The Physics of War (26 page)

Diagram of wing showing angle of attack.

DETAILS OF DRAG

Drag is a mechanical force, and to be generated, the body must be in contact with the air. This is, of course, true in the case of the wing passing through air. Simply, it is friction between the air and the wing, and it is generated because of the difference in velocity between the wing and the air. Furthermore, it acts in a direction exactly opposite to the motion of the airplane. And finally, it is classified as an aerodynamic friction.
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Three types of drag friction exist: skin friction, form friction, and induced friction. Skin friction is the friction between the moving molecules of air and the molecules of the solid surface of the wing, so it depends on the interaction between these molecules. This means that a very smooth surface will have less skin friction than a rough one. It also depends on the viscosity of the air, where viscosity is a measure of the internal resistance of a fluid to deformation. For example, molasses has greater viscosity than water. When air is in contact with a moving surface, the air will try to follow the surface. In other words, it has a sort of “stickiness”; as a result, the relative velocity between the wing and the air at the surface of the wing is zero. As you move away from the wing, however, it gradually increases.

Form friction is an aerodynamic resistance to the motion of an object through air that depends on the shape of the object. The more streamlined the shape, the less the form friction. A teardrop shape has one of the lowest form frictions. This type of friction is particularly important in the case of cars; we stream them to decrease this type of drag as much as possible, which increases their fuel efficiency.

Induced friction occurs near the tip of wings that are curved or distorted. The “effective curving” causes a pressure difference between the top and the bottom of the region near the tip of the wing. It's called induced friction because it is induced by the action of vortices near the tip of the wings. Its magnitude depends on the shape of the wings and the amount of lift they produce. Longer, thinner wings produce less induced drag.

STEERING AND MANEUVERING THE AIRPLANE

As we saw earlier, after considerable experimentation the Wright brothers finally developed an effective three-axis control that allowed them to control and properly maneuver their airplanes. Wing warping was used for roll, or lateral motion, and a forward elevator on the wings was used to control up-and-down
motion, or pitch, while a rear rudder was used to control side-to-side motion, or yaw. Within a few years, however, Glenn Curtiss of New York developed what are now called
ailerons
to replace the wing warping of the Wright brothers. Ailerons are small control surfaces that are attached to the trailing edge of the wing.

So how do we maintain control over an aircraft? As it turns out, takeoff, landing, and cruising each have to be stabilized and maneuvered differently. Wings are generally designed for an appropriate amount of lift, along with a minimum of drag, during cruising. But it's fairly obvious that things have to be quite different during takeoff and landing. The plane's speed is much less at this time, and the plane must be adjusted accordingly. And this is where flaps and slats come in. Without them the pilot would not be able to take off or land.

Flaps are hinged surfaces on the trailing edge of the wings that are used to reduce the speed of the airplane so that it can safely take off and land. They decrease the distance needed for both landing and takeoff. When they are extended downward from the trailing edge of the wing they effectively alter the shape of the wing so that it creates more lift on takeoff and more drag on landing.

Slats perform a similar function, but they are mounted on the front edge of the wing. Again, they are used to temporarily alter the shape of the wing to increase lift. In effect, they temporarily change the angle of attack of the wings. Using them, a pilot can fly at slower speeds during takeoff and can land in shorter distances.

The slats and flaps of an airplane.

The tail, showing elevator and rudder, and the wing showing aileron.

The tail of an airplane has two small wings that are referred to as the horizontal and vertical stabilizers. They are flaps that are used to control the direction of the airplane. The flaps on the horizontal tail wing are called elevators, and they are used to move the plane in the up-and-down direction. They change the horizontal stabilizer's effective angle of attack, which creates a lift on the rear of the airplane, which moves the nose downward. The vertical tail wing performs the same function as a rudder on a boat. It moves the plane to the left and to the right.

Getting back to the main wings, we have the ailerons, which are located near the tail end of each wing. Again, they are flaps that allow the plane to bank, or lean, to the right or left. There is one on each wing, and they work in opposition to one another; in other words, when one is up the other is down. As a result, more lift is generated on one wing, which creates a rolling or banking motion.

An important question at this point is, how exactly does a plane roll? This also applies to other motions of the plane, and it brings us to the center of gravity of the airplane. As we saw earlier, this is the point within the plane where its entire weight can be considered to be concentrated. If you suspended the plane from this point
it would remain in equilibrium in any position. With this in mind, imagine a line from the plane's nose that runs through the center of gravity and out to the tail. This is called the roll axis, and when a plane rolls, or banks, it moves around this axis.

