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Home , Avro Manchester, Blackburn Beverley, Blackburn Roc, Fantasy of Flight, Harry Ricardo, Horsepower

Aircraft By: Norm Helmkay

My interest in sleeve-valve engines was first perked when I bought a 1928 Willys Knight, Model 56 rumble seat coupe, in 1969. The research for this article, as you will read, actually began in 1986. After, getting my first Knight , I acquired another and in reading about how to repair them, learned there were other sleeve-valve engine designs besides the Knight double-sleeve arrangement.

High on the list of unique sleeve-valve engines were the Bristol series and that powered many on This drawing shows the pressure air-cooling the Bristol series and Napier Sabre system used in the 24-cylinder Rolls-Royce Exe II engine with counter rotating fan blades that powered many of the British World right behind the hub. This system War II aircraft which I had dreamed of ensures that even the cylinders at the rear of the flying as a boy, when war broke out in engine receive adequate cooling air. 1939.

Flying was to be my passion in life, but all hopes of a flying career in the air were dashed when I washed-out of RCAF pilot training in 1948, with suddenly deteriorating eyesight.

Over many years, I had collected facts and articles about the great World War II warplanes, but only when I got involved in sleeve-valve engined did I realize many of these aircraft were powered with sleeve-valve engines.

Several events rekindled my fascination, beginning in 1985 when my wife, Marion and I visited "Old Warden" an aerodrome about fifty from , the home of the famous Shuttleworth Aircraft Collection. At that time, they had over 40 planes restored to flying condition, the oldest being a 1909 Bleriot.

During our first visit, we were invited back on a "flying day", as guests of men and women who did the restoration on these aircraft in their spare time. The Shuttleworth Trust often has parts rebuilt by associated enthusiasts in nearby towns. Sections of an aircraft (like a rudder, wing, etc.) can be done by these volunteer craftsmen and the pieces are then assembled at "Old Warden”.

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It was our pleasure to return another day to see the "old timers", in the air and have lunch with our new friends, especially a retired Bristol development engineer. He related how hard they all had worked to make Bristol's sleeve-valve engines successful. Bristol and Firth-Vickers tried over 60 steel variations with well over a thousand different heat-treatments before finding the right combination for production. Bristol spent over 10 million (1930-40) dollars to get sleeve production started. To put this in perspective, this was over twice what the British gave to develop and improve the first .

Also, in the summer of 1986 we visited the London Science and Industry Museum, the Museum at Yoevilton and RAF Museums at Cosford and Hendon. This was followed up with a visit to the National Museum of Technology in Ottawa, Canada in 1989. All of the above displayed one or more aircraft sleeve-valve engines of up to 3,600 hp.

This article is the result of rediscovering my old notes and finding a 1939 Bristol Aeroplane Company of Canada engine catalog, at a flea market. Last, but certainly not least, was finding a friend in the Willys-Overland Knight Club, Chris Lansdell in , who did some marvelous leg-work to research data for me over there. Chris was an RAF pilot who flew aircraft with sleeve-valve engines.

First, one must understand, in 1909, Britain had good aircraft designs, but was sadly lacking in motor development, due in part to the dreaded "Red Flag Act" that stifled English auto development until 1904.

To help put the situation right, a private individual, Patrick Alexander, offered a prize of 1,000 pounds sterling ($5,000 US dollars) for the first British made to run 24 hours nonstop, without maintenance. A winner was not declared until 1911.

In 1910, the Bristol Company was formed and by the beginning of the Great War in 1914, was making good aeroplanes, initially with foreign designed Gnome engines (made in Coventry under license) until their own engines came into production in 1915.

At this point, we need to know the renowned Daimler Company in 1908, announced that all it's cars, beginning in 1909 would have sleeve-valve engines. In the early 1900’s, , a famous English engine designer, had

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predicted the end of the poppet-valve engine and suggested, to contemporary engineers, that the sleeve-valve design was the direction of the future.

Ricardo received many acclaims for his unique discovery and designs, but few are aware that he was behind the decision of Bristol to travel down the sleeve-valve engine path. Ricardo was later knighted for his contribution to the motor industry.

In 1913, Ricardo became intrigued with the Argyll sleeve-valve aero engine because of its performance and the fact that the had been raised a whole atmosphere higher than was possible with existing poppet-valved designs.

