Towards the close of the second world war the German army introduced a several new "wonder weapons" with the hope that they could save the Reich from destruction by its numerous and ever victorious enemies. One of these was the V1 flying bomb, a pilotless guided aircraft carrying a payload of explosives that was used to attack targets in Europe.

The V1 was developed by the company Fiesler (who also built the famous Fiesler Storch recon aircraft) and was originally designated the Fi-103 but at the insistence of the Propaganda Minister Joseph Goebbels, was renamed the "Vergeltungswaffen 1 FZG-76 (V1)". Vergeltungswaffen loosely translates to "Vengeance Weapon" and emphasised Hitler's growing desire to wreak the same destruction on London as was being wrought on Berlin, Stuttgart, Frankfurt and other major German cities every day and night by allied bombing raids. The V1 was nicknamed the "buzzbomb" and "Doodlebug" by the Londoners who were on the receiving end.

The V1 was powered by a Pulse Jet engine (invented by the German Dr. Paul Schmidt several years earlier) and was guided by a gyro servo system that maintained a constant direction of travel during flight. The Pulse Jet produced the characteristic buzzing sound that gave it its name of "buzzbomb".

Though ultimately unsuccessful as weapon, and certainly no "wonder weapon", the V1 and later the V2 rocket effectively put the first steps onto the path of modern missile warfare. The V1 was the first "cruise missile", and the tactic of launching disposable guided missiles both from ground and from carrier planes (the V1s were also launched in the air from He-111 bombers) continues stronger than ever to this day, as demonstrated in the recent American-Iraqi war.

The V1 was a simple device, designed by Robert Liisser of Fieseler. It was quick to construct, being made mainly from sheet metal, and cost as little as 125 pounds to produce - equivalent to producing a VW Beetle. It used an Argus Pulse Jet engine as a power plant which provided around 300 kg of thrust, yielding a top speed of 624 kph and a range of 240 kms initially, later increased to 400. Physical dimensions: 7.9 m long, 5.3m wingspan, weight 2.18 tons and delivered an 850 kg payload of explosives.

The Siemens guidance system was relatively crude but reasonably effective. After the V1 was launched, an autopilot took over, regulating altitude and speed. A clever coupling of pitch, roll and the sensors meant that rudder control was sufficient without the need for any seperate banking mechanism. A small fan blade on the tip of the nose was used to determine distance travelled; every 30 rotations decreased an internal counter in the V1, and once the counter reached zero the V1 had reached its "destination". The desired altitude was set to negative and the controller would begin a dive. However, the steep descent caused the fuel starvation of the pulse jet and the V1 would then commence a powerless drop.

The first test flights of the V1 occurred in late 1941 and early 1942 at Peendemuende (site of a large secret weapons research facility), and the first offensive launch occured on June 12, 1944. The bulk of V1s launched were directed against London, though later, when the Allies overrun the coastal launching sites the remaining V1s were launched against Antwerp.

V1 defences initially consisted primarily of interception by fast moving fighters (such as the Hawker Tempest) and shooting them down. However, the steel skin of the V1 was effectively immune to machine gun fire so the pilots had to use their larger calibre cannon. However, as this required them to get closer the exploding V1 could destroy the aircraft. One method of disabling the V1 was to fly close enough to it so that the air flow disturbed its gyro and sent it off course. Barrage balloons also stopped some V1s though anti-aircraft fire was generally ineffectual against such small and fast moving targets.

A large number never made it to their desired destination due to problems with guidance system and other mechanical failures. To compensate for wind and other factors the V1s launched in the morning would be equipped with radio transmitters and through triangulation the German's could determine where they ended up and adjust the bearing of the V1s launched later on in the day.

The German Command had the hopes of launching a V1 every 12 minutes against London (about 500 a day) but bombing, material shortage and many other factors meant this target was never achieved. Nevertheless some 10,000 were fired at England up to 29th of March, 1945. Of these, some 7000 struck England and 3876 hit Greater London.

The V1 really was a "terror" weapon and little more, as it did not inflict sufficient damage to change the course of the war in any way. However, unlike conventionally bombing raids that were generally aimed at industrial areas of the cities, the fact that it did not discriminate meant that both the rich and the poor in London lived in the shadow of the V1, and later the supersonic rocket, the V2. The dramatic image on the right shows a V1 on its descent somewhere in England.

Pulse Jets are close to the simplest power sources to manufacture. They have very few moving parts and are extremely simple in operation. However, they have several very important downsides that have pushed them far behind the turbo- and ramjets that dominate our modern aircraft industry.

The pulsejet was invented by a German, Dr. Paul Schmidt, for the company Argus. This was the model of pulsejet used on V1. A pulse jet engine is basically a combustion chamber with an inlet valve on one end and an opening on the other, and some force of fuel inlet system. As the aircraft flies, air is drawn through the inlet valve into the combustion chamber. In the simplest models, fuel vapour is sucked from a fuel source via a venturi and a spark plug ignites the mixture in chamber. At this point, the ignition forces the inlet valve to close and the mass of ignited fuel-air mixture is expelled out the back of the combustion chamber as a jet, propelling the aircraft forwards. The valve opens and air is once again drawn into the combustion chamber, and the cycle continues. This discrete ignition of fuel-air vapour gives the pulsejet it's name.

The bulk of small pulsejet engines use a petal valve, but the Argus engine used an array of rectangular spring steel valves attached to a holding strips. This grid valve system was easy to manufacture by unskilled labour, which in wartime is clearly advantageous. Additionally, the fuel vapour was actually directly injected into the combustion chamber (as were so many German designed engines of the war). The injectors used the same source of compressed air that was used to drive the gyros and the control surfaces.

Obviously, one of the flaws of the pulsejet is that like the ramjet, it needs sufficient air speed to actually begin working. The German's overcame this problem by launching them from steam catapults using the decomposition of hydrogen-peroxide when mixed with water (interestly, the same power source used to drive the fuel pump in the V2 rocket), or by air launching them from He 111s! Once ignition had occured, the heat developed in the combustion chamber was actually sufficient to ignite the next batch of fuel-air mixture and so the spark plug was used only once.

However, though the pulsejet is very simple it does have its drawbacks. One that poses a serious problem for use on aircraft is that the wear on the delicate components such as the inlet valves is incredible. The V1 engine could not last more than approximately 40 minutes of continous running before the valves were destroyed. Clearly, this was not a big problem for the V1 as it would ideally have detonated before that. Other problems with the pulsejet engine include the low fuel efficiency and the tremendous noise they produce. Current research is being done pulse detonation engines that detonate the fuel-air mixture and therefore have much greater fuel efficiency. However, component wear and noise are even higher with this technology and so far research is still in an infant stage.

Finally, you can download this very interesting report published by NACA (what would later become NASA) after the war on the V1 Pulse Jet motor. The American's had been experimenting on unmanned weapons during the war but with very poor results, so they were naturally very interested in the world's first successful unmanned cruise missile and studied it, and it's rocket cousin, the V2 extensively. Of course, they then had Werner Von Braun and many other German rocket scientists in their pay so it wasn't long before they had unmanned missiles in production.