Merlin

The Power Behind the Spitfire, Mosquito and Lancaster

Graham Hoyland

• Editore: William Collins
• Anno: 2020
• ISBN:
  9780008359287
• Argomento: History
• Categoria: Modern British History

The most iconic planes of WWII, the Supermarine Spitfire, Hawker Hurricane, DeHavilland Mosquito and the Avro Lancaster, were all powered by one engine, the Rolls-Royce Merlin. The story of the Merlin is one of British ingenuity at its height, of artistry and problem-solving that resulted in a war-winning design.

Chapter One

Non est ad astra mollis e terris via –

There is no easy way from the earth to the stars

The Langley ‘Aerodrome’ in flight – just. (Hulton Archive/Getty Images)

As a child Albert Einstein was given a Russian toy steam train by a favourite uncle. Three years after winning the Nobel Prize for Physics he wrote to Caesar Koch to thank him once again. Einstein, the author of the theory of relativity, maintained that it was the steam engine that initiated his interest in science.

Steam engines are easy to understand and easy to love, as Thomas the Tank Engine shows. Fuel, either alcohol in the case of Einstein’s toy or coal in a full-sized engine, is burned outside a water-filled boiler. This is external combustion. Steam is generated and tries to expand a thousandfold in volume. It passes through pipes and valves into a cylinder, where it pushes a piston down. The piston is connected by a rod to a crank which drives a wheel round, which drives the steam engine along. You can see the whole process going on, together with delightful smells of fuel, hot oil and smoke and the vision of an animate machine with long metal legs and pumping lungs.

The brilliance of the invention of the internal combustion piston engine was that it dispensed with a man shovelling coal, the filthy firebox, the water, steam and heavy boiler, and instead burned petroleum fuel inside the cylinder. Everything else – pistons, connecting rods, crankshafts and flywheels – remained recognisably related to steam engines. Sadly though, these engines are hard to appreciate in the same way as steam. If you lift the engine cover of a car all you can see is an immobile cylinder block made of aluminium or cast iron, and all you can hear is the whirring and clicking of innumerable parts: valves, camshafts, pistons and crankshafts. It’s all going on inside. Drive or fly behind a piston engine, though, and listen to the operatic howl of many cylinders, and your soul may begin to be stirred by something beyond words.

The story of the piston aero engine is surely the most romantic story in engineering history. Heavier-than-air machines were dreamed of but literally could not take off until light and powerful internal combustion engines were built. Steam engines were simply too heavy.

Mankind had always dreamed of flight. And made up stories about flight. According to the scholar Ben Sherira, flying carpets were issued to readers in the ancient library of Alexandria (c. 283 BCE) in exchange for their slippers. Reclined on their carpet, students were able to reach the highest shelves and hovered near the ceiling, engrossed in their studies. Later, in the Baopuzi text (320 CE), the Chinese master Ge Hong described the principles of ascending into the vast inane: ‘some have made flying cars with wood from the inner part of a jujube tree, using ox or leather straps fastened to blades so as to set the machine in motion.’1 He seems to be describing a Jin dynasty helicopter.

In around 559 the Emperor Wenxuan of Northern Qi decided to conduct experiments with flight. Volunteers failed to come forward, so prisoners were forced to leap off a tower attached to man-carrying kites. There was only one survivor, Yuan Huangtou of Ye, who successfully managed to glide over the city walls and land safely. He was later executed.2 In the eleventh century Eilmer of Malmesbury, an English Benedictine monk, attempted to emulate Daedalus of the Greek myth by attaching wings and leaping off a hill near the abbey. He flew for a furlong (200 metres), but crashed more like Icarus, breaking both legs, which rendered him lame for life. ‘I lacked a tail,’ he remarked ruefully later, showing that at least he had a grasp of aeronautics.3

These stories make Leonardo da Vinci’s interest in flight seem rather late in the day. In 1485 he drew a man-powered rotor that could not have flown, as the body of the machine would have rotated in the opposite direction to the rotor. He drew other man-powered flying machines with flapping wings which are unlikely to have got very far. However, he also designed a hang glider which could have flown, and indeed flying examples have been built. But what Leonardo needed was more power, and he realised this. He didn’t know that what he really needed was a petrol engine, and he would probably have swapped a couple of dozen sketches for a really good lawnmower.

