Principles of Guided Missiles and Nuclear Weapons, 1959, was created to introduce ROTC officers to these weapons. This document was never classified and does not contain any classified information. It is provided as a historical document demonstrating the technology and implied tactics midway through the US-Soviet Cold War.

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PREFACE

This is the second volume of a three-volume series of texts dealing with Naval weapons. The series is intended for use in the Naval Science curriculum of NROTC universities, and in other Navy training programs.

The first volume, Principles of Naval Ordnance and Gunnery, NavPers 10783, deals with conventional Naval weapons, and with the principles of fire control.

The present volume describes the principles of guided missiles and nuclear weapons, insofar as they can be discussed in an unclassified text. The treatment is necessarily of a general nature, with minimum reference to actual weapons in current use.

The third volume, a classified supplement to this text, will describe specific Navy missiles and nuclear weapons.

Part 1

GUIDED MISSILES

A GUIDED MISSILE is an unmanned vehicle that travels above the earth's surface; it carries an explosive war head or other useful payload; and it contains within itself some means for controlling its own trajectory or flight path. A glide bomb is propelled only by gravity. But it contains a device for controlling its flight path, and is therefore a guided missile.

The Navy's guided missiles, including Terrier, Talos, Sidewinder, Sparrow, Regulus, and Polaris, meet all the requirements of the above definition.

The Army's Honest John is a 3-ton rocket that is capable of carrying a nuclear warhead. But because it contains no guidance system, Honest John is not a guided missile. The Navy's homing torpedoes are self-propelled weapons with elaborate guidance systems. The homing torpedo can hunt for a target and, when it finds one, steer toward it on a collision course. But because it does not travel above the earth's surface, the homing torpedo is not a guided missile.

A MISSILE is any object that can be projected or thrown at a target. This definition includes stones and arrows as well as gun projectiles, bombs, torpedoes, and rockets. But in current military usage, the word MISSILE is gradually becoming synonymous with GUIDED MISSILE. It will be so used in this text; we will use the terms MISSILE and GUIDED MISSILE interchangeably.

1A2. Scope of the text

Part 1 of this book is a brief introduction to the basic principles that govern the design, construction, and use of guided missiles. Many of the principles we will discuss apply to all missiles; most of them apply to more than one. The treatment will necessarily be general. Security requirements prevent any detailed description of specific missiles in an unclassified text. This text will therefore contain very little information about specific missiles; they

The reader will find some repetition in this text; this is intentional. The subject is complex; it deals with many different phases of science and technology. The beginning student of guided missiles faces a paradox. We might say that you can't thoroughly understand any part of a guided missile unless you understand all the other parts first. We will deal with this problem by first discussing the guided missile as a whole, with a brief consideration of its propulsion, control, guidance, and launching systems. Each of these subjects will then be treated at some length in one or more later chapters.

All guided missiles contain electronic devices; some of these devices are very complex. A sound understanding of the operating principles of missile guidance is impossible without some background in basic electricity and electronics. Appendix A of this text covers these subjects briefly. It may be used for a quick review. Students who have no background in electronics should use appendix A as an introduction to the subject; it should, if possible, be supplemented by further reading in basic texts on electricity and electronics.

1A3. Purposes and uses of guided missiles

As you well know, the primary mission of our Navy is control of the seas. We propose to keep the sea lanes open for our own and for friendly commerce; in time of war, we propose to deny use of the sea to our enemy. Historically, this mission has been accomplished by the use of warships armed with the most advanced weapons of their time. When John Paul Jones challenged the British control of the seas, his warships carried guns having an effective range of a few hundred yards. The Union Navy maintained a successful blockade of southern ports with the help of guns that could shoot a little more than a mile. The battleships of World War I carried rifled guns with an effective range in the order of 20 miles. When aircraft became more effective

When a navy so controls the seas that it can safely approach the enemy coast, it can extend its striking power inland to the distance its weapons can reach. A battleship can bombard enemy installations more than 20 miles inland. Carrier-based aircraft extend the Navy's force for hundreds of miles over enemy territory. Thus, during the Korean War, the whole of North Korea was subject to attack by carrier-based aircraft of the U. S. Navy. The Navy's Regulus guided missile has a range comparable to that of carrier-based aircraft. And because it can be launched from submarines, Regulus can be used effectively even where we do not control the surface of the sea. The Polaris missile, also submarine-launched, will extend the Navy's striking power to 1,500 miles inland. And only a relatively small part of the earth's land surface lies more than 1,500 miles from the sea.

One of the strongest elements in our national defense is the Strategic Air Command, which can launch a devastating nuclear attack against any enemy on a few minutes notice. But SAC bases are large, and expensive to build and maintain. Their position is known to our possible enemies. At the outbreak of war, they would probably be the first objective in a surprise attack.

The intercontinental ballistic missile (ICBM) will carry a nuclear or thermonuclear warhead. It will reach its target, on another continent, within minutes after launching. It will approach the target at such a speed that any countermeasures may be very difficult. Its launching sites will be small, relatively cheap to build and maintain, and relatively easy to conceal. Because they can be widely dispersed, they will be difficult to attack even if their location is known. And the ICBM will not face the problem of returning safely to friendly territory after completing its mission, for guided missiles are expendable by design, while our strategic bombers and their crews are not. It is likely that SAC will first be supplemented, then replaced, by the ICBM.

The Navy's Polaris is an intermediate-range ballistic missile (IRBM). Polaris is another important element in our national

Modern military aircraft can fly so high and so fast that conventional antiaircraft guns are ineffectual against them. As you know, a gun is not aimed directly at a moving target; it must be so aimed that both the projectile and the target will reach a predicted point at the same time. During the flight time of the projectile, a high-speed high-altitude aircraft will travel several miles. Any slight change of course during that time will take it beyond the lethal range of the projectile burst.

The surface-to-air guided missile is a more effective means of defense against enemy aircraft. The missile can intercept attacking aircraft at greater heights, and greater ranges, than any projectile. And the aircraft is unlikely to escape a missile by taking evasive action. The missile is faster and more maneuverable. If the attacking aircraft changes its course, the missile guidance system will change the course of the missile accordingly, up to the instant of interception.

Guided missiles are becoming increasingly important in aircraft armament. When two jet aircraft are approaching each other head-on, the range closes at a speed between half a mile and one mile per second. Under these conditions it is difficult even to see an enemy aircraft, and hitting it with conventional aircraft weapons would be largely a matter of luck. But the air-to-air missile can "lock on" the hostile aircraft while it is still miles away, and it can pursue and hit the target in spite of its evasive maneuvers.

In the future, the defense of a naval task force against air attack will be somewhat similar to that of an American city or industrial area. The enemy attack will be detected by long-range search radar while the attacking planes are hundreds of miles from the target. Ashore, the early warning radars are located at distant outposts in Canada. At sea, they will be aboard picket vessels at some distance from the main body of the task force. The

Because the defense system outlined above is formidable, it is improbable that enemy aircraft will try to bomb our cities, or attack a task force with bombs or torpedoes. Enemy aircraft are more likely to attack with air-to-surface missiles, launched at a range of perhaps a hundred miles.

One question remains: how are we to defend ourselves against enemy intercontinental ballistic missiles, and air -to-ground missiles? Our present surface-to-air missiles such as Nike and Terrier were designed for defense against jet aircraft. But Nike and Terrier are not fast enough for reliable defense against enemy missiles, which will approach at several times the speed of sound. The answer is an anti-missile missile, which will be relatively small, capable of launching on very short notice, extremely fast, and extremely maneuverable. Such missiles are now being developed.

When the anti-missile missile becomes operational it will probably lead to further developments. Our aircraft carry air-to-air missiles for defense against enemy aircraft; an intercontinental ballistic missile might carry air-to-air missiles for defense against other missiles. These might be called anti-anti-missile missile missiles, though if we have the ingenuity to develop such weapons we may be able to think of a shorter name for them.

