German Explosives
V-1
General
The V-1 is a bomb constructed in the form of a midwing monoplane with a single fin and rudder. The after portion of the fuselage is surmounted by a jet-propulsion unit. Two general types were found; the automatically controlled missile, and the piloted missile.
General performance figures are as follows:
Speed at End of Launching Ramp: 400 km/h
Airspeed of Recent Models: 900 km/h
Older Models Airspeed: 800 km/h
Maximum Range: 200 km (Approx.)
The bomb is launched by a fin attached to a piston fired from a long catapult. The catapult tube has a slit running its entire length through which the fin projects. The launching fuels are hydrogen peroxide and potassium permanganate used in combination. Either type of missile can also be launched from the He-111 or the Hs-177 aircraft.
[Editor's note: The original text is a typo, and should be the He-177]
Control of the V-1 in flight is effected by an automatic pilot unit monitored by a magnetic compass. The only control surfaces are a pair of elevators and a vertical fin.
The control equipment causes the V-1 to:
A. Climb to a predetermined altitude and level off.
B. Execute a right or left turn of predetermined duration, if desired.
C. Maintain the correct altitude.
D. Follow the desired compass course.
E. After the proper distance has been traveled, go into its final dive.
The models which were modified to have a human pilot aboard had the conventional stick and pivoted-crossbar flight controls. A gyro compass was mounted in a chock-mounted bracket with a small 24-volt wet battery and a 3-phase inverter. This assembly was mounted on the deck between the pilot's knees, so that the compass was just below the instrument panel.
These bombs were intended specifically to be launched from aircraft. The pilot was to fly his missile toward his target until he was relatively certain of accuracy, then lock the controls and attempt to save himself. Although the pilots were equipped with parachutes, according to one Luftwaffe executive in a V-1 assembly plant, it was expected that 99 percent would not survive.
Airframe: The V-1a is constructed in the form of a mid-wing monoplane surmounted by a jet-propulsion unit. Except for the nose and the control surfaces which are of light metal, the structure is entirely of steel.
There are variations of the order of two feet maximum in the dimensions of various models, but the following characteristics are given as representative.
Length of Fuselage: 6,655 mm
Length of Propulsion Unit: 3,415 mm
Overall Length: 8,235 mm
Maximum Diameter of Fuselage: 840 mm
Maximum Diameter of Propulsion Unit: 577 mm
Wing Span: 5,370 mm
Root Chord: 1,220 mm
Tip Chord: 813 mm
Wing Area (Gross): 5,116,000 sq. mm
Aspect Ratio: 4.7
The mainplane is built around a continuous tubular spar which passes through a sleeve mounted across the center of the pressurized fuel tank.
The two wing sections which are of steel construction throughout, are designed for rapid assembly on the spare. There was no ailerons and the plane has no dihedral.
The tail unit has a single fin and rudder and is mounted on a cone which forms the rear end of the fuselage. The plane is fitted with elevators which, together with the rudder, are operated by a pneumatic servo mechanism housed inside the fuselage.
The fuselage houses the following units:
-Magnetic compass
-Warhead
-Pressurized fuel tank
-Compressed air tank
-Automatic pilot control unit
-Radio transmitter (if carried)
-Pneumatic servo motors
Intelligence and Control System: The intelligence and control system is made up of the following principal units:
-Main steering control gyro
-Rate gyro for turn control
-Rate gyro for pitch control
-Aneroids altitude control
-Clock for timing of turn
-Magnetic compass for monitoring gyro
-Air log for determining range
-Spring-operated diving mechanism
-Pneumatic servos
After launching, the V-1a climbs until it reaches the altitude for which it has been set into the clock mechanism, and straightens out onto a course controlled by the compass through the gyro. After the air log registers the proper distance traveled, the spring mechanism removes the gyro control and sets the missile into its final dive.
Main Steering Control Gyro: The main gyro is located on the forward side of the automatic pilot assembly and consists of an air-driven gyro, double gimbal mounted, with normal axis of spin in a vertical plane through the missile's axis and inclined about 30 degrees from the horizontal. The inner gimbal axis is normally in a vertical plane at right angles to the axis of spin and the outer gimbal axis is horizontal and at right angles to the axis of the V-1. Cam followers with mechanical linkages utilize the motion of the gyro in each of its two components relative to the chassis to traverse a small compressed air nozzle across two holes, thus building up a higher pressure in one or the other of the pressure tubes when the position is off normal.
