The Damped Gyroscope

• How a Controlled Gyro may be converted to a controlled or North Settling Gyro using

gravity control and damping in tilt or azimuth

• Sperry Type Gyro• Brown Type Gyro

The Damped GyroscopeIn the case of the Sperry gyro scope the mercury pots are arranged in pairs about the North and South end of the gyro spin axis. One N/S pair on the east side of the spin axis and the other on the west side of the axis.

The Pots are held in a yolk which connects the North and South pots on each end of the axis. The yolk also runs below the Rotor casing and is connected to the casing below the rotor.

The connection of the yolk to the casing is not situated directly below the centre of gravity of the rotor, but is offset slightly to the east of bottom dead centre.

S

Gyro Rotor

Yolk holding LiquidPots at each end of the spin axis

Liquid Pots

Connecting pipesBetween N and S pots

Connection of yolk to rotor casing

Rotor CasingView from S end of the Spin Axis

• The offset of the connection point causes the following;• When the north end tips up, mercury will flow under gravity

from the North pot to the south pot, hence causing control precession.

• The connection point of the yolk is no longer under the rotor and now sits under the N end and to the east of the centre of gravity of the rotor.

• This gives rise to a force at the North trying to force it to the west and to tilt down. The downwards force will be overcome by the transfer of mercury, however the westwards force on the N end will remain.

• This will give rise to an eastwards force on the S end.

The Damped Gyroscope

The Damped Gyroscope

S

Fv

Pc

Spin direction of Sperry Gyro when viewed from South

Vertical Component causing Pc

The Damped Gyroscope

SFH

PD

Spin direction of Sperry Gyro when viewed from South

Horizontal Component causing PD

The Damped Gyroscope

• The Eastwards force on the South end (FH)), caused by the offset of the connection point, gives rise to an upwards precession on the South end (PD).

• This will cause a downwards precession on the North end.

• The downwards precession will start to act as soon as the N-end starts to tip up above the horizon.

• The effect of this downwards precession is to cause the path of the N-end to change from the elliptical control path to a spiral path, finally reaching a settling position.

To PoleEasterly Drift

Control Precession

Tilt (Up/Down)

Damping Precession (Down)

• Note the settling position of the gyro will be to the East of the meridian and above the Horizon.

• The reason for this is that the spin axis must be above the horizon so that there will be westerly control precession to counter act the easterly drift due to the Earth.

• The spin axis must settle to the east of the meridian so the downwards damping precession will counteract the upwards tilt due the Earth. (Note on the west of the meridian the tilt would be downwards)

The Damped Gyroscope

The Damped Gyro(Brown Gyro)

• The Brown gyro uses a slightly different method of obtaining damping. In this case a second set of oil bottles are used which are smaller than the working bottles. (66% of working bottles). The working bottles are on the eastern side of the gyro and the damping bottles are on the west side of the gyro.

• The damping bottles are connected to the air valve on the brown gyro but are connected in the opposite way from the working bottles.

The Damped Gyro(Brown Gyro)

• The north damping bottle is connected to the N end of the air valve and the south damping bottle is connected directly to the S end of the air valve.

• Therefore when the N end of the gyro tips up air will be directed to the N damping bottle, causing excess pressure in the N bottle and moving oil to the S bottle. (i.e. the S end will become heavy). The arrangement is shown in the next diagram

N

S

N Working Bottle

S Working Bottle

N Damping Bottle

S Damping Bottle

GYRO Rotor

Air Valve

Connecting pipe below

gyroConnecting pipe below

gyro

The Damped GyroscopeBrown Gyro

The Damped GyroscopeBrown Gyro

N

S

N Working Bottle

S Working Bottle

N Damping Bottle

S Damping Bottle

GYRO Rotor

Air Valve

Connecting pipe below

gyroConnecting pipe below

gyro

To N Damping Bottle

To N Working Bottle

To S Damping BottleTo S Working Bottle

Air Valve

When the N end tips up air will flow from the air valve into the blue pipe.This will take the air to the South working bottle, giving rise to the control

Precession described previously.It also takes air to the N damping bottle.

This will tend to move oil from the N damping bottle to the S damping bottle.

The Damped GyroscopeBrown Gyro

The Damped GyroscopeBrown Gyro

• At first sight this may seem like a contradiction in terms as movement of oil from the North damping bottle to the S bottle will have the exact opposite effect to that of the main working bottles.

• i.e. it would reduce the amount of control precession.

• In order to prevent this the connecting pipe between the damping bottles has a constriction in it. This is shown as a red circle in the earlier slide.

The Damped GyroscopeBrown Gyro

• The result of adding the constriction is that more air pressure is required before the oil can flow from the N damping bottle to the S bottle.

• The only way for the air pressure in the system to increase is for the N end of the spin axis to tilt further upwards.

• The net result is that the damping bottles have no effect until the N end has gone through the first quarter of the control ellipse. (See next slide.)

The Damped GyroscopeBrown Gyro

NORTH

3

4

5

6 7

1 2

The Damped GyroscopeBrown Gyro

Initially the path traced out by the N end of the spin axis is the same as the control ellipse described earlier. However when the N end gets to position 3 the Damping bottles now come into play.

The N end is now high enough above the horizon for air pressure to transfer oilFrom the N damping bottle to the S damping bottle. This makes the S end of thedamping system heavier than the north end. This will give rise to a downwards force on the south end of the spin axis. Due to the rotor spinning clockwise whenViewed from the S end, this will cause the S end to precess to the EAST.

This works against the control precession, but the damping precession is smallcompared to the value of PC. This causes the gyro to move upwards and eastwards compared to the standard control ellipse. Control precession will still take the N end back to the meridian.

Once the N end crosses the meridian and starts to tilt downwards, the damping precession will take the N end back to the meridian faster and cause it to move in spiral path.

The Damped GyroscopeBrown Gyro

The N end of the gyro will eventually settle on the meridian and above thehorizon.

Since the damping precession acts in a horizontal plane (i.e he same plane asdrift and control precession, then to settle there must be no tilt as neither controlor damping precession can counteract it.

The only place where there is no tilt is on the meridian.

The height above the horizon is such that the combined effect of drift and damping precession just matches the effect of control precession.

Hence the Brown gyro is said to be damped in azimuth as opposed to the Sperry,Which is said to be damped in tilt.