Such speculations about the future are not very instructive. But this prediction is safe: the effort to develop faster and better missiles, and the race between missiles and missile countermeasures, will continue as long as the threat of war exists, or until some new and unforeseen weapon makes guided missiles obsolete.

To perform the various functions outlined above, missiles of many different types must be developed. A list, later in this chapter, will show the number of missile types now operational or in various stages of development. It can be assumed that other missiles, not yet announced, are being developed.

The Navy's Sidewinder is a relatively small air-to-air missile with a range of a few miles. A Sidewinder costs about as much as a good used car. It resembles an ordinary aircraft rocket; it differs, of course, in having a guidance system, and movable control surfaces by which the guidance system can control its flight path. At the other extreme, the ICBM has a range of thousands of miles, with size and weight in proportion; its proportional cost is even higher. The ICBM, like most missiles, has the familiar rocket shape. But the Air Force Snark and the Navy's Regulus I, among others, resemble conventional aircraft; they differ in having a guidance system rather than a pilot, and they are designed to dive into their targets rather than release a bomb load and return.

Guided missiles are classified in a number of different ways; perhaps most often by function, such as air-to-air, surface-to-air, or air-to-surface. A nonballistic missile is propelled during all or the major part of its flight time; the propulsion system of a ballistic missile operates for a relatively short time at the beginning of flight; thereafter, the missile follows a free ballistic trajectory like a bullet (except that this trajectory may be subject to correction, if necessary, by the guidance system). Some missiles are designed to travel beyond the earth's atmosphere, and re-enter as they near the target. Others depend on the presence of air for proper operation of the control surfaces, the propulsion system, or both.

Missiles may be further classified by type of propulsion system, such as turbo-jet, ramjet, or rocket; or by type of guidance, such as command, beam-riding, or homing.

1A5. Introduction to missile guidance

The missile guidance system keeps the missile on the course that will cause it to intercept the target. It does this in spite of

From the paragraph above, it might be inferred that the guidance system is an intelligent mechanism that can think. This, of course, is untrue. The missile guidance system is based on a relatively simple electronic computer. But even the most complex computers, such as Univac and other "giant brains," cannot think. Thinking is a conscious process, confined to man and a few of the higher animals. No matter how complex it may be, a computer is simply a machine built so that when certain things happen, certain other things will result. The design of a computer is nothing more than an advanced exercise in the logic of cause and effect. A computer can take no action that isn't built into it by its designer (except, of course, the erratic action that might result from a bad connection or a faulty component).

But in the later chapters of this text you will find many statements such as this: "When Terrier detects an AM signal, it knows it is off the beam center; but it does not know, from the AM signal, which way to go to get back to beam center." We will make such statements without further apology. But it is essential that the students understand what we are doing. We are using a convention, because it saves time and space. Remember that a missile doesn't "know," or "see," or "think," or "decide."

Several distinct types of guidance are possible; a given missile may use one type, or a combination of two or more. Although it can not be called a guided missile, the air-steam torpedo has a simple guidance system. Before launching, its gyro is set for a predetermined course; the gyro holds the torpedo on that course throughout its run to the target. The torpedo is capable of steering itself, but it receives no information after the instant of

The German V-2 used a combination of preset and COMMAND guidance. Before launching, it was set to climb vertically for a certain distance, and then turn onto the desired course. Speed and position of the V-2 were determined by a radar at the launching site. This information was analyzed by a computer, which determined when the missile had reached a position and speed that would carry it, along a ballistic trajectory, to its target. At that instant, the missile propulsion system was shut down by radio command.

The Army's Nike surface-to-air missile is a more modern example of command guidance. Throughout the missile flight, radars at the launching site track both the missile and its target. A computer continuously calculates the course that the missile must follow to reach the point of intercept. Throughout its flight, Nike is steered along the desired course by radio commands from the ground.

Sidewinder has a HOMING guidance system. Sidewinder is sensitive to infrared (heat) radiation, and will steer itself toward any strong source of infrared. The exhaust of a jet aircraft is such a source, and Sidewinder can steer itself "right up the tailpipe" of an enemy jet.

Infrared is not the only basis for homing guidance. A missile can be designed to home on light, radio, or radar energy given off by, or reflected from, the target. (It could also, like a homing torpedo, be designed to home on a source of sound waves; but because a guided missile travels at from one to a dozen times the speed of sound, such a system would not be practical.)

Because its source of information is energy given off by the target itself, Sidewinder guidance is an example of PASSIVE homing. Other missiles carry a radar transmitter, "illuminate" the target with a radar beam, and home on the radar energy reflected from the target. This is an ACTIVE homing guidance system. A SEMI-ACTIVE system is also possible; the target is illuminated by a radar beam from the launching site or other control point, and the missile homes on energy reflected from the target.

Intermediate-range (around 1,500 miles) and long-range (3,000 miles or more) missiles may use a NAVIGATIONAL guidance system. The missile determines its own position in relation to the target, calculates the course required to reach the target position, and steers itself along that course. A missile may be designed to navigate with the help of radio or radar beacons, just as a ship may navigate with the help of Loran. A missile may navigate by dead reckoning, through the

As previously stated, a missile may have more than one type of guidance system, and switch from one to another during its flight. For example, a long-range missile may climb to a preset height and turn onto a preset course shortly after launching, then navigate to the target vicinity, and finally home on the infrared or other energy given off by the target. Or a surface-to-air missile may ride a radar beam until it gets near the target, then switch over to active homing guidance.

The brief sketch that follows will enable the student to view the present-day guided missile in a historical perspective, and to consider the most recent developments in their relation to early experiments. It serves no other purpose; it is not necessary to memorize the dates listed here.

Guided missiles, as defined at the beginning of this chapter, were first used in World War II. But they could not have been built at that time without previous experiments in both propulsion systems and guidance. We will look briefly at early developments in both of those fields. Our latest missiles, of course, are based also on developments in many other fields, including mass production techniques, metallurgy, aerodynamics, radar, and electronic computers; but we cannot describe the evolution of those developments here.

1B2. Propulsion systems

Glide bombs and other gravity-powered missiles are obsolete. And although propeller-driven aircraft, under radio control, have been used as target drones, a propeller-driven guided missile would be too slow to be effective. All current missiles depend on some form of jet or rocket propulsion

After Campini's successful flight, development of improved jet engines was undertaken in several countries. In England, in 1930, Frank Whittle patented a jet engine based on the principles used in modern jet aircraft. After combustion, the exhaust gases of the jet were used to spin a turbine; the turbine, in turn, drove the compressor. The first successful flight of a turbo-jet powered aircraft was made in England in May, 1941. In the U. S., development of jet engines was turned over to General Electric Company, because of its experience with turbine-driven superchargers. At present, nearly every manufacturer of aircraft engines is developing and building turbo-jet engines.

The ram-jet also depends on forward motion for compression, but it differs from the pulse-jet in having no moving parts. The basic idea of a ram-jet was patented by Rene Lorin, a French engineer, in 1913. This was followed by a Hungarian patent in 1928, and another French patent, by Leduc, in 1933. None of these patents resulted in a workable ram-jet engine. The basic ideas were sound; but successful development of a ram-jet engine had to wait for extensive data on the behavior of fluids at extremely high speeds. In June of 1945, the Applied Physics Laboratory of the Johns Hopkins University made the first successful ram-jet flight, in the course of developing a power plant for the Navy's Talos missile.

Turbo-jets, pulse-jets, and ram-jets all depend on the presence of air for the combustion of their fuel. Consequently, none of them can operate beyond the earth's atmosphere. Rockets, on the other hand, carry their own source of oxygen for combustion; and they operate even more efficiently in a vacuum than they do in air. Rocket-propelled vehicles are theoretically capable of flight to the moon and the planets.

