SGP Sla 16 X-16 front

SGP Sla 16 (Porsche Type 203) X-16 Tank Engine

By William Pearce

In 1943, Simmering-Graz-Pauker (SGP) in Vienna, Austria was tasked by the Heereswaffenamt (HWA, German Army Weapons Agency) to develop a new main tank engine for the Heer (German Army). The requested engine was an air-cooled diesel that would only require minor modifications to be interchangeable with the existing engine installed in various German tanks. The existing engine was the liquid-cooled Maybach HL230 V-12 that produced 690 hp at 3,000 rpm and displaced 1,409 cu in (23.1 L). However, reliability issues with the HL230 limited the engine to 2,500 rpm and 600 hp (447 kW). The demand for an air-cooled diesel was dictated by Adolf Hitler, and SGP was to work closely with Porsche GmbH to develop the new engine.

SGP Sla 16 X-16 front

Front view of the basic Simmering-Graz-Pauker Sla 16 engine without the airbox, turbochargers, or cooling fans. The intake manifolds and some baffling can be seen in the 45-degee Vee formed by the cylinders. Note that the intake ports are on the top of the cylinders.

Led by Ferdinand Porsche, the Porsche design and consulting firm had experience with air-cooled engines and took on the brunt of the preliminary design work for the new engine. Ferdinand Porsche had been discussing tanks and diesel tank engines with Hitler since 1942. Designed by Porsche’s Paul Netzker, the new engine was an X-16 layout consisting of four banks of four cylinders. The cylinder banks were spaced 135 degrees apart on the top and bottom and 45 degrees apart on the sides. The engine was issued Porsche designation Type 203 and SGP designation Sla 16 (which will be used for the remainder of this article).

The Simmering-Graz-Pauker Sla 16 was made of a sheet steel crankcase and used a single crankshaft with four master connecting rods. Three articulating connecting rods attached to each master rod. The cylinders were comprised of a substantially finned aluminum cylinder head screwed onto a finned, steel cylinder barrel. At the front of each cylinder bank was an injection pump that fed fuel to that bank’s cylinders. The fuel injector was positioned in the cylinder head and angled toward the 135-degree side of the cylinder. At the base of each cylinder bank was a camshaft positioned on the 135-degree side. The four camshafts were driven from the rear of the engine and operated the two valves per cylinder via pushrods and rockers. The intake and exhaust ports were located on the 45-degree side of the cylinders, with the intake port on the top of the cylinder.

SGP Sla 16 X-16 section

Transverse cross section of the Sla 16 illustrates the engine’s X configuration and the drive for the cooling fans. Note the master and articulated connecting rods and the four exhaust manifolds in the left side of the drawing.

Induction air was drawn in through a large filter placed above the engine. The air then flowed through twin turbochargers located at the engine’s rear. Two separate intake manifolds branched out from each turbocharger, with one manifold supplying the upper cylinder bank and the other manifold supplying the lower cylinder bank. The exhaust from two cylinders was paired in a single manifold so that each side of the engine had four exhaust manifolds leading to the turbocharger. The turbochargers were made by Brown Boveri and spun at a maximum of 28,000 rpm. The boost from the turbochargers was conservative at 7.3 psi (.5 bar).

To cool the engine, a fan was placed above and outside each of the two upper cylinder banks. The fans extracted warm air out from between the tight, 45-degree cylinder bank sections, which were closely baffled. As a result, cool air was drawn in through the cylinders’ cooling fins and into the 45-degree Vee. Each fan was driven via a beveled gear shaft that extended from the cooling fan to the rear of the engine. Here, an enclosed drive shaft with two universal joints and beveled gears took power from the crankshaft at the extreme rear of the engine and powered the shafts that led to the fans. The cooling fans were developed by FKFS (Forschungsinstitut für Kraftfahrwesen und Fahrzeugmotoren Stuttgart or Research Institute of Automotive Engineering and Vehicle Engines Stuttgart). The fans were 20.5 in (520 mm) in diameter and operated at 2.05 times crankshaft speed. Two oil coolers flanked each engine cooling fan.

SGP Sla 16 X-16 rear

Without all of the engine’s accessories, the drive for the cooling fans can be seen protruding from the back of the Sla 16 engine. The push rod tubes and fuel injectors are visible on the far cylinder bank. The four passageways in the rear baffle are for the exhaust manifolds.

Helical gears increased the speed of the Sla 16’s output shaft to 1.5 times crankshaft speed. The speed increase was needed because of the operating speed difference between the Sla 16 and the Maybach HL230. In order to be a direct replacement, the 2,000 rpm Sla 16 needed to have an output speed multiplier to match the 3,000 rpm HL230. Since the Sla 16’s crankshaft was in the middle of the engine’s X configuration, the step-up gears also lowered the output shaft to align with the existing transmission used with the V-12 HL230.

The Sla 16 had a 14.5 to 1 compression ratio, a 5.3 in (135 mm) bore, and a 6.3 in (160 mm) stroke. The engine’s total displacement was 2,236 cu in (36.6 L). The Sla 16 was forecasted to produce 750 hp (559 kW) at 2,000 rpm. With the cooling fans, the complete engine was approximately 5.5 ft (1.68 m) long, 8.2 ft (2.50 m) wide, and 3.8 ft (1.15 m) tall. The Sla 16 weighed 4,960 lb (2,250 kg).

By late 1943, a single-cylinder 140 cu in (2.3 L) test engine had been built and designated Type 192. The Type 192 engine passed a 48-hour test run on 6 November 1943. The single cylinder engine produced 47 hp (35 kW) at 2,100 rpm, which scaled to an output of 752 hp (561 kW) for the complete 16-cylinder engine. The listed output did not take into consideration the power needed to drive the cooling fans. With favorable results from the Type 192 tests, work moved forward on the full-size Sla 16 X-16 engine.

SGP Sla 16 X-16 fans rear

Rear view of the complete Sla 16. The airbox on the top of the engine fed air into the turbochargers via a bifurcated manifold. Note the oil coolers and cooling fans. The enclosed drive shafts for the cooling fans can been seen below the turbocharger exhaust outlets.

The first Sla 16 engine was tested in late 1944 and produced 770 hp (574 kW) at 2,200 rpm without the cooling fans. It took around 95 hp (71 kW) to drive the cooling fans, which reduced the engine’s output to 685 hp (511 kW). On 10 January 1945, two Sla 16 test engines had completed a combined 300 hours of test operation. Porsche’s involvement with the engine had essentially stopped by this time. Plans were made for Sla 16 production to start in June 1945 at the Steyr-Daimler-Puch factory in Austria. Steyr-Daimler-Puch was producing Daimler-Benz DB 603 engines (although the factory built DB 605s from October 1942 to October 1943), and production of the DB 603 would give way for the Sla 16. Some changes were incorporated into the Sla 16 production engines, such as the use of two fuel injection pumps rather than the four pumps used on the prototype engines. It is possible that the production engines carried the Porsche Type 220 designation. However, the Sla 16 engine never entered production because of the German surrender in May 1945.

A Sla 16 engine was reportedly installed in the chassis of the experimental Panzerjäger Tiger Ausf. B (Tank Hunter Tiger Variant B or Jagdtiger, Hunting Tiger) and underwent some feasibility tests. Initially, the lower cylinder banks ran hot, but modifications to the cooling fans and air baffles resolved the issue. In addition, a Panzerkampfwagen Tiger Ausf. B (Armored Fighting Vehicle Tiger Variant B), or Tiger II, was modified to accept a Sla 16 engine and waited for the engine’s installation. However, the installation was never completed. The engine was also proposed for the VK 45.02 P2 (Porsche Type 181C), which was never built. The majority of Sla 16 parts, tooling, and equipment were captured by the Soviet Union at the end of World War II.

SGP Sla 16 X-16 stand

The left image (engine inverted) shows the camshaft drives at the rear of the engine. In the center image (engine upright), the engine’s output can be seen below the crankshaft. The right image (engine almost inverted) displays the cylinder’s valves. The exhaust ports on the side of the cylinders are easily seen, while the intake ports on the top of the cylinders have been covered.

In late 1943, FKFS contemplated using the 140 cu in (2.3 L) cylinder from the Sla 16 as the starting point for a new tank engine to power the proposed Panzerkampfwagen Panther II. The FKFS engine consisted of two V-12 engines mounted 90-degrees apart on a common crankcase. The 24-cylinder engine would have displaced 3,354 cu in (55.0 L) and produced 1,100 hp (820 kW). Four engine-driven, FKFS cooling fans would have been installed, with two above each V-12 engine section. The FKFS 24-cylinder engine project did not progress beyond the drawing board, and the Panther II was never built.

A larger version of the X-16 engine was investigated under the Porsche Type 212 designation. This engine had a 5.9 in (150 mm) bore and a 6.7 in (170 mm) stroke. Total displacement of the Type 212 was 2,933 cu in (48 L), and the engine was forecasted to produce 1,500 hp (1,119 kW) at 2,500 rpm. A 183 cu in (3.0 L), single-cylinder test engine was evaluated as the Type 213, but it does not appear that the tests were completed or that a complete Type 212 engine was built. The Type 212 was proposed to power the Panzerkampfwagen VIII Maus (Porsche Type 205), but the engine was rejected by Albert Speer, the Minister of Armaments.

SGP Sla 16 X-16 test

The Sla 16 engine under test in late 1944 without cooling fans or turbochargers. However, the test equipment most likely provided forced induction.

