Controllable Pitch Propeller
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