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Overview

Hovercraft performance depends on stable lift generation, efficient thrust, and controllable tracking. The craft rides on a pressurized air cushion contained by a skirt; design choices balance leakage, stability, and energy use.

Lift physics

Cushion pressure: supports weight W over effective cushion area A → p_c ≈ W/A. Higher pressure allows smaller area but increases skirt loads and leakage sensitivity.
Leakage and plenum: lift fans supply volumetric flow Q; leakage through skirt gaps/holes requires Q to maintain p_c. Too little Q → sag and ground contact; too much → wasted power.
Skirt compliance: flexible skirts accommodate surface irregularities; segmented/single‑bag designs trade stability and drag.

Skirt design

Hole sizing/placement: distribute small holes for uniform pressure; edge leakage provides restoring forces against tilt.
Materials: low‑friction, durable fabrics; seam strength and airtightness are critical.
Geometry: keep skirt height modest to reduce rocking; add internal baffles for stability when allowed.

Thrust and steering

Propulsor: match prop pitch/diameter to motor curve; shrouds/nozzles can raise static thrust; avoid stall at operating point.
Ducting: minimize turns and separation; smooth inlets/outlets reduce losses.
Control: rudders/vanes deflect flow; differential thrust or vectoring improves yaw authority; CG forward of thrust line reduces pitch coupling.

Mass and balance

Center of gravity: too high → roll instabilities; too far aft → pitch‑up under thrust. Keep mass low and centralized.
Structural stiffness: rigid deck prevents oscillations; isolate motor vibrations.

Calibration and logs

Lift margin test: record cushion pressure vs added mass until skirt contact; ensure reserve margin for variability.
Thrust tests: measure acceleration and top speed over known distances; build a repeatable run protocol.
Environment: floor texture, seams, and drafts alter drag and leakage; document conditions.

Worked micro‑examples

Cushion pressure estimate

Craft mass 0.45 kg → W ≈ 4.41 N. Effective area 0.030 m² → p_c ≈ 4.41/0.03 ≈ 147 Pa. Ensure lift fan can maintain this with leakage.

Leakage intuition

Doubling skirt gap height increases leakage roughly with area and velocity through the opening; small gap increases stability but demands more Q. Tune hole area to balance.

CG shift

Moving battery 30 mm forward reduces pitch oscillation under throttle; verify by measuring nose height changes at fixed thrust.

Pitfalls

Over‑inflated skirt causing lift “pogo” and directional loss.
Sharp duct bends and rough edges reducing thrust dramatically.
Ignoring skirt seam leaks; small pinholes compound and drop cushion pressure.

Practice prompts

Design a hole pattern for a rectangular skirt and justify spacing for uniform pressure.
Propose a duct and rudder layout minimizing losses while maximizing yaw authority.
Create a lift margin test plan and acceptance criteria based on mass and pressure.

References

SciOly Wiki – Hovercraft: https://scioly.org/wiki/index.php/Hovercraft

Hovercraft