— Products — Rotary actuator
Remove the gearbox. Lighten the aircraft.
A fully electric, direct-drive rotary actuator. One primary moving part. No gearing, no hydraulics.
— Engineered for flight
— The product
High torque, one moving part. The KRA is a high torque rotary actuator built on Shape Memory Alloy (SMA) torsion tube technology. Electrically powered, fully self-contained and sealed, it is the ultimate rotary actuator: its direct-drive architecture eliminates gear reduction entirely — improving reliability and efficiency — and the torsion tube scales to accommodate a wide range of aerospace applications.
SMA work density delivers high output torque from minimal mass and volume — four standard models from ±4 to ±128 N·m continuous.
The SMA element is the motion driver. No motor, no gearbox, no linkages — a fraction of the part count of electromechanical or hydraulic equivalents.
On loss of power the actuator returns to a defined fail-safe position, with limit switch feedback as standard.
Resistive heating of the SMA element keeps drive electronics simple, and is compatible with AC or DC power sources.
The KRA family
Four torque classes. Two orders of magnitude. One platform.
KRA004 · KRA008 · KRA032 · KRA128 — a common sealed direct-drive architecture, sized by the SMA torsion element and frame.
— The technology
Motion without machinery. Shape Memory Alloys are metals that change shape when heated and recover when cooled. Inside the KRA, an SMA torsion tube twists to produce rotary motion directly: heating the tube electrically drives the output shaft through its stroke, and cooling returns it.
Because the SMA element is itself the motion driver, there is no motor and no gear train to package, lubricate, or qualify. The result is a sealed, quiet, solid-state actuator with exceptional work density.
The architecture scales. SMA torsion tubes from 2.5 mm to 38 mm [0.1″ to 1.5″] outer diameter have been manufactured and tested across four orders of magnitude of torque — from 1.7 to 1,700 N·m [15 to 15,000 in-lbs] — increasing commonality within and across product lines.
For aerospace, work density is the headline: high output per unit mass means significant weight savings against electric motor and hydraulic alternatives — and weight is fuel.
Proven scalability
Why it matters
Fewer parts. Lower mass. Higher reliability.
Solid-state actuation replaces the failure modes of gears, brushes, and hydraulic seals with a single engineered element — simplifying maintenance and the reliability story alike.
— Technical specifications
| Operating Voltage | 28 VDC |
|---|---|
| Maximum Travel Range | 90° |
| Positional Accuracy1 | 0.2° |
| Operating Temperature Range | −55 to 50 °C [−67 to 122 °F] |
| Fail-safe Position | Defined default position on loss of power |
| Feedback | Limit switches standard · position feedback optional |
| Mechanical Interface | NEMA and ISO standard frames · frameless option |
| Travel Limiting | Optional internal hard stops |
| Specification | KRA004 | KRA008 | KRA032 | KRA128 |
|---|---|---|---|---|
| Continuous Rated Torque, N·m [lbf·in] | ±4 [±35] | ±8 [±71] | ±32 [±283] | ±128 [±1133] |
| Peak Torque2, N·m [lbf·in] | ±11 [±94] | ±23 [±205] | ±85 [±755] | ±341 [±3021] |
| Maximum Speed, °/sec | 20 | 10 | 10 | 6 |
| Size, mm | 58 × 58 × 288 | 75 × 75 × 373 | 116 × 116 × 576 | 184 × 184 × 914 |
| Size, in | 2.3 × 2.3 × 11.3 | 3 × 3 × 14.7 | 4.6 × 4.6 × 22.7 | 7.2 × 7.2 × 36 |
| Weight, kg [lb] | 1.1 [2.4] | 1.8 [4.0] | 3.3 [7.2] | 5.9 [13.0] |
1 With positioner option. 2 Short-duration rating. Model number denotes continuous rated torque in N·m.
Dimensions are for reference only and subject to configuration. Contact Kinitics for installation and interface control drawings before committing interfacing designs.