The principle of rocket propulsion has been known for nearly 2,000 years. In the Far East, rockets were used in warfare as early as the 13th century. Several western armies used rocket projectiles in the early part of the 19th century, but not very effectively. They seem to have been of more value in frightening the enemy than in doing physical damage. The British used rockets in their attack on Washington in 1812; and in the Star Spangled Banner, Francis Scott Key referred to the "rocket's red glare" during the bombardment of Fort McHenry. (But some historians believe that the British were using rockets as signals, rather than weapons.) Military interest in rockets lapsed after the middle of the 19th century, because developments in gunnery made gun projectiles superior to rockets in range, and far superior in accuracy.

Before Goddard's experiments, rockets consisted of a quantity of propellant packed in a cylindrical tube. Goddard discovered that by forming the after end of the tube into a smooth, tapered nozzle, he could increase the ejection velocity of the combustion gases eight times, without increasing the weight of the fuel. According to Goddard's calculations this would, for a given weight of fuel, drive the rocket eight times as fast and sixty-four times as far.

Goddard was given a Navy commission in 1917, and assigned to the job of improving the Navy's signal rockets. This assignment enabled him to continue his development of rocket theory. After the war he summarized his theories and experience in a paper called A Method of Reaching Extreme Altitudes. This report was published by the Smithsonian Institution in 1920. It consisted almost entirely of equations, formulas, and tables, but it contained one statement of general interest. It proposed the idea of multi-stage or step rockets that is, one rocket carrying another-and said that by this means a rocket could be sent to the moon, where it could explode a charge of flash powder to make a light visible from the earth.

During the twenties and early thirties, Goddard continued his experiments with the help of a small salary (as professor of physics at Clark University) and grants from the Guggenheim and Carnegie Foundations. His list of accomplishments is impressive. We have mentioned his idea of multi-stage rockets, and his design of the tapered nozzle. He was the first to suggest that a liquid-fueled rocket could provide the sustained thrust necessary for sending a vehicle into space. He was the first to actually launch a successful

But Goddard was forced to end his experiments in 1935, for lack of funds. During World War II he again worked for the Navy, this time to develop rockets to aid the take-off of the Navy's flying boats. He died in 1945.

A group or rocket enthusiasts, inspired by Goddard's experiments, formed the American Rocket Society in 1930. During the thirties this group performed a number of important experiments with rocket motors, but their work was limited in scope by lack of money.

Hermann Oberth is a German counterpart of Goddard. Like Goddard, he worked on the physics and mathematics of rocket propulsion during the first World War. There is good evidence that he independently conceived the idea of multiple-stage liquid fuel rockets. He read Goddard's report shortly after it was published, and in 1923 published a book of his own, called The Rocket into Interplanetary Space. Goddard's principal interest was in scientific exploration of the upper atmosphere; but to Oberth, every improvement in rocketry was simply a step toward the eventual development of space ships. Oberth's book discussed the possibility of putting an artificial satellite into orbit around the earth. (Except for a science-fiction story published in 1870, that was the first time this idea had been expressed in print.) Oberth believed that passengers could travel to and from the satellite in smaller "landing rockets." In this way, the satellite could be transformed into a manned space station, which could ultimately serve as a launching point for space ships. Neither Goddard nor Oberth mentioned the possible use of rockets as military weapons.

The German "Society for Space Travel, Inc." was organized in 1927, with Oberth as president and Willy Ley as vice president. The society began at once to experiment with liquid-fueled rocket engines. The rockets carried two tanks-one of gasoline and one of

The Versailles peace treaty limited the German army to 100,000 men; it was forbidden to have aircraft or antiaircraft guns, or field artillery of more than 3-inch caliber. This may explain why the German army took an early interest in rocket development; the treaty of Versailles didn't mention rockets at all. In 1932, the army established a small research project under the direction of Captain (later General) Walter Dornberger, to develop liquid-fueled rockets for use as weapons. No one in Germany had any experience with rocket propulsion, except the members of the Society for Space Travel. Dornberger visited the society, and hired a very young member named Wernher von Braun.

The team of Dornberger and von Braun, with a small staff of assistants, began to test rocket motors on an artillery testing range near Berlin. In December of 1934, they succeeded in firing two rockets to a height of about 6,500 feet. This news eventually filtered up to the high command. In 1936, General von Fritsch went to the test range for a demonstration. The general was impressed. The result

1B3. Guidance systems

The history of guidance systems is short. All of the significant developments are recent, principally because the state of electronics before the nineteen forties was relatively primitive.

The Americans developed a flying bomb called the Bug during the first World War; it was simply a pilotless aircraft, with a range of about 400 miles. The Bug was ready for production by the middle of 1918. But by that time it was apparent that the war would be over in a few months, and the Bug was never produced. Its accuracy would have been poor; it had no guidance system. But the Bug led to the suggestion that pilotless aircraft could be controlled by radio. Beginning in 1924, both the Army and Navy experimented with radio-controlled planes. Several moderately successful flights were made, with the pilotless plane controlled by radio from a parent plane that flew nearby. This project was dropped in 1932 for lack of money.

In 1935, an American high-school student named Walter Good built and flew a radio-controlled model airplane. This was the first time on record that a plane of any kind had been successfully launched, flown, and landed while under complete radio control from the ground. One of the problems that plagued the armed forces was stabilization-keeping the aircraft on an even keel so that it could respond properly to radio commands. Because a well-built model airplane is inherently stable, Good didn't have to worry about this problem. His contribution was to design and build a miniature radio receiver coupled to the control surfaces through a miniature servo system.

The Army and Navy resumed their experiments with radio command during the late thirties, and by 1940 both had developed radio-controlled planes for use as target drones. As we will note below, missiles with elementary preset and command guidance were used during World War II. But successful beam-riding, radar and infrared homing, hyperbolic, and inertial guidance systems are all postwar developments.

1B4. Guided missiles in World War II

During World War II, the Japanese developed and used two devices of interest in the history of guided missiles. One of these was an air-launched, radio-controlled, rocket-assisted glide bomb. Its performance was limited. It had to be launched from a plane at low altitude, within two and a half miles of the target. This made the launching planes highly vulnerable to antiaircraft fire, especially after we began to use the proximity fuze. The Japanese dropped this project before the end of the war.

The second Japanese missile was the baka bomb. This was a rocket-propelled glide bomb designed for use against shipping. It carried a human suicide pilot; for this reason we can't call it a true guided missile. The baka bomb had poor maneuverability, and because of this we were able to shoot down a great many of them with antiaircraft fire.

Of the guided missiles used during World War II, those made by the Germans were the most advanced, and the most effective. The V-1 and V-2 are familiar to nearly everyone. The V-1 was developed early in the war, and was successfully flight-tested at Peenemunde as early as the spring of 1942. By 1943, the Peenemunde center was working on 48 different antiaircraft missiles. Because of this dilution of effort, progress was slow. The work was later consolidated into 12 projects in an effort to get the missiles into production in time to influence the outcome of the war.

The V-1 was a robot bomb-a pulse-jet midwing monoplane with a conventional airframe and tail construction. It used gyro

The V-2 was a large missile, with a length of 46 ft 11 in., and a diameter of 5 ft 5 in. Its total weight at launching was over 14 tons, including a 1650-pound warhead. The V-2 was propelled by liquid-fuel rockets. It was launched vertically, and preset to tilt over to a 41- to 47-degree angle a short time after launching. When it reached a speed calculated to take it to the target, its propulsion system was shut down by radio command, and it then traveled a ballistic trajectory. Its accuracy was not high, and its maximum range was only about 200 miles. But it descended almost vertically on its target, at speeds of from 1800 to about 3300 mph. Active countermeasures against it were impossible; no V-2 missile was ever intercepted, or shot down by antiaircraft fire. If armed with a nuclear warhead, the V-2, within the limits imposed by its range, would be a formidable weapon even now.

