The radial engine is a reciprocating type internal combustion engine
configuration in which the cylinders "radiate" outward from a central
crankcase like the spokes of a wheel. It resembles a stylized star
when viewed from the front, and is called a "star engine" (German
Sternmotor, French moteur en étoile, Japanese hoshigata enjin,
Italian Motore Stellare) in some languages. The radial configuration
was commonly used for aircraft engines before gas turbine engines
1 Engine operation
2.1 World War II
2.2 Modern radials
3 Comparison with inline engines
4 Other types of radial engine
4.1 Multi-row radials
4.2 Diesel radials
4.3 Compressed air radial engines
4.4 Model radial engines
5 See also
8 External links
Since the axes of the cylinders are coplanar, the connecting rods
cannot all be directly attached to the crankshaft unless mechanically
complex forked connecting rods are used, none of which have been
successful. Instead, the pistons are connected to the crankshaft with
a master-and-articulating-rod assembly. One piston, the uppermost one
in the animation, has a master rod with a direct attachment to the
crankshaft. The remaining pistons pin their connecting rods'
attachments to rings around the edge of the master rod. Extra "rows"
of radial cylinders can be added in order to increase the capacity of
the engine without adding to its diameter.
Four-stroke radials have an odd number of cylinders per row, so that a
consistent every-other-piston firing order can be maintained,
providing smooth operation. For example, on a five-cylinder engine the
firing order is 1, 3, 5, 2, 4 and back to cylinder 1. Moreover, this
always leaves a one-piston gap between the piston on its combustion
stroke and the piston on compression. The active stroke directly helps
compress the next cylinder to fire, making the motion more uniform. If
an even number of cylinders were used, an equally timed firing cycle
would not be feasible. The prototype radial Zoche aero-diesels
(below) have an even number of cylinders, either four or eight; but
this is not problematic, because they are two-stroke engines, with
twice the number of power strokes as a four-stroke engine.
The radial engine normally uses fewer cam lobes than other types. As
with most four-strokes, the crankshaft takes two revolutions to
complete the four strokes of each piston (intake, compression,
combustion, exhaust). The camshaft ring is geared to spin slower and
in the opposite direction to the crankshaft. The cam lobes are placed
in two rows for the intake and exhaust. For the example, four cam
lobes serve all five cylinders, whereas 10 would be required for a
typical inline engine with the same number of cylinders and
Most radial engines use overhead poppet valves driven by pushrods and
lifters on a cam plate which is concentric with the crankshaft, with a
few smaller radials, like the
Kinner B-5 and Russian Shvetsov M-11,
using individual camshafts within the crankcase for each cylinder. A
few engines use sleeve valves such as the 14-cylinder Bristol Hercules
and the 18-cylinder Bristol Centaurus, which are quieter and smoother
running but require much tighter manufacturing tolerances.[citation
A Continental radial engine, 1944
A Pratt & Whitney R-1340 radial engine mounted in Sikorsky H-19
C. M. Manly
C. M. Manly constructed a water-cooled five-cylinder radial engine in
1901, a conversion of one of Stephen Balzer's rotary engines, for
Langley's Aerodrome aircraft. Manly's engine produced 52 hp
(39 kW) at 950 rpm.
Jacob Ellehammer used his experience constructing
motorcycles to build the world's first air-cooled radial engine, a
three-cylinder engine which he used as the basis for a more powerful
five-cylinder model in 1907. This was installed in his triplane and
made a number of short free-flight hops.
Another early radial engine was the three-cylinder Anzani, originally
built as a W3 "fan" configuration, one of which powered Louis
Blériot XI across the English Channel. Before 1914,
Anzani had developed radial engines ranging from 3
cylinders (spaced 120° apart) — early enough to have been used on a
few French-built examples of the famous
Blériot XI from the original
Blériot factory — to a massive 20-cylinder engine of 200 hp
(150 kW), with its cylinders arranged in four rows of five
Most radial engines are air-cooled, but one of the most successful of
the early radial engines was the
Salmson 9Z series of nine-cylinder
water-cooled radial engines that were produced in large numbers during
the First World War. Georges Canton and Pierre Unné patented the
original engine design in 1909, offering it to the
the engine was often known as the Canton-Unné.
