How The Merlin Aircraft Engine Changed War History


Charles Rolls and Sir Henry Royce

In the early decades of the 19th century, consistent and sustained powered heavier-than-air flight remained an impossibility because of the lack of suitable power plants. The level of technology that would permit even limited powered flight lay somewhere over the horizon over a century later in the future. The development of clockwork mechanisms and other sorts of spring-powered systems were not yet available to facilitate human flight. The aeronautical potential of propulsion systems ranging from hot-air engines to gunpowder to compressed air and even to carbonic-acid power plants was discussed during the century. Nevertheless, steam and internal-combustion engines quickly emerged as the choice of most serious experimenters.


Thomas Newcomen, Inventor

The engine that is considered one of the first ever created was the Newcomen atmospheric steam engine created by Englishman, Thomas Newcomen in 1712. Thomas Savery had also created a rudimentary pump and was awarded a broad patent in 1698. Newcomen could not patent his engine. Therefore, Newcomen entered into a partnership with Savery. One of the major problems with mineral mining in his day was flooding. Newcomen’s engine provided a way for mine operators to pump out water, resulting in saving lives. In design and shape the Newcomen engine resembled an oil derrick. In purpose they have similar functions; oil derricks pump oil up from the ground, while the Newcomen pumped water from the ground. So how did the Newcomen work? The steam engine was the center piece of the system. On the other side was the pump used to drill deep into a mine. Above the engine was a heavy wooden beam and a fulcrum that provided a seesaw motion with arch-heads and chains which transferred motion between the two sides. This type of pumping action was not new, however, what was new was the steam engine itself. The engine consisted of the following elements – a, piston a cylinder, a tank of water, and a fire beneath. And a tank of water above the wooden beam, and a set of valves. The steam engine was able to produce 12 cycles per minute. The process begins with the pump side being heavier, as a result the piston is pulled up.


Newcomen Steam Engine

Improvement Of The Newcomen Steam Engine

Improvement of the Newcomen steam engine was later improved by British inventor, James Watt. In 1764, Watt was assigned the task of repairing a Newcomen steam engine. He started working on it and soon discovered its deficiencies. Watt proposed a major addition. Watt astutely noticed that what was needed was a way to prevent steam from escaping from the engine by adding a separate condensing chamber. Watt sought out a patent and it was granted. Watt’s idea paved the way for other mechanical design work. With Watt’s improvements steam engines were soon used in many different industries and for many purposes. They were bought by mine owners, cotton mills, and waterworks and as a result, the steam engines helped to power the Industrial Revolution, allowing once very manual work to be replaced by engines.


James Watt, Inventor

In addition to mining and textile steam engines were monumental in revolutionizing the transportation industry. In particular, early trains and boats used steam engine technology. In 1807, Robert Fulton used steam power to create the first steamboat. His invention revolutionized travel and trade throughout Europe and in Britain in particular. In 1814, George Stephenson, utilized the steam engine to develop the first steam train. Like the steamboat, the steam train increased the ability of industrialized nations to transport people and goods long distances. This allowed industrialized nations, such as Britain, to move goods to market and to transport raw materials into factories. Fulton’s craft, the Clermont, made its first voyage in August of 1807, sailing up the Hudson River from New York City to Albany, New York, at an impressive speed of eight kilometers (five miles) per hour. Fulton then began making this round trip on a regular basis for paying customers.


Robert Fulton, Inventor

Following this introduction, steamboat traffic grew steadily along the river lifeline, namely the Mississippi River along with other river systems in the inland United States. There were numerous kinds of steamboats that had different functions. The most common type plowing along Southern rivers was the packet boat. Packet boats carried human passengers as well as commercial cargo, such as bales of cotton from Southern plantations. Compared to other types of craft used at the time, such as flatboats, keelboats, and barges, steamboats greatly reduced both the time and expense of shipping goods to distant markets. For this reason, they were enormously important in the growth and consolidation of the U.S. A clear example of the improvement in travel time between steam power and sail power was the time it took to cross the Atlantic Ocean. In the case of sail, if the weather conditions were perfect, the voyage could take around six weeks. If the weather conditions were less than ideal, it could take up to fourteen weeks. In the case of steam one the earliest voyages the steamship Great Western can be considered one of the first liners, crossed the Atlantic in 15.5 days in 1838. And at that height of steam voyage five days was the norm.

