Glossary – UAV, UAS and Actuator Terminology

AAM includes eVTOL and eSTOL platforms integrated with advanced avionics, automation and airspace management systems. Typical use cases include passenger transport, emergency missions and time-critical logistics.

Actuators used in AAM platforms must support frequent duty cycles, high reliability, fail-safe behavior and minimal maintenance, meeting both safety and economic requirements.

Backlash describes the clearance or gap between meshing gear teeth within a mechanical gear train. This gap leads to a small amount of free movement at the output shaft before the drive torque is fully transmitted.

In precision actuator systems, backlash is a critical design parameter because it directly affects positioning accuracy and control behavior. Excessive backlash can introduce delays in torque transmission, reduce system stiffness and negatively impact closed-loop control performance.

In dynamic applications with rapidly changing loads or frequent direction reversals, backlash can lead to oscillations, reduced control stability and decreased positioning repeatability. Minimizing backlash is therefore essential for high-performance motion control systems.

Electromechanical actuators used in UAV flight control and industrial applications are typically designed with optimized gear geometries, high-precision manufacturing and tight tolerances to reduce backlash. Low backlash contributes to improved positioning accuracy, faster system response and overall control quality.

A Brushless DC (BLDC) motor is an electric motor in which electronic commutation replaces the mechanical brush-and-commutator system used in conventional DC motors. Permanent magnets are mounted on the rotor, while the stator contains wound coils that are energized sequentially by an electronic motor controller.

This design eliminates mechanical wear components associated with brushes and enables higher efficiency, reduced electromagnetic interference and improved thermal performance. As a result, BLDC motors offer significantly longer service life and more stable operation compared to brushed DC motors.

BLDC motors are characterized by high power density, precise controllability and excellent dynamic response. These properties make them particularly suitable for applications requiring accurate motion control and continuous operation under demanding conditions.

In UAV and aerospace actuation systems, BLDC motors are widely used due to their reliability, robustness and efficiency. They form a core component of electromechanical servo actuators, where they enable precise positioning, fast response times and long-term operational stability in safety-critical environments.

BVLOS describes unmanned aircraft operations in which the remote pilot cannot maintain continuous visual contact with the UAV using unaided vision. These operations significantly extend mission range, endurance and operational flexibility compared to visual line-of-sight (VLOS) flights.

BVLOS missions rely on advanced system architectures, including reliable communication data links, high-integrity navigation systems, onboard detect-and-avoid (DAA) capabilities and robust flight control systems. Safe operation requires continuous situational awareness despite the absence of direct visual observation.

From a regulatory perspective, BVLOS operations are subject to specific approval processes and airworthiness requirements in most jurisdictions. Certification frameworks are evolving to address increasing demand in commercial, industrial and governmental applications.

From an actuator system perspective, BVLOS introduces higher demands on reliability, redundancy and fault tolerance. Since immediate pilot intervention is not possible, actuator systems must ensure fail-safe or fail-operational behavior under all conditions. Redundant actuator architectures play a critical role in maintaining controlled flight and mission continuity in case of component-level failures.

eSTOL aircraft combine the aerodynamic efficiency of fixed-wing platforms with advanced high-lift concepts that enable short-field performance without the mechanical and energy complexity associated with vertical lift systems.

Typical applications include regional air mobility, cargo and logistics transport, special mission operations and access to remote or infrastructure-limited airfields. Compared to eVTOL platforms, eSTOL aircraft generally offer higher cruise efficiency, longer range and greater payload capability.

A defining technical characteristic is the use of distributed or hybrid-electric propulsion systems combined with advanced high-lift technologies such as blown wings, optimized flap systems or propeller–wing interaction concepts. These configurations increase lift during take-off and landing while maintaining efficient cruise performance.

eSTOL platforms require highly integrated flight control, propulsion and actuation architectures. Actuators must precisely control flaps, high-lift devices and primary flight control surfaces under dynamic aerodynamic loads. Key requirements include high reliability, low weight, energy efficiency and suitability for frequent operational cycles.

eVTOL aircraft are a key enabling technology for Urban Air Mobility (UAM) and Advanced Air Mobility (AAM) concepts.

These platforms are typically optimized for short- to medium-range missions with high operational frequency. Typical applications include air taxi services, medical transport, logistics and unmanned aerial operations.

