Rolls Royce Crecy - The Most Advanced Piston Aero Engine Never Made.

I'm pretty sure

most

of us are familiar with the Rolls-Royce Merlin

engine

, the driving force behind many of the

most

important aircraft of World War II, such as the Spitfire Mustang Hurricane Mosquito and the Lancaster, to name just a few, but behind the scenes. Another Rolls-Royce

engine

was prepared to take on what had been done with the Merlin and advance significantly with a radical design that not only

made

the money look simple in comparison, but was also much more powerful and for its 26 liter capacity it had the highest specific power of any

piston

aero

engine then or since this is the story of the

rolls

-

royce

cressie, a revolutionary two-stroke

aero

engine and what could have become of it if it had been a few years earlier this video is sponsored by brilliant the story of the cressie begins in the mid 1930s this was at a time when germany was rearming and the buildup of its luffwaffle was causing concern among the government and the british army the plan at the time was to have aircraft patrolling along the Coast at altitude on surveillance, but there were a limited number of them available and they could only patrol as long as they had fuel.

As testing of the first British radar progressed, it was shown that there would be an opportunity for a high-speed speed engine. Henry Tizard, later, of the Tizard mission to the United States, at a meeting of the aeronautical research committee or the Arch of which he was president, asked: if an engine of this type could be manufactured, could they ignore the consumption of fuel and oil to obtain very high performance for short flights? Only in the era when aeronautical engines were large but not as efficient, the specific power output of a Pratt and Whitney Twin Wasp, for example, which was one of the most common engines of the time, was 0.66 horsepower. of force per cubic inch and simply making them larger and more powerful did not solve the power-to-weight ratio, so new engine designs and materials were created.

It would be necessary to manufacture lighter and more powerful engines on both sides of the Atlantic. There was a race to produce a hyperdrive that had a specific power of one horsepower per cubic inch. Tizzard was a good friend of Harry Ricardo, now considered one of the most prominent Los 20th century engine designers Ricardo had been working on a sleeve-valve two-stroke compression-ignition diesel aero engine that could match the power of a conventional gasoline aero engine for several years, a couple of months after meeting Del Arco in a letter to Ricardo Tiszard suggested that his diesel engine could be converted to spark ignition to produce an extremely high power engine with a small frontal area.

This engine would become the cressie and would be developed by Rolls Royce and Ricardo's company, as Tiszard oversaw all engine development. Throughout the arc, he was also encouraging people like Hane Constant and Frank Whittle as they worked on the first turbojet engines, so the development of jet engines and

advanced

piston

engines was seen as the best approach to deal with the future. Luftwaffe threat. ricardo thought that more traditional poppet valve engines, such as the merlin with two valves in the cylinder head, would probably not make more than 1,500 horsepower because there is a limit to the size of the valves in relation to the cylinder and therefore therefore, to its size.

The mixture of air, fuel and exhaust could quickly enter and exit the engine. He had already published a study on sleeve valve engines in 1927 and thought these would be the next generation, as they offered greater volumetric efficiency. He can now be forgiven for thinking what is a sleeve valve engine? Well, they have a very different design that became popular in luxury cars around the 1920s, instead of the two-valve cylinder head design we think of as normal now, the piston goes up and down in a sleeve that has holes in it. cut into it, which functions as inlet and exhaust valves, a bit like a two-stroke engine, but with one difference, the difference here was that the sleeve itself then moves up and down and side to side to align the intake and exhaust ports with sleeve cutouts as the engine goes through its four-stroke cycle, this sleeve allows for multiple larger ports that would be larger than the valves in the cylinder head design and consequently the engine can breathe better, also

made

it less susceptible. to pre-ignition or detonation due to the poor quality of the fuel at the time, but there is one disadvantage of these engines: the gear mechanism used to make the sleeve move up and down and side to side at the same time as the piston makes them very much more complicated, it's not that bad on a single cylinder engine, but on a V12 or rotary there are a lot of extra crankshafts and gears involved.

Pinch valve engines were used in other aero engines during the war. Frank Halford who worked in Ricardo's London office from 1919 to 21 went to Napier to design the 24 cylinder saber sleeve valve engine which became one of the most powerful engines of the war and was used in the Hawker Typhoon while ricardo worked with the Bristol Airplane Company to design a range. of rotary sleeve engines for the bristol beaufighter the difference between those and the

rolls

-

royce

cressie was that the cressi was a two-stroke with gasoline injection and a single variable thrust supercharger the simplicity of the two-stroke design combined with the valves shirt could be a game-changer with power up to twice that of a normal four-stroke engine.