Notes: Sources are split on the Porsche Type designation for the 750 hp (559 kW) Sla 16. Many refer to the engine as the Type 203, and just as many use Type 212. In addition, Type 180, 181, 192, and 220 are also used. Type 180 was a tank design (VK 45.02 P) that originally used Porsche’s Type 101 V-10 engine. Type 181 was the same tank reengined with the Sla 16 after the V-10 encountered problems. As mentioned in the article, Type 192 was a single-cylinder test engine for the Sla 16. Since Type 213 was a single-cylinder test engine for the larger X-16, it makes sense for the larger X-16 to be Type 212. This leaves Type 203 as the logical choice for the Sla 16. As stated in the article, Type 220 may have been the production version of the Sla 16.

Furthermore, a number of sources list the larger, 1,500 hp (1,119 kW) engine as an X-18. However, there can be no X-18 engine; to add up to a total of 18 cylinders, two banks would need to have five cylinders each, and two banks would need to have four cylinders each. Such an armament would be ill-advised. Most likely, “X-16” was either mistyped or misread as “X-18” on some scarce document captured at the end of World War II, and the misnomer stuck. However.

Lastly, the Porsche Type 181B (VK 45.02 P2) tank design was to be powered by two 16-cylinder engines. The 16-cylinder engine was an air-cooled diesel that produced 370 hp (276 kW) at 2,000 rpm. Reportedly, the design of this engine was a collaboration with Deutz. Some sources indicate the engine was a V-16, while others state it was an X-16. It is not clear whether the smaller 16-cylinder engine had anything in common with the Sla 16 or what its Type number was. The small 16-cylinder engine had a 4.3 in (110 mm) bore, a 5.1 in (130 mm) stroke, and a total displacement of 1,206 cu in (19.8 L). The small 16-cylinder engine was never built.

SGP Sla 16 X-16 general arrangement rear

General arrangement drawing of the Sla 16 engine.

Professor Porsche’s Wars by Karl Ludvigsen (2014)
Der Panzer-Kampfwagen Tiger und seine Abarten by Walter J. Spielberger (1998)
AFV Weapons Profile: Elefant and Maus (+ E-100) by Walter J. Spielberger and John Milsom (October 1973)
Wunibald I. E. Kamm – Wegbereiter der modernen Kraftfahrtechnik by Jurgen Potthoff and Ingobert C. Schmid (2012)
Daimler-Benz in the Third Reich by Neil Gregor (1998)

Otto-Langen Atmospheric Engine

Otto-Langen Atmospheric Engine

By William Pearce

Before devoting his life to engine development, Nicolaus Otto worked selling merchandise to grocery stores around Cologne, Germany, but he always had an interest in science and technology. Otto became entirely focused on internal combustion engines around 1860, after reading about Étienne Lenoir’s engine. He was so fascinated that he had an example built for experimentation in 1861.

Otto-Langen 1866 drawing

Drawing of the Otto-Langen engine circa 1866. Note the piston (K) and its rack (X) in the cylinder (A). The drawing also shows an early version of the over-running clutch (S).

Otto tried a wide-range of modifications to the Lenoir atmospheric engine in search of better performance. One interesting finding was that when the engine’s cylinder and piston were used to compress the incoming air and fuel charge, the resulting power stroke had enough energy to rotate the crankshaft through several revolutions. While Otto had discovered a number of improvements for the Lenoir atmospheric engine, creating a compression engine was a bit beyond the contemporary technology. Otto had already spent his saving and what he had borrowed from friends. To continue his research and develop an atmospheric engine, he needed money.

For some time, Eugen Langen ran his family’s sugar refining business in Cologne, Germany, but, like Nicolaus Otto, his true passion was for science and technology. Langen had become a fairly wealthy man from the family business and from a few of his own ventures. In 1863, his business was running smoothly, and he was looking for a new enterprise. Langen had read of the Lenoir engine and contemplated how such a device could benefit industry.

Otto-Langen repro overrunning clutch

A reproduction of the over-running clutch built by Wayne Grenning of Grenning Models. Counterclockwise movement of the gear brings the shoes to their stops and allows the gear to rotate free from the inner hub. When the gear rotates clockwise, the shoes slide on their rollers until they are wedged between the gear and the inner hub, locking the two together. The clutch was originally designed by Franz Reuleaux, and later clutches used on the Otto-Langen had three shoes. (Wayne Grenning image)

Exactly how Otto and Langen met is not known. Perhaps Otto sought out Langen as a financial backer, or perhaps they met through a third party. Regardless, Langen witnessed Otto’s unrefined atmospheric engine running on 9 February 1864. Langen saw potential in the engine and its inventor. Langen and Otto formed N.A. Otto & Cie on 31 March 1864 to develop and manufacture internal combustion engines.

Otto-Langen repro piston rack

Other reproduction parts built by Wayne Grenning. The piston with its rack attached are shown outside of the cylinder housing column. The piston and rack weigh around 80 lb (36 kg). The studs seen at the base of the column are where the slide valve mounts. (Wayne Grenning image)

Three years of experimentation and refinement occurred before N.A. Otto & Cie had a marketable engine that was superior to the competition. The Otto-Langen .5 hp (.37 kW), single-cylinder, atmospheric engine made its public debut at the 1867 International Exposition in Paris, France (Exposition universelle de 1867). Nothing about the engine appeared remarkable, but interest piqued when a demonstration showed that the engine consumed half the gas of other engines of the same power. The engine’s remarkably efficient performance won it the grand prize.

The Otto-Langen engine consisted of a vertical column that formed a single cylinder. A free piston was installed in the cylinder, with the piston head facing down. Attached to the upper part of the piston was a rack gear that extended out vertically above the engine. The rack engaged the one-way, over-running (sprag) clutch that was mounted on the engine’s main drive shaft. The clutch was the first of its type and was designed by Franz Reuleaux. The flywheel was mounted on one side of the main drive shaft, and the belt drive pulley was mounted on the other side. On the flywheel side of the main drive shaft was the main drive gear. The main gear engaged an accessory gear, which drove the accessory shaft. Typically, the accessory gear was larger and had more teeth than the main gear. The difference resulted in an accessory gear speed slower than that of the main gear, which helped reduce impact forces on the accessory gear drive.

Otto-Langen Rough Tumble Engineers top

Top view of the Otto-Langen engine at the Rough and Tumble Engineers Historical Association in Kinzers, Pennsylvania. It is the oldest internal combustion engine in the Americas. Installed on the main drive shaft (top) from left to right are the flywheel, main drive gear, over-running clutch, and belt drive. Installed on the accessory shaft (bottom) from left to right are the accessory drive gear, secondary eccentric, main eccentric, and ratcheting gear. (Rough and Tumble Engineers image)

The accessory gear was mounted on and drove the accessory shaft. Also on the accessory shaft were two eccentrics and a ratcheting gear. The ratcheting gear was attached directly to and turned with the accessory shaft. The two eccentrics operated independently of the accessory shaft and were mostly stationary. A pawl would engage the ratcheting gear and drive the main eccentric. This eccentric lifted the piston and rack assembly and also drove the second eccentric, which operated the hand-scraped slide valve at the base of the engine via a control rod. When the eccentrics raised the piston and slide valve, the air and fuel mixture was draw into the cylinder. The slide valve then aligned to a port with an internal flame that ignited the gaseous mixture in the cylinder.

On the power stroke, the free piston had unrestricted upward movement in the cylinder and took advantage of the complete expansion of gasses during the combustion process. As the piston moved up, the rack attached to the upper side of the piston moved freely on the clutch. As atmospheric pressure and gravity pulled the rack and piston back down, the rack engaged the over-running clutch that drove the main drive shaft. A flyball governor was driven by the accessory shaft and controlled an exhaust valve. With a closed exhaust valve, the piston could not fully descend. As the speed of the accessory shaft decreased below the desired rpm, the governor opened the exhaust valve, which allowed the piston to descend. This movement of the piston and its attached rack assembly tripped an arm that engaged the pawl to the ratcheting gear, driving the eccentrics and subsequently firing the engine.

Otto-Langen reproduction pawl

Grenning’s full-size reproduction of a .5 hp (.37 kW) Otto-Langen engine under power. The accessory shaft is in the foreground, and the pawl in the center of the image is about to engage the ratcheting gear. The ratcheting gear will then drive the eccentrics. (Wayne Grenning image)

The internal flame that ignited the gaseous mixture in the cylinder was extinguished on each power stroke. The internal flame was relit by an external flame via a port on the slide valve that aligned as the valve moved. The Otto-Langen engine was run on illuminating gas, which was typically distributed at around .07 psi (.005 bar). When firing, the engine needed more gas than the line could supply. An accumulator bag was used, which held a surplus of gas. The Otto-Langen engine would draw from the bag when firing, and the gas would be replenished between firings from the low-pressure supply line.

For cooling, an integral water jacket surrounded the cylinder. The Otto-Langen engine employed thermosyphon circulation. As the water was heated, it expanded out of a port in the upper part of the water jacket and flowed to an external reservoir. At the same time, cool water was drawn from the external reservoir and to the engine. The engine relied on manual, external lubrication, which could be (and was) supplied while the engine was in operation. The Otto Langen’s design and features allowed for a quick start and continuous running.

