Schwerer Gustav firing test

Krupp 80 cm Kanone Schwerer Gustav (Dora) Railway Gun

By William Pearce

In the 1930s, France constructed the Maginot Line, which was a series of fortifications and obstacles intended to protect the country against invasion from the east (Germany). The Maginot Line was to serve as an impenetrable wall of defense. Naturally, when one country develops a new defensive technology, other countries rush to develop a way to defeat that technology.

Schwerer Gustav firing test

The Krupp 80 cm Kanone (E) Schwerer Gustav / Dora being readied for a test firing on 19 March 1943 at Rügenwalde, Germany. Albert Speer (right), Adolf Hitler (second from right), and a number of other officials observed the firing. Hitler referred to the impractical gun as “meine stählerne faust (my steel fist).”

After studying details of Maginot Line fortifications that were published in French newspapers, it became apparent to German Wehrmacht (combined armed forces) planners that they did not possess any weapon capable of penetrating the fortifications. In 1935, the Wehrmacht requested Friedrich Krupp AG (Krupp), a heavy industry conglomerate in Essen, Germany, to prepare ballistics reports for guns firing 27.6, 31.5, 33.5, and 39.4 in (70, 80, 85, and 100 cm) shells. The goal was to fire the gun outside of the enemy’s artillery range and be able to penetrate 23 ft (7 m) of reinforced concrete or 3 ft (1 m) of steel armor. The Krupp factory dutifully ran the calculations and supplied the requested information but took no further action.

In March 1936, Adolf Hitler visited the Krupp factory and asked Gustav Krupp (von Bohlen und Halbach), head of the Krupp organization, what type of weapon was needed to smash through the Maginot Line. Krupp, recalling the recent report, was able to answer Hitler’s question in some detail. Krupp explained that a 33.5 in (80 cm) railway gun could be constructed and would be able to defeat the Maginot Line. After Hitler’s visit, Krupp directed his design staff to begin the layout of such a weapon. Erich Müller was the head of the artillery development department at Krupp and began working on the gun’s design.

Schwerer Gustav cradle assymbly

Nicknamed Dora by its crew, the massive gun was broken down into 25 pieces and transported by rail to its firing location. Two gantry cranes were used to reassemble the gun. Here, the cradle is being positioned into the carrier. Note the three normal railroad tracks and the special track for the cranes.

In early 1937, Krupp met with Hitler and presented him with the design for the 33.5 in (80 cm) railway gun. Hitler approved of what he saw, and the German Army High Command (Oberkommando des Heeres) commissioned Krupp to build three guns under the designation 80 cm Kanone (E). However, the guns quickly became known as Schwerer Gustav (Heavy Gustav), named after Gustav Krupp. Hitler wanted the first gun to be ready by March 1940.

The Schwerer Gustav was an absolutely huge weapon. The rifled barrel consisted of two halves, with the rear half covered by a jacket. The complete barrel was 106 ft 7 in (32.48 m) long, and its rifling was .39 in (10 mm) deep. Attached to the rear of the barrel was the cradle and breechblock. Mounted to the cradle were four hydraulic recoil absorbers. Trunnions held the gun’s cradle in two huge carriers and enabled the barrel to be elevated from 0 to 65 degrees. Each carrier was supported by four railroad trucks: two in the front and two in the rear. Each of the eight trucks was made up of five axles, giving the Schwerer Gustav a total of 80 wheels that were carried on two parallel sets of railroad tracks. The gun used a diesel-powered generator to provide power to run its systems. The Schwerer Gustav was 155 ft 2 in (47.30 m) long, 23 ft 4 in (7.10 m) wide, and 38 ft 1 in (11.60 m) tall. The barrel, cradle, and breech weighed 881,848 lb (400,000 kg), and the complete gun weighed 2,976,237 lb (1,350,000 kg).

Schwerer Gustav assymbly tracks

This image gives a good view of the tracks needed to assemble the Schwerer Gustav. One pair of D 311 locomotives is positioned in front of the gun.

In addition to needing parallel tracks, the Schwerer Gustav required its track to be curved up to 15 degrees. The gun had no built-in ability to traverse, so horizontal aiming (azimuth) was accomplished by moving the entire gun along the curved track. Extra bracing was added to the inside rail of both tracks along the shooting curve. This bracing helped prevent the tracks from being damaged due to the gun’s recoil. A massive effort was needed to transport and set up the Schwerer Gustav for firing.

The gun was broken down and transported on 25 freight cars, which did not include crew or supplies. Near where the gun was to be deployed, a spur line was laid from the main rail line. Three parallel tracks were then laid where the Schwerer Gustav was to be assembled. Two of the tracks supported the gun, and the third track allowed for parts and equipment to be brought in. A single rail was laid on both sides of the three parallel tracks. These widespread rails were for two gantry cranes to take parts from the third track and move them in position to assemble the Schwerer Gustav. Two parallel tracks extended from the assembly point to the firing position of the Schwerer Gustav. Dirt was piled up high on both sides of the double track to protect the gun from attack and allow it to be covered by camouflage netting. It took around 250 men 54 hours to assemble the Schwerer Gustav, and it took weeks for 2,000 to 4,500 men to lay the needed tracks and prepare the gun’s firing position. In addition, two Flak (Flugabwehrkanone or air defense cannon) battalions were needed to protect the gun from an aerial assault.

Schwerer Gustav captured shell

Allied soldiers pose in front of a captured projectile (left) and an obturation case (right). The projectile had a ballistic nose cone made of aluminum.

Krupp built special diesel-electric locomotives to move the Schwerer Gustav into firing position and to transport supplies. These locomotives were designated D 311, and two were paired together to act as a single unit, for a total of four engines to move the gun. Each locomotive was powered by a 940 hp (700 kW) six-cylinder MAN diesel engine. The engine ran a generator that provided power to traction motors mounted on the locomotive’s bogies. Ammunition was delivered via the twin rails behind the Schwerer Gustav. Hoists on the back of the gun would lift the ammunition to the firing deck. The shell was hoisted up one side of the gun, and the powder bags and a brass obturation case were hoisted up the other side. A hydraulic ram loaded the shell into the breach, followed by the powder bags and the case. Once loaded, the gun was raised into firing position. It took 20 to 45 minutes to load the gun and prepare it for firing. Only 14 to 16 shots could be fired each day.

Two types of shells were fired from the Schwerer Gustav: armor piercing (AP) and high explosive (HE). The AP rounds were 11 ft 10 in (3.6 m) long and were fired with 4,630 lb (2,100 kg) of propellant. The AP round was made of chrome-nickel steel. It weighed 15,653 lb (7,100 kg) and carried 551 lb (250 kg) of explosives. The AP shell had a muzzle velocity of 2,362 fps (720 m/s) and a maximum range of 23.6 miles (38 km). At maximum range, the AP projectile reached an altitude of around 39,370 ft (12 km) and was in the air for two minutes. The HE ammunition was around 13 ft 9 in (4.2 m) long and was fired with 4,938 lb (2,240 kg) of propellant. The HE rounds weighed 10,582 lb (4,800 kg) and carried 1,543 lb (700 kg) of explosives. The HE shell had a muzzle velocity of 2,690 fps (820 m/s) and a maximum range of 29.2 miles (47 km). Upon impact, the HE projectile created a crater some 33 ft (10 m) wide and deep. The muzzle velocity for both the AP and HE shells was over twice the speed of sound, and both were fitted with an aluminum alloy ballistic nose cone. Spotter aircraft were used to direct the gun’s fire and assess the results.

Construction of the Schwerer Gustav started in the spring of 1937, but forging the huge and complex barrel resulted in serious delays. By 1939, Alfried Krupp (von Bohlen und Halbach) began to take over company leadership from his father, whose health had begun to fail. In late 1939, testing started on sample components, and the gun’s AP projectile was able to successfully penetrate 23 ft (7 m) of concrete or 3 ft (1 m) of steel. It was obvious that the Schwerer Gustav would not be ready by the March 1940 deadline Hitler had requested.

Schwerer Gustav hoists

Shells and propellant for the gun were delivered by rail and hoisted up to the firing deck. The shell is on the far side, and the case with powder bags is in front of it (to the right). It took 20 to 45 minutes to reload the gun and prepare it for firing.

In May 1940, Germany invaded Belgium and France. Since the Maginot Line ended at Belgium, rather than extending to the English Channel, Germany was able to simply go around the static fortifications and enter France. On 25 June 1940, France surrendered to Germany.

With the fall of France, the Schwerer Gustav was no longer needed, but discussions ensued regarding other fortifications that the gun could be used against. Many in the Wehrmacht felt the gun was impractical and not worth the resources its construction consumed, let alone the manpower needed to deploy the gun. However, the Schwerer Gustav had become one of Hitler’s personal projects, so its development continued. Alfried Krupp hosted Hitler for a test firing during the gun’s acceptance trials in early 1941 at Rügenwalde, Germany (now Darłowo, Poland). Further tests and development continued through 1941. Some sources indicate that 250 rounds were fired from the gun during its testing.

Schwerer Gustav firing position

The gun was positioned on a shooting curve to allow for horizontal aiming. Rectangular braces were positioned on both sides of the inner rails to protect the tracks from the forces of firing the gun.

On 8 January 1942, Schwere Artillerie-Abteilung (E) 672 (Heavy Artillery Division E 672) was established with 1,420 men and with Oberst (Colonel) Robert Böhm as its commander. The unit was formed to deploy the Schwerer Gustav. As the artillerymen worked on the gun, they called it “Dora,” and the nickname stuck. From that time on, the gun was typically referred to as Dora, rather than Schwerer Gustav. The different names led to some confusion regarding how many guns were built and when they were used. German sources typically indicate that Dora was a nickname from the artillerymen and that only one gun was ever deployed. However, many English sources state that Gustav and Dora were the first and second guns built and that the Dora gun was named in honor of Erich Müller’s wife.

In February 1942, the division was sent to Bakhchisaray in the Crimean Peninsula, then part of the Soviet Union. The gun was to be used on the port city of Sevastopol, 18.6 miles (30 km) southwest of Bakhchisaray. Sevastopol had been under siege by German forces since November 1941. Five separate trains were used to transport the gun, the division, ammunition, supplies, and workshops to the deployment site. The Schwerer Gustav arrived in early March. In May, German troops and civilian workers laid a 1.2 mile (2 km) long access track to the firing site, followed by parallel tracks .75 miles (1.2 km) long for gun assembly and deployment. Once the track was ready, assembly of the gun commenced.