Five other German missiles, which were in various stages of final testing when the war ended, are worth a brief mention:

Rheinbote was a surface-to-surface missile propelled by a three-stage rocket, with booster-assisted take-off. Its overall length was 37 ft; length of the third stage was 13 ft. The third stage carried 88 pounds of explosive; it reached a speed of over 3200 mph about 25 seconds after launching, and had a range of about 135 miles.

Wasserfall was a supersonic surface-to-air missile, propelled by a liquid-fuel rocket and guided by radio command. Length: 25 ft; weight: 4 tons; speed: 560 mph; range: 30 miles; war head: 200 pounds.

Schmetterling was a smaller version of Wasserfall, intended for use against low-altitude targets at ranges up to 10 miles. It carried a 55-pound warhead.

The X-4 was an air-to-air missile designed for launching from fighter aircraft as shown in figure 1B1. It was propelled by liquid-fuel rocket, and stabilized by four fins placed symmetrically. Length: about 6-1/2 ft; span about 2-1/2 ft; range 1-1/2 miles; speed 560 mph at an altitude of 21,000 ft. The X-4 was guided by commands from the launching aircraft, through a pair of fine wires that unrolled from two coils mounted on the tips of the missile fins. The X-4 was successfully tested before the end of the war, but it was not used in combat.

In the United States, the Army Air Corps began the development of guided glide bombs in 1941. Azon was a vertical bomb controlled in azimuth only; it was put into production in 1943. Razon, a bomb controlled in both azimuth and range, was started in 1942 but not completed until the end of the war. The limits of control of Azon and Razon bombs are indicated in figure 1B2. A medium-angle glide bomb called the ROC, and a 12,000-pound bomb called Tarzon, both controlled in azimuth and range, were developed during the war but were not used in combat. The Tarzon project was dropped in 1946 but resumed in 1948, and Tarzon was used successfully during the Korean war.

In 1944, we carried out a glide-bomb mission against Cologne, Germany, and a majority of the bombs reached the target area. In this same year remote television-control equipment was developed and installed in bombing aircraft. These aircraft were used to control television-sighted, explosive-laden bombers unfit for further service. These radio-controlled bombers saw some service over Germany in the "Weary Willie" project.

Our first jet-propelled missile was a radio-controlled flying wing; a later version was a copy of the German V-1, with a few improvements.

By the end of the war, the Navy had a number of guided missile projects in various

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As we have shown, the principal guided missile developments during World War II were German. The United States lagged far behind. Japanese and British missile developments were insignificant, and as far as we know the Russians had none at all. In 1945, the Russians captured most of the production engineers and technicians of the V-2 project, as well as several tons of missile data and perhaps a few V-2 missiles. We were luckier than the Russians. The design staff of the Peenemunde project, including von Braun and his principal assistants, took pains to surrender to the Americans rather than to the

During the first few years after the war, both American and Russian missile effort was partially devoted to assimilating the German developments. Our own experiments with the captured V-2' s provided valuable training for launching crews, and valuable knowledge of missile engineering. Our "V-2 Program" ran from March 1946 to June 1951. One of its principal successes was a high-altitude record of 250 miles, achieved by a WAC-Corporal

Postwar missile development has been rapid. Many missiles are now operational; many others have been abandoned at various stages of development, or rendered obsolete by more advanced weapons. We will not try to cover these developments here; a list of obsolete missiles would probably be longer than a list of those now current.

Although missiles are popularly known by their names, such as Sidewinder or Terrier, every missile is assigned a designation consisting of letters and numerals. The first three letters indicate the intended use of the missile:

AAM-air-to-air missile ASM-air-to-surface AUM-air-to-underwater SAM-surface-to-air SSM-surface-to-surface UAM-underwater-to-air USM-underwater-to-surface

These three letters are followed by a hyphen and then a service letter: A for Air Force, N for Navy, and G for Army. After another hyphen comes the model number, followed by a lowercase letter indicating successive modifications. A one-letter prefix may be used to indicate the status of the missile: X means experimental, Y means service test, and Z

ASM-G-3c-An air-to-surface missile used by the Army; third model and third modification, operational.

XSAM-N-7-A surface-to-air missile used by the Navy, seventh model, experimental. (This designation was used for an early version of Terrier.)

All missiles in service, as well as most of those still under development, have been given popular names. Some of these names follow this pattern:

AAM-Winged creatures (except birds of prey and game birds). Example: Sparrow. SAM-Mythological terms. Example: Talos. SSM-Astronomical terms. Example: Polaris.

At the present time, most missiles appear to be exceptions to the above "rules." For example, Sidewinder and Bullpup are not winged creatures; Terrier is not a mythological term; Snark, Thor, Lacrosse, and Dart are not astronomical terms.

Because of the rapid developments in the guided missile field, the lists given below will be out of date before you can read them. Some of the missiles listed may have become obsolete. Others, now under development, will probably be announced.

Nike-Ajax SAM is the Army's first supersonic anti-aircraft guided missile. It is designed to intercept and destroy attacking enemy aircraft regardless of evasive action. Nike guided missile units are now deployed around vital industrial, highly populated, and strategic

Corporal SSM may be equipped with either a nuclear or a conventional warhead. It can engage tactical targets at ranges of 75 miles or more. Corporal gives the Army field commander great firepower on the battlefield, and enables him to strike selected targets deep in enemy rear areas. Corporal follows a ballistic trajectory during most of its flight; weather and visibility conditions place no restriction on its use. The propulsion system uses a liquid-fuel rocket motor. The missile travels through space at several times the speed of sound. A Corporal battalion has 250 men. Each battalion has two batteries-a firing battery and a Headquarters Service battery. There are two operational launchers to a battalion. Corporal battalions are now deployed in Europe.

Sergeant SSM is a ballistic guided missile intended to replace Corporal, with improvements in power, range, and accuracy.

Redstone SSM is a supersonic ballistic missile with a range of several hundred miles, designed to extend and supplement the range and fire power of Army artillery.

Jupiter SSM is the Army's intermediate-range ballistic missile. Its range is in the order of 1,500 miles, and it is propelled by a liquid-fuel rocket.

Lacrosse SSM is used in close tactical support of ground troops. It is an all-weather missile, propelled by a solid-fuel rocket motor, and capable of carrying highly effective area-type warheads. It will supplement, and perhaps eventually replace, conventional artillery. The Lacrosse system includes the missile, a launcher mounted on a standard Army truck, and other ground equipment.

Dart SSM is a guided anti-tank missile, propelled by a solid-fuel rocket, and designed for use by front-line troops. It carries a warhead capable of defeating the heaviest known enemy armor, and delivers this warhead with pinpoint accuracy. The Dart can be launched

Nike-Hercules SAM is capable of carrying a nuclear warhead; it is designed for use against either single aircraft or whole formations of aircraft. The missile is 27 ft long, the booster 14-1/2 ft long. Both use solid propellant. The warhead is provided with a safety feature, so that it can detonate only at altitudes sufficiently high to prevent damage to friendly surrounding terrain.

Hawk SAM is designed to supplement the Nike missile system by destroying attacking aircraft at low altitudes. The launching facilities are sufficiently portable to be used by fast-moving combat troops. Hawk is propelled by a solid-fuel rocket. The missile is about 17 ft long, and about 14 in. in diameter.

Nike-Zeus SAM is an anti-missile missile equipped with a nuclear warhead, and designed to defend the United States against attack by enemy intercontinental ballistic missiles.

Talos SAM Defense Unit is a land-based version of the Navy's Talos, Shipboard Missile System.

