Monday, 20 February 2017

British Explosive Ordnance - Cluster Projectiles Part 1






British Explosive Ordnance








  

Cluster Projectiles Introduction
   


A cluster projectile is an assemblage of small bombs or flares held together primarily by resilient straps and beams.  It is constructed so as to be an amiable projectile, and is usually fitted with a tail unit for purposes of stabilization.

At present there are cluster projectiles for flares, incendiary bombs, smoke bombs, and small fragmentation bombs.  The cluster projectiles are rapidly replacing the Small Bomb containers as the preferred method for carrying small bombs and flares.  Advantages of the cluster projectile include ease of loading and installation in the aircraft, increased number of bombs or flares contained in the same space, and increased accuracy.

A new and improved type of cluster, called the Nose Ejection Cluster, was put into production just before the end of World War II.  These clusters are discussed in general at the end of this chapter, and available details listed in tabular form.

Fuzes are incorporated in the cluster projectiles to disintegrate the cluster itself and so permit the individuals bombs or flares to disperse and fall freely.  Cluster projectiles have explosive channels and pellets so designed as to break up the cluster without injuring any of the contained bombs.  Flare and incendiary clusters are fuzed either at the nose or at the tail, while fragmentation and smoke bomb clusters now in service are fuzed in the tail only.   Nose ejection clusters are tail fuzed only and use two tail fuzes to insure functioning.

The bombs or flares are usually shipped already packed in the cluster projectile, so that assembly of the complete round is not necessary in the field.  The fuze of the cluster is generally installed just prior to loading the projectile on the aircraft.









Cluster Projectile 270lb No.1 Mk I (Service)


Contents: Seven 4.5-inch flares
Overall length: 62.75 inches
Body diameter: 18 inches
Total weight: 260 pounds

Fuzing: Nose Fuze No.42, 848, 849, or 860 Mk II
Tail No.: No.69 Mk I
  

Color and markings: Dark green overall

  
Description: The cluster is a cylindrical metal container consisting of a nose unit, recessed to receive the noses of seven 4.5-inch reconnaissance flares, and a fuze adapter, from which radiate six flash tubes to the flare igniters and three flash channels leading to the explosive pellets in the piston housings.  The nose unit is secured to the panel locating plate and the tail plate by the T-section suspension bar and the clamping bars.  The clamping bars consist of a bar to which are welded two panels.  The clamping bars locate the panels and are secured through the panel locating plates to the tail plate and to the nose unit by spring washers and nuts.  The nuts securing the clamping bars to the piston housings are further secured by split pins.  The tail tie rod is screwed into the tail plate and the tail unit fastened to it by a spring washer and nut.

The flares, from which the suspension lugs and domed caps have been removed, are located by the recesses in the nose unit and panel locating plate.  The flares are fuzed with special igniters, consisting of the body and dome portion of the Fuze No.42 without the percussion cap and striker mechanism, and sealed with primed cambric.
 

Tail Construction: The Tail No.69 Mk I consists of a sheet-metal tail cone to which a cylindrical strut is attached by four fins.  The tail unit is attached to the tail plate of the cluster by a tie rod, which passes down the center axis of the tail wire.


Functioning: On release from the aircraft, the cluster falls normally until the fuze functions.  When the fuze functions, the flash from the magazine passes through the flash tubes to ignite the igniters in the nose of each flare, and through the flash channels to explode the gunpowder pellets in the piston housings.  The explosion of the pellets forces the pistons out of their housings, causing the clamping bars to swing outwards, thus releasing the nose unit, panels, and initiated flares.  The flares then function in the normal manner.


Suspension: The cluster is suspended by a single lug secured to a T-section suspension bar, which runs from the nose to the base of the cluster.

 







Cluster Projectile 140lb No.2 Mk I (Service)
   

Contents: Four 4.5-inch flares
Overall length: 53.25 inches
Body diameter: 12.35 inches
Total weight: 140 pounds (approx.)

Fuzing: Nose Fuze No. 848, 849, or 860 Mk II
Tail No.: No.70 Mk I
  

Color and markings: Dark green overall

  
Description: This cluster is designed to hold four 4.5-inch flares.  The components of the cluster consist of a nose unit, four flat caps which replace the dome-shaped tail closing caps of the flares, a T-bar, a panel locating plate, a tail plate, two clamping bars, two panels, and a tail unit.

When the cluster projectile is assembled, the four flares are located between the nose unit and the panel locating plate, and the assembly is held together by the clamping bars.  The tail plate is also retained in position by the clamping bars, and the tail unit is secured to the tail plate by a nut and washers fitted to one end of a tie-rod, whose other end is screwed into the tail plate.  The panels enclose the flares, and the T-bar, which positions the panel locating plate and the tail plate relative to the nose unit, carries a suspension lug by which the cluster projectile is attached to a bomb carrier.


Tail Construction: Tail Unit No.70 Mk I consists of a shortened tail cone, the base of which fits over the rim of the tail plate, and a tail strut secured to the tail cone by four fins.  The tail unit is attached to the tail plate of the cluster by a tie-rod which passes down the center axis of the tail cone.


Functioning: The fuzed cluster projectile is released from the aircraft, and the fuze is set in operation.  When the gunpowder in the fuze magazine explodes, the flash ignites the gunpowder contained in the small bag in the fuze adapter of the nose unit.  The boosted flash passes through the six flash tubes, initiates the igniters fitted to the four flares, and fires the gunpowder in the piston housings.