On 5 June 1942, the Schwerer Gustav fired its first round at Sevastopol, and 13 additional shots followed that day. On 6 June, the Schwerer Gustav achieved the highpoint of its career. An ammunition magazine at White Cliff suffered a direct hit from the Schwerer Gustav. The magazine was buried 98 ft (30 m) under Severnaya Bay and had 33 ft (10 m) of concrete protection. The AP round passed though the water, ground, and concrete before detonating the magazine. At least one ship was also sunk after being damaged by blast waves from the impact of nearby shells.

Schwerer Gustav firing

The Schwerer Gustav could fire a 15,653 lb (7,100 kg) AP shell 23.6 miles (38 km) or a 10,582 lb (4,800 kg) HE shell 29.2 miles (47 km). A spotter aircraft directed fire and assessed the results.

The gun was used on three additional days before its ammunition was exhausted. The Schwerer Gustav fired a total of 48 shells at the city, and its barrel had become worn. Some sources claim that the barrel had a 300-round life and was the same one that had fired the 250 test rounds. Other sources state the barrel was new and should have been able to fire 100 shots before it became worn, but signs of wear were seen after as few as 15 shots. Regardless, the Schwerer Gustav’s barrel was replaced with a spare, and the original barrel was transported back to Germany for repairs. Of the 48 rounds fired, only 10 fell within 197 ft (60 m) of their target, with the most off-target shot landing 2,428 ft (740 m) from its intended point of impact. However, each huge shell caused massive damage all around its impact site.

A few weeks after Sevastopol fell on 4 July 1942, Gustav Krupp gave the first Schwerer Gustav to Hitler as a personal gift and a sign of his support and allegiance to the Third Reich. The Krupp company would only accept payment for subsequent guns. The Schwerer Gustav was moved and redeployed for a planned offensive against Leningrad, which was also under siege. The gun had been assembled and placed in firing position, but its planned use was cancelled. The Schwerer Gustav was disassembled and taken back to Rügenwalde.

The gun was overhauled, and an improved, lined barrel was fitted. A test firing on 19 March 1943 at Rügenwalde was attended by Hitler, Albert Speer, Alfried Krupp, and a number of other officials. Two shots were fired, with the second shell impacting 29.2 miles (47 km) away. The Schwerer Gustav was then disassembled and placed in storage near Chemnitz, Germany in September 1943. The gun remained there until 14 April 1945, when it was destroyed by German troops one day before US soldiers captured the area. Parts of the Schwerer Gustav were recovered by the Soviets and supposedly transported to Russia. The second Schwerer Gustav was reportedly completed but never deployed. In March 1945, it was moved from Rügenwalde to Grafenwöhr, Germany, where it was destroyed on 19 April 1945.

Schwerer Gustav shooting curve

While it was a powerful weapon, the Schwerer Gustav required a tremendous amount of resources for its construct and deployment. Its size and complexity severely limited where and when the gun could be deployed and also made it very susceptible to aerial attack.

Around November 1943, plans were initiated to use a cannon to shell Britain from across the English Channel. It was decided that the third Krupp 80 cm Kanone (E) would be built as the gun for this purpose. In order to send a shell 99 to 124 miles (160 to 200 km), a projectile 20.5 in (52 cm) in diameter and weighing 1,499 lb (680 kg) would be shot out of a barrel 157 ft (48 m) long. This gun was named Länger Gustav (Longer Gustav). The gun was damaged during a bombing raid while it was still under construction. Some components for the Länger Gustav were discovered at the Krupp factory in Essen by Allied troops in 1945.

In December 1942, Krupp proposed a self-propelled 80 cm Kanone (E) known as the Landkreuzer P. 1500 Monster. The P. 1500 used the same 31.5 in (80 cm) main gun as the Schwerer Gustav, but it also had two 5.9 in (15 cm) sFH 18.1 L/30 field guns and a number of 15 mm MG151/15 cannons. Powering the P. 1500 were four 2,170 hp (1,618 kW) nine-cylinder MAN M9V 40/46 diesel engines. The P. 1500 was 137 ft 10 in (42 m) long, 59 ft 1 in (18 m) wide, and 23 ft (7 m) tall. True to its name, the Monster weighed 3,306,930 lb (1,500,000 kg). Requiring a crew of over 100, the machine had an estimated top speed of 9.3 mph (15 km/h) and a range of 31 miles (50 km). The P. 1500 project was cancelled in 1943 by Albert Speer, the Minister for Armaments, before any serious work had been done.

After the war, Alfried Krupp and Erich Müller, the gun’s designer, were sentenced to 12 years in prison for crimes against humanity by participating in the plundering, devastation, and exploitation of occupied countries and by participating in the murder, extermination, enslavement, deportation, imprisonment, torture, and use for slave labor of German nationals, prisoners of war, and civilians who came under German control. Krupp was pardoned after three years, and Müller was released after four years.

Schwerer Gustav 1 destruction

The first Schwerer Gustav gun was destroyed by German troops on 14 April 1945 to prevent its capture by US forces. Some sources state that the gun was recovered by the Soviets. A US soldier poses in front of the gun’s cradle. The girders attached to the cradle were used for transporting and mounting the cradle to the rest of the gun. The circular pad behind the soldier is a trunnion mount.

While the Schwerer Gustav was mechanically a well-engineered weapon, its requirements for use made it very impractical and nearly useless. The Maginot Line was easily bypassed, rather than penetrated, calling into question why the Schwerer Gustav was needed in the first place. However, Hitler liked the gun and called it his “steel fist.” It was the type of grandiose weapon that Hitler felt displayed the technological superiority of the Third Reich.

No large pieces of the Schwerer Gustav guns remain. However, a number of inert projectiles and cases are preserved in various museums. After the war, the D 331 locomotives were redesignated V 188 and used to haul freight for the West German Railway (Deutsche Bundesbahn).

Schwerer Gustav 2 destruction

Germans destroyed part of the second Schwerer Gustav on 19 April 1945 to prevent its capture. A US soldier gives scale to the gun’s barrel. The second gun’s cradle, which was blown up, can be seen on the left.

Sources:
http://de.wikipedia.org/wiki/80-cm-Kanone_(E)
http://en.wikipedia.org/wiki/Schwerer_Gustav
http://ww2db.com/weapon.php?q=89
http://samilitaryhistory.org/vol124lw.html
http://html2.free.fr/canons/dora.htm
http://de.wikipedia.org/wiki/Wehrmachtslokomotive_D_311
http://www.modellbahn.com/37283.V188.html
http://www.e94114.de/V188.htm
http://www.militaryfactory.com/armor/detail.asp?armor_id=480
http://en.wikipedia.org/wiki/Landkreuzer_P._1500_Monster

Rumpler Loutzkoy-Taube front ground

Rumpler-Loutzkoy-Taube Aircraft

By William Pearce

Boris Loutzkoy (also spelled Lutskoi, Luskoy, Lutsky, and probably other ways) was a Russian engineer who went to Germany to continue his education in the 1880s. Initially, his main interests were with internal combustion engines and automobiles, but it was not long before Loutzkoy turned his focus and engineering talents to aviation.

Rumpler Loutzkoy-Taube front ground

The tandem-engine Rumpler-Loutzkoy-Taube employed coaxial propellers that rotated the same direction. The second engine can just be seen behind the first engine and between the wings. Note the aircraft’s double main wheels.

By 1911, he had teamed up with Rumpler Flugzeugwerke in Berlin, Germany to test an innovative propulsion concept. Loutzkoy’s idea was to use two engines to power separate propellers on a common shaft. Since the propellers shared the same shaft, they were coaxial. However, they were not contra-rotating, because they rotated the same direction. The propellers in Loutzkoy’s system were of different sizes and turned at different speeds. Loutzkoy believed this power arrangement would improve the aircraft’s low- and high-speed performance, with the twin propellers achieving a level of efficiency beyond what could be obtained with a single propeller of any size. In addition, two engines with separate propellers would provide a level of reliability well beyond that of a single power plant. At the time, engines were notoriously unreliable.

To test his theories, Loutzkoy made many modifications to a Rumpler Taube aircraft. The Taube (Dove) was designed in 1909 by Igo Etrich of Austria-Hungary. The aircraft first flew in 1910 and proved to be very stable. A number of manufacturers purchased licenses to build copies, and Rumpler probably produced the most. The Taube was a monoplane with a mostly wooden frame. The front of the aircraft and back to the cockpit was covered in metal, but the rest of the aircraft was fabric-covered. The Taube used wing warping for roll control.

Rumpler Loutzkoy-Taube front

This drawing of the Loutzkoy-Taube illustrates the aircraft’s similarity to a standard Taube. The obvious differences include the double propellers and two main gear wheels.

The Loutzkoy-modified aircraft was named the Rumpler-Loutzkoy-Taube. Changes from a standard Taube included a slightly modified and strengthened airframe, strengthened landing gear (including double wheels), and a slightly larger wing. These changes were made to handle the extra weight and power of a second engine. The approximate dimensions of the Loutzkoy-Taube were a wingspan of 49 ft 10 in (14.3 m) and a length of 34 ft 1 in (10.4 m). The aircraft weighed around 1,764 lb (800 kg) empty. The Loutzkoy-Taube had a top speed of 93 mph (150 km/h), about 31 mph (50 km/h) more than a standard Rumpler Taube.

Powering the Loutzkoy-Taube were two Argus Type 4 engines. The Type 4 was an inline, four-cylinder, water-cooled engine with a 5.51 in (140 mm) bore and stroke. The engine displaced 526 cu in (8.62 L) and produced 100 hp (75 kW) at 1,300 rpm. The two engines drove separate propellers that were mounted on a common shaft: the front engine drove the front propeller, and the second engine drove the second propeller. Both sets of propellers had two blades.

Rumpler Loutzkoy-Taube engines

A basic drawing of the engine installation in the Loutzkoy-Taube.

The front engine was positioned in its normal location, in the nose of the aircraft. However, rather than having its propeller mounted directly to the engine, a short extension shaft was used. The second engine was mounted behind and below the front engine. Power from the second engine was transferred to the front of the aircraft via an extension shaft that ran under the front engine. A sprocket on the end of the extension shaft was connected via a chain to the second propeller, which was positioned between the first propeller and the front engine.