Now imagine another line starting at the top of the airplane that goes through the center of gravity and out through its belly. This is called the yaw axis. It is important when a pilot moves the plane's rudder. It creates a side force that rotates the tail in one direction and the nose in the other. This motion is around the yaw axis. Finally, imagine a line that is roughly parallel to the wings and passes through the center of gravity. It is called the pitch axis. When the elevators of the airplane are changed (creating pitch) the plane moves around the pitch axis.

An illustration of the pitch, yaw, and roll axes.

FIRST USE OF AIRPLANES IN WAR

The most important aspect of airplanes, as far as this book is concerned, is their use in war. Technology developed quickly after the early flights of the Wright brothers. In 1909 the French pilot Louis Bleriot made the first flight across
the English Channel. And by 1911 Glenn Curtiss of New York had built the Curtis model D; it was the first airplane in the world that was built and sold in large numbers. It was different from the Wright brothers' airplane in one major way: Curtiss used ailerons on his wings instead of wing warping. Like the Wright brothers' model, however, it was a pusher with the wing behind the pilot. Because of this, it is frequently referred to as the Curtiss pusher. Using his model D, Curtiss became the first pilot to take off from and land on a ship. In 1913, Roland Garros of France was the first to fly over the Mediterranean; he flew from the south of France to Tunisia. In 1915, Garros was the first to mount a machine gun on an airplane. Within two weeks he downed four German observation planes with it.

The first official use of an airplane in war, however, came in 1911 when the Italians, who were at war with the Turks, used one to drop grenades on the enemy below. By the time World War I broke out in 1914, however, there were only a few planes on either side, and those available were relatively slow. The earliest British model, for example, had a top speed of seventy-two miles per hour, and it was powered by a ninety-horsepower engine. But technology developed rapidly, and by the end of the war the British SES, a fighter, had a top speed of 138 miles per hour and was powered by a two-hundred-horsepower engine.
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At the beginning of the war all airplanes were of the pusher design with the propeller behind the pilot, and most were used for observation and reconnaissance. It didn't take long, however, to discover that a propeller in the front, pulling the airplane, was more effective, and by the end of the war nearly all airplanes were pullers, or of the “tractor” design. All early planes also had rotary engines with the pistons mounted in a circle around the crankshaft. In effect, the pistons rotated, carrying a propeller with them. It was soon discovered, however, that the in-line, water-cooled engine was much more powerful. And by the end of the war, almost all airplanes had in-line engines.
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Although planes were used only for observation at the beginning of the war, generals on both sides soon realized that they could be used much more effectively, and they soon were used for tactical and strategic bombing, and for naval warfare. And, of course, the fighter plane was soon developed, and it played a critical role in the war.

In the
last chapter
we saw how airplanes were developed, and how physics is important in relation to them. In this chapter we will see how the airplane was used in war, and also in other ways. We now refer to the war that took place between 1914 and 1918 as World War I, but before 1939 it was known as the Great War, and it was, indeed, the largest, most all-encompassing war the world had ever seen. For years there had been a huge buildup of weapons in Europe, and with the new breakthroughs in science, many of the weapons had never been used in a large engagement before. Horrific scenes resulted, such as hundreds of soldiers being mowed down by machine guns within minutes, whole units wiped out by strange, new deadly gases, and ships sunk with new and powerful torpedoes. Perhaps the most ironic part of the war was its futility. Because of the new weapons—particularly the machine gun—the war soon became a stalemate, with neither side able to move. The opposing armies sat facing one another along hundreds of miles of trenches, with the trenches only a few hundred yards apart.

There's no doubt that many of the advances in weaponry were a result of breakthroughs in physics, but it was really the application of applied physics to weapons that led to the huge stalemate. Some of the weapons in which physics played a role were the machine gun, large cannons that now had become deadly accurate, airplanes, new types of rifles, hand grenades, flamethrowers, torpedoes, submarines, tanks, and new types of ships. And with these new weapons, over the four years of the war, millions of soldiers lost their lives without anything really being solved.

