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The Rolls-Royce Merlin – Could it be the best piston engine ever?

By Warbird January 11, 2011 Engines, Rolls-Royce 5 Comments

The RAF fighters which resisted the German invasion in 1940 during the Battle of Britain, were all equipped with the same engine, the Rolls-Royce Merlin.  This same engine also powered the majority of the bombers of RAF Bomber Command, and some of the best fighters of the 8th USAAF.   Named after a bird of prey, like all piston engines that Rolls-Royce produced, the Merlin is a unique engine for several reasons.

  • Unlike other engines, which changed relatively little during the war, between 1939 and 1945, no fewer than 52 different versions of the Merlin were produced
  • Powered a wide variety of aircraft, including both fighters and bombers.  These included the Spitfire, Hurricane, Boulton Paul Defiant, Avro Lancaster, De Havilland Mosquito, Handley Page Halifax, Armstrong-Whitworth Whitley, and the P-51 Mustang.  The Merlin even replaced the Hercules II version of the Bristol Beaufighter and the Pegasus in version II of Wellington.
  • The Merlin transforms two of the most important aircraft of World War II.  From the poor performing Manchester was born the transformed Merlin powered Lancaster, the legendary aircraft of Bomber Command.  The P-51 Mustang became one of the best fighters in WWII once the under-powered Allison’s were replaced with the Merlin.  With the new found extended range, it became the only fighter to effectively protect the 8th USAF B-17 deep into enemy territory.
  • Finally, it is the only engine to be built in large numbers simultaneously on both sides of the Atlantic during WWII.

The Birth of the Merlin

The Merlin is a conventional engine, derived from relatively older power trains, as engineers and technicians at Rolls-Royce simply evolved the Merlin from existing proven designs. The Merlin was born into a family of  V12 engines whose origin dates back at Rolls-Royce to the First World War.  As mentioned, they all  bear the names of birds of prey, when studying reciprocating engines from Rolls Royce, you also get a lesson in  ornithology.   Rolls entry into aeronautical engines begins with the Eagle in 1915.  The V-12 Eagle propels the Short Bomber (1916), the Vickers Vimy (1917), the Handley Page O/100 (1916), the Handley Page V/1500 (1918), and fighters like the AIRCO DH.4 (1917).  The Eagle is also mounted in the U.S. aircraft (Fairey F.17).  The Eagle was rated between  250 and 375 hp in its various versions, which for the time was a considerable amount of power, and advantage that the water-cooled engines had over the air-cooled engines of the day.   During this time period the Americans, British and French prefer the V-12 engines from  Rolls Royce, Hispano-Suiza, Renault, and Liberty.  The Germans and Italians are loyal to the 6-cylinder Mercedes, Fiat and Isotta-Fraschini.

After the war, Rolls-Royce began, like all its competitors, the race for power, while remaining faithful to the formula of V-12 liquid cooling.  Advances in design, metallurgy, and fuel allow for an increase in the speed (RPM) and compression ratio of the engine.  In 10 years, the compression ratio increases by 50% (it goes from 4: 1-6: 1) and the rotational speed from approximately 1800 to 2400 rpm. In 1927, the Kestrel 21.25 liter engine is released, which soon powers the Hawker biplanes (Audax, Fury, Hart) in the early 1930s.  The Kestrel develops 745 hp, double the power of the engines produced at the end of WWI.  In order to compensate for lower density air at higher altitudes, the Kestrel gets a mechanical compressor, the super-charger, the first turbocharged engine Rolls-Royce produces.  With the gasoline at that time rated at 87 octane, it allowed for a boost pressure of 5.6PSI.

The Kestrel turns out to be a great engine, with innovations such as the use of ethylene glycol for cooling which reduces the size of the radiators.  Interestingly, Messerschmidt, which still awaits the Daimler-Benz V12 engine, will acquire a Kestrel to test the first version of the BF 109 in 1935.  However, the displacement of the Kestrel is a bit inadequate for the next generation of fighters will require, such as Britain’s future Spitfire.

The Kestrel was followed in 1929 by the Buzzard (36.7 liters), which was named Type R in its competition form. It is with the 2300 hp R-type aircraft that race Supermarine S6 allows England to win for the third consecutive time in the 1931 Schneider Cup and beat the world speed record at 407MPH.  However, the Type R is a racing engine, whose performance can only be sustained for a short period of time.

