Fixed-wing fundamentals

Summary¶

Fixed-wing aircraft generate lift from the aerodynamic shape of a wing moving through air, rather than from continuous powered thrust vectored downward as in a multirotor. This fundamental difference makes fixed-wing aircraft far more efficient at covering area — a fixed-wing travelling at cruise speed generates lift nearly for free, while a multirotor must continuously expend energy to oppose gravity even when stationary. For survey applications where area coverage per battery matters more than hover capability or vertical take-off, fixed-wing is the architecturally correct choice.

Concept¶

Lift from motion vs lift from thrust¶

A multirotor generates lift by accelerating air downward through its rotors. Every joule of hover energy is spent entirely on overcoming gravity. Travelling forward is an additional energy cost on top of hover.

A fixed-wing generates lift from pressure difference: the wing's camber causes air to travel faster over the upper surface than the lower, reducing pressure above the wing relative to below. The forward motion that generates this pressure difference is maintained by a single propeller or motor at a fraction of the power required to hover at the same weight. The glide ratio — the distance travelled horizontally per unit of altitude lost with motor off — is typically 8:1 to 15:1 for foam flying wings. A multirotor's glide ratio without power is approximately 1:1 (it drops).

Efficiency in survey terms¶

For a survey platform at 50 m AGL covering a 30-hectare field:

A multirotor covers ground by flying horizontal transects — every metre of forward travel is powered by hover thrust plus forward thrust. Power consumption is approximately proportional to flight time regardless of speed.

A fixed-wing covers the same ground at cruise speed (12–15 m/s vs a multirotor's 5–8 m/s), using only cruise thrust to maintain altitude. Typical flying wing power consumption at cruise is 40–80 W. A comparable multirotor in forward flight consumes 150–300 W. The area coverage rate per watt is 3–5× better for fixed-wing at survey speeds.

This efficiency directly translates to endurance: the same 4S LiPo that provides 12 minutes of multirotor hover provides 45–60 minutes of fixed-wing cruise.

Flight characteristics vs multirotor¶

Fixed-wing aircraft cannot hover. They must maintain a minimum airspeed above the stall speed — typically 8–12 m/s for flying wings — or lose lift and descend. Launching and landing require either a runway, hand launch, bungee, or VTOL capability. ArduPilot handles auto-takeoff (climb to altitude after hand launch) and auto-land (RTH → landing pattern → touchdown) in ArduPlane.

Control axes are different: roll is controlled by ailerons or elevons (not motor differential), pitch by elevator, yaw by rudder or differential thrust. A flying wing like the Skywalker X8 uses elevons — combined elevator/aileron surfaces — and has no separate rudder. ArduPilot configures mixing for the correct geometry.

Wind affects fixed-wing flight differently from multirotor. A multirotor maintains position against wind by tilting into it. A fixed-wing must maintain airspeed — a headwind reduces groundspeed but does not stall the aircraft; a tailwind increases groundspeed and decreases control authority at low throttle. ArduPilot's TECS (Total Energy Control System) manages the throttle/pitch relationship to maintain the target airspeed regardless of wind. See → ardupilot-plane for TECS configuration.

Reference¶

Procedure¶

Rationale¶

Understanding the fixed-wing efficiency advantage is a prerequisite for evaluating Wing as a platform choice. Institutions or operators accustomed to multirotor operations often underestimate the endurance and coverage rate difference — it is not incremental (20% better) but categorical (3–5× better for area coverage). Equally, the absence of hover capability is not a limitation to minimise but a trade to understand: if the mission requires hover (inspection, precise delivery), fixed-wing is wrong; if the mission requires area coverage (survey, search, monitoring), fixed-wing is correct. The libdrone platform family is designed so the correct variant is available for both mission types.

Connections¶

requires: - lift-and-thrust - hover-and-forward-flight related: - wing-variant - ardupilot-plane - six-degrees-of-freedom - propellers leads_to: - wing-variant - ardupilot-plane