The Rolls-Royce Merlin Engine

Welcome to Air Space here at the Imperial War Museum Duxford. A regular conversation for the last eighty years, from anything from parliament to a pub, is what couldn't we have won the war without? Couldn't we have won the war without a Spitfire or a Hurricane? Could we have won the war without a Lancaster or a Mosquito or a Mustang? But one thing that surely has to go into that equation and that conversation is something that all those aeroplanes I've just said have in common. The Rolls-Royce Merlin Engine.

 A lot of people remember the Merlin Engine for the famous aeroplanes, the Spitfire, the Hurricane, the Mustang, the Lancaster. The Merlin was also used in aeroplanes like the Fairey Battle and the Boulton Paul Defiant. But in all its production life, over 50 different development types of the Merlin were produced; from the initial just over a thousand horsepower, to right at the end of the war and a beautiful aeroplane, the de Havilland Hornet, with a two-speed, two-stage integral supercharged Merlin engine, giving 2,050 horsepower each. Two of them.

Rolls-Royce made a lot of very successful aero engines. Some not so successful, like the Peregrine and the Vulture. And some more successful, like the Kestrel and the Merlin. Rolls-Royce developed the engine from 1933 from an engine called the PV12. Initially of about 900 to 990 horsepower on the bench, then in full production, once made reliable, in the Mk I Spitfire and the Hurricane with over 1100 horsepower. The Merlin engine is a small engine. I won't say it's the mini-8 series of the aviation world: it's 27 litres. For our friends across the pond, that's about 1650, just less, cubic inches. Against a Daimler-Benz 601 from Germany, 39 litres. And the BMW 801 series in the Focke-Wulf 190 at 42 litres. It's a very compact, small little engine. So with the help of the 100 octane fuel developed in the USA at the time, this little Merlin engine was fantastic for development.

What about the Merlin engine? Well that was marvellous. That was that was a wonderful piece of machinery. There's no doubt about it. It was the making of the Spitfire, and it was the making of the fact that Rolls-Royce went on producing more and more power out of the Merlin. That's what enabled the Spitfire to be developed to the extent that it was. That was a very happy partnership between Rolls-Royce and Supermarine.

As magnificent as the Rolls-Royce Merlin engine is, it did have a few flaws. Carburettor fed. As I've said in previous videos, a negative manoeuvre would result in the carburettor flooding and the engine missing and coughing. Not good in the middle of a dogfight. The header tank for the coolant was right at the front. Initially, the coolant was ethanol glycol, very flammable if it was hit by an incendiary round. Later on, diluted and pressured, not so much of a problem, but initially quite a worry.

There actually was a Spitfire that could perform in a negative G dive, possibly only one, though. The Germans got hold of one or two Spitfires and retrofitted it with the inverted Daimler-Benz engine. With its fuel injection system, that aeroplane was tested and was proved to be quite manoeuvrable.

Once a P-51, that became the Mustang, had been fitted with the Rolls-Royce Merlin – the Allison engine, like I've said before, a very good strong engine, but getting a little bit asthmatic at high level. Tested here at the Fighting Development Unit, the Mustang fitted with a Rolls-Royce Merlin engine became the world beating aeroplane it was.

Of course, in wartime, the production demands were very heavy. When the Mustang was developed with the Merlin engine, Rolls-Royce then gave Packard in the United States license to build the Merlin Engines and Packard themselves, using the American mass production technique, between 1942 and 1945 produced over 55,000 Merlin engines. Of course, in the wartime in the UK, British factories were being bombed most nights, so the collaboration was vital. In 1940, a contract was actually offered to Ford of America to build Merlin engines. Initially that was taken on, but controversially, in the end Henry Ford himself actually pulled the plug, not wanting to send or sell materials to any foreign power involved in a conflict. Despite this decision in 1940, by the end of the war, Ford in Trafford in Manchester were employing 17,000 people involved in making Merlin engines.

Now, Rolls-Royce never have been involved in mass production, but the motor company, of course, was brilliant at it. They were built in America and then flown over here. I understand that one of the first things that was done at the beginning of the war was that a complete set of Rolls-Royce Merlin engine drawings was flown to America, just in case anything did happen back here. But one difference between a Packard engine and a Derby engine we used to say was that the Packard engine was all polished up, and it had got chrome plated nuts and bolts on, whereas we were still struggling with plating.

