The Evolution of Piston Aircraft Engines: Development, Performance Indicators, and Technological Advancements
Jakub Pełczyński
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Published Online: Mar 31, 2025
Page range: 1 - 26
Received: Sep 18, 2024
Accepted: Jan 18, 2025
DOI: https://doi.org/10.2478/tar-2025-0001
Keywords
© 2025 Jakub Pełczyński, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
The development of piston aircraft engines has progressed through a number of stages, shaped by various factors. Armed conflicts, in particular, have played a significant role in driving innovation, making them useful reference points for defining distinct periods of development. At the same time, advancements in engine design and improvements in fuel composition have contributed to enhanced operational performance [1]. This article aims to systematize the historical development of piston aircraft engines by categorizing them into key periods and analyzing changes in operational indicators. These changes are illustrated through charts based on data from several hundred engines, providing a comprehensive overview of their evolution.
The operational indicators analyzed in this study are derived from an extensive collection of source materials. The dataset is primarily based on original manufacturer catalogues and publications spanning over a century. Additionally, numerous contemporary publications from a given era serve as valuable sources, not only compiling catalogue information but also presenting research findings from their respective periods. Of particular importance is the British series
In Poland, published research on the development of piston aircraft engines has been more limited. Relevant publications include a 2005 volume by W. Balicki et al. on the history and prospects of aircraft propulsion development [8], which nevertheless only superficially treats the issue of piston engines, J. Walentynowicz’s 2011 book on the history of heat engine development [9], which dedicates a single chapter to the topic, and the most recent publication, K. Wisłocki’s 2023 book on aircraft propulsion, covering fundamentals, classification, history, and design [10]. A certain number of research articles on the development of aircraft engines have also been published in Poland, including in the journal
This article summarizes many years of research into the evolution of piston aircraft engines. Data was collected through an extensive review of archival publications and manufacturer catalogs.
The first aeroplane capable of carrying a person, the Éole built by the French engineer Clément Ader, was powered by an external combustion engine [9]. However, due to the unfavorable power-to-weight ratio, steam engines proved impractical as a propulsion system for aircraft [18]. The development of internal combustion engines in the automotive industry also played a crucial role in the development of aviation. The first and most important designs were the Wright brothers’ engine and the Manly-Balzer engine [15], compared in Table 1.
The Manly-Balzer engine, which powered the Aerodrome plane designed by Professor Langley, was the first radial aircraft engine. It was developed several months before the Wright brothers’ aircraft [15], but the first successful flight of the plane did not take place until much later. This delay was due to the inadequate piloting skills of Charles Manly, who was also a co-creator of the engine [1].
Comparison of the Manly-Balzer and Wright Flyer I engines [1, 14, 16, 19–20].
| Manly-Balzer | Wright Flyer I | |
|---|---|---|
| 52 | 16 | |
| 62 | 81.4 | |
| 8.85 | 3.28 | |
| 950 | 1025 | |
| 0.839 | 0.197 | |
| 5.876 | 4.878 | |
| 7.006 | 24.817 |
The development of piston aircraft engines can be divided into several distinct historical stages [21]:
the period from the beginning of the 20th century to the end of World War I – which can be subdivided into two phases: the years leading up to 1914 and the wartime years between 1914 and 1918 [16]; the interwar period – marked by the widespread adoption of supercharging in aircraft engines; the period of World War II – a time of significant advancements and mass production of piston engines [2, 11, 22]; the end of the World War II to the early 1950s – a period of postwar advancements, when increasingly advanced piston aircraft engines began to be created in parallel with the first turbine engines [2,3,4,5, 23–14]. the transition to turbine engines – starting in the 1940s and 1950s, piston engines gradually came to be replaced by turbine engines in most applications [8, 17]. However, they remained in use for aircraft flying at low altitudes and low ceilings, predominantly in ultralight, light and general aviation aircraft [21].
This article will analyze the evolution of piston aircraft engines through these stages, emphasizing how advancements in engine design contributed to improved operational parameters, as each period introduced new solutions and refinements [21]. However, due to the broad scope of this topic, this study will focus primarily on the first three periods – which can be described as the “glory days” of piston aircraft engines. The final stage, characterized more by decline than by innovation, extends over the longest timeframe and falls beyond the scope of this discussion.
