History is the winning side's propaganda writ large. And you'd do well to remember that.
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| Merlin engine in a Spitfire |
One of my pastimes is examining received wisdom, and investigating to see how much is actually true. And here's a nice little example that follows on from a recent post: the Rolls Royce Merlin. This legendary powerplant helped us win the Battle of Britain (actually the whole of WWII would not be much of an exaggeration!). But how much of the legend is actually myth? The problem with certain legends (this being one) is that questioning their veracity is seen as distasteful, disloyal and practically treasonous. Nevertheless...
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| Rolls Royce R in an S6B |
So, where to begin? At the beginning, and there's our first problem. The legend has the Merlin springing from the Rolls Royce "R" engines which powered the Schneider Trophy winners. Not true - the PV12 (Merlin prototype) was an all-new design, roughly a supercharged & enlarged Kestrel. The "R" was an altogether different beast: but what it did was give the RR engineers a great deal of experience working with high-performance V12 engines in general, and 100-octane fuel in particular. Indeed, the success of the "R" powered S-series racers was instrumental in persuading the Air Ministry to invest in the infrastructure required to allow the RAF to switch over to 100 octane operation in time for WWII.
In the 1930s the race was on for 1000hp aero engines for the new breed of monoplane fighters then being considered. And all the contenders (Rolls Royce, Daimler Benz, Curtis-Wright, Isotta Fraschini and the rest) homed in on the water-cooled V12 as being able to give the required power with the smallest possible frontal area. The airframe boys then designed the smallest possible fuselage to house it: the result being the fighters that contested European airspace during the first half of WW2. Rolls could use 100 octane fuel, and achieved this with a displacement of 27 litres. Germany's Daimler Benz couldn't: so the DB601 needed 34 liters. The bigger engine needed a slightly beefier airframe: in the end the BF109 was a couple of hundred kilos heavier than the Spitfire. And it was this, as much as the elegant aerodynamics, that gave the RAF pilots their edge in the Battle of Britain.
But this wonderfulness came at a cost: the cooling was extremely vulnerable. A single bullet, or tiny bit of shrapnel, would cause a leak. Once this had happened engine failure was seconds away: if you were unlucky it would overheat and catch fire. In it's designed role as a power unit for defense interceptor, this was not necessarily disastrous. With a modicum of skill, and a bit of luck, you could turn the ignition & fuel off, glide down into a Kentish field, cadge a cup of a tea off the farmer and be back in the mess for supper. It was a very different story if you had 30 miles of sea to cross...
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| Lancaster MkII |
But the real problem with the Merlin was the temptation to slap it on the front of anything with wings, even when it was not really appropriate. And nowhere is this more apparent than the Lancaster. The Lancaster was created from the Manchester by replacing its two ill-starred Rolls Royce Vultures with four Merlins. The rest, as they say, is history. But the legends obscure an uncomfortable fact: the Merlin probably wasn't the best engine for the job. Not only was the vulnerability of the cooling system very much more serious when spending hours at a time over occupied Europe, but the engine itself wasn't happy in its new role. It was designed for the interceptors: a couple of brief spurts of full power, an hour or so stooging around, then back for tea & TLC. Bombing raids required the engines to flog themselves to death for eight hours at a time. And they didn't like it: it's a tribute to Rolls - and the ground crews - that they lasted at all. Now, this would understandable if the Merlin was the only game in town: but it wasn't. The Bristol Hercules was also a fully paid-up member of the 1000hp club (it actually produced more power than the equivalent Merlin for most of the war). It was a big, robust, air-cooled radial engine, with an awesome reputation for reliability and toughness. And the bigger cross-section was pretty irrelevant given the size of the big bombers then being built. It was the engine of choice for both the Stirling & Halifax bombers - and there was even a version of the Lancaster fitted with Hercules engines (the MkII) which was not noticeably inferior to its Merlin engined sibling. And so the question has to be asked: how many aircrew, consigned to a watery grave in the North Sea by damaged Merlins, would have made it home if they had had Hercules engines?
By a twist of fate, by the end of the war, there had been a reversal of fortune. The air was full of Merlin engined Lancasters. And the RAF's state-of-the-art fighter (the Hawker Fury, which actually emerged as the Fleet Air Arm's Sea Fury) used a radial engine. As did the USN's F4U Corsair and the Soviet LA7. Although, famously, the USAF's Mustang stuck with the Merlin, becoming the iconic fighter of the late war period.
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