BAvn Bachelor of Aviation Bachelor of Aviation Theory of Flight 5 — Questions and Answers
Question 1: What is 'P-factor' (asymmetric blade effect) and when is it most pronounced in a single-engine propeller aircraft?
- Gyroscopic precession when yawing; most pronounced at high speed in level flight
- The descending blade produces more thrust than the ascending blade; most pronounced at high power and high angle of attack (Correct answer)
- Propeller torque reaction; most pronounced during cruise at altitude
- Slipstream effect on the vertical stabilizer; most pronounced during sideslip
Correct answer: The descending blade produces more thrust than the ascending blade; most pronounced at high power and high angle of attack
P-factor occurs because the descending blade has a higher effective angle of attack than the ascending blade during high AoA flight, creating asymmetric thrust yawing toward the ascending blade side.
Question 2: In transonic flight, what is 'wave drag' and how does it arise?
- Drag from acoustic shockwaves radiating from the propeller tips at high RPM
- Drag resulting from the formation of shockwaves on the aircraft, converting kinetic energy into heat (Correct answer)
- Increased induced drag caused by compressibility effects reducing effective angle of attack
- Drag from vortex shedding at the wing-fuselage junction during buffet
Correct answer: Drag resulting from the formation of shockwaves on the aircraft, converting kinetic energy into heat
Wave drag arises when shockwaves form on the aircraft surface; the shockwave is a discontinuity that converts organized kinetic energy into thermal energy and entropy, creating drag.
Question 3: How does wing dihedral contribute to lateral-directional static stability?
- It shifts the center of gravity downward, increasing pendulum stability
- When the aircraft sideslips, the lower wing generates more lift than the upper wing, creating a restoring roll moment (Correct answer)
- It increases the aspect ratio, reducing induced drag and stabilizing yaw
- Dihedral moves the neutral point aft, improving pitch stability
Correct answer: When the aircraft sideslips, the lower wing generates more lift than the upper wing, creating a restoring roll moment
In a sideslip, the lower dihedral wing meets the airflow at a greater effective angle of attack, generating more lift and rolling the aircraft back toward wings-level.
Question 4: What is 'Dutch roll' and which design feature primarily counteracts it?
- A coupled roll-yaw oscillation; counteracted by a yaw damper system (Correct answer)
- A pitch-roll coupling in swept-wing aircraft; counteracted by anhedral design
- A high-frequency wing flutter mode; counteracted by mass balancers in the wingtips
- A porpoising pitch oscillation; counteracted by an auto-throttle system
Correct answer: A coupled roll-yaw oscillation; counteracted by a yaw damper system
Dutch roll is a coupled lateral-directional oscillation where yaw and roll reinforce each other; it is primarily damped by an electronic yaw damper system.
Question 5: When an aircraft transitions from subsonic to supersonic flight, what happens to the aerodynamic center (neutral point)?
- Moves from approximately the quarter-chord forward to the leading edge
- Moves from approximately the quarter-chord aft to approximately the mid-chord (50%) (Correct answer)
- Remains fixed at the quarter-chord point regardless of Mach number
- Moves forward from the quarter-chord to approximately the 10% chord position
Correct answer: Moves from approximately the quarter-chord aft to approximately the mid-chord (50%)
In supersonic flow, linearized theory places the aerodynamic center at the 50% chord, compared to the 25% chord (quarter-chord) position in subsonic flow.
Question 6: What is 'pitch coupling' (inertia coupling) and why is it a concern for high-speed aircraft?
- The tendency of a highly loaded elevator to cause oscillatory pitch at high dynamic pressure
- Cross-coupling of roll and pitch motions due to gyroscopic and inertial effects at high roll rates, potentially causing divergent oscillations (Correct answer)
- Aerodynamic coupling between elevator and aileron inputs in fly-by-wire systems
- Feedback between the autopilot pitch channel and the autothrottle at cruise altitude
Correct answer: Cross-coupling of roll and pitch motions due to gyroscopic and inertial effects at high roll rates, potentially causing divergent oscillations
Inertia coupling at high roll rates causes the pitch and yaw axes to interact through inertial moments, potentially exceeding structural limits or control authority.
Question 7: For a given aircraft at constant altitude, what happens to total drag as airspeed decreases below the minimum drag speed?
- Total drag decreases because parasite drag decreases faster than induced drag increases
- Total drag increases because the rise in induced drag more than offsets the reduction in parasite drag (Correct answer)
- Total drag remains approximately constant across a wide low-speed range
- Total drag decreases proportionally to the square of the speed reduction
Correct answer: Total drag increases because the rise in induced drag more than offsets the reduction in parasite drag
Below minimum drag speed (L/D max), the required angle of attack and lift coefficient increase rapidly, causing induced drag to rise faster than parasite drag falls, increasing total drag.
BAvn Bachelor of Aviation Bachelor of Aviation Theory of Flight 5
What is 'P-factor' (asymmetric blade effect) and when is it most pronounced in a single-engine propeller aircraft?