Balloons were the first successful aircraft, and they relied on weighing less than the air they displaced, but they were large, delicate and slow, blown across the sky like tender elephants. Balloonists wanted to progress in their own choice of direction instead of that of the wind, so various methods of propulsion were tried. Human-powered flapping wings were employed in 1784 by the balloonist Jean-Pierre Blanchard who, helped by the wind, managed to cross the English Channel, flapping manfully and steering with a bird-like tail. In 1852 another Frenchman, Henri Giffard, combined a highly explosive hydrogen balloon with a disturbingly flammable steam engine, which proved able to perform limited manoeuvres but was not powerful enough to fly against the wind. This was clearly not the way to go.

Countless attempts were made to build a heavier-than-air machine, but the mistake the inventors usually made was to try to copy the flapping motion of birds’ wings. One honourable exception was the Frenchman Alphonse Pénaud. He pioneered the use of rubber-band-powered model aircraft with fixed wings and a propeller rather like the children’s toys available today. His model aeroplane of 1871, which he called the Planophore, was the first aerodynamically stable flying model. Poor Pénaud tried to attract interest and funds for a full-sized machine, but failed. He committed suicide in despair, aged just 30.

The immortal Robert Hooke, inventor of the sash window and theorist of springs, realised that manpower was insufficient and built a spring-powered winged ornithopter. The flapping wings theme was pursued by the inventive Frenchman Gustave Trouvé, whose model of 1890 flew for 80 metres in a demonstration for the French Academy of Sciences. His wings were flapped by gunpowder in cartridges exploding in sequence. We can only be grateful that his style of flight did not catch on. Someone had to apply some proper science.

At last someone did exactly that: the Yorkshireman Sir George Cayley (1773–1857).4 He observed the soaring flight of seagulls and realised that it was the angle and shape of the wings that produced lift. Flapping produced propulsion, not lift. This was a moment of epiphany, similar to the inspirational moment that produced the wheel axle, the screw-thread or the lever.

Cayley then described four paired forces acting upon a flying machine: weight and lift, thrust and drag. He had a silver disc engraved with a design for an aircraft, with the four forces engraved on the reverse side of it. He decided that fixed-wing flight was easier to achieve than trying to imitate the flapping wings of birds, and that cambered wings set at an angle to the wind would provide lift. He realised the importance of the dihedral angle: the upwards tilt of aircraft wings that provides stability. He also predicted that sustained flight would not be achieved until a lightweight source of power could be invented to provide thrust and lift. And he even attempted to invent a suitable internal combustion engine.

Cayley didn’t know that in 1806 two French brothers, Nicéphore and Claude Niépce, had made what was probably the world’s first internal combustion engine, which they called the Pyréolophore. Bizarrely, it was fuelled by lycopodium powder (dried spores of the lycopodium clubmoss plant) and coal dust. It worked rather like a toy steam pop-pop boat but would only operate in water. The brothers’ patent was signed by Emperor Napoleon Bonaparte, but the brothers failed to capitalise on their engine. Claude moved to Kew, London, to spend all the family fortune on trying to sell the Pyréolophore and descended into delirium, and his brother got on with inventing photography.

Cayley wrote a treatise entitled On Aerial Navigation and continued his experiments. In the pursuit of lightness for his aircraft he reinvented the wheel: wire-spoked wheels, which suspend the load from wires in tension rather than using heavy wooden spokes in compression. His wheels are still in use today on bicycles. He realised that he lacked a suitable source of power and tried to build internal combustion engines running on gunpowder or hot air, but the technology still eluded him.

