History of the aircraft propeller

History of the 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" 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. 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.

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. The foundations of a disciplined approach to propeller design evolved soon thereafter.

With the advancements and refinements made by early inventors, engineers could use those test results to design propellers with better performance and structural reliability. 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. These theories were expanded during WWI. The war 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
dural-blade ground adjustable propeller. With this adjustable
propeller, the pilot could choose whether or not they wanted to have
great takeoff performance orgreat 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 Hydromatic
propeller, 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 new idea deals
with transport category aircraft and the introduction of the
"un-ducted fan". This design incorporates the reliability of the
turbine engine, with the efficiency of a prop. Expected savings of 25%
in fuel costs drive the ongoing interest in this application. The
design utilizes 8-10 thin but very wide, closely spaced, swept angle
blades to propel an aircraft at speeds approaching the speed of sound
(mach.

8). It will be interesting to see how the role of the propeller
develops as time goes on. This report has sparked my interest in
propellers. I have never researched this topic before and feel that
I've benefited from writing it. I enjoyed researching the history of
the propeller and 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 to write.