To fill the existing hole in the range between Kestrel and Buzzard, Rolls began to privately develop a new V12 called the PV 12 (Private Venture 12).  In October 1934, the Air Ministry officially orders the PV12 into production and it is given the name Merlin.  For the next 10 years, Rolls-Royce will continue to develop the Merlin, to make it ever more powerful and versatile.

The Merlin I and II : In July 1934, Rolls releases the first pre-production Merlin A, which like many motors, has a bore (137 mm) which is slightly less compared to the stroke (152 mm), a feature that promotes low-end torque. The Merlin is estimated at 790 hp at 2500 rpm at an altitude of 12,000 feet, already outstanding performance for a block that weighs less than 1322 pounds dry (no oil or coolant).  At the same time (Feb 1935), another version (Merlin B) is produced with a redesigned combustion chamber and 4 valves per cylinder, it reached 960 hp at 11,000 feet. The changes follow through F, to be released in small numbers with the name of Merlin I. The Merlin G (called Merlin II production) is the first type for mass production, it reached 1030 hp at 3000 rpm and 16,250 feet. Compared to the type A, the Merlin type G has gained 30% in power, while the weight has increased by 220 pounds. The Merlin II has a single-speed super-charger, and with 87-octane fuel limit has a boost pressure up to 5.6PSI, and in 1939 with the introduction of 100 octane fuel, this was increased to 11.2PSI, improving power at high-altitude.

The X Merlin : The Merlin X represented a milestone in the evolution of Merlin with the introduction of a two-speed compressor.  Driven by the engine, the supercharger requires power to compress the incoming air.  Therefore, it is important that the power required to compress the air does not exceed the power gained.  The two-speed compressor would allow a lower pressure when the engine was at low to medium altitude, and only use maximum pressure at high altitude.  With the adoption of this compressor Rolls-Royce significantly improves the performance of the Merlin.

Series 60 and Beyond : For the 60 series, the Merlin receives a two-stage compressor. Rather than resorting to turbocharging, which Rolls Royce has no experience, and requires special alloys, Sir Stanley Hooker (Merlin Head Engineer) prefers to mount a two-stage compressor.  This again allows efficient low altitude performance, while increasing high altitude performance.  The ultimate development of this technology will lead to the series 100, which develops over 2000 hp at sea level, and retains a power of 1000 hp at 12,000 ft, with a boost pressure of  2.8PSI.  With the two-stage compressor, Rolls-Royce has the Merlin which is the envy of American turbocharged engines.

The Merlin in Action

Almost all British aircraft, fighters or bombers, were, during the war, equipped with the Merlin. With its V configuration, Merlin offered a reduced frontal area, which was perfect for swift fighters.  Two of these mythical Battle of Britain fighters were the Spitfire and Hurricane. The first Spitfire and Hurricane used the Merlin II. Although designed for fighters, the Merlin also powers almost all British bombers, first the twin-engine bombers (Stirling, Whitley, Mosquito) and then the four-engined Lancaster and Halifax.  The Merlin power plant is also installed in two American fighters, the Curtis P-40 in limited numbers, and the P-51 Mustang almost excusively.

Bell P-39N Airacobra – Little Sir Echo – Small Fry

By Warbird September 7, 2010 Bell, P-39 Airacobra, Planes, Planes of Fame 2 Comments

Bell P-39 Airacobra - Little Sir Echo

This is P-39N-5 “Little Sir Echo / Small Fry” Serial Number 42-19027 which served with the USAAF 5th Air Force (AF), 71st Tactical Reconnaissance Group (TRG), 82nd Tactical Reconnaissance Squadron (TRS), from June 1943 to July 16, 1944. It was abandoned at Tadji, Papua New Guinea, a Japanese airfield that was liberated by the US Army on April 26, 1944. Tadji became a major Allied air depot for American and Australian forces, and the resting place for this P-39 for the next thirty years. It is now on static display at the Planes of Fame Museum in Chino, CA.

This specific P-39 was delivered to the US Army on April 28, 1943, and sent to the Pacific in May. Lyndall W. Tate was assigned to this aircraft. Lyndall was born Oct 20, 1920 in Texas, and passed away Sept 15, 2008. He served over 28 years in the military. If anyone else has any further information on Lyndall, please let us know more about this hero. The aircraft was recovered from Tadji in a 1974 salvage operation funded by David Talichet’s Yesterday’s Air Force (MARC). It currently is on static display at the Planes of Fame museum. It still supports its original markings of Olive Drab over Neutral Grey with White New Guinea theatre markings on tail unit, wing leading edges and spinner (thin White band on nose). In addition it features an interesting shark mouth on the center drop-tank.

