Theaircraft propeller looks like a simple mechanism to the uneducated individual. To the educated, an aircraft propeller represents the highest sophistication inaerodynamics, mechanical engineering and structural design.
This report willtouch on the history of the propeller, from early pioneers/experiments,advancement during/after the war, all the way up to current applications of thepropeller. The creation of the propeller can be traced back to Leonardo daVinci. Da Vinci’s “helical screw” helicopter is believed to be theancestor of the air propeller and the helicopter rotor. The first idea of apropulsive airscrew, however, belongs to J. P.
Paucton, a French mathematician. Paucton envisioned a flying machine that had two airscrews, one for propulsionand the other for sustaining flight. The idea of using an airscrew forpropulsion was utilized during the late 1700’s to early 1800’s. Only afterexperimentation did the inventors conclude that more propulsive power could beobtained by merely straightening out the surface of the airscrew blades.Order now
Attempts to utilize the “straight blade” propeller were made by balloonists. These contraptions were quite strange and hardly fulfilled their purpose ofactually propelling the balloon. The basic propeller had evolved from the simpleconcepts of da Vinci, and was slowly becoming an effective means of aerialpropulsion. To reach the next plateau of flight an increased knowledge of thepropeller would be needed, and the mysteries of the propeller and mechanicalpower would need to be solved.
These substantial tasks remained for aviation’spioneers to tackle during the 19th century. Throughout the 19th century,aviation pioneers explored and tinkered with the concepts of flight to design aviable airship. Some pioneers tried to transform the balloons into navigablecigar shaped airships by experimenting with sails, propellers, and paddlewheelsbut all produced limited results. Other experimenters, who were convinced thatman flight should have wings, worked to establish basic principles inaerodynamics, flight stability and control, as well as propulsion. Controlledmechanical flight came on August 9, 1884. Charles Renard and A.
C. Krebs flew theairship “La France” on a closed circuit from Chalais-Meudon to Villacoublayand back in 23 minutes. The airship “La France” was powered by a 9horsepower electric motor that drove a 23ft diameter propeller and reached aspeed of 14. 5 mph.
This flight was the birth of the dirigible, a steerable,lighter-than-air ship with adequate propulsion. Another important milestone inaviation, was the understanding of aerodynamics. Sir George Cayley, a Britishtheorist, was acclaimed as the father of aerodynamics. He established a solidfoundation of aerodynamic principles that were essential to the success of otherpioneers. In 1875, Thomas Moy created a large model that had twin 12ftpropellers with 6 blades each! Interestingly enough these blades could beadjusted to produce maximum thrust under certain conditions, an earlyrecognition of the need for changing blade pitch.
Without a doubt, the mostexpensive and spectacular project of its time was that carried out by Sir HiramMaxim. His numerous experiments with propellers, culminated in the constructionof a huge, four-ton biplane in 1890. This contraption was powered by two 180hpsteam engines that each drove propellers 17ft, 10inches in diameter and weighing135lbs. The two-blade propellers, inversely tapered and squared at the tips 5 ?ft wide, were made of American Pine, planed smooth, covered with glued canvasand stayed to the propeller shafts with steel wire to handle the high thrustloads.
These massive propellers produced 1,100lbs of thrust each during fullpower while rotating at 425rpm. Maxim’s jumbo creation didn’t last longhowever, it jumped the test track and suffered extensive damage. Hands down, themost influential aviation pioneers were the Wright brothers. They had concludedthat a propeller was simply a whirling wing, but didn’t have the appropriateinformation to consult when comprehending the fundamental principles of bladeshape and motion.
This dilemma made designing the propeller one of the Wrightbrothers most challenging problems. Despite the lack of previous information toconsult, the brothers were able to learn, through investigation and trial/error,that large propeller diameters would produce high thrust for a given powerinput. The brothers also determined that high torque produced by large, slowturning blades adversely affected the flying qualities (p-factor). On theirfirst aircraft, they utilized 8 ? ft propellers installed behind the wind tominimize airflow disturbance, incorporated counter-rotating propellers toeliminate the problems associated with torque, and gained thrust efficiency byreducing the blades’ rotational speed using a chain and sprocket transmission.
