Propeller

Propeller (pronounced pruh-pel-er)

(1) A person or thing that propels.

(2) A device with a hub to which are attached evenly spaced & shaped radiating blades, rotating on a shaft to pitch against air or water to propel an aircraft, ship etc.

(3) A wind-driven (usually three-bladed) device that provides mechanical energy, as for driving an electric alternator in wind plants (not a universal use).

(4) A steamboat thus propelled; a screw steamer (now rare).

(5) In fishing, a spinnerbait.

1780: The construct was propel + -er and the original sense was “one who or that which that propels”, an agent noun from the verb propel.  The verb propel was a mid-fifteenth century form from the Middle English propellen (to drive away, expel), from the Latin propellere (push forward, drive forward, drive forth; move, impel), the construct being pro- (the prefix here use in the sense of “forward direction, forward movement”) + pellere (to push, drive), from the primitive Indo-European root pel- (to thrust, strike, drive).  The meaning “to drive onward, cause to move forward” emerged in the 1650s.  The –er suffix was from the Middle English –er & -ere, from the Old English -ere, from the Proto-Germanic -ārijaz, thought most likely to have been borrowed from the Latin –ārius where, as a suffix, it was used to form adjectives from nouns or numerals.  In English, the –er suffix, when added to a verb, created an agent noun: the person or thing that doing the action indicated by the root verb.   The use in English was reinforced by the synonymous but unrelated Old French –or & -eor (the Anglo-Norman variant -our), from the Latin -ātor & -tor, from the primitive Indo-European -tōr.  When appended to a noun, it created the noun denoting an occupation or describing the person whose occupation is the noun.  The alternative spelling propellor dates from the early days of aviation in the first years of the twentieth century and is now extinct.  The standard abbreviation is “prop”, the use noted from military aviation since 1914.  Propeller is a noun; the noun plural is propellers.

Although the concept was used in antiquity and inventors and others (most famously Leonardo da Vinci (1452–1519))  had for centuries experimented, the use of the word in mechanical engineering dates from 1809 and was from nautical design describing the application of a “device for moving vessels on or under the water”.  In aircraft design the theory of the use of “propeller” appears in papers and drawings in the 1840s (in what were then described as “flying machines”) and models were built which demonstrated a “proof of concept” although it would be decades before lightweight engines of sufficient power existed to allow experiments in aerodynamics and construction to be powered.  The first known rendering of an aircraft propeller in a recognizably modern form dates from 1853.  The modern propeller uses two or (usually) more twisted, airfoil-shaped blades mounted around a shaft which are spun to provide propulsion of a vehicle through water or air, or to cause fluid flow, as in a pump.  The lift generated by the spinning blades provides the force that propels the vehicle or the fluid although this lift does not of necessity have to induce an actual upward force; its direction is simply parallel to the rotating shaft.

Lindsay Lohan getting off the propeller driven (technically a turbo-prop) NAPA Shuttle, The Parent Trap (1998).

The term “to disembark” was borrowed from nautical use and of late "to deplane" has entered English which seems unnecessary but the companion “to disemplane” seems more absurd still; real people continue to “get on” and “get off” aircraft.

The terms “impeller” & “propeller” both describe devices which use various implantations of the “rotating blade(s) design and are used in mechanical systems to take advantage of the properties of fluid dynamics to harness specific energy for some purpose.  A propeller is a type of rotating device with blades designed to propel or move a fluid (typically a gas or a liquid) by generating thrust; they are most associated with marine vessels, aircraft and some industrial applications.  In aircraft, propellers can be attached to wing-mounted engines or mounted just about anywhere on a fuselage although historically a location at the front has been most common.  In marine applications, propellers have on specialized vessels been located to the sides of the hull but they almost always emerge at or close to the stern.  An impeller is a rotating component with blades or vanes (almost always enclosed in a housing), typically used for fluid or air distribution, such as a pump or a compressor, the primary purpose being to increase flow or pressure.  The classic impellers those in centrifugal pumps where they spin, creating a flow of fluid (liquid or air) by imparting centrifugal force to the substance; in practice, impellers such accelerate liquids are more common.

So an impeller & propeller do much the same thing, using blades to propel some form of fluid.  The use of different terms is helpful because in practice they are very different devices and the distinction that one is external and the other located within a housing is handy and the origin of that seems to lie in the construct of impeller which came first, dating from circa 1680 (as an agent noun from the verb impel) in the sense of “someone or something which impels”.  What the design of an impeller does is use the energy from the rotation to increase the flow or pressure of the fluid and it that it’s the reverse of a turbine, the rotation of which extracts energy from, and reduces the pressure of the flow.  Engineers also have a number of highly technical rules about what is and is not defined as an impeller base on the whether the entry and exit of the fluids occur axially or radially but it seemed impossible to construct such definitions as absolutes so for most the simpler distinctions are more helpful.  In engineering, impellers have been recorded as a machine or component name since 1836.

News Corp website 22 January 2024.  To refer to a jet engine’s nacelle as a propeller could (almost) be defended on the basis it’s the jet engine which “propels” the aircraft but this is more likely an example of (1) the decline in the quality of journalists and (2) what happens when there are no sub-editors to correct the mistakes.  In time, artificial intelligence (AI) should improve things.    

