The completed Sperry, a "shining example" of effort and commitment.
(Image Trevor Smith)
Searchlight, May 5th 2007. (Image Dick Woodard)
HISTORY AND USE
The high intensity arc searchlight was developed in 1918 by the American
inventor, Elmer A Sperry (18601930). It became the standard equipment
of the main military forces of the world, and also widely used commercially.
This example was manufactured in 1941 for anti-aircraft purposes by the
Sperry Gyroscope Company of Brooklyn, New York.
Gordon taking measurements at the start of the project.
THE ANGLO-BOER WAR (1899-1902)
In the early nineteenth century, primitive searchlights were used to
protect the sorting floors of diamond mines at night. During the
Anglo-Boer War, these lights were used for:
Defence of besieged towns.
Signalling and Communication.
Sweeping beams of light across the veld from armoured trains.
Vernon cleaning off years of grime, getting ready for the paint
removal.
THE FIRST WORLD WAR (1914-1918)
The value of the searchlight in anti-aircraft defence was discovered
when airships and aircraft were first used for night bombing raids over
large towns.
Gordon hefting an axle.
THE SECOND WORLD WAR (1939-1945)
In the early part of the war, the British devised a defensive system
whereby the target was simultaneously illuminated by at least three searchlights.
As it moved on, a new searchlight lit up, and the one left behind was doused.
The target was continually illuminated and could then be destroyed, either
by anti-aircraft fire from the ground or by a fighter in the sky.
Ready for an undercoat.
Later in the war, when faster aircraft were developed, time became a
vital consideration. The sky was divided into boxes and when
the target entered the box, many searchlights trained their beams on
it so that the enemy could be rapidly destroyed.
At first, the German air defence system was so weak that allied bombers
were surprised at the lack of opposition. By mid-1942, however, the
box system was also being used in Europe and Germany with great effect.
During the Second World War, anti-aircraft searchlights were used for:
Detection and illumination of enemy aircraft.
Enabling day-fighters to be used in the night sky.
Forcing enemy bombers into higher altitudes.
Blinding and confusing the crew of the enemy aircraft.
Acting as beacons for the landing of damaged aircraft.
Enabling the destruction of flying bombs in mid-air.
Trevor Smith, project leader.
Other uses included:
Extensive use of coastal defence.
Use by patrolling aircraft and ships at sea.
Illumination of the battlefield for night attacks.
Fitted to tanks to blind the opposing land forces.
Signalling other units and allied forces.
HOW IT WORKS
The Beam
When a light source is kept at or near the focal point of a mirror,
it is magnified to the diameter of the mirror and reflected as a beam of
light . The beam produced by this searchlight can illuminate a high-flying
target in the night sky.
The Searchlight Lamp
The earlier searchlights used kerosene or acetylene flames and, later,
electric filament lamps as the light source. However, these were
replaced by the far more effective carbon arc lamp. A carbon arc
is a bridge of light that is formed in the space between the tips
of two oppositely charged carbon rods.
The light source of the searchlight is produced by a far brighter high
intensity arc. The core of the positive carbon is filled with
the rare earths, cerium and lanthanum, which burn off as a bright,
incandescent gas. The flame of the negative carbon confines this
light source to the tip of the positive carbon which is automatically
kept at the focal point of the mirror.
The searchlight lamp is kept within a large drum . The drum is
well ventilated to prevent a build-up of high temperatures and light absorbing
dust and gases , allowing the searchlight to be used for long periods of
time.
The Searchlight Equipment
1. The searchlight manufactured by the Sperry gyroscope co.
2. The generator providing the power needed to run the searchlight
manufactured by General Electric. The unit is powered by a Hercules JXD
six cylinder side valve motor.
3. Early in the war, a sound locator could be used to detect an approaching
aircraft at a distance of 16 km. Later, it was replaced by more accurate
radar systems.
4. The searchlight could also be controlled manually through the extended
hand controller, which fitted into the searchlight drum. By pushing
the rod left or right, the operator moved the searchlight into the correct
horizontal position. By turning the wheel on the end of the rod,
the beam was lifted to the desired elevation.
The GE Generator.
Searchlights were produced from 1932 to 1944 by Sperry and General Electric
at a cost of $60,000 each!
Light Source: 1 inch Carbon Arc (no light bulb!)
Power: 78 Volts @ 150 Amps
Candle Power: 800,000,000 (800 million)
Effective Beam length: 5.6 miles
Effective Beam visibility: 28~35 miles
Glass Weight Totals: 75 lbs
Brass Rhodium Coated Mirror: 180 lbs
GENERATOR:
Generator Power: 15 KWV nominal - 16.7 KWV max.(15,000~16,700 watts
D.C.)
Powered By: Inline 6 cyl. "Hercules" Flathead Engine
Generator Engine Fuel: Gasoline (can also be run using Kerosene or
Gasohol) 26 gallon capacity
Under searchlight load burns about 3 gallons per hour
Combined Weight: 6,000 pounds (3 tons, or the weight of 3 Ford Mustangs
combined!)
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