From 1909 to 1919 the radial engine was overshadowed by its close
relative, the rotary engine, which differed from the so-called
"stationary" radial in that the crankcase and cylinders revolved with
the propeller. It was similar in concept to the later radial, the main
difference being that the propeller was bolted to the engine, and the
crankshaft to the airframe. The problem of the cooling of the
cylinders, a major factor with the early "stationary" radials, was
alleviated by the engine generating its own cooling airflow.
World War I
World War I many French and other Allied aircraft flew with Gnome,
Le Rhône, Clerget and Bentley rotary engines, the ultimate examples
of which reached 250 hp (190 kW) although none of those over
160 hp (120 kW) were successful. By 1917 rotary engine
development was lagging behind new inline and V-type engines, which by
1918 were producing as much as 400 hp (300 kW), and were
powering almost all of the new French and British combat aircraft.
Most German aircraft of the time used water-cooled inline 6-cylinder
Motorenfabrik Oberursel made licensed copies of the Gnome and
Le Rhône rotary powerplants, and
Siemens-Halske built their own
designs, including the
Siemens-Halske Sh.III eleven-cylinder rotary
engine, which was unusual for the period in being geared so that the
engine spun at a higher speed and in the opposite direction to the
By the end of the war the rotary engine had reached the limits of the
design, particularly in regard to the amount of fuel and air that
could be drawn into the cylinders through the hollow crankshaft, while
advances in both metallurgy and cylinder cooling finally allowed
stationary radial engines to supersede rotary engines. In the early
Le Rhône converted a number of their rotary engines into
stationary radial engines.
By 1918 the potential advantages of air-cooled radials over the
water-cooled inline engine and air-cooled rotary engine that had
World War I
World War I aircraft were appreciated but were unrealized.
British designers had produced the
ABC Dragonfly radial in 1917, but
were unable to resolve the cooling problems, and it was not until the
1920s that Bristol and
Armstrong Siddeley produced reliable air-cooled
radials such as the
Bristol Jupiter and the Armstrong Siddeley
In the United States the National Advisory Committee for Aeronautics
(NACA) noted in 1920 that air-cooled radials could offer an increase
in power-to-weight ratio and reliability; by 1921 the U.S. Navy had
announced it would only order aircraft fitted with air-cooled radials
and other naval air arms followed suit. Charles Lawrance's J-1 engine
was developed in 1922 with Navy funding, and using aluminium cylinders
with steel liners ran for an unprecedented 300 hours, at a time when
50 hours endurance was normal. At the urging of the Army and Navy the
Wright Aeronautical Corporation
Wright Aeronautical Corporation bought Lawrance's company, and
subsequent engines were built under the Wright name. The radial
engines gave confidence to Navy pilots performing long-range overwater
Wright's 225 hp (168 kW) J-5 Whirlwind radial engine of 1925
was widely claimed as "the first truly reliable aircraft engine".
Giuseppe Mario Bellanca
Giuseppe Mario Bellanca to design an aircraft to
showcase it, and the result was the Wright-Bellanca 1, or WB-1, which
first flew later that year. The J-5 was used on many advanced aircraft
of the day, including Charles Lindbergh's Spirit of St. Louis, in
which he made the first solo trans-Atlantic flight.
