Monthly Archives: September 2015

Junkers Jumo 223 Aircraft Engine

By William Pearce

In 1892, Hugo Junkers began experimental development of two-stroke, opposed-piston, gas engines. By 1910, Junkers had combined the opposed-piston principal with the diesel combustion cycle (compression ignition). Junkers investigated adapting this style of engine for aircraft use, but World War I and its aftermath prolonged development. In 1923, Junkers formed the Junkers Motorenbau (Jumo) to construct aircraft engines. Jumo’s first two-stroke, opposed-piston, diesel aircraft engine was commercially available in 1930. Originally known as the Jumo 4, the engine’s designation was changed in 1932 to Jumo 204.

The 24-cylinder Junkers Jumo 223 two-stroke, opposed-piston, diesel aircraft engine was one of the most unusual engines ever built. The engine’s coolant exit ports can be seen by the upper crankshaft. The two starters at the front of the engine engaged the propeller shaft.

Throughout the 1930s, Junkers developed a number of two-stroke, opposed-piston, diesel aircraft engines. There is no cylinder head on an opposed-piston engine. Rather, each cylinder has two pistons that move toward the center of the cylinder during the compression stroke. Ports in the cylinder wall allow the admission of air and expulsion of exhaust. These ports are covered and uncovered by the pistons as they move. The Junkers opposed-piston diesels were six-cylinder, inline engines with two crankshafts—one at the top of the engine and one at the bottom. Each crankshaft had a complete set of six pistons.

For installation in aircraft, there were practical limits to the Junker’s inline, opposed-piston engine configuration. Its double piston design made it a very tall engine, adding more cylinders to the Junkers diesels would have created a very long engine with a long crankshaft susceptible to torsional stresses. Increasing the engine’s bore and/or stroke would result in a larger engine with a lot of rotating mass, necessitating relatively low rpm. Engines capable of a continuous 2,000 hp (1,490 kW) output were needed for proposed large transoceanic aircraft, but an inline, opposed-piston aircraft engine able to produce 2,000 hp (1,490 kW) of continuous power was simply not feasible.

The Jumo 204 was the first diesel aircraft engine commercially available from Junkers. Its basic configuration was repeated in later Jumo diesels—collectively the most successful diesel aircraft engines produced.

By 1936, Junkers engineer Dr. Johannes Gasterstädt had come up with an opposed-piston engine configuration that would enable 2,000 hp (1,490 kW) in a compact package suitable for aircraft use. The configuration consisted of four cylinder banks positioned 90 degrees to each other so that they formed a rhombus—a square balanced on one point (◇). The pistons for two adjacent cylinder banks were connected to a crankshaft positioned at each corner of the rhombus. Each cylinder bank had six cylinders. The complete engine had four crankshafts, 24 cylinders, and 48 pistons.

Junkers’ rhombus-configured engine investigation was designated P2000. Dr. Gasterstädt passed away in 1937, and Prof. Otto Mader and Manfred Gerlach took over the P2000 project. By the end of 1937, a single cylinder test engine and a complete six-cylinder block had been built and run. In April 1938, the RLM (Reichsluftfahrtministerium or German Ministry of Aviation) redesignated the P2000 engine as the Jumo 223. By December 1939, a full-scale Jumo 223 engine was completed, and that engine was run-in by a dyno (the dyno turning the engine) in January 1940.

This picture of the separate castings that made up the Jumo 223 helps to illustrate the engine’s complexity. Note the scuffing and carbon deposits on the pistons, indicating they have been run.

The Jumo 223 was one of the most unusual engines ever built. The engine was constructed from two large and complex aluminum castings—one for the front of the engine and one for the rear. Each casting had four banks of three-cylinders. A large central gear was at the center of the engine where the two castings joined. Each crankshaft was made up of two main sections bolted together via a gear at its center. The gear on each crankshaft meshed with the central gear to transfer power from the crankshafts to the central gear. Drive shafts extended through the center of the engine from the front and rear of the central gear. The rear shaft powered the engine’s blower (weak supercharger) and accessories via a series of other gears. The front shaft led to the propeller. The central gear provided a .26 reduction in engine speed. At the front of the engine were two starters that engaged the propeller shaft to start the engine.

