|The V1 Flying bomb (c) by Göran Jansson 2007|
|Back||Retaliation Weapon V-1
Planners of war have long dreamed of the possibility of sending self-propelled crewless missiles carrying quantities of explosives against towns and cities in enemy territory. During WWI, technicians in England and USA designed and built experimental aeroplanes to explore the practicality of sending radio-controlled crewless aeroplanes loaded with explosives against Germany from bases in France. When considered as flying machines these weapons were conventional aeroplanes except for their system of control. Subsequent to 1918, War strategists in many countries of the globe realised the potential values of such a weapon provided that it could be made simple enough to require few man hours for its manufacture. A minimum of precision-made parts and fraction of raw materials which would, in time of War, be more urgent required for the manufacture of other weapons, must be used in its production. These conditions ruled out the possibility of using explosive-carrying-crewless aeroplanes of conventional size and complexity because the cost in man hours and materials would be prohibitive when weighed against the damage they could inflict with their relatively small loads of explosive. The chief problem was to produce a propulsion unit which, though simpler in construction than the internal-combustion reciprocating motor, would be sufficiently powerful to propel the missile to its target. The development y the Germans of a simple reaction-propulsion unit, easy and chip to make, has been the means of overcoming the economic limitations of the Flying Bombs as practical weapon.
|Back||Design and Developments
Development of reaction-propulsion by the Germans for eventual application to military uses was started soon after WWI to evade the terms of the Treaty of Versailles which forbade Germany to develop certain classes of internal-combustion reciprocating motors. Little is known of the progress of these experiments, but shortly before WWII the Germans evolved the principles embodied in the reaction-propulsion unit fitted to the V1 Flying Bomb. Soon after this, the Flying Bomb itself was designed. In conception it is the simplest and smallest structure which the Germans have been able to evolve capable of carrying three-quarter of a ton of high explosive, sufficient fuel to enable the missile to operate over a reasonable range, control apparatus and lifting and stabilising surface to enable it to fly. Had the Battle of Britain gone well for the Germans the need for speedy exploitation of a practical Flying Bomb would not have been necessary. The Flying Bomb makes but one highly inaccurate bombing attack and is then, of course, written off. In comparing Flying Bomb and conventional WWII aircraft, one must bear in mind that the former can be used in daylight with some success. Assuming that destruction of London was considered by the Germans of first strategic importance and knowing that air superiority was a thing of the past for the Luftwaffe, one must confess that the Germans produces an ideal weapon. Whether this savage attempt at reprisals, lunched at the expense of normal aircraft production at a critical moment, helped the German cause must be judged by the individual. The construction and "flight" testing of Flying Bombs became of great urgency to the Germans after the defeat of the Luftwaffe in 1940. London, the most perfect target in the World for Flying Bombs, lay 120 miles from possible launching sites on the French coast. An aerial bombardment of Southern England by masses of these missiles would, the Germans justifiable hoped, bring Great Britain to her knees. While 100 launching sites - capable of launching a total of about 1,000 missiles a day - were built along the coast of the English Channel, the Luftwaffe experimental air station at Peenemunde, as well as several other Luftwaffe units, continued develop the weapon. During 1942, trouble was experienced with the wings, which were found to break loose after a short period of flight. To discover the cause of this weakness, a Flying Bomb was built, in which the warhead was replaced by a similarly shaped fuselage section designated to accommodate a person lying in the prone position. Hanna Reich was chosen for this experiment, according to German propaganda reports, because of her diminutive stature and ability to withstand abnormal strains caused by the gyration of the missile. After four days of test flights during which observations were made through a periscope of the behaviour of the wings in flight, the weakness was discovered, but during the final landing the pilot was severely injured. On November 8, 1943, a British photographic reconnaissance aeroplane flying a sortie over Peenemunde photographed an experimental launching ramp with a Flying Bomb in place ready for take-off. This photograph roused the interest of officials in England and the launching ramp was compared with varies structures then being built in the Pas de Calais. Examination of the latter showed the new structures in France to be similar to the forms and layout to the launching ramps and assembly buildings at Peenemunde. Intelligence reports confirmed the knowledge that Germans were preparing a new weapon for the use against England. Every one of the original hundred launching sites was then tracked down and completely destroyed or rendered unusable. By then, whoever, the Germans were committed to the use of the weapon. Many factories had been turned over from the production of conventional aeroplanes to the production of the new missile and their power units. More launching sites, of a simpler and more easily camouflaged design were constructed despite constant attention by aeroplanes from U.S.A.A.F. and R.A.F. Several Flying Bombs were launched over the Baltic sea in the direction of Sweden to discover three exact range and deviation from course. Then, on Tuesday, June 13, 1944, the Germans launched their first Flying Bombs against Southern England.