The gases formed by the ignition of the gunpowder in the piston housings force the pistons out of the housings, shearing the brass shear pins, and so causing the clamping bars to swing outward on the U-bolts.  This outward movement of the clamping bars releases the nose unit, the panels, and the initiated flares.  The parts of the disintegrated cluster fall separately, and the flares, initiated by their igniters, function in the normal manner.


Suspension: This cluster is designed for suspension in British aircraft only.  A single suspension lug is fitted to the T-bar of the cluster.


Remarks: In addition to normal stencilling in English, propaganda messages in German are stencilled in white paint on the sides of the panels.











Cluster Projectiles 400lb No.3 Mk I (Service)
  

Contents: Four 7-inch hooded flares
Overall length: 72.5 inches
Body diameter: 18 inches
Total weight: 400 pounds 

Fuzing: Nose Fuze No. 860
  

Color and markings: Black overall

  
Description: The cluster projectile consists of a flare-supporting unit, heavy nose, half securing bands, and the hooded flares.  The flare supporting unit consists of a square cast-iron plate, on which is painted a narrow white alignment strip, and a steel tube to which is welded a suspension web.  The rear end of the tube is flanged, and four equispaced pins are riveted to the flange.  External threads on the fuze housing receive the plate-securing ring, which secures the plate to the tube.  The tube is also internally threaded at the nose end to receive the fuze and a centrally drilled separating plug.

Four flash channels are drilled through the walls of the fuze housing immediately above the separating plug.  Four flash tubes lead from these flash channels to the four equispaced holes in the plate drilled to receive the flare igniters.  The piston, flanged at the protruding tail end, is housed in the tube and retained in position at the nose end by two shear pins.  A space between the nose end of the piston and the centrally drilled separating plug forms a burster chamber, which is filled with a small fabric bag containing 80 grams of gunpowder when the cluster is fuzed.  The heavy cast-iron nose, on which is painted a white alignment strip, and to which the flare supporting unit is bolted, is slotted to receive the flash tubes and the Fuze No.860.  The nose end plate is retained in position by the fuze.  The four flares are fitted with special igniters instead of fuzes, and are retained in position in the cluster by half securing bands.  The igniters are located in the drilled hole in the plate.

The four half securing bands of the flare securing unit are seated on the flange, and each is retained in position by a socket, welded to the outside of the band, engaging with a corresponding dowel pin.  The sockets are covered by metal bridges in which are cut horizontal slots to receive the flange of the piston.  This prevents premature displacement of the flares.  The four remaining half securing bands are placed in position round the flares and bolted to the other half bands.  A cruciform distance piece is bolted to the tail end of the piston.


Functioning: On release from the aircraft, the cluster falls in a normal manner until the fuze functions.  The flash from the fuze magazine passes through the flash channels and the flash tubes to activate the igniters, and through the separating plug to the burster charge.  The explosion of the burster charge forces the piston towards the tail end of the cluster to sever the shear pins and to lift the half securing bands off the dowel pins by means of the flange of the piston engaging in the bridges.  The four flares are thus lifted off the plate of the flare supporting unit.  A three-second delay in the flare igniters allows the cluster to disintegrate before the flares function.




 




Cluster Projectile 500lb No.4 Mk I (Service)


Contents: Fourteen 30lb Type J incendiary bombs
Overall length: 72.5 inches
Body diameter: 18 inches
Total weight: 400 pounds 

Fuzing: Tail Fuze No.867 Mk I or No.885 Mk I
Tail No.: No.44 Mk I or II
  

Color and markings: Dull red overall, one of the tensioning straps painted bright red.

  
Description: This cluster is hexagonal in shape, and contains fourteen 30lb type "J" incendiaries, in two fagots of seven bombs each.  The bombs are placed nose-to-nose and arranged in super-imposed rows of 2, 3, and 2 in each fagot.  The bombs are retained in position by the front and rear end plates, the top and bottom beams, the side fairings, tensioning straps, and the retaining bar.  The front and rear end plates secure the spring-loaded covers of the bomb parasheet containers.  Lateral pins on the retaining bar engage with and hold the tabs of the tensioning straps in position.  A shear wire near the end plate acts as a safety device for the retaining bar.  To the rear end of the retaining bar is secured a pivoted lever, the lower end of which engages with the piston in the fuze adapter.

The fuze adapter is fixed to the channel plate, which in turn is fastened to the rear end plate.  A nut, welded to the center of the rear end plate, received the tail tie rod to which the tail unit is secured by a tension nut.  A nose fairing is secured to the front end plate, and fairing are fitted to the top beam.  The fairing adjoining the rear end plate is slotted to receive the fuzing lanyard of the fuze and the safety wire of the tail unit.


Tail Construction: The Tail Unit No.44 Mk I is located by two dowel pins and is provided with two inspection windows to ensure correct alignment of the arming forks.  A tie rod connects the tail unit to the cluster.


Functioning: On release from the aircraft, the fuze-setting control link withdraws the safety wire from the tail unit and, at the same time, breaks the shear wire of the fuze by means of the fuzing lanyard.  The cluster falls normally until the fuze functions.  The explosion of the fuze magazine forces the piston forward in its housing to cause a rocking movement of the pivoted lever.  The sudden movement of the pivoted lever exerts a pull on the retaining bar to break its shear wire and disengage the lateral pins from the tabs of the tensioning straps.  The straps, thus released, fly outwards to release the 14 bombs, which function normally on impact.


Suspension: A single suspension lug is fitted to the top beam, and tapped holes are also provided for the fitting of American lugs where necessary.