In 1925 the American Pratt & Whitney company was founded,
competing with Wright's radial engines. Pratt & Whitney's initial
offering, the R-1340 Wasp, was test run later that year, beginning a
line of engines over the next 25 years that included the 14-cylinder,
twin-row Pratt & Whitney R-1830 Twin Wasp. More aircraft engines
of this design were produced than any other; nearly 175,000 were
In the United Kingdom the
Bristol Aeroplane Company
Bristol Aeroplane Company was concentrating
on developing radials such as the Jupiter, Mercury and sleeve valve
Hercules radials. Germany, Russia and Japan started with building
licensed versions of the Armstrong Siddeley, Bristol, Wright, or Pratt
& Whitney radials before producing their own improved
versions. France continued its development of various
rotary engines but also produced engines derived from Bristol designs,
especially the Jupiter.
Although other piston configurations and turboprops have taken over in
modern propeller-driven aircraft, Rare Bear, which is a Grumman F8F
Bearcat equipped with a
Wright R-3350 Duplex-Cyclone
Wright R-3350 Duplex-Cyclone radial engine, is
still the fastest piston-powered aircraft.
World War II
125,334 of the American twin-row, 18-cylinder Pratt & Whitney
R-2800 Double Wasp, with a displacement of 2,800 in³ (46 L) and
between 2,000 and 2,400 hp (1,500-1,800 kW), powered the American
single-engine Vought F4U Corsair, Grumman F6F Hellcat, Republic P-47
Thunderbolt, twin-engine Martin B-26 Marauder, Douglas A-26 Invader,
Northrop P-61 Black Widow, etc. The same firm's aforementioned
smaller-displacement (at 30 litres), Twin Wasp 14-cylinder twin-row
radial was used as the main engine design for the B-24 Liberator, PBY
Catalina and Douglas C-47, each design being among the production
leaders in all-time production numbers for each type of airframe
Wright Cyclone series
Wright Cyclone series twin-row radials powered American
warplanes: the nearly-43 litre displacement, 14-cylinder Twin Cyclone
powered the single-engine Grumman TBF Avenger, twin-engine North
B-25 Mitchell and some versions of the Douglas A-20 Havoc,
with the massive twin-row, nearly 55-litre displacement, 18-cylinder
Duplex-Cyclone powering the four-engine
Boeing B-29 Superfortress
Boeing B-29 Superfortress and
Over 28,000 of the German 42-litre displacement, 14-cylinder, two-row
BMW 801, with between 1,560 and 2,000 PS (1,540-1,970 hp, or
1,150-1,470 kW), powered the German single-seat, single-engine
Focke-Wulf Fw 190
Focke-Wulf Fw 190 Würger, and twin-engine Junkers Ju 88.
In Japan, most airplanes were powered by air-cooled radial engines
like the 14-cylinder
Mitsubishi Zuisei (11,903 units, e.g. Kawasaki
Mitsubishi Kinsei (12,228 units, e.g. Aichi D3A), Mitsubishi
Kasei (16,486 units, e.g. Kawanishi H8K),
Nakajima Sakae (30,233
Mitsubishi A6M and Nakajima Ki-43) and 18-cylinder
Nakajima Homare (9,089 units, e.g. Nakajima Ki-84).
Kawasaki Ki-61 and
Yokosuka D4Y were rare example of Japanese liquid-cooled inline engine
aircraft at that time but later, they also redesigned to fit radial
Kawasaki Ki-100 and Yokosuka D4Y3.
In Britain, Bristol produced both sleeve valved and conventional
poppet valved radials: of the sleeve valved designs, more than 57,400
Hercules engines powered the Vickers Wellington, Short Stirling,
Handley Page Halifax
Handley Page Halifax and some versions of the Avro Lancaster, over
8,000 of the pioneering sleeve-valved
Bristol Perseus were used in
various types, and more than 2,500 of the largest-displacement
production British radial from the Bristol firm to use sleeve valving,
Bristol Centaurus were used to power the
Hawker Tempest II, and
Hawker Fury. The same firm's poppet-valved radials included: around
Bristol Pegasus used in the Short Sunderland, Handley Page
Fairey Swordfish and over 20,000 examples of the firm's
1925-origin nine-cylinder Mercury were used to power the Westland
Bristol Blenheim and Blackburn Skua,
In the years leading up to World War II, as the need for armored
vehicles was realized, designers were faced with the problem of how to
power the vehicles, and turned to using aircraft engines, among them
radial types. The radial aircraft engines provided greater
power-to-weight ratios and were more reliable than conventional inline
vehicle engines available at the time. This reliance had a downside
though: if the engines were mounted vertically, as in the
M3 Lee and
M4 Sherman, their comparatively large diameter gave the tank a higher
silhouette than designs using inline engines.
