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Harrier SAAHS Rate Gyro Mechanism

Technical Information

Catalogue No: C0659
Category: Gyro
Object Type: Module/Sub-Assembly/Component
Object Name: Harrier SAAHS Rate Gyro Mechanism
Part No: 8201-00009
Serial No: 7048-82
Manufacturer: Marconi Avionics
Division: Flight Controls [FCD]
Platform(s): Harrier
Year of Manufacture: circa 1982
Width (mm):
Height (mm):
Depth (mm):
Weight (g):
Location: Rack RAA09 [Main Store]



This Rate Gyro was supplied for the Harrier SAAHS, (Stability Augmentation and Attitude Hold System). It was manufactured by Elliotts using a Northrop GR-H4 Gyro.

As well as the given P/N & S/N the item is also marked:
"12578-82" and
"4400-4240 Iss 2".

Within the item is a rate gyro marked:
"Marconi Avionics
Code No. K0656
GR-H4 20-52
Ser. No. 12758/82
Spec No. 205-S-52 Iss 2
Rochester, England"

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.

In a rate indicating gyroscope, the gyroscope is turned at a steady rate about its input axis and a torque is applied to the spin axis. This causes the gyroscope to precess about the output axis. The rate indicating gyroscope consists of a damping fluid between the float assembly can and the outer casing. This viscous fluid resists the motion of the gimbal precession. This causes the gimbal to accelerate initially in the fluid, until the damping effect is equal to the precessing force. The rate of precession will hence be directly proportional to the rate of turn of the gyroscope about its input axis and the total angle of movement about the output axis will be proportional to the speed and length of time the input axis is turning.

In a typical application (e.g. an aircraft), the output axis could have revolved 180 degrees clockwise in 20 seconds, then 80° anti-clockwise (say if the aircraft was changing direction again). This output would then be fed to a computer to calculate the total distance traveled

Honeywell Licence

In April 1958 English Electric acquired a licence to manufacture Honeywell gyros at Stevenage. English Electric Aviation Ltd became a founding constituent of the British Aircraft Corporation (BAC) in 1960 and the guided weapons division was added to BAC in 1963. In 1975 BAC bought out the future royalties for the Honeywell license and BAC became part of the new BAE Systems in 1999.

The Miniature Rate Gyro (MIG) employs a gimbal floated at neutral buoyancy in a fluorocarbon fluid and pivoted between jewelled bearings. The manufacture and assembly of such a gyro called for standards of precision unprecedented not only in industry but even in specialist laboratories. A crucial issue was vibration. The Instrument Wing was located between the Eastern Region main line to the north and the new Stevenage by-pass road, and further vibration came from machinery in the company's plant—and even from the footfalls of the staff. Accordingly, test equipment was mounted on concrete plinths carried on 50-ton concrete rafts supported on air bellows resting on heavy foundations deep in the earth.

The assembly and test area were clean rooms fully temperature and humidity controlled and it is the only miniature inertial quality gyro in production in Europe. These Gyros were used in inertial guidance systems for missiles and torpedoes for example.

Northrop Licence

 Marconi licenced a range of gyros from Northrop; initially the GR-H4 in the mid-60's and then the G1-G6 in 1980.

The GR-H4 rate-gyroscope was built under licence from Northrop, producer of the original version. The gyro is contained in a 1in x 2 in cylinder and is extremely accurate and strong. It is fluid damped, but requires no heater controls. In 1968 Dick Scott and the Gyro Division team landed a major contract for Elliott Nortronics sub-miniature rate gyros for the television guidance head of the Anglo-French Martel air-to-surface missile; the ultimate value of the order iat that time was expected to exceed £900,000.

In 1980 Marconi Avionics of Rochester has just completed its 10,000th rate-gyroscope, marking 15 years of manufacture. The GR-H4 rate-gyroscope is built under licence from Northrop, producer of the original version. Applications of the Marconi Avionics-built gyroscope include the Sea Vixen carrier-borne interceptor guidance, the guidance system of Sky Flash, the RAF's most advanced air-to-air missile, and stabilisation of Harrier and the Sea Dart ship-to-air missile. While building GR-H4s, Marconi Avionics introduced several improvements, independently of Northrop. At the same time unit cost was reduced, by a factor of almost three. (The 1980 cost of the rate-gyroscope was £850-£l,300, depending on application.) Marconi Avionics improvements include replacement of the steel gyro casing with one of Monel nickel alloy incorporation of a mu-metal screen to isolate the gyroscope motor's magnetic field; introduction of chemical etching (in place of lapping) to trim the torsion bar; adaption of semi-automatic test equipment and multiple jigging to simplify production. Marconi Avionics also introducedplastic damping vanes and replaced hand-wired parts by flexi-circuits. In 1980 GR-H4 production rate was roughly 100 units a month.

In 1981 Marconi  introduced the GI-G6 into production in a £750,000 development. The G6 is proposed for the Spearfish torpedo (formally Naval Staff Target 7525), and a strapdown system using the gyro was fitted to the Machan experimental unmanned aircraft.

The input rate range is +/- 10deg/sec to +/- 1000 deg/sec.


Allied Signal  aquisition

Allied Signal was an American aerospace, automotive and engineering company created through the 1985 merger of Allied Corp. and Signal Companies. It acquired Bendix Corp. gyroscope business which was later sold to Condor Pacific Industries in 1999. Condor Pacific was established in 1964 to manufacture miniature mechanical, spinning wheel gyros. Condor later went on to acquire Allied Signal's gyro manufacturing business (1999) and shortly afterwards was itself acquired by BAE Systems (2002). BAE Systems acquires Condor Pacific and forms the BAE Systems Inertial Products Division.

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