The time from the beginning of the 20th century to the end of World War I saw the emergence of the first practical aircraft engines, with most of their basic types then being developed. Within just over a decade, piston aircraft engines developed from experimental units with low power to fully functional designs capable of producing up to 1,000 hp, manufactured in thousands of units [17].
The configurations developed during this period included: inline, V, W and radial systems [25], of which rotary engines were a special type. Their characteristic feature was that the crankshaft was fixedly connected to the aircraft structure, while the entire crankcase, along with the cylinders and the propeller attached to it, rotated around the crankshaft [16].
Initially, all aircraft engines were water-cooled [6], as designers feared that high temperatures could lead to overheating [1]. However, just a few years after the Wright brothers’ first flight, air-cooled aircraft engines were introduced. Here we can mention the Anzani engine and the Gnome rotary engine [16]. Early air-cooled engines were relatively small, but rotary engines, rotating at high speed, provided good cooling [9].
In-line engines, including single-row, V-type and W-type configurations, were built with separate, water-cooled cylinders [7, 26–27]. Air-cooled designs were less common, such as some early Renault engines. A common solution in water-cooled engines was to connect the cylinders in pairs or groups of three [7]. It was not until 1915 that Hispano-Suiza V-engines, produced in France, featured cylinders connected into blocks consisting of a whole row [7, 14]. In 1917, the Napier Lion [28] W engine was created in Great Britain, the cylinders of which were connected into three blocks [29].
Before and during World War I, aluminum alloys were increasingly used in aircraft engines [30–31]. Components such as pistons, cylinder heads, and crankcases were made from aluminum alloys.
Carburetors in the early 20th century were relatively simple and primitive. In the Manly-Balzer engine, for instance, the fuel jet was made of wood [15]. For this reason, more effective indirect injection began to be developed. In 1906, the Antoinette engine featured multi-point indirect fuel injection. This solution was adopted by the Wright brothers – all the engine models that they produced from 1907 to 1912 were equipped with them. The development of fuel atomizers led to the widespread adoption of modern float carburetors, which have come to replace other solutions during few next years [15].
A significant problem for early engines was the poor quality of fuel, which had a low octane value [15–16]. The first tests during World War I showed the beneficial effect of benzol, with its anti-knock properties, on the combustion process [1, 16].
From 1903 to 1909, engine power increased only slightly, but from 1910 it began to increase more rapidly. The impact of warfare in 1914–1918 was clearly visible [11, 32], as the average increase in the power of aircraft during this period followed a near-parabolic trend (Fig. 1).
The power-to-mass ratio [hp/kg] and power-to-displacement ratio [hp/dm3] were significantly influenced by engine developments during World War I [11] (Fig. 2). The amount of power achieved per unit of mass increased rapidly in response to wartime demands (Fig. 2). Power per unit of displacement also increased, although less rapidly than the maximum power-to-weight ratio [hp/kg] (Fig. 3).
Achieving the highest possible power-to-mass and power-to-displacement ratios depended heavily on the crankshaft rotational speed [15] (Fig. 4). The first Wright Flyer I and Manly-Balzer aircraft engines had a low rotational speed [1, 14–15, 19]. The years 1908–1909 were a period of rapid development in both new aircraft designs and new types of engines [14]. However, a significant increase in crankshaft rotational speed coincided with the outbreak of World War I.
Moreover, a comparative analysis of the characteristics of radial and in-line engines will be presented to better illustrate changes in operating parameters. As shown in the chart (Fig. 5) the power of a radial engine per 1 kg of mass is greater than that of an inline engine.
The first Manly-Balzer radial engine far outperformed all other aircraft engines until 1911 [15]. The development of radial engines proceeded continuously [7], but a significant increase in the power-to-weight ratio only became evident from 1917 onward (Fig. 6), thanks to engines such as the Gnome 9N [7], Salmson Canton-Unne 9Z [33], A.B.C. Dragonfly, and Cosmos Mercury [28]. These models demonstrated the advantages of fixed radial engines over rotary ones [1].