The Jumo 223’s central gear was powered by gears at the center of the engine’s four crankshafts. Note the fork-and-blade connecting rods.

The left and right crankshaft gears each drove separate camshafts for an upper and lower row of fuel injection pumps. These camshafts and the injection pumps were located near the left and right crankshafts. Cast directly under each row of injection pumps was a square port that ran along the engine. This port took air from the blower and delivered it to a small chamber around each steel cylinder liner. Air entered the cylinders via a series of holes around the cylinder liner’s circumference. The fuel injectors were located in the center of the cylinder. As the pistons moved toward each other, the intake holes were covered and the air was compressed. Diesel fuel was injected and ignited by the heat of compression. The expanding gases forced the pistons away from each other, uncovering the intake holes (for scavenging) and then the exhaust ports, which were located near the upper and lower crankshafts. Exhaust gases flowed out the ports in the cylinder liner into a small chamber surrounding the liner. The exhaust gases for each cylinder bank were collected by a manifold that led to a turbocharger at the rear of the engine. It is not clear if the turbocharger was ever tested, but there is one photo that shows a Jumo 223 with the turbocharger or a mockup of it. The pistons were connected to the crankshaft via fork-and-blade connecting rods. Each crankshaft was secured in the crankcase by eight main bearings.

A triangular port for coolant was cast on both sides of the engine near the upper and lower crankshafts. Coolant flowed from the coolant pump located on the bottom rear of the engine and into the lower triangular ports. The coolant circulated throughout the engine and exited near the upper crankshaft via the coolant ports at the front of the engine.

The central gear and front half of the engine is shown in this picture. Note the gears for the fuel injection pump camshafts by the left and right crankshafts. Coolant flowed through the triangular ports near the upper and lower crankshafts. Air flowed through the square ports near the left and right crankshafts.

The Jumo 223 engine had a 3.15 in (80 mm) bore and a 4.72 in (120 mm) stroke x 2 (for the two pistons per cylinder). Total displacement was 1,767 cu in (28.95 L). Without the propeller, the engine was 81.5 in (2.07 m) long, 48.8 in (1.24 m) wide, 53.0 in (1.345 m) tall, and weighed 3,086 lb (1,400 kg). The opposed pistons created a compression ratio of 17 to 1. With its planned intercooled turbocharger, the Jumo 223 was designed to produce 2,500 hp (1,860 kW) at an astonishing 4,400 rpm. That rpm would yield a fairly high average piston speed of 3,465 fpm (17.6 m/s). The Jumo 223 had a critical altitude rating of 1,800 hp (1,340 kW) at 16,404 ft (5,000 m) with the possibility of increasing the altitude to 32,808 ft (10,000 m) as the engine was further developed. Specific fuel consumption was .391 lb/hp/hr (238 g/kW/hr). The engine was contemplated for use in the four-engine Messerschmitt Me 264 long-range bomber, the six-engine Junkers EF100 commercial airliner, and other military aircraft projects.

The Jumo 223 engine ran for the first time on 27 February 1940. Without the turbocharger, the only boost came from the engine’s blower that was just intended to scavenge the cylinders. Peak high temperatures of 2,552 degrees F (1,400 degrees C) were encountered in the cylinders during combustion and caused pitting and seizure of the pistons. The issue was caused by the asymmetrical injection of fuel, a result of locating the injectors only on the outside of the engine, for ease of service, rather than having additional injectors inside the engine’s “square.”

The blower at the rear of the Jumo 223 can clearly be seen in this picture. The pipes leading away from the blower provided air to the passageways cast in the engine. The coolant pump is at the bottom of the engine.

Fuel injectors were modified, and tests continued throughout 1940. Three engines had been built by early 1941. In February 1941, the second engine was run for 100 hours and achieved a peak of 1,830 hp (1,360 kW) at 3,810 rpm. On 20 March 1941, the Jumo 223 passed the 2,000 hp (1,490 kW) mark by producing 2,040 hp (1,520 kW) at 3,980 rpm. During a 100 hour engine run in July 1941, crankshaft bolts and crankshafts were broken, indicating resonance vibration issues. In October 1941, the third engine completed a 100 hour test run at 1,500 hp (1,115 kW). The engine was run at a lower power because of the issues encountered when the Jumo 223 engine produced more power. The second engine was back in the test cell for a short run on 23 December 1941. The run set the mark for the highest power achieved by the Jumo 223 engine, producing 2,380 hp (1,770 kW) at 4,200 rpm.