Although the propellers turned the same direction, the second propeller was a larger diameter, turned at a slower rpm, and had a coarser pitch. The first propeller was 8 ft 2 in (2.5 m) in diameter, direct drive, and turned about 1,300 rpm. The second propeller was 9 ft 10 in (3.0 m) in diameter, had a .615 reduction through the chain-drive, and turned around 800 rpm. The aircraft could be flown on either engine if a failure occurred, but the intention was to have both engines operating at all times.

Rumpler Loutzkoy-Taube patent

A drawing from Loutzkoy’s patent shows the basic engine layout that was used in the Loutzkoy-Taube aircraft and includes a change-over gearbox. The gearbox was meant to provide braking after touchdown by reversing the rotation of the second propeller. However, such a gearbox was never installed in the aircraft.

In his German patent no. 263,059 (granted 29 October 1911), Loutzkoy explained how a change-over gearbox could be used to reverse the rotation of the second propeller. This feature would be used for braking after the aircraft landed. In flight, shortly before landing, the second engine would be stopped and the change-over gearbox engaged. The second engine could then be started on touchdown. Its propeller rotating in the opposite direction would slow the aircraft down. Most aircraft at the time did not have any brakes, and using the propeller as a brake would become common with turboprops. However, the reversing propeller idea was never implemented on the Loutzkoy-Taube aircraft.

Rumpler Loutzkoy-Taube Argus engines

Detailed right and left views of the Loutzkoy-Taube’s twin-Argus engine installation. Note the size difference of the propellers. The extension shaft and chain drive from the second engine to the larger propeller can clearly be seen.

The Loutzkoy-Taube was first flown in early 1912, possibly in February, at Johannisthal airfield, near Berlin. With a combined rating of 200 hp (149 kW), the Loutzkoy-Taube was one of the most powerful and fastest aircraft of its time. A number of subsequent flights were made, and Hellmuth Hirth was the pilot for most of the Loutzkoy-Taube’s flights. The aircraft passed an inspection test for the Russian Army on 8 March 1912, achieving a speed of 81 mph (130 km/h). The Loutzkoy-Taube was displayed at the Berlin Airshow in April 1912. However, engine drive issues continued to plague the aircraft. By 1913, Loutzkoy had moved on to another aircraft project. Nothing more was heard of the twin-engine Loutzkoy-Taube and its coaxial propellers.

While it was not the first twin-engine aircraft to fly, the Loutzkoy-Taube was certainly the first aircraft to fly using coaxial, non-contra-rotating propellers. A very small number of aircraft have used this method of propulsion, as it really does not have many advantages over a single propeller and has disadvantages over contra-rotating propellers. Still, Loutzkoy’s ideas demonstrate innovation and creativity in the early days of aviation.

Rumpler Loutzkoy-Taube rear

This rear view of the Loutzkoy-Taube illustrates the aircraft’s similarity, with the exception of the double propellers, to a standard Taube. Note the fuel tanks attached to the cabane strut above the cockpit.

Sources:
“The Loutzkoy 200-Horsepower Monoplane” Daily Consular and Trade Reports (29 May 1912)
“Rumpler-Taube mit Zwei-Motoren-Anlage System Loutzkoy” Flugsport (13 March 1912)
“Polytechnische Rundschau: Rumpler-Taube mit Motoranlage nach System Loutzkoy” Dinglers Polytechnisches Journal (16 March 1912)
“Flugzeug mit zwei gleichachsig und unmittelbar hintereinander angeordnetem Propellern” German patent no. 263,059 by Boris Loutzkoy (granted 29 October 1911)
Rumpler: zehn jahre deutsche Flugtechnik (1919)
Typenhandbuch der deutschen Luftfahrttechnik by Bruno Lange (1986)
Argus – Flugmotoren und Mehr by Wulf Kisselmann (2012)
http://rusaviagold.narod.ru/HISTORY/lutskoi.htm
http://alternathistory.com/samoletostroitelnyi-zavod-rumpler-flugzeugwerke-i-ego-razvitie-v-1908-1913-e-gody
http://flyingmachines.ru/Site2/Crafts/Craft26875.htm

Allison V-3420-A front

Allison V-3420 24-Cylinder Aircraft Engine

By William Pearce

In the mid-1930s, the United States Army Air Corps (AAC) was interested in a long-range bomber. Boeing won a contract to build the aircraft, which was originally designated XBLR-1 (eXperimental Bomber Long Range-1), but ultimately became the XB-15. By 1935, the AAC realized that current engines, and those under development, lacked the power needed for such a large aircraft. At the time, the AAC was pursuing its next experimental long-range bomber, the Douglas XBLR-2. The AAC requested the Allison Engineering Company build a 1,600 hp (1,193 kW) engine for the XBLR-2, which later became the XB-19.

Allison V-3420-A front

The Allison V-3420 was much more than two V-1710 engines coupled together. However, as many V-1710 components were used as possible, resulting in only 340 new parts. This is a V-3420-A engine with an attached single-rotation gear reduction.

In 1935, Allison was in the middle of developing its 1,000 hp (746 kW) V-1710 engine. The AAC requested that the new 1,600 hp (1,193 kW) engine have a single crankshaft and use as many V-1710 components as possible to keep development time to a minimum. After evaluating a few different configurations, Allison decided to double the V-1710 to create a 24-cylinder engine in an X configuration. This engine became the X-3420.

The X-3420 would have an entirely new crankcase, crankshaft, gear reduction, supercharger, and accessory section, but it would keep the basic V-1710 cylinder and head. The X-3420 had a flattened X arrangement with a left and right cylinder bank angle of 60 degrees, an upper cylinder bank angle of 90 degrees, and a lower cylinder bank angle of 150 degrees. The fuel-injected engine would produce 1,600 hp (1,193 kW) at 2,400 rpm for takeoff and 1,000 hp (746 kW) at 1,800 rpm for economical cruise. The engine would have an 8.5 to 1 compression ratio and weigh 2,160 lb (980 kg).

While using as many V-1710 components as possible made Allison’s job easier, the X-3420’s single crankshaft and its master and articulating rods required much design work, as did its fuel-injection system. Very quickly, Allison realized it did not have the resources to develop the X-3420 and needed to focus on the V-1710, which was encountering technical issues. Development of the X-3420 was effectively abandoned in 1936. As an alternative, Ron Hazen, Allison’s Chief Engineer, proposed a new 2,000 hp (1,491 kW) engine that had two crankshafts and was more closely based on the V-1710. The engine would produce more power than the X-3420 and be developed in less time. The AAC approved of Hazen’s proposed engine, which became the V-3420. The engine was often referred to as a W-24 or double Vee (DV) and was occasionally called the DV-3420.

Allison V-3420-A rear

Rear view of the V-3420-A shows the supercharger mounted behind the right engine section and various accessories mounted behind the left engine section. The V-3420’s design enabled the engine to produce more power than its X-3420 progenitor.

The Allison V-3420 design was more complex than just coupling two V-1710 engines together. As with the proposed X-3420, a new crankcase, gear reduction, supercharger, and accessory section were at the center of the engine, but the V-3420 would utilize many V-1710 components. The use of two V-1710 crankshafts along with their connecting rods made the V-3420’s design and development much more manageable for Allison. The engine consisted of two 60 degree V-12 engine sections mounted on a common crankcase and separated by 90 degrees, which gave the inner cylinder banks 30 degrees of separation.

As V-1710 development progressed, Allison was able to offer the V-3420 with 2,300 hp (1,715 kW) for takeoff. At 2,300 lb (1,043 kg), the engine would only weigh 140 lb (64 kg) more than the single crankshaft X-3420, but it would produce an additional 700 hp (522 kW). In May 1937, the AAC contracted Allison to build the V-3420 engine prototype.

A large aluminum crankcase sat at the center of the 24-cylinder V-3420 engine. Attached to the crankcase were four cylinder banks. Each cylinder bank consisted of six steel cylinder barrels shrink fitted to a one-piece aluminum cylinder head. Each cylinder barrel was surrounded by an aluminum water jacket. A single overhead camshaft actuated two intake and two exhaust valves for each cylinder. Each cylinder had a 5.5 in (140 mm) bore and a 6.0 in (152 mm) stroke. The engine displaced 3,421 cu in (56.1 L) and had a compression ratio of 6.65 to 1. At the rear of the engine was a supercharger driven by the right crankshaft, and all accessories were driven by the left crankshaft. The engine was also intended to be used with a General Electric turbosupercharger.

Allison V-3420-B NMUSAF rear

This V-3420-B was the type installed in the Fisher XP-75. About 15 ft (4.6 m) of shafting separated the engine from the gear reduction. Note the much larger supercharger compared to the image of the V-3420-A engine. The V-3420-B used a two-stage supercharger and no turbosupercharger. (Gary Brossett image via the Aircraft Engine Historical Society)

There were only 340 parts unique to the V-3420 engine, and those accounted for 930 pieces of the 11,630 that made up the engine. Initially, the V-3420 had a takeoff rating of 2,300 hp (1,715 kW) at 3,000 rpm, a maximum rating of 2,000 hp (1,491 kW) at 2,600 rpm, and a cruise rating of 1,500 hp (1,119 kW) at 2,280 rpm. The basic 24-cylinder engine was 97.7 in (2.48 m) long, 60.0 in (1.52 m) wide, and 38.7 in (.98 m) tall. The engine weighed 2,665 lb (1,209 kg)—365 lb (166 kg) more than the original estimate.

In January 1938, Allison was authorized to release V-3420 engine specifications to aircraft manufacturers and airlines. This resulted in a number of aircraft designs incorporating the engine; however, only four V-3420-powered aircraft types were actually flown. The V-3420 engine was first run in April 1938, followed by an AAC order for six engines in June 1938. An engine was also displayed in the 1939 World’s Fair in New York.

The US Navy was aware of the V-3420 engine and asked Allison if it could be converted for marine use. Allison responded with the appropriate designs. In December 1939, the Navy ordered two V-3420 marine engines for installation in a new, aluminum-hulled Patrol Torpedo boat designated PT-8. The two V-3420 marine engines were delivered to the Navy, and the PT-8 boat started trials in November 1940. The PT-8 was tested through 1941, but no further boats or V-3420 marine engines were ordered. The sole PT-8 was later re-engined and still exists as of 2017.

