Motion control for aerospace and aviation

In short:Aerospace motion splits into two jobs: equipment that flies, where weight, temperature range, fault tolerance and DO-160G qualification drive every choice, and the ground test rigs and assembly cells that prove and build it. Electric actuation is taking over secondary flight functions, test benches and riveting, but a jam-tolerant design and documented qualification matter more than raw force.

Typical requirements

Machinery we specify motion for

• Flight control and utility actuators
• eVTOL tilt-motor and flap actuators
• Helicopter rescue hoists
• Helicopter EO/IR sensor turrets
• Inflight entertainment systems
• ATC and tracking radar
• Automated riveting and drilling cells
• Automated fibre placement
• Aerospace component and structural test rigs

What aerospace motion has to deliver

Aerospace motion control covers two very different kinds of machine. The first is equipment that flies: actuators, hoists, sensor turrets, radar and cabin systems, where every gram counts, temperatures swing from well below freezing to hot-soak, and the equipment must pass environmental qualification and fit a safety case. The second is the equipment on the ground that builds and proves the aircraft: test rigs, iron birds, drilling and riveting cells and fibre placement machines. These are industrial machines with aerospace-grade demands on accuracy, data and traceability.

In the UK the sector is large enough to have its own trade body: ADS represents more than 1,700 member companies across aerospace, defence, security and space. Most engineers specifying motion components here work for a tier-one or tier-two supplier, a test house or an automation integrator, and the first question we ask is always: does it fly?

Where motion components sit in aerospace

Harmonic Drive lists helicopter rescue hoists and eVTOL tilting motors and jet flaps among its aviation applications. Schleifring describes slip rings in ATC and tracking radar, helicopter EO/IR sensors and inflight entertainment.

Electromechanical actuators for aircraft: the jamming question

The “more electric aircraft” replaces hydraulic actuators with electromechanical actuators (EMAs) to save weight, remove hydraulic lines and allow condition monitoring. Progress has been steady but selective. A review of EMA jamming mitigation lists EMAs on the A380’s slats and horizontal stabiliser, and on four of the 787’s 14 spoilers and its wheel brakes, all classed as secondary functions.

The reason is jamming. A ball screw that seizes is a single point of failure, and the review identifies friction build-up, debris contamination and spalling of the screw surface as the precursors. Onset tends to be abrupt, which makes it hard to predict. Mitigations described include:

• Redundant actuation: two EMAs summed onto one surface through a lever.
• Fault-tolerant motors and drives: dual or triple lanes, multi-phase machines and independent converters.
• Anti-jam mechanisms: decoupling the nut from the output so the surface returns to a safe position.
• Health monitoring: combining model-based and data-driven methods to spot rising friction early.

For a component specifier, this means the motor, gear and encoder choices follow from the actuator’s failure strategy, not the other way round. Read our guide to moving from hydraulic to electric actuators and the ball screw vs roller screw comparison before fixing the screw type.

Strain-wave gears, frameless motors and encoders

Rotary actuators for tilt mechanisms, hoists and pointing combine a frameless torque motor with a strain-wave gear and an output encoder, the same packaging logic as a robot joint. Harmonic Drive notes that its gears flew on the Apollo missions and that one installation has been in an aircraft wing for about 30 years. Compare reducer types in harmonic vs planetary vs cycloidal and browse gearboxes.

Feedback must work across the airborne temperature range. Capacitive encoders such as the Netzer VLT, published at -55 to +125 °C, mount around a hollow shaft without bearings. Inductive designs such as the Celera Motion Mini Ultra IncOder are non-contact and sealed. See absolute vs incremental encoders.

Slip rings for radar, EO/IR turrets and cabin systems

Any axis that rotates continuously needs a slip ring or contactless link. Schleifring lists the environment as severe temperature swings, shock, vibration and, for space and some radar, radiation, and requires EMC performance, qualification, certification and full traceability. Airborne rings are usually developed to order. Ground radar and test equipment can often use catalogue designs such as a fibre optic integrated slip ring for electro-optical pods, or the RR Series RF rotary joint. Our pages on slip rings for radar antennas and gimbals cover the detail.

Aerospace test rigs and assembly

Large structural tests are mostly hydraulic. A Moog account of aircraft structural testing describes one full-scale programme running 83 hydraulic and 7 pneumatic channels with a 1,200-channel data system, testing to three lifetimes for monitored airframes and five for non-monitored ones, with about 10 minutes of testing per flight hour. In Belfast, Moog supplied a 24-channel test system for fatigue testing the CSeries carbon fibre wing, with an active load abort system that unloads the structure if the primary loading fails.

Component and subsystem rigs are where electric actuation has moved in: actuator endurance rigs, landing-gear and door rigs, seat tests and rotating rigs. Rotating rigs need instrumentation slip rings; Michigan Scientific, for example, quotes end-of-shaft rings up to 12,000 rpm with precious-metal contacts for low noise. See slip rings for test rigs.

Worked example: sizing an actuator for a load rig

A rig must load a control-surface actuator with ±20 kN while moving it ±25 mm at 2 Hz (sinusoidal), for a 1-million-cycle endurance test.

1. Peak velocity: 2π × 2 × 0.025 = 0.31 m/s.
2. Peak acceleration: (2π × 2)² × 0.025 = 3.9 m/s². With a 50 kg moving mass that adds about 200 N, small next to the load.
3. Peak power: at worst, 20 kN × 0.31 m/s is about 6.3 kW at the screw, so the motor and drive are in the 7–10 kW class once efficiency is included.
4. Screw speed: with a 10 mm lead, 0.31 m/s is about 1,880 rpm.
5. Duration: 1 million cycles at 2 Hz is about 139 hours of running, so screw life at the RMS load is the real check. A roller screw is the usual answer at this force and duty.
6. Control: the rig needs force control from a load cell, not just position control, and a defined abort that unloads the unit under test.

An actuator in the class of the Tolomatic RSX (published to 294 kN and 760 mm/s) covers this envelope. Confirm with the supplier’s life calculation; our linear actuator sizing guide explains the method.

Qualification and documentation

Airborne equipment is tested to RTCA DO-160G, which covers temperature, humidity, vibration, water, power input, voltage spikes, RF susceptibility and emissions, lightning and electrostatic discharge. Programmable electronics fall under DO-178C (software) and DO-254 (hardware). Suppliers to the sector usually work to EN 9100 / AS9100. Catalogue industrial components are normally used on ground equipment, test rigs and prototypes. For flight hardware, plan qualification and any custom build with the supplier from the start.

Typical pitfalls

1. Treating a flight actuator like an industrial axis. The failure strategy drives the design.
2. Forgetting temperature at the low end. Lubricants, seals and encoders often limit cold performance before the motor does.
3. Under-sizing rig actuators on peak force when months of cycling make RMS load and screw life the limit.
4. Leaving the abort behaviour undefined on test rigs, so a fault damages the test article.
5. Late documentation requests. Traceability and qualification data are hard to add after the order.

Tell us whether your part flies, its loads, envelope and environment, and our specialist engineering and supply partners can propose actuators, gears, encoders, drives and slip rings to suit.

Standards to have in view

• RTCA DO-160G (environmental conditions and test procedures for airborne equipment)
• RTCA DO-178C (software considerations in airborne systems)
• RTCA DO-254 (design assurance for airborne electronic hardware)
• SAE ARP4754 (development of civil aircraft and systems)
• SAE ARP4761 (safety assessment process for civil airborne systems)
• EN 9100 / AS9100 (quality management for aviation, space and defence organisations)

Which standards apply depends on the end product and its market. Your engineer will confirm what the component itself needs to meet.