Otto-Langen reproduction base

The base of Grenning’s Otto-Langen reproduction shows the safety slide valve (with brass connector) and the main slide valve behind it. The main slide valve was operated by the secondary eccentric. The rod with the coiled spring is the governor-controlled exhaust valve. Later engines did not have the safety slide valve, and the governor controlled the pawl’s engagement. (Wayne Grenning image)

Because of the free piston, cylinder firing was not directly linked to the rpm of the drive shaft. With a light load, the cylinder could fire once for every 25 revolutions of the main drive shaft. Under heavy loads, the cylinder could fire once for every two revolutions. The engine was typically operated with a main drive shaft speed of 90 rpm. However, the speed could be increased to 120 rpm or decreased to around 30 rpm. The high and low speeds were dictated by the mechanical limitations of the eccentrics and slide valve movement.

Otto-Langen repro complete

Grenning’s completed Otto-Langen reproduction is a fantastic display of a modern-day master-craftsman’s appreciation of old-world engineering. After spending years researching the Otto-Langen, it took Grenning 14 months to build his reproduction engine. (Wayne Grenning image)

The cylinder housing on the early Otto-Langen engines was fluted and resembled a Grecian column, but this expensive feature was not included on later engines. In addition, early engines did not have a governor and had a second slide valve. The secondary slide valve acted as a safety feature to cut the gas flow to the cylinder. Extensive engine operation showed that the safety slide valve was not needed, and it was eliminated to cut down on manufacturing costs.

The success at the International Exposition in Paris brought in a flood of orders that N.A. Otto & Cie could not fulfill due to a lack of existing capital. Ludwig August Roosen-Runge, a businessman from Hamburg, lent financial support, and the company was renamed Langen, Otto & Roosen in 1869. That same year, the factory was relocated to Deutz, Germany. More capital was sought and found, and a new company, Gasmotoren-Fabrik Deutz AG (Deutz), was established in January 1872. That same year, Gottlieb Daimler and his protégé, Wilhelm Maybach, joined Deutz.

Maybach was tasked with redesigning the Otto-Langen engine to simplify its construction and lower its production cost. The updated design eliminated the accessory shaft and ran everything from the main drive shaft. The governor controlled cylinder firing with the pawl and not with the exhaust valve. The updated engine was available at the end of 1873.

Otto-Langen repro drive

View of the accessory shaft on Grenning’s engine. The left side of the shaft drives the flyball governor. In the background are the black gas accumulator bag and copper water reservoir. (Wayne Grenning image)

The .25 hp (.19 kW) version was the smallest Otto-Langen, and it stood 7 ft (2.1 m) tall and weighed 900 lb (408 kg). To make more power, the engine was basically scaled-up to a larger size. However, the design of the Otto-Langen engine limited just how large the engine could be while still being practical. With its vertical cylinder and long rack attached to the piston, the Otto-Langen was a tall and heavy engine. There were practical limits on the engine’s height and weight. The vertical piston had a tendency to send significant vibrations through the ground with every stroke. This shook foundations, could damage nearby equipment, and made most above ground level installations unfeasible. The largest Otto-Langen engine was the 3 hp (2.24 kW) model. It was 12.7 ft (3.9 m) tall and weighed 4,450 lb (2,018 kg).

The .5 hp (.37 kW) Otto-Langen engine created its power at 110 rpm at the flywheel with 40 power strokes per minute. The cylinder had a 5.9 in (150 mm) bore and a 38.7 in (985 mm) maximum stroke. Maximum displacement was 1,062 cu in (17.4 L). The engine was 8.8 ft (2.65 m) tall and weighed 1,600 lb (725 kg). The piston and rack assembly of the .5 hp (.37 kW) engine weighed around 80 lb (36 kg).

The 2 hp (1.49 kW) engine operated at 90 rpm at the flywheel with 30 power strokes per minute. The cylinder had a 12.5 in (318 mm) bore and a 40.5 in (1,030 mm) maximum stroke. Maximum displacement was 4,992 cu in (81.8 L). The 2 hp (1.49 kW) engine was 10.7 ft (3.25 m) tall and weighed 4,000 lb (1,815 kg). The piston and rack alone weighed 116 lb (52.6 kg).

Otto-Langen no1 Technikum

The first Otto-Langen engine is on display in the Deutz Technikum Engine Museum in Cologne, Germany. This engine has no governor, and the safety slide valve was removed sometime after the engine was built. The gas accumulator bag is on the right. (Wayne Grenning image)

By 1875, there was competition in the form of George Brayton’s Ready Motor and other engines. Otto felt that the atmospheric engine had reached its zenith, yet Daimler was still interested in pursuing the type. Tension existed between Otto and Daimler, and the men did not work well together. In 1876, Otto first ran his four-stroke, internal combustion engine using the combustion cycle that would revolutionize the world. Development of the Otto-Langen engine stopped around 1877, and production of the engine at Deutz stopped around 1878. Daimler and Maybach left Deutz in 1880 and formed a new company to develop engines and automobiles. The Deutz company is still in business designing and manufacturing internal combustion engines.

Between 1864 and 1882, Deutz and its predecessors built 2,649 Otto-Langen engines. Around 2,000 more engines were built by subsidiaries or under license in Austria (Langen & Wolf), Belgium (E. Schenck & Co.), Britain (Crossley Brothers), and France (Sarazin / Panhard). For a brief time, the Otto-Langen atmospheric engine led the industry, and it was the world’s first commercially successful internal combustion engine. Perhaps the Otto-Langen’s greatest achievement was to serve as a stepping stone to the four-stroke, Otto-cycle engine. Around 23 Otto-Langen engines survive, including the very first engine built, which won the grand prize in 1867. The over 150-year-old first engine is on display at the Deutz Technikum Engine Museum in Cologne, Germany, and it is run on special occasions.

Wayne Grenning of Grenning Models has built a number of reproduction Otto-Langen engines. He gives a detailed explanation of the engine’s operation in the video below.

Internal Fire by C. Lyle Cummins, Jr. (1989)
Flame Ignition by Wayne S. Grenning (2014)
Startup & Instructional Explanation of 1867 Otto Langen Engine Operation by Wayne Grenning (5 March 2017)
“Improvements in Air-Engines,” US patent 67,659 by Eugen Langen and Nicol. Auguste Otto (granted 13 August 1867)
“Improvements in Gas-Motor Engines,” US patent 153,245 by Gottlieb Daimler (granted 21 July 1874)

NAA XA2J Super Savage top

North American XA2J Super Savage Medium Bomber

By William Pearce

At the close of World War II, the United States Navy lacked the ability to carry out a nuclear strike. The nuclear bombs of the time were large and heavy, and no aircraft operating from an aircraft carrier could accommodate the bomb’s size and weight. The Navy did not want nuclear strikes to be the sole responsibility of the Army Air Force (AAF). In addition, the Navy felt that launching an attack with a medium-sized aircraft from a carrier that was hundreds of miles from the target offered advantages compared to large AAF bombers traveling thousands of miles to the target. On 13 August 1945, the Navy sponsored a design competition for a carrier-based, nuclear-strike aircraft. The competition was won by the North American AJ Savage.

NAA AJ Savage

Typical example of a production North American AJ-1 Savage, with its R-2800 engines on the wings and J33 jet in the rear fuselage. The intake for the jet was just before the vertical stabilizer and was closed when the jet was not in use.

First flown on 3 July 1948, the AJ Savage was a unique aircraft that spanned the gap between the piston-engine and jet-engine eras. The Savage was powered by two Pratt & Whitney R-2800 engines and a single Allison J33 turbojet that was mounted in the rear fuselage. The jet engine was used for takeoff and to make a final, high-speed dash to the target. In December 1947, before the AJ prototype had even flown, North American Aviation (NAA) proposed an improved version of the Savage that benefited from the continued advancement of turboprop engines. Designated NA-158 by the manufacturer, a mockup was inspected in September 1948, and the Navy ordered two examples and a static test airframe in October 1948—only three months after the AJ Savage’s first flight. The new aircraft was designated XA2J Super Savage, and the two prototypes ordered were given Navy Bureau of Aeronautics (BuAer) serial numbers 124439 and 124440.

Originally, the North American XA2J Super Savage was to be very different from the AJ Savage, but the jet engine in the rear fuselage would be retained. As the project moved through 1949, emphasis was placed on improving the XA2J’s deck performance over that of its predecessor. As a result, the XA2J became an entirely new aircraft but still resembled the AJ Savage. A mockup of the updated XA2J design, the NA-163, was inspected by the Navy in September 1949, and approval was given for NAA to begin construction.

NAA XA2J Super Savage Apr 1949

Concept drawing of the XA2J Super Savage from April 1949. Note how the aircraft bears little resemblance to the AJ Savage. The intake for the jet engine can be seen just before the vertical stabilizer. The pilot sat alone under the canopy, and the co-pilot/bombardier and gunner sat in the fuselage, behind and below the pilot.

The XA2J had the same basic configuration as its predecessor but was a larger aircraft overall. The Super Savage was of all metal construction and utilized tricycle landing gear. The high-mounted, straight wing was equipped with a drooping leading edge and large trailing edge flaps. To be brought below deck on a carrier, the aircraft’s wings and tail folded hydraulically. The pressurized cockpit accommodated the three-man crew, which consisted of a pilot, a co-pilot/bombardier, and a gunner. The pilot and co-pilot/bombardier sat side-by-side, and the rear-facing gunner sat behind them. Cockpit entry was via a side door, and an escape chute provided emergency egress out of the bottom of the aircraft. The co-pilot/bombardier was responsible for the up to 10,500 lb (4,763 kg) of bombs stored in a large, internal bomb bay. The gunner managed the radar-equipped tail turret with its two 20 mm cannons and 1,000 rpg. The defensive armament was never fitted to the prototype.

