Aircraft Propeller Essays - Aerodynamics, Propellers, Blade Pitch

Aircraft Propeller The aircraft propeller looks like a simple mechanism to the uneducated individual. To the educated, an aircraft propeller represents the highest sophistication in aerodynamics, mechanical engineering and structural design. This report will touch on the history of the propeller, from early pioneers/experiments, advancement during/after the war, all the way up to current applications of the propeller. The creation of the propeller can be traced back to Leonardo da Vinci. Da Vinci's "helical screw" helicopter is believed to be the ancestor of the air propeller and the helicopter rotor. The first idea of a propulsive airscrew, however, belongs to J.P. Paucton, a French mathematician. Paucton envisioned a flying machine that had two airscrews, one for propulsion and the other for sustaining flight. The idea of using an airscrew for propulsion was utilized during the late 1700's to early 1800's. Only after experimentation did the inventors conclude that more propulsive power could be obtained by merely straightening out the surface of the airscrew blades. Attempts to utilize the "straight blade" propeller were made by balloonists. These contraptions were quite strange and hardly fulfilled their purpose of actually propelling the balloon. The basic propeller had evolved from the simple concepts of da Vinci, and was slowly becoming an effective means of aerial propulsion. To reach the next plateau of flight an increased knowledge of the propeller would be needed, and the mysteries of the propeller and mechanical power would need to be solved. These substantial tasks remained for aviation's pioneers to tackle during the 19th century. Throughout the 19th century, aviation pioneers explored and tinkered with the concepts of flight to design a viable airship. Some pioneers tried to transform the balloons into navigable cigar shaped airships by experimenting with sails, propellers, and paddlewheels but all produced limited results. Other experimenters, who were convinced that man flight should have wings, worked to establish basic principles in aerodynamics, flight stability and control, as well as propulsion. Controlled mechanical flight came on August 9, 1884. Charles Renard and A.C. Krebs flew the airship "La France" on a closed circuit from Chalais-Meudon to Villacoublay and back in 23 minutes. The airship "La France" was powered by a 9 horsepower electric motor that drove a 23ft diameter propeller and reached a speed of 14.5 mph. This flight was the birth of the dirigible, a steerable, lighter-than-air ship with adequate propulsion. Another important milestone in aviation, was the understanding of aerodynamics. Sir George Cayley, a British theorist, was acclaimed as the father of aerodynamics. He established a solid foundation of aerodynamic principles that were essential to the success of other pioneers. In 1875, Thomas Moy created a large model that had twin 12ft propellers with 6 blades each! Interestingly enough these blades could be adjusted to produce maximum thrust under certain conditions, an early recognition of the need for changing blade pitch. Without a doubt, the most expensive and spectacular project of its time was that carried out by Sir Hiram Maxim. His numerous experiments with propellers, culminated in the construction of a huge, four-ton biplane in 1890. This contraption was powered by two 180hp steam engines that each drove propellers 17ft, 10inches in diameter and weighing 135lbs. The two-blade propellers, inversely tapered and squared at the tips 5 ? ft wide, were made of American Pine, planed smooth, covered with glued canvas and stayed to the propeller shafts with steel wire to handle the high thrust loads. These massive propellers produced 1,100lbs of thrust each during full power while rotating at 425rpm. Maxim's jumbo creation didn't last long however, it jumped the test track and suffered extensive damage. Hands down, the most influential aviation pioneers were the Wright brothers. They had concluded that a propeller was simply a whirling wing, but didn't have the appropriate information to consult when comprehending the fundamental principles of blade shape and motion. This dilemma made designing the propeller one of the Wright brothers most challenging problems. Despite the lack of previous information to consult, the brothers were able to learn, through investigation and trial/error, that large propeller diameters would produce high thrust for a given power input. The brothers also determined that high torque produced by large, slow turning blades adversely affected the flying qualities (p-factor). On their first aircraft, they utilized 8 ? ft propellers installed behind the wind to minimize airflow disturbance, incorporated counter-rotating propellers to eliminate the problems associated with torque, and gained thrust efficiency by reducing the blades' rotational speed using a chain and sprocket transmission. The Wright brother's propeller was 66% efficient which was much higher that any other propeller of the