The Continental R-670, a 7-cylinder radial aero engine which first
flew in 1931, became a widely used tank powerplant, being installed in
the M1 Combat Car, M2 Light Tank, M3 Stuart, M3 Lee, LVT-2 Water
The Guiberson T-1020, a 9-cylinder radial diesel aero engine, was used
in the M1A1E1, while the Continental R975 saw service in the M4
Sherman, M7 Priest,
M18 Hellcat tank destroyer, and the M44 self
propelled howitzer.
Four-stroke aircraft radial engine Scarlett mini 5
A number of companies continue to build radials today. Vedeneyev
produces the M-14P radial of 360–450 hp (270–340 kW) as
Sukhoi aerobatic aircraft. The M-14P is also used
by builders of homebuilt aircraft, such as the Culp Special, and Culp
Sopwith Pup, Pitts S12 "Monster" and the Murphy "Moose".
110 hp (82 kW) 7-cylinder and 150 hp (110 kW)
9-cylinder engines are available from Australia's Rotec Aerosport. HCI
Aviation offers the R180 5-cylinder (75 hp (56 kW)) and R220
7-cylinder (110 hp (82 kW)), available "ready to fly" and as
a build-it-yourself kit.
Verner Motor of the Czech Republic builds
several radial engines ranging in power from 25 to 150 hp (19 to
112 kW). Miniature radial engines for model airplanes are
available from O. S. Engines, Saito Seisakusho of Japan and
Shijiazhuang of China, and Evolution (designed by Wolfgang Seidel of
Germany, and made in India) and Technopower in the USA.[citation
Comparison with inline engines
The 1935 Monaco-Trossi race car, a rare example of automobile use.
Air-cooled radial engines often weigh less than equivalent
liquid-cooled inline engines.
Damage tolerance: Liquid cooling systems are generally more vulnerable
to battle damage. Even minor shrapnel damage can easily result in a
loss of coolant and consequent engine overheating, while an air-cooled
radial may be largely unaffected by minor damage.
Simplicity: Radials have shorter and stiffer crankshafts, a single
bank radial needing only two crankshaft bearings as opposed to the
seven required for a liquid-cooled six-cylinder inline engine of
Reliability:The shorter crankshaft also produces less vibration and
hence higher reliability through reduced wear and fatigue.[citation
Smooth running: It is typically easier to achieve smooth running with
a radial engine
Cooling: While a single bank radial permits all cylinders to be cooled
equally, the same is not true for multi-row engines where the rear
cylinders can be affected by the heat coming off the front row, and
air flow being masked.
Drag: Having the cylinders exposed to the airflow increases drag
considerably. The answer was the addition of specially designed
cowlings with baffles to force the air between the cylinders. The
first effective drag reducing cowling that didn't impair engine
cooling was the British
Townend ring or "drag ring" which formed a
narrow band around the engine covering the cylinder heads, reducing
National Advisory Committee for Aeronautics
National Advisory Committee for Aeronautics studied the
problem, developing the
NACA cowling which further reduced drag and
improved cooling. Nearly all aircraft radial engines since have used
NACA-type cowlings.[Note 1] Because radial engines are often wider
than similar inlines or vees, it is more difficult to design an
aircraft to minimize cross sectional area, a major cause of drag,
although by the beginning of the Second World War, this disadvantage
had largely disappeared as aircraft sizes increased, and multi-row
radials increased the power produced in relation to the cross
sectional area.