Like in any momentous discoveries there is often another competing idea at the very same time. In the case of steam power, the combustion engine was in its earliest stages. A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the energy to do a variety of tasks. In 1863, Belgian inventor Étienne Lenoir had driven his “hippomobile” the nine kilometers from Paris to Joinville-le-Pont on a round-trip journey. It was powered by Lenoir's own gas engine and his propellent was a turpentine derivative - thus becoming the distinction of the first vehicle with an internal combustion engine. The development of the internal combustion engine helped to free men from the hardest manual labor, made possible the airplane, automobiles, and countless other forms of machinery, and ushered in a new age of power generation.


Étienne Lenoir and Combustion Engine

In 1902, the Wright brothers sent out a request for bids to several engine makers for an 8-hp, "vibration-free," gas-fueled engine that would weigh no more than 200 lb. No one took them up on the offer. Undeterred, the brothers did the next best thing, they built one themselves. The year before, the creative brothers successfully built a one-cylinder, 3-hp, cast-iron engine to power their machine shop. They finished it eight weeks later with the aid of Charles Taylor , a mechanic and machinist, but without drawings. The 12-hp, four-cylinder inline engine weighed 170 lbs, including the radiator, water and fuel tanks, and 1.5 gallon of gas. It had no throttle. The four-stroke engine always ran at about 1,000 rpm. But output could be somewhat controlled by retarding or advancing the spark timing.


Wright 1903 Flyer Engine

At the start of World War I the automobile industry had the most experience at producing combustion engines. Stand only to reason that aircraft manufacturers would turn to them to produce aircraft engines, as the winds of war drew closer. The design and manufacture of aircraft design came a long way in the years between the Wright brothers’ first flight in 1903 and the outbreak of World War One in 1914. And because of the increasingly competitive atmosphere, even more radical changes continued to be made over the course of the next few years as well. This was especially true in the development of aircraft engines. Therefore, horsepower to weight ratios increased dramatically, yet engine design and performance was far from uniform. Three basic engine designs were adapted for aviation use. These were inline, and rotary. Each version had its shares of pros and cons in the process of engine development. Radial and rotary engines had cylinders radiating out from the engine axis like spokes. With all the cylinders exposed equally to the airflow, they were efficiently air-cooled.


WW1 Rotary Engine

In this configuration, all the cylinders were connected to a single point on the crankshaft. Dictating that this meant that there had to be an odd number of cylinders in these engines. When the crankshaft made one rotation, the pistons in the even-numbered cylinders would each, in turn, go through the power and exhaust strokes while the odd-numbered cylinders would go through the intake and compression strokes. At the end of a single rotation, the even-numbered cylinders would be ready for intake and compression and simultaneously, the odd numbered ones would be firing and expelling the exhaust. The primary difference between radial and rotary engines was that the radial engine was fixed to the airframe and the crankshaft turned the propeller, while the entire cylinder block of a rotary engine spun with the propeller while the crankshaft was fixed to the airframe. The rotary engines produced the highest power to weight ratios and were widely relied upon in the race to give lightweight WWI fighter planes an advantage over their opponents. However, the rotary engines also had significant operational drawbacks that limited their use and their size and eventually led to their being replaced by the radial engine.

WW2 Aircraft Engines

Most of the aircraft engines which would see service in World War II started production in the early 1930’s. The task in engine design was driven by the push for altitude capability, where thinner air placed great emphasis on the supercharger. This in turn would require more power via increased supercharger pressure ratios and engine compression ratios also required improvements in fuel quality. For many fighters and bombers, engines of at least 1,000 horsepower were specified in the procurements of the mid-1930s. By 1938 and 1939, 2,000 hp engines were specified for fighters and bombers. Engine design had to become more sophisticated as greater power was sought at higher engine rotating speeds. This focused attention on small design details because of the resultant higher stresses and temperatures.


2 stage supercharger

Consequently, the engines used early in World War II often had up to two stages of supercharging, with the pilot able to select from two different supercharger impeller speeds. The effect of this high supercharged power rating was lower engine life, with time between overhauls ranging from a low of 50 to a high of 500 hours. In the main, all power requirements were met with radial air-cooled engines and inline liquid-cooled engines. While other approaches were tried (liquid-cooled radials, and air-cooled inlines) they were not major factors. The bomber typically needed efficiency, reliability, and system survivability, and was usually equipped with air-cooled radials. The fighter needed higher power per unit of weight per unit of frontal area, and initially received the supercharged liquid-cooled inline engines.

