Six days after the Allies had invaded Normandy, the first flying bomb hit England to introduce one of the most destructive single weapons of the war. And subsequent capture of the so-called rocket coast did not stop them.
Although a war weapon, the V-1 bomb is of even broader interest to aviation men because of the all-steel construction. robot controls, and impulse motor.
Examination of parts and a full-scale model of V-1 disclose many interesting structural details and indicate quite clearly the probable method of the control and the operation of the engine. However, as far as possible deductions of this correspondent will be carefully indicated. Aerodynamically the robot bomb is an all-steel mid-wing type monoplane with an impulse duct engine mounted about 30" above the fuselage. The use of sheet steel unquestionably adds to the ease and rapidity of fabrication and also reduces the cost.
The complete V-1 unit may be roughly divided into eight major sections: The nose, warhead or high explosive carrier, wing and gas tank, compressed air chamber, automatic pilot, its compartment, empennage unit with air-servo controls, and the impulse duct engine.
According to various press reports, the nose is made of wood or a non-magnetic alloy so as to accommodate a magnetic compass. Since the rest of the structure is all-steel a compass could not be used inside it. There are also reports that a radio device is contained in the nose. This might be used to establish the position of the bomb when it starts its final dive, and radiosonde such as used in meteorological balloons could easily be adapted for that purpose. It is, as a matter of fact, difficult to understand why the bombs are not radio controlled, for the extra weight apparently would be no handicap. Perhaps it is because the British counteract the radio control.
Apparently the Nazis equip the bomb with a dry-battery-powered electric system for ignition purposes and for direction control, since there are wire connections on the automatic pilot unit. If there is a pilot compass in the nose, it would probably be connected by wires to the rudder or azimuth controlling gyro. On the bomb studied there was no connection between the automatic pilot and the rudder, since the latter had been tom off the fuselage. However, there is a graduated dial on the automatic pilot. It is not graduated in degrees, but there might have been a control that could be pre-set to determine the heading or course of the bomb after launching.
The space immediately in front of the wing contains the explosive. This section is conical, varying from about 24" dia at the front to 30" at the rear end. It is about 4' long, and in it go 1,880 lb of high explosive.
The third section is most interesting because the fuel tank and wing are built together as an integral structure. The fuel tank is cylindrical, of about 32" dia and 44" long. The main wing spar passes through it, as does the lifting tube which is attached at the bottom to the launching shoe, and there is provided a detachable lifting eye at the top. This is apparently close to the center of gravity of the unit as well as to the center of lift of the wing. Since the 130-gal (probably Imp gal, equivalent to 162.5 US) fuel tank is also located at this same point, the balance of the bomb should not be affected as the fuel is consumed during flight. The tank has a filler opening at the top, an opening which is closed with a flush-type cap. In the middle of the tank is a 1/6" thick vertical baffle plate to reduce surge when launching. Heavy steel-wire screens are welded over the top and bottom openings in this baffle plate. The walls of the tank, of about 1/16" steel, form the center section of the fuselage.
The wing is quite thick, about 10" deep at the root and 6" at the tip. The over-all width is given by the British as 17' 6". The leading edge is nearly straight. Root and tip chords are about 44" and 28", respectively.
Wing skin, fully 1/16" thick, apparently is welded to the ribs. It is possible that the top and bottom and leading edge were formed, in one piece, with the trailing edge then welded along a transverse seam to complete the wing. There is apparently no dihedral in the wings. Neither are there any ailerons. The wing tips are square and are closed by separate stampings welded to the end of the wing skins. The spar is tubular and extends from tip to tip through the fuel tank. It is of approximately 5" dia, with 1/8" wall seamless-steel tube, reinforced by another 1/8" wall tubular member rolled around it from a steel strip. This is about 3' shorter than the main spar tube. There is a 1/8" gap on the rear neutral axis of the spar where the edges of the strip fail to meet. Here the edges are welded together and to the inner tube at about 1½" intervals.
