Tiltrotor UAV

Overview

A tiltrotor UAV combines helicopter and aeroplane in one airframe by rotating its propulsion rather than adding more of it. Two Tilting Rotor Nacelle pods at the wingtips point their rotors upward for takeoff and landing, then swing forward through about 95 degrees so the Wing carries the weight in cruise. The payoff is in the power figures: this 17 kg aircraft burns about 3.5 kW to hover but only 600 W in wing-borne cruise. A multirotor of the same weight would spend its whole flight at the hover number; the tiltrotor spends two minutes there per sortie and cruises for two and a half hours on the same Power System.

The same trade made the V-22 Osprey worth its complexity at 27 tonnes. At UAV scale the mechanism is far simpler, no cross-shafting, no blade pitch links, because an electric motor in each nacelle can be throttled in milliseconds, letting differential thrust do the work that swashplates do on a helicopter.

Nacelles and propulsion

Each nacelle packages a Proprotor, a Brushless Motor and its Electronic Speed Controller on a Tilt Spindle, a hollow titanium shaft that carries thrust and gyroscopic loads into the Wing Spar while motor power and signal wiring pass through its bore, avoiding flexing cables at the pivot. A standard Servo Motor drives the tilt through a geared linkage, with a Hall Sensor closing the angle loop; tilt rate is limited to about 15 degrees per second so the flight controller can track the shifting thrust vector.

The proprotor is the central compromise of the type. Hover wants a large disc and low disc loading; cruise wants a small, fast, coarse-pitch propeller. A fixed-pitch carbon two-blade of intermediate size gives away perhaps 15 per cent of hover efficiency and some cruise speed, which at this scale is cheaper than variable pitch. The Electronic Speed Controller runs field-oriented control through its six-Power MOSFET bridge, giving the smooth low-speed torque needed when the rotors are the only attitude control available.

Hover, transition, cruise

In hover the aircraft is a twin rotor: differential thrust rolls it, differential tilt yaws it, and synchronous tilt nudges it fore and aft. Pitch is the awkward axis, with only two rotors on the same lateral line there is no thrust couple in pitch, so the flight controller biases both nacelles slightly and uses the Ruddervator Surface ruddervators as soon as any airspeed exists.

Transition is a scheduled corridor, not a single moment. The Flight Controller tilts the nacelles forward in steps, holding altitude as lift transfers from rotors to wing across roughly 12 seconds and 0–22 m/s. Throughout, it blends two control allocations, rotor-based and surface-based, weighted by dynamic pressure from the Pressure Sensor airspeed source. The reverse transition is harder: the wing keeps lifting until deep into the deceleration, the rotors re-enter their own wake, and the controller must avoid the region of the corridor where neither rotors nor surfaces have full authority. Loss-of-control statistics for VTOL UAVs cluster in back-transition, which is why the autopilot, not the operator, always flies it.

The autopilot board carries dual Inertial Measurement Unit units sampled at 1 kHz, a GNSS Module good to about 1.5 m, and dual Microcontroller processors split between estimation/control and IO. Attitude comes from an extended Kalman filter fusing all of it.

Airframe

The Wing Spar is a full-span carbon tube, the one structural member that sees everything: lift bending, the cantilevered mass of two nacelles at its tips, and the torque pulse each time a nacelle tilts. Wingtip-mounted nacelles also place motor mass exactly where flutter analysis least wants it, so spar torsional stiffness, not strength, sizes the tube. Moulded Wing Skin sandwich shells and Aileron surfaces complete the wing. The Fuselage is a clamshell Fuselage Shell over a Bulkhead Set, with sprung Landing Skid rails, a tiltrotor lands vertically, so there is no undercarriage beyond them. The Tail Boom pushes the inverted-V tail far enough aft for cruise stability.

Power, link and payload

The Power System is a 12S string of LiPo Cell units (about 1.1 kWh) supervised by a BMS Board, feeding the ESCs through a current-sensing Power Distribution Board. Sizing is dictated by the 4 kW hover peak, not the cruise average, the pack must deliver roughly 8C briefly while spending most of the flight below 1C, an unusual duty cycle that favours high-power cells over maximum energy density.

The Datalink uses a frequency-hopping RF Transceiver at 2.4 GHz with AES-256 encryption and a diversity Antenna pair, holding telemetry and compressed video to about 40 km line of sight. The standard payload is a two-axis Payload Gimbal: an CMOS Image Sensor behind a 10x Lens Assembly, stabilised by Servo Motor axes with Encoder feedback in a Gimbal Frame hung from the vibration-isolated Payload Bay. Typical missions, pipeline patrol, maritime search, artillery spotting, exploit exactly what the configuration offers: launch from a ship deck or forest clearing, then cover 200 km of survey line without a runway at either end.