The rise in inline engine powers coincided with the outbreak of World War I [14]. Inline engines were often designed to achieve higher maximum power outputs than radial engines [7, 26], partly due to the inherent limitations of rotary engines [15] (Fig. 7).
The interwar period saw further advancements in piston aircraft engines, with a particular focus on supercharging [43] and improved fuel composition [44]. The interwar period was also a time when the issue of high-altitude flights [15], which was eventually resolved through the development of mechanically driven superchargers [45] and turbosuperchargers [24]. After World War I, work on mechanical chargers and turbochargers intensified. In 1918, the U.S. Aircraft Engineering Division commissioned General Electric to design a turbocharger. The experimental model was tested with a Liberty engine, first on the ground later that year, and then in flight in 1919. This allowed several flight altitude records to be set [15].
However, mechanically driven superchargers became much more common than turbochargers due to their lower thermal loads [23]. Despite this, the first successful aviation mechanical supercharger was created later than the first successful aviation turbochargers, only emerging in the second half of the 1920s [15]. To optimize altitude performance across the widest possible altitude range, two-speed superchargers were introduced [25]. This allowed the gear ratio from the crankshaft to the supercharger rotor to be changed, thereby increasing the compression depending on the altitude. In the late 1930s, the first two-stage systems appeared, allowing for easier achievement of high boost pressure at various altitudes. Depending on demand, charging could be done using one stage or both [4].
A distinct technological division emerged: all radial engines were air-cooled, while high-power in-line engines were water-cooled, and later water-glycol-cooled [1]. Small inline engines, however, were often air-cooled. During the interwar period, carburetor technology was further developed [46], including floatless carburetors [20, 47–48]. In Germany, direct injection systems were developed in the late 1930s [49]. In addition to aluminum alloys, magnesium alloys also began to be used, such as Elektron [1, 3].
Thanks to the introduction of lead compounds (tetraethyl lead – TEL), which significantly increased the octane rating of aviation fuels [15]. By the 1930s, 87-octane gasoline, developed in 1930, had become standard in most air forces worldwide, followed shortly by 92-octane gasoline [16, 28]. In 1935, the United States Army commissioned Standard Oil to develop 100-octane gasoline for combat aircraft. This was achieved in 1938 and it became the standard fuel for the USAAF from the end of that year. In 1935 in Great Britain, Dr. S. F. Birch discovered the alkalization process, which allowed the octane number to be increased above 100 [16].
In the interwar period, the trend line of maximum engine power increased significantly (Fig. 8). Until the mid-1930s the rise in engine power was relatively slow – although from the late 1920s to early 1930s, a notable increase came with development of charging systems [11, 23] and the introduction of higher-quality fuels. From around 1935, however, a sharp increase in the power of manufactured engines became apparent, coinciding with rapid advancements in aircraft designs. The period also saw several significant armed conflicts, involving powers such as Germany [50], the USSR [51], Japan [52] and Italy [53], which were preparing for significant territorial expansion.
The power-to-weight ratio (Fig. 9) and power-to-displacement ratio (Fig. 10) continued to increase steadily. As aircraft engine technology advanced, progressively higher operational indicators were achieved. The power-to-weight ratio saw steady growth until the mid-1920s, largely as a result of earlier development for military operations during World War I [21]. Until the mid-1930s, the increase is small and nearly linear, but around 1935, the power-to-displacement ratio began to follow a more exponential trend.
As shown in the chart (Fig. 11), the increase in the rotational speed trend line is close to linear throughout the entire period, although it began to accelerate slightly after 1934 (Fig. 11). This acceleration was due to the appearance of several high rotational speed engines, which in this case reached a rotational speed of approximately 4000 rpm – including the Napier Dagger [54], Napier Rapier, Rolls-Royce Exe [28] and PZL Foka [13, 55].
As illustrated in the chart, inline engines continued the trend established during World War I, typically achieving higher power-to-displacement ratios than radial engines [21]. In the early 1920s, many obsolete high-power radial engines were retired [1]. However, within a few years new ones with the power of inline engines began to be developed (Fig. 14).