The Bell P-39 was one of the US’s main-line fighters when war first broke out in the Pacific at the beginning of World War II. It was unique at the time for having a tricycle undercarriage and a mid-mounted engine located behind the pilot. This arrangement was due to the proposed installation of a powerful 30 mm cannon in the nose. Ultimately, the P-39 was unable to achieve the same performance of later US and European fighters, mainly due to a lack of a turbo-supercharged engine which greatly limited the P-39’s ceiling and speed. However, its low-altitude performance, mid-mounted engine, and armor plating allowed it to become a great ground-support aircraft, most notably used by the Soviet Air Force. In the end, the Bell P-39 became Bell’s most successful fixed-wing aircraft that they ever produced.

A-10 Thunderbolt II by Fairchild

By Warbird August 13, 2010 A-10 Thunderbolt II, Fairchild Republic No Comments

Great shot of an A-10 over Afghanistan.  In this picture, Capt. Andrew Quinn flies his OA/A-10 Thunderbolt II observation/attack aircraft to a refueling position behind a KC-135 Stratotanker.  This picture was taken  on Sunday, March 26, 2006 by U.S. Air Force photo/Master Sgt. Lance Cheung.  Captain Quinn is currently deployed to the 355th Expeditionary Fighter Squadron at Bagram Air Base, Afghanistan.   The A-10 Thunderbolt II is a single-seat, twin-engine, straight-wing jet aircraft designed to provide close air support (CAS) of ground forces.

It was the first U.S. Air Force aircraft, designed in the 1970’s, exclusively for close air support . The A-10’s official name comes from the Republic P-47 Thunderbolt of World War II, a fighter that was particularly effective at close air support. The A-10 is more commonly known by its nickname “Warthog” or simply “Hog”.

Tondelayo – The Collings Foundation B-25 Mitchell

By Warbird April 9, 2009 B-25 Mitchell, Museum, North American Aviation, Wings of Freedom 3 Comments

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The famed “Tondelayo” of the 345th Bombardment Group known as the “Air Apaches” as it served in the 500th BS. The Tondelayo was one of three B-25Ds that sunk a 6,000-ton freighter in the South Pacific during World War II. Its story was unique in the fact that During the battle, the Tondelayo’s engine was shot out and for over an hour it combated 50 Japanese fighter planes as it headed down the New Britain coast. The other two accompanying B-25s were shot down during the battle. The plane’s turret gunner was given credit for shooting down five Japanese fighters and the crew earned the Distinguished Unit Citation and Silver Stars. Despite tremendous damage “Tondelayo” was returned to service after it was repaired… like a phoenix rising from the ashes.

Tondelayo was named after the sexy actress Hedy Lamar’s character “Tondelayo” in the 1942 film White Cargo.

North American P-51 Mustang

By Warbird April 1, 2009 North American Aviation, P-51 Mustang, Planes 5 Comments

U.S. Army Air Force (USAAF) fighter aircraft manufactured by North American Aviation, Inc., between 1942 and 1945. In its role as a long-range bomber escort in the European Theater of Operations during World War II, the P-51 exhibited its greatest influence and is credited by many as the airplane that shifted the European airwar in favor of the allied forces.

This P-51 was used by the USAFF, USAF and various U.S. Air National Guard units during and after World War II, performing a variety of missions, including interception of enemy aircraft, long-range bomber escort, armament support for land and sea forces, photographic reconnaissance and flight training.

The P-51 performed at levels surpassing other single-engine, propeller driven fighter aircraft during World War II.  The wingspan of 44-73287 is 37.03 feet and has a wing area of 236 square feet. The plane’s two-section, semimonocoque fuselage is constructed entirely of aluminum alloy and is 32 feet and 2 5/8 inches in length.

Laminar flow airfoil was used during World War II in the design of the wings for the North American P-51 Mustang, as well as some other aircraft. Operationally, the wing did not enhance performance as dramatically as tunnel tests suggested. For the best performance, manufacturing tolerances had to be perfect and maintenance of wing surfaces needed to be thorough. The rush of mass production during the war and the tasks of meticulous maintenance in combat zones never met the standards of NACA laboratories. Still, the work on the laminar flow wing pointed the way to a new family of successful high-speed airfoils. These and other NACA wing sections became the patterns for aircraft around the world.

P-51 Mustang

Boeing B-17 Flying Fortress

By Warbird September 23, 2008 B-17 Flying Fortress, Boeing, Planes 15 Comments

The B-17 Flying Fortress is one of the most famous airplanes ever built. The B17 prototype first flew July 28, 1935. Few B-17s were in service on Dec. 7, 1941, but production quickly accelerated. The aircraft served in every World War II combat zone, but is best known for daylight strategic bombing of German industrial targets. Production ended in May 1945, and totaled 12,726.


