Science: How the Robomb Works

The whole story about V1, the German flying bomb, was told last week by the British Ministry of Aircraft Production. An ingenious machine that can be built for less than $1,000, the robomb was revealed to be much more accurate than the British had previously cared to admit.

Chief news was the description of controls that made it possible to guide the bomb to its target with a maximum error of only a few thousand yards. Carrying 136 gallons of gasoline and burning a little less than a gallon a mile, the bomb has a top range of 150 miles. It can be set to fly at anywhere between 2,000 and 5,000 feet, thus taking advantage of any cloud cover available. Three gyroscopes, driven by bottles of compressed air and assisted by a magnetic compass in the nose (see cut), keep the bomb on its course. A small windmill in the nose regulates the range. Operating a counter as it turns, the wind mill acts as a timing device: at the set time it jams the controls and throws the bomb into a steep dive at its target. To check on accuracy, wind drift, etc., the Nazis equipped every tenth bomb with a radio signal (see WORLD BATTLEFRONTS).

Easier Way. But to engineers the chief point of interest was the bomb’s simple power system. In the usual jet-propulsion machine, air is taken in at the front, compressed by a turbine-driven mechanical compressor (e.g., a fan), then mixed with fuel in a combustion chamber and expelled at the rear, the impact of the expanding air and gas, like a gun’s recoil, giving the machine its push. But a compressor would have added greatly to the bomb’s weight and complexity. To eliminate it, the Nazis hit on a way to use the force of the inrushing air itself. A grill with nine small jets is mounted in front (see cut, right). Behind it is a gas-combustion chamber. At the takeoff, the gas is ignited. When the bomb is in motion, air rushing into the jets opens them, passes into the combustion chamber, sets off an explosion which closes the jets and expels the expanding vapors from the rear end, giving the bomb a forward push. As the vapor escapes, air opens the jets again and the process is repeated, 45 times a second, to give the machine an almost continuous thrust.

But high air speed is necessary to develop enough air pressure to open the jets; at less than 150 m.p.h. the jet bomb stalls and falls to the ground. To get the craft into the air, therefore, it is necessary to drive it along a launching platform (on a car) or carry it pickaback on a plane until it reaches 200 m.p.h. At that speed, the bomb takes off under its own power, gradually accelerates to 360 m.p.h.