1D3. Air Force missiles

Matador SSM is a tactical missile driven by a turbojet engine at a speed of 650 mph. It has a length of about 29 ft and a wing span of about 40 ft. It can carry a nuclear warhead, and may be guided by radio command or by a navigational system. Its range is more than 650 miles. Tactical missile groups armed with Matador are now deployed in Europe and on Formosa.

Falcon AAM comes in two versions, one with radar guidance and the other with infrared homing. Falcon is a supersonic missile, propelled by a solid-fuel rocket. It weighs about 100 pounds, and is about 6 ft long.

Genie AAM is a rocket-propelled air defense missile that may be armed with a nuclear warhead.

Snark SSM is actually a pilotless aircraft. It can carry a nuclear warhead at high subsonic speed. Snark has an inertial or other navigational guidance system. In tests it has been accurately placed on a target at a range of 5,000 miles.

Rascal ASM is a rocket-powered missile 32 ft long and 4 ft in diameter. It is designed for launching from B-47 Stratojet bombers at high altitude and high speed, at

Bomarc SAM is a long-range air defense missile that can destroy attacking aircraft at ranges of more than 100 miles, and altitudes above 60,000 ft. The missile is about 47 ft long, has a wing span of about 18ft, and weighs about 15,000 pounds. It is launched vertically by solid-fuel boosters, and sustained in flight by twin ram-jet engines.

Thor SSM is the Air Force's intermediate range ballistic missile (IRBM). It is propelled by a liquid-fuel rocket at a speed of Mach 10; range is over 1,500 miles. Thor is provided with an inertial guidance system.

Atlas SSM is an intercontinental ballistic missile with a range of more than 5,000 miles. It is launched by rocket engines that develop many tons of thrust, and millions of horsepower, within a few seconds. Atlas reaches a top speed of about Mach 15-more than 10,000 miles an hour. It will descend on its target at that speed, from a height of about 800 miles.

Titan SSM is also an intercontinental ballistic missile. In general it is similar to Atlas, except that Titan has a second-stage motor. It is likely that one of these two missiles will be discontinued, and all the effort now going into both developments will be concentrated on only one of them.

Minuteman SSM is a solid-fuel intercontinental ballistic missile that will eventually replace both Atlas and Titan.

1D4. Navy missiles

Sidewinder AAM (fig. 1D1) is probably the simplest and cheapest of all guided missiles. It is about 9 ft long, and weighs about 155 pounds. It has only about 24 moving parts, and no more electronic parts than a table radio. It attains a speed of Mach 2 relative to the launcher, and a range of several miles; it is designed to destroy high-performance aircraft from sea level to altitudes above 50,000 ft. It has an infrared homing system. Sidewinder was named after a desert rattlesnake. (The Sidewinder snake, like all of the pit vipers, has infrared receptors on its head that enable it to detect the presence of prey by its body heat.) Sidewinder is now the primary airborne missile used by squadrons in

Figure 1D1.-Sidewinder missile and pilot with pressure suit.

the Sixth Fleet in the Mediterranean, and the Seventh Fleet in the Western Pacific.

Sparrow I AAM is 12 ft long and weighs 300 pounds; it reaches a speed of Mach 2.5 relative to the launcher, within a few seconds after launching. It is provided with beam-rider guidance, and is propelled by a solid-fuel

Sparrow II AAM was developed as an experimental missile, and not intended to become operational. It has, however, been adopted for operational use by the Royal Canadian Air Force.

Sparrow III AAM is very similar to Sparrow I, but with a much more sophisticated guidance system. It is slightly heavier than Sparrow I, a little faster, and has a longer range. It will first supplement, and then replace Sparrow I in the Fleet.

Petrel ASM is nearly obsolete; although a few of these missiles may still be found in the Fleet, they are no longer in production. Petrel

Bullpup ASM is 11 ft long and weighs about 540 pounds. It is relatively inexpensive, simple in design, and extremely accurate. Bullpup is a tactical missile with a conventional warhead, designed for use by carrier-based aircraft against small targets such as pillboxes, tanks, and truck convoys, in support of ground troops. It is powered by a solid-fuel rocket, and has a range of 15,000 ft at a speed of Mach 2.

Corvus ASM is a supersonic missile, propelled by a solid-fuel rocket, and designed for use by carrier-based aircraft. No further details have been released.

Tartar SAM is similar in function to Terrier; except it is propelled by a dual-thrust rocket, and is launched without a booster. The Tartar system will be installed aboard the guided missile destroyers 2 through 14, and aboard the cruisers Chicago, Albany, and Fall River.

Talos SAM (fig. 1D3) is designed to bring down attacking enemy aircraft and missiles at ranges of 65 miles or more. It is 20 ft long, and weighs 1-1/2 tons. It is launched with solid-fuel boosters, and sustained in flight by a ram-jet; it reaches a speed in excess of Mach 2 within about 10 seconds of launching. It can be armed with a nuclear warhead. During the first part of its flight, Talos is a beam rider. As it approaches its target, it switches over to homing guidance. Talos systems are now installed on the cruisers Galveston, Little Rock, and Oklahoma City. It is scheduled for installation on the cruisers Albany, Fall River, and Chicago, and on the nuclear powered cruiser Long Beach.

Regulus I SSM (fig. 1D4) is intended primarily for use against enemy shore installations, but it can also be used against ships. Regulus I is about 30 ft long, and resembles a conventional swept-wing fighter aircraft. It is powered by a turbojet engine, and flies at the speed of Mach 1 for a range of about 500 miles. It can be armed with a nuclear warhead. Launching equipment for this missile can be installed in a short time on several types of ships, at relatively low cost and with little modification of the ship itself. Among the ships that can now launch Regulus I are the cruisers Macon, Helena, Toledo, and Los Angeles, submarines Tunny and Barbero, and carriers Randolph, Hancock, Forrestal,

Figure 1D3.-Talos missiles on launcher at White Sands Proving Ground.

Saratoga, Lake Champlain, Franklin D. Roosevelt, Lexington, Bennington, Bon Homme Richard, and Shangri-La. Two different versions of Regulus I have been developed. The tactical version is nonrecoverable. The test version is provided with retractable landing gear and parachute braking. It can be launched and recovered repeatedly-a factor that drastically reduces the cost of evaluating and testing the missile system.

Regulus II SSM (fig. 1D5) is 57 ft long, and has a 20-ft wingspan. It is propelled by a turbojet engine with afterburner at a speed of Mach 2. Its range is more than 1,000 miles, and its altitude capability more than 60,000 ft. Like Regulus I it can carry a nuclear warhead, and is made in both a tactical and a recoverable test version. Regulus II may be guided by either a command system or an inertial navigation system. Unlike ballistic missiles, which are capable of only one path of approach to a target, Regulus can be guided to its target

However, due to budgetary limitations the Regulus II program has been cancelled. The

Polaris SSM-USM (fig. 1D6) is the Navy's intermediate-range ballistic missile, with a range of about 1,500 miles. It is designed for launching either from surface ships or from submerged submarines. It is propelled by solid fuel. There are, at present, plans to build nine submarines capable of launching Polaris. Each submarine will carry 10 or more missiles.

A. Introduction
 

A guided missile, by definition, flies above the surface of the earth. Aerodynamic long-range missiles, as well as all missiles of short and medium range, are subject throughout their flight to the forces imposed by the earth's atmosphere. Ballistic missiles, though they follow a trajectory that takes them into space, must climb through the atmosphere after launching, and must descend through it before striking the target. All missiles are subject to gravitational and inertial forces. This chapter will briefly discuss the principal forces that act on a guided missile during its flight. It will show how the missile trajectory may be controlled by designing the missile airframe and control surfaces to utilize or overcome the forces acting on them.