DEVELOPMENT OF THE MACHINE GUN

The machine gun played such a central role in the war that World War I is now sometimes referred to as the machine-gun war. The Gatling gun had been
invented much earlier, but it was a toy compared to the 1870 invention of the British engineer Hiram Maxim. He devised a system that used the explosive gases set off by one bullet to propel the next one. The gun therefore ejected each spent cartridge and inserted a new one. Ammunition was fed into the firing chamber using a belt-fed system. A water-filled steel jacket surrounded the barrel; it kept the temperature cool enough so the barrel would not crack or melt as a result of the intense heat generated by the explosive gases.
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The major problem with the Maxim gun was that it was relatively heavy and difficult to use. In particular, it needed several men to operate it, and it wasn't highly reliable. Because of this, it had seen limited use before the beginning of World War I. In 1896, however, the Maxim was improved quite significantly. The Vickers Company in England purchased the Maxim Company, and Vickers redesigned and improved the gun. First, Vickers decreased the gun's weight by using lighter metals in its construction, and then he simplified the action. Basically it was now a water-cooled gun that used .303 British shells, the same shells that were used in the standard British rifle, the Lee-Enfield.

Although it took six men to operate it—one to fire it, one to feed ammunition, and four to move it around and set it up—it was quite reliable once it was set up, and as a result it became a favorite weapon among British troops. It was three feet, eight inches long with a firing rate of 450 to 600 rounds per minute, and it had maximum range of about 4,500 yards. It could be fired for twelve hours without overheating or breaking down, and about ten thousand rounds could be fired each hour. At the end of this time, however, the barrel had to be changed. It was particularly effective against troops in the open, and it was one of the major reasons for the stalemate in the war. Later in the war (after 1916) it was used in airplanes, both by the British and the French.
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Another machine gun referred to as the Lewis gun was also used extensively. It was an American-designed gun that was much lighter than the Vickers. It was widely used by the British. Strangely, although it was designed by a US colonel named Isaac Lewis in 1911, it was not used extensively by American troops in the war. Lewis, in fact, became disillusioned with the US Army in 1913 because its leaders refused to adopt his gun, and he left the United States, went briefly to Belgium, and then went to the United Kingdom, where he worked with British manufacturers to build the gun. At twenty-eight pounds, it was only about half the weight of the Vickers, and its length was barely over four feet, so it could easily be carried by a single soldier. It used the British .303 bullet (although some models use the .30-06), and its rate of fire was about six hundred rounds per minute, with an effective range of about 880 yards and a maximum range of 3,500 yards.

The French 75 millimeter field gun also played an important role in several battles, particularly near the beginning of the war. It had a recoil mechanism that allowed the barrel to slide back and forth after it was fired before returning to its original firing position. Because it did this without moving the gun, no reaiming was required. It was tremendously accurate and could fire fifteen shots per minute. For anyone in the open it meant certain death, and in the Battle of Marne over two thousand German soldiers were mowed down in four minutes.

OTHER WEAPONS

It may sound like the machine gun was the only weapon used in World War I. This wasn't the case, and some of the other guns were almost as lethal as the machine gun. Rifles had improved significantly, along with cannons and other artillery, and hand grenades began to play a large role. Flamethrowers were also used. And, as mentioned earlier, it was the large array of new and powerful weapons that led to the stalemate. Furthermore, most of them were a result of breakthroughs in science—particularly physics.
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The muskets of the Civil War were replaced on the British side by the bolt-action Lee-Enfield rifle. The name comes from its inventor, James Perris Lee, and the factory in Enfield, England, where it was first produced. Cartridges were placed in a metal box called the magazine, with a spring at the bottom. When the bolt was open, the spring pushed the cartridge upward into position. As the bolt was closed, the top cartridge was pushed into the chamber, ready to fire. After firing, the bolt was opened, causing the empty cartridge to eject, and a new cartridge was loaded. The magazine held ten shells and was loaded with .303 British ammunition.

The bolt-action was fast and easy to use, and with its relatively large detachable magazine, it was an excellent rifle. A well-trained rifleman could easily fire twenty to thirty rounds a minute with it. It was accurate up to two thousand feet, and it had a range of about 4,500 feet. The Germans used the Mauser Gewehr, which was also a bolt-action gun that was well known for its accuracy. And they also used the Mauser T as an antitank gun toward the end of the war. In addition, pistols such as the British Webley, the German Lugar, and the American Colt .45 were used extensively during the war. They were usually carried by officers.

Cannons and large artillery had also been improved significantly. Howitzers, which are cannons that fire shells in a high, curving trajectory, were used quite effectively against fortifications and hidden targets. They fired heavy shells through relatively short barrels, and were used by the Germans early in the war in Belgium.
The huge howitzer known as “Big Bertha” pounded fortresses in Belgium during the German advance through the country. The biggest problem with the large guns was their weight, but this was finally overcome by using railroads. Many were, in fact, mounted on railroad cars, which also helped to overcome their recoil. Such guns could fire huge shells to distances of up to thirty miles.