A coincidence ties Ricardo to the Willys Company. Ricardo designed the 150 hp V12 engines used to the first in . These engines were built by Crossley who later teamed up with Willys to manufacture Overland automobiles in England.

Knowing this background, we move on to 1920 when Bristol opened a special engine shop at Filton. Few people, even today, have any idea how important the sleeve-valve engines from this group were to become during World War II. Hershel Smith, author of "A History of Aircraft Engines" states: "Yet in at least one case, British stubbornness in pursuing unlikely ideas paid off handsomely, without work done on the sleeve-valve, the World War might have turned out differently."

I can't agree with the last part of Smith's statement, but there's no question the sleeve-valve engine played an important role in the Allied victory. On a visit to the Bristol plant at Filton during the war, Churchill was said to have muttered: "Without these sleeve engines, the war would surely be an arms length longer."

In 1927, Bristol's looked at characteristics of various existing auto and aircraft engine types. Bearing in mind the wide use of liquid-cooled sleeve- valve engines in the best automobiles of Europe, beginning with the 1909 Daimler (Argyle, Mercedes, Minerva, Voisin, etc.) Fedden decided, for aircraft and ease of maintenance, the single-sleeve Burt-McCollum concept used in the Argyle, offered major advantages over existing poppet-valve types, if the manufacturing problems of an air-cooled design could be overcome.

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The single-sleeve design is quite different from the Knight double-sleeve engine where two sleeves go up and down vertically. Peter Burt and James McCollum (a Canadian) together invented a unique rotary-vertical pattern for the single-sleeve with somewhat triangular shaped ports. The Burt-McCollum design was used in the Argyle and motorcycles made in the 1920's by Barr & Stroud.

Prophetically, of Rolls Royce talked of a single-sleeve engine design in 1907 before either McCollum or Burt had filed patents for their single sleeve designs.

Sleeve-valve engines were more efficient than those with poppet valves, as the airflow was not restricted through the intake and exhaust ports. Also, with no hot exhaust valve in the , compression ratios could be higher, contributing to improved fuel economy. In Bristol tests, all other things being equal (except compression ratio), sleeve-valve engines of the same , and speed gave at least 14 percent more power and used 10 percent less fuel than Bristol's own poppet-valve engines.

Other sleeve-valve radial design advantages were: less frontal area drag (valve rocker mechanisms were not needed on the top of the cylinder), fewer parts (49 vs. 150 pieces per cylinder in the Bristol design), were lighter and had no valve float as the sleeves were opened and closed mechanically.

Between 1927 and 1930, Ricardo - experimented on sleeve-valve engines with the goal of using a safer fuel and extending the service range. He modified two Rolls Royce Kestrel engines (from which the famous Rolls Royce Merlin was developed), one using , the other, . The diesel version was used by Captain George Eyston to capture the Diesel Land Speed record in 1936. This record of 159 mph stood until 1953. The gasoline version showed a jump from 450 hp for the standard Kestrel to 689 hp for the sleeved version.

As mentioned earlier, it took six years of persistent work and a large sum of money, to work out the difficult details of aluminum/steel/cast-iron coexistence, heat expansion variances, cylinder warping, mass production tolerances and the like, before the first engines were offered for sale. Bristol management wisely did not put "all their eggs in one basket", and continued work on conventional poppet-valve engines while developing the Aquila and Perseus sleeve-valve designs. The 26.8 litre Perseus was first run in 1932. Installed in a Bristol Bulldog fighter, it was first shown in the 1934 Hendon Air Pageant.

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In 1936, Bristol offered a sleeve- valve Perseus and Mercury with exactly the same 580 horsepower rating. By 1939 however, the Bristol sales catalog shows both engines with the same bore (5 3/4") and stroke (6 1/2"), but at the same engine speed (2,650 rpm), the sleeve-valve Perseus rating is up to 830 hp, while the Mercury was only 725 hp.

This view of the Rolls-Royce Eagle 22 sleeve-valve The Vildebeest Mark IV, a torpedo drive mechanism shows how sleeves of two cylinders are driven for a double-throw crank that bomber, was the first sleeve-valve provides both a vertical and rotary motion to the equipped plane in sleeves. The triangular openings are the intake and 1937. exhaust ports.

