German Explosives
BLC 50 Photoflash Bomb
Overall Length: 42 inches
Maximum Body Diameter: 8 inchesLength of Detonating Fuse: 31.5 inches
Weight of Standard Charge: 15 kilograms
Peaklight Intensity: 450 million Hefner candles
Time of Peak Intensity: 70 milliseconds
Total Light Output: 63 million Int. candle seconds
General: It has been found that the Luftwaffe employed a photoflash bomb containing powdered aluminum, which was scattered into the surrounding air by the explosion of the inner core of black powder. Due to the heat of the explosion, the aluminum powder burned in the oxygen of the air and produced a rapid flash. The bomb weighed considerably more than the conventional type of photoflash bomb, which employs an intimate mixture of powdered oxidizing agent and magnesium or aluminum, and it produced a slightly lower peak candle power output. The time to reach peak intensity was also lower. However, the German bomb possessed a very great advantage in the fact that it was not sensitive to bullet impact, and was therefore much safer to employ.
Description: The BLC 50 50 photoflash bomb consists of a comparatively light steel casing approximately 42.9 inches long and 8 inches in diameter. The total weight of the bomb is 42kg. There is a heavy concrete nose piece which acts as a ballast to stabilize the flight of the bomb. The bomb itself consists of three approximately concentric tubes. The outer tube contains 15kg of aluminum "pyroschliff", which is an extremely fine, flaked aluminum powder, having the following characteristics:
-Metal Content: 87 - 92%
-Fat content: Less than 0.1%
-Moisture: Less than 0.5%
Another tube placed within the outer tube contains 3.5kg of black powder, serving as the explosive which scatters and ignites the outer charge of aluminum powder. The black powder, "Marine-Geschutz" pluver, possesses the following characteristics:
-Moisture content: Less than 1.3%
-Granulation range: 0.68 to 1.3 mm
Chemical Composition:
-Potassium Nitrate: 75%
-Sulphur: 9%
-Beech charcoal: 16%
The black powder is exploded by means of an 80cm length of detonating fuse which is place inside a third tube passing through the black powder charge. The ends of the detonating fuse are dipped in a 4% solution of collodion, and allowed to dry.
The bomb is ignited by means of the standard type of electrically ignited delay fuse which is inserted in the fuse well in the side of the bomb.
Remarks: In order to increase the usable light output of the BLC 50 photoflash bomb, the following researches were carried out recently:
A. The fine, flanker aluminum "pyroschliff" powder was replaced with an atomized aluminum powder called "griess". The new, atomized powder possessed spherical particles, and therefore had approximately twice the apparent density of the flaked form. Approximately 30 kilograms of the atomized powder could be placed in the volume formerly occupied by 15 kgs of aluminum "pyroschliff". This procedure increased the peak intensity from 450 to 800 million Hefner candles. However, the flash was very much slower, that is, the time to reach peak intensity was longer, and the total duration of the flash was longer. It was also stated that the results could not be reproduced, because of variations in the characteristics of the atomized aluminum powder.
B. The 15kg charge of flaked aluminum powder was replaced by 28kgs of pellets (13mm diameter and 7mm height) composed of the following composition:
-Magnesium powder: 39%
-Barium nitrate: 53%
-Synthetic phenolic resin: 6%
-Talcum: 2%
These pellets were packed int he outer tube of the bomb together with 9kg of black powder and then a length of detonating fuse added.
This bomb, when exploded, produced a peak intensity which was only 80 percent of that of the standard BLC 50 bomb. The time to reach peak intensity (100 milliseconds) was longer than that of the standard bomb, and the durations of the flash at one-half and one-tenth maximum intensity were much longer (230 and 550 milliseconds, respectively). In addition, this bomb was found to be sensitive to bullet impact.
C. The standard 15kg aluminum powder charge was replaced by one huge pellet weighing 24kg. The composition of the pellet was as follows:
-PTN: 50%
-Magnesium powder: 50%
The results of the firing tests conducted with this bomb were very disappointing. They indicated a peak intensity only one-fifth of that of the standard bomb. The flash was very slow, since the durations at one-half and one-tenth maximum intensity were 500 and 1,000 milliseconds, respectively.
