Radial engine
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" in some other languages.
The radial configuration was commonly used for aircraft engines before gas turbine engines became predominant.
Engine operation
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.
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. Its cam lobes are placed in two rows; one for the intake valves and one for the exhaust valves. The radial engine normally uses fewer cam lobes than other types. For example, in the engine in the animated illustration, four cam lobes serve all 10 valves across the five cylinders, whereas 10 would be required for a typical inline engine with the same number of cylinders and valves.
Most radial engines use overhead
History
Aircraft
In 1903–1904 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.[2]
Another early radial engine was the three-cylinder Anzani, originally built as a W3 "fan" configuration, one of which powered Louis Blériot's Blériot XI across the English Channel. Before 1914, Alessandro 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 cylinders apiece.[1]
Most radial engines are
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.[4]
In
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 engines.
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 1920s 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
In the United States the
Wright's 225 hp (168 kW)
In 1925 the American
In the United Kingdom the Bristol Aeroplane Company was concentrating on developing radials such as the Jupiter, Mercury, and sleeve valve Hercules radials. Germany, Japan, and the Soviet Union started with building licensed versions of the Armstrong Siddeley, Bristol, Wright, or Pratt & Whitney radials before producing their own improved versions.[citation needed] France continued its development of various rotary engines but also produced engines derived from Bristol designs, especially the Jupiter.
Although other piston configurations and
125,334 of the American twin-row, 18-cylinder
The American
The Soviet
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 Würger, and twin-engine Junkers Ju 88.
In Japan, most airplanes were powered by air-cooled radial engines like the 14-cylinder
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, 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, the Bristol Centaurus were used to power the Hawker Tempest II and Sea Fury. The same firm's poppet-valved radials included: around 32,000 of Bristol Pegasus used in the Short Sunderland, Handley Page Hampden, and Fairey Swordfish and over 20,000 examples of the firm's 1925-origin nine-cylinder Mercury were used to power the Westland Lysander, Bristol Blenheim, and Blackburn Skua.
Tanks
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.[citation needed]
The
]The
Modern radials
A number of companies continue to build radials today.
Comparison with inline engines
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 engine may be largely unaffected by minor damage.[16] Radials have shorter and stiffer crankshafts, a single-bank radial engine needing only two crankshaft bearings as opposed to the seven required for a liquid-cooled, six-cylinder, inline engine of similar stiffness.[17]
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.[18]
A potential disadvantage of radial engines is that 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 drag. The 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]
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.
Hydrolock
Whenever a radial engine remains shut down for more than a few minutes, oil or fuel may drain into the combustion chambers of the lower cylinders or accumulate in the lower intake pipes, ready to be drawn into the cylinders when the engine starts. As the piston approaches
Other types of radial engine
Multi-row radials
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.[citation needed]
The solution was introduced with the BMW 801 14-cylinder twin-row radial. 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.[citation needed] Examples include the Bristol Centaurus in the Hawker Sea Fury, and the Shvetsov ASh-82 in the Lavochkin La-7.[citation needed]
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.[citation needed]
A major study[
Large radials continued to be built for other uses, although they are no longer common. An example is the 5-ton
Diesel radials
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.[citation needed]
- Packard
Packard designed and built a 9-cylinder 980 cubic inch (16.06 litre) displacement diesel radial aircraft engine, the 225 horsepower (168 kW)
- Bristol
The experimental 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.[citation needed]
- Clerget
In 1932 the French company Clerget developed the 14D, a 14-cylinder
- Nordberg
The
- EMD
Electro-Motive Diesel (EMD) built the "pancake" engines 16-184 and 16-338 for marine use.[25]
- Zoche
Zoche aero-diesels are a prototype radial design that 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 per crankshaft rotation.[26][third-party source needed]
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 compressors.[27]
Model radial engines
A number of multi-cylinder 4-stroke
See also
- List of aircraft engines
- Swashplate engine
- Quasiturbine
- Wankel engine
Notes
- 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.[19] 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,[20] and it offered a minor improvement in later radial-engined aircraft, including the Fw 190.
References
- ^ a b Vivian, E. Charles (1920). A History of Aeronautics. Dayton History Books Online. Archived from the original on 2009-05-23. Retrieved 2008-07-05.
- ISBN 0-415-06042-7.
- ^ Lumsden 2003, p. 225.
- ISBN 1-900747-12-X.
- ISBN 1-85260-163-9.
- ISBN 978-0-8203-3214-7.
- ISBN 0-395-56114-0.
- ^ "The Spirit of St. Louis". Charles Lindergh: An American Aviator, Retrieved 21 August 2015.
- ^ - Archived (Nov. 11, 2013) manufacturer's product page, R-1830 Retrieved: 7 February 2019
- ^ Lewis Vintage Collection (2018), "'Rare Bear' web site." Archived 2013-10-27 at the Wayback Machine. Retrieved: 6 January 2018.
- ^ Aerospaceweb, "Aircraft speed records." AeroSpaceWeb.org. Retrieved: 6 January 2018.
- ^ "Aircraft". Culp Specialties. Retrieved 2013-12-22.
- ^ "HCI (USA)". Aerospace Engines A to Z. Retrieved 2023-02-11.
- ^ "Verner Motor range of engines". Verner Motor. Archived from the original on 6 October 2014. Retrieved 23 April 2013.
- ^ "MONACO - TROSSI mod. da competizione". museoauto.it. Retrieved 10 November 2016.
- ISBN 0-7680-0537-X.
- ^ Some six-cylinder inline engines used as few as three bearings, 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 investigation
- ^ Price 1977, p. 24.
- Department of the Air Force. 1953. pp. 53–54.
- ^ Chapter 1: Development of the Diesel Aircraft Engine" Archived 2012-02-12 at the Wayback Machine Aircraft Engine Historical Society — Diesels p.4 Retrieved: 30 January 2009.
- ^ Aviation Chronology Retrieved: 7 February 2009.
- ^ "Nordberg Diesel Engines". OldEngine. Archived from the original on 2018-09-19. Retrieved 2006-11-20.
- ^ Pearce, William (18 August 2014). "General Motors / Electro-Motive 16-184 Diesel Engine". oldmachinepress.com. Retrieved 30 May 2016.
- ^ "zoche aero-diesels homepage". zoche.de. Retrieved 30 May 2016.
- ^ "Bock radial piston compressor". Bock.de. 2009-10-19. Archived from the original on 2011-10-08. Retrieved 2011-12-06.
- ^ Saito Seisakusho Worldwide E-book catalog, pages 9, 17 & 18