History of the Altimeter

Measuring Distance Above Sea Level or the Ground Below Aircraft

The altimeter is an instrument which measures vertical distance with respect to a reference level. It can give the altitude of the land surface above sea level, or the altitude of an airplane over the ground. Louis Paul Cailletet was the French physicist who invented the altimeter and the high-pressure manometer.

Louis Paul Cailletet (1832-1913)

The French physicist was the first to liquefy oxygen, hydrogen, nitrogen, and air in 1877-78.

He had been studying the composition of gas given off by iron in the blast furnace of his father's ironworks. At the same time, Swiss physician Raoul-Pierre Pictet liquefied oxygen by another method. Cailletet had an interest in aeronautics which led to developing an altimeter to measure the altitude of an airplane.

Barometric Altimeter - Paul Kollsman (1900-1982)

In 1928, German-American inventor Paul Kollsman changed the world of aviation with the invention of the world's first accurate barometric altimeter also called the “Kollsman Window”. His altimeter converted barometric pressure into distance above sea level in feet. It allowed pilots to fly blind.

Kollsman was born in Germany, where he studied civil engineering. He emigrated to the United States in 1923 and worked in New York as a truck driver for Pioneer Instruments Co. He formed the Kollsman Instrument Company in 1928 when Pioneer didn't accept his design.

When he had then-Lieutenant Jimmy Doolittle conduct a test flight with the altimeter in 1929, he was able to sell them to the United States Navy.

Kollsman sold his company to Square D Company in 1940 for 4 million dollars. Kollsman Instrument eventually became a division of Sun Chemical Corporation.

Kollsman went on to file hundreds of other patents, including those for converting salt water into fresh water and for a slip-resistant bathroom surface. He owned one of the earliest ski areas in the United States, Snow Valley in Vermont. He married actress Baroness Julie "Luli" Deste and purchased The Enchanted Hill estate in Beverly Hills.

Radio Altimeter - Lloyd Espenschied (1889-1986)

Lloyd Espenschied invented the first radio altimeter in 1924. The principle is that a beam of radiowaves is transmitted by an aircraft and then their time to return as reflected from the ground is used to calculate altitude above the ground. The radio altimeter differs from the barometric altimeter in showing altitude above the ground below rather than above sea level. That is a critical difference for flight safety.

In 1938, the FM radio altimeter was first demonstrated in New York by Bell Labs. In the first public display of the device, radio signals were bounced off the ground, showing pilots the altitude of an aircraft.

Lloyd Espenschied was a native of St. Louis, Missouri who graduated from the the Pratt Institute with a degree in electrical engineering. He was interested in wireless and radio communications and worked for telephone and telegraph companies, becoming a director of high-frequency transmission development at Bell Telephone Laboratories.

He was the co-creator of the coaxial cable, an important component of television and long distance telephone service. He held over 100 patents in communications technology.