TAKE OFF

Flight and Propulsion


Propeller Driven Aircraft


Propeller

Originally a ROTAX-582 was installed in the Kitfox. After the first forced landing, a new engine was installed after all appropriate repairs were completed. N9KF was now flying with a modified 98 horsepower Subaru engine. The Kitfox experienced essentially the same type of problem in each of the forced landings only with two different engines.

The Kitfox utilized a propeller driven propulsion system for each engine. N9KF had three propeller blades that generated the thrust for the airplane. Each propeller blade was designed to act like a wing or airfoil, and the propeller generated thrust much the same way as a wing generates lift. By Bernoulli's Principle, a low pressure area is created in front of the propeller blades while a high pressure area is created behind the propeller blades thus causing the airplane to move forward toward the lower pressure region.(JEPPESEN 3-35)

Thrust is increased by using the throttle to increase the power in the engine. With an increase in engine power, the airplane will accelerate because the thrust force exceeds the drag force. At this point in time though, the drag will also begin to increase. Once the force of thrust no longer exceeds the force of drag, the airplane will stop accelerating, but will be flying at a higher airspeed than before. The reverse is also true when power to the engine is decreased. This time the plane will be flying at a slower airspeed than it started at since drag will exceed thrust. (JEPPESEN 1-21)

The glide ratio is the distance that a plane will travel in relation to the altitude lost when a plane experiences an engine failure, i.e loss of power. Depending on the situation, a pilot may be able to choose a gliding attitude and/or airspeed that can increases time in the air or distance traveled. (JEPPESEN 1-29) A detailed derivation and method of calculation of the glide ratio for any given situation can be found in "Mechanics of Flight," by Warren F. Phillips.



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Heather Christian
fnhlc@uaf.edu
Phys 211x-SF01 - General Physics I
Last update 11/22/2004