Dobrynin VD-4K CPO Saturn

Dobrynin M-250, VD-3TK, and VD-4K Aircraft Engines

By William Pearce

In early 1939, Soviet authorities sought the design and development of a new aircraft engine rated in excess of 2,000 hp (1,491 kW). Soviet aircraft engine technology was falling behind that of the western powers at the time, and this new engine was intended to close the gap. Gleb S. Skubachevskiy at the Moskovskiy Aviatsionniy Institut (Moscow Aviation Institute or MAI) completed the preliminary design of the new 2,000+ hp (1,490+ kW) engine, and development of a prototype was approved in July 1939. The new engine was given the designation M-250. Vladimir A. Dobrynin was brought in to assist Skubachevskiy on the M-250.

Dobrynin M-250

The six bank, 24-cylinder, 3,111 cu in (51.0 L) M-250 aircraft engine with contra-rotating propeller shafts.

The M-250 was a 24-cylinder, water cooled engine. The engine had six cylinder banks, each with four cylinders. This configuration is sometimes called an inline radial or hexagonal engine. The cylinder banks were arranged at 60 degree intervals around the crankcase, with one horizontal bank on each side of the engine. The M-250 employed a master/articulating connecting rod arrangement as used in a typical radial engine. The engine had a single-stage, three-speed supercharger mounted at its rear. A carbureted version of the engine was built along with a direct fuel injected version. The engine had a compression ratio of 6.2 to 1.

Each cylinder bank had a single overhead camshaft that was driven by a vertical shaft at the front of the bank. Intake and exhaust manifolding occupied the space between alternating cylinder banks, and the spark plugs were located in the intake Vee. At the front of the engine, the crankshaft drove contra-rotating propeller shafts via a reduction gearing. The M-250 had a 5.5 in (140 mm) bore and a 5.4 in (138 mm) stroke. The total displacement from the 24-cylinder engine was 3,111 cu in (51.0 L), and the engine weighed 2,822 lb (1,280 kg). The M-250 produced 2,200 to 2,500 hp (1,640 to 1,864 kW).

Dobrynin VD-3TK

The M-250 was developed into the 3,628 cu in (59.5 L), 3.500 hp (2,610 kW) Dobrynin VD-3TK.

Dobrynin was sent to Voronezh, Russia to assist with the M-250’s construction and testing while Skubachevskiy remained at the MAI. The M-250 was first run on 22 June 1941. However, the M-250 development team was evacuated from Voronezh in October 1941 because of advancing German troops. Skubachevskiy was also evacuated from the MAI in Moscow and was no longer involved with the M-250 as a result. After the evacuation from Voronezh, the M-250 design team and the manufacturing team were split, which caused long delays in further engine testing and the completion of additional prototypes.

M-250 development and testing was continued at what later became OKB-36 (Opytno-Konstruktorskoye Byuro-36 or Experimental Design Bureau-36) in Rybinsk, Russia. However, the M-250 engine program was never able to fully recover after the evacuation, and the project was cancelled on 25 June 1946. A total of 10 M-250 prototype engines were built. The M-250 engine was proposed for use in several projects: a version of the Ilyushin Il-2 Sturmovik attack aircraft, an undesignated Yakovlev heavy fighter, the Alekseyev I-218 attack aircraft, and an undesignated Alekseyev fighter. However, none of these projects progressed beyond the drawing board, and the M-250 was never installed in any aircraft.

Tu-4LL Dobrynin VD-3TK

A Tupolev Tu-4LL testbed with a contra-rotating Dobrynin VD-3TK engine installed in each outer position. The LL in the aircraft’s designation stood for “letayushchaya laboratoriya,” which means flying laboratory.

While at OKB-36 and under Dobrynin’s supervision, A. L. Dynkin developed the M-251TK from the M-250. Compared to the M-250, the M-251TK had a larger bore and stroke, a higher compression ratio of 6.6 to 1, and strengthened internal components. In addition, the engine was fitted with fuel injection, a single-speed supercharger, and two turbosuperchargers. Two versions of the M-251TK were developed—one with a standard propeller shaft and one with contra-rotating propeller shafts.

After the M-250 was cancelled, the M-251TK was approved for prototype manufacture in late 1946 and was first run in August 1947. The M-251TK passed various certification tests throughout 1948, including 50 and 100 hour tests. The engine was approved for manufacture in January 1949 as the VD-3TK. The VD-3TK had a 5.8 in (148 mm) bore and a 5.7 in (144 mm) stroke. The engine’s total displacement was 3,628 cu in (59.5 L), and it weighed 3,351 lb (1,520 kg). The VD-3TK had a takeoff rating of 3,500 hp (2,610 kW) and a continuous rating of 2,500 hp (1,864 kW).