Two precessing magnets are mounted on the side of the gyro, one for producing right-hand precession for azimuth control, and the other left-hand. The circuits from the magnets are controlled by the clock during the turn and by the magnetic compass thereafter.
Precession in a vertical plane is produced by a reaction force from the escape through side vents of the compressed air after it has been used to drive the gyro motor. These vents are on the sides of the forward bearing housing and are partially covered by two pendulous strips of brass. If the spin axis, owing to fiction or any other cause, tilts up or down from its desired position, the pendulums will cover more of the vents on one side and less on the other, resulting in a horizontal reaction force and causing a vertical precession back to the proper angle of tilt.
The main gyro is locked in its normal position during the launching and uncaged electrically when a switch on the fuselage is operated by a protrusion on the end of the launching ramp.
Rate Gyro for Turn Control: The auxiliary gyros are for the purpose of introducing a rate-of-charge element into the control, so as to avoid the jerkiness and possible "hunting" inherent in a control which is direction proportional to error.
The horizontal rate gyro spins normally about a horizontal axis at right angles to the ship's axis. It is mounted in a frame which can have a restricted motion about a fore and aft horizontal axis. This frame is held in a normal position by a leaf spring, and it also has an air dashpot for damping. As on the main gyro, the frame carries an air jet which plays between two receiving holes, and produces a differential pressure in the connecting tubes whenever the rate gyro is displaced from its normal position. The output tubes are cross-connected to the corresponding tubes from the horizontal take-off element of the main gyro.
In operation, a sudden change in horizontal angle of the ship will result in a corresponding change in rate gyro position relative to its frame, providing a pressure differential opposing this change. The spring force, modified by that of the dashpot, gradually brings the rate gyro back to its normal position. It acts during this transient period only, smoothing the response of the missile to the main gyro.
The pressures in the differential tubes are resultant or composite pressures from both the main gyro horizontal take-off element and the horizontal rate gyro. The differential pressure between the two tubes actuates the pneumatic servo described below.
Rate Gyro for Pitch Control: The rate gyro for pitch control is a duplicate of the horizontal rate gyro but has its normal axis of spin vertical. Its differential pressure take-off tubes are cross-connected to those from the elevation element of the main gyro.
Aneroid Altitude Control: This is an altitude control with an adjusting knob graduated in millibars atmospheric pressure between 700 and 1,000. Turning the knob changes the tension of a spring which is balanced against atmospheric pressure on the principle of the aneroid barometer. A pneumatic servo controlled by this unit tilts the framework supporting the main gyro.
In operation, as the V-1 climbs to higher altitude, the lower barometric pressure results in a backward movement of the spring, diaphragm and piston, and a tilting upward of the frame. The gyro maintains its original angle between axis of spin and the horizontal, and there is produced a relative motion between the air jet holes of the vertical take-off which acts in the end through servos, to lower the elevators and thus reduce the climb of the plane. This continues until an altitude is attained at which a proper balance is reached, and the missile then flies a level course in an atmosphere whose pressure in millibars is that at which the adjusting knob has been set.
Clock for Timing of Turn: The clock controls the delay before the turn begins, and the duration of the turn. The turning feature is for the purpose of enabling the V-1 to be launched against a target which is not in line with the launching ramp, and making it more difficult for the enemy to determine the location of the launching ramp by observation of the line of flight. The delay before turning also reduces the probability of crashing since the V-1 is enabled to attain a more satisfactory altitude and velocity before attempting any evolutions. The delay mechanism runs for a maximum of about 10 minutes, although it has scale markings only up to 3 minutes (on the minute wheel, plus 60 seconds on the second wheel). The turning time may be set anywhere between zero and 60 seconds.
The turning if effected by the closing of one of the horizontal precessing magnet circuits by the clock mechanism. The direction of turn is controlled by a switch mounted on the clock, and the rate of turn may be set between the limits of approximately one-tenth degree per second and 1 degree per second by varying a register in the magnet circuit.