The German flying bomb is a simple little aircraft, built almost entirely of welded mild-steel plate, and driven by the simplest form of jet-reaction engine yet devised. The machine had a parallel wing of 3 ft. 5in chord, with a span of 17ft 8in. The whole design of the V.1. is of the simplest and cheapest kind. It is a real mass-production job. The thing that strikes one when looking at a general arrangement drawing of this aircraft is, first, the high thrust line and, secondly, the great mass of weight, due to the rearward placing of the jet-propulsion engine. The machine have a very high longitudinal moment of inertia. Another thing is the absence of ailerons. Obviously the guiding principle here was to cheapen and simplify the machine. What happens is something like this: the axis of the master gyro is elevated some 25 deg. To the horizontal in a vertical plane so that a roll appears to the auto-pilot as a reduced amount of yaw. Hence if the left wing should drop, it puts on the right rudder, steering to the right and giving a higher velocity over the left wing, thus raising it to the normal position. The single lifting lug was well in front-indeed some 6 inches-of the main wing spar and of the probable centre of gravity of the aircraft. The probable explanation is that when hoisting at the lifting lug, the machine will take a tail-down attitude on the launching platform.
The V.1. is a remarkable aircraft, and in describing it we must begin, in an unorthodox way, with the fuel tank - since this is essentially the backbone of the whole structure - which is a plain cylinder with domed ends. It carries the launching rail, and is, therefore, subjected to all the catapulting forces and these probably amount to something like 10g. Also, it is under the high pressure of some 100 lb. per sq. Inch which provides the forced fuel feed to the jet-reaction engine. The fuel tank holds about 150 gallons, and the main wing spar tube passes right through it. The single lifting lug, through which the machine is hoisted on the launching ramp, is also built into the tank. As the tank constitutes the centre portion of the fuselage, and being subjected to all the forces mentioned, it is built of heavy gauge, mild-steel plate - thickness at about 12 gauge. A coarse filter panel is built into the bottom of the tank with a finer filter further down the pipeline. Carried directly in the front of the fuel tank is the 1,870lb (850 kg) war head or bomb. It is attached by four bolts with external lugs. The war head itself is welded-up from mild-steel sheet of about 2 mm thickens, thus giving the maximum percentage weight of explosive - this being essentially a blast type of bomb. In the front of the war head is a light-alloy fairing with a detachable nose cap built of the same material. The object of using duralumin at this point is to keep down magnetic influences, since the magnetic compass is carried in the nose. The compass can be pre-set to guide the aircraft on the desired course; it is carried in a large bowl-shaped wooden receptacle. Impact and other fuses are located in this forward structure, as well as the tiny air-log windmill at the extreme nose. After the fuel tank is a compartment carrying the two spherical air bottles, the construction and purpose of which will be describe later. This compartment is welded to the fuel tank, and forms one unit with it. There is then a joint at the rear for the attachment of the tail-end of the fuselage, which can be removed as a complete by undoing four bolts. The entire fuselage structure consists of stressed skin and bulkheads only - there are no longitudinals. Of special interest is the tail part of the fuselage. It carries the automatic pilot, with the three air driven gyroscopes, and also the height and range-setting controls. The electrical gear and other gadgets are also fitted in this section, as well as the wireless transmitting unit, when a machine is so equipped. The fin is in one unit with the rear-section fuselage, and is spot-welded to it. The tailplane, witch passes in one piece through the fuselage, has, mounted on top of it, the two pneumatic servos operating the rudder and elevators. All this intricate mechanism is easily accessible through large openings covered by bolted-on panels. The jet engine itself is carried at its forward end at two points on a trunnion, rather similar to a tail wheel fork, and this fork transmits the engine thrust to the aircraft. The fork itself is a beautiful example of a welded-up steel pressing, made in halves. The aft support of the jet tube is at a single point on the fin. All three points are rubber-mounted. We will return to the impulse jet engine later, so let us now consider the wing. This is built from mild-steel sheet, and is spot-welded throughout. The aerofoil is bi-convex with a chord of 3 ft. 5in., and has a thickness at the maximum ordinate of 6,5 in., i.e., 15 per cent. of the chord. The maximum wing thickness coincides with the position of the single tubular spar, witch is located 10,5 in. From the leading edge, i.e., a little more than 25 per cent. aft along the cord. The ribs are simple flanged pressings with circular flanged lightening holes. The material is about 22 gauge. The skin is a little thicker- about 20 gauge. The aerofoil used is of symmetrical section. The top surface are painted olive drab, and the underside a kind of duck-egg blue.