Allison V-3420-B NMUSAF

On the V-3420-B engine, an idler gear kept the crankshafts in sync. The engine’s large crankcase can be seen in this image. The large aluminum casting had front and rear covers and a magnesium oil pan. (Gary Brossett image via the Aircraft Engine Historical Society)

For aircraft use, the V-3420 required further development, which was slow due to Allison’s ongoing commitments to the V-1710 engine as well as the AAC’s preoccupation with vastly expanding its resources for the coming war. In late 1940, Allison focused on two major models of the V-3420 engine: -A and -B. The V-3420-A had crankshafts that rotated the same direction—either clockwise or counterclockwise, depending on the desired rotation of the propeller. The -A engine used a single-rotation propeller with either an attached or remote gear reduction, but most commonly with an attached gear reduction. The V-3420-B had crankshafts that rotated in opposite directions and was used with contra-rotating propellers. Different versions of the -B engine could accommodate either an attached or remote gear reduction, which allowed a number of propeller shaft configurations, including right-angle drives. The -B engine almost always had a remote gear reduction. The two crankshafts of the V-3420-B were kept in sync by idler gears at the front of the engine. The idler gears also balanced power loads from the crankshafts to the contra-rotating propeller shafts.

In September 1940, Allison’s V-1710 commitments became overwhelming, and development of the V-3420 engine was put on hold. As a result, the XB-19 had four 2,000 hp (1,491 kW) Wright R-3350 18-cylinder radial engines installed in place of the V-3420s. However, the R-3350 was encountering its own extensive developmental issues that put its use in the Boeing B-29 Superfortress in question. In February 1941, the AAC requested that Allison restart development of the V-3420-A with an output of 3,000 hp (2,237 kW) as a possible replacement for the Wright R-3350. The B-29 bomber was too important for its fate to be tied to one engine.

Allison V-3420-B right-angle drive

One V-3420-B engine was built to be mounted in an aircraft’s fuselage with extension shafts leading through the wings to right angle drives that would connect to the propellers. This type of engine configuration would have been used in the McDonnell Model 1. Only one engine was built with this configuration.

A V-3420 engine was delivered to Wright Field in October 1941, but with the bombing of Pearl Harbor in December, the V-3420 program was again put on hold so that Allison could focus on the V-1710 engine. History repeated itself in mid-1942 when the suitability of the R-3350 engine was again in question. Allison was instructed by the Army Air Force (AAF—the AAC was renamed in June 1941) to prepare the V-3420 for installation in a B-29, which was redesignated XB-39. Nine engines were built and delivered by October 1942. On 1 October 1942, the AAF ordered two Fisher XP-75 Eagle fighter prototypes that were powered by the V-3420-B engine. This was followed by an order placed on 28 October for 500 V-3420-A engines for installation in 100 production B-39 aircraft.

As the aircraft projects were underway, continued development of the V-3420 engine increased its output to a takeoff rating of 2,600 hp (1,939 kW) at 3,000 rpm with 8 psi (.55 bar) of boost, a normal rating of 2,100 hp (1,566 kW) at 2,600 rpm at 25,000 ft (7,620 m), and a cruise rating of 1,575 hp (1,175 kW) at 2,300 rpm at 25,000 ft (7,620 m). However, the engine could be overboosted in emergency situations to 3,000 hp (2,237 kW) at 3,000 rpm with 10.2 psi of boost (.70 bar).

Fisher P-75A Eagle

The Fisher P-75A was the end of a very tumultuous fighter program. The original design consisted of various parts from other aircraft that, when combined, would somehow make an aircraft superior to all others. The reality was that the combined parts created an aircraft that was downright dangerous and needed to be redesigned. A partial redesign did not completely cure the problems, and problems still existed after a subsequent complete redesigned. Still, 2,500 aircraft were ordered before better judgment prevailed and the program was cancelled. The P-75 was the only aircraft flown with V-3420-B engines.

The first aircraft to fly with the V-3420 was the Fisher XP-75. Developed by the Fisher Body Division of General Motors, the XP-75 was a long-range escort fighter. Through 1943, the AAF felt a desperate need for such an aircraft and ordered six additional XP-75 prototypes, bringing the total to eight. In addition, the AAF expressed its intent to purchase 2,500 P-75s if the prototypes met their performance estimates. The V-3420-B engine for the P-75 had a two-stage, variable speed supercharger (and no turbosupercharger) that was hydraulically coupled to the right crankshaft. The engine alone weighed 2,750 lb (1,247 kg), and its weight increased to 3,275 lb (1,486 kg) with its 3.5 in (89 mm) diameter extension shafts and remote gear reduction.

The XP-75 first flew on 17 November 1943, and the aircraft almost immediately ran into issues. Its V-3420-B engine was not entirely trouble free either; unequal fuel distribution was a continuing problem for the V-3420. The issue was mostly solved by having each alternate engine section fire every 30 degrees of rotation, rather than both engine sections firing every 60 degrees of rotation. The aircraft was redesigned to correct its deficiencies and was given the new designation of P-75A. The AAF ordered 2,500 P-75As on 7 June 1944, and production started immediately. However, the entire P-75 program was cancelled four months later, in October 1944. The P-75A did not live up to expectations, it was outmatched by aircraft already in service, and the end of the war was in sight. Eight XP-75 and six P-75A aircraft were built, but three of the aircraft crashed during testing. One P-75A was preserved and is on display in the National Museum of the US Air Force. The rest of the surviving aircraft were scrapped.

Douglas XB-19A

With V-3420-A engines installed, the Douglass XB-19A realized a boost in its performance. While the engines proved reliable, it was very time-consuming for Fisher to design and fabricate the new nacelles to house the V-3420. The same basic nacelle was also used on the XB-39.

Actual work to install V-3420-A engines in the XB-19 started in November 1942 at Fisher. The aircraft was redesignated XB-19A and flew for the first time with its V-3420 engines in January 1944. The V-3420 installation served as a test for the engine’s use in the XB-39. With the exception of range, the XB-19A’s performance increased across the board: maximum speed increased by 40 mph (64 km/h); cruising speed increased by 50 mph (80 km/h); service ceiling increased by 16,000 ft (4,877 m), but normal range decreased by 1,000 miles (1,609 km). The XB-19A was strictly an experimental aircraft and was never intended to enter production.

In February 1943, V-3420-A engines were selected to power the Lockheed XP-58 Chain Lightning. The V-3420 was not Lockheed’s first choice, or second, or third. The XP-58 heavy fighter program was initiated in 1940 but was beset with constant design and role changes, which were made worse by developmental issues of the aircraft’s previously selected engines. By the time it was completed, the XP-58 was oversized, overweight, underpowered, and not needed. First flown on 6 June 1944, the aircraft’s lackluster performance matched Lockheed and the AAF’s enthusiasm for the project. Only one prototype was built, and the XP-58 program was cancelled in May 1945.

Allison V-3420 XB-19A nacelle

The men working on the V-3420 installed in the XB-19A give some perspective as to the engine’s size and the size of the aircraft. The V-3420’s radiator, oil cooler, turbosupercharger, and intercooler were all mounted in the nacelle, under the engine. This configuration prevented the need for heavily modifying the aircraft.

Even though it helped spur the V-3420 engine program, the V-3420-powered B-29 was the last aircraft to take flight with the engine. A B-29 (actually a YB-29, the first pre-production aircraft) was delivered to Fisher for conversion to an XB-39 with V-3420-A engines. Work on the XB-39 was slow because Fisher’s main focus was the XP-75. The XB-39 finally flew on 9 December 1944. Performance of the XB-39 was superior to that of the B-29: its top speed was 50 mph (80 km/h) faster, and it had a 3,000 ft (914 m) higher service ceiling. However, standard B-29s were proving to be more than adequate, and it was not worth the time or trouble to convert any other airframes to V-3420-power.

To meet the power needs for extremely large aircraft designs during World War II, Allison proposed the DV-6840. The DV-6840 consisted of two V-3420s driving a common remote gearbox for contra-rotating propellers. A gearbox for the DV-6840 was completed in 1946, but no information has been found regarding it being tested. Allison had also planned a further development of the V-3420. This fuel-injected V-3420-C engine had a forecasted emergency output of 4,800 hp (3,579 kW) and a takeoff/military rating of 4,000 hp (2,983 kW)—both ratings at 3,200 rpm with water injection. However, the V-3420-C was never built.

Lockheed XP-58 Chain Lightning

The Lockheed XP-58 was another program than inexplicably pressed on despite the many signs that it was heading nowhere. Somewhere between three to seven engines were selected before the V-3420-A was finally chosen to power the aircraft. It was not Lockheed’s fault; they had no control over which experimental engines would actually be produced. Lockheed also had no control over the constantly changing roles the AAF asked the XP-58 to fulfill.

The Allison V-3420 was not a trouble-free engine, but it did work well in its few applications once initial issues were resolved. The engine held a lot of potential, but that potential faded as its development languished. At the start of 1944, only 33 V-3420 engines had been delivered, and two of those were marine engines. Had the AAC committed to the engine in 1936 and provided Allison with the resources needed to develop the engine, the V-3420 very well could have powered the B-29 and various post-war aircraft. The four aircraft projects that used the V-3420 did not fail because of the engine. By the time the V-3420 program was in order in 1944, other engines were adequately fulfilling the 3,000 hp (2,237 kW) role.

Allison built a total of 157 V-3420 engines: 37 -A engines (including the two marine engines) and 120 -B engines. A number of V-3420s were sold as surplus after the war. Some eventually made their way into museums, while other engines were used in a hydroplane (Henry J. Kaiser’s Scooter Too driven by Jack Regas) and a tractor puller (E. J. Potter’s Double Ugly). However, none of the V-3420 engines took flight again.

Fisher XB-39

The Boeing / Fisher XB-39 program is what put the V-3420 engine back on track to production. It was the most promising aircraft out of the four powered by the V-3420. Delayed by Fisher’s work on the XP-75, there was little point to the aircraft when it took to the air in December 1944. The image above shows the V-3420 engines being installed at the Fisher plant in Cleveland, Ohio. Fisher was producing various subassemblies for the B-29, which can be seen in the background. On the right side of the image, just behind the XB-39’s wing, is the fuselage of a P-75A.