Rolls Royce Merlin engines are among the power units for Spitfires, Hurricanes and Defiants. As there are no fewer than 80 types of British warplanes and 40 American types, the great variety of aircraft stores is easily understood.

By late 1940 to mid 1943, Merlin engines were powering some of the most magnificent aeroplanes of the Second World War. Without the supercharging as a Meteor engine, the engine was even powering tanks by the middle of the war. The demand for this magnificent engine was huge, obviously being now produce both sides of the Atlantic, Rolls-Royce in England, Ford and Trafford, Packard in the United States.

By the end of the war, I personally was in charge of a test bench testing Merlin 66s and Merlin 72s that produced 1,875 horsepower. The same engine, but boosted up with two stage supercharging with intercooling. In other words, the air used to be pressured by the supercharger to such a degree that it used to get too hot and of course air expands when it's hot, so you had less oxygen getting into the cylinders so it was a self-defeating exercise. So they had to have huge intercoolers built all round the air ducts pumping the engine, with radiators filled with ethylene glycol to cool the air going into the engine to get the power.

Of course, in the wartime, over on the other side in Germany, the development of the Daimler-Benz 601 series was moving from the 601 all the way through to the 605, and also nearly doubling in power as well. Powering from the Messerschmitt 109 E through the F, then the G model, then the K model. Obviously by the end of the war, with the continued allied bombing from the Royal Air Force at night, the United States in the day, the production from Daimler-Benz was getting more and more difficult and moving from factories to underground catacombs and caves, employing slave laborers from concentration camps. Therefore, the initial quality towards the end of the war was not there.

The development of the Merlin continued improving all the way through the war from a thousand horsepower, a little bit less on the bench, a little bit more in first production, all the way, including 1,350 for a mk V Spitfire, 1,650, to 1,700 in a Mk IX, Mk VIII Spitfire and a P51, all the way up to 2,050 horsepower in the de Havilland Hornet, which was built too late to see action, but was initially going to be made for taking on the zeros in the Pacific War.

Of course, the nuclear bomb happened and Hornet didn't get the chance for service. But with two 2,050 horsepower Merlins, each with a two speed, two stage supercharger, a Hornet was just about the fastest production piston engine fighter ever made. Unfortunately, unless anybody knows different, I don't know of a whole Hornet anywhere in existence today.

What in all the types you've flown, do you consider what's the nicest aircraft, the one that gave you the most pleasure?

I've often thought of this, I would say without any question in my mind the de Havilland Hornet. It was a beautiful, instinctively beautiful shape. It just looked right. It has that rare quality which so often is missing an aircraft: it was overpowered. This was delightful. To such an extent that, I used to do acrobatic shows in this aircraft and do the whole show on one engine. And eventually do a loop with both feathered. It was that type of aeroplane. It was very, very streamlined, very, very fast. And if you dived it down, obviously at full power, just before you pull up, you feather, and you have enough inertia, to carry us right through the loop with no problem at all. But it was that type of aeroplane, delightful.

By 1943, at about 650 to 1700 horsepower in the Mk IX, the Mk XIV, the Mk VIII Spitfire and the P-51, was getting around about at the time towards the end of its development for that year. So Rolls-Royce took on the old Griffin engine, which at 36.9 litres is a good ten litres bigger than the Merlin. Initially put in the Mk XII Spitfire and then more totally in the Mk XIV, XVIII and the XX series right at the end and after the wartime, with 2050 horsepower, a big five bladed propeller and a crank, turning the opposite way to the Merlin engine. So the Spitfires with that engine had a huge tail to counteract the torque and the torque swing when taking off.

I have been here, funnily enough, working for the Imperial War Museum Duxford for 20 years today. And no matter how many times I hear a Merlin engine, I am never bored or find it complacent. To me it is the most beautiful sounding engine of all time. By the end of the war, over 150,000 of these magnificent engines had been made, and the contribution of this engine to the war effort and to the final victory of the Allies cannot be understated.