Chapter 15: Fluids
Applications

FLOATING IN THE AIR

On December 17, 1903, the Wright brothers flew the first airplane. However, air ships sailed the air long before that. Airplanes get their lift from air pressure difference, which is the result of different air stream speeds over different parts of the craft, airplane wings or helicopter propellers.

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, and the balloon continues to float at that elevation.

Ballooning is a beautiful sport. Visit, for example the Arizona Balloon Club.

Filling a container with a gas whose density is less than 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.

FLYING WITH BERNOULLI

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, and 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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Some memorable dates:

1909: The army purchases the first airplane from the Wrights
1910: First successful take-off from a ship.
1911: First wireless exchange between an airplane and ground
1915: A single airplane drops a ton of bombs on London
1919: Curtiss flies from U.S. to England with many stops on the way
1923: First non-stop flight across the U.S. The flight took 28 hours.
1927: Charles Lindberg flies the "Spirit of St. Louis" non-stop from New York to Paris in 33 hours and 39 minutes.
1931: First round-the-world flight in 8 days and 16 hours. Late 1930's: scheduled commercial flights, both domestic and transoceanic become common
1939: First flight of a jet aircraft in Germany.
1952: British Overseas Airways switch to jets on some commercial flights.

1960: Boeing 707 jet transport is introduced, followed by Boeing 727 and others.

Further study links:

Air Ships.

more history...

The Physics of Flying:

Further Study Questions.

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).