The tubular wing spar is in one piece, and is pushed through a tubular ferrule about 6/32 in. Thick, welded into the fuel tank. This tube - the main wing spar - is about 4ft. Shorter than the overall wing span. It consists of a single piece of 4,5in. Diameter by 12-gauge seamless steel tubing with a 10-gauge open-seam sleeve over most of its length. This is spot-welded through to the inner tube at the seam. A further short length of 10-gauge tube is fitted over the centre of the wing spar to cater for the increased bending moments. The tubular spar takes no wing torque, and in any case torque loads would be low in view of the bi-convex section and the position of the spar. What torque loads there are are taken out at a single point on a strengthened box rib at the fuselage side near the trailing edge. A sharp balloon cable cutter of steel is fitted inside the leading edge, immediately behind the skin plating. One could write pages about the construction of this wing - it is extremely ingenious. The top portion of the skin is first spot-welded to the ribs and to the shallow nose and tailing-edge webs. Similarly the bottom skin plating is spot-welded to another series of ribs, etc. The top and bottom halves are then brought together and welded up along the centre line of the vertical webs near the leading and trailing edges. This makes a very strong box structure, and the job is completed by welding-on the small nose and trailing-edge platings. The wing is perfectly flush, all plating joints being butted, and there are no protruding rivet heads.
|Back||Compressed air Bottles
The spherical compressed-air bottles are located in a compartment in the fuselage immediately behind the fuel tank. They are slightly staggered, on the left and the other to the right of the fuselage axis. The construction is extremely interesting, being wire-bound over an internal shell of welded mild-steel sheet. They contain the compressed air which provides the power for spinning the gyroscopes in the automatic pilot, for forcing the fuel up to the motor and for operating the pneumatic servos to the rudder and the elevators. These latter will probably absorb the bulk of the power, particularly in bumpy weather. Air at the surprisingly high pressure of 150 atmospheres is compressed into the bottles. A hydraulic test on a bottle at 3.000 lb. Per sq. In. Resulted in no leak or failure. Each bottle has an external diameter of 22 in. And a weighs 111 lb. When empty. When inflated to 150 atmospheres the weight of each bottle is increased by 31 lb. The internal mild-steel shell is pressed out in two hemispheres and welded round the equator. The spheres are then wire-bound with what is apparently 16-gauge piano wire under considerable tension. This wire winding is three to four layers thick and takes great-circle courses in twin bands abaout1,5 in. Wide, fixed with soldered tinned-steel clips. The two bottles are coupled together and therefore become in effect one container, in that if one were punctured the air would leak out of the other also. The high pressure in the bottles is broken-down through a reducing valve to a working pressure of about 100 lb. Per sq. In. The impulse duct engine is a fascinating form of power plant. Its only working parts are small spring-steel shutters in the frontal grill. These form what are in effect non-return valves and allow air to pass through the grill into the explosion chamber of the engine. This power unit has an maximum diameter of 1,9 ft. with an overall length of 11.25ft. The shell is built-up from welded mild-steel sheet of heavy gauge. No parts, except the small nose cowling have any double curvature and therefore the shell can be readily formed from that plates bent into cylindrical form and gas-welded down the single seams and ands. These welded seams are staggered on adjacent sections for obvious reasons. The tail pipe of the unit is about 12-gauge thick. There are no internal parts inside the tubular casing except for the three horizontal venturis immediately behind the frontal grill. This grill is built-up from moulded die castings, and it carries nine fuel jets in the face, each having a nozzle aperture of about 1/16 in. Diameter. Of special interest are valves which comprise in all 126 double rectangular leaves of very thin pen-nib steel, i.e., 252 leaves in all. They are formed to press against each other lightly on their inner edges. The constitute small non-return valves, closing the grill against excess pressure from within but opening readily with higher differential pressure from outside.