— Features & configurations
Specified at order. Every KRA is built from a configurable platform. Feedback, travel, default behaviour, and mechanical packaging are selected at time of order — so the unit that arrives is the unit the application needs.
Integral limit switches report end-of-travel state as standard. Position feedback options allow output angle to be monitored continuously for closed-loop control and health monitoring.
On loss of power the KRA returns to a defined fail-safe position. Default position and direction of rotation are configurable — open or closed, clockwise or counter-clockwise.
Fine trim adjustment allows end positions to be set precisely at installation, aligning actuator travel to the driven mechanism without shimming or linkage adjustment.
Choose a NEMA or ISO standard frame for drop-in mounting, or a frameless variant that integrates the actuator core directly into the surrounding structure.
With the positioner option, the KRA holds commanded intermediate positions within its 90° travel rather than operating two-position — with positional accuracy of 0.2°.
Optional internal hard stops bound the output travel mechanically, protecting the driven mechanism and providing a positive end-of-travel reference independent of the control system.
Program support
Kinitics supports aerospace programs with controlled documentation, requirement traceability, and revision-managed interfaces — from development units through line replaceable unit (LRU) deliveries.
The KRA’s reconfigurable design permits in-situ characterization of the SMA element, supporting element selection, acceptance testing, and qualification evidence — validated between Kinitics and customer laboratories.
— Case study · Ram air door actuator
Built to flight-test standard.
A joint Kinitics–Boeing weight savings study of commercial airplane architecture identified twenty-four actuator system types — thirty-one discrete actuators — in non-mission-critical applications where SMA-based actuators could replace existing electric motor or hydraulic units.
The KRA01 was developed as a line replaceable unit around an SMA torsion tube as the primary motion driver. Rotary output couples directly to the existing driven shaft, simplifying the ram air door mechanism. Electrically powered, fully self-contained and environmentally sealed, it interfaces with the airplane’s mechanical, structural, electrical, and environmental systems.
Flight-test hardware — the KRA01, in-flight performance sensors, and support electronics — completed system vibration testing and was prepared for assembly into a 777-200 aircraft. The actuator’s reconfigurable design also served as an in-situ SMA element test stand, with results validated between Kinitics and Boeing laboratories.
Figures from the peer-reviewed study published in Shape Memory and Superelasticity 11, 663–668 (2025), Pick et al., with Boeing Research & Technology and Boeing Commercial Airplanes. Read the story
— Applications
Wherever an electric motor drags a gearbox behind it, or a hydraulic line runs a long way to do a small job, the KRA offers a lighter, simpler answer.
Two-position door actuation with fail-safe return — the application class developed and tested with Boeing on the 777 nitrogen generation system (see the case study).
Gear doors, uplocks, and steering-adjacent functions where hydraulic simplification and weight reduction are program goals.
Secondary and utility control surfaces where high torque, low weight, and direct coupling to the hinge line simplify the mechanism.
High-torque, limited-travel rotation at the fold line — squarely in the torsion tube’s sweet spot, with scalability to large torque classes.
Latching, locking, and door drive functions benefit from the KRA’s holding behaviour and compact, sealed packaging.
Fluid system valves and environmental control dampers, on the airframe or in ground support equipment.
— Working with Kinitics
Share the motion requirement — torque, travel, envelope, environment — and Kinitics engineers will confirm fit against the standard family or scope a built-to-requirement variant.
Development units, interface documentation, and in-situ SMA characterization support move programs from evaluation to qualification with evidence at every step.
Start from your requirements, not from a part number. The four standard models are proven starting points — and the torsion tube architecture is designed to be reconfigured. Kinitics engineers work directly with your integration team on expanded travel, alternate mounting and connector provisions, non-standard environments, and torque classes beyond the standard range, from concept through qualification.
Request the KRA datasheet, installation drawings, or an application review.