Magnetic Compass for Monitoring Gyro: After completion of the turn, the clock mechanism completes the circuits by which the mastery gyro is controlled in azimuth by the magnetic compass. The main shaft of the compass, which is housed int eh nose of the missile, carries a cam so arrange that its edge will partially block the flow of air between either of two pairs of jets. This produces a differential pressure in its output tubes whenever the missile is not on the desired magnetic course. These output tubes are connected to an air relay which energizes the proper precessing magnet to bring the gyro to its desired setting.
Air Log for Determining Range: Range is determined by an air log driven by a small propeller-like spinner located at the nose of the missile. Counter wheels clock off the air distance and at a pre-set distance an electric contact is made which detonates a small charge to operate the diving mechanism.
Spring-Operated Diving Mechanism: The charge detonated by the air log mechanism releases a spring-loaded lever which depresses the elevators to the dive position and locks them. It also lowers two small hinged plates beneath the lower surface of the horizontal stabilizer, which are of different sizes and cause the V-1 to turn as it dives in.
Pneumatic Servos: In flight, the control surfaces of the V-1 are operated by piston-type pneumatic servos driven by air from the main pressure bottles, and pneumatically controlled by the differential pressure outputs from the automatic pilot control unit.
Radio Transmitter: Some V-1 bombs were equipped with a one-tube radio transmitter for the apparent purpose of enabling the launching crew to follow the flights with direction finding equipment in order to obtain plotting and wind data.
When the radio was used it was mounted int he rail of the fuselage abaft the automatic pilot unit. It included a wheel type coding unit and batteries to power both the transmitter and the coding unit The antenna, which is approximately 450 feet long is wound on a long rod and arrange in such a manner that it will be drawn out by the airstream after the missile is launched.
Propulsion Unit: The propulsion unit, which is mounted above the after end of the fuselage, has an overall length of 11 feet 3 inches. It tapers down from a maximum diameter of 1 foot 10 and 3/4 inches at the forward end to 1 foot 4 inches about halfway along its length; the rear portion is cylindrical. The unit is carried above the fuselage on two supports with shock-absorbing mountings to insulate the control system from vibration.
At the front of the unit there is a rectangular grill opening which is built up from a series of finned diecast strips. Between each pair of die castings there is a flat strip built up from two pieces of sheet steel. A series of small spring leaves is disposed along each side of the strip. Each pair of leaves is secured by two hollow rivets which also serve to hold the strips together.
Air pressure at the front of the grill, combined with a vacuum at the rear, causes the spring leaves to open and admit a charge of air. The fuel is forced by air pressure from the tank in the fuselage to nine jets which project from the back of the grill. The flow of fuel through the feed pipes is arranged to synchronize with the opening and closing of the spring leaves, so that a pulsating flow of fuel is obtained.
The jets, which are in three rows, project into venturi openings. These openings are formed by two hollow members extending across an open box structure secured to the rear of the grill, and having two sides shaped to complete the upper and lower venturi.
In operation, a charge is admitted, the fuel is injected, and combustion takes place. The rise of pressure inside the combustion chamber closes the spring leaves and the exhaust gases are expelled through the open rear end of the tube. As the pressure in the combustion chamber falls, the air pressure again causes the spring leaves to open and a fresh charge is admitted and the cycle of events is repeated.
The following estimated figures were obtained for the equipment:
Diameter: 580-600 mm
Range: 700 km
Static Thrust: 500 kg
Speed: 640 km/h
Weight: 215 kg
Pressure Ratio in Compressor: 2.8
Specific Fuel Consumption: 1.4 lbs/hr
Pressurized Fuel Compartment: The fuel compartment is located in the central section of the fuselage and consists of a steel cylinder of 130 gallons capacity with no armor protection and no self-sealing feature.
The fuel used is a low grade aviation gasoline similar to that which the Germans used in their training aircraft. Air from the pressure bottles is supplied to the upper part of the fuel compartment and forces the fuel out to the jets in the combustion chamber, by way of a control unit incorporating diaphragm valves.
Pressure Bottles: The pressure bottle compartment contains two spherical compressed air bottles 1 foot and 9 and 1/2 inches in diameter. The air from the bottles, which are filled to about 2,100 pounds per square inch is used to keep the fuel under pressure and to operate the automatic pilot and servo units.