The verb impel dates from the early fifteenth century and was from the Middle English impellen, from the Latin impellere (to push, strike against; set in motion, drive forward, urge on), the construct an assimilated form of in- (into, in, on, upon), from the primitive Indo-European root en- (in) + pellere (to push, drive), from the primitive Indo-European root pel- (to thrust, strike, drive).  The construct of the Latin impellō was in- +‎ pellō (push, drive), from the Proto-Italic pelnō or pelnaō, a nasal-infix present derived from the primitive Indo-European pelh- (to drive, strike, thrust).  The Latin prefix –in could be appended to create a negative (un-, non-, not etc) but here was used as an intensifier, another possible meaning (in, within, inside) coincidental to the mechanical devices being usually mounted within housings.

Propellers and impellers both use blades (although those of the latter are often in the form of a single piece wither cast, molded, or (occasionally) forged.  Turbines also use blade-like parts but these are called vanes and an industry which seems unable to decide on terminology is the burgeoning business of wind-power; the huge rotating assemblies on wind turbines are referred to variously as vanes, blades or rotors.  Rotor blades are familiar for the use in helicopters which is essentially an airframe where a large-scale propeller sits atop the structure, pointing upwards and rather than “propeller blades”, the accepted term is “rotor blades”, the design of which permits both lift and directional thrust although some exotic multi-engined machines have rotors in housings which, to maximize performance, can themselves be rotated to operate as conventional propellers.

Supermarine Seafang (1946) with contra-rotating propellers.  The Seafang was powered by the Rolls-Royce Griffon and was the final evolution of the Spitfire-derived Seafire and Spiteful, the trio all designed for use on Royal Navy aircraft carriers, the series enjoying success despite the basic design being hampered by the narrow undercarriage which made landings a challenge (something corrected on the Spiteful & Seafang).  Series production of the Seafang was contemplated but eventually only 18 were built because the jet-powered de Havilland Sea Vampire proved capable of carrier operations, surprising some at the Admiralty who doubted the jets could operate from anywhere but land.

The evolution of aircraft influenced propellers.  Once they had been fashioned from wood before the need for faster, more efficient shapes dictated the use of aluminium or other light metals.  By the time the first modern monoplane fighters appeared in the mid 1930s propellers were still two-bladed but as power increased over the years (something which accelerated during World War II (1939-1945)), three, four and five-bladed solutions were engineered.  The rising output however, although it permitted higher performance, created challenges for engineers, notably the “torque effect” which meant a tendency to cause the aircraft to roll in the direction of the propeller’s spin, a problem especially serious during take-offs.  In twin-engined aircraft the solution was to have the propellers rotate in opposite directions but in airframes with a single power-plant, sometimes used were contra-rotating propellers which, although introducing additional complexity and demanding additional maintenance, did offer advantages including: (1) harnessing more of an engine’s power, (2) increased thrust efficiency by a reduction in energy losses, (3) counteracting the torque effect, (4) improved low-speed manoeuvrability and ground-handling and (5) improved acceleration and climbing performance.

A flight of Republic P-47D Thunderbolts with under-wing drop-tanks.

The propeller also influenced other aspects of the aircraft.  When the prototype Republic P-47 Thunderbolt (1941-1945) first took to the air, it was the largest, heaviest single-seat piston-engined fighter ever produced (a distinction it still enjoys today).  Even the early versions used an engine rated at 2000 horsepower (later this would rise to 2800) and to harness this output demanded a large propeller.  The 12 foot (3.7 m) diameter of this four-bladed monster meant the landing-gear had to be extraordinarily long and the only way it could be accommodated was to have them retract inward, otherwise the heavy wing armament (8 x .50 inch (12.7 mm) M2 Browning machine guns (425 rounds per gun)) wouldn’t have fitted.

Chrysler XI-2220 V16.  The splined shaft is where the propeller attaches.

With things like the Thunderbolt, the Hawker Tempest and the later Supermarine Spitfires (and its derivatives), the piston-engined fighter achieved its final evolutionary form, the jet engine offering a path to performance unattainable while the physics of propellers imposed limits.  However, had the use of the A-Bombs not ended the war in 1945, development of the propeller aircraft would have continued because the early jets lacked thrust and reliability as well as suffering a rate of fuel consumption which rendered them unsuitable for long-distance operations.  With the war against Japan envisaged as lasting well into 1946, development of faster, more powerful piston engines continued although, given the parlous state of the Japanese military, it’s dubious at least there was much of a rationale for this but the military industrial complex is a creature of inertia and Chrysler’s research had perfected a new aero-engine for the Thunderbolt.  The XI-2220 was a 2,220 cubic inch (36.4 litre) V16 which was rated at a basic 2450 horsepower with some 4000 hp available when tuned for wartime use but with the end of the conflict, all such developments were cancelled and attention switched to the brave new world of jets and swept wings.  Thus ended the era of the big propeller-driven fighters, the V16 stillborn, as was the other extraordinary aero-engine on the drawing board: Britain's 32-cylinder Napier-Sabre H-32 which was a scaled-up version of their H24.