Remarks: This cluster projectile is designed to replace the Small Bomb Container as a means of carrying 30lb type "J" incendiaries.











Cluster Projectile 500lb No.6 Mks I and II (Service)
  

Contents: Ninety 4lb smoke bombs
Overall length: 72 inches
Width across flats: 16 inches
Tail length: 27 inches
Tail width: 16 inches
Total weight: 428 pounds 

Fuzing: Tail Fuze No.885 Mk I
Tail No.: No.45 Mk I
  

Color and markings: Dark green overall

  
Description: The cluster is hexagonal in cross section and comprises ninety 4lb smoke bombs, arranged in five fagots of eighteen bombs each.  The bombs are arranged nose-to-tail longitudinally, and in alternate rows the bomb fuzes point in opposite directions.  The bombs are held in place by a front end plate and a rear end plate, a top beam and a bottom beam, four side plates, tensioning straps, and a retaining bar.  Lateral pins on the retaining bar engage tabs forming part of shoes attached to the ends of the tensioning straps.  A shear wire passes through the retaining bar and a bridge on the top beam.  The four side plates, together with the two beams, completely surround the bomb cluster.  A channel secured to the rear end plate supports a fuze adapter, the outer end of which is closed by a transit plug and leather washer.  Inside the adapter is a piston through which is a pin to engage the lower end of a pivoted lever.  The fuze adapter and piston are slotted to receive the lever, which is connected at its upper end to the retaining bar.

The rear end plate has two dowels for locating the tail in position, and a nut welded to the center of the plate receives one end of a tail tie rod when the tail unit is fitted to the cluster.  The front end plate has two dowels for locating a nose cover in position.  A securing bolt is screwed into the center of the nose end plate to receive a fixing nut, when the nose cover is fitted to the cluster.


Tail Construction: The tail unit consists of a tail cone with an approximately hexagonal base, and a tail strut secured to the cone by fins.  A the base of the tail cone are two holes to fit over the dowels on the rear end plate of the cluster.  A tie rod passes through the center of the tail, and one end of this rod is threaded to screw into the central nut on the rear end plate.  The other end of the rod is fitted with a tensioning nut for securing the tail to the cluster.  The tail unit also has an arming spindle mounted in bearings, which has a fork at its inner end and an arming vane at its outer end.  The safety wire, when fitted, passes through holes in a bracket, a projection on the support for the arming spindle bearings, and a blade of the arming vane.  Two inspection windows in the tail cone are provided to enable the armorer to watch the fork of the arming spindle, when fitting the tail unit.


Functioning: When a cluster projectile fuzed with a Fuze No.867 is released, safety wire is withdrawn from the tail-unit arming vane and the shear wire of the fuze is broken to release the fuze safety pin.  After a period of delay during which the cluster projectile falls freely, the fuze magazine is fired.  The products of combustion of the magazine charge force the piston in the fuze adapter against the lower end of the pivoted lever, which is thus rocked about its pivot and exerts a pull on the retaining bar of the cluster.  The pull breaks the shear wire passing through the retaining bar, and moves the bar so that its pins disengage the tabs on the shoes attached to the tensioning straps.  The straps then fly outwards and the cluster disintegrates, its component parts falling away separately.  The individual bombs function on impact.


Suspension: A British type suspension lug is fitted to the top beam of the cluster, and tapped holes are provided for fitting American type lugs.


Remarks: The Cluster Mk I contains 90 4lb Smoke Bombs Mk III.  The Cluster Mk II is identical to the Mk I, except that it contains 90 4lb Smoke Bombs Mk II** or Mk IV.

If the smoke composition used in the 4lb smoke bombs gets wet, and especially if wetted by sea water, it is liable to spontaneous combustion through chemical action.











Cluster Projectile 500lb No.7 Mk I (Service)


Contents: Fifty-six 8lb F. Bombs Mk II
Overall length: 67 inches
Body diameter: 15 inches
Tail length: 27.75 inches
Tail width: 18 inches
Total weight: 550 pounds 

Fuzing: Tail Fuze No.885 Mk I
Tail No.: No.46 Mk II
  

Color and markings: Dark green overall, one tensioning strap painted red.

  
Description: This cluster consist of eight fagots of seven 8lb F. bombs each.  The fagots are retained by top and bottom beams, front and rear end plates, side fairings, and four tensioning straps.  The tensioning straps are held by lateral pegs on the release rod, which is located in the top beam.  The release rod is connected to a level and piston mechanism, the cylinder of which also serves as the adapter for the barometric fuze and is located on the rear end plate.  Before the fuze is fitted, the adapter is closed by the inverted cup portion of the safety device for the release mechanism.

To convert the cluster into an amiable cluster, a blunt nose fairing and drum-type tail are fitted to the front and rear end plates, respectively.  A special streamlined nose fairing is provided for use when the cluster is to be stowed externally on the plane.
 




Functioning: On release from the aircraft, the cluster falls until the fuze functions.  The explosion of the magazine forces the piston forward in its housing and causes a rocking motion of the pivoted lever.  The sudden movement of the lever exerts a pull on the retaining bar and breaks the shear wire, disengaging the lateral pins from the tabs of the tensioning straps.  The straps are thus released and fly outwards, releasing the contained bombs.








Next Time: Cluster Projectiles Part 2

Monday, 13 February 2017

British Explosive Ordnance - Aircraft Pyrotechnics Part 2





British Explosive Ordnance








  

Smoke Float No.1 Mks II, III, IV, and IVZ (Service)
   

Overall length: 22 inches
Body diameter: 6 inches
Total weight: 11.5 pounds
Burning time: 6 minutes
Color of smoke: White

Fuzing: Tail Pistol No.23
  

Color and markings: Body, head, and nose painted green,
tail cone vanes and strut painted yellow,
red ring 1/2-inch wide around head near nose.

