KARI - Korea Aerospace Research institute

To prepare for the emerging personal air vehicle (PAV) market, KARI developed the Quad Tilt-Prop UAV (QTP-UAV) using previously established tiltrotor technology. The QTP-UAV employs a distributed electric propulsion system driven by batteries, utilizing four electric motors and propellers. The direct power supply to each motor simplifies the system and enhances flight stability through the collective pitch control of the four rotors.
During takeoff and landing, the QTP-UAV’s four rotors are oriented vertically, like a helicopter. Once airborne, they tilt horizontally to produce forward thrust, like a fixed-wing aircraft, enabling high-speed flight. The development hinged on two core technologies: an attitude control system to maintain stability during both VTOL and cruise phases and a power management system to evenly distribute electrical power from the battery to each motor.
Between 2016 and 2018, the QTP-UAV was developed through a major R&D initiative. In the area of system integration, KARI carried out UAV system design, airframe sizing, performance analysis, aerodynamic shaping, load analysis of the propeller and tilt mechanisms, and ground and flight testing. For propulsion, a hybrid system combining engine, generator, and battery was developed. In control systems, flight control software and a ground control station (GCS) were implemented. The structural team handled load analysis and structural design, while aerodynamic experts conducted CFD analysis and wind tunnel testing. The rotorcraft team led the design and performance analysis of the propellers.

The QTP-UAV system consists of the aircraft, a ground control station, and communication equipment. The UAV is equipped with two UHF-band communication modules and an integrated flight control computer (FCC) with onboard sensors. Three units were built: two battery-powered flight versions and one wind tunnel test model, the latter of which was designed to be converted into a hybrid-powered version following initial testing.
Full-scale flight testing was conducted at the Goheung Aviation Center. The first free-flight in rotary-wing mode (without safety tethers) took place on September 11, 2018. The flight test program began with hover flights, followed by low-altitude runway overflight tests in the rotary-wing mode, progressing through manual piloting by an external operator, station-keeping mode by the internal controller, and eventually autonomous flight. After completing rotary-wing tests, transition flights were gradually performed using waypoint navigation at altitudes of 100–200 meters and radii of 500–600 meters. On September 18, 2018, the aircraft successfully performed a transition flight in waypoint mode, maintaining a zero-degree tilt and reaching a speed of 145 km/h. In a subsequent flight on October 25, the UAV achieved a top speed of 165 km/h after optimizing the control logic and gain settings to enhance flight performance.
The development of the QTP-UAV enabled KARI to secure key technologies related to the aerodynamic and flight control characteristics of quad tilt-prop aircraft. It also led to the successful acquisition of high-speed VTOL UAV system technologies in the 50 kg class. Furthermore, the foundational knowledge gained on distributed electric propulsion systems for VTOL flight laid the groundwork for future applications in electric personal air vehicles (ePAVs), a rapidly emerging segment in next-generation urban air mobility.

The QTP-UAV, originally powered by batteries and configured with four propellers, was limited to a maximum flight duration of under 30 minutes. To overcome this limitation, a hybrid propulsion system—comprising an engine, generator, and battery—was integrated into the platform. The hybrid system includes a 10-horsepower twin-cylinder reciprocating engine, a generator rated up to 5 kW, and a 600 Wh battery, all installed within the original battery compartment. In addition, the two front propellers were replaced with fixed-pitch lift props to reduce weight and improve propulsion efficiency. On December 16, 2019, DTP-H successfully completed a 62-minute flight at a low-power cruising speed of 60–70 km/h using approximately 4 liters of fuel.