Actuators in eVTOL systems must provide fast, precise and reliable control during vertical flight, transition and landing while remaining lightweight, energy-efficient and suitable for frequent duty cycles.

A Flight Control System (FCS) is the integrated set of sensors, computers, actuators and mechanical components responsible for stabilizing and controlling an aircraft during flight. It processes pilot inputs or autopilot commands and converts them into precise actuator movements that position control surfaces such as ailerons, elevators and rudders.

Modern FCS architectures rely on closed-loop control systems using continuous feedback from inertial sensors, air data systems and navigation sources. These systems continuously calculate control commands to maintain stability, trajectory and flight performance under changing conditions.

In fly-by-wire systems, there is no direct mechanical linkage between pilot controls and flight surfaces. Instead, all commands are transmitted electronically to the actuators, increasing flexibility, precision and system integration capabilities.

From an actuator perspective, the Flight Control System places demanding requirements on performance and reliability. Actuators must provide precise positioning, fast dynamic response and consistent behavior across the entire flight envelope. In safety-critical applications, redundant actuator architectures and defined fail-safe or fail-operational strategies are essential to maintain control authority in the event of component failures.

This aerodynamic principle enables efficient cruise performance, long range and stable flight characteristics. Fixed-wing aircraft are widely used in applications where efficiency, range and payload capacity are important operational factors.

Typical applications include commercial aviation, cargo transport, surveillance and reconnaissance missions, agricultural operations, environmental monitoring and scientific research. Compared to rotary-wing platforms, fixed-wing aircraft generally offer greater cruise efficiency, longer range and higher maximum speeds.

Flight control is achieved through aerodynamic control surfaces such as ailerons, elevators and rudders, which generate controlled moments around the aircraft’s roll, pitch and yaw axes. Additional high-lift devices such as flaps and slats are used to increase lift during take-off and landing, allowing safe operation at lower speeds.

Fixed-wing aircraft require precise and reliable actuation systems to control primary and secondary flight surfaces. Actuators must provide accurate positioning under varying aerodynamic loads across the entire flight envelope, from low-speed take-off and landing to high-speed cruise. Key requirements include high reliability, fast response, mechanical robustness and fail-safe behavior to ensure safe and stable flight operations.

HALE refers to unmanned aerial vehicles designed to operate at very high altitudes, typically above 15,000 meters, with some systems flying in the stratosphere at around 20,000 meters and beyond. Endurance ranges from several days to multiple weeks.

HALE UAVs operate where conventional aviation effectively ends, providing persistent wide-area coverage from extreme altitudes. They complement MALE platforms and satellite systems and are often deployed as part of High Altitude Platform Systems (HAPS).

Mission profiles include strategic intelligence, surveillance and reconnaissance (ISR), communications relay, early warning and environmental monitoring. Actuators used in HALE platforms must withstand extreme pressure and temperature conditions while delivering precise, reliable control throughout long-duration missions.

Rather than being defined by a specific aircraft type, HAPS are characterized by their operational role: providing persistent regional coverage.

HAPS platforms bridge the gap between satellite systems and lower-altitude UAV platforms such as MALE and HALE. They offer satellite-like capabilities while remaining within the atmosphere, enabling lower latency, recoverability and flexible system upgrades compared to space-based solutions.

Typical mission profiles include telecommunications relay, earth observation, environmental monitoring, disaster response and wide-area surveillance. Most HAPS concepts rely on solar-electric propulsion, resulting in highly weight- and energy-optimized system architectures.

Actuators used in HAPS platforms must operate reliably under extreme environmental conditions, including very low atmospheric pressure and temperatures below −70 °C, while remaining lightweight, energy-efficient and capable of precise control over long operational lifetimes.

Industrial actuators convert electrical control signals into controlled mechanical movement, typically providing accurate rotary positioning, high torque output and stable operation under demanding conditions.

In industrial and aerospace applications, actuators are used wherever precise motion control and long-term operational reliability are required. Typical use cases include control surface actuation in UAV platforms, industrial automation systems, mechanical positioning tasks and other demanding motion control environments.

A key characteristic of high-performance industrial actuators is the optimized balance between torque, weight and energy efficiency. Electromechanical actuator designs enable precise control of position, speed and torque while maintaining high operational reliability. Integrated sensors provide accurate feedback for closed-loop control systems.