The XA2J did away with the mixed propeller and jet propulsion of the earlier AJ Savage; instead, it relied on two wing-mounted Allison T40 turboprop engines. The T40 engine was made up of two Allison T38 engines positioned side-by-side and coupled to a common gear reduction for contra-rotating propellers. Either T38 power section could be decoupled from the gear reduction, and the remaining engine could drive the complete contra-rotating propeller unit. The engine produced 5,332 hp (3,976 kW) and 1,225 lbf (4.7 kN) of thrust, for a combined output equivalent to 5,850 hp (4,362 kW). The Aeroproducts propellers used on the XA2J had six-blades and were 15 ft (4.57 m) in diameter.

NAA XA2J Super Savage ground

The XA2J Super Savage as built only had turboprop engines. In this image, the wide propellers installed on the aircraft have different cuff styles. Markings on the propeller installed on the right engine would seem to indicate that the propeller (rounded cuff) is being tested. Note the cockpit entry side door and open bomb bay doors.

The Super Savage had a 71 ft 6 in (21.8 m) wingspan and was 70 ft 3 in (21.4 m) long and 24 ft 2 in (7.4 m) tall. Folded, the wingspan dropped to 46 ft (14 m), and height decreased to 16 ft (4.9 m). The aircraft had an empty weight of 35,354 lb (16,036 kg) and a maximum takeoff weight of 61,170 lb (27,746 kg). Two fuel tanks at each wing root and two fuselage fuel tanks gave the aircraft a total fuel capacity of 2,620 gallons (9,918 L). The XA2J’s estimated top speed was 451 mph (726 km/h) at 24,000 ft (7,315 m), and its cruise speed was 400 mph (644 km/h). The aircraft had a ceiling of 37,500 ft (11,430 m) and a combat range of 2,180 miles (3,508 km) with an 8,000 lb (3,629 kg) bomb load.

NAA believed that the Super Savage airframe could be more than just a carrier-based medium bomber. The company developed designs in which various equipment packages could be installed in the aircraft’s bomb bay. The XA2J could be changed into a photo-recon platform with the installation of a camera package. Or the aircraft could become a tanker once it was outfitted with a 1,400 gallon (5,300 L) fuel tank in the bomb bay and a probe-and-drogue refueling system. A target tug system was also designed.

NAA XA2J Super Savage top

The Super Savage over the desert of California. The Allison T40 engine created trouble for every aircraft in which it was installed. The jet exhaust divider between the T38 engine sections can just be seen at the rear of the engine nacelle. Both propellers installed on the aircraft have square cuffs.

Construction of the first XA2J Super Savage prototype (BuAer 124439) began in late 1949 and progressed rapidly. However, Allison experienced massive technological problems developing the T40 engines, and they were not delivered until late 1951. The XA2J finally made its first flight on 4 January 1952 and was piloted by Robert Baker. The aircraft took off from Los Angeles International Airport and was ferried to Edwards Air Force Base (Edwards) for testing. By the time of the XA2J’s first flight, superior aircraft designs, namely the Douglas A3D (A-3) Skywarrior, were nearing completion. In addition, Allison never solved all of the T40’s issues, and the engines were limited to 5,035 hp (3,755 kW).

Testing at Edwards revealed some difficulties with the Super Savage. All aircraft powered by the complex T40 experienced numerous power plant failures, and the XA2J was no exception. The Super Savage was around 4,000 lb (1,814 kg) overweight and was never tested to its full potential. The highest speed obtained during testing was just over 400 mph (644 km/h). Even the aircraft’s estimated performance did not offer a significant advantage over that of the AJ Savage already in service. The XA2J project was cancelled in mid-1953, and the second prototype (BuAer 124440) was never completed.

NAA XA2J Super Savage in flight

The Super Savage had an aggressive appearance that gave the impression that the aircraft could live up to its name. However, it was outclassed by the Douglas A3D (A-3) Skywarrior and had performance on par with the AJ Savage it was intended to replace.

North American Aircraft 1934-1999 Volume 2 by Kevin Thompson (1999)
Aircraft Descriptive Data for North American XA2J-1 (June 1953)
American Attack Aircraft Since 1926 by E.R. Johnson (2008)
The Allison Engine Catalog 1915–2007 by John M. Leonard (2008)
“They didn’t quite… 5: Turbine-Driven Savage,” Air Pictorial Vol. 21 No. 12. (December 1959);all

MAN 6-cyl WWI

MAN Double-Acting Diesel Marine Engines

By William Pearce

Maschinenfabrik Augsburg-Nürnberg (MAN) was involved with diesel engines since their inception. From 1893 to 1897, MAN* worked with Rudolf Diesel to develop his combustion cycle and build the first diesel engines. When Diesel’s engine first ran in 1894, it produced around 3 hp (2 kW) at 88 rpm. Just 15 years later, MAN was contracted to develop a diesel engine capable of 12,000 hp (8,948 kW) at 120 rpm.

MAN 6-cyl WWI

The MAN six-cylinder, double-acting, two-stroke, 12,000 hp, diesel marine engine under construction. The three workers provide a good reference as to the engine’s size.

The remarkable rise of diesel power caught the eye of many militaries. Anton von Rieppel, general manager of MAN at Nürnberg (Nuremberg), felt that diesels had matured enough to power the latest battleships. In August 1909, Rieppel proposed a new engine to the Reichsmarine (Germany Navy). By late 1909, a development contract was issued to MAN for the construction of a 12,000 hp (8,948 kW), six-cylinder diesel engine. Six of the engines would be needed to produce the 70,000 hp (52,199 kW) required for the latest German battleships. Given the uncharted territory MAN was traversing, a three-cylinder engine would be built first to prove that a six-cylinder engine could meet the desired specifications. Other companies were also contracted to build competing engines.

MAN’s design was an inline, two-stroke engine that used double-acting cylinders. Each of the closed cylinders had a combustion chamber at its top and bottom. Originally, each combustion chamber had four intake valves, four fuel valves, and two safety valves that were also used for air-starting the engine. The safety valves were located at the center of the combustion chamber. The locations of the remaining valves were split between passageways that branched off from either side of the upper combustion chamber. With the exception of the safety valves, the valves for each side of each combustion chamber were actuated by a single underhead camshaft. This configuration had a total of 20 valves for each cylinder and four camshafts for the engine. The final (seventh) combustion chamber design retained the four intake valves but had only two fuel valves and one safety valve (located in the upper combustion chamber). The changes lowered the number of valves per cylinder to 15. Exhaust ports were located in the middle of the cylinder and were covered and uncovered by the piston.

MAN 6-cyl section

A drawing of the final cylinder design of the World War I engine. Fuel valves are on the left of the drawing, and intake valves are on the right. The exhaust manifold is positioned at the center of the cylinder. Note how the two piston halves are bolted together.

The double-headed piston was constructed of two parts. The lower part was connected to a non-articulating piston rod, and the upper part of the piston was bolted to the lower part. The piston rod was connected to the connecting rod via a cross head. The cross head slid in vertical channels on both sides of the inner crankcase. Oil was circulated through the piston to cool it. The oil flowed up through passageways in the piston rod and into the lower part of the piston. The oil then flowed to the upper part of the piston and down the center of the piston rod. The upper and lower combustion chamber sections were bolted to the center section of the cylinder, and the assembly was attached to the crankcase. A water jacket surrounded the cylinder. The center section of the cylinder and of the upper combustion chamber were made of cast iron. The crankcase, piston, lower combustion chamber, and many other components were made of cast steel. Each complete cylinder assembly was around 12 ft (3.5 m) tall, and the engine was over 24 ft 3 in (7.4 m) tall.

Each cylinder had a 33.4 in (850 mm) bore and a 41.3 in (1,050 mm) stroke. Since the piston was double-acting and there was a lower combustion chamber, each cylinder’s displacement was nearly doubled, as if it were two conventional cylinders. The upper combustion chamber displaced 36,359 cu in (595.8 L). However, the connecting rod passing through the lower combustion chamber took up around 3,021 cu in (49.5 L) of volume. Displacement for the lower combustion chamber was approximately 33,337 cu in (546.3 L). The cylinder’s total displacement was around 69,697 cu in (1,142 L). The three-cylinder test engine displaced 209,094 cu in (3,426 L), and the six-cylinder engine displaced 418,187 cu in (6,853 L). The engine drove three double-acting air pumps to scavenge the engine. Each air pump had a 52.0 in (1,320 mm) bore and a 31.5 in (800 mm) stroke.

The three-cylinder engine was first run on 12 March 1911. Severe delays occurred as technological issues were encountered. In January 1912, a failure caused the intake manifolds to explode, killing ten workers. By June 1913, the three-cylinder engine had met its requirement by producing 5,400 hp (4,027 kW) at 90% power. Construction of a six-cylinder engine followed.

The six-cylinder engine was first run on 23 February 1914. By September 1914, the engine was producing 10,000 hp (7,457 kW) at 130 rpm. By this time, World War I was underway; priorities shifted, and shortages were encountered. A single cylinder made a five-day run at over 2,000 hp (1,491 kW) in April 1915. On 24 March 1917, the six-cylinder engine produced 12,200 hp (9,098 kW) at 135 rpm for 12 hours. In April 1917, the engine passed its five-day acceptance test, running at 90% power and producing 10,800 hp (8,054 kW) at 130 rpm.