Introduction Of The Rolls-Royce Engine

Aircraft production in World War II will be forever remembered for the outstanding aircraft that rolled out of factories around the world. The beating heart of these aircraft were the engines that powered them to incredible heights and speeds. The Messerschmitt Bf 109 was powered by the Daimler-Benz DB 605 Inverted V-12 Engine, while Fw 190 soared with the BMW 139 14-cylinder two-row radial engine. While in comparison, the Lockheed P-38 featured the Allison V-1710-111/113 liquid-cooled engines. However, the engine that captured the world’s imagination was undoubtedly the Rolls-Royce Merlin engine. During its production run variations of the Merlin powered an astounding forty aircraft. Just the mere mention of the British Supermarine Spitfire conjures up images of a fiery merlin roaring to life.


Merlin Aircraft Engine

A 1904 meeting in England between auto enthusiasts Charles Rolls and Sir Henry Royce would later forge one of the finest enterprises in automobile manufacturing history. While building their elite company, at the same time, each had an eye towards the sky in the fledgling aircraft industry. Sadly, Charles Rolls would not live to see the fruits of his labor, he was tragically killed in a crash of his Wright Flyer in an air crash at Southbourne, Bournemouth on July 12, 1910. Rolls-Royce’s foray into aircraft engine production began in 1914 at the behest of the Royal Aircraft Factory. The RAF approached RR with a request to produce a 200 hp air-cooled engines. However, RR balked at the idea of air-cooled engine, instead they insisted on a liquid-cooled engine which they were more proficient in that technology. On 3 January 1915 the Admiralty ordered twenty-five of the new engines. The Eagle first ran on a test bed at Rolls-Royce's Derby works in February 1915, producing 225 hp at 1,600 rpm. This was quickly increased to 1,800, then in August 1915 to 2,000 rpm where it produced 300 hp. Further testing moved the RAF to approve the engine for production at 1,800 rpm and 225 hp; 1,900 rpm was allowed for short periods.

Flush with the success of their aero engines in World War I, Rolls-Royce stepped it up a notch when they began their association Supermarine and their seaplane racers that dominated the Schneider Trophy contest during the late 1920’s and into the 1930’s. Powered by the Rolls-Royce R was an aero engine designed and built specifically for air racing purposes by Rolls-Royce Limited. A total of nineteen R engines were assembled in a limited production run between 1929 and 1931. Developed from the Rolls-Royce Buzzard, it was a 37-litre capacity, supercharged V-12 capable of producing just under an impressive 2,800 horsepower and weighed 1,640 pounds. The R was fine tuned to near perfection by redesigning the components, greatly improving reliability. But what would soon solidify this legendary engine was the injection of a special fuel blend that resulted in the Supermarine S.6B aircraft setting a new airspeed record of over 400 miles per hour. In addition, the R engines were used to achieve various land and water speed records.

It is little wonder that British aircraft manufacturers, and in turn, the RAF turned to Rolls-Royce to power the latest generation of military aircraft. It was the Rolls-Royce’s process to name their engines after birds-of-prey. Examples are the afore mentioned Eagle, the Kestrel, Peregrine, Vulture and Merlin. The Merlin (a species of falcon with thin, pointed wings that allow it to dive at high speeds) began its life after the run of the Kestrel. The first engines were labeled PV-12 which indicated Private Venture 12-cylinder (a private industry venture), were ready for bench testing in 1933, rated at 790 hp. The engine, now uprated to 950 hp, first flew in 1935 in a Hawker Hart, Sydney Camm’s end of an era last biplane and a forerunner of his Hurricane. Extensive trials testing revealed disturbing problems. In particular, the cylinder head design, bearings, and gears—which had to be corrected for the engine to become a practical power plant. By the mid-1930s it was still unreliable, repeatedly failing the civilian 50-hour type test. It appeared that the merlin’s future might be in doubt.