Power: Because each cylinder on a radial engine has its own head, it
is impractical to use a multivalve valvetrain on a radial engine.
Therefore, almost all radial engines use a two valve pushrod-type
valvetrain which may result in less power for a given displacement
than multi-valve inline engines. The limitations of the poppet valve
were largely overcome by the development of the sleeve valve, but at
the cost of increased complexity, maintenance costs and reduced
Visibility: Pilot visibility may be poorer due to the width of the
engine on single-engine aircraft, although tight fitting cowlings
helped reduce this factor somewhat. Equivalent inline engines often
resulted in overly long noses, which similarly impaired visibility
directly forward.
Installation: It is more difficult to ensure adequate cooling air in a
buried engine installation or with pusher configurations.[citation
Roughness: The smallest classes of radial engines, with three and five
cylinders, are very rough running and unreliable when compared to
equivalent inline, vee, or opposed engines which have ultimately
become more popular for light aircraft as a result.
While inline liquid-cooled engines continued to be common in new
designs until late in World War II, radial engines dominated
afterwards until overtaken by jet engines, with the late-war Hawker
Sea Fury and Grumman F8F Bearcat, two of the fastest production
piston-engined aircraft ever built, using radial engines.
Other types of radial engine
The Wasp Major, a four-row radial.
Originally radial engines had one row of cylinders, but as engine
sizes increased it became necessary to add extra rows. The first
radial-configuration engine known to use a twin-row design was the
160 hp Gnôme "Double Lambda" rotary engine of 1912, designed as
a 14-cylinder twin-row version of the firm's 80 hp Lambda
single-row seven-cylinder rotary, however reliability and cooling
problems limited its success.
Two-row designs began to appear in large numbers during the 1930s,
when aircraft size and weight grew to the point where single-row
engines of the required power were simply too large to be practical.
Two-row designs often had cooling problems with the rear bank of
cylinders, but a variety of baffles and fins were introduced that
largely eliminated these problems. The downside was a relatively large
frontal area that had to be left open to provide enough airflow, which
increased drag. This led to significant arguments in the industry in
the late 1930s about the possibility of using radials for high-speed
aircraft like modern fighters.
The solution was introduced with the
BMW 801 14-cylinder twin-row
Kurt Tank designed a new cooling system for this engine that
used a high-speed fan to blow compressed air into channels that carry
air to the middle of the banks, where a series of baffles directed the
air over all of the cylinders. This allowed the cowling to be tightly
fitted around the engine, reducing drag, while still providing (after
a number of experiments and modifications) enough cooling air to the
rear. This basic concept was soon copied by many other manufacturers,
and many late-WWII aircraft returned to the radial design as newer and
much larger designs began to be introduced. Examples
Bristol Centaurus in the Hawker Sea Fury, and the Shvetsov
ASh-82 in the Lavochkin La-7.
For even greater power, adding further rows was not considered viable
due to the difficulty of providing the required airflow to the rear
banks. Larger engines were designed, mostly using water cooling
although this greatly increased complexity and eliminated some of the
advantages of the radial air-cooled design. One example of this
concept is the BMW 803, which never entered service.
A major study[which?] into the airflow around radials using wind
tunnels and other systems was carried out in the US, and demonstrated
that ample airflow was available with careful design. This led to the
R-4360, which has 28 cylinders arranged in a 4 row corncob
configuration. The R-4360 saw service on large American aircraft in
World War II
World War II period. The US and
Soviet Union continued
experiments with larger radials, but the UK abandoned such designs in
favour of newer versions of the Centaurus and rapid movement to the
use of turboprops such as the
Armstrong Siddeley Python and Bristol
Proteus, which easily produced more power than radials without the
weight or complexity.
