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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: Unknown
Division: Unknown
Platform(s): Harrier 
Year of Manufacture: circa 1982
Dimensions:
Width (mm):
85 
Height (mm):
45 
Depth (mm):
45 
Weight (g):
186 
Location: Main Object Store
Inscription(s):

None

Notes:

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"

This is very similar to ODGY0842.

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.

The original concept of an integrating rate gyro was a design by Siemens dating from 1939. The concept was developed further in Germany during WWII where it formed part of the rudder control system on the Hs129 and was possibly used in the "V2" weapon. After the War the design was brought to RAE Farnborough eventually being offered to industry.

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 English Electric Lightning and the FIAT "Flying Bedstead" and although it was proposed for Concorde it was not actually used.

 

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. 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 to be used in the television guidance head of the Anglo-French Martel air-to-surface missile. The ultimate value of the order is expected to exceed £900,000.

Other applications of the gyroscope included the Sea Vixen carrier-borne interceptor guidance, Sky Flash, an  air-to-air missile launched from Phantoms and Tornado, the Javelin missile, stabilisation of  the Hawker Siddeley P.1127 and ultimately the Harrier and the Sea Dart ship-to-air missile.

In March 1980 Marconi Avionics completed its 10,000th rate gyroscope, marking 15 years of manufacture which continued further. While building GR-H4s, Marconi Avionics introduced several improvements, independently of Northrop. These included 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 semiautomatic test equipment and multiple jigging to simplify production. At the same time unit cost was reduced, in real terms, by a factor of almost three. The input rate range is +/- 10deg/sec to +/- 1000 deg/sec.

In 1980 GR-H4 production rate was roughly 100 units a month.

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