Aircraft Performance and Forces Quiz

Theory of Flight

• Four forces act on an airplane: thrust, lift, weight, and drag.
• Thrust is the forward force propelling the airplane; it varies with engine power.
• Lift is the upward force created by airflow over and under the wings; it opposes weight.
• Weight is the downward pull of gravity.
• Drag is the backward force that resists the airplane's motion. It opposes thrust.

Introduction

• Students should be able to:
  • Describe the relationship between lift, weight, thrust, and drag.
  • Describe glide ratio.
  • Describe steady-state flight and performance.
  • Describe the theory of the turn.
  • Describe load factor (affecting stalling, flight envelope, and structural limitations).
  • Describe methods of lift augmentation.

Four Forces of Flight

• Lift is the upward force created by airflow around the wings.
• Weight is the downward force due to gravity.
• Thrust is the forward force that moves the aircraft.
• Drag is the backward force that opposes thrust

Vectors

• Arrows representing forces are called vectors.
• Vector length indicates force magnitude.
• Vector direction indicates force orientation.
• Combined forces create a resultant force.

Lift

• Lift is the key aerodynamic force opposing weight.
• Airplane equilibrium occurs when lift equals weight.
• Wings create lift by directing airflow to create high pressure below the wing and lower pressure above, generating a pressure differential.

Weight

• Weight acts downward through the aircraft center of gravity (CG).
• Lift is required to counteract weight.

Centre of Gravity

• The center of gravity (CG) is the point where all the aircraft's weight is concentrated.
• CG position affects stability.
• The designer of the aircraft will choose the centre of gravity in front of the center of pressure.

Adverse Forward Center of Gravity

• This shifts the CG forward, leading to:
  • Increased dive tendency.
  • Difficulty raising the nose during landing.
  • Increased oscillation tendency.
  • Increased stalling risk and danger.
  • Dangerous potential spin characteristics

Adverse Rear Center of Gravity

• This shifts the CG rearwards, potentially causing:
  • Decreased flying speed.
  • Decreased range.
  • Increased risk of stalls.
  • Dangerous spin characteristics.
  • Decreased stability.
  • Accident risk.

Effect of Stall Speed on Center of Gravity

• This section discusses the effect of stall speed on centre of gravity.

Aircraft Turn

• Turning an aircraft requires overcoming inertia.
• Banking the aircraft inclines lift, creating a horizontal component (centripetal force) to turn.

Turning Flight (Maintaining Altitude)

• To maintain altitude during a turn, lift must be increased by increasing back pressure that increases the angle of attack.
• This causes increase in the vertical component of lift, cancelling out the increase in weight.

Turning Flight and The V-n Diagram- Summary

• Various turning flight conditions exist: level turns, pull-ups, and pull-downs.
• Each condition has distinct altitude changes.

Level Turn (Coordinated Turn)

• During a level turn lift, a horizontal component is generated by banking the aircraft, creating a turning force.

Load Factor

• Load factor is the ratio of lift to weight, usually expressed in 'g's.
• Higher load factors mean greater stresses on the aircraft structure.

Load Factor During a Turn

• Lift during a turn is greater than lift in straight flight; this is due to the additional force required for the turn.

Wing Loading

• Wing loading is the ratio of an aircraft's weight to its wing area.
• Lower wing loading correlates to lower stall speed; higher wing loading correlates to higher stall speed.
• As weight increases, so does wing loading, potentially increasing stall speed.

Load Factor Angle of Bank

• Formula to calculate minimum speed during banking: W/L = cos θ or L = W/cos θ
• Example values for stall speeds at varying bank angles.

Maneuver Point

• The maneuver point is where the stall and structural limits intersect on the V-n diagram.