At the tip end of the spar and at two points equidistant between it and the fuselage there are 1/8" x 3/4" bands, either to reinforce the tubing or the points where the wing ribs are welded to the spar. It is quite possible that with this steel construction only three ribs are necessary between the fuselage and the tip.
The steel wings appear to lend something of an armor function. The starboard wing of a wrecked bomb, for example, was well creased by machine-gun bullets, but it evidently took a shell to pierce it. Even though this shell exploded inside the wing, the skin was only pushed outward about an inch adjacent to the point of explosion.
Contained in the fourth section of the fuselage are two spherical air pressure tanks. These are apparently designed to take high pressure, for they are wound with piano wire and look very much like a housewife's ball of string because of the way the hands arc criss-crossed. Each band comprises three layers of 16 strands of about 1/16-in dia wire.
The spherical tanks are of approximately 20" dia, probably welded at the equator. Taps for air are at the top and bottom poles, and air line connections can be reached through an inspection plate on the port side of the fuselage section. At the rear end of this section there is bolted a 1/8" steel bulkhead. This may be part of the automatic control section or a reinforcement to take the thrust of the impulse engine. Each air tank is held in place by a single heavy strap arranged diagonally across the fuselage.
The automatic pilot section apparently contains a horizontal shelf across its middle to support the automatic pilot. A large door is bolted to the upper port quarter of this section of the fuselage to give access to the automatic pilot. At the front end of this section of the fuselage there is a vertical, heavy-walled tube supporting the impulse motor. Attached to the top and bottom of the fuselage, this tube has a forked arrangement on the upper end. The fork is fastened with trunnion bolts to the sides of the impulse-engine casting at its horizontal centerline.
Last section of the fuselage is a conical member that carries the stabilizer, elevators, fin, and rudder. In it are the air-servo controls which direct and control the elevation of the bomb. A vertical tubular member attached to the rear end of the tail cone forms the back of the fin and the hinge member for the rudder. At its upper end it forms a cradle in which the engine tube rests.
It is not evident whether this is secured to the engine duct, but judging from the red oxide coloring of the duct, it would evidently be desirable to leave it unattached so the duct can expand freely under the red hot operating temperatures at which it appears to function.
According to the British, the air pressure is used to feed the fuel and run the automatic pilot. The light rubber tubes attached to the remains of the automatic pilot would suggest that low air pressure runs the gyros and controls. A pressure reducing valve obviously must be used, although none was visible.
Centerline of the impulse engine is about 30" above the center line of fuselage, and nose cowling of the engine is of about 20" dia, while the tail end of the duct is between 12" or 13" dia. The nose cowling apparently takes the entire thrust of the engine and transmits it through the vertical tube to the fuselage. The tube not only drives but supports the heavy steel vertical grill in the front of the engine tube.
On the back of the grill there appear to be a series of quick-acting reed-type valves which are instantly responsive to variations in pressure. Inside the duct, a short distance behind the grill are three venturi passages through which the mixture of air and gas must pass. There are nine fuel jets on the rear surface of the grill. The feed line probably comes from the automatic pilot chamber through the vertical driving tube to the grill jets. The fuel is fed by air pressure.
The English explanation is that the three top jets also include air jets to atomize the fuel. Arrangement of the jets in the grill provides the proper fluctuating supply of fuel to the combustion chamber, it is claimed, and corrects the mixture strength according to the forward speed of the bomb, and also for altitude changes. Nothing was visible of this structure; but from what could be observed, our illustrative sketch was made to suggest how it might be accomplished.
Operation of the engine is very simple. The bomb is launched by a catapult device which gives it a speed of about 150 mph. The air pressure thus built up in front of the grill opens the reed valves and air is forced into the combustion chamber. When the valves open up they probably allow the fuel to flow into the air stream through the nine jets in the grill, thus forming an explosive mixture.
In the venturi section there is a sparkplug which starts the combustion. Once the combustion is initiated the subsequent charges are fired by the temperature of the tube walls, heated by the previous charge.