MAN M9Z 42-58

One of the MAN M9Z 42/58 engines built for installation in a Deutschland-class cruiser. At least 24 of the engines were made. The fuel injection pumps for each cylinder can be seen above and below the housing along the engine’s side.

By mid-1917, it was obvious that due to delays and the war, the engine would never be used, and the other five engines would never be built. MAN decided to test the engine to its limits. The engine test stand at MAN could not absorb the maximum anticipated power of the complete six-cylinder engine, so just one cylinder was run. On 16 October 1917, a single cylinder produced 3,570 hp (2,662 kW) at 145 rpm. If all six cylinders could match that performance, the complete engine would produce 21,420 hp (15,973 kW). The engine was later scrapped as a result of the Treaty of Versailles.

After World War I, Germany entered a period of economic ruin. It was not until 1926 that MAN designed the first engine in a new series of double-acting, two-stroke diesels. Overseen by engineer Gustav Pielstick, the new engines were similar in concept to the double-acting engine built during World War I, but they incorporated many new features. Pielstick had developed MAN submarine engines during World War I but did not work on the large double-acting engine.

MAN MZ42-58

Sectional drawings of a MAN M9Z 42/58 engine. The rotary exhaust valves are positioned in a runner between the cylinder and the exhaust manifold. Note the long through bolts that pass through the entire engine.

The main structure of the new engines was made of steel plates welded together. This construction kept the engine rigid, but made it lighter than using cast components. Pairs of very long through bolts were positioned between the cylinders. They held the center part of the cylinder, crankcase, and crankshaft together and allowed for the disassembly of individual cylinders without compromising the integrity of the overall engine. The double-headed pistons were again made in two parts. From the top, the piston rod passed through the lower part of the piston, which was threaded to a shoulder on the rod. The upper part of the piston was threaded to the top of the piston rod. The skirt of the upper part of the piston slid into the skirt of the lower part. A sealed gap between the skirts allowed for the differential expansion of the individual piston halves. The piston was oil-cooled, like the World War I engine. The lower part of the piston rod was threaded into the cross head. Unlike the World War I engine, the cross head of the new series slid in a mount attached only to one side of the crankcase.

The new engine had no valves in the cylinder. In the middle of the cylinder were two rows of intake ports. The top row serviced the upper combustion chamber, and the bottom row serviced the lower combustion chamber. Air was forced into the cylinder by an auxiliary “pumping” engine. Fuel entered the cylinder via a single injector in the upper combustion chamber and two injectors on each side of the piston rod in the lower combustion chamber. The injectors were water-cooled and provided fuel to each cylinder at 3,625–4,350 psi (250–300 bar). Mounted to the side of the engine was a camshaft that drove the fuel injection pumps. Each cylinder had an upper and lower injection pump that respectively provided fuel to the upper and lower combustion chambers. Both pumps for each cylinder were controlled by a single lobe on the camshaft.

MAN LZ 19-30 section

Sectional view of the MAN L11Z 19/30 shows that the rotary exhaust valves have been placed inside of the exhaust manifold to conserve space. Otherwise, the engine and cylinder are very similar to the larger engines.

Each combustion chamber had its own exhaust ports which led to separate manifolds for the upper and lower combustion chambers. The intake and exhaust ports were on the same side of each cylinder, and their relative positions allowed the cylinder to be loop scavenged. Rotary valves inside of the exhaust manifolds closed off the exhaust port before the piston and allowed the cylinder to be charged with incoming air. The valve itself was supported by a hollow tube through which water was circulated to keep the valve cool. Otherwise, the intake and exhaust ports were covered and uncovered by the piston. All the engines of the new series used the same basic cylinder design, but the engines differed in their bore, stroke, and number of cylinders.

After cylinder testing, the first complete engine built of this type was the D4Z 23/34. In MAN nomenclature, “4” represents the number of cylinders per bank and “23/34” the bore/stroke in cm. With its 9.1 in (230 mm) bore and 13.4 in (340 mm) stroke in a double-acting cylinder, the engine displaced around 6,591 cu in (108 L). The D4Z 23/34 produced 1,000 hp (746 kW) at 800 rpm. The D4Z 23/34 was run in 1927, and tests went well.

On 27 March 1928, the Reichsmarine contracted MAN to develop a larger engine for what would become the cruiser Leipzig. Four M7Z 30/34 engines powered the middle shaft in the Leipzig, while two other shafts were powered by steam turbines. The seven-cylinder M7Z 30/34 engine had a 11.8 in (300 mm) bore and a 13.4 in (340 mm) stroke. Each engine displaced around 19,624 cu in (321.6 L) and produced 3,100 hp (2,312 kW) at 800 rpm, giving a total of 12,400 hp (9,247 kW) for the four engines.

Compared to a steam turbine, the diesel engine took up less space, was simpler to operate, had nearly instant power, and could suffer damage without disastrous consequences. Shrapnel passing through a diesel engine would shut down the engine, most likely one of several. Shrapnel passing through a steam boiler would cause the boiler to explode, most likely killing some of the crew in the room.

MAN LZ 19-30

Front view of the MAN L11Z 19/30. The camshaft ran to the side of the cylinders and controlled the fuel injection pumps. The handle on the front of the camshaft was used to adjust the camshaft when the engine was run in reverse. (Hermann Historica image)

The Reichsmarine decided to use only diesel-power for the Deutschland-class Panzerschiffe (armored ships) cruisers: Deutschland (later renamed Lützow), Admiral Scheer, and Admiral Graf Spee. In these ships, four nine-cylinder engines powered each of two propeller shafts. Engines were ordered in October 1928 for the Deutschland, on 9 January 1930 for the Admiral Scheer, and on 14 March 1931 for the Admiral Graf Spee. The engine type for these ships was the M9Z 42/58. With a 16.5 in (420 mm) bore and a 22.8 in (580 mm) stroke, the nine-cylinder, double-acting engine displaced 84,359 cu in (1,382 L). Each engine produced 7,100 hp (2,494 kW) at 450 rpm and weighed around 110 tons (100 tonnes). Combined, the eight engines provided a total of 56,800 hp (42,356 kW).

The artillery training ship (Artillerieschulschiff) Bremse was ordered in 1931. Powering the ship were eight M8Z 30/44 engines—four engines on each of the two propeller shafts. The M8Z 30/44 was the same engine used in the Leipzig but with an additional cylinder. The eight-cylinder M8Z 30/44 engine had a 11.8 in (300 mm) bore and a 13.4 in (340 mm) stroke. It displaced 22,427 cu in (367.5 L) and produced 3,350 hp (2,498 kW) at 600 rpm, giving a total of 26,800 hp (19,985 kW) for the eight engines.

The light cruiser Nürnberg was ordered in 1933 and used a combination of diesel engines and steam turbines, like its sister ship, the Leipzig. Four M7Z 32/44 engines powered the ship’s center shaft. The engines were larger than the ones used on the Leipzig but appear to have the same rated output. The M7Z 32/44 engine had a 12.6 in (320 mm) bore and a 17.3 in (440 mm) stroke. The seven-cylinder engine displaced 28,894 cu in (473 L) and produced around 3,100 hp (2,312 kW) at 600 rpm, giving a total of 12,400 hp (9,247 kW) for the four engines.

MAN piston rods

The piston, piston rod, connecting rod, and crankshaft section for a M9Z 65/95. The piston halves were threaded onto the piston rod, which was threaded to the cross head. An oil line can be seen attached to the cross head. The assembly is displayed in the Deutsches Museum in Munich. (enwo image)

Around 1933, the Reichsmarine looked to steam turbines to fulfill their power needs, so the funding for MAN’s large diesel marine engines was severely cut. At the same time, a new engine was needed to power the latest German airships, the LZ 129 Hindenburg and LZ 130 Graf Zeppelin II. Pielstick adapted the basic design of the double-acting diesel to create a lighter, smaller engine, the L7Z 19/30. After the Daimler-Benz DB 602 engine was selected to power the airships, MAN added four cylinders to the L7Z engine to create the 11-cylinder L11Z 19/30 for marine use. The L11Z 19/30 used an engine-driven blower to provide intake air and cylinder scavenging. The engine had a 7.48 in (190 mm) bore, a 11.81 in (300 mm) stroke, and a total displacement of around 10,979 cu in (179.9 L). The L11Z 19/30 had a maximum output of 2,000 hp (1,491 kW) at 1,050 rpm and a continuous output of 1,400 hp (1,044 kW) at 900 rpm. The engine was approximately 157 in (4.0 m) long, 39 in (1.0 m) wide, and 98 in (2.5 m) tall. It weighed around 8,378 lb (3,800 kg) and was reversible. L11Z 19/30 engines were used in torpedo boats, with three engines installed in each Schnellboot S 14 to S 17 (S 14 was launched in January 1936) and four engines installed in the Versuchs Schnellboot VS 5 (launched in January 1941). The three L11Z 19/30 engines from S 15 survived. One engine is in the MAN Museum in Augsburg; one is in the Deutsches Museum in Munich, and one is in a private collection.

