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Air ships get their lift from the pressure difference due to buoyancy. The net upward force exceeds the weight of the ship and its cargo. The simplest air ship is a hot air balloon, often used for recreation and advertising. A hot air balloon is an inverted container from which some of the air has been expelled by thermal expansion.
The density of air inside the balloon is less than the density of air outside the balloon. Hence the balloon floats in the air that surrounds it. As the balloon rises it eventually reaches an elevation where the air density outside the balloon equals the air density inside the balloon. The balloon continues to float at that elevation.
Ballooning is a beautiful sport. Visit, for example the
Quebec Association of Balloonists who have provided the balloon picture on this page.
Filling a container with a gas whose density is less that that of air is another option when constructing an air ship. The most famous air ship of that kind was the Hindenburg. A substantial portion of its claim to fame is due to its spectacular demise.
Almost exactly 100 years separate the event pictured on the left and the event pictured on the right. During the period 1891 - 1896 the German engineer Otto Lilienthal successfully flew a controlled gliding machine. One hundred years later the United States built the
B-2 bomber
pictured on the right. Lilienthal applied the Bernoulli principle to keep his glider in the air and he used his body to control the center of mass of the glider to which he was attached. Thereby he controlled the stability and the steering of the craft. Lilienthal died in a gliding accident in 1896. The publicity given to the accident (including photographs) inspired the Wright brothers in America.
On December 17, 1903, at Kill Devil Hill, N.C. the Wright brothers' "The Flyer", the first powered airplane, rose into the air. The event was recorded for posterity in the photograph on the left. Devil Hill is near Kitty Hawk, N.C. where the brothers built their planes. The first of four flights on that day lasted 12 seconds.
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1. You are designing a helium filled birthday balloon to levitate your baby sister who weighs 60 lbs. Estimate the volume of the balloon (in cubic feet).
For extra credit answer the following questions.
1. You are designing a helium filled birthday balloon to levitate your baby sister who weighs 60 lbs. Estimate the volume of the balloon (in cubic feet).
2. Why is there a propeller on the tail of a helicopter?
3. What is stealth technology?