flight mechanics

at which aerodynamic expression is the highest cruise velocity occurring

Cl^(1/2)/Cd

what is the primary advantage of a high aspect ratio wing

low induced drag - Low induced drag means the aircraft produces lift efficiently with minimal energy loss

what is the primary motivation for swept wings?

higher drag divergence mach number, essentially, swept wings let planes fly faster by delaying transonic drag

name three geometric features of an airplane that determine the amount of dihedral

• Wing mounting angle – The angle at which the wing is attached to the fuselage affects dihedral.

• Wing position – High-wing aircraft often need less dihedral; low-wing aircraft typically require more for stability.

• Wing planform shape – Tapered or swept wings can influence how much dihedral is needed for lateral stability.

5 factors that effect ground roll length

• air density at airport

• Cl max

• thrust available

• wing area

• ground roll friction

• weight of aircraft

how is a small turn radius with a high turn rate achieved (therefore high manoeuvrability)

• at a low altitude

• small wing loading

• large Cl max

• large n max

T or F : The generation of a rolling moment following a sideslip perturbation is known as the dihedral effect.

✅ Correct

• The dihedral effect refers to the rolling moment generated by sideslip (yawing into the wind).

• It contributes to lateral stability: when the airplane rolls and sideslips, the geometry causes the aircraft to roll back toward level flight.

T or F: Two airplanes cruise at the same altitude. They carry different payloads but are otherwise identical. In order to maximise range, the one with more payload needs to fly faster than the one with less payload.

✅ Correct

• For a heavier airplane, the lift required is greater, which increases the required speed to stay at optimal L/D.

• Maximum range for jet aircraft occurs at max L/DL/DL/D, and for the same configuration, the heavier airplane must fly faster to maintain this.

T or F: The Oswald efficiency factor depends on the airplane geometry

• True

• The Oswald efficiency factor accounts for non-elliptic lift distribution, wing shape, aspect ratio, and interference.

• It’s a geometric correction in the drag polar

T or F: The flight speed that minimises drag is larger than the flight speed which minimises power required.

✅ Correct

• For propeller aircraft:

  • Minimum drag occurs at higher speed (max L/DL/DL/D)

  • Minimum power required is at lower speed, because power = drag × velocity

• Graphically, on a power required curve, the min drag point is right of the min power point.

T or F: In order to maximise the angular velocity in a level-turn, an airplane needs to be flown close to the stall effect.

• TRUE

• Angular velocity in a level turn:

  To maximize ANGULAR VELOCITY fly at low speed (near stall) and high bank angle.

• Therefore, max turn rate occurs near minimum speed, just above stall.

T or F: The horizontal tail of a classically configured airplane is needed to generate sufficient lift to balance the airplane weight.

❌ Incorrect

• The wing generates most of the lift to support the airplane weight.

• The horizontal tail often produces downforce, not lift, to balance pitching moments, not weight.

T or F: In order to trim an airplane after unsymmetric engine failure (assume sufficient thrust is still available) it needs to be flown at a negative sideslip angle.

❌ Incorrect

• To counter asymmetric thrust (e.g., engine failure), the aircraft must fly with a positive sideslip angle into the working engine, using rudder to balance yawing moment.

T or F: Wing sweepback decreases the dihedral effect.

❌ Incorrect

• Wing sweep actually increases dihedral effect.

• The sweep makes the wingtip more rearward, increasing the restoring rolling moment from a sideslip.

T or F: The adverse yaw effect can be controlled by appropriate elevator deflection.

❌ Incorrect

• Adverse yaw is a yawing motion due to aileron drag, not pitch.

• It must be corrected with rudder, not elevator.

T or F: Directional stability is independent from lateral and longitudinal motion.

❌ Incorrect

• While analytically separable, real flight involves coupled motions:

  • Yaw affects roll (via dihedral effect)

  • Roll affects yaw (via adverse yaw)

• So, directional, lateral, and longitudinal motions are interdependent.

T or F: Propeller-driven airplanes can stay airborne for longer at high altitudes.

❌ Incorrect

• At high altitudes, air density is lower, reducing engine power and propeller efficiency.

• Jet engines benefit more at high altitudes due to efficiency at high speeds and lower drag.

T or F: Fuel consumption of jet-propelled airplanes per distance flown is minimal at the flight velocity associated with minimum drag.

❌ Incorrect

• Minimum fuel per distance is at maximum L/D, not minimum drag.