Dobrynin VD-4K CPO Saturn

The restored Dobrynin VD-4K engine preserved at the CPO Saturn facility in Rybinsk, Russia. The power recovery turbines are mounted in the exhaust Vees of the engine. The red plates cover inlets through which air flowed to cool the units. The 4,300 hp (3,207 kW) VD-4K represented the pinnacle of piston-engine development in the Soviet Union. ( image)

In the first half of 1950, VD-3TK engines were test-flown in the outboard positions on a Tupolev Tu-4 bomber. The engine was also proposed for the Alekseyev Sh-218 attack aircraft, which was never built. The VD-3TK did not enter series production, and only 34 engines were made.

In 1949, Dobrynin’s team at OKB-36 had begun further engine development, this time based on the M-251TK. The intent was to create an engine with improved fuel economy to be used for a new long range, strategic bomber. The new engine was known as the M-253K, and its development proceeded under chief designer P. A. Kolesov. Along with other modifications, the engine’s compression ratio was raised to 7.0 to 1, and three power recovery turbines were installed in the exhaust Vees. These turbines would recover energy from the exhaust gases and feed that power back to the engine’s crankshaft. The two turbosuperchargers used with the M-251TK engine were replaced by a single, large unit that incorporated an adjustable jet outlet to harness thrust from the exhaust gases.

Tupolev Tu-85

The Tupolev Tu-85 strategic bomber was the only aircraft powered by VD-4K engines. The engines and aircraft preformed well, but the future lay with turboprop and jet engines. Note the turbosupercharger housing above each engine nacelle.

The first M-253K was completed in January 1950. Prototype engines were tested and developed throughout 1950. During this time, test engines passed 50 and 100 hour tests and were flown as the No. 3 engine on a Tu-4. Twenty-three engines were built and given the designation VD-4K. While the VD-4K had the same bore and stroke as the VD-3TK, the VD-4K produced a lot more power. The engine had a takeoff rating of 4,300 hp (3,207 kW) at 2,900 rpm and a continuous rating of 3,800 hp (2,834 kW) at 2,700 rpm. The VD-4K was fuel injected and achieved a specific fuel consumption of .408 lb/hp/hr (284 g/kW/hr) at cruse power. The engine was 63 in (1.6 m) in diameter, 119 in (3.0 m) long, and weighed 4,552 lb (2,065 kg). The turbosupercharger weighed an additional 485 lb (220 kg).

VD-4K engines were installed in Tupolev’s new strategic bomber, the Tu-85. The Tu-85 was ordered in 1949 and made its first flight on 9 January 1951—Aleksei Perelyot was at the controls. The Tu-85 had a 183.5 ft (55.9 m) wingspan and was 130.9 ft (39.9 m) long. The aircraft had a maximum speed of 396 mph (638 km/h) at 32,810 ft (10,000 m). Designed to counter the long-range Convair B-36 Peacemaker, the Tu-85 could deliver 11,000 lb (1,000 kg) of bombs 7,580 mi (12,300 km) or carry 44,000 lb (20,000 kg) of bombs.

Dobrynin VD-4K

A diagram showing the VD-4K’s installation in the Tu-85 and its intake and exhaust paths. Note the cooling fan and how air is diverted from the turbosupercharger inlet to flow through an aftercooler.

In the Tu-85, an annular radiator was installed around the front of the VD-4K engine. An axillary fan was added behind the spinner to increase the flow of cooling air, but it appears no other major improvements were needed. The turbosupercharger for the VD-4K engine was positioned on top of the nacelle, and the engine exhaust flowed back over the wing. Incoming air to the engine was compressed by the turbosupercharger, flowed through an aftercooler, and was then delivered to the engine.

While the Tu-85 and its VD-4K engines achieved excellent test results, the Tupolev Tu-95 “Bear” strategic turboprop bomber was under development and showed greater promise than the Tu-85. As a result, development of the Tu-85 and the VD-4K engine was stopped. Both Tu-85 prototypes were later scrapped.

The VD-4K was the last piston engine developed by Dobrynin and OKB-36; their efforts shifted to designing and building turbojets engines. A VD-4K engine is preserved at the NPO Saturn (former OKB-36) facility in Rybinsk.

Tupolev Tu-85 side

With its impressive range and payload, the Tu-85 was one of the most capable piston-engine bombers ever built. Because of the transition to turbine engines, the Tu-85 was outclassed and never went into production.