As for the previous period, a comparison of radial and in-line engines will be presented (Fig. 12). During World War I, radial engines had a higher the power-to-weight ratio (Fig. 13) than that of inline engines [21]. Just after the end of World War I, however, new versions of the inline Napier Lion and the inline Napier Cub [28] and Curtiss C-12 [69] appeared, which had a very favorable ratio. It was only Bristol and then Pratt & Whitney that this trend began to shift [28, 70]. In the 1930s, the trend line for the power-to-weight ratio of radial engines again began to surpass that of inline engines [21].
In the 1930s, inline engines with rotational speeds of around 4,000 rpm were being developed [28, 71], while radial engines exceeding 3,000 rpm were almost non-existent (Fig. 15). One exception was the Polish PZL GR-760 [13, 71, 72], which reached 3,300 rpm. Two years later, the Gnome-Rhône 14M was capable of 3,030 rpm [21]. Due to the larger number of connecting rods and, consequently, the greater mass located on one crank of the crankshaft, it is more difficult to obtain high rotational speed in radial engines, in contrast to inline engines: single-row, V, X, W, H, U and boxers. A similar difficulty occurs in multi-row engines, for the same reason.
During World War II, the most common engine types were single-row radial engines, two-row radial engines, and twelve-cylinder V engines [23]. All radial engines were air-cooled, while most inline engines were liquid-cooled [14]. The exception was small engines used to power training aircraft and other light planes, etc., which were typically air-cooled [5].
Different countries exhibited distinct trends in engine use, depending on their system:
Great Britain – Both inline engines (mainly V-type) and radial engines were produced. Most British fighters were equipped with V engines, such as the Rolls-Royce Merlin and Rolls-Royce Griffon. The Hawker Typhoon and Hawker Tempest aircraft use larger, twenty-four-cylinder H-type Napier Sabre engines. Radial engines, on the other hand, were used in Great Britain primarily in bombers such as the Handley Page Halifax or heavy fighters such as the Bristol Beaufighter [28]. USSR – Both inline and radial engines were produced, and used in both fighter and bomber aircraft. Most Soviet engines were not original, but derived from French, German and American designs [51]. USA – Only one type of high-power inline engine, designed in the USA, was produced in larger quantities: the Allison V-1710, used in many types of fighters. In addition, Packard began licensed production of the Rolls-Royce Merlin engine for both Great Britain and the USAAF. American bombers and US Navy fighters were powered by radial engines. In addition, USAAF fighters such as the Republic P-47 Thunderbolt or night fighter Northrop P-61 Black Widow were equipped with eighteen-cylinder Pratt & Whitney R-2800, a two-row radial engine. In general, most American high-power aircraft engines were of the radial type [24]. Germany – Both fighters and bombers were powered by twelve-cylinder V-engines, but unlike those produced in Great Britain, the USA or the USSR, the German V-engine cylinders were usually inverted. The basic engine types were the Daimler-Benz DB 600, 601, 603, 605, 606, 610, etc. series, as well as the Junkers Jumo 210, 211, and 213 series. Training aircraft were powered by smaller, air-cooled Argus or Hirth designs. The BMW 801 was unique among German engines, being the only large German radial engine and the only radial engine designed to power fighter aircraft, such as the Focke-Wulf Fw 190 [50]. Italy – Many types of inline engines were produced in Italy in the 1930s, but these were not developed during the war. Most aircraft were powered by radial engines produced by Fiat, Alfa Romeo and Piaggio. The most successful fighters such as the Macchi C.202 Folgore, Macchi C.205 Veltro, Reggiane Re.2001 Falco II and Reggiane Re.2005 Sagittario were powered by Daimler-Benz DB 601 engines produced under license by Alfa Romeo and Daimler-Benz DB 605 engines produced by Fiat [3, 5, 53]. Japan – Almost all aircraft were powered by radial engines manufactured by Mitsubishi and Nakajima. Small inline engines from Hitachi, Gasuden, Hiro, and Yokosuka were also produced. The Aichi and Kawasaki companies produced German Daimler-Benz DB 601 engines under license for Japanese fighters [52].
World War II saw major developments in supercharging systems. Two-speed and two-stage compressors became standard [15], and turbocharger technology was refined, particularly in the United States [24]. Research on turbochargers was also conducted in many other countries, including Germany [24, 49], USSR [51], Great Britain [28], and Japan [52].
