Tuesday, August 12, 2014

History Lesson: Importance of the Inclinometer for Flight

Orville and Wilbur Wright may have never found success if not for the inclinometer. Their original aircraft designs were missing a critical piece of innovation that was being used by foresters and other industry pioneers. This simple device is known as an inclinometer (or slip indicator).

The 1902 Flyer had problems maintaining level flight throughout a turn due to the aircraft slipping or skidding through the air, which dramatically reduced the lift generated by the wings they had designed.

While in his sleep, Orville awoke one night after a dream in which he saw the problem:  he needed to add yaw to an aircraft's turn which at the time only included roll. The Wright 1903 Flyer was the first model designed by the Wright brothers to include a rudder, which allowed the aircraft to fly balanced (coordinated) through a turn instead of sliding sideways through a turn using only roll from the ailerons located on the wings. The use of inclinometers on flying aircraft was immediately needed for the pilot to know how much input was needed from the rudders for a coordinated turn.

Early inclinometers were as simple as a pendulum hung where the pilot could see how his aircraft was moving through the air with respect to the force of gravity. The most famous early inclinometer was found in the Spirit of St. Louis piloted by Charles Lindbergh. This Rieker inclinometer used by Charles on his solo flight across the Atlantic Ocean was a simple yet reliable design that is still used today.

As flight instrumentation advanced, the inclinometer became more commonly known as the slip indicator. Modern day inclinometers are sealed glass tubes curved upwards with a ball sitting at the bottom surrounded by fluid in the tube. The ball gives an indication of how coordinated the turn is, whether the aircraft is slipping (skidding) or flying coordinated throughout the turn. The forces of gravity against the aircraft precession forces cause movement of the ball within the tube.

Flight instructors will often tell their students to step on the ball meaning the inclinometers' ball is not centered at the bottom of the tube and the student pilot must add rudder to the aircraft turn to become balanced and coordinated.

The reason why coordinated turns are so important is due to how gravity is felt and applied to the opposing force (lift) generated by the aircraft wings. While an aircraft is slipping or skidding through turns gravity is felt to the side and it pulls the aircraft sideways towards the earth making the lift generated by the wings less effective. When an aircraft becomes coordinated, gravity is pulling directly through the center of the aircraft perfectly opposite of the lift being generated by the wings. This results in a more pleasant feeling for the passengers aboard the aircraft as well as a more efficient flight. In a perfectly coordinated turn many passengers will not feel the aircraft is turning at all due to the weight of gravity being applied directly perpendicular to the seat they are sitting in.

Thelma Micco is a freelance writer for Rieker Inc., a leading manufacturer of inclinometers, tilt switches and other tilt sensing devices. Interested in finding out more about Rieker Inc.? Visit our website today for more information.

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