Russian Piston Aero Engines by Vladimir Kotelnikov (2005)
Unflown Wings by Yefim Gordon and Sergey Komissarov (2013)
Soviet and Russian Testbed Aircraft by Yefim Gordon and Dmitriy Komissarov (2011)
Tupolev Aircraft since 1922 by Bill Gunston (1995)

Coanda 1911 Monoplane prop

Coandă 1911 Monoplane

By William Pearce

Romanian Henri Marie Coandă is perhaps best known for observing the way a stream of fluid (such as air) is attracted to and will flow over a nearby surface. This component of fluid dynamics became known as the Coandă Effect. Coandă recognized this phenomenon while testing his first aircraft, built in 1910. This aircraft had a unique propulsion system that Coandă called a turbo-propulseur, and it is recognized as the first “jet” aircraft. A four-cylinder, 50 hp Clerget engine was used to power a rotary compressor that provided thrust. While there is some debate about the validity of the aircraft’s first and only flight and its subsequent destruction, the aircraft was certainly built to be propelled by a jet of fast-flowing air.

Coanda 1911 Monoplane front

Henri Coandă’s 1911 monoplane at the Concours Militaire in Reims, France in October 1911. Note the tandem main gear wheels.

Coandă’s second aircraft was built in France and completed in 1911. It utilized some salvaged and spare parts from the 1910 aircraft. The 1911 aircraft was originally designed to use a turbo-propulseur, but it was finished with a conventional propeller. The aircraft’s engine arrangement, however, was not conventional.

The 1911 aircraft was a rather large monoplane with a parasol wing mounted above the cockpit. A small lifting surface with a nickel steel spar joined the two main landing gear which were each comprised of two tandem wheels. Each main gear wheel set was encased in a large fairing. A single vertical strut made of nickel steel extended above each gear fairing and supported the wing. The wings had a nickel steel spar and were covered by fabric. The aircraft’s roll control was achieved by wing warping. Coandă’s 1911 aircraft had a cruciform tail similar to that used on the 1910 aircraft. The fins of the tail formed an X, and each fin had a trailing control surface that acted as both a rudder and an elevator.

Coanda 1911 Monoplane Getty

This photo shows a detailed view of the Gnome installation on Coandă’s 1911 aircraft. Note the various struts and braces used on the aircraft. The aluminum-covered front fuselage is easy distinguished from the plywood-covered cockpit section. The aircraft’s control wheel can just be seen at right. (Huton Archives image via Getty Images)

A rectangular support structure was formed by the upper and lower spar and the vertical struts above the wheels. The fuselage was suspended in this support structure by a series of brace wires and small struts. Additional wire bracing and struts supported the rest of the aircraft’s structure. Except for where the engines were mounted, the fuselage had a circular cross section that narrowed to a point at the tail. The front of the fuselage was covered by aluminum sheeting, the cockpit section was covered by plywood sheeting, and the rear of the aircraft was fabric-covered.

Perhaps the most unusual feature of Coandă’s 1911 monoplane was its engine installation and propeller drive. At the front of the aircraft were two Gnome 7 Gamma rotary engines. The seven-cylinder engines had a 5.1 in (130 mm) bore, a 4.7 in (120 mm) stroke, and a total displacement of 680 cu in (11.1 L). The 7 Gamma produced 70 hp (52 kW) at 1,200 rpm and weighed 194 lb (88 kg).

Coanda 1911 Monoplane engines

This photo shows an engine and gearbox arrangement similar to that used on Coandă’s 1911 monoplane. It is not clear when this photo was taken, but it may have been at the Salon de l’Aeronautique in Paris, France held mid-December 1911 through early January 1912. (Harry Stine image via New Fluid Technology)

The engines were installed front-to-front with their crankshafts perpendicular to the aircraft’s fuselage. While the engines’ cylinders were exposed to the slipstream for cooling, the front of the engines were enclosed within the fuselage. Mounted between the engines was a gearbox that drove a propeller shaft. The propeller shaft extended to the front of the aircraft where it drove a four-blade propeller. The engines and gearbox were mounted to a steel frame. Coandă claimed that the aircraft could fly with just one engine operating.

Most likely, the engines turned in opposite directions relative to each other. While this arrangement would cancel out the gyroscopic effects of the rotary engines along the pitch axis, it would induce some tendency to roll, even if just slightly. Some sources indicate the engines were “handed” —they rotated the same direction relative to each other. In addition to the complications in making a rotary engine run “backward,” the “handed” engine configuration would create a noticeable pitch moment on the aircraft as the engines were throttled (blipped), but it would also alleviate any tendency for the aircraft to roll. However, an early sketch of the engine arrangement indicates “handed” engines were not installed, and that a simple beveled gear arrangement was used to transfer power from the engines to the propeller shaft. Additionally, the transfer gearbox did not appear to be of sufficient size to accommodate the differential gearing needed for a “handed” engine arrangement.

Coanda 1911 Monoplane side

Note the cruciform tail and its control surfaces in this photo of the Coandă 1911 monoplane. Also, the plywood-covered cockpit section can be easily distinguished from the fabric-covered rear fuselage.

