The Napier Sabre - the apotheosis of the high-performance piston engine
A personal essay written from the heart, before memories of this brilliant engine fade into history.
Written by Mike Le Brocq in Feb 2001
I can well remember over thirty years ago, whilst I was at university, reading what was then an expensive book on the history of the motorcycle about the Brough Superior Golden Dream, George Brough's pinnacle of motorcycle development, sadly cut short by the onset of the Second World War, and only exhibited once at the 1938 Motorcycle show. What so impressed me was the perfect balance of the engine, quite unique, I believe, due to the design of two horizontally-opposed cylinders (à la BMW) being placed on top of two more horizontally-opposed cylinders, with the two resulting crankshafts being geared. Such an engine would suffer from none of the vibrations of my old vertical twin Triumph, nor the uneven firing intervals of a 45° Harley-Davidson, and should be able to run at considerably higher engine speed, with the consequence of much greater power delivery. Sadly, the Second World War put paid to this perfect design, and the austerity period afterwards secured its demise for ever.
Some twenty-seven years later, I purchased a thin, but highly informative book by John Sweetman entitled High Speed Flight - it is still available in our local library - much of the information contained therein was not new to me, having been an aircraft enthusiast since the age of five or so - congenital myopia put paid to a prospective flying career at the age of seven, but the enthusiasm has never waned. Amongst other things, this book kindled a new interest, with the mention of the most powerful / fastest piston-engined aircraft of the Second World War. The Vickers-Supermarine Spitfire (later variants), de Havilland Mosquito, North American Mustang (particularly P-51 H), Kurt Tank's Ta 152 (the final development of the Focke-Wulf 190), and (not mentioned) the quirky Dornier Do 335 Pfeil (Arrow) all took their places in this superlative breed, but the remaining aircraft mentioned, which has been largely forgotten since, was, quite possibly, the ultimate king of this breed; the final wartime offering from Sidney Camm (of Hawker Hart, Hurricane, and finally in the very early sixties the Hawker P 1127, the granddaddy of the Harrier), the Hawker Tempest.
The successor to the Hurricane was on the drawing board before the start of the war, in mid-1939, and was to replace the Hurricane with an all-metal monocoque construction, with superlative fire-power and speed. Two variants were designed; the Tornado (where have I heard of that name since!), powered by a Rolls-Royce Vulture engine (basically two Peregrine engines sharing one crankshaft, the one mounted upside down of the other), and the Typhoon (another name now becoming more familiar these days), powered by an engine of considerable complexity, manufactured by a smaller rival of Rolls-Royce, the Napier Sabre. Designed by Major Frank Halford, its pedigree consisted of the Lion, a W-formation engine used for many speed attempts after the First World War, with considerable success, including the Schneider Trophy victory in R J Mitchell's Sea Lion of 1923, and subsequently in its final development stage in the Supermarine S-5, the 1927 winner. This fine engine was subsequently followed by the Rapier, a much smaller engine, which consisted of sixteen cylinders in 'H' formation, and used in, amongst others, Major Robert Mayo's flying-boat 'Mercury', built by Short Brothers (of Sunderland fame) in 1938, and which until very recently held the long-distance record for seaplane flight of 6,907 miles from England to the Orange River in Natal; it achieved this incredible distance by being air-launched from 'Maia', a much larger C-class variant, specially adapted to carry Mercury aloft with fuel and passengers.
During the late Thirties, aero engine designers were constantly in search of greater power, in order to fly at greater speeds, or to travel longer distances (taking off with very heavy fuel loads in order to be able to achieve transcontinental ranges). The only aircraft that were capable of this, immediately prior to the war, were the large flying boats produced by the Glenn L Martin Corporation - the 'Mars', and by Walter Boeing's company - the Boeing 314 Clipper - but both needed long water runways in order to be able to achieve flight; their engines produced just over 1,000 h.p. at sea level. The engine that was required by the aircraft designers was to be capable of producing at least 1 h.p. per cubic inch of engine displacement, and it became known as the 'Hyper' engine. Various engine manufacturers were looking at this requirement; for example the Pratt & Whitney Twin Wasp, the R-1820, developing some 1,200 h.p. in the Douglas DC-3 would be required to produce at least fifty percent more power, or 1,820 h.p. Radical engine development was therefore needed; Pratt & Whitney and Lycoming were two manufacturers who looked earnestly at the requirement; ultimately the former manufacturer would go the American route of 'more cubes are best' and would produce the ultimate 72 litre 28 cylinder 4-row radial which they named the Wasp Major, the R-4360, initially developing some 3,000 h.p. and finally 3,500 h.p. in standard form; powering such giants as the Boeing B-36 Peacemaker, the final variant of the Boeing B-29, the B-50, one of which, Lucky Lady, was the first aircraft to circumnavigate the world in 1950, the final pre-jet passenger carrier, the Boeing 377 Stratocruiser, with its two decks, and perhaps most famous of all, Howard Hughes' Spruce Goose, flown just once in November 1947, with eight of these monster engines - the sound of that take-off must have been something to behold! Incidentally, during my early youth, I remember lying in bed late at night, and hearing a very deep rumble, which vibrated the sash windows in our farmhouse; no other aircraft ever produced this sound, but in 1988 the mystery was solved when I viewed the 'Bombers' episode of the excellent video series 'Reach for the Skies' narrated by the late Anthony Quayle - the sound of the B-36 taking off brought the thirty-plus old memories back as if it was yesterday, with the realisation that these aircraft flying at 55,000 feet above us were probably carrying nuclear weapons, part of General Curtis LeMay's Strategic Air Command, so invaluable during those cold war years.
