SYNCHRO

SYNCHRO
Name	SYNCHRO
Type	Rotary position sensor / synchro system
Developer	Multiple manufacturers (e.g., Collins Radio, General Electric, Westinghouse)
Introduced	1930s–1940s
Used by	United States Navy, Royal Air Force, Soviet Union, Northrop Grumman, Boeing, Lockheed Martin
Wavelength	N/A
Frequency	Power-frequency electromechanical
Precision	arcminutes–degrees (model-dependent)
Country	United States, United Kingdom, Soviet Union, Germany, France, Japan

SYNCHRO

SYNCHRO denotes a family of rotary electromechanical transducers developed for transmitting angular position or torque between remote locations. Widely used in avionics, naval fire-control, industrial automation, and early computer peripherals, SYNCHRO systems enabled real-time angular feedback between platforms such as Grumman F6F Hellcat, Northrop Grumman E-2 Hawkeye, USS Iowa (BB-61), and ground installations like SAGE (Semi-Automatic Ground Environment) radar sites. The technology influenced the design of later resolvers, encoders, and servo loops adopted by firms including Honeywell, Raytheon, and Siemens.

Introduction

SYNCHRO assemblies are three-phase, rotary transformers that convert mechanical shaft angle into electrical signals and vice versa; primary examples include torque transmitters, control transformers, and receivers. Contemporary and historical implementations appeared alongside systems from Collins Radio, General Electric, Westinghouse Electric Company, Ferranti, and Siemens-Schuckertwerke, integrating with platforms such as B-52 Stratofortress, F-16 Fighting Falcon, Concorde, and naval directors on HMS Ark Royal (R09). The devices bridged control links across systems like AN/SPG-55 fire control radar, NAVSTAR GPS-era inertial navigation, and early electromechanical computers such as the Harvard Mark I lineage.

History and Development

SYNCHRO-like devices trace to rotary transformer concepts explored in the interwar and WWII periods by corporations and military establishments like Bell Labs, MIT Radiation Laboratory, Royal Aircraft Establishment, and Bureau of Ships. During WWII, manufacturers including Sperry Corporation, Elliott Brothers, and Siemens scaled production for Battle of the Atlantic convoy escort vessels and aircraft such as Supermarine Spitfire derivatives. Postwar expansion saw adoption in Cold War systems—Ballistic Missile Early Warning System installations and NACA research facilities adopted synchro networks for gimbal and control-link tasks. Standardization efforts involved agencies such as MIL-STD-167 successor committees and industry consortia including RTCA.

Technical Design and Operation

A typical SYNCHRO comprises a rotor winding and three-phase stator windings spaced electrically at 120° within a laminated magnetic core; rotation modulates induced voltages. Units operate as transmitters (TX), receivers (TR), or control transformers (CT). Functionally similar to resolvers used by Hughes Aircraft Company and Thomson-CSF, SYNCHROs differ in winding configurations, insulation, and mounting standardized for platforms like C-130 Hercules and V-22 Osprey. Interfaces employed transformers, synchro-to-digital converters (SDCs), and servo amplifiers from manufacturers such as Bosch Rexroth, Curtiss-Wright, and Mitsubishi Heavy Industries. Signal characteristics matched legacy avionics and naval gear, integrating with multiplexers in systems like AN/SPY-1 and analog computers in Norden bombsight-era instruments.

Applications and Usage

SYNCHROs served in turrets and gimbal controls on Mark 37 Gun Fire Control System, stabilizers on USS Missouri (BB-63), heading reference systems in Lockheed L-1011 TriStar, and antenna positioning in satellite ground stations like those supporting Intelsat. Industrial uses included telemetry for machine tools in facilities run by Rolls-Royce, General Motors, and Siemens AG factories, as well as integration into hydraulic servos on Panavia Tornado and Eurofighter Typhoon prototypes. Research installations at CERN and Oak Ridge National Laboratory used synchro-derived resolvers for precision motion stages.

Variants and Compatibility

Variants include selsyn (self-synchronous transmitters), boltholes designed to meet NATO fits, brushless designs from Moog Inc., and sealed units for use on U-boat-type hulls or Ilyushin Il-76 freighters. Compatibility matrices addressed voltage levels, phase reference, and mechanical shaft keys to match standards from MIL-E-5400-era specifications, or civilian instrumentation norms adopted by ISO committees. Conversion modules—e.g., resolver-to-digital and synchro-to-digital—were developed by Analog Devices, Texas Instruments, and National Semiconductor to integrate legacy synchros with modern avionics buses like MIL-STD-1553 and ARINC 429.

Maintenance and Safety Considerations

Routine maintenance practices derived from manuals by Boeing, Lockheed Martin, and Northrop Grumman emphasize inspection of bearings, brush assemblies on non-brushless types, and insulation testing per procedures referenced by FAA airworthiness directives. Safety concerns include electrical isolation in systems certified under NAVSEA and Department of Defense safety directives to prevent inadvertent actuation of servomechanisms on platforms such as Oliver Hazard Perry-class frigate and Nimitz-class aircraft carrier. Spare parts supply has often been managed by aftermarket specialists like Curtiss-Wright Controls and remanufacturers servicing legacy fleets.

Cultural and Legacy Impact

Though largely superseded by optical encoders and solid-state inertial measurement units from Honeywell Aerospace and Northrop Grumman Sensing Systems, SYNCHRO technology left a legacy in engineering pedagogy and preservation communities, appearing in museum exhibits at National Air and Space Museum, Imperial War Museum, and technical collections at Smithsonian Institution. Historic restorations of B-17 Flying Fortress and HMS Belfast retain operational synchros for authenticity. The term and components remain referenced in restoration manuals, technical histories by IEEE History Center, and in legal archives concerning retrofitting projects overseen by General Dynamics and BAE Systems.

Category:Electromechanical transducers