Quoting from the sales catalog, "The principal advantage of the sleeve-valve is valve maintenance is entirely eliminated, with generally less exhaust noise and fire risk due to lower exhaust temperatures, these are further characteristics of appeal to the military."

Both the Aquila and Perseus were nine cylinder, single bank sleeve-valve engines. The Aquila at 365 hp was a small engine by military standards at only 15.6 litres. It powered an experimental Vickers Venom at the 1936 Society of British Aircraft Constructor Air Show at Farnborough, but the Aquila never went into mass production. Luckily, its cylinder barrel design was just the right size for building the 14 cylinder, 25.4 litre, twin row 1,000 hp Taurus engine, for the Fairey Albacore torpedo bomber and the Bristol Beaufort bomber in 1939, just before the war.

A Bristol bomber was the first Allied aircraft to raid Germany four days after World War II began in September 1939. Also a first, a dive- bomber, powered by a Perseus, was the first British plane to claim a victory in World War II, having shot down a Dornier bomber. The Perseus powered the , a British carrier plane (the Roc was a legendary bird) .In the ROC also meant Rise Off Carrier. The successful Perseus engine

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was also used in the Mark III army liaison plane. During its long life, the Perseus went from 580 to over 1,000 hp.

With the success of the Taurus engine, using Aquila cylinders, Bristol tried the idea again with the Perseus cylinder barrels to develop the now famous Hercules, a 14 cylinder, 38.7 litre, two bank engine which first appeared in 1940 at 1,375 hp. In 1942 this was upped to 1,650 hp. The Hercules saw service in the Armstrong Whitworth Albermarle, Fairey Albacore, Sterling, , Bristol Beaufort bomber and Mark IV flying boat; the only remaining airworthy example of the Sunderland is at the Fantasy of Flight Collection near Lakeland, Florida.

Next, Bristol developed the "Hercules Power Egg", an interchangeable engine and cowling package, with common mounting points for the Sterling, Halifax, Wellington and Lancaster Mark II bombers. Nearly indestructible, the Hercules could run 3,000 hours between major overhauls with routine maintenance. By wars end, Hercules power was up to 1,800 hp.

The Lancaster was a four-engine variation of the Avro originally designed to use two 24-cylinder Rolls-Royce Vulture engines. These engines were one of Rolls Royce's few dismal failures and the design was scrapped in 1940. The Manchester was redesigned with a new wing for four engines and renamed the Lancaster. Most Lancasters were Rolls-Royce Merlin powered, but the Lancaster II had sleeve-valve engines.

A little known fact is the Lancaster, loaded with 22,000 pounds of bombs, could fly faster than an empty B-17 Flying Fortress. Also, with a single 11 ton Block- Buster bomb, the Lancaster had a greater bomb-load capacity than the Boeing B-29 Super Fortress. Many military historians believe the Lancaster was the best four-engined bomber used in Europe.

Bristol’s last sleeve-valve engine achievement was the Centaurus, a 2,500 hp, 53.6 litre, 18-cylinder two-row engine, yet another reconfiguration of the Perseus cylinder design. Replacing the Vulture engine, the Centaurus, whose design began in 1938, was fitted to the remaining that had not been converted to Lancasters and near the end of the war, the Centaurus was also used on the Warwick bomber (an improved Wellington) and Bristol Buckingham transport. The Wellington and Warwick were unique aircraft designed by Dr. Barnes WaIlis using geodesic basket weave) construction which could take heavy punishment. Dr. Wallis is better remembered for his design of the special

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rotating mine bombs used by the ’s "Dam Busters" to blow the dams along the Ruhr Valley in 1943.

Britain’s last piston engined fighter, the 2 (1944/5) used the Bristol Centaurus in two prototypes for testing, but in mass production was fitted with a much more powerful sleeve-valve engine made by Napier.

Napier of World War 1 fame, had little engine success between the wars. When WW II broke out in 1939, Napier were developing a very large engine called the Sabre. Using some of Bristol’s ideas, Napier had, before the war, developed a 12-cylinder sleeve-valve opposed engine called the Dagger. This design was the basis of the 24-cylinder Napier "Sabre", an "H" type Liquid-cooled sleeve-valve engine with two stacked opposed 12-cylinder blocks.