The 1911 Coandă monoplane had a wingspan of 53 ft 6 in (16.3 m) and a length of 41 ft (12.5 m). The aircraft had an empty weight of 1,036 lb (470 kg) and a maximum weight of 2,756 lb (1,250 kg). Two fuel tanks of around 30 gallons (115 L) each were housed in the center section of the wing. Reportedly, the aircraft could accommodate a pilot and two passengers. The estimated speed of the 1911 monoplane was 81 mph (130 km/h).

Coandă’s 1911 monoplane was tested in the Concours Militaire (Military Competition), held in Reims, France in late October 1911. Georges de Boutiny flew the aircraft, but it reportedly did not meet performance expectations. Later, wing extensions were added to the wheel fairings, turning the aircraft into a sesquiplane. Along with additional wire bracing, a vertical strut connected the end of the wing extension to the upper wing.

Coanda 1911 Monoplane prop

Mechanic George Bonneuil checks a Gnome engine as pilot George de Boutiny looks on from the cockpit. (Harry Stine image via New Fluid Technology)

A Coandă aircraft catalog from 1911 offered both the monoplane and sesquiplane versions of the aircraft with either 50 hp (37 kW) Omega or 70 hp (52 kW) Gamma Gnome rotary engines. It appears that only the single prototype of the Coandă 1911 aircraft was built, and exactly what happened to it is not known. The 1911 aircraft faded into history, and Henri Coandă went on to build other aircraft and further explore fluid dynamics.

Note: Some claim that Coandă’s 1911 aircraft was the first twin-engine aircraft. However, at least four other twin-engine aircraft preceded it in flight: the Daimler Lutskoy No. 1 (flew 10 March 1910, or possibly earlier), Edward Andrew’s twin (flew early 1910), Roger Sommer’s twin (flew 27 September 1910), and the Queen Speed Monoplane (flew 10 July 1911).

Coanda 1911 Monoplane extensions

This photo shows Coandă’s 1911 aircraft with its wing extensions. The extensions effectively made the aircraft a sesquiplane. Additional struts and braces for the extensions can be seen. Note the three people in the cockpit and also the warp of the wing tip.

Henri Coandă and His Technical Work During 1906-1918 by Dan Antoniu, et al (2010)
French Aeroplanes before the Great War by Leonard E. Opdycke (1999)
Romanian Aeronautical Constructors 1905-1974 by Gudju, Iacibescu, and Ionescu (1974)
Henri Coanda: The Facts by New Fluid Technology (4.3 MB pdf),18780.15.html

NYC M-497 tow

New York Central M-497 Black Beetle

By William Pearce

As the popularity of personal automobiles increased, passenger train travel decreased. In the United States, the decline quickened in the 1960s as the Interstate Highway System came on line and jet engines made air travel affordable. Railroad companies realized their long haul passenger service could not compete with the more modern forms of transportation but felt they could develop a better service in the short haul and mid-haul markets to win back customers.

NYC M-497 tow

New York Central’s M-497 Black Beetle tested the feasibility of using jet engines to propel a train at high speed on a conventional track. M-497 is seen here with a support car and engine. Note the red pitot tube just under the lights on the front of the train.

In 1965, James Wright, director of the New York Central (NYC) Railroad’s Technical Research Center, thought of an experiment to drastically increase a train’s speed in the shortest amount of time and with minimal changes to the train and track. Simply put, Wright’s idea was to use a jet engine to propel the train to much higher speeds. Wright discussed his proposal with the president of NYC, Alfred Perlman, but the talks died off.

Around a year later, in early June 1966, Wright received a call from Perlman authorizing the jet engine experiment and requesting that it be completed in 30 days. The project was a daunting one; not only was a train needed that could be modified for jet propulsion, but the team also had to find jet engines and a section of track suitable for high-speed tests. The rush was on to turn a visionary idea into a tangible reality.

NYC M-497 crew

The completed jet-powered M-497 and some of the crew that worked tirelessly at the Collinwood Technical Center to create the locomotive.

For the experiment, the NYC decided to use a Budd Company Rail Diesel Car-3 (RDC-3). The RDC-3 was a self-propelled commuter railcar powered by two 275 hp (205 kW) Detroit Diesel six-cylinder engines. The RDC-3 accommodated 48 passengers, was 85 ft (25.9 m) long, and had a top speed of 85 mph (137 km/h). The RDC-3 chosen was No. M-497, which NYC had purchased 13 years earlier, in 1953. M-497 was the first of three RDC-3s that the NYC owned. For $5,000, the NYC was able to obtain from Davis-Monthan Air Force Base in Arizona a surplus jet pod from a Convair B-36 Peacemaker. The pod contained two General Electric J47-GE-19 jet engines capable of 5,200 lb (23.1 kN) thrust each.

