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FlightTable of Contents
Teaching Tip: Principles of Flight Have you ever wondered about the "science" behind flight? The basic principles of flight, which include many elementary physics concepts, can be easily observed in the structure of an airplane. There are four main forces involved in flight. Lift is caused by the variation in air pressure when air flows under and over an airplane's wings. It is opposed by weight, or the force of gravity, pulling downward. Thrust is caused by the action of the propellers moving the plane forward. Opposed to that is drag, caused by air resistance. If lift is more than weight, the plane will rise. If thrust is more than drag, the plane will slowly accelerate. Airplane wings are designed to take advantage of lift. They are shaped so that air has to travel farther over the top of the wing than underneath it. The reason for this is explained in Bernoulli's Principle, which states that an increase in the velocity (speed) of air or any fluid results in a decrease in pressure. When the air has to travel farther over the top of the airplane wing, it must also travel faster, which results in lower pressure. The shorter distance under the wings results in higher pressure, causing the airplane to move upward. You can demonstrate Bernoulli's Principle with a piece of notebook paper. Fold the paper in half the short way, so that you have a tent shape. Now, set the tent on a table and blow very carefully (slow and firm) through one of the open ends. The sides of the tent will stick together but the tent won't collapse. This occurs because the velocity of your breath is more than that of the air outside of the tent, causing lower pressure. The air outside the tent has higher pressure and pushes the sides of the tent inward. Other major considerations in airplane design are the three axes of motion: pitch, roll, and yaw. Pitch is the up or down movement of an airplane's nose. Airplanes are built with horizontal stabilizers in the rear to control the pitch. These stabilizers have hinged sections called elevators. The pilot can change the position of the elevator to raise or lower the nose of the airplane. Roll, the second axis of motion, is the rolling of an airplane from side to side, which causes the wings to go up or down. The hinged sections at the rear of each wing, called ailerons, help control the roll. The ailerons work in opposition: if one goes up, the other goes down. The third axis of motion, yaw, is the motion of an airplane's nose from side to side. The vertical stabilizer and the rudder in the tail are used to control the yaw. Teaching Tip: Rocketry A rocket can be defined simply as "a chamber enclosing gas under pressure." A small opening allows the air to escape, causing thrust. Before learning about more advanced rockets, you can demonstrate this definition with a balloon. Thread a drinking straw onto a piece of string and tie the string to two solid objects that are far apart. (Two door knobs will work.) Blow up a balloon, but don't tie it off. The balloon is now a chamber enclosing pressurized gas that wants to escape. Continue to hold the balloon closed while you attach it to the straw with masking tape. Once it is fixed in place, you can launch your "rocket" by letting go of the end. The air is now free to escape, and as it does so it creates the thrust to drive the balloon forward. Though primitive rockets made of bamboo sticks stuffed with gunpowder were in use by the Chinese around AD 1200, the foundation for the modern science of rocketry was laid by Sir Isaac Newton near the end of the 17th century. Newton's three Laws of Motion are essential to rocket flight. The three laws are as follows:
Since the thrust of a rocket depends on how the gas escapes, one of the most important parts of a rocket is the nozzle. The nozzle is the opening that lets the gasses out. It increases the acceleration of the gas by cutting down on the opening through which it escapes. Use the spray nozzle on your garden hose to see how it works. When you twist the nozzle so that the opening is bigger, the water doesn't spray as far. The smaller the opening is, the farther and harder the water sprays out. It works the same way on a rocket: the smaller the opening, the more thrust caused by the escaping gas. Because the gases are very hot as they leave the rocket, another important part of the design is insulation to protect the nozzle and the body of the rocket, or "case." Rockets are propelled by a mixture of fuel and oxygen (called the "oxidizer"). In solid fuel rockets, the fuel and the oxidizer are combined in a chemical form which is fired by an igniter. In liquid fuel rockets, the fuel (kerosene or liquid hydrogen) and the oxidizer (liquid oxygen) are kept separately and mixed when the engine fires. Because of the differences in propellant, there are also differences in structure between solid and liquid fuel rockets. In addition to the nozzle, case, insulation, and propellant, a liquid fuel rocket must have separate storage tanks for the fuel and the oxidizer, pumps to get them out of the tanks, and a combustion chamber where they can be mixed. Noteworthy Scientist: Wernher Von Braun (1912-1977) Perhaps you've heard of rocket scientist Wernher Von Braun in a science magazine, a history of rocketry, or even in the movie October Sky. Von Braun lived a life filled with adventure--working for the German military during the second world war, escaping to America, and working on the rockets that launched the Apollo series. He was also a committed Christian, who publicly stated his belief in a Creator. Wernher Von Braun was born in Wirsitz, Germany, in 1912, the son of a baron and baroness. He was interested in science throughout his childhood, and in his early teenage years he discovered what was to be a life-long fascination: rocketry and space travel. In 1932, at the age of twenty, Von Braun received his bachelor's degree and then in 1934 he received a PhD in physics from the University of Berlin. During