  
Description: The Smoke Float No. 1 Mk IV comprises a cylindrical body, closed at one end by a conical head and a heavy nose.  A retarding band is secured to the body adjacent to the head.  A tail cone, carrying three vanes to support the vane ring, is secured to the opposite end of the body.  The end of the tail cone houses a pistol adapter for the tail pistol, which is locked in place by a grub screw.  Inserted in the pistol adapter is a cup, containing a cartridge base and a small quantity of flash composition, sealed with a paper disc.  A sleeve leads from the bottom of the pistol adapter into the funnel-shaped upper end of the tube, known as the container cap tube. 

The container for the smoke composition has a fusible cup inserted into the top of the smoke composition, which is filled with pressed priming composition, and a primed cambric disc through which is threaded a length of quickmatch.  The cylinder, provided with a ring of holes, surrounds the container.  The rest of the body and the tail cone comprise a buoyancy chamber.  The tail cone is provided with a sinking disc, which is scored, so that if a floating smoke float is found, the disc can be easily pierced to sink the float, the water entering the tail cone and passing into the body through the holes in the central cylinder.


   
Functioning: When the fuzed smoke float has been dropped from the aircraft, impact of the nose on the surface of the water causes the striker of the pistol to hit the cartridge base, and the ensuing flash ignites the flash composition.  The flash from the flash composition passes down the container cap tube and ignites the primed cambric disc and quickmatch, which ignite the primings.  The fusible cup melts, and the primings ignite the smoke composition.  Smoke rises up the container cap tube, and as the pressure increases, bursts the seal of the tail cone.  The short period between impact with the water and bursting of the seal is sufficient to enable the smoke float, after submerging, to rise to the surface, owing to its buoyancy.



Suspension: A suspension lug provided on the body permits attachment of the smoke float to a Light Series Bomb Carrier.



Remarks: In the Float No.1 Mk II, the container cap tube serves only to carry smoke from the container to the sealed hole in the tail cone.  A length of safety fuze, giving a 20-sec delay, extends between the pistol adapter and the container.  In the Float No.1 Mk III, the container cap tube also serves only to carry the smoke from the container to the sealed hole in the tail cone.  A separate flash tube guides the flash from the flash composition to the container.  The Float No.1 Mk IVZ differs from the Float Mk IV only in the nature of the smoke composition used.

Should water, especially salt water, come into contact with the smoke composition, it is liable to spontaneous combustion due to chemical action.














Smoke Float No.2 Mks I and II (Obsolete)


Overall length: 45.5 inches
Body diameter: 13 inches
Total weight: 108 pounds (empty)
Duration of burning: 8-10 minutes

Fuzing: Tail Pistol No.48
  

Color and markings: Green overall, red band around nose, yellow band around tail.

  
Description: This float consists of a cylindrical body with a rounded nose containing the smoke composition.  The nose piece is riveted to a metal band passing around the body at the joint.  The rest of the body is cylindrical and contains a central well filled with primed cambric.  At the after end of the central well is the pistol well.  The body has several internal stiffening rings.



Functioning: When the fuzed float is dropped, the striker overcomes the creep spring on water impact, and fires a detonator located below the pistol in the pistol well.  The flash is carried to the smoke composition in the nose of the float by means of the primed cambric in the central well.



Suspension: The float is suspended by means of a single lug attached near the nose.



Remarks: The Float No.2 Mk I has its forward end reduced in diameter about 1 and 1/2-inch for a distance of about one foot.

 







Smoke Float No.3 Mk I (Obsolescent)
   

Overall length: 10.1 inches
Body diameter: 6.7 inches by 4.95 inches
Filling: Calcium magnesium phosphide
Color of smoke: Red

Duration of burning: 40 seconds

Fuzing: Pull-percussion igniter
  

Color and markings: Upper half of body is yellow,
lower half of body is green, with red band 1/2-inch wide 2 inches from bottom.

  
Description: The float consists of a thin metal body at the upper end of which six smoke-emission holes, covered by a fabric seal, are located.  A wire gauze washer, held in place by an upper and lower liner, divides the body into two portions, the upper portion comprising a buoyancy chamber, and the lower portion housing a number of large and small smoke pellets disposed around a pull-percussion igniter.  The large smoke pellets are arranged in tiers.  The pellets in the upper tier are each contained in a primed cambric cylinder.  Below the wire gauze washer, a primed cambric washer rests on the upper ends of the primed pellets, and strips of primed cambric cross over the igniter.  The igniter, which is secured to the body, includes a split-headed clutch which is movable lengthwise in the igniter body.  A whipcord becket is secured to the head of the clutch and threaded through a rubber disc.  The upper end of the clutch is sprung over one end of a striker, which is spring-loaded when the clutch is pulled out.  Opposite the free end of the striker is a percussion cap, and an anvil housed in an ignited plug screwed into the igniter body.  A length of safety fuse, enclosed in a tube, terminates in a capsule filled with igniter composition.

When the float is to be used, proceed as follows: Remove the adhesive tapes securing the covers and remove both covers.  Press in the center of the press-cap to release the cap, and then remove the cap.  Pull the whipcord becket and the clutch out of the float, and immediately throw the smoke float overboard to leeward.