M-497 and the J47 jet engines were relocated to NYC’s Collinwood Technical Center near Cleveland, Ohio. Under Donald Wetzel, the Assistant to the Director of Technical Research, modifications were made to combine the jet engine pod and railcar. Ruth Wetzel, Don’s wife and a commercial artist, drew up the basic sketches for the jet engine placement as well as an aerodynamic fairing for the front (B end) of the blunt-nosed RDC. She also outlined the paint scheme for the completed M-497. The fairing combined with the paint scheme ultimately earned M-497 its Black Beetle nickname.

NYC M-497 rear

This picture of the rear of M-497 shows the covered door and the fairings that extended down from the sides of the train. These changes to the Budd RDC-3 railcar improved its aerodynamics.

The engine pod was mounted above the front of the railcar at a five degree nose-down angle. The pod’s installation on the train was inverted as compared to the B-36, so the engines were rotated 180 degrees in their housings. The J-47 engines were converted to run on diesel fuel, and additional fuel tanks were installed in the mail section of the RDC. Some seats were removed from the front of the RDC to allow for the jet engine mounting structure. The drive shafts from the original diesel engines were disconnected, and M-497 was outfitted for the tests with more than 50 instruments in its baggage area. After scale models were verified in a wind tunnel, the aerodynamic fairing was built up over the front of the RDC. The fairing added 5 ft 7 in (1.7 m) to M-497’s length, making the modified train 90 ft 7 in (27.6 m) long. Based on wind tunnel tests, the back (A end) of the car was also slightly modified (the door was faired over), and the car’s sides were extended down to further improve its aerodynamics.

Wetzel was selected as M-497’s engineer because of his experience with the project. He also had experience with jet engines from his service in the military. M-497 was taken to a stretch of track between Toledo, Ohio and Butler, Indianan that had been specially prepared (rails welded together) for high-speed runs. This location offered a 68.5 mile (111 km) section of straight, multiple track. Initial tests revealed that the hot exhaust from the jet engines passed over the roof radiators for the diesel engines, which were used to power the brakes and accessories of the RDC. The lack of cooling air caused the engines to get too hot, and they shut down automatically. The auto-shut-down feature was disabled for subsequent runs; although the engines ran hot, the runs were short and the engines were not producing much power, so they were not in danger of being damaged. No other serious issues were encountered, and the high-speed tests proceeded.

NYC M-497 front

Never intended to be put in service or production, the J47 jet engines propelled M-497 to a record speed of 183.85 mph (295.88 km/h).

For the high-speed runs, a Beechcraft Model 18 flew ahead of M-497 to make sure the track was clear. On the second run on 23 July 1966, with Wetzel, Wright, Perlman, and other engineers on board, M-497 raced eastward on the track from Butler, Indiana. Wetzel had been asked to run around 180 mph (290 km/h), but as he approached the speed trap at milepost 352 (near Bryan, Ohio), he saw M-497 was traveling at 196 mph (315 km/h). He reduced power, and M-497 was recorded at 183.85* mph (295.88 km/h). This was and still is the fastest speed a train has traveled on open track in the United States. M-497 finished the run near Stryker, Ohio, some 21 miles (34 km) from the start. As a precaution, railroad ties were placed across the track near Toledo, Ohio to derail M-497 in case it ran away.

Additional tests were conducted the next day, but they never approached the speed from the previous day. One of the J47 engines refused to light. M-497 accelerated on one engine until the dead engine could be air-started.

After a short time in the limelight, M-497 was returned to its standard RDC-3 configuration and pressed back into normal service. The NYC’s M-497 had shown that high-speed rail service was possible on a conventional track, and that was the true goal of the experiment. The train’s configuration was not practical, as the jet engines required a vertical clearance in excess of what was standard at the time. In addition, the jet-powered M-497 did not have a reverse and needed another engine to pull it back to the starting point after a run. Of course, these problems could have been overcome with a specially designed engine, but it was already the sunset of rail travel in the United States.

NYC M-497 run

The jet-propelled M-497 at speed on the track between Butler, Indiana and Stryker, Ohio.

NYC, which had been in business since 1853, merged with the Pennsylvania Railroad in 1968 and formed the Penn Central Transportation Company (PC). In 1970, PC became the largest company to file for bankruptcy protection. PC stumbled on until 1976 when it was finally broken up. M-497 outlasted both NYC and PC. Although given a new number with each new owner, the RDC-3 once known as M-497 and the fastest train in the United States was in service until 1977 and was finally scrapped in 1984. A plaque commemorating the record run was dedicated in Bryan, Ohio on 14 November 2003.