Warhead
The warhead is bolted to the forward end of the pressurized fuel compartment and is approximately equivalent in size and effect to the German SB 1,000-kg thin case bomb, the charge-weight ratio being exceptionally high. The thickness of the bomb casing is about 2 mm. The explosive filling is Trialen 106, same as that used in the SB 1000. There are three fuze pockets in the warhead: Two transverse fuze pockets which house the mechanical delay fuzes, and one central exploder tube which takes the El. A. Z. 106 electrical impact fuze at the forward end.
Fuzing System: In designing the fuzing system of this bomb, the Germans wanted to insure detonation on impact, so they included a "belly switch" in addition to the nose switch, and the inertia bolt switch. These three switches all operated through an adaptation of the Rheinmetall electric fuze El. A. Z. 106. In addition to the electrical system, two mechanical fuzes; one "all-ways" action impact fuze and one mechanical clockwork delay fuze, were used to further insure detonation of the missile.
Electrical System: The electrical system consists of the impact fuze El. A. Z. 106, the Ent. 106 which is mainly a container for the second condenser and the choke coils, the "belly" switch, and the nose switch.
The El. A. Z. 106 is located in the axial fuze pocket and is essentially a switching device. The aluminum fuze head has two female electric inlets. The electrical connections are made by means of a three-contact plug, the larger prong serving as a locating pin. Under the fuze head is a plastic molding which houses an electrical igniter. Below this, a second housing contains a thermite pot around which are grouped three spring-loaded switches. One is held in its closed position by a polystyrene plug, the other two are connected to the bottom of the thermite pot by means of lumps of Wood's material. An inertia bolt switch rated at 150 g plus 10 is mounted so that it will be activated on nose impact.
The Ent. 106 is bolted to a circular bracket on the warhead, close to the El. A. Z. 106. It contains a large tinfoil condenser, two iron core choke coils, a 0.95 M ohm resistance all separated by beeswax and held in plastic housings.
The nose switch is directly behind thar end on the air log shaft. It consists of a diaphragm switch mounted on a collapsible rod. On impact, this nose switch can be closed either by the shaft of the air log being driven back, or the outer tube may collapse and make contact with the inner tube completing the circuit. These two switches will function only if the nose of the bomb itself is subjected to impact and distortion.
The "belly" switch is on the underside of the nose housing in a projection called the blister. It is a simple push button type of switch which will close the firing circuit in the event of a belly landing.
As the bomb progresses through the air, the airscrew of the air log rotates and causes the Veeder counter to rotate backward to zero. The length of the safety period is determined by the initial setting of this Veeder counter. At the zero mark, it closes the electrical contact and throws the 30-volt dry battery into the fuze circuit. This causes the condenser in the Ent. 106 component to become charged and fires the electric bridge through switch No. 1. This electric bridge ignites the thermite pot directly below it, which in turn melts the polystyrene plug on the spring-loaded switch No. 1, and the switch opens. The heat from this thermite pot also causes switch No. 2 to close and switch No. 3 to open. This operation removes the shunt across the igniter No. 2 and puts the return line to the battery into the circuit. The electrical system at this point is fully armed.
If the bomb strikes nose first, the diaphragm switch will close and fire the warhead through igniter No. 2, or the inertia switch int he El. A. Z. 106 will close and fire the warhead through igniter No. 1. If the bomb glides to the ground, the belly switch which is in parallel with the nose diaphragm switch will fire the warhead.
Mechanical Fuze System: The mechanical fuze system consists of the 80 A all-ways action impact fuze and the Z. 17 Bm clockwork delay fuze. These two fuzes are usually found in the forward and aft transverse fuze pockets respectively.
The 80 A is used primarily as insurance against the possible malfunctioning of the electrical fuze system on impact. The Z. 17 Bm is intended only as a demolition fuze. If there was ever a complete failure of both systems when the bomb landed on enemy territory, this fuze would detonate the warhead within a few minutes after the missile had landed and thereby keep the valuable intelligence out of the enemy's hands.
Next Time: Rockets (Part 6)
Source: German Explosive Ordnance Vol. 1: Bombs, Rockets, Grenades, Mines, Fuzes & Igniters
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