|Rochester Photo Negative
|Gyro Test/Calibration Clean Area
|Negatives Cabinet PC ("C" Negs) [RAA Office]
In an attempt to make use of the experience gained in the 1960’s designing the inertial navigator for the ‘Blue Steel' air-to-surface missile the Company embarked on the development of a general-purpose instrument for aircraft navigation, and an experimental stable platform, E5 was built. This project was not completed, as it was realised that the platform was likely to be too bulky for many applications, and improvements in technique appeared to offer scope for a reduction in size. A project to develop a new platform was commenced in the Company Research Laboratory, FARL, where fortuitously the majority of the small team of engineers had been in the Inertial Navigation Division including the Chief Engineer 'Dick' Collinson and the Chief Designer 'Staff' Ellis. FARL produced the E3 stable platform, using a novel gimbal system which permitted a very compact construction. A trial of this platform was madse in early 1963 at Cranfield with the E3 Platform mounted under the canopy of a Gloster Javaelin. This design entered production for the Hawker Siddeley Aviation HS801 'Nimrod' maritime strike and reconnaissance aircraft and between 1964 and 1970 over 100 platforms were delivered.
However a further development of the E-3 platform, the E-3R which permitted a wider range of manoeuvre, was specified for the BAC/Breguet 'Jaguar' fighter, and entered service in 1970 rapidly becoming an industry standard. The E3-R had a fourth gimbal and incorporated continuous rotation of the two vertical gyros and horizontal accelerometers to achieve 'rotaional averaging' giving greatly increased accuracy.
The Jaguar Navigation and Weapon Aiming Sub-System NAVWASS comprised the MCS920M central digital computer, E3R inertial platform, projected map display and horizontal situation indicator together with the necessary power supply, electronic, interface and control units.
The main unit of the inertial subsystem is the platform assembly which contains a stabilized inertial platform or stable element, the basic attitude reference for the system. The chief function of the platform is to provide a means of accurately locating the gyros and accelerometers and to maintain their orientation fixed to the local vertical and to true north regardless of anv aircraft motion. The electronic control amplifier contains the electronic amplifiers and special excitation sources required for alignment and operation of the inertial platform. These include the gimbal servo amplifiers and the gyro spin motor power supply.
Vibrating shell gyros have a bell-like structure; the Solid-State Angular Rate Transducer (START) Gyro is cylindrical in shape. START operates on the principle, that Coriolis forces produced by rotation cause a transfer of energy between two of the gyro's modes of vibration.
START is a gyro dependent for its operation on the rotation sensing properties of a resonant shell. A complete gyro requires both a resonant element (the cylinder) and a means of maintaining and measuring the vibration pattern about it. START uses a small electronic module for these vibration control purposes and to provide a usable interface to the user systems. The START Gyro is capable of withstanding the high shock environment of precision guided munitions (PGM). Successfully shock tested at 25,000g on a 155mm artillery shell trials range, this low-cost device was developed for short time of flight applications including precision guided munitions, terminally guided submunitions, hypervelocity missiles and light anti-armour weapons. However, the device has since seen application in active suspension systems in cars where its low cost and extreme ruggedness is ideal. It is simple to produce and therefore ideally suited to inexpensive mass production techniques.
In addition, START offers significant advantages in terms of small size, light weight, instantaneous start and very low power. Alone or in a 3-axis configuration it competes successfully against current, more conventional technologies.
The START gyro trades simplicity for performance and is a relatively low-cost item. The resolution is about 0.02 deg/s and scale factor of 0.3% and START typically has g-sensitivity of the order of 0.05 deg/s/g normal to the input. Start-up time is in the range 0.1-0.5 s; the drive power is about 10 mW.
The range is adjustable up to 3000deg.sec. The Power requirement is +/-15VDC at about 1Watt. The weight is 40gms and overall dimensions are 24mm diameter (the square mount is 26mm) and 28mm length (with another 10mm for the pins).
In 1990 GEC Avionics Guidance Systems Division were a finalist in the Prince of Wales Award for Innovation with the START Gyro.
See ‘Modern Inertial Technology: Navigation, Guidance, and Control
By Anthony Lawrence
This was Marconi Electronic Systems product, produced at Rochester, that went into many systems; most notably when developed further with Bosch to form an anti-roll sensor for car suspension control. Mercedes used the system. When the merger with BAE took place and BAE Systems was formed there existed a solid state gyro business in Plymouth that was bigger in business and that became the centre of further gyro production while activity at Rochester declined and closed down. (Note courtesy of Steve Pink)
A rate gyro is a type of gyroscope, which rather than indicating direction, indicates the rate of change of angle with time. The gyro has only one gimbal ring, with consequently only two planes of freedom and is used to measure the rate of angular movement. Rate Gyros output a voltage that is proportional to the rate of turn about its sensitive axis.
The original concept of this Rate Gyro was a design by Siemens dating from the late 1930s used in their K12 Autopilot. The concept was developed further in Germany during WWII where it formed part of the rudder control system on the Henschel Hs 129 and in the ‘V2’ rocket weapon. After the War the design was brought to RAE Farnborough eventually being offered to industry, By 1953 Elliott Bros had developed the autostabiliser which was according to FLIGHT Magazine of 1953 necessary to correct the ‘snaking’ activity of certain high speed aircraft. This gyro was fitted near to the c of g of the aircraft and operated a remote actuator unit for the rudder servo tab via a control box. The design was further developed into the Type ‘B’ Autopilot.
Each Rate Gyroscope consists of a 1.5" hysteresis gyro motor mounted in a single gimbal to give a precessional torque which is proportional to the rate of instrument rotation about the sensitive axis. A multi-coil assembly is mounted on an arm from the gimbal ring, so positioned that the windings move axially in an annular permanent magnet when the gyro precesses. A second arm carries a fine wire pick-off making contact with a fixed winding which is fed from a 28VDC supply and can be set for correct zeroing of the instrument. The voltage between the centre-tap of the DC supply and the pick-offs fed to one of the coils so that interaction of the magnetic fields opposes the precessional torque; thus the gyro precesses against an "electrical spring”. Other moving coils (the gyro shown has three coils but some models only have two) can be used for transient velocity damping or for enforcing an artificial precession, or can be short-circuited for electromagnetic damping.
The voltage between the pick-off and the supply centre-tap is proportional to the magnitude and direction of the precessional torque, so it is also used as the output signal. If a large capacitor is wired between the pick-off and the spring coil the spring still resists precession, but the gimbal does not return to its "neutral" position when the precessional torque ceases With this treatment, the output signal from the pick-off is proportional to the integrated rate of rotation.
The RAE design was modified by Don Kierley of Elliott Bros but was made in Flight Controls Division not Gyro Division. Variants of the gyro were fitted to Elliotts' Flight Control System for the Jindivik in the late 1940s and subsequently to the Lightning (the Type "B") and the FIAT "Flying Bedstead" and although it was proposed for Concorde it was not actually used.