Tests continued into 1942, but the engine’s reliability was a concern. The vibration issues seemed to be a result of the two-piece crankshafts and crankcase and the high rpm needed to produce the desired power. Along with the Jumo 223, Junkers was developing the Jumo 222—a 24-cylinder, spark ignition engine close to the same power and physical size as the Jumo 223, but lighter and of greater displacement. The Jumo 222 engine had more than its share of problems, and it made little sense to develop two engines in the same power class at the same time. In addition, developmental engines capable of more power than the Jumo 223 were needed.

This photo shows a Jumo 223 with a turbocharger. The exhaust manifolds can be seen leading to the turbocharger at the rear of the engine. Unfortunately, no information has been found regarding tests of this engine. It is possible that the turbocharger was only a mockup.

Development of the Jumo 223 as a production engine was halted in mid-1942. However, work on the engine continued, as it would serve as a model for a new, larger engine—the Jumo 224. By October 1942, six Jumo 223 engines were completed and two more were under construction. The eighth and last Jumo 223 prototype engine was run up to 2,200 hp (1,640 kW) on 28 February 1943. While this run was intended to be the last, Soviet forces had different ideas after the war. The Junkers factory was in Dessau, Germany and was part of the territory occupied by Soviet troops. The Soviets were interested in the Jumo 223 engine. The eighth example was run again on 23 March 1946 and for the last time on 4 April 1946. The last run was for a Soviet delegation and lasted 73 minutes. The run was halted after two pistons failed. Reportedly, at least one of the Junkers Jumo 223 engines was taken to State Factory No.500 in Tushino (now part of Moscow), Russia for further research, but no Jumo 223 engines are known to exist.

Note: There is no doubt that the Junkers Jumo opposed-piston engines in some way inspired the Napier Deltic, especially since Napier purchased licenses to build the Jumo 204 and 205 engines (to be built as the Culverin and Cutlass) in the 1930s. However, there is no indication that information on the Jumo 223 or 224 engines was applied to the design of the Deltic. In fact, the Deltic possessed many unique design characteristics, such as one crankshaft rotating the opposite direction compared to the other two.

The first Jumo 223 engine running on a test stand at the Junkers works in Dessau, Germany in early 1940.

Sources:
– Junkers Flugtriebwerke by Reinhard Müller (2006)
– Flugmotoren und Strahltriebwerke by Kyrill von Gersdorff, et. al. (2007)
– Opposed Piston Engines by Jean-Pierre Pirault and Martin Flint (2010)
– http://histomobile.com/dvd2.php?lien2=usa/tech/121-2.htm
– http://p-d-m.livejournal.com/28230.html

Yakovlev Yak-3 VK-108 Fighter

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By William Pearce

In 1944, Yakovlev sought to achieve higher performance from its Yak-3 fighter by installing a Klimov VK-108* engine. The standard Yak-3 was originally designated Yak-1M and designed in 1942 as a lightweight Yak-1. When this new aircraft entered production in 1943, it was redesignated Yak-3, taking the designation used for an earlier fighter prototype (the I-30) that did not enter production. Thus, Yak-3 production followed that of the Yak-7 and Yak-9 fighters.

The Yak-3 VK-108 built in the closing days of World War II was the fastest Soviet piston-powered aircraft. Note the heat-resistant panels behind the exhaust stacks and the inlet for the supercharger under the engine. The upper row of exhaust stacks can just be seen.

The Yak-3 was a maneuverable fighter that incorporated everything the Yakovlev team had learned by producing its previous fighter aircraft. The fuselage was of metal construction and covered by duralumin from the cockpit forward, with plywood covering the rear fuselage. The aircraft’s wings had duralumin spars and wooden ribs and stringers. The wings were skinned with plywood that was covered with doped fabric. The Yak-3’s control surfaces consisted of a duralumin frame covered with fabric. The standard Yak 3 was powered by a VK-105PF2 engine producing 1,290 hp (962 kW) for takeoff and 1,240 hp (925 kW) at 6,890 ft (2,100 m) altitude.