An understanding of missile aerodynamics requires a familiarity with several of the

In general, missile aerodynamics are the same for both subsonic and supersonic flight. The basic requirement is common to all craft intended to fly: in order to fly successfully, the craft must be aerodynamically sound. But the high speeds and high altitudes attained by current guided missiles give rise to new problems not encountered by most conventional aircraft. An example is the shock wave that is produced when a flying object attains the speed of sound. Problems of oxygen supply for air breathing missiles arise at high altitudes, and problems of skin heating by friction with the air arise at high speeds.

Gravity, friction, air resistance, and other factors produce forces that act on all parts of a missile moving through the air. One such force is that which the missile exerts on the air as it moves through it. In opposition to this is the force that the air delivers to the missile. The force of gravity constantly attracts the missile toward the earth, and the missile must exert a corresponding upward force to remain in flight.

Figure 2B1 illustrates the forces acting on a body in level flight through the air, at a uniform speed. Note that the force tending to produce motion (toward the left) exactly balances that resisting the motion. The force of gravity is exactly opposed by the lifting force. In accordance with Newton's first law (discussed below), a moving body on which all forces are balanced will continue to move in the same directions and at the same speed.

Figure 2B1.-Forces acting on a body moving through air.

Figure 2B2 illustrates the effect of unbalanced forces acting on a body. The length of the arrows is proportional to the respective magnitude of the forces, and the arrowheads point in the direction in which these forces are applied. The illustration shows that forces

Figure 2B2.-Unequal forces acting on a body.

A and B are equal and opposite, and that C and D are equal and opposite. But force F is opposite to and greater than force E. As a result, the body shown will accelerate in the direction of force F. This figure is an example of vector representation of the forces acting on a body. Any number of forces may be shown by vector representation. They can be resolved, or simplified, into resultant force that is the net effect of all the forces applied.

2B2. Relativity of motion

To an observer standing on the ground and watching the flight of a missile through the air, it appears that the missile is moving and the air standing still. It would seem that the opposing force exerted by the air is entirely the result of the missile motion through it. But if it were possible for an observer to ride the missile itself, it would appear that the missile is standing still, and that the air is moving past the missile at high speed.

This illustrates the basic concept of relativity of motion. The forces that the air exerts on the missile are the same, regardless of which is considered to be in motion. The force exerted by the air on an object does not depend on the absolute velocity of either but only on the relative velocities between them. This principle can be put to good use in the study of missile aerodynamics, and in the design of missile airframes and control surfaces. In a wind tunnel, the missile or model remains stationary, while air moves past it at high speed. The measured forces are the same as those that would result if the missile, or model, were moving at the same relative speed through a stationary mass of air.

Newton's first law states: "A body in a state of rest remains at rest, and a body in motion remains in uniform motion, unless acted upon by some outside force." This means that if an object is in motion, it will continue in the same direction and at the same speed until some unbalanced force is applied. And, whenever there are unbalanced forces acting on an object, that object must change its state of motion. For example, if you were to push against a book lying on a table, you would have to supply sufficient force to overcome friction in order to set the book in motion. If you would eliminate all of the restraining forces acting on the book once it is in motion, it would continue to move uniformly until acted upon by some outside force. It is these restraining forces with which we are mainly concerned in the study of aerodynamics.

Newton's second law states: "The rate of change in momentum of an object is proportional to the force acting on the object, and in the direction of the force." The momentum of an object may be defined as the force that object would exert to resist any change of its motion.

Newton's third law states: "To every action there is an equal and opposite reaction." This law means that when a force is applied to any object, there must be a reaction opposite to and equal to the applied force. If an object is in motion, and we try to change either the direction or rate of that motion, the object will exert an equal and opposite force. That force is directly proportional to the mass of the object, and to the change in its velocity. This can be stated as:

Force = Mass times Acceleration,

or

F = ma

Thus any object in motion is capable of exerting a force. Whenever a force is applied through a distance, it does work. We can express this as:

Work = Force times Distance

or

W = Fd

2B4. Lift and drag

Figure 2B3 represents a flat surface moving through an airstream. In accordance with the principle of relativity, the forces acting on the surface are the same, regardless of whether we think of the surface as moving to the left, or of the airstream as moving to the right. One of the forces acting on the surface is that produced by friction with the air. This force acts in a direction parallel to the surface, as indicated by the small white arrow at the lower right. As the air strikes the surface, it will be deflected downward. Because the air has mass, this change in its motion will result in a force applied to the surface. This force acts at a right angle to the surface, as indicated by the long black arrow in figure 2B3. The resultant of the frictional and deflection forces, indicating the net effect of the two, is represented by the long white arrow. We can resolve this resultant force into its horizontal and vertical components. The horizontal component, operating in a direction opposite to the motion of the surface, is drag. The vertical force, operating upward, is lift. The angle that the moving surface makes with the air stream is the angle of attack. This angle affects both the frictional and the deflection force, and therefore affects both lift and drag.

Figure 2B4 represents the flow of air over a wing section. Note that the air that passes over the wing must travel a greater distance than air passing under it. Since the two parts of the airstream reach the trailing edge of the wing at the same time, the air that flows over the wing must move faster than the air that flows under. In accordance with Bernoulli's theorem, this results in a lower pressure on the top than on the bottom of the wing. This pressure differential tends to force the wing upward. and gives it lift.

Figure 2B4.-Airflow over a wing section.

A discussion of the problems of aerodynamic forces involves the use of several flight terms that require explanation. The following definitions are intended to be as simple and basic as possible. They are not necessarily the definitions an aeronautical engineer would use.

AIRFOIL. An airfoil is any structure around which air flows in a manner that is useful in controlling flight. The airfoils of a guided missile are its wings or fins, its tail surfaces, and its fuselage.

DRAG is the resistance of an object to the flow of air around it. It is due in part to the boundary layer, and in part to the piling up of air in front of the object. One of the problems of missile design is to reduce drag while maintaining the required lift and stability.

STREAMLINES are lines representing the path of air particles as they flow past an object, as shown in figure 2B4.

WING SPAN is the measured distance from the tip of one wing to the tip of the other.

ATTITUDE. This term refers to the orientation of a missile with respect to a selected reference.

STABILITY. A stable body is one that returns to its initial position after it has been disturbed by some outside force. If outside forces disturb a stable missile from its normal flight attitude, the missile tends to return to its original attitude when the outside forces are removed. If a body, when disturbed from its original position, assumes a new position and neither returns to its origin nor moves any farther from it, the body is said to be neutrally stable. If the attitude of a neutrally

A third type of stability is negative stability, or instability. In this case a body displaced from its original position tends to move even farther away. For example, if an unstable aircraft is put into a climb, it tends to climb more and more steeply until it stalls.

AXIS. A missile in flight can be considered to move about three axes, as shown in figure 2C 1. In normal level flight, the vertical line is the yawing axis; the longitudinal line through the missile center is the rolling axis; and the horizontal line through the center of gravity at right angles to the rolling axis is the pitching axis. Whenever there is a displacement of a missile about any of these three axes, the missile may do any one of the following:

1. It may oscillate about the axis. 2. It may increase its displacement and get out of control. 3. It may return to its original position readily, without oscillation.

The last possibility, which indicates a stable missile, is the one desired. We will show later how this problem of stability is met in missile design.

2C2. Effects of aerodynamic forces

CENTER OF PRESSURE. On every point of a moving airfoil, a small force is present. This force is different in both magnitude and direction from that acting on any other point on the airfoil. It is possible to add mathematically all of these small forces. Their sum is the resultant force. The resultant has

In actual flight, a change in the angle of attack will change the airspeed. But if for test purposes we maintain a constant velocity of the airstream while changing the angle of attack, the results on a nonsymmetrical wing will be as shown in figure 2C2. The sketches show a wing section at various angles of attack, and the effect of these different angles on the resultant force and the position of the center of pressure.