Finally, at the age of 75, Sir George and his helpers at Wydale Hall flew a full-sized glider across Brompton Dale in 1853. According to one author the pilot was his ten-year-old grandson George. So a boy could well have been the first person to be carried by a modern fixed-wing heavier-than-air flying machine.

Sir George Cayley was one of the most important pioneers of flight, and was the first to take a truly scientific approach to the study of aeronautics. He really deserves his title of ‘father of aeronautics’. If he’d only had a suitable lightweight engine the world’s first pilot-controlled powered flight could have taken place over the moors of North Yorkshire in the middle of the nineteenth century.

Then in 1876, after the efforts of dozens of engineers and scientists, a viable internal combustion piston engine finally arrived. This engine had been developed by a Belgian, Jean Joseph Étienne Lenoir, but his machine was heavy and inefficient, as it followed the old steam engines in its design. Running on lighting gas, it produced only 2 horsepower for 18 litres of cylinder capacity. This design was then considerably improved by the German Nikolaus Otto, who perfected a way of compressing air and fuel and igniting it to provide power using four distinct strokes of the piston. This was the inventive step that made powered flight possible.

The way an Otto-cycle four-stroke petrol engine works is the same in a Merlin or a modern car engine (my apologies to those readers who already know this). A piston, which looks like a soup can with one end removed, slides up and down a tube or cylinder. The piston is connected to a rod called, unsurprisingly, a connecting rod. This is attached to a crankshaft so that the piston sliding up and down pushes the crankshaft around rather as a cyclist’s leg pushes a pedal crank around. The crankshaft can be connected to car wheels or to an airscrew propeller.

Above the piston is where the magic of internal combustion takes place. The top of the cylinder is closed but is provided with an inlet ‘poppet’ valve to let in a mixture of air and fuel as the piston descends on the first, or inlet, stroke. This valve then closes when the piston reaches the bottom and starts up again on the second, or compression stroke. The gaseous mixture of air and fuel is now squeezed tightly and is highly explosive. At the top of the compression stroke a sparking plug ignites the mixture and it duly explodes. The piston is now pushed down on its third stroke, the power stroke. On its way back up an exhaust valve opens, and the hot gas is forced out by the ascending piston on the fourth, exhaust, stroke.* Just think ‘suck, squeeze, bang, blow’.

Otto’s inventive step was to manage these four distinct phases inside a cylinder with a piston travelling up and down, and he did this by arranging the valves to open at specific times during two revolutions of the crankshaft, or four strokes of the piston. This was done by using a camshaft, which looks something like a knobbly stick, to push the valves open with oval-shaped lobes. By making the camshaft rotate only once for every two rotations of the crankshaft the valves open at the correct times.

Now speed the whole engine up to make more power. A modern 1-litre car engine can run its crankshaft at 6,000 revolutions per minute (rpm), which means that it rotates 100 times in a second. So a piston is going down, stopping, reversing direction and going up again 200 times a second, and the four Otto cycles are happening in milliseconds. A typical car piston weighs around 0.3 kilograms at rest, but when changing direction at 6,000 rpm it would effectively ‘weigh’ 900 kilograms! That’s as much as a car. No wonder pistons are made of immensely strong and light aluminium alloy. A 27-litre Rolls-Royce Merlin revolves at only 3,000 rpm, but even then the load on the crankshaft main bearings is around nine tonnes – the weight of a bus.

Virtually all petrol and diesel engines share the same kinds of pistons, cylinders and valves. There may be as many as 36 cylinders in various configurations, and the Merlin and most modern cars have two inlet valves and two exhaust valves per cylinder. A typical car engine will have four cylinders in a row above the crankshaft, but a rotary aero engine has the cylinders and propeller whirling around a stationary crankshaft. A radial aero engine has stationary cylinders arranged in a star shape, with a rotating crankshaft driving the propeller. And the Rolls-Royce Merlin had 12 cylinders arranged in two rows of six sharing one crankshaft: a V12 configuration. There are advantages and disadvantages for all these formats.