The Sabre engine began service at 2,300 hp and was first intended to replace the ill-fated Vulture engines in the Manchester. However, for some unrecorded reason, British Material command directed the powerful Sabre into the production for the Hawker Tempest fighter and , a torpedo bomber that replaced the obsolete bi-wing Fairy Swordfish affectionately known as the "String Bag" (because of all the wire bracing between the wings). Blackburn built 227 Firebrands using the Sabre engine. Near the wars end, improved Sabres, rated at 3,000 hp, were fitted to the , which, along with the Tempest, were fast enough to catch the German V-1 Buzz Bombs.

Why British Material Command decided to switch the Sabre from the Manchester is a mystery, but one must understand this powerful engine was in great demand and under severe supply constraints. Being more suited to the power requirement of a heavy single engine plane, the Sabre was used where best needed. The Sabre was Hawker's engine of choice and used it to produce 3,270 Typhoons and 1,418 Tempests. Eventually, the Centaurus (with comparable power) ended up in the Manchester.

The Sabre was a huge engine with a cylinder bore of 6 1/2 . At take-off or in combat, the could be pushed up to 3,850 rpm (with a 5 limit), compared to 3,000 rpm for Rolls Royce Merlin. The Typhoon propeller was an enormous 11-, four blade Rotol. Through 4.8 to 1 reduction gearing, top rpm was dropped down to a propeller speed of about 800 rpm. on take-off was so strong, full rudder was needed to keep a straight line. True to sleeve- valve lore, the Sabre engine used quite a bit of oil. At start-up, it had to be revved up over 2,000 rpm to clear the engine before take-off.

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Like all new engines, the Sabre had teething problems. By stages, it was developed into one of the most reliable piston engines ever made. Mike Bassano of Devon, a Typhoon pilot in the Middle East, who flew many hundreds of hours behind a Sabre sleeve-valve engine, said,: "Even after so long ago, I still look on this engine with awe. In 18 months, we and a sister squadron only had one engine failure, and this came about when a fitter failed to replace the cap on the header , leading to a total loss of coolant." Going on, he said, "Above all, the Sabre was a man-sized engine, driving a man-sized aeroplane. To us, Spitfires were toys, with no room to move in their tiny cockpits!"

All Bristol sleeve-valve engines were air-cooled. While they were the most successful, there were other sleeve-valve efforts by famous engine makers. As we will see later, Rolls-Royce, virtually unknown in sleeve-valve engine development, were the ones to add the final touch.

Meanwhile, a strange paradox occurred at almost the same time, on both sides of the Atlantic. In American, Pratt & Whitney, arguably the all-time champion of big air-cooled piston engines, in the late 30’s and early 40’s, began development of two different 24-cylinder sleeve-valve liquid-cooled engines. In England, Rolls- Royce, perhaps the liquid-cooled poppet valve engine king, developed four different sleeve-valve engines. Even more unusual for Rolls-Royce, two of these designs were air-cooled.

The Pratt & Whitney (P&W) X-1800 (2,000 hp) and larger H-3130 (2,650 hp) were inline liquid-cooled, sleeve-valve engines with plenty of room for development to much higher horsepower ratings. These were unique for in-line liquid-cooled engines as they had separate cylinder barrels. No doubt this was because P&W manufacturing equipment was geared for the individual cylinders used to make their air-cooled radial engines.

P&W's sleeve-valve involvement came about as a result of the friendship between George Mead, P&W Chief Engineer, and Sir Roy Fedden, head of Bristol. Political and military intervention with the US entering the war in December 1941, gave P&W little alternative but to concentrate on improving the R-4360 Wasp Major, instead of starting in a new direction by building the sleeve- valve H-3130.

Turning time back to November 14, 1934, in England, we would see the first drawing completed by Harry Sutcliffe on the Rolls-Royce DC (Direct Cooling)

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engine, called the "Exe" a 24-cylinder inline sleeve-valve engine. Unique for Rolls-Royce, not just because of the sleeve-valve design, but also as it was to be air-cooled. The Rolls-Royce "Exe" had a relatively small frontal area. It used pressurized air-cooling, similar to that of the Franklin and 1923 Copper-cooled Chevrolet or the Corvair of the 60’s with a blower and ducts to distribute the rooting air. "Exe" was an apt name for an X shaped motor of 24 cylinders (four rows of six around a single crank).