The plans to produce the 'Hyper' engine all fell by the wayside for one reason or another, with the exception of the Sabre. It is just as well that this engine came to fruition, firstly because D-Day might not have been the success that it became, and secondly, the V-1 flying bomb menace to southern England in the last year of the war would have had a very different effect on the morale of the civilian population, as I will endeavour to explain in due course.
Initially, the Sabre was type-tested at 2,200 h.p. in late 1938; bearing in mind that its engine displacement was just over 36 litres (or 2,238 cu.in.), it was already at the zenith of performance, no mean feat bearing in mind the complexity of the engine. Major Halford had taken a different route to many designers, equipping the Sabre with sleeve valves, rather than the much less-efficient poppet valves still in use in the motor industry today, thus removing at a stroke (pardon the pun!) many of the deficiencies of the poppet valve with the reciprocating mass, valve float and closure requiring spring assistance (the desmodromic engine used so successfully by the Italian motorcycle manufacturer Ducati had not yet been developed). The other factor contributing so greatly to the Sabre's success was its perfect balance, achieved by mounting two 12 cylinder horizontally-opposed engines (so-called Boxer configuration) together, gearing them to a common crankshaft producing perfect engine balance, both primary and secondary. These two master strokes gave the Sabre the ability to run to some 3,750 r.p.m. in normal combat trim, compared to the 2,800 r.p.m. achieved by the 'V' configuration engines such as the Merlin, Griffon, Daimler-Benz 601 and 603, which became its main competitors.
Even at that early stage, the anticipated performance encouraged the design of an ultimate speed aircraft, the Napier-Heston racer. This was a small, all-wood aircraft designed around the Sabre, and intended, on a standard production Sabre developing 2,400 h.p., to achieve a maximum speed in excess of 500 m.p.h. (800 k.p.h) - finally breaking Francesco Agello's 1934 record of 464.37 m.p.h. in the Macchi M-52, the unsuccessful competitor to the fimal Supermarine S-6B in the 1931 Schneider Trophy race (which itself went on to achieve 407.8 m.p.h. flown by P/O Boothman). Sadly, the first prototype, of two projected, stalled after taking off on its maiden flight; the crash destroyed what would almost certainly have been Great Britain's glory, leaving the field open for the Heinkel He 209 to break the M-52 record by a mere 10 m.p.h.
Mention should be made here of the competitor's engine, the Vulture. Generating some 1,800 h.p., it was not perhaps the success that it might have been, but perhaps in retrospect, an engine is usually designed to operate either the right(!) way up, à la Merlin for example, or inverted, such as the Daimler-Benz 600 family or the many successful engines produced by the de Havilland Company, ending up with the Gypsy Queens and twelve cylinder King installed in the Albatross airliner also produced at the onset of the war, but not both. Certainly we should all be grateful to Sir Henry for single-mindedly pursuing development of the PV-12 in 1933, which ultimately became the Merlin, else the Avro Lancaster would never have been the most successful heavy bomber of the war, because it started life as a twin-engined aircraft powered by a pair of Vultures. Fortunately for us the late Roy Chadwick was able to redesign the Manchester wing to take four Merlins, and ultimately to carry a greater bomb load than any other WW-II aircraft at 22,000 lb., or just under ten tons.
With the demise of the Tornado, due to the major problems encountered with the Vulture, the path was open for the Typhoon - the airframe had some nasty surprises for some pilots, particularly when the tailplane parted company with the fuselage, and the thick wing, designed to be able to carry four cannon internally, caused some compressibility problems, but the powerplant was not initially very reliable; demands made by the Sabre on the induction and cooling systems were never completely sorted, leading to occasional engine failures, but development for this engine was never given the priority that it deserved, partly due to the unofficial but weighty opinions of the Rolls-Royce Company that their engines were better; if imitation is the sincerest form of flattery, then it is worthy of note that the final piston engine produced by that company was a 36 litre, 24 cylinder horizontally-opposed sleeve-valve engine named the Eagle (the first Eagle powered the Vickers Vimy which was flown across the Atlantic in June 1919 by Sir John Alcock and Sir Arthur Whitten-Brown, landing in a bog in County Mayo in (Southern) Ireland, winning the Daily Mail £10,000 prize for the first Atlantic crossing in history).