The burble point referred to in the lower sketch is the point at which airflow over the upper surface becomes rough, causing an uneven distribution of pressure. The burble point is generally reached when the angle of attack is increased to about 18° or 20°. At small angles of attack, the resultant is comparatively small. Its direction is upward and back from the vertical, and its center of pressure is well back from the leading edge. Note that the center of pressure changes with the angle

Figure 2C2.-Effect of angle of attack on center of pressure.

Drag is the resistance of air to motion through it. The drag component of the resultant force on a wing is the component parallel to the direction of motion. This force resists the forward motion of the missile. If the missile is to fly, drag must be overcome by thrust-the force tending to push the missile forward. Drag depends on the missile area, the air density, and the square of the velocity. Air resists the motion of all parts of the missile, including the wings, fuselage, tail airfoils, and other surfaces. The resistance to those parts that contribute lift to the missile is called induced drag. The resistance to all parts that do not contribute lift is parasitic drag.

From Newton's laws, we know two things: First, if all the forces applied to a missile are in balance, then if the missile is stationary it will remain so; if it is moving, it will continue to move in the same direction at the same speed until an outside force is applied to it. Second, if an unbalanced force-one not counteracted by an equal and opposite force-is applied to the missile, it will accelerate in the direction of the unbalanced force.

At the instant of launching, missile speed is zero, and there is no drag. (We will, for the moment, disregard air-launched missiles.) The force of thrust developed by the propulsion system will be unbalanced, and as a result the missile will accelerate in the direction of thrust. (A solid-fuel rocket develops full thrust almost instantly. When a long-range liquid-fuel rocket is launched, it may be physically held down until its engines have developed sufficient thrust.) When thrust weight ratio reaches its maximum value,

If the propulsive thrust is decreased for any reason (such as a command from the guidance system, or incipient fuel exhaustion) the force of drag will exceed the thrust. The missile will slow down until the two are again in balance. When the missile fuel is exhausted, or the propulsion system is shut down by the guidance system, there is no more thrust. The force of drag will then be unbalanced, and will cause a negative acceleration, resulting in a decrease in speed. But, as the speed decreases, drag will also decrease. Thus the rate of decrease in speed also decreases.

As we have shown, a missile will maintain a uniform forward motion when thrust and drag are equal. The power required to maintain uniform forward motion is equal to the product of the drag and the speed. If drag is expressed in pounds, and speed in feet per second, the product is power in foot-pounds per second. By definition, one horsepower is 550 foot-pounds per second. The horsepower expended by a missile in uniform forward motion is then

hp = DV/550

where D is the drag in pounds, and V the speed in feet per second.

2C3. Problems of missile control

A missile must be so designed and constructed that it will fly a specified course without continual changes in direction. The degree of stability of a missile has a direct effect on the behavior of its controls, and for this reason a high degree of stability must be maintained. As the speed of a missile increases, its stability is changed by shifts in the center of pressure. A pressure shift causes changes in the airflow acting on the missile surfaces. Even

Figure 2C3 represents a missile in level flight; it is longitudinally stable about its lateral axis through the center of gravity. Airflow over the wing is deflected downward toward the elevator. This angle of deflection is called the downwash angle. When lift decreases as a result of reduced speed, this downwash angle decreases, and produces pressure changes. There will be certain speeds at which unstable conditions are set up as a result of such pressure shifts. When an unstable condition occurs, the control system must quickly compensate by moving the control surfaces or changing the missile speed; otherwise the missile may get out of control.

As we will show in the next section of this chapter, unstable conditions are most serious at transonic speeds. Most missiles have dive control and roll recovery devices to overcome unstable conditions. For example, the horizontal tail surfaces may be placed high on the fin, to minimize the effects of downwash.

Unstable airflow over the wings of a missile may cause the ailerons to oscillate, creating a condition known as "buzz." A similar condition called "snaking" may exist about the yaw axis as a result of rudder oscillation. The troubles may be partially compensated for by nonreversible control systems, or by variable - incidence control surfaces.

STABILITY ABOUT THE VERTICAL AXIS is usually provided for by vertical fins. If a missile begins to yaw to the right, air pressure on the left side of the vertical fins is increased. This increased pressure resists the yaw, and tends to force the tail in the opposite direction. In some missiles the vertical fin may be divided, and have a movable part, called the rudder, that is used for directional control. In addition to the rudder,

Another means for obtaining yaw stability is by sweepback of wings. Sweepback is the angle between the leading edge of a wing and a line at right angles to the longitudinal axis of the missile. If a missile yaws to the right, the leading edge of the left sweptback wing becomes more perpendicular to the relative wind, while the right wing becomes less so. This puts more drag on the left wing, and less on the right. The unbalanced drag at the two sides of the missile tends to force it back to its original attitude.

STABILITY ABOUT THE LONGITUDINAL AXIS may be provided by dihedral--an upward angle of the wings. As the missile starts to roll, the lift force is no longer vertical, but moves toward the side to which the missile is rolling. As a result, the missile begins to sideslip. This increases the angle of attack of the lower wing, and decreases that of the upper. Lift on the lower wing will therefore increase, while lift on the upper wing decreases. This unbalanced lift tends to roll the missile back to its original attitude.

STABILITY ABOUT THE LATERAL AXIS is accomplished by horizontal surfaces at the tail of the missile. The stationary part of these surfaces is the stabilizer; the movable part is the elevator. Pitch stability results from the change in forces on the stabilizer when the missile changes its angle of attack. For example, if the missile nose begins to pitch downward, the force of the airstream against the upper surface of the stabilizer will increase. This will tend to push the tail downward, and thus return the missile to its original attitude.

515354 O-59-3

SHOCK WAVE. As a missile moves through the air, the air tends to be compressed, and to pile up in front of the missile. Because compressed air can flow at speeds up to the speed of sound, it can flow smoothly around a low-speed missile. But as the missile approaches the speed of sound, the air can no longer get out of the way fast enough. The missile surfaces split the airstream, producing shock waves. A shock wave is a sharp boundary between two masses of air at different pressures.

Shock waves can seriously alter the forces acting on a missile, requiring radical changes in trim. The missile tail surfaces may be seriously buffeted and wing drag rises. Any deflection of the control surfaces in an attempt to overcome these conditions may cause new shock waves, which interact with those already present. For this reason there may be certain speeds at which the controls become entirely useless.

MACH NUMBER is the ratio of flight speed to the speed of sound. It was named in honor of Ernst Mach (pronounced mock), an Austrian scientist who first pointed out its importance in 1887. If a missile travels at twice the speed of sound, it has a flight speed of Mach 2.0. If its speed is half that of sound, it has a flight speed of Mach 0.5. The speed of sound varies with both pressure and temperature. It decreases from an average of about 760 mph at sea level to about 675 mph at 30,000 feet.

REYNOLDS NUMBER. During the development of a new missile design, scale models of the proposed missile are tested in wind tunnels. But the performance of the model does not necessarily indicate the performance of the actual missile, even when all known variables are scaled down. In some cases the effect of a given variable on the model may be opposite to its effect on the full-size missile. Reynolds number is a mathematical ratio involving relative wind speeds, air viscosity and density, relative sizes of the model and missile, and other factors. The use of this ratio makes it possible to predict missile behavior under actual flight conditions from the behavior of the model in the wind tunnel.

SPEED CLASSIFICATIONS. Missile speeds may be divided into four categories: subsonic, transonic, supersonic, and hypersonic. A missile is moving at subsonic speed when the relative velocity of air at all points on its surface is less than the speed of sound. In the transonic range of speeds, air moves over some parts of the missile at less than the speed of sound, and over other parts at more than the speed of sound. Under these conditions, shock waves are present; the airflow is turbulent, and the missile may be severely buffeted. A high-speed missile should be made to accelerate through the transonic zone in the least possible time, to prevent these disturbances. A missile is moving at supersonic speed when the relative speed of the air at all points of its surface is greater than the speed of sound. In supersonic flow, little turbulence is present.