In 1935 and under Nazi leadership, the Reichsmarine was renamed Kriegsmarine. That same year, the Kriegsmarine initiated the design of new H-class battleships. The first of the ships would be powered by diesel engines. In 1938, the Kriegsmarine showed a renewed interest in large diesel marine engines, and MAN’s developmental funding was substantially increased. MAN developed the M9Z 65/95 engine for the H-class battleships in 1938. Four of these engines would power each of three shafts. The nine-cylinder engine had a 25.6 in (650 mm) bore, a 37.4 in (950 mm) stroke, and a total displacement of approximately 330,945 cu in (5,423 L). The M9Z 65/95 weighed around 248 tons (225 tonnes) and had a continuous output of 12,500 hp (9,321 kW) at 256 rpm and an emergency output of 13,750 hp (10,253 kW) at 265 rpm. The 12 engines gave a total of 150,000 hp (111,855 kW) for continuous operation and 165,000 hp (123,040 kW) for emergencies. In early 1939, 24 M9Z 65/95 engines were ordered by the Kriegsmarine, followed later in the year by another order for 24 engines. However, the orders were cancelled in late 1939, and only one test engine was built. This engine was tested in 1940 but was destroyed during an Allied air raid. A piston and rod assembly survived and is displayed in the Deutsches Museum in Munich. No H-class battleships were completed.

MAN V12Z 32-44 section

Sectional view of the MAN V12Z 32/44 engine illustrates a cylinder design similar to that used on the inline engines but with a completely different manifold arrangement. The large upper manifold was the intake, and the three other manifolds were for exhaust. Note the camshaft and fuel injection pumps on the outside of the cylinder banks.

By 1939, Pielstick used the basic cylinder design of previous engines to create larger and more powerful engines in a V configuration with 24 cylinders. The V-24 engines had a 45 degree bank angle and a new manifold arrangement, but the cylinder design and other components were similar to the previous inline engines. Positioned in the Vee of the engine was a lower exhaust manifold that collected the exhaust gases from the lower combustion chambers. Above this manifold was the intake manifold that serviced all the cylinders. Each cylinder bank had an upper exhaust manifold that collected the exhaust gases from the upper combustion chambers. These manifolds were positioned between the intake manifold and the respective cylinder bank. The fuel injection camshaft and pumps were located on the outer side of the cylinder banks. An engine-driven blower was positioned at the rear of the engine and fed air into the intake manifold.

The first V-24 was designated V12Z 42/58, and the engine was designed for the German O-class battlecruisers, with four engines powering each of two shafts. A third shaft was powered by a steam turbine. The V12Z 42/58 had a 16.5 in (420 mm) bore, a 22.8 in (580 mm) stroke, and displaced around 224,957 cu in (3,686 L). The 150.5-ton (136.5-tonne) engine produced 15,600 hp (11,633) at 450 rpm. The eight engines planned for use in the O-class would have produced a total of 124,800 hp (93,063 kW), but the O-class was cancelled, and no ships were built. One V12Z 42/58 engine was built and completed a 200-hour test run, generating a continuous 10,000 hp (7,457 kW) at 243 rpm.

A second, smaller V-24 engine was the V12Z 32/44 (sometimes called the V24Z 32/44). This engine was designed in 1940 for the Zerstörer 1942, of which one was built, the Z 51. Most sources state that the Z 51 was powered by six engines, with two engines powering each of three shafts. Other sources claim the center shaft had four engines and that the outer shafts had one engine each. The V12Z 32/44 had a 12.6 in (320 mm) bore and a 17.3 in (440 mm) stroke. The engine displaced around 99,066 cu in (1,623 L) and produced 10,000 hp (7,457 kW) at 600 rpm. A turbocharged version was planned that would increase output to 16,000 hp (11,931 kW). The V12Z 32/44 weighed 56.0 tons (50.8 tonnes), and the turbocharged version weighed 66 tons (60 tonnes). The Z 51 destroyer was nearly complete when it was sunk during an allied attack on 21 March 1945. Sources state that either four or six V12Z 32/44 engines were built. One engine was preserved and is on display in the Auto & Technik Museum in Sinsheim.

MAN V12Z 32-44 construction

The MAN V12Z 32/44 engine under construction. The blower was mounted to the rear of the engine. Note the many access panels incorporated into the engine’s crankcase.

In the early 1950s, MAN again offered their double-acting, two-stroke diesel engines. The largest of these post-war engines was the D8Z 70/120. With a 27.6 in (700 mm) bore and a 47.2 in (1,200 mm) stroke, the eight-cylinder engine displaced 430,953 cu in (7,062 L) and produced 8,000 hp (5,966 kW) at 120 rpm. More efficient engines that required less maintenance overtook the double-acting, two-stroke power plants. Today, MAN continues to build diesels for automotive, industrial, and marine use.

*Maschinenfabrik Augsburg AG worked with Rudolf Diesel. The company merged with Maschinenbau-AG Nürnberg in 1898 to become Vereinigten Maschinenfabrik Augsburg und Maschinenbaugesellschaft Nürnberg (United Machine Factory Augsburg and Machinery Construction Company Nuremberg). In 1908, the company was renamed Maschinenfabrik Augsburg-Nürnberg (MAN).

MAN V12Z 32-44

The 24-cylinder MAN V12Z 32/44 engine as displayed in the Auto & Technik Museum in Sinsheim. The cars behind the engine give an indication of the engine’s size. Note the large blower housing attached to the engine. Six of these engines were to power the Z 51 destroyer. (Technik Museum Sinsheim und Speyer image)

“Multicylinder Combustion Engine” US patent 1,836,498 by Gustav Pielstick (granted 15 December 1931)
“Internal Combustion Engine” US patent 1,887,661 by Gustav Pielstick (granted 15 November 1932)
“Fuel Valve” US patent 1,919,904 by Gustav Pielstick (granted 25 July 1933)
“Piston for Double Acting Internal Combustion Engines” US patent 1,922,393 by Gustav Pielstick (granted 15 August 1933)
“Internal Combustion Engine” US patent 1,962,523 by Gustav Pielstick (granted 12 June 1934)
“Housing for a Vertical Combustion Power Engine” US patent 1,969,031 by Gustav Pielstick (granted 7 August 1934)
Diesel’s Engine by Lyle Cummins (1993)
Ungewöhnliche Motoren by Stefan Zima and Reinhold Ficht (2010)
Pocket Battleships of the Deutschland Class by Gerhard Koop and Klaus-Peter Schmolke (2014)

Engelmann VS 5 side

Versuchs Schnellboot 5 (VS 5) Semi-submersible Attack Boat

By William Pearce

In the early 1930s, Rudolf Engelmann of Berlin, Germany began investigating designs to improve the hull shape of seagoing ships. Engelmann felt that a new hull shape could be devised that would significantly improve how efficiently a sea-going ship plowed through the water. At the time, the fastest ocean liners and destroyers were capable of around 35 mph (56 km/h) and 46 mph (74 km/h) respectively. Engelmann’s goals were to increase speed to 46–58 mph (74–93 km/h) with the same amount of power and enable ships to maintain higher speeds through rough seas.

Engelmann patent drawings

Rudolf Engelmann’s original concept of a semi-submersible ship is illustrated in Fig 3 and Fig 4 from his first patent (651,390). Fig 10 shows the updated design from his second patent (651,892), with the exception of line 14. Line 14 indicates the chines that were added in the third patent (651,893).

Engelmann used models to test various hull shapes. On 25 March 1934, Engelmann applied for a German patent (no. 651,390) that outlined his design. Engelmann’s ship had a shape that was very similar to a modern-day submarine—a cigar-shaped (fusiform or spindle-shaped) hull with a propeller at its end and a superstructure in the middle. However, Engelmann’s ship was not fully submersible. The hull traveled beneath the water’s surface, but the superstructure sat above the waterline. The hull’s cross section was pear-shaped, with the narrow part in the middle positioned at the waterline. The submerged hull increased the ship’s efficiency and improved the ship’s stability in rough seas. The superstructure had a streamlined form to cut through the water and slice through waves.

After the first patent, Engelmann continued to develop the semi-submersible design. He applied for two other patents in 1935 that detailed an updated hull shape. The difference between the two later patents was detailed in German patent 651,893, which included a chine added to the superstructure. Tests indicated that in rough seas, the superstructure of the previous designs had a tendency to build up a bow wave. In addition, the design’s minimal reserve buoyancy caused the ship to plow under waves. To correct these issues, the thickness of the leading edge of the superstructure was reduced, and chines were added above the waterline. The chines tapered back and were blended into the sides of the superstructure. They directed water down from the superstructure rather than over it. The additional area created by the chines increased the ship’s displacement and buoyancy with the wave action.

Engelmann VS 5 drawing

A drawing of the Versuchs Schnellboot 5 (VS 5) shows the ship’s profile as very similar to what was depicted in Engelmann’s second and third patents. Note how the ship narrowed at the waterline, which is where the hull and superstructure joined.

Engelmann’s experiments caught the attention of the Kriegsmarine (German Navy), which felt the hull design had military applications. Having the superstructure as the only part of the ship above the water decreased the ship’s detection range and also presented a small target for an enemy to hit. Combined with its high speed, a ship of Engelmann’s design could get very close to an enemy ship undetected, launch torpedoes, and then quickly retreat to a safe distance. Around 1938, the Kriegsmarine ordered a proof-of-concept prototype be built.

