CLMAX Augmentation (High Lift Devices)

081-01-09Pablo Asensio Martínez2026-04-011 min

Purpose

To increase $C_{L_{max}}$ allows the aircraft to fly at lower speeds (Stall speed is reduced) safely for Take-off and Landing. $ V_{stall} = \sqrt{\frac{2W}{\rho S C_{L_{max}}}} $

Trailing Edge Flaps

Increase camber and (usually) surface area.

  1. Plain Flap: Simple looking hinge. Increases camber. Small $C_L$ increase.
  2. Split Flap: Lower surface hinges down. High Drag.
  3. Slotted Flap: Gap allows high energy air from bottom to re-energize boundary layer on top. Delays separation.
  4. Fowler Flap: Moves back and down. Increases Surface Area ($S$) and Camber. Very effective.

Effects:

  • Increases $C_{L_{max}}$ significantly (up to 50-90%).
  • Reduces Stalling Angle of Attack (e.g., from 16° to 12°).
  • Increases Drag (Desirable for landing).
  • Nose-down pitching moment.

Leading Edge Devices

  1. Krueger Flaps: Hinged flap on leading edge.
  2. Slats: Moveable leading edge section. Creates a Slot.
  3. Slots: Fixed gap.

Effects:

  • Re-energizes boundary layer.
  • Increases Critical Angle of Attack (e.g., from 16° to 22°).
  • Increases $C_{L_{max}}$.