|Back||Power unit operation
Three small compressed-air nozzles connected to an external supply on the launching site are located immediately above the upper row of three fuel jets. These jets are used for starting the prior to launching. An ordinary sparking plug is located externally about 2,5ft. down the casing behind the grill. Like the three jets this plug is used only for starting the engine on the launching platform. The power unit is a simple blowpipe and a pure jet or reaction propulsion engine. There is no turbine or compressor. Let us assume that the machine is in flight at top speed with motor functioning, that the frontal shutters are closed, and that an explosion is taking place inside the engine. The gas pressure generated cannot get out through the non-return valves, nor can it blow open the wall of the pipe. It therefore propels the mass of burning gas down the pipe towards the exit and the open air. Now to move a mass of any kind requires a force. There is also an equal and opposite reaction to that force and this, acting on the closed shutters of the grill, produces forward thrust on the aircraft. Further, once a mass has been put into a state of motion it requires a force to stop it. The burning gas hurtling through the tube therefor tends to continue moving because of its inertia. As the mass progresses down the tube, the force tending to oppose it is a gradually increasing depression behind the grill. When this depression has reached a certain point the shutters are forced open, and a new charge of air comes through into the combustion chamber. This immediately burns, heats-up and expands, producing high pressure which closes the valves. The mass whistles down the tube, drawing a new charge behind it. The frequency of the explosions in the motor (sound of engine.mp3) is about 45 per second, i.e., 2.7000 per minute. There will be terrific vibration on this particular power unit, and this accounts in part for the fact that the whole engine is mounted on very large rubber trunnions. The forked yoke supporting the front of the unit transmits the engine thrust to the aircraft. With so many explosions per second the combustion of gases down the tube is partially continuous, and the fuel jets are spraying continuously. In an engine of this type the frequency of the explosions is determinated by the resonance frequency of the tube, and the time for one cycle will equal to twice the length of the tube divided by the velocity of sound. I have no information as to the velocity of sound through gases heated to maybe 900 deg. C, but by dividing twice the length in feet i.e. 22.5 by 1.100 I secured figure for the time cycle of 0.02 sec. I.e. 50 explosions per second. I feel that designers of organs and particularly of organ pipes would understand this perfectly. The depression wave will start at the tail orifice and travel rapidly forward up the tube to the mixing chamber immediately behind the grill. The engine is operated with ordinary motor fuel of quite low octane number. This is to be expected in view of the extremely low initial compression of the gas, which in turn partly explains the very low thermal efficiency of this engine. It develops a thrust of approximately 600 lb. At a speed of 360 miles an hour, at which velocity the drag of the aircraft is about equal to the thrust. Under such conditions it will be developing 575 thrust horse-power, equivalent to about 725 horse-power from a normal piston engine. Its fuel consumption is about one gallon every 10 seconds, in which time it will fly one mile. One of the most cunning gadgets on the whole aircraft is the automatic fuel supply control to the engine. This is actuated by a simple pitot which opens up the fuel supply with increase in speed. Another evacuated metallic capsule expanding and contracting with changes in altitude and pressure overrides the pitot control, tending to cut down fuel supply with increased altitude. There is even a third override in that if pressure inside the jet engine should reach dangerous limits, the back pressure on the fuel jets will also cut down fuel supply, thus restoring conditions to normal.