A word about horsepower. This is a much-abused measure of the power of an engine, originally invented by the Scottish engineer James Watt in the late eighteenth century to compare the power of mine horses with his steam engines. So does one horse produce one horsepower? Well, no. The maximum power of a horse has been measured at 14.9 horsepower for a few seconds, and as for humans, the Jamaican sprinter Usain Bolt produced 3.5 horsepower during his 100-metre world record in 2009. How so?

The point is that you would need to keep around 15 horses to provide a continual 1 horsepower: after all, the poor creatures need to be rested and fed. Watt’s estimate was based on mine horses working a four-hour shift.

A story goes that the measurement was created by Watt when one of his customers, a rascally brewer, demanded a steam engine that could match his horse. He chose the strongest horse he could find and drove it to exhaustion. Watt, well aware of what was going on, accepted the brewer’s challenge and built an engine that exceeded the figure achieved by the poor horse. When calculating the measurement Watt allowed for the fact that a single horse cannot work day and night and adjusted accordingly.

The accepted measure of one mechanical horsepower is the ability to lift 550 pounds one foot in one second, or 745.7 Watts.† You can calculate horsepower by multiplying the torque (or twisting force) by revolutions (the distance travelled) and then dividing by 5,252 (the time – don’t ask).

At least the suffering of countless draught horses was alleviated by engines. But horsepower as a measure has attracted so many qualifications and fudges that it has to be used with caution.

Nikolaus Otto and his factory manager Gottlieb Daimler disagreed about what to do next with his four-stroke invention. Otto wasn’t really interested in transport and wanted his engine to replace large stationary steam engines. Daimler wanted to make small engines suitable for bicycles or carriages. As a result, Daimler left Otto and set about evading his patents so that he could avoid paying royalties. By a subterfuge involving the ‘previous art’ of a patent granted in 1862, Daimler overturned Otto’s patent and went on to build an empire. In 1885 he and Wilhelm Maybach built a small single-cylindered half-horsepower engine and put it in a bicycle. So the first person in the world to ride an Otto-cycle motorised vehicle was Adolf, Daimler’s 14-year-old son.

We now have to uncover an extraordinary attempt to unfairly claim the first powered flight by that most upright and sober of American institutions: the Smithsonian. Samuel Langley was the founder of the Smithsonian Astrophysical Observatory, but he then took up an interest in aviation, building rubber-band-powered model aircraft based on Pénaud’s designs. Colleagues noticed that his models did not seem to stay in the air very long. Then he managed to make steam-engined flying models. Around this time Rudyard Kipling was visiting his friend (and soon to be president) Teddy Roosevelt in Washington. He encountered the professor with the passion for toy aircraft:

Through Roosevelt I met Professor Langley of the Smithsonian, an old man who had designed a model aeroplane driven – for petrol had not yet arrived – by a miniature flash-boiler engine, a marvel of delicate craftsmanship. It flew on trial over two hundred yards, and drowned itself in the waters of the Potomac, which was cause o...

Indice dei contenuti

• Title Page
• Copyright
• Dedication
• Contents
• Introduction
• Chapter One
• Chapter Two
• Chapter Three
• Chapter Four
• Chapter Five
• Chapter Six
• Chapter Seven
• Chapter Eight
• Chapter Nine
• Chapter Ten
• Chapter Eleven
• Chapter Twelve
• Chapter Thirteen
• Chapter Fourteen
• Chapter Fifteen
• Chapter Sixteen
• Chapter Seventeen
• Chapter Eighteen
• Chapter Nineteen
• Epilogue
• In Memoriam
• Acknowledgements
• Notes
• Bibliography
• Index
• Also by Graham Hoyland
• About the Author
• About the Publisher