The mortar was also used during World War I. Like the howitzer, it was a high-trajectory gun, but much smaller. The projectile could easily be dropped into its broad, stubby barrel and fired quickly. It could fire shells as far as twenty-two hundred yards. And antiaircraft guns were also developed soon after airplanes started to play a large role in the war. They could fire four rounds per minute to a distance of three thousand yards.

Crude hand grenades had been around for years. The early Chinese used them, and they were also used by the French in the fifteenth century. Considerable effort went into perfecting them during World War I. The Germans were well prepared with hand grenades at the beginning of the war, but other countries quickly caught up. Trench warfare, in particular, made them very effective. “Bombing parties” from both sides would attack the enemy trenches using hand grenades of various types, and these missions increased in frequency as the war progressed. The British had very few hand grenades at the beginning of the war, but within a year they were producing half a million a week.

Grenades could be detonated in either of two ways: on impact (percussion) or using a timed fuse. The fuse-type grenade was generally preferred because of the danger of setting off the percussion-type grenade accidentally. In the timed grenades a pin that could be extracted by hand became common in the later stages of the war. And they came in all shapes and sizes. The stick grenade had a handle, one of the others was cylindrical, but later on most were oval shaped. Grenades could be either thrown or launched with a rifle. Rifle grenades were attached to a rod that was placed down the barrel of a gun or placed in a cup that was attached to the barrel. A blank cartridge was used to launch them. Cup grenades were particularly popular with the British and French; although they were not very accurate, they could be thrown a couple hundred yards by the blast.

The Mills grenade was introduced by the British in May 1915 and quickly became very popular. It had a serrated exterior so that when it detonated it broke into many fragments, and it was fairly light at 1.25 pounds. A safety pin held down a strike lever. After the pin was removed, the strike lever was held down by hand until the grenade was thrown. It had a four second fuse.

The Germans also had an array of different grenades: stick, ball, disk, and egg shaped. They preferred the egg-shaped grenade because it could relatively easily be thrown up to fifty yards.

Perhaps the greatest terror of the war, at least for the soldiers it was used against, was the flamethrower. Although crude flamethrowers had been used in earlier wars, this was the first war in which an efficient, well-designed flamethrower was used. It was used by the Germans against the British and French soldiers in the early phases of the war in 1914. The Germans had begun experimenting with flamethrowers as early as 1900. They used pressurized air, carbon dioxide, or nitrogen to push oil through a nozzle. As the mixture hit the air it was ignited by a small trigger and became a jet of flame. Early flamethrowers had a range of about eighty feet, but this was later increased to about 130 feet. This made them quite effective in trench warfare.

The Germans had two models, a relatively small portable one that could be carried by a single man, and a larger, much heavier one, that had an effective range double that of the small one. It required several people to transport it. The first use of the smaller variety came at The Hague in Flanders, Belgium. It occurred on July 30, 1915, when Germans with gas cylinders strapped to their backs attacked a British line. The huge flames terrified the unsuspecting British at first, but, after losing some ground, they managed to hold their position. The Germans were pleased with its success and started using it in most of their successive battles. The men armed with flamethrowers soon became marked men, however; British and French soldiers concentrated their fire on the operators, and few lived very long.

The British soon began experimenting with their own flamethrowers. They constructed several models, ranging from a relatively light portable model up to very heavy ones. The larger ones had a range of about ninety yards. The French also developed several models. They were quite effective in the Battle of the Somme in France.

Other weapons that were used extensively included poisonous gas and tanks. They will be discussed in a later section.

HOW THE WAR STARTED

The spark that ignited the war was the assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, at Sarajevo on June 28, 1914. It led to a sequence of almost mindless events that occurred very quickly, mostly because all the nations involved had treaties and alliances with other nations. Even though Franz Ferdinand was quite unpopular, the Austro-Hungarians immediately accused the Serbians of a conspiracy (Ferdinand was actually killed by a young terrorist from a group called the Black Hand) and issued
several ultimatums to them. The Serbs rejected some of the ultimatums, and, as a result, the Austro-Hungarians mobilized their army on July 28, 1914. But Russia, bound by a treaty to Serbia, quickly came to the rescue. In the same way, Germany had a treaty with Austria-Hungry, and, as a result, Germany was likewise drawn into the war on August 1. Then came France, which had a treaty with Russia; it declared war on August 3. As a result of Germany's invasion of Belgium, Great Britain was pulled into the war when the King of Belgium appealed to Britain for help.
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