|Back||Launching the Missile
The V-1 was design to be launched from a stationary ground platform, preferably a heavy permanent structure. Let us assume that the aircraft has been erected and inspected, lifted on to its launching trolley, the tank has been filled with fuel, sealed down, and the air bottles inflated to 150 atmospheres. The magnetic compass in the nose has been set on a calculated course, based either on the meteorological data immediately available, from a trial flight of a V-1. equipped with wireless transmitter. The height and range-setting controls have all been adjusted, and the apparatus for propelling the aircraft along the runway is in position. The compressed air is turned on, starting the gyroscopes and blowing up the fuel tank. An external compressed air supply has been connected to a fixed point on the aircraft fuselage communicating with the three air jets into the combustion chamber, and a connection has been made to the sparking plug from a starting coil. The fuel is turned on and begins to spray through the nine jets into the combustion chamber along with compressed air from the three jets. A spark at the plus ignites the mixture and the motor starts. It will now be operating like a gigantic blow-pipe. When it has warmed up it will pre-ignite satisfactorily, the sparking plug connection is removed and the aircraft is ready for launching. Once on its course the ground crews can do nothing more about it. The fundamental defect of this aircraft is that its first flight is its last, and there are such a multiplicity of bits, pieces, gadgets and adjustments, that something or other is almost certain to go wrong. It is fundamentally an inaccurate, and therefore indiscriminate weapon.
|Back||Function of the Air-log
Mounted on the nose of the fuselage is a freely rotating windmill or air log which actuates a Veeder-type counter. It is an important bit of the mechanism, as it is responsible for the arming of the bomb after some 60 kilometres have been covered, and it also controls the range of the machine. Further, on those aircraft fitted with a wireless transmitter, the mechanism also starts up the transmitter some 56 kilometres before the calculated destination. The Veeder counter is set to a figure which, all things considered, should determine the required range of the machine. As the windmill spins in the flight the Veeder counter figures returns gradually to zero, and at this point two electrically fired detonators in the tail of the fuselage are discharged. They blow out a piece of metal, forcing down small spoilers on the tail-plane, the effect of which is greatly to increase the lift on the tail. At the sane time the elevator push-rod is jammed, and a guillotine severs the pneumatic controlling tubes of the rudder servo which becomes locked. This quick succession of events puts the machine in to a steep dive. Centrifugal force caused by the radius of the curve throws any remaining fuel to the top of the tank - this action is incidental and not intentional. When the machine strikes the ground the warhead is detonated by the various fuses in the nose.
This consists of three air-driven gyros (a master gyro and two secondary gyros). The master gyro controls both elevators and rudder through pneumatic servos. The secondary gyros provide damping against oscillations. The master gyroscope will maintain its axis of rotation in a fixed direction for a long period of time. It thus provides a definite fixed direction in the aircraft, and any deviation from a pre-set course is detected by the gyroscope, witch moves the control surface through the pneumatic servos to correct the deviation. The gyroscope tends to wander off its initial setting after some time, and, to counter this, a magnetic compass has been added in the nose. Electrical connections from this compass police the gyros directions in a horizontal plane. The flying height is set on the automatic pilot by a simple dial. It gives a choice of operating heights up to 10,000ft, the usual height being about 2,000ft, and few bombs have been encountered above 5,000ft. Height control at the auto pilot is through an evacuated metallic capsule which expands with a decrease of atmospheric pressure, and vice versa, thus indicating to the automatic pilot that greater or less altitude is desirable. The electric supply is from a nest of 42 dry cells of 1,5 volts each, coupled in two parallel blocks of 21, thus giving some 30 volts.