When you initiate a go-around, why do we retract flaps to 20° immediately but wait later for the rest?

    What a DPE expects to hear

    • Retracting first notch (30° to 20°) removes significant parasite drag without losing much lift — allows acceleration and climb
    • Retracting remaining flaps too early could cause aircraft to sink because stall speed increases as flaps retract

    SourcePOH Section 4; ACS Task IV.N