• These speeds are close, but not identical — especially for jets.

T or F: Longitudinal static stability requires that the centre of gravity of a classically configured airplane is located behind the neutral point.

❌ Incorrect

• It’s the opposite:

  • For positive longitudinal static stability, CG must be ahead of the neutral point.

T or F: The runway length for take-off is approximately proportional to the airplane weight.

❌ Incorrect

• Take-off distance depends on weight squared in simplified models:

  So, runway length increases faster than linearly with weight.

T or F: Induced drag increases as an airplane flies faster.

❌ Incorrect

• Induced drag decreases with speed because:

  So as velocity increases, CLC_LCL​ decreases and so does induced drag.

T or F: Wave drag occurs when the aeroplane is exposed to headwind gusts at regular intervals.

❌ Incorrect

• Wave drag is a compressibility effect in transonic and supersonic flight.

• It's caused by shock waves forming on the aircraft, not due to gusts.

T or F: The primary purpose of wing sweep is to reduce induced drag.

❌ Incorrect

• The primary purpose of wing sweep is to delay the onset of shock waves and increase the drag divergence Mach number.

• It helps in transonic flight, but it actually increases induced drag at low speeds.

T or F: Propeller-driven aeroplanes can stay airborne for longer at high altitudes.

❌ Incorrect

• Propeller efficiency drops at high altitudes due to lower air density.

• In general, jet aircraft benefit more from high-altitude cruise.

T or F: The horizontal tail of a classically configured aeroplane is needed to generate sufficient lift to balance the aeroplane weight.

❌ Incorrect

• The wings primarily support the aircraft weight.

• The horizontal tail provides pitch stability, often generating downforce, not lift.

T or F: Lift and drag forces are oriented, respectively, perpendicular and parallel to the zero-lift line of an aeroplane.

❌ Incorrect

• Lift and drag are defined relative to the free stream airflow (flight path), not the zero-lift line.

• The zero-lift line is a geometric property of the airfoil; forces don’t align to it in general.

T or F: The generation of a rolling moment following a sideslip perturbation is known as the dihedral effect.

✅ Correct
This defines the dihedral effect, a key lateral stability mechanism.

T or F: The flight speed that minimises drag is larger than the flight speed which minimises power required.

✅ Correct

• True for propeller-driven aircraft:

  • Minimum drag at higher speed than minimum power.

  • On the power curve, min power occurs left of min drag.

T or F: In order to maximise the angular velocity in a level-turn, an aeroplane needs to be flown close to the stall effect.

✅ Correct

• To maximise turn rate (ω=gtan⁡ϕV\omega = \frac{g \tan\phi}{V}ω=Vgtanϕ​), reduce speed — close to stall.

• So yes, it's near the stall but not stalling.

T or F: Adverse yaw can be corrected by rudder deflection.

✅ Correct

• Adverse yaw is caused by differential aileron drag.

• It's countered by coordinated rudder input.

T or F: The minimum glide angle of an aeroplane is independent of the air density

✅ Correct

• Glide angle depends on L/D​, which is independent of air density — it's a ratio of forces.

T or F: Minimum thrust required by a jet aeroplane at higher altitude is equal to the minimum thrust required at sea-level.

✅ Correct

• Somewhat nuanced. Although thrust available drops with altitude, the minimum thrust required (for steady level flight) at high altitude can remain similar, since drag is also lower.

• This is theoretically true under ideal assumptions.

T or F: The runway length for take-off is approximately proportional to the square of the aeroplane weight.

✅ Correct

• From energy balance:

  So yes, takeoff distance increases quadratically with weight.

T or F: The Oswald efficiency factor depends on the aeroplane geometry.

✅ Correct

• The Oswald efficiency factor eee adjusts for non-elliptic lift distribution and depends on:

  • Aspect ratio, wing planform, and configuration.

T or F: The phenomena of flutter, wing divergence and excessive pressure in the stagnation point impose a maximum flight speed.

✅ Correct

• These are aeroelastic or compressibility limits (e.g., V_NE, Mach buffet, flutter speed).

• They all define a structural or aerodynamic speed limit.

T or F: Induced drag decreases as an aeroplane flies faster.

✅ Correct

• As speed V increases, CLC_LCL​ and induced drag decrease.

Name the three major design criteria which determine the amount of dihedral of
a classically configured aeroplane.

• wing placement on the wing (whether its high wing or low wing)

• dihedral angle

• wing sweep