Industrial actuators must operate reliably under varying environmental conditions, mechanical loads and continuous duty cycles. Key design requirements include mechanical robustness, thermal stability, high efficiency, low backlash and long service life. These characteristics make industrial actuators suitable for both airborne and ground-based technical applications.

In actuator systems, input signals provide the interface between the control unit and the actuator. These signals transmit commands such as position targets, speed commands or control parameters required for actuator operation.

Different signal architectures are used depending on system design and application requirements. Common control interfaces include PWM (Pulse Width Modulation), differential PWM, serial communication protocols such as RS485 and fieldbus systems such as CANopen. These interfaces allow integration with flight control computers, autopilots and industrial control systems.

The selection of an input signal type influences several important system characteristics, including signal integrity, latency, redundancy architecture and overall system integration complexity. In safety-critical aerospace applications such as UAV or OPV platforms, robust and reliable communication between the control system and actuator is essential.

Electromechanical actuators such as those in the PEGASUS PA-R and PA-RR series support multiple input signal options to enable flexible integration into both aerospace and industrial control architectures.

MALE UAVs bridge the operational gap between short-range tactical drones and HALE systems. They offer a balanced combination of payload capacity, range and operating cost, making them widely used across military, governmental and civil applications.

Typical missions include intelligence, surveillance and reconnaissance (ISR), border security, maritime patrol, environmental monitoring and disaster response. Actuators used in MALE platforms must provide reliable and precise control under reduced atmospheric pressure and low temperatures throughout extended mission lifecycles.

This dual capability allows a single platform to perform both conventional piloted missions and fully automated operations while retaining the option for direct human intervention.

OPVs combine characteristics of traditional manned aircraft and unmanned aircraft systems (UAS). They are typically used in applications where operational flexibility and safety are critical. Typical mission profiles include surveillance, reconnaissance, research flights, system validation and special operations support.

A key requirement for OPV platforms is the seamless transition between piloted and unmanned flight modes. This requires advanced flight control architectures that support both automated control systems and direct pilot input without interruptions or loss of information.

From a technical perspective, OPV aircraft frequently use electromechanical actuators equipped with electromagnetic clutch systems. When the clutch is disengaged, the actuator output shaft can move freely, allowing the pilot to control the flight surface directly. Position feedback remains available because the angle sensor is coupled to the clutch output. Engagement and disengagement of the clutch can occur at any position, ensuring smooth transitions between automated and manual control modes.

The PA-ME³ is a proprietary position sensor developed by PEGASUS Actuators GmbH, designed specifically for integration into redundant electromechanical servo actuators. It provides three independent position measurement channels within a single compact sensor unit.

The contactless measurement principle eliminates mechanical wear caused by physical interaction between sensing components and the rotating shaft. This results in increased durability, stable signal quality and long operational life, even under demanding environmental conditions.

The triple-redundant architecture enables continuous and reliable position feedback even in the event of individual sensor channel failures. Each channel operates independently, allowing the actuator system to detect faults and maintain correct position information without loss of control performance.

As a core component of PEGASUS redundant actuator systems, the PA-ME³ sensor supports single-point failure tolerance. It ensures that accurate position feedback remains available under all operating conditions, enabling safe and uninterrupted actuator function in safety-critical UAV and aerospace applications.

The PA-RA-3 and PA-RA-4 are electromagnetic clutch assemblies developed by PEGASUS Actuators GmbH and designed as add-on modules for electromechanical actuator systems. They enable fast and position-accurate switching between manual pilot control and automatic actuator regulation.

These clutch systems are a key enabler for Optionally Piloted Vehicles (OPV), which can be operated both manned and unmanned. In normal operation, the clutch is engaged, mechanically coupling the actuator to the control surface and allowing automatic control. When disengaged, the output shaft moves freely, enabling direct and unrestricted manual pilot input at any time and at any position.

A central design feature is the direct coupling between the clutch output and the actuator’s internal position sensor. This ensures that position feedback remains available even when the clutch is disengaged. Upon re-engagement, the actuator resumes operation seamlessly at the current position without transients, jumps or the need for realignment.

From a safety perspective, the PA-RA assembly is designed with fail-safe behavior. In the event of a system failure, the clutch automatically disengages, allowing immediate manual override by the pilot. This principle is comparable to a deadman function and ensures that control authority is always maintained.