When any object moves through the air, the molecules of air require a finite time to adjust themselves to its presence, and to readjust themselves after it has passed. This period of adjustment and readjustment is called the relaxation time. If the time required for a

MACH ANGLE. This term is illustrated by analogy in figure 2D1, which represents a boat in four different conditions of motion over the surface of a lake. Assume that any wave

In the sketch at the upper left of figure 2D1, the boat is at rest. If the wind makes the boat bob up and down, the boat will generate a series of ripples that spread out in concentric circles at the rate of 10 mph. In the upper right sketch, the boat is moving at 5 mph (representing a speed of Mach 0.5). After the boat generates a ripple, it will move with respect to that

A the lower left, figure 2D1, the boat is traveling at the speed of wave propagation, representing a speed of Mach 1.0. Because the boat is moving at the same rate the waves spread out, all the waves are tangent to each other at the bow of the boat. At the lower right, the boat is moving at Mach 2.0-twice the wave speed-and it leaves the ripples behind. The wave pattern now becomes a wedge on the surface of the water. In the air, with three dimensional flow, the pattern would be a cone. The semi-vertex angle is the MACH ANGLE. The greater the speed above Mach 1, the smaller the angle. The bow wave of the boat is closely analogous to the conical shock wave

NORMAL SHOCK WAVE. This term refers to a shock wave at a right angle to the direction of motion, that appears on any surface over which air is moving at the speed of sound. Figure 2D2 represents the flow of air over a section of a missile wing at four different speeds. In the upper sketch the missile is moving at subsonic speed. Air flows past every point on the wing at less than the speed of sound. The second wing section from the top is that of a missile in the transonic zone. The missile itself is moving at less than the speed of sound. But the air, in order to travel over the curved surface of the wing, must

The third wing section from the top (fig. 2D2) is moving at exactly the speed of sound. The normal shock wave now forms at the leading edge of the wing. Airflow over the whole wing surface is turbulent; lift and control are decreased, or lost altogether.

OBLIQUE SHOCK WAVE. The lowest of the four wing sections shown in figure 2D2 is moving at supersonic speed. The shock wave still forms at the leading edge of the wing; but now, because the missile is moving faster than the air can flow, the Mach angle is less than 90°, and an oblique shock wave spreads out from the leading edge of the wing. As we have said, a shock wave is a sharp boundary between two masses of air at different pressure. Air behind the oblique shock wave has a lower relative speed than that in front, and therefore has a higher pressure.

2D2. Control of supersonic missiles

Aerodynamic control is the connecting link between the guidance system and the missile flight path. Effective control of the flight path requires smooth and exact operation of the missile control surfaces. The control surfaces must have the best possible design configuration for the intended speed of the missile. They must be moved with enough force to produce the necessary change of direction. Methods must be found for balancing the various controls, and for changing them to meet the variations of lift and drag at different Mach speeds.

EXTERNAL CONTROL SURFACES. The simplest control surfaces are fixed fins. Fixed fins abaft the center of gravity provide "weathercock stability," in the same way that the feathers on an arrow give it a stable flight. Fixed fins are used on most current missiles. They are usually called vertical stabilizers or horizontal stabilizers, depending on their position and function.

All guided missiles are also provided with movable control surfaces, since stationary fins cannot provide the precise control needed to keep the missile on a desired course. Movable control surfaces can be divided into two

The two ailerons move differentially. The three lower diagrams in figure 2D3 show how they control the roll of the missile about its longitudinal axis. With both ailerons in neutral position, both wings have the same lift. But when an aileron moves up, it decreases lift; when it moves down, lift increases. Thus, the wing with the raised aileron will move down and the other will move up, as shown in the diagram.

Figure 2D3 also shows the effect of the elevators and rudder. The elevators are the movable parts of the horizontal stabilizers; they control the movement of the missile about its axis of pitch. Both elevator surfaces move together. If they move down, they will deflect air downward from the tail. The tail will react by moving upward, and the nose of the missile will pitch downward.

The rudder consists of one or two movable surfaces on the trailing edge of the vertical stabilizer. If the rudder is in two parts, both move together. The rudder controls the movement of the missile about its axis of yaw. For example if the rudder moves to the right, the tail moves to the left, and the missile yaws to the right.

Secondary control surfaces include tabs, spoilers, and slots. A tab is a small independently movable surface on the trailing edge of a larger control surface. Tabs control the missile indirectly. For example, consider a tab on an elevator. If the tab moves upward, the deflected air will exert a downward force on the elevator. The elevator will then move down. Note that it is still the elevator, not the tab, that directly controls the missile.

A spoiler can be any of several devices-for example a hinged flap on the upper surface of the wing. Suppose that a gust of air causes the left wing to lose lift. The spoiler on the right wing can be raised to "spoil" the smooth flow of air over it, and thus decrease its lift to equal that of the other wing.

A slot is basically a high-lift device located at the leading edge of the wing. At a normal angle of attack, it has no effect. At high angles of attack the slot can be opened to allow air to spill through and thus prevent a stall.

CONTROL AT STARTING SPEEDS. Surface-launched missiles start out with zero

EXHAUST VANES are surfaces mounted directly in the exhaust path of a jet or rocket engine. When the exhaust vanes are moved, they deflect the direction of exhaust, and thus

JET CONTROL is similar to exhaust vane control in that both deflect the exhaust to produce a lateral component of thrust. One method of jet control consists in mounting the engine itself in gimbals, and turning the whole engine to deflect the exhaust stream. This system requires that the engine be fed by flexible fuel lines; and the control system that turns the engine must be very powerful. Another method of jet control consists in mounting several auxiliary jets at various points on the missile surface. By turning on one or more of the auxiliary jets, it is possible for the guidance and control systems to change the missile course as required. The use of auxiliary jets makes it possible to eliminate the outside control surfaces entirely. This is the steering method most likely to be used for control of missiles after they leave the atmosphere (and, eventually, for the control of space ships).

2D3. Effects of missile configuration

The configuration of a guided missile is the principal factor controlling the drag and lift forces that act on it. And these two forces largely determine the overall efficiency of the missile.

DRAG REDUCTION. It is essential that supersonic missiles be designed for minimum drag. A low drag configuration makes it possible to use a smaller power plant, with a lower rate of fuel consumption. The resulting saving in bulk and weight can be used to extend the range of the missile, add to its war head payload, reduce its over-all size, or any combination of these three.

Figure 2D4.-High speed configuration characteristics.

The conditions of flight associated with subsonic airflow are well known. Airflow phenomena at supersonic speeds are orderly, and can be analyzed mathematically. But in the transonic speed range, major design problems arise. A great deal remains to be learned about airflow in this range.

Airflow over an ideal wing would be subsonic until the missile reaches a velocity of Mach 1, and it would then immediately become supersonic. In other words, an ideal wing, if it were possible to make one, would eliminate the transonic range. Actually, the transonic range begins when the flow over any part of the missile becomes supersonic, and continues until the flow over all parts of the missile becomes supersonic. The free-stream Mach number at which transonic flow begins on any given missile is called the critical Mach number for that missile.

Every missile is designed for a cruising speed either below the transonic region or above it; no missile is intended to cruise within this region. For supersonic missiles,

Figure 2D5 represents three common airfoil plan forms for guided missiles. The optimum arrangement of airfoils on a missile is governed by many factors, such as speed, rate of acceleration during the launching phase, range, and whether or not the missile is to be recovered. The sketches in figure 2D6 show some of the more common arrangements of missile airfoils. In s