Straight and Level

Aim

To understand the forces which affect the aircraft during straight and level flight, and to maintain constant height at varying airspeeds.

Objectives

1. To recall from memory the power setting used for straight and level flight in a normal cruise configuration.

2. From memory, identify the four forces acting on an aeroplane in a straight and level flight.

3. Correctly recall from memory, the 2 work cycles to configure and maintain an aircraft for straight and level flight.

Work Cycles

• Changing Cruise (PAST)

  • Power

  • Attitude

  • Speed

  • Trim

• Maintaining Cruise (ALAP)

  • Attitude

  • Lookout

  • Attitude

  • Performance

Briefing Notes

• Four forces for straight and level flight

  1. Weight

  • BEW Basic Empty Weight

  • MTOW Maximum Take-Off Weight

  • TOW Take-Off Weight

  2. Lift

  • Increase AoA against decrease IAS and vice-versa

  • The lift equation, lift coefficient (Cl)

    • L = Cl * (A * .5 * r * V^2)

    • Cl = L / (A * .5 * r * V^2)

  3. Drag

  4. Induced Drag

  * By-product of lift
  
  * Decreases as IAS increases

  2. Parasite Drag

  * Types
  
    * Form
  
    * Skin Friction
  
    * Interference
  
  * Increases as IAS increases, not as much as induced drag

  • Horizontal stabiliser accounts for higher induced drag against parasite drag as IAS increases
  4. Thrust
  • thrust = drag at straight and level

• Stability

  • Types

    • Positive

    • Neutral

    • Negative

  • Axes

    • Longitudinal axis

      • Axis on which aircraft rolls

      • Stability of pitch

      • Positive stability

    • Lateral axis

      • Axis on which aircraft pitches

      • Stability of roll

      • Neutral stability

    • Directional axis

      • Axis on which aircraft yaws

      • Positive stability

• Application

  • Normal cruise

    • Power = 2300 rpm

    • “5 fingers” attitude

    • Gives performance = 100KIAS

  • Fast cruise

    • Power = 2500rpm

    • “6 fingers” attitude

    • Gives performance = 110KIAS

  • Slow cruise

    • Power = 2100rpm

    • “4 fingers” attitude

    • Gives performance = 80KIAS

  • Slow cruise (with flaps)

    • Power = 2100rpm

    • “5 fingers” attitude

    • Gives performance = 70KIAS

Handout