The resultant combustion raises the internal pressure above that on the front of the grill and so causes the reed valves to close. Therefore the products of combustion can only escape from the rear end of the engine duct, giving jet propulsion. As soon as the internal pressure drops below that on the front of the grill, air rushes in again, picks up more fuel. forms a mixture, is ignited, causing the reed valves to close, and the cycle is repeated.
Weight of the complete ready-to-launch flying bomb is given as 4,700 lb. Its speed is variously given from 250 to 360 mph, although the latter figure seems pretty high.
The impulse engine is said to develop 600 hp, if it can be so rated. It consumes eight times as much fuel as a conventional gasoline aircraft engine, according to press dispatches. However, it only requires low-grade fuel instead of high octane gas.
Although the British description of the automatic pilot says there are three air driven gyros, remains of the automatic pilot indicate that it only has two. Since there are no ailerons to operate, a third gyro might be considered unnecessary. The writer has been told that if the two gyros are placed at the proper angle it might be possible to obtain the kind of control which the flying bomb obviously has.
One gyro controls the rudder and has wires which probably connect it to the magnetic compass in the nose. This would provide the means of putting the craft on course, and there must be a control which can be set to determine the final course of the bomb.
The elevator is apparently controlled by another gyro, but it evidently has a barometric capsule control attached in such a manner that it maintains the bomb's flying altitude. One of the control dials on the automatic control had graduations reading 375-400-425-450, etc. This may have been for pre-setting the altitude control. Calibration was judged to be in meters.
The pneumatic servo mechanisms for operating both rudder and elevators look alike. They appear to be die-cast aluminum cylinders of about 1½" dia with about a 2" stroke, On the side of the cylinder there is what appears to be a housing with control tubes to each side. Each diaphragm must control the valve that causes the servo piston to move. It is obviously a servo mechanism because of a spring attached to the piston rod on one end and probably to the valve on the other end, so that it cuts off the air supply when the correct piston movement has been obtained.
There is much speculation as to how the flight distance is determined. Some think the supply of fuel carried determines this. Another theory is that when the air pressure fails the bomb falls. Clocks may also he a means of setting off the bomb. Some say a pin wheel device on the nose does it a method used to arm most bombs.
The clock method sounds quite rational. The failure of air pressure does not seem practical, for there is evidence that air pressure may he needed to lock the empennage controls and release the spoilers when the bomb is ready to be fired. Whether this action also cuts off the fuel was not evident from the wrecked sample, but it is quite possible. This is substantiated by a spring-operated mechanism on the underside of the stabilizer which seems to be released by air pressure before the spoilers can come into action and nose the bomb down.
For starting purposes, there is a valve on the bottom of the automatic pilot section which apparently controls the fuel and ignition. This is operated by a push button and is in the "off" position until the bomb leaves the ramp. then it is spring-opened, whereupon fuel flows to the grill and an electric ignition switch is closed to spark the engine. This control is a very important part, for the wires are carried through a key-lock switch on the starboard side. This is a tumbler lock operated from the outside with a key, and is apparently a safety device.
It is reported that the bombs are launched from ramps 170' long and of 32" gage, but the exact manner in which they are catapulted into the air has not yet been explained. To get the bomb into the air with a terminal velocity of 150 mph in 170 ft only requires 1.5 sec and the application of about 1,000 hp/sec. Perhaps an explosive charge is used to accomplish this.
Apparently 150 mph is the minimum speed at which the impulse engine can he started, but once started it has power enough to continue accelerating until it has reached its top speed.
Some of the launching ramps are in a direction other than that toward the objective, thus requiring a timing device perhaps a spring- or electrically-operated clock used to time both the turn and the total length of flight. This may explain why some bombs have been found with clockworks in them. For the first stage of the flight the compass control must be cut out, but after a certain number of seconds of free flight, the compass control would be automatically connected and the bomb required to follow the preset course under compass control.
This article was originally printed in the November, 1944, issue of Aviation magazine, vol 43, no 11, pp 190-191, 289, 291-293.
The original article includes 8 drawings one phantom view and 7 detail drawings.
Drawings are credited (as sketches) to the author