The Sabre was always the prima donna of the wartime piston engine, as the Air Ministry never really appreciated the virtues of the superlative design - being more often than not guided by Rolls-Royce - but initially the Typhoon, designed as a successor to the Hurricane, was unable to perform successfully above 12,500 ft.; this however was turned into a virtue when its ability to deliver a heavy attack of bombs, rockets and cannon-fire at low level turned it into the world's first ground-attack fighter, and it became the most successful tank-busting platform before, during and after D-Day, saving many Allied lives by its ability to strike accurately at its targets, and able to achieve a maximum speed of 412 m.p.h.. Eventually the limitations of the thick wing, and to a lesser degree the tailplane, resulted in a redesign of the airframe, incorporating a Mustang-type so-called laminar-flow wing; the redesign was major enough to replace the name by the Tempest. This incidentally occurred during the latter half of 1943, and the new airframe went into production in early 1944, with basically the same Sabre engine as in the Typhoon some two and a half years earlier; however it was even in that guise successful enough to be described in the Daily Mail of 25th July 1944 as the world's fastest aeroplane, which apart from the new jets starting to emerge, it was - with the proviso that this was at low to medium altitude - 426 m.p.h. at sea level would see off any adversary.
When the V-1 (Fi-103) started being launched from the ramps in Northern France in the spring of 1944, it was fairly soon realised that the Tempest ,alone, could not only dive to catch the pilotless weapon, but could overhaul it in level flight - this resulted in a final tally of over 600 'kills' by the Tempest pilots, accounting for over one-third of all V-1's downed or destroyed before reaching their target. Who really knows what might have happened without the development of this superlative engine, and the two invaluable aircraft that it powered.
Right at the end of the war, the Sabre started to receive the recognition that it was so long overdue, with assistance from the Bristol Aeroplane Company (the masters of sleeve valve production, and ultimately the designers of the Sabre's replacement in the Tempest II, the Centaurus (53.6 litres, and less ultimate horsepower!)). Finally, improvements to the cooling and induction system resulted in the development of the Sabre VII, initially rated at 3,055 h.p., the most powerful piston engine produced in Great Britain, and at the time more powerful than the P & W Wasp Major, which was twice the displacement. This variant of the Sabre would have powered the Tempest VII, and might have produced the fastest piston-engined aircraft of all time; the Tempest prototype achieved 458 m.p.h. in 1943 on a standard 2,340 h.p. Sabre, but with low-drag cooling in the leading edge à la de Havilland Mosquito; I believe that over 500 m.p.h. would have been easily attainable, and perhaps as much as 520/525 m.p.h. Incidentally the Tempest, with its maximum dive speed of 535 m.p.h. IAS was the most successful Allied destroyer of the Me-262 twin-jet aircraft, and many of its pilots still sing the praises of an aircraft capable of diving at high subsonic speeds, but remaining in full control of the airframe, and indeed with a stable gun platform to boot - no wonder that the Me-262 pilots still had something to fear from a piston-engined aircraft!
The 50th anniversary of D-Day has now long since passed; I remember seeing B-17's flying over the landing beaches during that summer, but sadly neither of Sidney Camm's creations were represented there - or anywhere else for that matter; will the youngsters of today ever hear the unmistakable sound (whine) of the Sabre in full song, as did those who travelled over to France in June 1944, or those who lived in 'Doodlebug Alley' in the summer of 1944.
Let us earnestly hope that Nick Grace's dream of restoring a Sabre-engined Tempest will be realised by Kermit Weeks in Kissimmee in the next few years - but I suppose EJ693 will be too valuable (and unique) to export over the pond for the 60th anniversary celebrations of D-Day in three years time, and also to commemorate the destruction of so many V-1's also in three year's time.
It is long, long overdue that this aircraft, and particularly this engine, should receive the reward and recognition that it has for so long been denied. I would particularly like to think that Roland ('Bee') Beamont, who was so instrumental in the development of the Tempest, will, once again be able to enjoy the unique sound in the flesh of the Napier Sabre, surely the world's greatest piston engine. Those who have even been fortunate enough to hear recordings of this engine will recognise it as probably the only true transition engine between piston and turbojet, with its continuous, unmodulated sound (whine) - what could have been had a larger version of (say) 50 litres displacement been built - but Sir Frank Whittle ultimately put paid to all of this, but we lost some of the greatest man-made sounds in history!
Mike Le Brocq