Functioning: When the clutch is pulled out, the striker is released and fires the percussion cap.  The flash from the cap ignites the safety fuse, which fires the igniter composition in the capsule after a delay of not less than eight seconds.  The flash from the igniter composition is conveyed by the primed cambric strips and the primed cambric washer to the pellets in the upper tier.  The smoke produced raises the pressure in the buoyancy chamber until the pressure bursts the fabric seal, and the smoke escapes to the atmosphere through the smoke-emission holes.



Remarks: This smoke float is intended for use from an emergency dinghy after a forced landing has been made, to assist search planes.












Aluminum Sea Marker Mk I (Service)
  

Length: 4.5 inches
Width: 3.5 inches (square)
Weight: 1 pound

Fuzing: None; impact initiated
  

Color and markings: Aluminum overall

  
Description: The marker consists of a fragile, paper-side body of square cross section, fitted with wooden end pieces, and filled with aluminum powder.  The outside is coated with aluminum paint.  The body is surrounded by a loose cardboard sheath to protect it from damage while being handled.



Functioning: When the sea marker is dropped from a plane, the cardboard sheath separates from the marker, and the latter ruptures on impact with the sea, leaving a patch of aluminum powder floating on the surface.



Remarks: This marker contains no explosive.





   




Aluminum Sea Marker Mk III (Service)


Overall length: 23.12 inches
Body diameter: 4.4 inches
Total weight: 10.25 pounds

Fuzing: Simple impact striker
  

Color and markings: Aluminum overall

  
Description: The sea marker consists of a cylindrical tin-plate body and tail cone containing aluminum powder, and a detonator-burster charge, which explodes when the marker is dropped on the sea.  The body has an internal strengthening band near each end.  The tail cone is soldered to the body and carries the fnis to which a circular strut is secured.  At the other end, the body is closed by a steel diaphragm.  The diaphragm has a central opening, threaded to receive a plug, which carries a detonator-burster tube.  A nose is fitted to this diaphragm and secured in position by three set screws.  Screwed into the nose is a striker guide in which slides a striker needle, secured to a striker head which projects outside the nose.  When in its operative position, a transit safety pin engages with the striker head, preventing it from moving inwards.  A second safety pin is provided in the nose.  This pin is flanged and is spring-loaded outward, but normally is held in position by a split pin to which a withdrawal wire is secured.  A securing wire is passed through the eye of the split pin, around the head of the safety pin and the nose of the marker, and through a boring in the transit safety pin.



Functioning: When the sea marker has been prepared for use and dropped on the surface of the sea, impact of the striker head with the water drives the striker needle inwards and explodes the detonator-burster charge, which disrupts the body and tail cone and scatters the aluminum powder.











Aluminum Sea Marker Mk V (Service)
  

Overall length: 12.5 inches (telescoped); 20 inches (extended)
Body diameter: 3 inches
Total weight: 10 pounds
 

Fuzing: None; impact initiated
  

Color and markings: Aluminum overall

  
Description: The sea marker body has an inner case of sheet metal, the lower end of which is pressed on to a heavy, aperture head.  The aperture in the head is sealed by a paper disc and is traversed by a pin.  A circular retaining piece is secured to the upper end of the inner case.  Inside the inner case is a fabric bag containing aluminum powder, each end of the bag being tied with thread to close it.  The thread at the lower end of the fabric bag is passed around a pin, to hold the bag in contact with the head.  An outer case slides over the inner case.  At its upper end the outer case is closed by two millboard discs, and inside its lower end a circular retaining piece is secured to provide a stop to prevent its being withdrawn completely from the inner case.  A cutter is provided immediately below the millboard discs.  The cutter is a ring secured inside the outer case and cut across in four places at about 45 degrees.  The cut ends are bent up at right angles to form four sharp projections with the outer case.



Functioning: The head is the heaviest part of the marker and consequently will strike the water first when dropped.  Impact with the surface of the water breaks the paper disc sealing the aperture in the head.  Water enters this aperture and carries the fabric bag rearwards from the head, breaking the thread which anchors it to the pin and also ejecting the millboard discs sealing the aperture at the tail end of the outer case.  As the bag passes through this aperture it strikes the sharp projecting parts of the cutter, which slit it, releasing its contents.  As a result, a slick of aluminum powder is formed on the surface of the sea.



Remarks: This marker contains no explosive.












Smoke Generator No.6 Mks I and II (Service)


Overall length: 7.13 inches
Body diameter: 2.42 inches
Total weight: 1 pound
Emission time: 2 and 1/2 minutes
Smoke Color: Orange
 

Fuzing: Percussion igniter
  

Color and markings: Light green overall

  
Description: The generator consists of a cylindrical metal body containing smoke composition in a metal foil cup, a quantity of priming composition, and a length of quickmatch.  When prepared for use, a percussion igniter replaces the adapter plug.  A tail unit is formed integrally with the body, and the upper end of the body is closed by a lid.  The igniter consists of an igniter body, a striker supported above the cartridge base by a shear wire, and a safety pin.  The cartridge base includes a small quantity of cap composition located between a percussion cap and an anvil.



Functioning: The safety pin is removed just before the generator is dropped.  On impact the striker moves downwards, breaks the shear wire, and fires the cap composition in the cartridge base.  The flash from the cap composition ignites the quickmatch, which, in turn, ignites the priming composition in the adapter.  The priming composition ignites the igniter composition, which then ignites the smoke composition.  The heat due to the combustion of the smoke composition loosens the metal discs covering the smoke-emission holes in the top lid, and the pressure of the smoke forces the discs off the top lid, allowing the smoke to escape to the atmosphere.