At the beginning of World War II, most countries used 87-octane gasoline. Germany faced challenges in securing adequate aviation fuel, which led to a strong focus on developing direct fuel injection systems [50]. In Great Britain and the United States, research concentrated more on the composition of aviation fuels [15], hence most solutions were adapted to 100-octane gasoline at the beginning of World War II. Soon, 100-octane gasoline with a performance octane number of 130 (100/130) was created. It became standard in the RAF and USAAF [16]. During this time, Germany managed to develop 92-octane and 96-octane gasoline [50]. From 1944, gasoline with a performance octane number of 150 (100/150) and 115-octane gasoline with a performance number of 145 (115/145) were available in Great Britain and the United States [51]. The Rolls-Royce Merlin 61 engine, using 100/130 gasoline, achieved a power of 1,565 hp (1,235 kW), and with 100/150 gasoline, as much as 1,810 hp (1,331 kW) [51].
To enable short-term increases in boost pressure during air combat, more efficient cooling systems were required [22]. For this purpose the principle is used that evaporating liquid absorbs heat, which lowers the intake temperature. The simplest solution to utilize this principle is to use water injection into the charge air [22, 70].
World War II lasted only few years, but it saw continuous increases in engine power (Fig. 16). Both the power-to-weight ratio and the power-to-displacement ratio increased (Fig. 17), although the rate of improvement gradually slowed. Among aircraft engines, British designs were particularly outstanding in terms of operational indicators, such as the power-to-displacement ratio (Fig. 18). The Rolls-Royce Merlin [2] was a notable example, its late versions being the only ones to achieve a power-to-displacement ratio exceeding 70 hp/dm3 and even 80 hp/dm3. Apart from Rolls-Royce designs, the only engine to surpass 60 hp/dm3 was the Napier Sabre [5, 28]. Among radial engines, the Japanese manufacturer Nakajima stood out, achieving a power-to-displacement ratio exceeding 50 hp/dm3 [52].
The engine speed trend line during World War II showed a gradual increase (Fig. 19). Higher rotational speeds led to a significant increase in engine power and, consequently, higher power concentration and power-to-weight and power-to-displacement ratios.
The power-to-weight ratios for both radial and inline engines, shown in the graph below (Fig. 20), remained quite close, but slightly higher for inline engines.
As shown in the graph (Fig. 21), inline engines continued their previous trend of achieving a higher power-to-displacement ratio than radial engines (Fig. 21). Engine power increased in both radial and inline engines during World War II. Some countries, such as Japan or the USA, preferred radial systems [24, 52], and some, such as Germany [50], preferred inline systems. Hence, increasingly larger engines with greater power concentration were created in both systems (Fig. 22).
Throughout World War II, inline engines achieved higher rotational speeds (Fig. 23), as in previous periods. The trend line shows a slight, almost linear increase in rotational speeds. In the early years of the war, inline engine speeds continued to rise, but by around 1942, they had largely stabilized at a similar level. Given the technologies of the time and the radial engine systems used, higher rotational speeds would have been extremely difficult to achieve.
This article presents the results of research into the historical development of piston aircraft engines. The graphs presented are based on both data from the literature and primary source materials [1,2,3,4,5, 7, 10, 12,13,14,15,16,17, 21, 24, 26,27,28,29,30,31, 33,34,35,36,37,38,39,40,41,42, 45, 49,50,51,52, 54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70, 73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89]. As a part of the broader research effort, a set of operational indicators was developed – indicators which have largely not previously been included in any scientific publications.
Changes in the operational indicators of aircraft engines were influenced by evolving design features, advancements in supercharging methods, and improvements in the fuels used [90]. At the same time, these changes noticeably correlate with larger armed conflicts [11]. Both the engine power (Fig. 24) and the power-to-displacement ratio (Fig. 25) steadily increased, though at different rates depending on the given stage of technological development. It is easy to distinguish four distinct periods: the period before World War I, the period of World War I itself, the interwar period, and the time of World War II. Accelerated growth in operational indicators in the 1930s coincided with the development of supercharging systems and fuel composition [16].