Ricardo's company did most of the development work on single-cylinder and V-twin engines. The V-twins were particularly loose with pinch valves. This was normal. To come up with the best design before building multi-cylinder engines like a V12, one of the unique features Ricardo created was a cone-shaped cylinder head with a bulbous upper chamber with two spark plugs and a central fuel injector on top. This bulbous chamber allowed the fuel air charge to precombust in a rich mixture around the spark plugs before spreading to the rest of a weaker mixture in the rest of the cylinder, allowing it to run on lower octane fuel or at boost pressures. higher without detonation, something that delayed many other engine designs during the war until 130 to 150 fuel octane became available later, as the cressi was a two-stroke, when the v12 ran at its maximum speed of 3000 rpm, there would be 36,000 exhaust strokes per minute twice as many as a four-stroke engine like the Merlin, so it would really scream like a German Yonko Ju-88 Stuka dive bomber that used two wind-driven sirens known as the trumpets. of jericho to create that characteristic current that would scare the living. of anyone on the ground, the watercress escape would do that on its own.

The sleeve valve had another advantage: the opening of the ports could be done with an eccentric gear, so that it opened much faster than that of a typical air valve. valve driven by a cam, the effect of this almost instantaneous opening of the valve was to cause the exhaust gases to exit much faster, which combined with the double firing rate of a cylinder gave the cressie up to 350 pounds of thrust alone from the exhausts, Merlin engines also used thrust from the exhaust, but it could only achieve about 150 pounds of thrust at 300 miles per hour, each pound of thrust was equivalent to one horsepower through an efficient 80 propeller, this exhaust explosive and the frequency doubling also made it extremely noisy, it's a shame there were no images. or an audio recording from when it was being tested, as it was said that when it was running on the test stand it could be heard over five miles away and when they started testing it, it set off air raid sirens 15 miles away in December. 21 Cressie engine number 10 from 1944, a 26.1 liter v12 engine achieved 1798 horsepower with a normally aspirated engine running on 100 octane fuel when the calculated fan power was added, it would have been 2350 horsepower, but once corrected for dyno losses it was approximately 2,500 horsepower when compared to the most powerful Merlin derivative, the Griffin, which was 37 liters, 11 liters larger than a cressie and ran on 150 fuel. octane with a two stage supercharger, up to the cressy single fan which produced 2220 horsepower again if I compared the specific horsepower of the two, the cressie was 1.77 horsepower per cubic inch with the 0.91 per cubic inch Griffin's, easily surpassing the hyperdrive's one horsepower per cubic inch goal, Tiszard speaking in 1946 said that research had shown that the two-stroke sleeve-valve engine was capable of generating almost 200 horsepower per liter, a a figure that today is only surpassed by higher performance racing engines that operate at much higher revolutions, since the Cressi was a 26.1 liter V12 and its total power could have been 5,000 horsepower, the double.

Basically, it came too late and had been a low priority throughout the war, with design and manufacturing talent assigned to more important tasks, such as building and improving the Merlin and its derivatives because they were used in many RAF and other aircraft during war due to its added complexity was unreliable and broke down many times, but you have to remember that this was still in development and combined a lot of different technology was used in newly developed metals in an engine, something that had not been done before was tested on a Spitfire, but it was found that the airframe was not strong enough to handle the power, so a p-51 was thought to be more suitable for the engine, but no further action was taken, so which was to be tested in flight in a Hawker Henley, but when no engine was available, the Hawker test aircraft remained inactive until the end of the war, when it was scrapped in 1945, it became clear that the jet engine would become in the future and resources were directed towards that and away from the cressi due to its high fuel efficiency, there were plans to use it in civil transport after the war, but again the development of the Jet put an end to those plans, only six full-size v12 cressies and eight v-twin test engines, the v12s ran for a total of one thousand sixty hours and the v twins for eight thousand six hundred hours, but all of them only ran.

On the test bench, Cressy number 12 was to use a shaft-driven exhaust gas turbine blower, which was a mid-scale WR1 turbojet, as an energy recovery device to harness exhaust thrust, as well as the supercharger. variable thrust mechanism which would have made it more fuel efficient for larger transport aircraft, the back pressure created by the turbine would also have worked to increase the power of a two-stroke engine, whereas in a four-stroke engine there would have been lost power, but by then rolls-royce had decided it was too much effort to bring the cressie to the reliability of the merlin when the market for high-power piston engines declined at the end of a war and the jet engine took off, so The Cressy became just an interesting footnote in aviation history.

It is unknown what happened to the six Cressie engines but to date none have been found complete or in pieces. In a letter to Ricardo, Cressie project engineer Harry Wood said that if he had been given another six months of development, not only would it have been a lot more powerful but also reliable it is also said that if whittle and von hayne, the designers of the first jet engines, had been born 10 years later, but cressie would have been the filler between the merlin and the jet engine in the race to create the better aerodynamics. war engine it wasn't just cressie that lost, it was the piston engine itself, the jets simply did a better job, as history shows, but it was only thanks to the dog-like determination of a few highly qualified engineers like frank Whittle and Hans. von hayne that this came up now skills and innovative thinking are something our sponsors this brilliant video can help you with.

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