the 1930s, Von Braun worked for the German military, building and testing rockets. He led the team that worked on the V-2 combat rocket for Adolph Hitler. Toward the end of the war, he was arrested for the "crime" of saying that rockets could be built that would orbit the earth and land on the moon. He was released so that he could finish the V-2, but Von Braun had different plans: he decided to surrender to the Americans. He used forged papers to steal a train and lead about 500 people, including the other engineers who were involved in the V-2 project, across Germany to find the American troops--evading their own soldiers on the way. In June of 1945, the U.S. Secretary of State gave his approval for Von Braun and the other scientists (more than 100) who had escaped with him to come to America. They carried on their work at a military station in Texas--"prisoners of peace" who couldn't leave without an escort. After that time, Von Braun sent a marriage proposal to his cousin, Maria von Quistorp. They were married in 1947 and their first child was born the following year. In 1955, Von Braun became a naturalized U.S. citizen. During the 1950s Von Braun worked with Walt Disney to try to increase interest in space programs; he directed the Development Operations Division of the Army Ballistic Missile Agency; and he worked on the Jupiter-C rocket which launched the Explorer 1 satellite in 1958. Soon after NASA was started in 1959, Von Braun and his team were transferred to one of its divisions, the Marshall Space Flight Center. While he was there he helped develop the Saturn rockets, one of which launched the crew of Apollo 11 to the Moon in 1969. Von Braun retired from NASA in 1972, although he continued to promote space flight. He died of cancer in 1977. Science in the News: Breaking the Sound Barrier Before 1947, many scientists and engineers thought that an airplane could not go faster than the speed of sound without disintegrating. Since the speed of sound varies with the atmospheric conditions and temperature, scientists use "Mach" numbers to describe it, with Mach 1 being the speed of sound. As a plane neared Mach 1 it would begin shaking violently and the controls would lose their effectiveness, placing plane and pilot in great danger. Scientists named this impasse the "sound barrier," though pilots liked to refer to it as "the brick wall in the sky." No one knew if they could punch a hole through that brick wall, but they were determined to try. As an airplane moves through the sky it creates disturbances in the air that move out in all directions at the speed of sound. These are called sound waves. When the aircraft begins to approach the speed of sound, it "catches up" with these sound waves and compresses them together in front of the plane. The compressed sound waves are called shock waves and are what make the plane buffet wildly. On October 14, 1947, Chuck Yeager, who was then a captain in the Air Force, climbed into his tiny Bell X-1 airplane (named "Glamorous Glennis" after his wife) and took off on a historic flight. The X-1 was carried up to 20,000 feet by a B29 "mother ship." The B29 turned into a shallow dive to achieve the speed of 250 mph, and then dropped the X-1 like a bomb. Yeager lit the four rocket chambers and the X-1 streaked up into the sky. As the plane approached the speed of sound it began to shake violently from the shock waves. At .97 Mach, or 97% of the speed of sound, the machmeter in the X-1 went off the scale, and the plane accelerated to 1.07 Mach. When the plane broke through the "sound barrier" and flew faster than Mach 1 (approximately 650 mph at 42,000 feet), the shock waves that were built up in front of it moved out and down from the plane, causing the buffeting to smooth out. As the shock waves reached the ground the sudden change in pressure created a loud bang, called a "sonic boom." When Yeager ran out of fuel he shut off the rocket chambers and glided back down for a landing--the fastest man on earth. Due to national security worries with the Soviet Union, the news of Yeager's feat was not released to the public until the following year. The breaking of the sound barrier provided the knowledge of high speed aeronautics needed to develop the space program that would eventually send Americans to the moon. Fabulous Facts How much fuel? In order to launch a rocket through earth's atmosphere, the mass of the different parts must be very carefully distributed. The ideal rocket mass is 91% propellant, 3% tanks, engines, fins, etc., and 6% "payload." The payload includes astronauts, satellites, or spacecraft. What does this mean? Rockets need a lot of fuel! Stepping up? In the 16th century the primitive rockets of the time were used more for fireworks than for warfare. A German fireworks maker, Johann Schmidlap, invented a "step rocket" to take his fireworks to higher altitudes. He sent up a small rocket on top of a big one, and when the big rocket burned out the smaller one continued to take the fireworks higher before they exploded. Schmidlap's idea of rocket stages is now used on all rockets fired into outer space. The Scientific Speaker Aeronautics: This word comes from the Greek word for "air" and the Greek word for "to sail." It is the study of flight and the operation of an aircraft. Science Links For an entire curriculum on rocketry and aerodynamics, go to http://www.grc.nasa.gov/WWW/K-12/airplane/shortr.html (rocketry) and http://www.grc.nasa.gov/WWW/K-12/airplane/short.html (aerodynamics). These sites from NASA are not only packed with information, they also have interactive features to help explain the concept of the sound barrier, the three axes of motion, and more. To see an amazing picture of a plane breaking the sound barrier, go to http://www.gmi.edu/~drussell/Demos/doppler/mach1.html! NOTE: Home Science Tools does not necessarily agree with or endorse all opinions and information expressed on the sites listed in this newsletter. Please use at your discretion. |
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