In response for the Army’s request for a large, multiengine bomber, the B-17 (Model 299) prototype, financed entirely by Boeing, went from design board to flight test in less than 12 months. General features on the B-17 include its mid-wing monoplane design, aluminum-clad exterior, four radial engines, massive wing structure and heavy armament. It was the first Boeing airplane with the distinctive, and enormous, tail for improved control and stability during high-altitude bombing.

Although many U.S. airmen and craft contributed to the Allied victory in World War II, the B-17 has become especially symbolic of the self-reliance, daring and sacrifice of American airmen during the war. American confidence in the B-17 became the cornerstone for the Air Corps doctrine of strategic “daylight” bombing in German-occupied Europe.

The G series could hold a crew of 10, including pilot, co-pilot, bombardier, radio operator, navigator, dorsal turret gunner, two waist gunners, ball turret gunner and tail gunner. Typical for B-17Gs are the four 1,380-horsepower Wright GR1820-97 Cyclone air-cooled, nine-cylinder radial engines equipped with exhaust driven turbochargers.  General features include the raised cockpit section and Plexiglas nose cone. Characteristic of all B-17s, starting with the E series, is the massive dorsal fin, which gracefully sweeps to merge with the fuselage. All B-17s have retractable tail-wheel landing gear. The empty weight of the airplane is 32,720 pounds. Fully armed and loaded, B-17s weigh 65,600 pounds. Payloads of 4,000-5,000 pounds were typical but up to 17,600 pounds could be carried for less than maximum range. The maximum speed was 300 miles per hour at 30,000 feet.

While the B-17s were used in the Pacific, by 1944 the B-29 had replaced the B-17 for use in the Pacific Theater. While in the Pacific, the planes earned a deadly reputation with the Japanese, who dubbed them “four-engine fighters.” The Fortresses were also legendary for their ability to stay in the air after taking brutal poundings. They sometimes limped back to their bases with large chunks of the fuselage shot off. B-17s were initially intended as a fast, land-based bomber, which could patrol at sea and intercept naval vessels.

The B-17 went through several alterations in each of its design stages and variants. By the time the definitive B-17 G appeared, the number of guns had been increased from seven to 13, the designs of the gun stations were finalized, and other adjustments were complete. The B-17 G was the final version of the B-17, incorporating all changes made to its predecessor, the B-17 F, and in total 8,680 was built, the last one on 9 April 1945. Boeing plants built a total of 6,981 B-17s in various models, and another 5,745 were built under a nationwide collaborative effort by Douglas and Lockheed (Vega). Many B-17 Gs were converted for other missions such as cargo hauling, engine testing and reconnaissance. Initially designated SB-17G, a number of B-17Gs were also converted for search-and-rescue duties, later to be re-designated B-17H.

Late in World War II, at least 25 B-17s were fitted with radio controls, loaded with 20,000 pounds (9,000 kg) of high-explosives, dubbed “BQ-7 Aphrodite missiles”, and used against U-boat pens and bomb-resistant fortifications.

Specifications

Wing Span: 103 feet, 10 inches
Length: 74 feet, 4 inches
Height: 19 feet, 1 inches
Weight: 55,000 pounds loaded
Armament: Thirteen .50-caliber machine guns with normal bomb load of 6,000 pounds
Engines: Four Wright “Cyclone” R-1820s of 1,200 horsepower each
Cost: $276,000
Maximum speed: 300 mph.
Cruising speed: 170 mph.
Range: 1,850 miles
Service Ceiling: 35,000 feet

EASTERN EUROPE -- The vapor trails from two Boeing B-17 Flying Fortress aircraft light up the night sky. The B-17 is one of the most famous airplanes ever built. The B-17 prototype first flew on July 28, 1935. Few B-17s were in service on December 7, 1941, but production quickly accelerated. The aircraft served in every WW II combat zone, but is best known for daylight strategic bombing of German industrial targets. (U.S. Air Force file photo)

Vapor trails from Boeing B-17 Flying Fortresses.The Flying Fortress is one of the most famous airplanes ever built. The B-17 prototype first flew on July 28, 1935. Few B-17s were in service on December 7, 1941, but production quickly accelerated. The aircraft served in every WW II combat zone, but is best known for daylight strategic bombing of German industrial targets. Production ended in May 1945 and totaled 12,726.