Remarks: This smoke generator is designed to be dropped from an aircraft to enable the pilot to ascertain the direction of the wind on the ground before making an emergency landing.







Next Time: Cluster Projectiles Part 1

Monday, 6 February 2017

British Explosive Ordnance - Aircraft Pyrotechnics Part 1





British Explosive Ordnance




Aircraft Pyrotechnics Introduction


This chapter includes data on flame floats, marine markers, smoke floats, sea markers, and smoke generators dropped from aircraft.

Flame floats and marine markers are devices designed to give off a flame to illuminate surrounding areas of water.  Generally calcium phosphide is used as the filler for flame floats.  When moistened, this chemical gives off phosphine, a gas spontaneously inflammable on contact with air.

Smoke floats generate smoke by the combustion of a smoke-composition filler.  The smoke so produced may be used for indicating a position, for obscurement, or for signalling.  Although all smoke floats are designed primarily for use at sea, they differ from each other in construction and design according to the purpose for which the smoke is intended.  There are three essential types of smoke floats in use, one fore each of the following purposes:  to mark a position at sea for navigational or bombing purposes; to create a smoke screen; and to be thrown by hand from a plane or dinghy to attract attention following a forced landing.

Sea markers are designed to be dropped at sea to produce a distinctive surface patch on the water readily visible from the air in daylight for purposes of navigation or identification.  Generally, aluminum powder with stearic acid is used as the filling to form a slick.

Smoke generators are designed to emit smoke, sometimes colored, upon ignition of their filling.  Only one type of generator is discussed, since it is the only one intended to be dropped from aircraft in flight.


 
 

Navigation Flame Float Mk I (Obsolescent)
   

Overall length: 17 inches (Extended); 8 inches (Collapsed)
Body diameter: 3.7 inches
Filling: Calcium Phosphide
Filling weight: 2 pounds
Total weight: 3.2 ounces
Burning time: 5 minutes

Fuzing: Non; water initiated
  

Color and markings: Cylinder painted red with yellow label on lid.

  
Description: The float consists of a cylindrical tin-plate canister with a tin-plate lid, having a central aperture, soldered over the top of the canister, and a slotted brass sealing patch soldered over the aperture.  Soldered to the lid is an iron gauze tube, which extends axially nearly to the bottom of the canister, and is closed at its lower end.  The annular space outside the gauze tube is filled with granular calcium phosphide.  At its base the canister is closed by a cap, which fits over its outside.

The canister is surrounded by an outer fabric bag, which is considerably longer than the canister.  Secured by a double row of stitching inside the outer fabric bag and above the canister, is a second fabric bag, termed the inner fabric bag.  Two eyelets are located above the top of the canister in the walls of the inner and outer fabric bags at different levels.  The pull-off line passes through the aperture in the leather patch at the top of the inner fabric bag and through the neck of the outer fabric bag.  The aperture has a fairly snug fit on the line.

   
Functioning: When the flame float has been prepared for use by removing the brass sealing patch and has been dropped into the sea, water enters the canister through the aperture in its lid and passes through the eyelets.  The water enters the gauze tube, through which it penetrates into the calcium phosphide filling.  Phosphine is then evolved, inflating the inner fabric bag, and providing sufficient buoyancy to bring the flame float to the surface of the sea.  The gas escapes from the neck of the outer fabric bag, and takes fire spontaneously on contact with the air, producing a highly luminous flame.


Remarks: The flare may be dropped from any height and gives a reasonably steady and bright flame for about five minutes.  A flame continues for an additional 15 minutes, but it becomes increasingly feeble and intermittent.  If the sealing patch of the canister has been removed, the flame float must be dropped or removed to a safe place for disposal.









Navigational Flame Float Mk II, and No.4 Mk I, 
and Message Carrying Flame Float Mk I(Service)


Overall length: 23.4 inches
Body diameter: 5.9 inches
Filling: Calcium Phosphide
Filling weight: 1.8 pounds
Total weight: 11.8 pounds
Effective illumination: 6 minutes

Fuzing: Integral striker mechanism
  

Color and markings: Body, strut supports, strut, and protecting cap painted red,
tail cone painted yellow.

  
Description: The Flame Float Mk II consists of two main parts, a body and a container.  The body is a cylindrical casting, to one end of which three strut supports are riveted.  A cylindrical strut is riveted to the supports.  Secured to the fin by a securing wire is a punch to which is attached an instruction tag.  The body is thickened at the nose end, and has an attached conical nose of thin sheet steel.  A protecting cap is fitted over the nose, and a safety pin passes through holes in both the cap and nose.

The container consists of a sheet-metal cylinder, to one end of which is attached a sheet-metal tail cone.  The opposite end of the container is closed by a cap.  The cap is apertured and carried a correspondingly apertured spigot and a wire gauze socket on the side facing the tail cone.  Passing axially along the container is a central tube, one end of which is soldered to the narrow end of the tail cone, while the other end fits into the socket.  Near the tail end, the tube is closed by a sealing cup, projecting from which is a punch sleeve closed by a paper cap.  On the side opposite the spigot the cap carries a diaphragm, which retains a striker.  The striker is bored to receive the safety pin.

The lower part of the container is filled with granular calcium phosphide, which is held in position by a closing disc.  This material surrounds the slotted portion of the central tube.  Beyond the closing disc the annular space between the container and the central tube forms a sealed buoyancy chamber.


Functioning: Before the float is dropped, the punch is removed from the strut by cutting the securing wire, and the sealing cup on the punch sleeve is punctured with it.  After the sealing cup has been broken, the flame float must be dropped from the aircraft immediately. 

