| Aircraft Propeller Essay, Research Paper
Time Line of the Aviation 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. 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.
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. Throughout the 19th century, aviation pioneers explored and tinkered with the concepts of flight to design a viable airship. 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\” as 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.
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. 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 time.
These advancements led to the development of the first generation of well-designed propellers. One of the first designs was the \”Integrale\”, developed by Lucien Chauviere, the world\’s first industry standard propeller manufacturer. By 1910, the number of propeller producers multiplied, and numerous advancements were made. While most of the manufacturers were focusing on wooden propellers, a few visionaries were experimenting with metal propellers and variable pitch blades. Geoffrey deHavilland, an English engineer, tested propellers whose aluminum blades could be adjusted to change their angle. At the same time, German pioneers Hugo Junkers and Hans Reissner experimented with lightweight metal propellers.
The first U.S. propeller production facility was the Requa Gibson Company founded in 1909, which was headed by Canadian, engineer Wallace R. Turnbull. Turnbull tested and confirmed that the large, slow-speed propellers produced higher thrust efficiencies than those compared with smaller, high-speed propellers. More importantly, Turnbull confirmed the universal law of aerodynamics: the efficiency of any aerodynamic device rises as the amount of air it acts upon increases and the velocity of that air decreases.
WWI brought much advancement to the propeller. Stronger materials were created through \”bonding\” which made propellers compatible with the larger, more powerful engines. Propeller balancing techniques were developed, which greatly smoothed out the ride. Experiments with variable pitch blades were introduced as well. Two major breakthroughs occurred after the war: the once piece metal propeller, and the ground adjustable pitch propeller. The metal propeller allowed operations in all climates, whereas the wooden prop would fail in extreme conditions. The metal propeller could be made thinner than a comparable wooden propeller, which allowed for faster cruising speeds due to less drag from compressibility. Thinner blades also improved efficiency at higher speeds. The only drawbacks to the early metal propeller were their weight and fixed pitch blade angles. The development of the ground adjustable propeller was a major improvement. The best propeller of this kind at the time was the dual-blade ground adjustable propeller. With this adjustable propeller, the pilot could choose whether or not they wanted to have great takeoff performance or great cruise performance. In 1927, the idea of changing the pitch of a propeller was taken one step further with the development of the in-flight adjustable propeller. This gearshift device allowed pilots to change the pitch angle in flight to get the best performance out of their aircraft during takeoffs and during cruise. One of the most interesting developments during this period was the introduction of a propeller that could \”feather\”. This greatly reduced prop drag and was a multi-engine pilot\’s savior when one of his engines quit. Hamilton Standard, on their Hydromaticpropeller, introduced the \”feathering blade\”.
After WWII, the Hydromatic propeller was improved by Hamilton Standard to include features such as reversible pitch, automatic synchronization, and electrical blade deicing. Many large propeller transports switched to this new system for its reliability and pilot friendly features. The age of the Turboprop brought a few changes to the propeller. Four bladed, wide chord, aluminum alloy propellers, were utilized by most turboprop transports because of their durability. Engineers designed wide, super-thin, hollow blades to increase the performance of the aircraft at high speeds. Advanced applications of the propeller are currently being experimented by Hamilton Standard.
The aviation propeller has constantly evolved with increasing technology. The propeller may be close to achieving its maximum potential with the development of the modern turbo-fan engine. However, today\’s propellers will be in service for many years to come. This article has been a brief overview of this amazing device.
|