*Some modern sources list the speed as 183.681 mph (295.606 km/h), but this does not appear to be correct. Contemporary information and the plaque dedicated in 2003 record the speed as 183.85 mph (295.88 km/h).

Below is a video made by General Electric commemorating Don Wetzel and the M-497’s speed run.

Flight of the M-497 by Hank Morris with Don Wetzel (2007/2012)

Sunbeam Sikh I

Sunbeam Sikh I, II, and III Aircraft Engines

By William Pearce

Toward the end of World War I, a number of companies were pursuing the concept of a very large engine powering a very large aircraft. Just about every country that had extensive experience in the field of aeronautics expended resources to create the large engine and aircraft combination. As history unfolded, all of these projects came to naught, although the experience gained did pave the way for future projects.

Sunbeam Sikh I

Side view of the 800 hp (597 kW) Sunbeam Sikh I V-12 engine. Carburetors can be seen attached to the first and last cylinders. Note the two water pumps under the engine and the exposed valves.

The Sunbeam Motor Car Company based in Wolverhampton, England had added aircraft engine design and manufacture to its existing automotive business in 1913. Sunbeam’s aircraft engines were designed by Louis Coatalen, their chief engineer, and were sometimes referred to as Sunbeam-Coatalen Aircraft Engines. As with so many other companies, Sunbeam designed a large aircraft engine during the closing days of World War I. This large engine was named Sikh (or Sikh I), and it was intended for use in either large aircraft or airships.

The Sikh was a 60 degree V-12 engine. Its individual cylinders were a departure from the standard Coatalen-designed engines. The cylinders were machined from steel forgings and had welded sheet metal water jackets. Each cylinder had four spark plugs positioned under its six exposed valves. The three intake valves were positioned on the Vee side of the cylinder, and the three exhaust valves were positioned on the outside of the cylinder. The intake and exhaust valves were operated by separate rocker groups positioned above the valves. This configuration allowed all intake (or exhaust) valves to be opened or closed simultaneously. Each rocker group was actuated by a pushrod that was driven by a camshaft mounted in the Vee of the engine and geared to the crankshaft. Four magnetos at the rear of the engine fired the spark plugs.

Sunbeam Sikh I Ad copy

A Sunbeam Sikh ad from 1920 touts the engine as the most powerful in the world but prophetically adds, “at the moment.” The Duesenberg H developed at the same time as the Sikh I had the same output, and the 1,000 hp (746 kW) Napier Cub would eclipse both engines later in 1920.

Two water pumps were positioned under the engine and driven by vertical shafts from an accessory gear. Each pump supplied cooling water to one cylinder bank. The Sikh had four carburetors—one attached to the first and last cylinders of each row. For each cylinder row, the air/fuel mixture flowed through an intake manifold attached to the cylinders inside the Vee of the engine. The engine used aluminum pistons mounted to H section, forked connecting rods attached to the crankshaft. The hollow crankshaft was made of nickel-chromium steel. Via spur reduction gears, the propeller shaft turned at 0.657 engine speed. The crankcase of the Sikh was an aluminum casting.

The Sunbeam Sikh had a 7.09 in (180 mm) bore and 8.27 in (210 mm) stroke. The engine’s total displacement was 3,913 cu in (64.1 L), and it produced 800 hp (597 kW) at 1,400 rpm. The Sikh had a dry weight of 1,952 lb (885 kg).

The engine was first run on 11 May 1919 and was displayed at a number of aviation shows. Although the Sikh passed British Air Ministry tests to prove its airworthiness, Sunbeam did not receive any orders for the engine. Large engines and large aircraft were simply not practical in the early 1920s, and there was little interest in airships in the immediate post-war era.

In addition to the Sikh, Sunbeam co-developed a smaller engine known as the Sikh II (or Semi-Sikh). The inline-six Sikh II was essentially half a Sikh. The cylinders were the same but they were mounted on a new crankcase. The Sikh II was direct drive without any gear reduction, and the camshaft was mounted on the left side of the engine. With the same bore and stroke as the Sikh, the Sikh II had a total displacement of 1,956 cu in (32.1 L) and produced 425 hp (317 kW) at 1,400 rpm. The engine had a dry weight of 1,120 lb (508 kg). Unfortunately for Sunbeam, the Sikh II, like the Sikh, found no applications.

Sunbeam Sikh I Olympia 1920

The Sunbeam Sikh I as displayed at the Olympia Air Show in 1920. Note the two spark plugs positioned under the valves on both sides of the cylinder, the pushrods in the Vee of the engine, and the four magnetos. In the left corner of the picture is the Short Silver Streak. (Stilltime Collection Image)

By 1927, British airship development had been renewed, and the R100 and R101 programs were underway. Sunbeam saw a new opportunity for the Sikh engine and developed the Sikh III strictly for airship use. The Sikh III was again a 60 degree V-12 engine, and most sources say it possessed the same bore, stroke, and displacement as the original Sikh. However, some original sources (Jane’s and Flight) say the bore was increased to 7.28 in (185 mm), which would give a total displacement of 4,134 cu in (67.7 L).