Large radials continued to be built for other uses, although they are
no longer common. An example is the 5-ton
Zvezda M503 diesel engine
with 42 cylinders in 6 rows of 7, displacing 143.6 litres
(8,760 cu in) and producing 3,942 hp (2,940 kW).
Three of these were used on the fast Osa class missile boats.[citation
Packard DR-980 diesel radial aircraft engine.
Nordberg Manufacturing Company
Nordberg Manufacturing Company two-stroke diesel radial engine for
power generation and pump drive purposes.
While most radial engines have been produced for gasoline, there have
been diesel radial engines. Two major advantages favour diesel engines
— lower fuel consumption and reduced fire risk.
Packard designed and built a 9-cylinder 980 cubic inch
(16,000 cm3) displacement diesel radial aircraft engine, the 225
horsepower (168 kW) DR-980, in 1928. On 28 May 1931, a DR-980
powered Bellanca CH-300, with 481 gallons of fuel, piloted by Walter
Edwin Lees and
Frederick Brossy set a record for staying aloft for 84
hours and 32 minutes without being refueled. This record stood for
55 years until broken by the Rutan Voyager.
Bristol Phoenix of 1928–1932 was successfully
flight tested in a
Westland Wapiti and set altitude records in 1934
that lasted until World War II.
In 1932 the French company Clerget developed the 14D, a 14-cylinder
two-stroke diesel radial engine. After a series of improvements, in
1938 the 14F2 model produced 520 hp (390 kW) at 1910 rpm
cruise power, with a power-to-weight ratio near that of contemporary
gasoline engines and a specific fuel consumption of roughly 80% that
for an equivalent gasoline engine. During WWII the research continued,
but no mass-production occurred because of the Nazi occupation. By
1943 the engine had grown to produce over 1,000 hp (750 kW)
with a turbocharger. After the war, the Clerget company was integrated
SNECMA company and had plans for a 32-cylinder diesel engine of
4,000 hp (3,000 kW), but in 1947 the company abandoned
piston engine development in favour of the emerging turbine
Nordberg Manufacturing Company
Nordberg Manufacturing Company of the United States developed and
produced a series of large two-stroke radial diesel engines from the
late 1940s for electrical production, primarily at aluminium smelters
and for pumping water. They differed from most radials in that they
had an even number of cylinders in a single bank (or row) and an
unusual double master connecting rod. Variants were built that could
be run on either diesel oil or gasoline or mixtures of both. A number
of powerhouse installations utilising large numbers of these engines
were made in the U.S.
Electro-Motive Diesel (EMD) built the "pancake" engines 16-184 and
16-338 for marine use.
Compressed air radial engines
A number of radial motors operating on compressed air have been
designed, mostly for use in model airplanes and in gas
Model radial engines
A number of multi-cylinder 4-stroke model engines have been
commercially available in a radial configuration, beginning with the
O.S. Max firm's FR5-300 five-cylinder, 3.0 cu.in.
(50 cm3) displacement "Sirius" radial in 1986. The American
"Technopower" firm had made smaller-displacement five- and
seven-cylinder model radial engines as early as 1976, but the OS
firm's engine was the first mass-produced radial engine design in
aeromodelling history. The rival Saito Seisakusho firm in Japan has
since produced a similarly sized five-cylinder radial four-stroke
model engine of their own as a direct rival to the OS design, with
Saito also creating a trio of three-cylinder radial engines ranging
from 0.90 cu.in. (15 cm3) to 4.50 cu.in. (75 cm3) in
displacement, also all now available in spark-ignition format up to
84 cm3 displacement for use with gasoline. The German Seidel
firm formerly made both seven- and nine-cylinder "large" (starting at
35 cm3 displacement) radio control model radial engines, mostly
for glow plug ignition, with an experimental fourteen-cylinder
twin-row radial being tried out - the American Evolution firm now
sells the Seidel-designed radials, with their manufacturing being done
in India.