The prototype was designated Versuchs Schnellboot 5 (Experimental Fast Boat 5 or VS 5) and was also referred to as the Engelmann-Boot. The ship was a semi-submersible, fast-attack torpedo boat for use in coastal waters. The VS 5 was built along the lines specified in Engelmann’s third patent. Rudders and stern planes at the rear of the ship provided control. The VS 5’s armament consisted of two forward-firing, 21 in (533 mm) torpedo tubes in the bow of the hull and two 20 mm cannons atop the superstructure. However, it is not clear if the weapons were ever installed in the prototype.

Engelmann VS 5 front

The VS 5 in dry-dock, most likely before it was launched in January 1941. The completed ship looked very much like a submarine with an odd sail. Note the chines on the superstructure. Engelmann stated in his patents that the top of the superstructure could be built with an overhang so that its leading edge was angled back to the hull. This configuration would further reduce the tendency of waves to pass over the superstructure.

Power was provided by four MAN (Maschinenfabrik Augsburg-Nürnberg) L11Z 19/30 diesel engines. The L11Z 19/30 was an 11-cylinder, double-acting, two-stroke, inline engine capable of reverse operation. Each of its closed cylinders had a combustion chamber at the top and bottom of the cylinder. A single intake manifold brought air into the cylinders, where the air was directed either above or below the double-sided piston, depending on its stroke. Separate exhaust manifolds collected exhaust gasses from the upper and lower combustion chambers. The engine had a 7.48 in (190 mm) bore and a 11.81 in (300 mm) stroke. Since the piston was double-acting and there was an upper and lower combustion chamber, the engine’s displacement was nearly doubled, as if it had 22 cylinders. However, the connecting rod passing through the lower combustion chamber took up around 40 cu in (.66 L) of volume. Total displacement for the upper combustion chambers was 5,710 cu in (93.56 L). Total displacement for the lower combustion chambers was approximately 5,269 cu in (86.35 L). The L11Z 19/30’s total displacement was around 10,979 cu in (179.91 L). The engine had a maximum output of 2,000 hp (1,491 kW) at 1,050 rpm and a continuous output of 1,400 hp (1,044 kW) at 900 rpm. The four L11Z 19/30 engines were installed in two rows in the middle of the VS 5 and were connected to a common gearbox that drove a single propeller.

MAN LZ 19-30 engine side

The VS 5 was powered by four MAN L11Z 19/30 double-acting, two-stroke, 11-cylinder engines. Note the upper and lower exhaust manifolds separated by the single intake manifold. The gap under the lower exhaust manifold is where the two fuel injectors for the lower combustion chamber were installed. A covered connecting rod passed through the center of each gap. (Hermann Historica image)

The VS 5 was 160 ft 3 in (48.84 m) long and 9 ft 3 in (2.82 m) wide. The keel sat about 11 ft 10 in (3.6 m) under the waterline. The superstructure was around 66 ft (20 m) long and rose about 12 ft 6 in (3.8 m) out of the water. The VS 5 displaced some 292 tons (265 tonnes) and had a forecasted top speed of 58 mph (93 km/h). The ship had a full crew of 17. Some sources state the VS 5 could sink in shallow water to hide from enemy ships. Once submerged, it could not move (other than surfacing), as the ship did not have batteries or the capability to run its engines while underwater. However, the ability to intentionally sink is not mentioned by all sources.

Engelmann VS 5 side

For normal operation, the hull of the VS 5 was completely submerged, and only the superstructure sat above the waterline. The 12 ft 6 in (3.8 m) tall and 66 ft (20 m) long superstructure was a small target for enemy ships to detect and hit.

Construction of the VS 5 started on 1 April 1940, and the ship was built by Deutsche Schiff- und Maschinenbau Aktiengesellschaft (Deschimag) in Bremen, Germany. Deschimag was a conglomerate of eight German shipyards. The VS 5 was launched on 14 January 1941, and trouble was encountered soon after testing began. Despite the changes in Engelmann’s design, the VS 5 still had a tendency to plow under waves in heavy seas. In addition, torque from the single propeller caused the whole ship to list around 14 degrees as full power was applied. The issue was so severe that a speed of 32 mph (52 km/h) could not be exceeded because of the tilt.

The VS 5 project was apparently abandoned in 1942, and what happened to the ship is not known. Plans for a larger 661-ton (600-tonne) ship were cancelled. Twin propellers were planned for the larger ship, and their configuration would have cured the list issues caused by the single-propeller. Engelmann’s design concept was passed over as the Kriegsmarine focused on submarines and fast boats, rather than a combination of the two.

Engelmann VS 5 rear

The chine on the superstructure can easily be seen in this image of the VS 5. The VS 5 had a severe list under full power, an issue that would have been corrected if other ships of the same type had been built. The VS 5 combined elements of both a fast boat and a submarine but did not really offer any advantages over other types of ships.

“Schiff” German patent 651,390 by Rudolf Engelmann (granted 23 September 1937)
“Schiff” German patent 651,892 by Rudolf Engelmann (granted 30 September 1937)
“Schiff” German patent 651,893 by Rudolf Engelmann (granted 30 September 1937)
“Improvements relating to the construction of Ships” GB patent 455,466 by Rudolf Engelmann (granted 21 October 1936)
“Improvements relating to the Construction of Ships” GB patent 470,907 by Rudolf Engelmann (granted 20 August 1937)
“High Speed Seagoing Ship” US patent 2,101,613 by Rudolf Engelmann (granted 7 December 1937)

Riout 102T wings up

Riout 102T Alérion Ornithopter

By William Pearce

French engineer René Louis Riout was interested in ornithopters—aircraft that used flapping wings to achieve flight. His first ornithopter, the DuBois-Riout, was originally built in 1913, but testing was delayed because of World War I. The aircraft never achieved sustained flight and was destroyed in an accident in 1916.

Riout 102T wing frame

The nearly-finished Riout 102T Alérion is just missing the fabric covering for its wings and tail. Note the wing structure and how the spars are mounted to the fuselage.

After the war, Riout designed a new ornithopter that had two sets of flapping wings. He continued to refine his ornithopter design, but no one was interested in producing such a machine. Riout worked for a few other companies, including a time with Société des Avions Bernard (Bernard Aircraft Company) from 1927 to 1933. While at Bernard, Riout was involved with their Schneider Trophy racer projects.

In 1933, Riout presented his ornithopter designs and research to the Service Technique de l’Aéronautique (STAé or Technical Service of Aeronautics). Riout’s presentation included designs and models of two- and four-wing ornithopters. The models weighed 3.5 and 17.6 oz (100 and 500 g) and performed flights up to 328 ft (100 m). As a result of these tests, STAé ordered a 1/5-scale model with wings powered by an electric motor.

Riout 102T wings up

Completed, the Riout 102T ornithopter resembled a dragonfly. An engine cylinder and its exhaust stack can be seen behind the rear wing. Note the enclosed cockpit; the rear section slides forward for entry.

The 1/5-scale model was built in 1934. From 11 November 1934 to 1 February 1935, the model underwent 200 hours of testing in the wind tunnel at Issy-les-Moulineaux, near Paris, France. The successful tests established the feasibility of Riout’s design and indicated the ornithopter would be capable of 124 mph (200 km/h) if it were powered by a 90 hp (67 kW) engine. Based on the test results, STAé ordered a full-scale ornithopter to be built and tested in the wind tunnel for research purposes. On 23 April 1937, Riout was awarded a contract for the construction of an ornithopter prototype.

The ornithopter was designated Riout 102T Alérion. The word alérion, or avalerion, is the name of a mythical bird about the size of an eagle. The single-place ornithopter had a cigar-shaped fuselage. Its frame was made of tubular-steel and skinned with aluminum. The enclosed cockpit occupied the nose of the aircraft. Two wheels on each side of the aircraft retracted into the fuselage sides. The landing gear had a 4 ft 3 in (1.3 m) track.

Behind the cockpit were two pairs of flapping wings. The two-spar wings had metal frames and were fabric-covered. A hinge at each spar mounted the wing to a large structure in the center of the fuselage. Immediately behind the wings, a 75 hp (56 kW) JAP (John Alfred Prestwich) overhead valve V-twin engine was installed with its cylinders exposed to the slipstream for air-cooling. The exact engine model has not been found, but the 61 cu in (996 cc) JAP 8/75 is a good fit. The 102T ornithopter had conventional vertical and horizontal stabilizers that were made of tubular steel frames and covered with fabric.

Riout 102T wind tunnel

On 12 April 1938, the wings of the 102T failed during a wind tunnel test. Stronger wings could have been designed and fitted, but the impractically of the ornithopter left little incentive to do so. The landing gear was removed for the tests. Note the engine cylinder behind the rear wing.

A drawing indicated the wings had 50 degrees of travel—40 degrees above horizontal and 10 degrees below. However, a detailed description of how the wings were flapped has not been found. The method appears to be somewhat similar to the system used on the DuBois-Riout ornithopter of 1913, in which the engine was geared to a crankshaft that ran between the wings. A connecting rod joined each wing to the crankshaft, but each wing was on a separate crankpin that was 180 degrees from the opposite wing. However, images of the 102T show both sets of wings in the up position, as well as one set of wings up and the other down. If a crankshaft was used for the wings, it must have employed clutches and separate sections for each pair of wings. It appears the standard operating configuration was for the wings to be on different strokes: one pair up and one pair down. Wing warping was used to achieve forward thrust, with the portion of the wing behind the rear spar moving.