On dropping from an aircraft, impact with the water crushes the nose of the float and causes the striker to penetrate the sealing disc.  At the same time the securing wires holding the container to the body are broken, and the container and tail cone are forced away from the body.  The buoyancy chamber maintains the tail cone uppermost in the water.  Water enters the aperture in the cap, and passes through the gauze socket and the slots in the central tube into the calcium phosphide.  The phosphine generated on entry of the water passes upwards through the central tube, from which it emerges through the hole pierced by the punch through the sealing cup, and, on contact with the air, takes fire spontaneously.


Remarks: The inner body of the Navigation Flame Float No.4 Mk I is identical to the inner body of the Float Mk II.

The Message Carrying Flame Float Mk I is almost identical to the Navigational Flame Float Mk II in dimensions and construction.  The essential difference is that a message container is suspended in the buoyancy chamber by a fixing wire secured to a plug, which is screwed into a bush in the tail cone.  The plug is provided with a handle to facilitate its removal from the bush, and a washer on the plug insures a water-tight joint.  An arrow and the words, MESSAGE HERE, are painted on the tail cone to direct attention to the message.
 







Navigational Flame Float No.3 Mk I (Obsolescent) and No.3 Mk II (Service)
   

Overall length: 18.5 inches
Body diameter: 2.9 inches
Filling: Calcium magnesium phosphide
Total weight: 2.5 pounds

Effective illumination: 5 minutes

Fuzing: None; water initiated
  

Color and markings: Yellow overall

  
Description: The Flame Float No.3 Mk I has a cylindrical tinplate body, the after end of which has four attached tail fins.  The tail end of the body is closed by a tail cover having a central hole.  The neck of the tail cap is closed by a thin rupture disk to which is secured a small pillar having a ring passing through it.  The forward end of the body is closed by a cast-iron nose having a central water-inlet hole.  The nose is contained in a tin-plate cover, having a central hole covered by a tear-off seal to which is secured either a ring or an eyelet.  Inside the body is a perforated zinc central tube surrounded by a swansdown bag containing calcium magnesium phosphide.  Cotton wool is packed around the tail end of the bag, and a layer of glass wool is located between the bag and the iron wire gauze.  The charcoal is provided to absorb any slight traces of gas which may be given off while the flame float is in storage.  The tail end of the body comprises the buoyancy chamber of the flame float.


Functioning: Before dropping, the tear-off seal at the nose is removed.  When dropped, the tail rupture disc is broken and the float rises to the surface.  Water enters through the water-inlet hole in the nose, passes through the perforated zinc tube, and soaks through the flannel finger into the swansdown bag, where it reacts with the calcium magnesium phosphide to give off spontaneously inflammable phosphine.  The phosphine, so generated, escapes through the broken rupture disc and takes fire on contact with fire.


Remarks: Should either of the seals be broken while in storage, the damaged flame float must be removed to a dry place where the possibility of its catching afire is an acceptable risk pending final disposal.

The Float Mk II differs from the Mk I in that a rear seal and tear-off cord are substituted for the tail rupture assembly of the Mk I.  The long perforated tube of the Mk I is considerably shortened in the Mk II.










Marine Marker Mk I (Obsolescent)
  

Overall length: 26.8 inches
Body diameter: 5.8 inches
Filling: Aluminum and magnesium phosphides
Total weight: 16 pounds

Effective illumination: 2 hours

Fuzing: None; water initiated
  

Color and markings: Body and nose red.  Tail and tail cap yellow.

  
Description: The marker consists of a light metal body and tail, which are separated by a diaphragm.  The tail is closed by a metal plate, having a tail cap connected to the main outlet tube.  The forward end of the body is closed by a heavy metal plate into which are set two water-inlet valves.  A tube passes from the central valve, through the filling and spring-loaded pressure plate, and almost to the diaphragm.  The pilot tube extends aft from the off-centre valve to the pressure plate.  The pilot outlet tube then continues to a strainer attached to the diaphragm from which the main outlet tube issues.  The pressure plate retains the main filling in the forward part of the body.


Functioning: When the marker has been prepared for use and dropped into water, the water jacket fills and the scalloped disc in the main valve and the large disc in the pilot valve are forced against the ledges in the valves, thus preventing too great an ingress of water while it is submerged.  Some water, however, enters the main outlet tube, passes through the pressure plate, and reacts with the calcium phosphide.  This reaction evolves impure phosphine gas, which ignites spontaneously when the marker surfaces.  As it surfaces, the pressure against the valves is relaxed, and the springs return the discs against the circlips, thus permitting the ingress of water though the scallops in the disc to the bottom of the inlet tube and pilot tube.  The water entering the main valves passes through the inlet tube into the perforated tube, and after passing through the perforated diaphragm percolates through the flannel sheath and reacts with the main charge to give off pure phosphine, which is not spontaneously inflammable.  The cap over the free end of the perforated tube prevents the water from percolating through the part of the flannel sheath above the pressure plate.

The water entering the pilot valve percolates through the flannel disc and dissolves the potassium bisulphate and the sodium nitrite.  The chemicals interact and evolve gaseous oxides of nitrogen which mix with the phosphine in the strainer.  The mixed gases are spontaneously inflammable in air, and, passing through the main outlet tube, ignite immediately on reaching the air.  The flame thus produced continues to burn evenly for approximately two hours, during the whole of which time the gases remain spontaneously inflammable, so that even if the flame is put out by a wave, it lights up again as soon as contact with air is re-established.