The VK-105 engine can trace its origin back to the 750 hp (559 kW) M-100 engine of 1935, which was a licensed-built Hispano-Suiza 12Ybrs. However, many changes had been implemented by the time VK-105 production began in 1939. For example, the M-100 had a single-stage, single-speed supercharger, a 5.91 in (150 mm) bore, and two valves per cylinder. The VK-105 had a single-stage, two-speed supercharger, a 5.83 in (148 mm) bore, and three valves per cylinder.

Constructed under the supervision of lead designer Vladimir Klimov, the VK-105 was a liquid-cooled, V-12 engine with provisions for firing a cannon through the propeller hub. With its 5.83 in (148 mm) bore and 6.69 in (170 mm) stroke, the engine had a total displacement of 2,142 cu in (35.1 L). Each cylinder bank had a single overhead camshaft that actuated the two intake valves and single exhaust valve. The engine’s intake and exhaust ports were located on the outer sides of the engine. The intake manifold for each cylinder bank incorporated three carburetors. The VK-105 had a compression ratio of 7.1 to 1.

This three-view drawing of the Yak-3 VK-108 shows that even with the cockpit moved aft 15.75 in (.40 m), the aircraft was very similar to a standard VK-105-powered Yak-3.

The ideal standard production Yak-3 had a top speed of 404 mph (650 km/h) at 14,108 ft (4,300 m) and 354 mph (570 km/h) at sea level. The aircraft could climb to 16,404 ft (5,000 m) in 4.2 minutes—averaging 3,906 fpm (19.8 m/s). The Yak-3 had an empty weight of 4,641 lb (2,105 kg) and a loaded weight of 5,864 lb (2,660 kg). The aircraft had a 20 mm cannon that fired through the propeller hub and two 12.7 mm machine guns mounted above the engine (the post-war Yak-3P was fitted with three 20 mm cannons).

It was on the standard Yak-3 platform that a VK-108 engine was substituted to create an aircraft of much higher performance. The VK-108 engine was a further evolution of the basic M-100 design, but by this time in its design history, the VK-108 had little in common with the original M-100 engine. The VK-108 was closely related to the VK-107 engine from which it was directly derived.

With the exception of the VK-107 engine, the VK-108 differed from previous Klimov engines by having new induction and exhaust systems, a new valve train with two intake and two exhaust valves per cylinder, strengthened components for increased rpm and power, an improved gear reduction, and increased boost via a redesigned supercharger drive. The VK-108 retained the 5.83 in (148 mm) bore, 6.69 in (170 mm) stroke, and 2,142 cu in (35.1 L) total displacement of previous Klimov engines.

Pictures of a Klimov VK-108 engine are hard to come by. Seen here is a VK-107A engine which was very similar to the VK-108. Note the silver induction manifold along the outer side of the engine. The yellow linkages are for the three carburetors. The remaining four intake runners provide air only into the cylinders. The exhaust manifolds in the Vee of the engine are missing; the VK-107 used six-into-one manifolds while the VK-108 used individual exhaust stacks. (Mike1979 Russia image via Wikimedia Commons)

The most unusual features of the VK-108 engine were its intake and exhaust systems and the function of its four valves per cylinder. Pressurized air from the single-stage, two-speed supercharger flowed through an intake manifold located on the outer side of each cylinder bank. Each intake manifold had seven intake runners that led to the cylinder head. Four of the runners provided air only; the remaining three runners had individual carburetors to supply the air/fuel mixture to the cylinders. The first runner supplied just air to the first cylinder. The second runner provided the air/fuel mixture to the first and second cylinders. The third runner supplied just air to the second and third cylinders. The fourth runner provided the air/fuel mixture to the third and fourth cylinders. The fifth runner supplied just air to the fourth and fifth cylinders. The sixth runner provided the air/fuel mixture to the fifth and sixth cylinders. The seventh runner supplied just air to the sixth cylinder. So each carburetor supplied air/fuel for two cylinders; the engine had a total of six carburetors.