D. The standard 15kg charge of aluminum was replaced by one composed of 28 pellets of the following composition:
-Sodium nitrate: 45%
-Magnesium: 50%
-Wax: 5%
Each pellet had hollow axial space, weighed 900 gm, and measured 60mm in diameter and 220mm in height. The total weight of pellets placed in the bomb was 25.2 kg. A length of detonating fuse was passed through each pellet and all of the ends of the fuze bound together.
The results of the firing tests conducted with this bomb indicated that the total peak intensity was approximately the same as that of the standard bomb. However, the peak intensity measured through a yellow filter (which is considered important when photographing at night in the presence of a slight ground haze) was 20 percent greater. Although the time intensity curve for the flash rose at the same rate as that of the standard bomb, the duration of the flash was very much longer, being 400 and 800 milliseconds at one-half and one-tenth maximum intensity, respectively.
This indicated that the total light output was very much greater than the standard bomb. However, this light would not be usable if short exposures were employed. In addition, the bomb was found to be sensitive to bullet impact.
E. In order to decrease the time of the flash, and thereby raise the peak intensity and concentrate it in a small time interval, a bomb was loaded using the same general procedure as C, but pressing each pyrotechnic pellet into a separate steel case in order to increase the confinement. A detonating fuze was inserted through each pellet as before. The results of the tests with this bomb showed that the peak intensity could not be appreciably raised. The bomb was also found to be sensitive to bullet impact.
F. The results of all of the above tests indicated that the peak intensity, and therefore the total usable light output, in a short exposure time could not be increased appreciably. However, most of the experimental bombs produced longer flash durations, with intensities consistently as high as that of the standard bomb. Therefore, efforts were directed toward the utilization of longer exposure times. A camera, known as the "E-5", employing a moving film holder to compensate the movement of the airplane, was developed recently. The "E-5" camera makes possible the use of very long exposure times, and thus permits the use of photoflash bombs producing a long, slow flash. In this manner the total usable light output can be multiplied three to four times.
Safe photoflash bomb, employing outer layers of large amounts of atomized magnesium or aluminum powder can then be used, because all of the light of the relatively slow flash is useful.
Target Indicator (Red)
Overall Length: 13.25 inches
Body Diameter: 3.4 inchesFilling: Flare composition
Construction: The flare composition is contained in a cardboard cylinder which fits into an aluminum casing and seats against a washer touching the suspension plate. It is secured at the nose end by two plates, the end of the casing being slightly indented to hold these. The suspension plate holds an eye to take the parachute shackle, and a pull igniter which is connected by a 4 and 3/4 inch length of safety fuse to a small bag containing gunpowder. This serves both to set off the igniter pellet in the top of the candle and to eject the latter from the casing when it falls freely to earth and acts as a ground marker. The pull igniter is attached to the loop of the shroud lines by a cord; the opening of the parachute gives the necessary pull for operating the igniter. There are two small fins at the nose end of the container; their purpose is not clear.
Suspension: The indicator is carried in Mark 250 BK-3SD2 container.
Remarks: Container from which indicators were recovered was marked with a red band corresponding to the color of the flare.
Marker Bomb (Sea)
Overall Length: 4 feet 8 and 1/2 inches
Body Diameter: 8 inchesWall Thickness: 1/32 inches
Tail length: 9 inches
Tail width: 10 inches
Color: Painted yellow overall
Construction: The sheet steel, bomb-shaped body is supported internally by a series of eight annular strengthening bulkheads. Welded to the after end of the body is a tail cone which terminates in a short parallel sided tube over which is assembled an adapter designed to accept the aluminum body of the lamp unit. Four stabilizing fins are welded to the tail cone and strengthened by metal struts. The nose portion of the bomb body is welded to the parallel-sided portion of the body and terminates in an annular flange to which the solid steel nose plug is bolted through a castellated collar. The rear face of the nose plug has been recessed to form a housing approximately 1 and 1/2 inches deep for the battery unit which is assembled inside a central tube of drawn steel 18 and 1/2 inches long and 4 and 1/8 inches internal diameter. The battery unit consists of a series of small dry cells contained with an insulate cylinder.