The PA-RA clutch assemblies are available for PEGASUS actuator platforms starting from the PA-R-250-8 (standard) and PA-RR-260-8 (redundant). For larger actuator systems from the PA-R-340 series onwards, the clutch can be combined with the integrated mechanical overload protection system PA-SC.

Redundant actuators incorporate internal redundancy mechanisms that allow the actuator to maintain functionality and safe system behavior even when individual components fail.

In contrast to conventional actuator architectures that rely primarily on external flight control computers for fault management, redundant actuators can perform critical monitoring and safety functions internally. When a malfunction occurs, the actuator evaluates the fault condition and initiates protective measures autonomously, without increasing the computational load on the autopilot.

A defining characteristic of redundant actuator systems is the integration of duplicated components such as sensors, control electronics and power paths. This architecture increases availability, enables fault tolerance and supports fail-operational behavior in safety-critical aerospace systems.

Redundant actuators are typically used in applications where system reliability and operational safety are essential. These include flight control systems in UAV, RPV and OPV platforms as well as other aerospace or industrial systems requiring continuous and precise motion control under demanding environmental and load conditions.

Unlike autonomous systems, RPVs require continuous human control input for flight operations. This allows pilots to make real-time decisions during a mission while remaining physically separated from the aircraft.

RPV aircraft are used in applications where human decision-making is essential but onboard pilot presence is impractical or too risky. Typical applications include military reconnaissance, surveillance, target acquisition, hazardous environment inspection and research missions. Compared to fully autonomous systems, RPVs offer greater operational flexibility and immediate response to changing mission conditions.

A key technical characteristic is the use of reliable data links between the aircraft and the ground control station. These communication systems enable real-time transmission of flight data, sensor information and control commands. Low latency and redundant communication architectures are particularly important for safe operations in beyond-visual-line-of-sight (BVLOS) missions.

RPV platforms require robust flight control and actuation architectures capable of responding precisely to remote pilot inputs. Actuators must control flight surfaces and payload mechanisms with high accuracy and reliability despite potential signal delays. Key requirements include fail-safe behavior, mechanical robustness, precise positioning and the ability to maintain safe flight conditions in the event of communication interruptions.

Torque represents the rotational equivalent of linear force and is typically specified in Newton-meters (Nm) or Newton-centimeters (Ncm). It defines the moment applied at an actuator’s output shaft to generate rotational motion.

In electromechanical actuator systems, torque determines the actuator’s ability to move mechanical loads such as control surfaces, positioning mechanisms or industrial components. The required torque level depends on factors such as aerodynamic loads, mechanical leverage ratios, system inertia and defined safety margins.

Torque directly influences actuator size, weight, power consumption and mechanical design. Higher torque capabilities generally require stronger drive systems, larger gear mechanisms and increased structural strength.

Accurate torque sizing is therefore essential for reliable and efficient system integration in industrial automation and aerospace applications, including UAV flight control systems and other demanding motion control environments.

UAM focuses on safety, low noise and environmental sustainability, supported by dedicated infrastructure such as vertiports, charging systems and digital traffic management.

From a technical standpoint, UAM platforms place high demands on actuation systems, which must enable precise control during vertical take-off, landing and transition phases under frequent operational cycles.

The term UAS emphasizes a system-level perspective, recognizing that safe and effective unmanned flight depends on seamless interaction between airborne and ground-based components.

Within a UAS, actuator systems play a critical role in enabling reliable control of flight surfaces, propulsion and payloads. These actuators must deliver high precision, robustness and long operational lifetimes under demanding environmental conditions.

UAVs exist in a wide range of sizes and configurations, from small multirotor drones to large fixed-wing aircraft capable of long-endurance missions. Applications include surveillance, mapping, inspection, logistics, environmental monitoring and research.

From a technical perspective, UAV performance relies heavily on flight control and actuator systems. Actuators enable precise control of flight surfaces, propulsion elements, landing gear and payload mechanisms and must be lightweight, energy-efficient and highly reliable.

This capability enables operations from confined or unprepared areas and provides high operational flexibility.

VTOL platforms exist in both manned and unmanned configurations and are used in military, logistics, emergency response and industrial applications. Common VTOL architectures include tiltrotor, tiltwing, lift-and-cruise and multirotor designs.

VTOL systems impose demanding requirements on propulsion, control and actuator systems, particularly during transition phases between vertical and forward flight.