The two intake valves were positioned in tandem on the cylinder’s centerline. One intake valve in each cylinder opened to let supercharged air into the cylinder while the other intake valve opened to bring in the air/fuel mixture from a carburetor. The air intake valve opened 65 degrees before and closed after the air/fuel intake valve. This allowed the supercharged air to scavenge the cylinder and also aid in its cooling.

One exhaust valve was positioned on the outer side of the engine, and the other exhaust valve was on the Vee side. This configuration meant that there were separate exhaust ports on each side of the cylinder head. The VK-108 engine had one row of six exhaust stacks on the outer side of the cylinder bank and one row of exhaust stacks on the Vee side of the cylinder bank. The complete engine had four rows of six exhaust stacks.

Basic drawing of the Klimov VK-108 valve arrangement. A single overhead camshaft acted directly on the intake valves and actuated the exhaust valves via a follower.

A single overhead camshaft was used with three lobes for each cylinder. The center lobe acted on a follower that actuated both exhaust valves. One of the other lobes actuated the fresh air valve, and the last lobe actuated the air/fuel mixture valve. This arrangement allowed for the completely different valve timing and duration of the two intake valves.

The VK-108 was cleared for up to 8.5 psi (0.6 bar) of boost and had a compression ratio of 6.75 to 1. The engine produced 1,850 hp (1,380 kW) at 3,200 rpm for takeoff, 1,650 hp (1,230 kW) at 4,921 ft (1,500 m), and 1500 hp (1,119 kW) at 14,764 ft (4,500 m). The VK-108 weighed 1,731 lb (785 kg).

The installation of the VK-108 engine necessitated some changes of the Yak-3 airframe. Built under the supervision of A. N. Kanookov, the Yak-3 VK-108 had a new radiator, oil cooler, and propeller installed. A new cowling was constructed to accommodate the two additional rows of exhaust stacks. Heat-resistant panels were added behind each of the four rows of exhaust stacks. The cowling also omitted the ports for the two machine guns which were deleted from the Yak-3 VK-108. The supercharger air inlet was relocated under the engine, and the aircraft’s ailerons were skinned in duralumin rather than fabric. Because of the heavier engine, the cockpit was moved 15.75 in (.40 m) aft to keep the aircraft’s center of gravity within limits.

The VK-108-powered Yak-3’s first flight was on 19 December 1944 with Viktor L. Rastorgooyev at the controls. The aircraft had a wingspan of 30 ft 2 in (9.2 m), a length of 28 ft 1 in (8.55 m), an empty weight of 5,251 lb (2,382 kg), and a loaded weight of 6,385 lb (2,896 kg). With no armament and a light fuel load, the Yak-3 VK-108 achieved a top speed of 463 mph (745 km/h) at 20,636 ft (6,290 m), making it the fastest piston-powered Soviet aircraft. The aircraft also exhibited a phenomenal climb rate, reaching 16,404 ft (5,000 m) in 3.5 minutes—averaging 4,687 fpm (23.8 m/s). The Yak-3 VK-108 had a service ceiling of 34,121 ft (10,400 m).

The upper exhaust stacks are well illustrated in this rear view of the Yak-3 VK-108. The aircraft had excellent performance, but the engine was not reliable.

Although the Yak-3 VK-108’s performance was very good, fight testing the aircraft was difficult because of engine issues. The VK-108’s high rpm and boost resulted in constant overheating problems. Vibration issues and excessive smoke were also encountered. The problems were so severe that flight testing was halted on 8 March 1945, with the aircraft only accumulating 1 hour and 17 minutes of flight time.

A second VK-108-powered Yak-3 was built in late 1945 under the supervision of V. G. Grigor’yev. This aircraft was reportedly armed with a 20 mm cannon that fired through the propeller hub and an additional 20 mm cannon mounted above the engine and offset to the left—each gun had 120 rounds of ammunition. A new radiator with additional surface area was installed to prevent overheating issues. However, engine trouble persisted. Despite its excellent performance, the Yak-3 VK-108 project was abandoned in favor of more reliable piston aircraft and jets.

*The Soviet Union changed some aircraft engine designations from starting with an “M” to starting with the designer’s initials. In 1944, the M-105 engine became the VK-105; the M-107 became the VK-107; and the M-108 became the VK-108—VK standing for Vladimir Klimov, the engine’s lead designer. The VK designation was used throughout this article for simplicity.