Provision is made for six cells in each later, the cells being arranged around a central tube through which a retaining bolt passes to secure it to the nose plug. The rear end of this tube is closed by means of a closing cap to which an annular brass contact disc is secured and which is held in place by means of a washer and nut. A contact is located in the tail adapter by a grub screw and slot arrangement. Passing through the contact bush and screwing into the tail adapter is a lamp unit which consists of a cast aluminum body with an insulated contact rod secured through the base of the casting by two grub screws. At the base of the rod, a spring switch is mounted with leads to the battery unit and the lamp unit.
Positioned between the two arms of the spring switch is an insulated inertia bolt which breaks the contact until closed on impact. The lamp unit is spring mounted to protect it from shock and covered by a Lucite type dome. When the marker is released from the aircraft, the inertia bolt is positioned between the plates of the spring switch and one side of the circuit between the lamp and the batteries is broken. On impact, the inertia bolt is forced out of position and the circuit between the lamp and battery is completed. As the batteries fill, only a portion of the bomb body and all joints are made tight by rubber washers, the marker floats on the surface of the water, and it is assumed, provides a recognition or bearing point for aircraft.
Suspension: Vertical
Lux EZ 50 SC (Sea Marker)
"Kennung K.B., Seiklange 200m, ZW"
"Verbrauchen B 15"
On the nose is stenciled: LUX.E 250
Construction: The marker is constructed in two parts. The rear portion consists of a cylindrical steel container to the rear end of which are attached four metal fins; behind these is situated a flat metal base plate of the same diameter as the marker and having attached to it a spring-loaded platform which in turn houses a green silk drogue. Projecting also from the base plate is a frosted globe.
At the other extremity of the rear portion of the marker is situated a fuze pocket sealed by a steel disc and locking ring. Forward of this and next to it is a carrying lug. The front portion of the marker consists of a heavy steel nose which is internally attached to the rear portion, the joint being visible as a thing groove. Screwed to the end of the nose is a circular steel plate which serves as a kopfring.
The forward portion of the marker contains another fuze pocket. Forward of this is a small hole covered by a thin steel disc held by a spring clip; a similar hole is situated on the other side of the nose diametrically opposite to it. Passing down the side of the marker is a piece of thin S.W.R. which passes through a small hole where the two halves of the marker join together.
Operation: Immediately upon release from the aircraft, the drogue is pulled out by means of a rip cord attached to the aircraft and the (17) A fuse in the forward end of the marker is charged. The speed of the marker's fall is slightly reduced by the drogue. Upon striking the water it sinks to the bottom, burying its nose.
After a preset delay up to 72 hours, the (17) A fuze fires a small charge of gunpowder contained in a bakelite gaine. The pressure created by this explosion releases the catch holding the two halves of the marker together. The front portion of the marker is forced off the rear portion by its spring-loaded plunger. As soon as the two halves separate, the electrical hydrostatic switch on the rear portion is free to close on release of water pressure. The rear portion of the marker having positive buoyancy now rises to the surface of the water, unwinding as it does so the S.W.R. contained on the drum of the forward portion of the marker which now acts as an anchor.
As soon as the cylindrical rear portion reaches the surface, the hydrostatic switch closes. The battery is now connected up in parallel with the motor and the lamp. The motor revolves and by means of a gear train operates a contact breaker, thus causing the 24-watt bulb to emit a series of light flashes. The frequency, alternation, and duration of the flashes emitted vary in each marker.
The closing of the hydrostatic switch also allows the battery to charge the (17) A fuze. After a delay the fuze fires. The electro-magnetic current inducer attached to it produces a flow of electricity which fires two ignition bridges in the end plates of the marker. The flooder plugs are blown out thus destroying the marker by permitting it to sink.
Suspension: Horizontal by standard German eyebolt.
Remarks: A soluble plug on the drogue housing allows the drogue to break free from the marker after it has entered the water.
Next Time: Pyrotechnics (Part 5)
Source: German Explosive Ordnance Vol. 1: Bombs, Rockets, Grenades, Mines, Fuzes & Igniters
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