The individual cylinders of the Sikh III were redesigned and refined using a carbon steel barrel and a cast steel head. In addition, the valve train was completely redesigned. Each cylinder still had three exhaust valves, but the number of intake valves was reduced to two. The valves for each cylinder were enclosed in a common rocker cover. The rockers extended though the cover and were actuated by pushrods that ran between the cylinders. On the left cylinder bank, the exhaust rocker arm protruded out the rear of the cover, and the intake rocker arm protruded out the front. This configuration was reversed for the right cylinder bank. The crankshaft was forged from nickel-chromium steel and had six throws. Each cylinder had two spark plugs that were enclosed by the rocker cover. The spark plugs were fired by two magnetos driven at the rear of the engine.

Sunbeam Sikh II

The inline-six Sunbeam Sikh II was essentially half a Sikh I. Note the camshaft and pushrod arrangement in the rear view on the left. The front view image on the right illustrates the engine’s carburetors, valves, and lack of a propeller gear reduction.

The engine used two carburetors, which, along with the intake manifolds, were positioned in the Vee of the engine. Each carburetor supplied the air/fuel mixture to three cylinders of each bank. The propeller shaft of the Sikh III was geared to the crankshaft at a 0.567 reduction. The Sikh III produced 1,000 hp (476 kW) at 1,650 rpm and had a dry weight of 2,760 lb (1,252 kg). The engine was 7 ft 2 in (2.2 m) long, 3 ft 4 in (1.0 m) wide, and 6 ft 2 in (1.9 m) tall.

The Sikh III was first run in 1928 and was displayed at shows in 1929 and 1930. However, engines for the R100 and R101 airships had already been selected. The disastrous crash of the R101 airship in 1930 caused Britain to cease all further airship development, leaving the Sikh III without any possible applications.

Only small numbers of Sikh I, Sikh II, and Sikh III engines were built. Like many large aircraft engines built over the years, the Sunbeam Sikh engines were never installed in any aircraft or airships.

Sunbeam Sikh III

The Sunbeam Sikh III was intended for airship use but never found an application. Note the new cylinder heads. The exhaust valve pushrod can been seen on the rear left cylinder.

Sunbeam Aero-Engines by Alec Brew (1998)
Aerosphere 1939 by Glenn D. Angle (1940)
Jane’s All the World’s Aircraft 1927 by C. G. Grey
Jane’s All the World’s Aircraft 1929 by C. G. Grey
– “The Sunbeam Motor Car Co., Ltd.” The Aeroplane (31 December 1919)
– “Aero Engines at Olympia” The Aeroplane (21 July 1920)
– “The Sunbeam Motor Car Co., Ltd.” Flight (18 July 1929)

Dorand Gyroplane G20 complete 1947

Dorand Gyroplane G.20 (G.II)

By William Pearce

Since the early 1900s, Frenchman Louis Bréguet was interested in rotorcraft. But, the technical challenges of controlling such machines and the lack of suitable power plants led Bréguet to pursue the development of aircraft instead. In the late 1920s, Bréguet’s interest returned to rotorcraft, and he created the Syndicat d’Etudes de Gyroplane (Syndicate for Gyroplane Studies) in 1931 with René Dorand as its Technical Director. The syndicate produced a successful experimental helicopter known as the Bréguet-Dorand Gyroplane Laboratoire, which first flew on 26 June 1935. The Gyroplane Laboratoire used two sets of two-blade, coaxial, contra-rotating rotors. No tail rotor was used, as the contra-rotating rotors cancelled out the torque reaction of the blades. The helicopter set a number of speed and distance records.

Dorand Gyroplane G20

A drawing of the Dorand Gyroplane G.20 in what appears to be its final form. The drawing illustrates one of the two inverted Renault inline-six engines and the two-person cockpit.

In 1938, Dorand amicably parted with Bréguet and established the Société Française du Gyroplane (French Gyroplane Company), abbreviated SFG or just Gyroplane for short. The French Navy (Marine Nationale) commissioned the SFG to design a combat helicopter for costal defense and anti-submarine warfare. Dorand designed the new machine, and its layout was similar to that of the Gyroplane Laboratoire. The new helicopter was designated the Gyroplane G.20, but it is also known as the Dorand G.20 or the Dorand G.II.

The G.20 had a cigar-shaped fuselage of all metal construction. A butterfly tail was attached to the extreme end of the fuselage, and the tail’s control surfaces were fabric-covered. The streamlined nose of the G.20 was covered with plexiglass panels. The pilot sat in the nose of the helicopter with either one or two crewmen behind.