This engine was first run in 1936. In April 1938, the Exe was installed in a Fairy Battle bomber (K9222) at Hucknall, but did not fly until November 30, 1938. Shepherd, Chief Test Pilot for Rolls, did a lot of test flying with the "Battle-Exe" and was very enthusiastic about it.

It started easily, warmed up more quickly that a liquid-cooled engine and not having valve clatter, was unusually quiet. Unfortunately, in 1939, with war clouds over Europe, the Exe development was shelved to devote more engineering time to improving the Merlin.

The liquid-cooled poppet-valve Rolls Royce Merlin was an upgrade of the 1920’s designed Kestrel, which was the basis of the Schneider Trophy winning engines used to power the S-4, S-5 and S-6 planes designed by R.J. Mitchell, the designer of the Spitfire. Eventually, the Griffon engine variant of the Merlin topped 3,000 hp to become the last big production poppet-valve engine made by Rolls-Royce.

Lessons learned by the short test period of the Exe were not lost on A.J. Rowledge, Chief Designer at Rolls. The simplicity of the sleeve-valve mechanism, the economy of operation, the ease of maintenance, the quiet running and the engine did not have the expensive magneto ignition.

Comparisons between the Rolls-Royce Merlin and Exe: Bore: Merlin - 5.4"; Exe - 4.25". Stroke: Merlin - 6.0"; Exe 4.0". Displacement: Merlin - 27 litres; Exe - 22 litres. Compression: Merlin 6 to 1; Exe 7 to 1. Horsepower: Merlin - 1,100; Exe - 1,175. Max RPM: Merlin - 3,000; Exe - 4,000.

Since the Exe was a much more efficient engine, why was it shelved in favor of the Merlin? Rolls-Royce was already tooled-up for quantity production of the Merlin and the impending war emergency favored improving a known proven design over an untried new one.

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Later, at the darkest hour of the war, after the entry of Japan, it was realized the war could go on for some time. Given the longer distances and higher payloads, there was a call for more powerful engines. A revamped Exe (called the Exe 45) was begun in late 1942 and the first test engine (renamed the Pennine) was delivered in December 1944.

The Pennine represented the culmination of Rolls-Royce experience over thirty years of building aircraft engines. It's specifications were impressive, 2,800 hp at 3,500 rpm from 45 litres. Triple the power of the Merlin, at just twice the displacement and being an air-cooled sleeve-valve engine it was much lighter than the liquid-cooled Merlin.

As Rolls started work on the Pennine, they began development on a liquid- cooled sleeve-valve engine that eventually was to become the "all-time" power champion of 4-stroke piston engines.

The "Exe" offspring, called the Rolls-Royce Eagle II (Mark 22) was very much like the Sabre, a 24-cylinder, "H" type configuration, but rated at 3,600 hp. It was two 12-cylinder horizontally opposed boxer type engines placed on top of each other, geared to a single propeller shaft. The sleeve-drive was done with worm shafts, on both sides of the engine.

The Eagle II was dropped for two reasons, the end of the war was near and gas- turbine engines were already a fact of life, with much higher power possibilities than any piston engine. The Eagle II was to power the Westland Wyvern, a carrier based fighter with distinctive contra rotating propellers. Delays in working out problems in the engine and airframe resulted in the production version being fitted with a turbo-prop engine.

Engineers had designed capabilities into the new Eagle II that would have taken up to 6,000 hp, but the introduction of the jet engine put an end for all time to the revival of the "Sleeve-Valve Champion."

Finally, there was a fourth Rolls-Royce liquid cooled sleeve-valve engine under development, which began in 1937, when Rolls engineers became interested in the virtues of two-stroke engines.

Little is publicly known about the Rolls Royce "Crecy", a 12-cylinder 90-degree, V type, fuel-injected engine, first run in mid-1941.

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Crecy development can be traced to a December 1935 meeting where the idea of a "sprint" engine for home defense aircraft came to light. In this application, fuel consumption and long range did not have to enter into design consideration.

In February 1936, Ricardo wrote a proposal for a High Power, Two- Cycle Special Purpose supercharged engine meeting the criteria discussed The Crecy 2 cycle sleeve-valve mechanism is much simpler with just a single cam to move the in the 1935 meeting. High output and sleeves up and down. In reality, the ball socket small frontal area were prime design attaching to the sleeve is slightly off center, factors. The proposed engine would which imparts an elliptical motion to the sleeve so the sleeve never stops moving at either the be single-sleeve, gasoline fuelled top or bottom of its stroke. The small piston over with a 7 to 1 compression ratio (then the cam ensures the cam will not try to turn with very high for a supercharged engine.) the crank driving it.