To their credit, during these difficult times, Rolls-Royce held firm to the principles of it founder; identifying the weakest link by gradually increasing the engine’s speed and load, redesigning the problem component, and going on to demand even more, even if this meant running it to destruction. The people behind the development of the merlin were of the highest quality. Alfred Cyril “A.C.” Lovesey was tabbed to lead the project. Lovesey joined the company in 1923 and had been instrumental on the development of the highly successful R engine. In 1930 Lovesey was awarded Aviators Certificate No. 9350 by the Royal Aero Club for his brilliant service. His contribution to the Merlin, doubling its power output and improving reliability at the same time, was a major achievement.


Alfred Cyril Lovesay, Engineer

Another Rolls-Royce associate who would make his mark was Stanley Hooker, he joined the firm in 1938. An Oxford trained mathematician, he had also done postgraduate work on fluid dynamics, and would become probably the world’s greatest expert in fluid- and thermodynamics applied to supercharging. As he weighed in on the problems of the current supercharger, he determined that redesigning the rotor and diffuser would yield an immediate 15-percent increase in efficiency, and that would only be the start. Within a few months Hooker, who had never previously seen an aero engine either, added 30 percent more power to the Merlin. Hooker would later be knighted by the Queen at the end of a magnificent career. During discussions about its possible use with the Merlin, Hooker pointed out the lack of suitable locations for a turbocharger on the several aircraft. Identifying the problem, he proposed that exhaust energy could be utilized in a much simpler way. Experiments with exhaust stack designs had produced a short ejector shape imparting reaction (“jet”) thrust that added aircraft speed equivalent to an additional 150 hp. This would be lost in turbocharging. He predicted that the turbocharger’s main benefit—maintaining power at high altitude—could be obtained by using two superchargers in series, driven by the same engine gears. In fact, the Merlin 61, the first equipped with a two-stage supercharger, boosted the Spitfire IX’s ceiling from 30,000 to 40,000 feet and its top speed by 70 mph.


Sir Stanley Hooker, Engineer

The true test of fire would come September 1, 1939, when the Allies declared war on Germany after their invasion of Poland. In what would become the Battle of Britain, in 1940, the air war took center stage. In the initial face-off the British interceptors, the Supermarine Spitfire and Hawker Hurricane, held their own against German Messerschmitt Bf 109’s. However, the unanticipated appearance in September 1941 of the new Focke Wulf Fw-190A, with its 42-liter BMW radial engine, came as a jolting shock to the RAF, as it easily outperformed the Merlin 45–powered Spitfire V in speed and climb. But quick to respond, within weeks, Rolls-Royce was producing the Merlin 61. Only two-thirds the size of the Fw-190’s engine, it nevertheless produced more power, especially at high altitudes, where most of the action took place. Equipped with the Merlin 61, the new Spitfire IX regained the upper hand, surprising Luftwaffe pilots with its performance surge, since the two Spitfire types looked almost identical.


Bayerische Motoren Werke Aircraft Engine

In early combat with the Me 109’s the Spitfires and Hurricanes were at a slight disadvantage. Direct fuel injection in the Daimler-Benz engines yielded a temporary advantage for the Germans. With a Spit on their tail, they could simply nose over and dash away. However, the same maneuver would cause the Merlin to cut out due to mixture leaning from negative G. Therefore, the carburetor’s float would respond to what it now thought was “down,” flooding the engine for several seconds. In deadly aerial duels seconds can mean life or death. In typical British style this dilemma was solved by another bright engineer, Beatrice “Tilly” Shilling, a scientist at the Royal Aircraft Establishment, designed a simple flow restrictor to solve the problem. Her device resembled a metal washer, it allowed a maximum fuel flow of what was required at full throttle. The device would later be known as the indelicate name “Miss Tilly’s Orifice.” Luftwaffe pilots, accustomed to escaping by diving, were now faced with a RAF pilot hot on their tail.


The Merlin is undoubtedly known for many accomplishments. Some will argue that one of the best accomplishments was the sweet marriage between the U.S. North American P-51 Mustang that was the result of a request from Britain to North American to produce a fighter aircraft on their behalf. While North American produced a great airframe and performed well at low level, its power was greatly reduced at higher altitudes. A RAF test pilot suggested replacing the current engine with a merlin. The results were simply phenomenal. The updated Mustang vaulted into the best fighter of the war. Its ability to escort heavy bombers on round trip mission to the heart of Germany saved thousands of Allied lives and smashed German industry. This would not have been accomplished without the merlin, which established its legendary status.

Evolution Of World War 2 Fighter Aircraft

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