Sources:
Vees For Victory!: The Story of the Allison V-1710 Aircraft Engine 1929-1948 by Dan Whitney (1998)
The Allison Engine Catalog 1915-2007 by John M. Leonard (2008)
Jim Allison’s Machine Shop: The First 30 Years by John M. Leonard (2016)
Aircraft Engines of the World 1946 by Paul H. Wilkinson (1946)
Allied Aircraft Piston Engines of World War II by Graham White (1995)
US Army Air Force Fighters Part 2 by William Green and Gordon Swanborough (1978)
McDonnell Douglas Aircraft since 1920: Volume I by Rene J. Francillon (1988)
Lockheed Aircraft since 1913 by Rene J. Francillon (1982/1987)
Boeing Aircraft since 1916 by Peter M. Bowers (1966/1989)

Fokker Dekker CI front

Dekker-Fokker C.I Rotary Propellers

By William Pearce

In the 1920s, Adriaan Jan Dekker helped redesign windmill sails in the Netherlands to improve their efficiency. His modified sails were streamlined and acted more as airfoils than the traditional sails in use. Dekker’s first sail was tested briefly in 1927, with more expansive tests in 1928. By 1930, 31 windmills were using Dekker’s sails, and the number increased to 75 by 1935.

Dekker patent rotary propellers

Drawings from Adriaan Dekker’s rotary propellers patent (US 2,186,064). The direction of rotation was actually opposite of the unit that was built and installed on a Fokker C.I. Note the airfoil sections of the blades.

In the 1930s, Dekker began to focus on improving aircraft propellers. In 1934, Dekker filed for a patent on a new type of turbine rotor blade for aircraft use. British patent 450,990 was awarded on 27 July 1936, and it outlined the use of a single rotation, four-blade rotary propeller. However, Dekker found that a single set of rotors caused a divergent airflow that virtually bypassed an aircraft’s tail. This caused control issues because it decreased airflow over the aircraft’s rudder and elevator.

Dekker continued to develop his design and applied for another patent in June 1936, before the first patent was awarded. The new British patent (476,226) was awarded on 3 December 1937 and outlined the use of contra-rotating rotors. Strangely, the gearing for the propellers was not included in the British patent but was included in the US (and French) patent filed on 19 May 1937 and granted patent 2,186,064 on 9 January 1940.

Dekker propeller construction

Construction images of the Dekker rotary propeller. The images are mainly the hub and blades of the front set of rotors. (hdekker.info image)

Almost all of the information contained in the British patent was also in the US patent. However, the US patent was more detailed and included additional information. The patents illustrate a large, streamlined hub from which two sets of four-blade rotors protrude. The original patent stated that the ideal blade length was one third of the hub diameter. The fixed-pitch blades were highly curved airfoils of a complex shape. The angle of the blade decreased from 40 degrees at the root to 5 degrees at the tip. In addition, the blade’s cord (length from leading edge to trailing edge) steadily increased from its root to its tip.

The two sets of blades were contra-rotating. The rear set of blades served to straighten the airflow from the front set, providing additional thrust and increasing efficiency. The contra-rotation of the blades also helped eliminate torque reactions. Through a gear reduction, the rear set of blades only turned at two-thirds the speed of the front set of blades. Dekker also noted that the rotary blades would be quieter than conventional propellers.

Fokker Dekker CI front

Dekker’s finished C.I with its large rotary propellers. Note the complex airfoil shape of the blades.

The drive for the rotors consisted of a sun gear mounted on the engine’s crankshaft that turned planetary gears against a fixed, internally-toothed ring gear. The planetary gears were mounted in a carrier from which a shaft extended to power the front set of blades. These blades rotated in the same direction as the engine and at an unspecified reduction. Attached to the shaft powering the front set of blades was another sun gear. This sun gear turned three idler gears that turned three planetary gears against another fixed, internally-toothed ring gear. This gear train reduced the rotation speed by 66% from the sun gear (and front set of blades). A hollow shaft extended from the planetary gear carrier to power the rear set of blades. Inside the hollow shaft was the propeller shaft for the front set of blades. The rear set of blades rotated the opposite direction of the engine.

To turn theory to reality, Dekker formed a company, Syndicaat Dekker Octrooien (Dekker Patents Syndicate), and acquired a Fokker C.I trainer aircraft around 28 March 1936. The C.I was a late World War I era biplane reconnaissance aircraft powered by a 185 hp BMW IIIa engine. As the aircraft’s design aged, transport and trainer versions were built. Dekker’s C.I was registered PH-APL on 15 April 1937.

Fokker Dekker CI taxi

Registered PH-APL, Dekker’s heavily modified Fokker C.I bears little resemblance to a standard C.I; the wings and tail are about all the aircraft have in common. Note how the fuselage shape tapers the diameter of the large propeller hub back to the tail. With its contra-rotating rotary propellers spinning, the aircraft is shown before taxi tests at Ypenburg airfield.

To accommodate the rotary propellers, Dekker’s aircraft was so heavily modified that it was nearly unrecognizable as a C.I. The aircraft retained the BMW engine but had the contra-rotating rotary propellers mounted to its front. The fuselage of the aircraft was modified and tapered from the very large propeller hub back to the tail. The fuselage was metal-covered immediately behind the propellers, but the rest of the fuselage was covered with fabric.

The rotary propellers differed from those illustrated in the patents in that six blades made up the front set of rotors, and seven blades made up the rear set. Construction of the individual blades was similar to that of a wing. The blades were made of a shaped aluminum sleeve fitted around three spars. The spars passed into and were connected to the hub. The roots of the blades were also attached to the hub. The hub was formed of an aluminum frame and covered with aluminum sheeting. Video indicates that the rear set of blades had roughly a 66% speed reduction compared to the front set—which matches what was stated in the patent.

Fokker Dekker CI captured Germans

Two views of Dekker’s C.I after it was captured by German forces. The right image clearly shows six blades on the front rotor and seven blades on the rear rotor.

The aircraft’s completion date is unknown, but Dekker’s C.I underwent taxi tests at Ypenburg airfield, near The Hauge, Netherlands. The aircraft reportedly made a few hops into the air, but no true flight was achieved. It is not clear if there was an issue with the rotary propellers (such as insufficient thrust or excessive vibrations) or if the project simply ran out of time. Dekker’s C.I was moved to Waalhaven Airport, where it was captured by German forces on 18 May 1940, eight days after the Germans started their invasion of the Netherlands at the start of World War II. Reportedly, the aircraft was taken to Johannisthal airfield near Berlin, Germany for testing. Some sources state the aircraft crashed on its first test flight and that its remains were later destroyed as Russian troops advanced late in the war. However, exactly what happened to Dekker’s C.I and its rotary propellers is not known.

Below is video uploaded to YouTube of the Fokker Dekker C.I undergoing taxi tests. Note the stroboscopic effect of the rotors turning at different speeds. Adriaan Dekker is shown at the end of the video. It is interesting to contemplate how much weight the rotary propellers added to the nose of the aircraft. Unfortunately, the date of the tests is not known.


Sources:
“Screw Propeller, Turbine Rotor, and Like Device” US patent 2,068,792 by Adriaan Jan Dekker (granted 26 January 1937)
“Rotary Propeller and the Like Device” US patent 2,186,064 by Adriaan Jan Dekker (granted 9 January 1940)
http://www.hdekker.info/DIVERSEN/Vragenrubriek.html
http://www.hdekker.info/registermap/TWEEDE.htm#PH-APL
http://www.fokker-aircraft.com/database/fokker-c-type/fokker-c.html
http://www.airhistory.org.uk/gy/reg_PH-.html
http://forum.keypublishing.com/showthread.php?132130-Question
Power from Wind: A History of Windmill Technology by Richard L. Hills (1996)

CTA - ITA Heliconair Convertiplano drawing

CTA / ITA Heliconair HC-I Convertiplano

By William Pearce

In 1923, Henrich Focke partnered with Georg Wulf to create Focke-Wulf Flugzeugbau (Aircraft Company) in Bremen, Germany. Focke became fascinated with helicopters and other rotorcraft in the 1930s. This interest led to what is considered the first practical helicopter, the Focke-Wulf Fw 61, which first flew in 1936. That same year, Focke was ousted from Focke-Wulf due to internal disagreements about allocating company resources. In 1937, Focke partnered with Gerd Achgelis, the Fw 61’s lead designer, to create Focke-Achgelis & Co in Hoykenkamp, Germany. The new company would focus on helicopter and rotorcraft designs.

CTA - ITA Convertiplano side

The Heliconair HC-Ib Convertiplano sits nearly finished in a hangar. The slit behind the cockpit was the intake for air used to cool the fuselage-mounted R-3350 engine. The scoop on the upper fuselage brought air to the engine’s carburetor. Note the Spitfire wings and main gear.

In 1941, the RLM (Reichsluftfahrtministerium or Germany Air Ministry) requested that Focke-Achgelis design a fighter capable of vertical takeoff and landing (VTOL). Focke-Achgelis responded with the Fa 269 design, which was a tiltrotor convertiplane. The Fa 269 had two rotors—one placed near the tip of each wing in a pusher configuration. The rotors were powered by an engine housed in the aircraft’s fuselage via extension shafts and gearboxes. The rotors and extension shafts leading from the right-angle gearboxes mounted in the aircraft’s wings rotated down to “push” the Fa 269 into the air, achieving vertical flight. Once airborne, the rotors and shafts would slowly translate back into the wing to propel the aircraft forward, allowing the aircraft’s wings to provide lift. The project moved forward until 1944, when much of the developmental work, including models, a mock-up, and gearboxes, was destroyed in an Allied bombing raid.

CTA - ITA Heliconair Convertiplano

Drawings of how the completed HC-Ib was anticipated to look reveal a pretty compact aircraft, considering the engine installation and associated shafting. The R-3350 engine took up the space intended for a passenger compartment in the Double Mamba-powered HC-I. The Double Mamba would have been installed aft of the passenger compartment.

Immediately following World War II, Germany was prohibited from designing and manufacturing aircraft. Post war, Focke assisted with helicopter development in France and worked for a car company in Germany. He also spent some time in the Netherlands, where he began to design a VTOL aircraft that was capable of relatively high speeds. In 1952, Focke was recruited by the CTA (Centro Técnico de Aeronáutica or Technical Center of Aeronautics) to work in the recently established ITA (Instituto Técnico de Aeronáutica or Technical Institute of Aeronautics). The ITA was the first of four institutes formed by the CTA, all of which were located in São José dos Campos, Brazil. Brazil was working on building an aeronautics and aerospace industry and was actively recruiting German engineers. In addition to Focke, many of his associates and former co-workers were also recruited.