Dorand Gyroplane G20 org drawing

A drawing of the original Dorand G.20 with its three-man crew and rotor mast gunner turret. Note the side-mounted machine gun (pointed toward the rear) and the bomb load. An inverted, inline, six-cylinder, Renault engine is also visible. The rotors on the left are shown in their normal position, while the rotors on the right are at their maximum upward deflection.

At the center of the helicopter were two three-blade, coaxial, contra-rotating rotors. The distance between the rotors was 2 ft 2 in (0.65 m), and the lower rotor had a smaller diameter than the top rotor to ensure the blades would not collide. The upper rotor had a diameter of 50 ft 6 in (15.4 m), and the lower rotor’s diameter was 42 ft 8 in (13.0 m)—7 ft 10 in (2.4 m) smaller.  The magnesium blades were made of two parts: a box forming the leading edge and a separate trailing edge. As with the Gyroplane Laboratoire, articulation of the blades allowed for both cyclic and collective pitch control, and no tail rotor was used.

The rotor blades were powered by two Renault 6Q-04 engines. The 6Q was an air-cooled, inverted, inline, six-cylinder engine with a 4.72 in (120 mm) bore and a 5.51 in (140 mm) stroke. The engine’s total displacement was 580 cu in (9.5 L). The 6Q-04 was supercharged and produced 240 hp (179 kW) at 2,500 rpm up to 13,123 ft (4,000 m). A special gearbox transferred power from the engines to the rotors. If one of the engines were to fail, that engine would be automatically disconnected, and the remaining engine would power both sets of rotors.

Dorand Gyroplane G20 org drw

This top view drawing of the G.20 clearly shows the side-mounted machine gun and engine placement. The outline of bombs can be seen under the rotor mast.

The G.20 was supported by two main wheels and a tailwheel. The tail and main wheels all retracted backward into the fuselage and were fully enclosed by gear doors. The space in the fuselage between the main gear and below the rotors was for either bombs or a depth charge. In addition, Dorand’s original design included a machine gun mounted on the helicopter’s side and a turret mounted on top of the rotor mast—with the guns operated by separate crewmen. The mast turret was unique in that it was essentially a hollow drum to which the rotors were attached. A gunner occupied the center of the drum and had a 360 degree field of fire. However, all armament and the rotor turret were omitted from the G.20. Most sources list the completed G.20 as having a two-person crew consisting of a pilot and copilot. The helicopter’s final role was defined as observation, liaison, and mail-carrying.

The G.20’s fuselage had a length of 36 ft 4 in (11.08 m) and a height of 10 ft 3 in (3.13 m). The helicopter’s empty weight was 3,086 lb (1,400 kg); normal operating weight was 5,512 lb (2,500 kg), and maximum weight was 6,614 lb (3,000 kg). The G.20’s hover ceiling was 9,843 ft (3,000 m), and it had a maximum ceiling of 16,404 ft (5,000 m). The helicopter’s range was 497 mi (800 km). Its cruise speed was 103 mph (165 km/h), and its maximum speed was 155 mph (250 km/h) at 8,202 ft (2,500 m).

Dorand Gyroplane G20 complete 1947

The completed Dorand G.20 after World War II. With the machine guns no longer part of the design, nothing is left to interrupt the helicopter’s sleek lines. Note the long gear door.

Construction of the G.20 started in Guethary in south-western France, near Spain. When the German Army invaded France in 1940, the helicopter was moved to Chambéry in south-eastern France, near Italy, and construction resumed. By this time, Marcel Vuillerme had taken over the project from Dorand. As the Germans pushed into southern France, the G.20 was discovered. The Germans showed little interest in the helicopter and allowed its construction to continue, albeit slowly.

The G.20 was completed in 1947 and underwent ground tests. It was the French officials who now showed little interest in the project, and funding was not forthcoming. Its estimated performance was optimistic, and while its streamlined appearance and retractable gear appeared futuristic, in many ways the G.20 was obsolete after war-time helicopter developments made in the United States and Germany. Further development and testing of the G.20 was abandoned, and the helicopter never flew. However, the SFG continued to develop helicopters for a time. The SFG worked with Bréguet to construct a four-passenger helicopter, the G.11E, which first flew in 1949. The G.111 was a follow-on project that first flew in 1951. The SFG went out of business in 1952.

Breguet G11E

The G.11E was designed by SFG after the G.20. It was built by Bréguet and powered by a 9-cylinder Potez 9E radial engine. It first flew in 1949 and had a layout similar to the G.20.

Les Avions Breguet 1940/1971 by Jean Cuny and Pierre Leyvastre (1973)
René Dorand: 50 Ans de Giraviation by Pierre Boyer (1992)