BAvn Bachelor of Aviation Bachelor of Aviation Theory of Flight 3 — Questions and Answers
Question 1: What is the standard definition of 'critical Mach number' (Mcrit)?
- The speed at which the aircraft first achieves supersonic flight
- The freestream Mach number at which airflow over some part of the wing first reaches Mach 1.0 (Correct answer)
- The Mach number at which shock-induced separation causes a buffet
- The speed at which wave drag becomes greater than induced drag
Correct answer: The freestream Mach number at which airflow over some part of the wing first reaches Mach 1.0
Mcrit is the lowest freestream Mach number at which local airflow on the wing surface first accelerates to exactly Mach 1.0.
Question 2: During a symmetric pull-up maneuver, which structural limit is the primary concern?
- Torsional divergence of the wing
- Exceeding the positive limit load factor (Correct answer)
- Compressor stall due to increased angle of attack
- Exceeding VMO/MMO
Correct answer: Exceeding the positive limit load factor
A pull-up maneuver increases load factor; exceeding the aircraft's positive limit load factor risks structural damage or failure.
Question 3: What physical explanation accounts for the Bernoulli principle generating lift on a cambered airfoil?
- Air traveling over the top must travel faster to rejoin air below, increasing static pressure on top
- The curved upper surface accelerates airflow, reducing static pressure relative to the lower surface (Correct answer)
- The flat lower surface deflects air downward, creating an equal and opposite reaction upward
- Air molecules impacting the lower surface at an angle create a pressure wave that lifts the wing
Correct answer: The curved upper surface accelerates airflow, reducing static pressure relative to the lower surface
Camber causes faster flow over the upper surface, reducing static pressure there compared to the lower surface, creating a net upward pressure force.
Question 4: An aircraft experiences 'Mach tuck.' What is the recommended immediate recovery action?
- Apply back pressure on the elevator and extend speed brakes
- Reduce thrust, extend speed brakes, and allow the aircraft to decelerate below Mcrit (Correct answer)
- Roll inverted and pull through to reduce altitude and airspeed quickly
- Advance thrust to supersonic speed to stabilize the shockwave
Correct answer: Reduce thrust, extend speed brakes, and allow the aircraft to decelerate below Mcrit
Mach tuck recovery requires slowing the aircraft below Mcrit by reducing thrust and deploying speed brakes, allowing the shockwave to dissipate.
Question 5: Which factor most directly determines the stall speed of an aircraft at a given weight?
- Maximum coefficient of lift (CLmax) and wing area (Correct answer)
- Wing sweep angle and aspect ratio
- Thrust-to-weight ratio
- Fuselage cross-sectional area
Correct answer: Maximum coefficient of lift (CLmax) and wing area
Stall speed is governed by Vs = sqrt(2W / (ρ × S × CLmax)), making wing area and maximum lift coefficient the primary aerodynamic determinants.
Question 6: What is 'spanwise flow' on a swept-wing aircraft and why is it significant?
- Airflow that moves from leading edge to trailing edge parallel to the aircraft centerline
- Chordwise flow that separates at the leading edge under high AoA conditions
- Outward flow along the span from root to tip, promoting tip stall and reducing aileron effectiveness (Correct answer)
- Supersonic flow behind a shockwave on the outer wing panels
Correct answer: Outward flow along the span from root to tip, promoting tip stall and reducing aileron effectiveness
Swept wings promote spanwise flow toward the tips, causing the boundary layer to thicken there first and producing tip stall before root stall.
Question 7: When an aircraft's weight increases, how does the induced drag change at a constant true airspeed?
- Induced drag decreases because more lift is generated efficiently
- Induced drag increases because a higher angle of attack is required (Correct answer)
- Induced drag remains constant as it depends only on wing geometry
- Induced drag decreases proportionally to the weight increase
Correct answer: Induced drag increases because a higher angle of attack is required
Greater weight requires a higher angle of attack to maintain lift, which increases the lift coefficient and thereby increases induced drag.
BAvn Bachelor of Aviation Bachelor of Aviation Theory of Flight 3
What is the standard definition of 'critical Mach number' (Mcrit)?