The CTA was impressed with Focke’s VTOL aircraft design and approved its construction. The CTA believed that the aircraft’s capabilities would allow it to reach remote parts of Brazil. Focke set to work on the aircraft—a tiltrotor convertiplane design that was partially inspired by the Fa 269. The aircraft was known as the Heliconair HC-I Convertiplano. Its fuselage and wings were fairly conventional for an aircraft, but it had of two sets of rotors. One pair of rotors was placed near the nose of the aircraft, and the other pair was placed between the wings and tail. All of the rotors were of a tractor configuration and rotated up for vertical flight. The HC-I accommodated two pilots in the cockpit and four passengers in the fuselage. The aircraft’s estimated performance included a top speed of 311 mph (500 km/h) and a range of 943 miles (1,517 km).

CTA - ITA Convertiplano engine test rig

The test rig for the engine, transmission, gearboxes, shafts, right-angle drives, and rotors illustrates the complexity of the HC-Ib’s power system. The R-3350 engine did not have any Power Recovery Turbines, which means it was not a Turbo Compound engine.

To save time and money, the decision was made to build the HC-I using the wings and the horizontal stabilizer from a Supermarine Spitfire. A Spitfire XIVe (RM874) was purchased without its Rolls-Royce Griffon 65 engine from Britain by the Brazilian Air Attaché on 19 December 1952. A new fuselage was built to house a 3,000 hp (2,237 kW) Armstrong Siddeley Double Mamba turboprop engine behind the passenger compartment. However, Armstrong Siddeley and the British did not want one of their new, advanced engines being used in such a radical project and declined selling a Double Mamba engine to Brazil.

Focke and the Convertiplano team changed the HC-I’s design to accommodate a 2,200 hp (1,641 kW) Wright R-3350 radial engine and redesignated the aircraft HC-Ib. The R-3350 was larger and heavier than the Double Mamba, and it produced less power. Some sources state a Turbo Compound R-3350-DA3 (3,250 hp / 2,424 kW) was used, but images show that there are no Power Recovery Turbines on the engine installed in a test rig. Extensive modifications to the aircraft’s fuselage were required to accommodate the air-cooled engine. The passenger compartment was omitted, and the R-3350 was installed in the middle of the fuselage. An annular slit behind the cockpit was added to bring in cooling air for the engine. After passing through the engine’s cylinders, the air exited via a jet-like duct at the rear of the aircraft. The Spitfire’s landing gear was strengthened to compensate for the R-3350’s weight.

CTA - ITA Convertiplano components

The HC-Ib sits in the background with the front and rear gearboxes and rotor drives in the foreground. The rotor blades, the only surviving component of the Convertiplano project, are not seen in the image. Note the opening at the rear of the fuselage, which was the exit for engine cooling air.

A gearbox transmission mounted to the front of the R-3350 split the engine’s power to two shafts. The front shaft extended from the engine to the front gearbox. The front gearbox had shafts that extended to the left and right. These shafts led to right-angle gearboxes that powered the front rotors. Power delivery for the rear rotors was more complex. A shaft extended vertically from the transmission on the front of the engine and met a right-angle gearbox positioned directly above the engine. From the right-angle gearbox, a shaft extended back to the rear gearbox. The rear gearbox had the same shafts and right-angle drives for the rear rotors as the front gearbox. The transmission and gearboxes were designed by Willi Bussmann and built by BMW in Germany. Bussmann was a former BMW employee and had worked with Focke on several Focke-Achgelis projects.

Each rotor consisted of three blades. The blades were built in Sweden and made of a steel frame that was covered with wood. The blades’ pitch automatically adjusted and had collective and cyclic control. The rotors were counter-rotating, with the right rotors turning counterclockwise and the left rotors turning clockwise. The HC-Ib had a 37 ft 6 in (11.42 m) wingspan and was 35 ft 3 in (10.74 m) long.

CTA - ITA Convertiplano engine hoist

Given the state of the aircraft and the surrounding unchecked growth of vegetation, it can be assumed this image is of the R-3350 engine being removed sometime after the HC-Ib project was cancelled. The image does give proof that the engine was installed in the airframe at one point.

A rig was built, and tests of the engine, gearboxes, shafts, right-angle drives, and rotors began in late 1953. However, vibrations from the radial engine caused some issues that took time to resolve. The HC-Ib airframe was almost completely constructed and had its engine installed when the project was cancelled in 1955. The aircraft was more expensive than anticipated, and interest in the HC-1b had steadily declined after the switch to the R-3350 engine. To make matters worse, many of the Germans returned to Europe or went to the United States as their contracts with the CTA expired. Some Germans did stay and ultimately became part of Embraer. After the project was cancelled, the HC-Ib Convertiplano was left to rot in outside storage for some time and was eventually scrapped in the 1970s. There are some reports that the rotor blades are the only part of the aircraft that survived.

A follow up Convertiplano project was considered. Designated HC-II, the aircraft would be powered by four 1,400 hp General Electric T58 turboshaft engines and reincorporate a four to six passenger cabin. The HC-II never progressed beyond the initial design phase.

CTA - ITA Convertiplano HC-II

The C-II Convertiplano had a GE T58 engine mounted directly to each of its four rotors. Otherwise, it retained the configuration of the original HC-I.

Sources:
Axis Aircraft in Latin America by Amaru Tincopa and Santiago Rivas (2016)
“Uma Breve História das Atividades do Prof. Focke no Brasil” by Joseph Kovacs, ABCM Engenharia Volume 9 Número 2 (April–September 2003)
http://www.internationalresinmodellers.com/articles_15_cta_heliconair_hc-i_-ii_convertiplano
http://aeromagazine.uol.com.br/artigo/convertiplano-o-pioneiro-esquecido_491.html
https://en.wikipedia.org/wiki/Henrich_Focke
https://en.wikipedia.org/wiki/Focke-Wulf
http://allspitfirepilots.org/aircraft/RM874
http://www.secretprojects.co.uk/forum/index.php?topic=25141.0
http://forum.keypublishing.com/showthread.php?24794-Mark12-s-Quiz&s=17aba5b94d69d4e1642b3d04aefcf85c

mercedes-benz-mb-518-v-20-rear

Mercedes-Benz 500 Series Diesel Marine Engines

By William Pearce

Daimler-Benz was formed in 1926 with the merger of Daimler Motoren Gesellschaft and Benz & Cie. Prior to their merger, both companies produced aircraft engines under the respective names Mercedes and Benz. After the merger, the Daimler-Benz name was used mostly for aircraft engines, and the Mercedes-Benz name was used mostly for automobile production. However, both names were regularly applied to marine engines. For clarity in this article, the name Daimler-Benz will refer to aircraft engines, and the name Mercedes-Benz will refer to marine engines.

mercedes-benz-mb-500-v-12

Two V-12 Mercedes-Benz diesel engines, most likely MB 500s. The MB 500 was the foundation for the post-war MB 820.

As Germany began its rearmament campaign in the 1930s, high-performance marine diesel engines were needed to power various motorboats. The Kriegsmarine (German Navy) turned to Mercedes-Benz to supply a series of high-speed diesel engines. These engines were part of the MB 500 series of engines that were based on the Daimler-Benz DB 602 (LOF-2) engine developed to power the LZ 129 Hindenburg and LZ 130 Graf Zeppelin II airships. The 500 series diesel engines were four-stroke, water-cooled, and utilized a “V” cylinder arrangement.

The first engine in the 500 series was the MB 500 V-12. The engine’s two cylinder banks were separated by 60 degrees. The MB 500 used individual steel cylinders that were attached to an aluminum alloy crankcase. About a third of the cylinder was above the crankcase, and the remaining two-thirds protruded into the crankcase. This arrangement helped eliminate lateral movement of the cylinders and decreased vibrations. The crankcase was made of two pieces and split horizontally through the crankshaft plane. The lower part of the crankcase was finned to increase its rigidity and help cool the engine oil.

mercedes-benz-mb-501-v-20-rear

The MB 501 shows the close family resemblance to the DB 602, but the engines had Vees of different angles and completely different valve trains. The tubes for the push rods can be seen on the outer side of the cylinders. Note the two water pumps on the rear sides of the engine.

Each cylinder had two intake and two exhaust valves. The camshaft had two sets of intake and exhaust lobes per cylinder. One set was for normal operation, and the other set was for running the engine in reverse. The fore and aft movement of the camshaft to engage and disengage reverse operation was pneumatically controlled. Bosch fuel injection pumps were located at the rear of the engine and were geared to the camshaft. Each injection pump provided fuel to the cylinders at 1,600 psi (110.3 bar). Fuel was injected into the center of the pre-combustion chamber, which was in the center of the cylinder head and between the four valves. For low-speed operation, fuel was cut from one bank of cylinders.

The MB 500 had a compression ratio of 16.0 to 1. The engine used fork-and-blade connecting rods that rode on roller bearings fitted to the crankshaft. The camshaft also used roller bearings, but the crankshaft was supported by plain bearings. Speed reduction of the engine’s output shaft was achieved through the use of bevel planetary gears. Two water pumps mounted to the rear sides of the engine circulated water through the cylinder banks. Each pump provided cooling water to one cylinder bank. The pumps were driven by a cross shaft at the rear of the engine. The engine was started with compressed air.

mercedes-benz-mb-501-v-20-crackington

The crankcases of the wrecked MB 501 engines on Crackington Haven Beach have completely dissolved over the years from constant exposure to salt water. Only the engine’s steel components remain. Note the fork-and-blade connecting rods. The engine’s gear reduction can be seen on the left side of the image. (gsexr image via 350z-uk.com)

The MB 500 had a 6.89 in (175 mm) bore and a 9.06 in (230 mm) stroke. This cylinder size directly corresponded to the cylinder size used on the DB 602. The MB 500’s displacement was 4,051 cu in (66.39 L). The engine had a continuous output of 700 hp (522 kW) at 1,460 rpm and a maximum output of 950 hp (708 kW) at 1,630 rpm. Fuel consumption was .397 lb/hp/hr (241 g/kW/hr). The MB 500 was 9.6 ft (2.93 m) long, 3.2 ft (.98 m) wide, and 5.7 ft (1.73 m) tall. The engine weighed around 4,784 lb (2,170 kg). MB 500 engines were installed in Schnellboote that Germany built for Bulgaria. A Schnellboot, or S-boot, was a fast attack boat and was referred to as an E-boat (Enemy boat) by the Allies. The MB 500 engine design served as a basis for the post-war MB 820 industrial engine that was used in the V 200 Class locomotives and various ships.