Changes in the ratio of aircraft engines’ power to their displacement volume [hp/dm3] in the years 1903–1945 [1,2,3,4,5, 7, 10, 12,13,14,15,16,17, 21, 24, 26,27,28,29,30,31, 33,34,35,36,37,38,39,40,41,42, 45, 49,50,51,52, 54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70, 73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89].
In the first period, the fundamental features and configurations of aircraft engines were established. These engines evolved from experimental designs into fully functional machines of great importance, produced in thousands of units for military purposes. The design of basic carburetors was fully developed during this period [7]. However, a lack of precise knowledge of the combustion process and the influence of fuel composition on it remained a challenge. The problem of high-altitude flights had also not yet been effectively solved [15].
These issues were addressed in the next stage of development of piston aircraft engines. Research into fuel composition led to the creation of high-octane mixtures resistant to knocking combustion [15]. In parallel, aircraft engine supercharging systems were developed in the form of mechanical superchargers and turbochargers. However, due to the limited availability of heat-resistant materials, the second of these became widespread.
The interwar period, in turn, was a time of significant engine advancements, many of which laid the foundations for modern aircraft engines (such as designs by Lycoming or Continental). Several types of engine created in that period are still being produced to this day. These include the Wright R-1820, produced as the ASz-62IR in Poland, or the Czech Walther Minor in the four-cylinder version as LOM Praha 332 [61] and the Walther Minor in the six-cylinder version as LOM Praha 337 [62].
During World War II, almost all aircraft engine production in most countries was directed to military demands. Aircraft factories in Central European countries ceased to exist, while those engines from other countries that maintained production underwent continuous improvements to enhance their operating indicators. A characteristic example is the Rolls-Royce Merlin, the first versions of which produced less than 1000 hp (735 kW) while the last ones reached 2000 hp (1470 kW) [28]. This is also an example of how increasingly better fuels with a high octane number influenced the engine’s operating indicators [16]. Multi-speed and multi-stage mechanically driven superchargers and turbochargers were also developed [15–16, 43]. Moreover, direct injection was increasingly being used instead of carburetors [24, 28, 50]. Some experts feel that at the end of World War II, piston aircraft engines reached the very peak of their capabilities.
It would appear that further advancements may have been possible. Several experimental two-stroke engines [91, 92] with sleeve valves were developed, like the Rolls-Royce Crecy [36, 93] and the Napier Nomad [28, 29]. They achieved higher operational indicators than conventional engines. Had it not been for the rise of turbine engines, which ultimately replaced piston engines in most applications, the next stage of piston engine development may have focused on these highly efficient two-stroke designs [93].
However, the 1950s saw a major regression in the development of piston aircraft engines. The most promising developmental directions were abandoned in favor of turbine engines, and production of the most advanced designs was discontinued. Only the simplest engines intended for general aviation continued to be developed, but they exhibited significantly worse operational indicators than engines intended for transport or military aircraft. Since then, there has been no significant development in their construction, with modifications mainly concerning fuel, supercharging and ignition systems.
One example is the Lycoming O-235, which has remained in production since 1942 [4]. Its power-to-displacement ratio is only 30.34 hp/dm3, which is typical for most modern piston aircraft engines. Its improved version IO-233, equipped with direct fuel injection, is not characterized by greater power. The newer Lycoming O-540 from the 1950s achieves a slightly better indicator of 33.7 hp/dm3 [94]. The Continental IO-370, which has been in production for only six years, also shows no progress, reaching 29.51 hp/dm3. Exceptions here include the Rotax engines, which obtain more favorable power-to-displacement ratio thanks to increased rotational speed of 5000-6000 rpm and relatively high compression ratios (around 9:1). Most of these designs originate from the 1980s. An example is the Rotax 912, reaching 65.98 hp/dm3. The Rotax 916, produced since 2023, achieves a much higher power-to-displacement ratio of 117.6 hp/dm3 [95], thus surpassing all engines produced during and immediately after World War II.
As demonstrated by the significant changes in engine construction and supported by the graphs (Fig. 24, Fig. 25), the history of piston aircraft engine development can be divided into several distinct periods. Each period brought major technological advancements, which clearly differentiate them from one another [21].