Bristol, Napier and Rolls-Royce were asked to bid on a design specification. Only Rolls agreed, but a contract was not issued until July 1939. The two-stroke, sleeve-valve fitted a notch between older 4-stroke engines and the new gas turbine, which by this time was under full development. The 1942 prototype had surprisingly low fuel consumption at the highest power output. A very large problem was the development of a reliable system. The Acton Company in England built German Bosch fuel injection systems under license, but because of the war, they were cut-off from the engineering development people in Germany. Eventually, a captured Focke Wolf 190 yielded a fuel injection system that was adaptable to the Crecy.

In December of 1945, after eight years of development, work on the Crecy was terminated. At that time the Crecy was capable of double the horsepower of conventional 4-stroke designs of the same displacement. Rolls was delivering operational gas turbine engines and had many others on the drawing board which were more reliable and needed less maintenance than any piston engine.

Only six Crecy engines were built, all with even serial numbers (2, 4, 6, 8, 10 and 12). This has led to confusion as to the number made. Crecy engine #10, achieved the highest test horsepower in December 1944, putting out the

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equivalent of 5,000 brake horsepower. After running 6,000 hours, the engine was torn-down and all parts were still within design tolerances.

Being a two-cycle, at 3,000 rpm there were 36,000 exhaust impulses per minute, which provided plenty of extra horsepower to spin the exhaust driven turbine . Just a litre smaller in displacement than the Merlin, the Crecy put out 50 percent more horsepower using less fuel with an unheard of projected engine life of 5,000 hours. It also had an operational ceiling of over 30,000 feet, much higher than either the Merlin or Griffon and being fuel injected, would not have had the tight turn restrictions imposed on the carbureted Merlin.

RW Corbitt, who worked on the first Exe engine between 1936 and 1938, was assigned the task of developing the Crecy supercharger. It is his contention that the two cycle sleeve-valve. Crecy was the finest piston engine ever made by anyone.

After the war, Bristol's sleeve-valve engines were still very much alive. Bristol developed the huge Brabazon airliner weighing over 300,000 pounds, three times bigger than any wartime bomber. It used eight Centaurus 20 sleeve-valve engines, coupled together in pairs, driving four huge contra rotating three blade propellers.

A number of multi-engine aircraft like the Bristol Brigand, Airspeed Ambassador and BEA Elizabethan, developed after the war used Centaurus 661 engines, which achieved the same 3,000-hour overhaul interval, granted to the wartime Hercules engines. To put 3,000 hours in perspective, that represents over 350 trips across the Atlantic.

The Centaurus was an incredibly long-lived engine, being built for nearly 30 years, from 1938 until the mid-60’s. There were many different models ending with the Models 1973 and 1975, which were used, in the , a huge military transport aircraft. The armored Beverley could carry a large tank with its crew or two cars and was larger than the first Lockheed C-130 Hercules transports.

Using Centaurus sleeve-valve engines, Britain’s version of a flying boxcar, had an "all-up" weight of 142,000 pounds and was the mainstay of the RAF transport fleet until replaced by later versions of the C-130 Hercules in 1967.

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The final British development of piston-powered fighters was the an incredible carrier-based fighter plane developed too late for use in the war. It was the prime fighter used by the Royal Navy and by some of the Arab countries as a ground based interceptor right up to the sixties.

Because of its beauty, design and strength the Sea Fury has become a collector’s dream and is an especially prized aircraft on the unlimited racing circuit like those held at Reno and Cleveland Air Races. The Centaurus powered Fury has competed with and, often won, against the top late model modified air- racers the crowds love to see.

Now going on for sixty years, the whine of Centaurus sleeve-valve engines can still be heard at some of the restored war birds meets like the Experimental Aircraft Association meets at Oshkosh, Wisconsin or Lakeland, Florida, as well as at the unlimited air races. A few Napier Sabre engines still power vintage unlimited displacement powerboats for crowds to see.

Old Autos Paper Monday, March 5, 2001

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