For more power, the MB 501 was built with two rows of ten cylinders, creating a V-20 engine. The MB 501 was similar to the MB 500, but it also had a number of differences. A 40 degree angle separated the cylinder banks, and the engine used two camshafts positioned in the upper crankcase, one on each side of the engine. Rollers on the lower end of the pushrods rode on the camshaft. Two pushrods for each cylinder extended up along the outer side of the cylinder bank to operate a set of duplex rocker arms for the two intake and two exhaust valves. The fork-and-blade connecting rods were attached to the crankshaft with plain bearings.

mercedes-benz-mb-502-v-16

With the exception of the different intake manifolds, the MB 502 was nearly identical to the DB 602. Note the Mercedes-Benz emblem on the rear of the V-16 engine.

The MB 501’s bore and stroke were increased over the MB 500’s to 7.28 in (185 mm) and 9.84 in (250 mm) respectively. The engine displaced 8,202 cu in (134.40 L). The MB 501 had a continuous output of 1,500 hp (1,119 kW) at 1,480 rpm and a maximum output of 2,000 hp (1,491 kW) at 1,630 rpm. Fuel consumption was .397 lb/hp/hr (241 g/kW/hr). The engine was 12.7 ft (3.88 m) long, 5.2 ft (1.58 m) wide, 5.6 ft (1.71 m) tall, and had a weight of 9,303 lb (4,220 kg). Three MB 501 engines were installed in each 1937 class Schnellboot. Six engines were installed in each of the U-180 and U-190 submarines. However, the MB 501 engines proved unsuitable in the submarines, and they were soon replaced by MAN diesels. The remains of three MB 501 engines can be found on Crackington Haven Beach in southeast Britain. The engines belonged to Schnellboot S-89, which was surrendered to the British after World War II. S-89 slipped its tow on 5 October 1946 and was wrecked upon the shore.

The MB 502 was essentially a Daimler-Benz DB 602, except it had water jacketed intake manifolds that protruded above the engine’s Vee. The rest of the MB 502’s specifics mirrored those of the DB 602. The MB 502 was a 50 degree V-16 with a single camshaft located in the Vee of the engine. The engine had a 6.89 in (175 mm) bore and a 9.06 in (230 mm) stroke. The MB 502 displaced 5,401 cu in (88.51 L) and had a continuous output of 900 hp (671 kW) at 1,500 rpm and a maximum output of 1,320 hp (984 kW) at 1,650 rpm. The engine was 9.9 ft (3.02 m) long, 4.0 ft (1.22 m) wide, and 6.2 ft (1.90 m) tall. The MB 502 weighed 5,952 lb (2,700 kg) and had a fuel consumption at cruising power of 0.37 lb/hp/hr (225 g/kW/hr). Three MB 502 engines were installed in each 1939 class Schnellboot.

mercedes-benz-mb-507-v-12

The MB 507 was based on the DB 603 inverted V-12 aircraft engine. Although the engine’s architecture was similar, the MB 507 had a completely different crankcase and reduction gear than the DB 603, and it was not supercharged.

The MB 507 was based on the Daimler-Benz DB 603 inverted V-12 aircraft engine, but some features from the DB 602 were incorporated. The normally aspirated MB 507 was an upright V-12 diesel engine that used monobloc cylinders and had a compression ratio of 17 to 1. A new finned crankcase was fitted that was similar to those used on other MB 500 series diesel engines. For the initial MB 507 engines, the bore was decreased from the 6.38 in (162 mm) used on the DB 603 to 6.22 in (158 mm). The stroke was unchanged at 7.09 in (180 mm). This gave the MB 507 a displacement of 2,584 cu in (42.35 L). The DB507 weighed 1,834 lb (850 kg). The engine had a continuous output of 700 hp (522 kW) and a maximum output of 850 hp (634 kW) at 2,300 rpm. An updated version of the engine, the MB 507 C, reverted back to the 6.38 in (162 mm) bore, which increased its displacement to 2,717 cu in (44.52 L). The MB 507 C produced 750 hp at 1,950 rpm and 1,000 hp at 2,400 rpm. The engine was 6.0 ft (1.83 m) long, 2.6 ft (.79 m) wide, 3.5 ft (1.06 m) tall, and had a weight of 1,742 lb (790 kg). Two MB 507 engines were used in a few LS boats (Leicht Schnellboot or Light Fast boat), and the engine was also installed in some land vehicles, such as the Karl-Gerät self-propelled mortar.

mercedes-benz-mb-511-v-20-aeronauticum

The MB 511 engine on display in the Aeronauticum museum in Germany. Note the finning on the lower half of the crankcase. On the front of the engine (left side of image) is the gear reduction with the supercharger above. The square connection above the engine is for the induction pipe. (Teta pk image via Wikimedia Commons)

The MB 511 was a supercharged version of the MB 501 V-20 engine. The bore, stroke, and displacement were unchanged, but the compression ratio was decreased to 14 to 1. The supercharger was positioned at the front of the engine, above the gear reduction. With the supercharger, output increased to 1,875 hp (1,398 kW) at 1,480 rpm for continuous power and 2,500 hp (1,864 kW) at 1,630 rpm for maximum power. The MB 511 was 13.1 ft (4.00 m) long, 5.2 ft (1.58 m) wide, and 7.6 ft (2.33 m) tall. The engine weighed 10,406 lb (4,720 kg). Three MB 511 engines were installed in each 1939/1940 class Schnellboot. An MB 511 engine is on display in the Aeronauticum maritime aircraft museum in Nordholz (Wurster Nordseeküste), Germany. Also, the MB 511 engine was built by VEB Motorenwerk Ludwigsfelde as the 20 KVD 25 in East Germany in the 1950s. Two 20 KVD 25 engines were installed in an experimental torpedo boat.

mercedes-benz-mb-518-v-20-drawings

The sectional and cylinder drawing are for the MB 518 but were basically the same for the MB 501 and MB 511—all were 40 degree V-20 engines. Note the pre-combustion chamber, valve train, and two camshafts.

The MB 512 was a supercharged version of the MB 502. Its compression was decreased to 14 to 1, but its output increased to 900 hp (1,398 kW) at 1,500 rpm for continuous power and 1,600 hp (1,864 kW) at 1,650 rpm for maximum power. The MB 512 was 10.0 ft (3.05 m) long, 4.2 ft (1.28 m) wide, and 6.3 ft (1.92 m) tall. The engine weighed 6,834 lb (3,100 kg). MB 512 engines replaced MB 502s in some Schnellboot installations.

The MB 517 diesel engine was a supercharged version of the MB 507. Returning to its DB 603 roots, the engine was inverted, but it retained the 6.22 in (158 mm) bore and 7.09 in (180 mm) stroke of the early MB 507. The supercharger boosted power from the 2,584 cu in (42.35 L) engine to 1,200 hp (895 kW) at 2,400 rpm. The MB 517 was installed in the Panzer VIII Maus V2 tank prototype.

mercedes-benz-mb-518-v-20-rear

The MB 518 was the last development of the V-20 engines. This image shows the large intercooler installed on the engine’s induction system.

The MB 518 was a continuation of the MB 511 and featured an intercooler. The large intercooler was positioned in the intake duct, above the engine and between the supercharger at the front of the engine and the intake manifolds in the engine’s Vee. The first MB 518s had a continuous output of 2,000 hp (1,696 kW) at 1,500 rpm and a maximum output of 3,000 hp (2,237 kW) at 1,720 rpm. After World War II, updated versions of the engine went into production starting in 1951. The MB 518 B had a continuous output of 2,275 hp (1,696 kW) and a maximum output of 3,000 hp (2,237 kW). The MB 518 C had a continuous output of 2,500 hp (1,864 kW) and a maximum output of 3,000 hp (2,237 kW). A turbocharger was added to create the MB 518 D. It had a continuous output of 2,900 hp (2,163 kW) and a maximum output of 3,500 hp (2,610 kW). The MB 518 engine was 14.8 ft (4.52 m) long, 5.2 ft (1.58 m) wide, and 8.0 ft (2.44 m) tall. The engine weighed around 11,332 lb (5,140 kg). MB 518 engines were used to power several different vessels for the German Navy and were also exported to 35 countries. Some of the engines are still in use today.

Schnellboot S-130, the only remaining German S-boot from World War II, was originally powered by three MB 511 engines. After the war, S-130 was reengined with two MB 518s, and one MB 511 was retained. S-130 is currently part of the Wheatcroft Collection and undergoing restoration. Four MB 518 C engines for the restoration were obtained from the Arthur of San Lorenzo, formerly known as the S39 Puma and originally built as a German Zobel Class fast patrol boat in the early 1960s.

mercedes-benz-mb-518-v-20-assembly

A number of MB 518 engines under construction show many different details. The lower crankcase half is on the floor, while the upper half is in the engine cradle; note the two camshaft tunnels. The crankshaft and its fork-and-blade connecting rods can be seen. Farther down the line is an engine with cylinder studs installed, and farther still is an engine with studs and pushrod tubes installed.

Sources:
http://alternathistory.com/dvigateli-nemetskikh-torpednykh-katerov-razrabatyvavshiesya-i-seriino-stroivshiesya-v-1920-1940-gody
https://de.wikipedia.org/wiki/Mercedes-Benz_MB_518
http://ftr.wot-news.com/2014/11/25/maus-engine-by-captiannemo/
https://ww2aircraft.net/forum/threads/opportunity-lost-db-16-cyl.21836/
http://www.german-navy.de/kriegsmarine/ships/fastattack/schnellboot1937/tech.html
http://www.german-navy.de/kriegsmarine/ships/fastattack/schnellboot1939/tech.html
http://www.german-navy.de/kriegsmarine/ships/fastattack/schnellboot1940/tech.html
http://www.wrecksite.eu/wreck.aspx?163703
http://www.shipspotting.com/gallery/photo.php?lid=1885985
http://s-boot.net/sboats-vm-forelle.html

daimler-benz-db602-zeppelin-museum

Daimler-Benz DB 602 (LOF-6) V-16 Diesel Airship Engine

By William Pearce

Around 1930, Daimler-Benz* developed the F-2 engine, initially intended for aviation use. The F-2 was a 60 degree, supercharged, V-12 engine with individual cylinders and overhead camshafts. The engine had a 6.50 in (165 mm) bore and an 8.27 in (210 mm) stroke. The F-2’s total displacement was 3,288 cu in (53.88 L), and it had a compression ratio of 6.0 to 1. The engine produced 800 hp (597 kW) at 1,500 rpm and 1,000 hp (746 kW) at 1,700 rpm. The engine was available with either direct drive or a .51 gear reduction, and weighed around 1,725 lb (782 kg). It is unlikely that the Daimler-Benz F-2 powered any aircraft, but it was used in a few speed boats.

