Controllable Pitch Propeller Essay, Research Paper

Canada is not exactly known for having produced several ground-breaking

inventions or discoveries in her time. However, the period of rapid

technological advancement that she incurred during the third period of the

history of engineering in Canada brought with it several important engineering

inventions which had their roots in Canada. The creation of the controllable

pitch propeller was one such invention which was perfected in Canada and was so

successful that this primarily Canadian development spread throughout the world.

Wallace Rupert Turnball lived in Rothesay and it was there that he carried out

his experiments in aeronautical theory beginning in 1902. His specialty was that

of dihedrals which he studied in a wind-tunnel. He looked at water borne

hydroplanes propelled by motor-driven airscrews. An airscrew the Great Britain

term for a propeller. A standard propeller consists of anywhere from two to four

blades each a section of a helix, the geometric form of a screw thread, hence

the term ?airscrew.? The first plane had two air-screws on each side whereas

the second one had only one, more highly efficient propeller located at the rear

end of craft, near the pilot?s seat. However, both had an uneven torque of

engine that was in fact destructive to the efforts of the propeller. Turnball

experimented with all different types of air-screws; some with a 30? gauge

track that were 300? long for truck. With each air-screw he tested, he

recorded the propeller thrust, rpm and the forward speed. What determines the

forward speed is the distance that a propeller will move in the forward

direction when the shaft of the propeller is rotated 360o. Assuming that there

is no slippage, this distance is termed the geometric pitch. The propellers that

Turnball tested had diameters ranging from 1.5? up to 3.5?, all different

dimensions and shapes. Upon his return to Rothesay in 1918, after the war, he

dove into his research and experimentation on a possible controllable pitch

propeller, an idea that he had been developing since the autumn of 1916. He ran

several tests using rotating electric motor apparatus in order to spin the

blades of his propeller. The finished product was a propeller whose pitch can be

adjusted by the pilot, at different angles, during flight giving the pilot the

ability to command the optimal combination of torque and speed for the situation

at any given moment from his aircraft. By means of a small electric motor

mounted just in front of the propeller, the pitch of the propeller itself could

eventually be adjusted which makes for more efficient take-offs and regular

flight than what would be achieved with an everyday ?fixed blade? propeller

incapable of any pitch change. Under the supervision of both the Ontario

government and the Canadian Air Force, a ground test was run in 1923 on Avro

aircraft at Camp Borden, Ontario only to conclude that more research and

experimentation was necessary. Four years later, on June 6, 1927, again at Camp

Borden on Avro Biplane, Flight Lieutenant G.G. Brookes took Turnball?s

controllable pitch propeller for it?s first air test. Funding was granted

immediately to perfect the invention it was such a success. The news of the

Canadian invention spread rapidly. Turnball wrote a treatise based on his

discoveries and new found technology called ?The Efficiency of Aerial

Propellers? which was published in the Scientific American on April 3, 1909.

His second and third publications on the subject were entitled ?Laws of

Air-Screws? and appeared in The Aeronautical Journal, in the October 1910 and

January 1911 issues. For his studies and discoveries, Turnball was awarded the

Bronze Medal of Royal Aeronautical Society and was, in addition, elected a

?Fellow.? Come 1914, Turnball had published several scientific articles and

found himself one of the world?s authorities on the subject. He sold the

patents to the controllable pitch propeller in December of 1929. The Curtiss

Wright Corporation won the American rights and the Bristol Aeroplane Company,

the English rights. In 1935, the Norseman, the most highly successful bush plane

in the world at the time, was designed in Canada by Robert Noorduyn, an aviation

engineer trained in Holland. The Norseman quickly caught the attention of the

entire world due to the effectiveness of its design. It had a large capacity for

cargo, flexible take-off and landing capabilities, ability to withstand harsh

weather, can be easily flown in either day or night and is capable of flying

great distances. Noorduyn?s Norseman, which utilized Turnbull?s controllable

pitch propeller, was adopted around the world by countries that required short

take off and landing (STOL) planes for their own reasons, most of which involved

mining, lumbering and exploring isolated expanses of land which could not

otherwise be reached quite as easily. W.R. Turnball?s invention of the

controllable pitch propeller was clearly one of the most successful Canadian

innovations in terms of world recognition. Once perfected, it was quickly bought

up by major aircraft manufacturing companies around the world and mass produced

to fulfill the global demand, at the time, for such a development in technology.