The Riout 102T had a 26 ft 3 in (8.0 m) wingspan and was 21 ft (6.4 m) long. At its lowest position, the wing had 2 ft 2 in (.67 m) of ground clearance. At its highest point, the wingtip was 13 ft 5 in (4.1 m) above the ground. The aircraft’s tail was 8 ft 2 in (2.5 m) tall. The ornithopter weighed 1,102 lb (500 kg) empty and 1,389 lb (630 kg) fully loaded.

The aircraft was built in Courbevoie, at the company of coachbuilder Émile Tonnelline (often spelled Tonneline). Final assembly was completed in late 1937 by Bréguet (Société des Ateliers d’Aviation Louis Bréguet or Luis Bréguet Aviation Workshop) in Villacoublay. With its four wings and side-mounted landing gear, the completed ornithopter resembled a dragonfly.

Riout 102T frame

Restoration efforts provide a good view of the Riout 102T’s frame. Note how neatly the landing gear folded into the fuselage. The ornithopter’s aluminum body was saved, but the original wings were lost. (Shunn311 image via

After some preliminary testing, the 102T was moved to the wind tunnel at Chalais-Meudon in early 1938. First, tests lasting two minutes with the wings stationary were conducted. These tests were followed by wing flapping tests. Eventually, the ornithopter test sessions lasted a continuous 20 minutes, but all tests were conducted without the wings warping (providing thrust). It was noted that the engine was only producing around 60 hp (45 kW), but the tests were continued. On 12 April 1938, the 102T was in the wind tunnel undergoing a flapping test with a wind velocity of 81 mph (130 km/h). When the engine speed was increased to 4,500 rpm, one wing folded, quickly followed by the other three. The outer third of all the wings bent, with the right wings folding up and the left wings folding down. At the time of the mishap, the ornithopter had operated in the wind tunnel for around three hours and had satisfied initial stability tests.

Before the wings failed, Riout had notified the STAé of some modification he would like to make to the ornithopter. However, there was no interest to fund repairs or continue the project after the aircraft was damaged. The damaged wings were discarded, but the fuselage of the 102T was somehow preserved. Today, the Riout 102T Alérion is undergoing restoration and is on display at the Espace Air Passion Musée Régional de l’Air in Angers, France. While a few manned ornithopters flights have been made, the aircraft type has been generally unsuccessful.

Riout 102T frame restoration

The frame of the ornithopter consisted of small diameter steel tubes that were welded together. The aluminum wing supports may not be original. The Riout 102T is currently on display in the Espace Air Passion Musée Régional de l’Air. (Jean-Marie Rochat image via

“Avion à ailes battantes Riout 102T” by Christian Ravel Le Trait D’Union No 225 (January-February 2006)
Les Avions Breguet Vol. 2 by Henri Lacaze (2016)
“Flying Machine with Flapping Wings” US patent 1,009,692 by René Louis Riout (granted 21 November 1911)

Dubois Riout front wings down

DuBois-Riout Ornithopter

By William Pearce

When humans began to contemplate heavier-than-air flight, it was only natural to emulate birds. However, the complications of an ornithopter—using flapping wings to achieve flight—proved to be insurmountable. By 1900, most aviation pioneers focused their efforts on propellers and fixed wings; however, some persisted with the ornithopter.

Riout 1911 Patent

Drawings from René Riout’s US patent of 1911. Fig 1 shows the ornithopter design, which had a passing similarity to the aircraft built in 1913. Fig 2 and Fig 3 show the wing flapping mechanism. Fig 4 and Fig 5 show the wing in a gliding position. Fig 6 and Fig 7 show the wing warped for thrust.

In the early 1900s, French engineer René Louis Riout shifted his focus from automobiles to aviation. Initially, Riout designed models of gliders and propeller-driven aircraft, but his attention soon turned to ornithopters. By 1907, Riout was successfully flying his model ornithopter designs. In 1909, one of Riout’s models flew 164 ft (50 m) at an altitude of 10 ft (3 m). In 1910, his ornithopter model was flying 558 ft (170 m), and the distance expanded to 722 ft (220 m) in 1911.

In late 1910, Riout was granted French patent 419,140 for his flapping wing mechanism and ornithopter design. The same invention was patented in Great Britain (191117951) and the United States (1,009,692) in 1911. Riout’s patent described how power from an engine was geared at a reduced speed to a crankshaft. The crankshaft had two crankpins that were positioned 180 degrees apart. A connecting rod linked each crankpin to the pivoting mechanism of one wing. As the crankshaft turned and the crankpin moved to the horizontal position nearest the wing, the wing was moved to its highest position. As the crankpin moved to the horizontal position farthest from the wing, the wing moved to its lowest position. Thus, the up and down movement of the wing was controlled by the speed of the engine. The drive system incorporated a heavy flywheel to smooth out power pulses from the engine. For small aircraft, a heavy spring could be substituted for the flywheel.

Dubois Riout front

Front view of the DuBois-Riout ornithopter with the three-cylinder Viale engine. The engine cylinders can be seen protruding above the cowling. The wings are positioned around 20 degrees above horizontal. Note the quarter-turn belt drive for the wheel axle.

The patent details how the wings would warp as they moved. The upstroke was made in a neutral, gliding position. On the downstroke, the wing’s trailing edge would deflect up to provide thrust. Springs in the wing regulated the warp to match the power of the downstroke. A slow downstroke would result in the wing maintaining its glide form. The warp of the wing was greatest at the tip, tapering to very little warp at the root.

By 1913, Riout had partnered with Jean Marie DuBois, and a full-scale ornithopter was built. Exactly what role DuBois played in the creation of the ornithopter has not been found, but the resulting machine was known as the DuBois-Riout monoplane. The DuBois-Riout ornithopter had a slender, streamlined airframe that was made from tubular-steel and covered in fabric. A vertical stabilizer with a rudder protruded from below the fuselage. A horizontal stabilizer extended to the sides from the top of the fuselage and incorporated an elevator. The single-place cockpit was positioned between the ornithopter’s wings. The wings had a tubular-steel frame and were fabric-covered. The aircraft was supported by taildragger landing gear.

Dubois Riout front wings down

The ornithopter’s wings in the down position were about 20 degrees below horizontal, which was enough to make them contact the ground. This is why wing flapping would only be initiated after the aircraft was airborne, having been propelled to takeoff speed by the wheels. A shroud can be seen covering the top part of the drive belt.

The ornithopter was powered by a three-cylinder Viale Type A engine. The three cylinders were spaced 65 degrees apart in a fan configuration. The air-cooled engine had a 4.13 in (105 mm) bore and a 5.12 in (130 mm) stroke. Its total displacement was 206 cu in (3.4 L), and it produced 35 hp (26 kW) at 1,500 rpm. The engine was positioned in the nose of the ornithopter and encased in a cowling, but its cylinders protruded into the air stream for cooling. The engine drove a crankshaft to flap the wings, just like the patent described.

A major problem facing ornithopter designs was how to start the takeoff roll and gain enough forward speed to achieve flight. Via a belt, the DuBois-Riout used engine power to drive the main wheels during the takeoff run. The drive pulley was positioned behind the engine, and the follower pulley was positioned on the main wheels’ axle and perpendicular to the drive pulley. The follower pulley was offset to the left so that its front edge was directly below the left side of the drive pulley. As the belt came off the rear of the follower, it traveled to the right to reconnect with the right side of the drive pulley. The belt twisting 90 degrees enabled the longitudinal rotation of the engine’s crankshaft to be converted to transverse rotation for the aircraft’s wheels. Once the ornithopter was up to speed, the machine was glided off the ground. Via clutches, engine power was transferred from the pulley to the flapping wings for sustained flight. The DuBois-Riout ornithopter had a 34 ft 5 in (10.5 m) wingspan and a predicted max speed of 84 mph (135 km/h). The machine weighed 794 lb (360 kg).

Dubois Riout side

Side view of the DuBois-Riout ornithopter illustrates the vertical stabilizer under the fuselage and the elongated horizontal stabilizer. Note the large pulley on the wheel’s axle.

In late 1913 or early 1914, Riout initiated tests of the ornithopter but encountered issues with the engine. It is not clear if the engine was not running correctly or if more power was needed. Before the issues were resolved, Riout left to serve in World War I. In 1916, Riout was granted permission to restart tests on the ornithopter. A 50 hp (37 kW) Gnome-Rhône engine was acquired and installed in the aircraft. No information has been found as to what modifications were made to the ornithopter to handle the rotary engine or its gyroscopic torque. Reportedly, the ornithopter made it into the air but quickly came down hard and was wrecked. No one was injured in the mishap, but Riout needed to return to the war, and no further work was done on the ornithopter.

One might think that with the destruction of the DuBois-Riout machine and conventional aircraft proving their worth throughout World War I, Riout would move away from the ornithopter design. However, he persisted, but 20 years passed before his next ornithopter, the Riout 102T Alérion, was built.

Dubois Riout rear

The ornithopter’s rudder can be seen in this rear view. Note the large control wheel in the cockpit and the fabric gap between the wings and fuselage.

“Flying Machine with Flapping Wings” US patent 1,009,692 by René Louis Riout (granted 21 November 1911)
“French Monoplane with Flapping Wings” Popular Mechanics (February 1913)
French Aeroplanes Before the Great War by Leonard E. Opdycke (2004)
Rotary Wing Aircraft Handbooks and History Volume 11: Special Types of Rotary Wing Aircraft by Eugene K. Liberatore (1954)
“Avion à ailes battantes Riout 102T” by Christian Ravel Le Trait D’Union No 225 (January-February 2006)