The Wright brother’s propeller was 66% efficient which was much higher thatany other propeller of the time. The foundations of a disciplined approach topropeller design evolved soon thereafter. With the advancements and refinementsmade by early inventors, engineers could use those test results to designpropellers with better performance and structural reliability. Theseadvancements led to the development of the first generation of well-designedpropellers. One of the first designs was the “Integrale”, developed byLucien Chauviere, the world’s first industry standard propeller manufacturer.
By 1910, the number of propeller producers multiplied, and numerous advancementswere made. While most of the manufacturers were focusing on wooden propellers, afew visionaries were experimenting with metal propellers and variable pitchblades. Geoffrey deHavilland, an English engineer, tested propellers whosealuminum blades could be adjusted to change their angle. At the same time,German pioneers Hugo Junkers and Hans Reissner experimented with lightweightmetal propellers. The first U. S.
propeller production facility was the RequaGibson Company founded in 1909, which was headed by Canadian engineer Wallace R. Turnbull. Turnbull tested and confirmed that the large, slow-speed propellersproduced higher thrust efficiencies than those compared with smaller, high-speedpropellers. More importantly, Turnbull confirmed the universal law ofaerodynamics: the efficiency of any aerodynamic device rises as the amount ofair it acts upon increases and the velocity of that air decreases.
Thesetheories were expanded during WWI. The war brought much advancement to thepropeller. Stronger materials were created through “bonding” which madepropellers compatible with the larger, more powerful engines. Propellerbalancing techniques were developed, which greatly smoothed out the ride. Experiments with variable pitch blades were introduced as well. Two majorbreakthroughs occurred after the war: the once piece metal propeller, and theground adjustable pitch propeller.
The metal propeller allowed operations in allclimates, whereas the wooden prop would fail in extreme conditions. The metalpropeller could be made thinner than a comparable wooden propeller, whichallowed for faster cruising speeds due to less drag from compressibility. Thinner blades also improved efficiency at higher speeds. The only drawbacks tothe early metal propeller were their weight and fixed pitch blade angles. Thedevelopment of the ground adjustable propeller was a major improvement.
The bestpropeller of this kind at the time was the dural-blade ground adjustablepropeller. With this adjustable propeller, the pilot could choose whether or notthey wanted to have great takeoff performance or great cruise performance. In1927, the idea of changing the pitch of a propeller was taken one step furtherwith the development of the in-flight adjustable propeller. This gearshiftdevice allowed pilots to change the pitch angle in flight to get the bestperformance out of their aircraft during takeoffs and during cruise.
One of themost interesting developments during this period was the introduction of apropeller that could “feather”. This greatly reduced prop drag and was amulti-engine pilot’s savior when one of his engines quit. Hamilton Standard,on their Hydromatic propeller, introduced the “feathering blade”. AfterWWII, the Hydromatic propeller was improved by Hamilton Standard to includefeatures such as reversible pitch, automatic synchronization, and electricalblade deicing. Many large propeller transports switched to this new system forits reliability and pilot friendly features.
The age of the Turboprop brought afew changes to the propeller. Four bladed, wide chord, aluminum alloypropellers, were utilized by most turboprop transports because of theirdurability. Engineers designed wide, super-thin, hollow blades to increase theperformance of the aircraft at high speeds. Advanced applications of thepropeller are currently being experimented by Hamilton Standard.
The new ideadeals with transport category aircraft and the introduction of the “un-ductedfan”. This design incorporates the reliability of the turbine engine, with theefficiency of a prop. Expected savings of 25% in fuel costs drive the ongoinginterest in this application. The design utilizes 8-10 thin but very wide,closely spaced, swept angle blades to propel an aircraft at speeds approachingthe speed of sound (mach . 8). It will be interesting to see how the role of thepropeller develops as time goes on.
This report has sparked my interest inpropellers. I have never researched this topic before and feel that I’vebenefited from writing it. I enjoyed researching the history of the propellerand it’s contributions to aviation milestones. I’ve taken you, the reader,from the early experiments of da Vinci, the wooden props of the Wright brothers,the design of the variable pitch propeller, through the advanced concept of the”un-ducted” fan.
I hope this report was as interesting to read as it was towrite.