List of aircraft engines
^ It has been claimed that the
NACA cowling generated extra thrust due
to the Meredith Effect, whereby the heat added to the air being forced
through the ducts between the cylinders expanded the exhausting
cooling air, producing thrust when forced through a nozzle. The
Meredith effect requires high airspeed and careful design to generate
a suitable high speed exhaust of the heated air - the
NACA cowling was
not designed to achieve this, nor would the effect have been
significant at low airspeeds. The effect was put to use in the
radiators of several mid-1940s aircraft that used liquid-cooled
engines such as the Spitfire and Mustang, and it offered a minor
improvement in later radial-engined aircraft, including the Fw-190.
^ "Firing order: Definition from". Answers.com. 2009-02-04. Retrieved
^ "zoche aero-diesels homepage". zoche.de. Retrieved 30 May
^ a b Vivian, E. Charles (1920). A History of Aeronautics. Dayton
History Books Online.
^ Day, Lance; Ian McNeil (1996). Biographical Dictionary of the
History of Technology. Taylor & Francis. p. 239.
^ Lumsden 2003, p. 225.
^ Nahum, Andrew (1999). The Rotary Aero Engine. NMSI Trading Ltd.
^ Bilstein, Roger E. (2008). Flight Patterns: Trends of Aeronautical
Development in the United States, 1918–1929. University of Georgia
Press. p. 26. ISBN 0-8203-3214-3.
^ Herrmann, Dorothy (1993). Anne Morrow Lindbergh: A Gift for Life.
Ticknor & Fields. p. 28. ISBN 0-395-56114-0.
^ "The Spirit of St. Louis". Charles Lindergh: An American Aviatior,
Retrieved 21 August 2015.
^ Lewis Vintage Collection (2018), "'Rare Bear' web site.". Retrieved:
6 January 2018.
^ Aerospaceweb, "Aircraft speed records." AeroSpaceWeb.org. Retrieved:
6 January 2018.
^ "Aircraft". Culp Specialties. Retrieved 2013-12-22.
Verner Motor range of engines". Verner Motor. Retrieved 23 April
^ "MONACO - TROSSI mod. da competizione". museoauto.it. Retrieved 10
^ Thurston, David B. (2000). The World's Most Significant and
Magnificent Aircraft: Evolution of the Modern Airplane. SAE.
p. 155. ISBN 0-7680-0537-X.
^ Some six-cylinder inline engines used as few as 3 bearing but at the
cost of heavier crankshafts, or crankshaft whipping.
^ Fedden, A.H.R. (28 February 1929). "
Air-cooled Engines in Service".
Flight. XXI (9): 169–173.
^ Becker, J.; The high-speed frontier: Case histories of four NACA
programs, 1920- SP-445, NASA (1980), Chapter 5: High-speed Cowlings,
Air Inlets and Outlets, and Internal-Flow Systems: The ramjet
^ Price 1977, p. 24.
^ Chapter 1: Development of the Diesel Aircraft Engine" Aircraft
Engine Historical Society — Diesels p.4 Retrieved: 30 January 2009.
^ Aviation Chronology Retrieved: 7 February 2009.
^ "Nordberg Diesel Engines". OldEngine. Retrieved 2006-11-20.
External link in publisher= (help)
^ Pearce, William (18 August 2014). "General Motors / Electro-Motive
16-184 Diesel Engine". oldmachinepress.com. Retrieved 30 May
^ "Bock radial piston compressor". Bock.de. 2009-10-19. Retrieved
^ Saito Seisakusho Worldwide E-book catalog, pages 9, 17 & 18
Wikimedia Commons has media related to Radial engine.
Cutaway radial engine in operation video on You Tube
Reciprocating engines and configurations
& number of cylinders
Inline / straight
V / Vee
Junkers Jumo 222
Cylinder head porting
Variable valve timing
Gasoline direct injection