The Daimler-Benz OF-2 diesel engine was very similar to the spark ignition F-2. Note the dual overhead camshafts in the Elektron housing above the individual cylinders. This was one of the OF-2’s features that was not incorporated into the LOF-6.

The Daimler-Benz OF-2 diesel engine was very similar to the spark ignition F-2. Note the dual overhead camshafts in the Elektron housing above the individual cylinders. This was one of the OF-2’s features that was not incorporated into the LOF-6.

In the early 1930s, Daimler-Benz used the F-2 to develop a diesel engine for airships. This diesel engine was designated OF-2, and it maintained the same basic V-12 configuration as the F-2. The individual cylinders were mounted on an Elektron (magnesium alloy) crankcase. Each cylinder had four valves that were actuated by dual overhead camshafts. The OF-2 had the same bore, stroke, and displacement as the F-2, but the OF-2’s compression ratio was increased to 15 to 1.

Fuel was injected into the cylinders at 1,330 psi (91.7 bar) via two, six-plunger injection pumps built by Bosch. The fuel was injected into a pre-combustion chamber located between the four valves in the cylinder head. This design had been used in automotive diesels built by Mercedes-Benz. Sources disagree on the gear reduction ratio, and it is possible that more than one ratio was offered. Listed ratios include .83, .67, and .58.

The Daimler-Benz OF-2 engine had a normal output of 700 hp (522 kW) at 1,675 rpm, a maximum output of 750 hp (559 kW) at 1,720 rpm, and it was capable of 800 hp (597 kW) at 1,790 rpm for very short periods of time. Fuel consumption at normal power was .392 lb/hp/hr (238 g/kW/hr). The engine was 74.0 in (1.88 m) long, 38.6 in (.98 m) wide, and 42.5 in (1.08 m) tall. The OF-2 weighed 2,061 lb (935 kg).

daimler-benz-lof-6-db602-diesel-rear

This view of a display-quality DB 602 engine shows the four Bosch fuel injection pumps at the rear of the engine. The individual valve covers for each cylinder can also be seen.

The OF-2 passed its type test in 1932. At the time, Germany was developing its latest line of airships, the LZ 129 Hindenburg and LZ 130 Graf Zeppelin II. These airships were larger than any previously built, and four OF-2 engines would not be able to provide sufficient power for either airship. As a result, Daimler-Benz began developing a new engine to power the airships in 1933. Daimler-Benz designated the new diesel engine LOF-6, but it was soon given the RLM (Reichsluftfahrtministerium or Germany Air Ministry) designation DB 602.

Designed by Arthur Berger, the Daimler-Benz DB 602 was built upon lessons learned from the OF-2, but it was a completely new engine. The simplest way to build a more powerful engine based on the OF-2 design was by adding two additional cylinders to each cylinder bank, which made the DB 602 a V-16 engine. The two banks of eight cylinders were positioned at 50 degrees. The 50 degree angle was selected over the 45 degree angle typically used for a V-16 engine. This gave the DB 602 an uneven firing order which helped avoid periodic vibrations.

The individual steel cylinders were mounted to the aluminum alloy crankcase. About a third of the cylinder was above the crankcase, and the remaining two-thirds protruded into the crankcase. This arrangement helped eliminate lateral movement of the cylinders and decreased vibrations. The crankcase was made of two pieces and split horizontally through the crankshaft plane. The lower part of the crankcase was finned to increase its rigidity and help cool the engine oil.

daimler-benz-lof-6-db602-diesel-engine

Originally called the LOF-6, the Daimler-Benz DB 602 was a large 16-cylinder diesel engine built to power the largest German airships. Note the three-pointed star emblems on the front valve covers. Propeller gear reduction was achieved through bevel planetary gears.

A single camshaft was located in the Vee of the engine. The camshaft had two sets of intake and exhaust lobes per cylinder. One set was for normal operation, and the other set was for running the engine in reverse. The fore and aft movement of the camshaft to engage and disengage reverse operation was pneumatically controlled. Separate pushrods for the intake and exhaust valves rode on the camshaft and acted on duplex rocker arms that actuated the valves. Each cylinder had two intake and two exhaust valves. Four Bosch fuel injection pumps were located at the rear of the engine and were geared to the camshaft. Each injection pump provided fuel at 1,600 psi (110.3 bar) to four cylinders. Fuel was injected into the center of the pre-combustion chamber, which was situated between the four valves. For slow idle (as low as 300 rpm), fuel was cut from one cylinder bank.

The DB 602 engine was not supercharged and had a .50 propeller gear reduction that used bevel planetary gears. The engine used fork-and-blade connecting rods that rode on roller bearings fitted to the crankshaft. The camshaft also used roller bearings, but the crankshaft was supported by plain bearings. Two water pumps were driven by a cross shaft at the rear of the engine. Each pump provided cooling water to one cylinder bank. The engine’s compression ratio was 16.0 to 1, and it was started with compressed air.

The DB 602 had a 6.89 in (175 mm) bore and a 9.06 in (230 mm) stroke, both larger than those of the OF-2. The engine displaced 5,401 cu in (88.51 L). Its maximum continuous output was 900 hp (671 kW) at 1,480 rpm, and it could produce 1,320 hp (984 kW) at 1,650 rpm for 5 minutes. The DB 602 was 105.9 in (2.69 m) long, 40.0 in (1.02 m) wide, and 53.0 in (1.35 m) tall. The engine weighed 4,409 lb (2,000 kg). Fuel consumption at cruising power was 0.37 lb/hp/hr (225 g/kW/hr).

lz-129-hindenburg

The ill-fated LZ 129 Hindenburg on a flight in 1936. The airship used four DB 602 engines housed in separate cars in a pusher configuration. Note the Olympic rings painted on the airship to celebrate the summer games that were held in Berlin.

Development of the DB 602 progressed well, and it completed two non-stop 150-hour endurance test runs. The runs proved the engine could operate for long periods at 900 hp (671 kW). Four engines were installed in both the LZ 129 Hindenburg and the LZ 130 Graf Zeppelin II. Each engine powered a two-stage compressor. Each compressor filled a 3,051 cu in (50 L) air tank to 850 psi (59 bar) that was used to start the engine and to manipulate the camshaft for engine reversing.

Plans for a water vapor recovery system that used the engines’ exhaust were never implemented, because the airships used hydrogen instead of the more expensive helium. The recovery system would have condensed vapor into water, and the collected water would have been used as ballast to help maintain the airship’s weight and enable the retention of helium. Without the system in place, expensive helium would have been vented to compensate for the airship steadily getting lighter as diesel fuel was consumed. With the United States unwilling to provide helium because of Germany’s aggression, the airships used inexpensive and volatile hydrogen, as it was readily available. The Hindenburg was launched on 4 March 1936, and the Graf Zeppelin II was launched on 14 September 1938.

Engines for the Hindenburg were mounted in a pusher configuration. In April 1936, the Hindenburg’s DB 602 engines experienced some mechanical issues on its first commercial passenger flight, which was to Rio de Janeiro, Brazil. The engines were rebuilt following the airship’s return to Germany, and no further issues were encountered. The Hindenburg tragically and famously burst into flames on 6 May 1937 while landing at Lakehurst, New Jersey.

daimler-benz-db602-musee-de-l-air-et-de-l-espace

Front view of the DB 602 engine in the Musée de l’Air et de l’Espace, in Le Bourget, France. Above the engine are the cooling water outlet pipes. In the Vee of the engine is the induction manifold, and the pushrod tubes for the front cylinders can be seen. Note the finning on the bottom half of the crankcase. (Stephen Shakland image via flickr.com)

The Graf Zeppelin II was still being built when the Hindenburg disaster occurred. Design changes were made to the Graf Zeppelin II that included mounting the DB 602 engines in a tractor configuration. The inability of Germany to obtain helium, the start of World War II, and the end of the airship era meant the Graf Zeppelin II would not be used for commercial travel. The airship was broken up in April 1940.

The DB 602 engine proved to be an outstanding and reliable power plant. However, its capabilities will forever be overshadowed by the Hindenburg disaster. Two DB 602 engines still exist and are on display; one is in the Zeppelin Museum in Friedrichshafen, Germany, and the other is in the Musée de l’Air et de l’Espace, in Le Bourget, France. Although the DB 602 was not used on a wide scale, it did serve as the basis for the Mercedes-Benz 500 series marine engines that powered a variety of fast attack boats (Schnellboot) during World War II.

*Daimler-Benz was formed in 1926 with the merger of Daimler Motoren Gesellschaft and Benz & Cie. Prior to their merger, both companies produced aircraft engines under the respective names Mercedes and Benz. After the merger, the Daimler-Benz name was used mostly for aircraft engines, and the Mercedes-Benz name was used mostly for automobiles. However, both names were occasionally applied to aircraft engines in the 1930s.

daimler-benz-db602-zeppelin-museum

Rear view of the DB 602 engine on display in the Zeppelin Museum in Friedrichshafen, Germany. A water pump on each side of the engine provided cooling water to a bank of cylinders. (Stahlkocher image via Wikimedia Commons)

Sources:
Aircraft Diesels by Paul H Wilkinson (1940)
Aerosphere 1939 by Glenn D. Angle (1940)
Diesel Engines by B. J. von Bongart (1938)
High Speed Diesel Engines by Arthur W. Judge (1941)
Diesel Aviation Engines by Paul H Wilkinson (1942)
“The Hindenburg’s New Diesels” Flight (26 March 1936)
“The L.Z.129’s Power Units” Flight (2 January 1936)
https://en.wikipedia.org/wiki/LZ_129_Hindenburg
https://en.wikipedia.org/wiki/LZ_130_Graf_Zeppelin_II