Sleeve Valve Aircraft Engines 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 engine, 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 Napier Sabre 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 turbine fan blades that powered many of the British World right behind the propeller 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 force 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 cars 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 miles from London, 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 work 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”. Page 1 of 13 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 Air Ministry gave Frank Whittle to develop and improve the first jet engine. Also, in the summer of 1986 we visited the London Science and Industry Museum, the Fleet Air Arm 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 Florida flea market. Last, but certainly not least, was finding a friend in the Willys-Overland Knight Club, Chris Lansdell in England, 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 aircraft engine 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, Harry Ricardo, a famous English engine designer, had Page 2 of 13 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 cylinder head 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 compression ratio 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 power the first tanks in World War I. 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 Piston 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 Second 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 Roy Fedden 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. Page 3 of 13 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 car and motorcycles made in the 1920's by Barr & Stroud. Prophetically, Henry Royce 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 combustion chamber, 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 bore, stroke 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 diesel fuel, the other, gasoline. 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 horsepower 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. Page 4 of 13 In 1936, Bristol offered a sleeve- valve Perseus and poppet valve 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.