Remarks: The flame is visible in daylight over a distance of at least three miles, and at night over a distance of about 20 miles.  White smoke is given off with the flame.  In damp atmosphere, after removal of the over-seals and press-caps, this marker evolves spontaneously inflammable phosphine, and for this reason should be prepared for use only just before it is to be launched.





   


Marine Marker Mk II (Service)

  
Overall length: 30 inches
Body diameter: 5.8 inches
Filling: Magnesium-aluminum phosphide
Total weight: 19 pounds

Burning time: 2 hours

Fuzing: None; water initiated
  

Color and markings: Body and nose transit cover painted red,
tail, tail cap, and tail transit cap painted yellow.

  
Description: The marker consists of a body with a steel nose at one end, having a central hole closed by a stopper which forms part of a thin bakelite disc secured to the nose by screws.  The disc is protected during transit and storage by a nose transit cover held in position by adhesive tape.  The tail constitutes a buoyancy chamber, and a main outlet tube extends between the diaphragm and a tail cap at the outer end of the tail.  The tail cap has a neck closed by a thin rupture disc, to which is secured a small pillar having a ring attached to it.  Two locating pieces, secured to the outside of the body, are provided to locate a suspension band in position if the marker is to be carried on a Light Series Bomb Carrier.


Functioning: When it is dropped into water, the bakelite disc is broken by impact with the water; the stopper falls away and the marker rises to float on the surface.  Water enters the central hole in the nose, and after passing through the gauze thimble, some of it soaks through the flannel washer, passes through the small hole in the valve body, and enters the brass tube after soaking through the flannel washer in the tube.  The remainder of the water passes through the water-inlet tube, percolates through the open-mesh metallic cylinder and its flannel sheath, and enters the body of the marker.  The brass cap prevents water from passing through the sheath and coming into direct contact with the calcium phosphide.  The water which enters through the nose reacts with the magnesium-aluminum phosphide and gives off pure phosphine, which is not spontaneously inflammable.  Some water, however, passes down the main outlet tube while the marker is submerged, and this water reacts with the calcium phosphide to produce phosphine which, in contact with the air, is spontaneously inflammable.  The supply of spontaneously inflammable gas lasts only about three minutes, and the flame is thereafter maintained by the phosphine evolved from the magnesium-aluminum phosphide mixing with the gaseous oxides of nitrogen given off by the interaction of the potassium bisulphate and the sodium nitrite, which are dissolved by some of the water which enters through the nose.









Marine Marker Mk III (Service)


Overall length: 36.8 inches
Body diameter: 6 inches
Filling: Magnesium-aluminum phosphide
Total weight: 21 pounds

Burning time: 2 hours

Fuzing: None; water initiated
  

Color and markings: Blue grey overall

  
Description: The outer casing of this marker consists of a body and a tail which are connected by a diaphragm.  A heavy nose is secured to the body.  The nose has a cavity to receive the time valve, and a central hole at the bottom of the cavity which is closed by a transit plug.  The valve is a clockwork device which permits the marker to remain in the water for a period up to six hours before it functions.  The period of delay is determined by setting the valve before the marker is released from the aircraft.  The main filling consists of magnesium-aluminum phosphide, and is packed round a gauze cylinder.  Inside the gauze cylinder is a quantity of fast calcium phosphide, which also extends over the top of the magnesium-aluminum phosphide.  The main filling is held in place by a thin steel plate having large holes covered by brass gauze, and a large spring anchored to a spring-supporting plate, which abuts against the diaphragm connecting the tail to the body of the weapon.  A layer of charcoal is provided beneath the steel plate to absorb any small quantities of phosphine gas generated by traces of moisture which may be in the body of the marking during filling, and a layer of glass wool beneath the charcoal which acts as a dust filter.  The tail constitutes a buoyancy chamber, and a main outlet tube extends between the diaphragm and a tail cap at the outer end of the tail.


Functioning: After entering the water, the marker rises to the surface and floats tail uppermost, water entering the nose cavity through the two small holes in the side of the nose.  At the expiration of the delay set on the time valve, the Welvic plug sealing the hole in the side of the time valve is opened and the water passes through the time valve and the central hole at the bottom of the nose cavity, into the water inlet valve in the nose.  Some of the water entering the water-inlet valve soaks through the flannel washer and passes through the small hole in the inlet valve into the brass tube to react with the filling in the brass tube.  The remaining water, after dissolving the soluble disc covering the nut, passes upwards through the water-inlet tube, percolates through the coarse-mesh cylinder, the flannel sheath, and the fine-mesh cylinder, and enters the body of the marker.  The brass cap prevents water from passing through that portion of the sheath which is above the fine-mesh cylinder.

The water passing through the fine-mesh cylinder, together with the small quantity which passes down the main outlet tube while the marker is submerged, reacts with the calcium phosphide in the gauze cylinder and covering the top of the main filling, to produce impure phosphine, which, in contact with air, is spontaneously inflammable.  This supply of gas lasts only for a few minutes, and is thereafter maintained by the pure phosphine evolved from the magnesium-aluminum phosphide mixing with the gaseous oxides of nitrogen given off by the interaction of the potassium bisulphate and the sodium nitrite, which are dissolved by the water entering the brass tube.


Remarks: When breaking the rupture disc, do not hold the head directly over the tail cap of the marker.  This avoids possibly injury to the eyes which might be caused should sufficient pressure be built up in the marker to force phosphide dust particles past the glass wool filter at the top of the main filling.



 



Next Time: Aircraft Pyrotechnics Part 2