High-Lift Systems (aerodynamics/high-lift/high-lift-systems)
Use when the task is high-lift device selection and performance: flap and slat clmax increments, wing maximum lift coefficient, and the stall speed that results.
Domain quick reference
Trailing-edge flaps raise the section clmax by an increment that depends on flap type, deflection, flap chord ratio, and flapped span fraction. Reference increments at full deflection and a flap chord ratio near 0.25 (widely cited textbook estimates, Raymer Aircraft Design: A Conceptual Approach, DATCOM-style scaling):
Delta clmax = Delta clmax_ref * K_delta * K_chord * K_span K_delta = sin(delta) / sin(delta_max), clamped at delta_max K_chord = (c_f / c) / (c_f / c)_ref K_span = flapped span fraction
Typical section clmax increments at full deflection (chord ratio near 0.25, full span): plain 0.9, split 0.9, slotted 1.3, Fowler 1.6. A Fowler flap extends the chord, adding extension chord as c_f = c_f_base + extension_frac * c.
Leading-edge devices add a further increment: a full-span slat about 0.4, a partial-span slat scaled by span fraction, a Krueger flap about 0.3.
Wing-level CLmax applies a three-dimensional and sweep reduction: CLmax_wing = 0.9 * clmax_section * cos(Lambda) with the sweep angle Lambda in degrees.
Stall speed: V_stall = sqrt(2 * W / (rho * S * CLmax_wing)), with weight W in N, area S in m^2, and rho in kg/m^3.
Drag increment: Delta CD0 = CD0_ref * sin(delta) / sin(delta_max), plus the induced-drag rise Delta CDi = Delta CL^2 / (pi * AR * e).
Pitching moment increment: Delta Cm = -Delta CL * (x_cp - x_ac) with the flap center-of-pressure and the wing aerodynamic center as fractions of chord.
Workflow
- Select the flap type and the maximum deflection; get the reference increment and scaling constants with flap_clmax_increment.
- For Fowler flaps, extend the chord with fowler_chord_ratio when the extension is known.
- Add leading-edge device increments with slat_clmax_increment and combine with combined_clmax_increment (superposition).
- Convert the section clmax to the wing value with wing_clmax using the sweep angle.
- Compute the stall speed with stall_speed; estimate the drag and pitching moment increments with flap_drag_increment and flap_pitch_moment_increment.
Pitfalls
- Mixing section and wing values: the 0.9 factor and the sweep cosine reduction apply once, at the wing level, not per device.
- Using full-span reference increments for partial-span flaps: scale by the flapped span fraction first.
- Forgetting the deflection clamp: beyond delta_max the increment stops growing (K_delta clamps at 1).
- Treating a Krueger flap as a slat: increments differ (about 0.3 vs 0.4 at full span), and the scaling rules are separate.
- Using stall speed with the clean CLmax: the whole point of the high-lift system is the flapped CLmax.
Behavior contract (gate 3)
The high-lift logic is exercised by the gate 3 contract test: scripts/test_high_lift_systems.py against scripts/high_lift_systems_logic.py (stdlib unittest, offline). Run: python3 scripts/test_high_lift_systems.py
Compliance
- The flap and slat increment values are widely cited textbook estimates (Raymer, Aircraft Design: A Conceptual Approach), paraphrased here. FAR-25 and CS-25 are cited as reference only for the stall and field performance context; no proprietary or copyrighted text is reproduced.
- compliance: STANDARDS-REF, gated: false.