That Merlin Crackle... Or Not?

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19 years 9 months

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Something has been bothering me for a while, and I'm sure the people to ask are hanging round here. As a kid, I remember Merlin engines having this wonderful crackle as they went past, which would make chills race up and down my spine - whereas Griffon-engined Spitfires had a more subdued note without the crackle. These days, the Merlins seem to have lost the crackle - they are still nice to hear, but have lost the thrilling bit. Is it to do with the exhaust fit? Or are pilots simply being lighter on the throttle? It's not my lug holes as I've heard other people say "Oh yes, it's got a modern engine, because it doesn't make the same noise". Hoping for enlightenment, and crackling in the pipes too, Adrian
Original post

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10 years 2 months

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The only "crackling" I have noticed is on planes coming in to land where the engine is more on idle and I presume what we hear is the odd backfire from unburnt fuel.
Profile picture for user R4118

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4 years 2 months

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Wes, that's my favourite sound in aviation! Absolutely love that poppimg sound just as they come in to.land!
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19 years 9 months

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Especially the last Spitfire before the Hurricane over the clifftop! Just an artefact of the amount of wellie it's being given? Adrian

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16 years 1 month

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The pops and crackles of the merlins being throttled back does seem fewer .My own video of the Griffon engine on a fast fly past and engine runs at the end.Taken in the old days of video tape. https://www.youtube.com/watch?v=0AMfPyQDB0c&t=579s
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Well, the models is crackling like a pork joint, but I'm thinking about the noise as they pass over in flight rather than as the throttle is closed. Adrian (though I won't moan if people keep posting videos!)
Profile picture for user Anon

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Merlins don't, or shouldn't, "crackle" when passing over at, for example, a cruise setting on the throttle, they have a smooth and wonderful sounding roar. It is only when throttling back or as the throttle is almost closed on final approach to land that a crackle will be very evident. It is pretty much standard on just about all powerful piston warbird or racing engines, designed and timed to run most efficiently at higher power settings. However, it is, as has been alluded to, a most delightful sound whether on the approach or a full-power fly-over. It's possible, of course, that the so-called "crackle" could be more noticeable on the Merlin due to its ignition timing and exhaust arrangement. There's only one, or two, things nicer than the Merlin's song - that of two or four Merlins synchronised together - simply wonderful! I'll never forget the old BAe Mossie, RR299, on the first show of the season at Hawarden air show families day taking off, disappearing for a few minutes then appearing from behind us, over our heads, at full throttle. It certainly did bring a tear or two to my eyes. Anon.
Profile picture for user Archer

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15 years 11 months

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Just a thought, but perhaps we're taking more care in adjusting the carburettors and ignition timings on these old(er) engines these days. Which period is it that you're referring to Adrian? I can think of another couple of variables as well.

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14 years 8 months

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Adrian, I too recall Spitfire fly-bys where the noise could simply be described as a "wonderful roar combined with crackling electric flatulence". I have linked a you-tube video (filmed by someone called 'roustus66') of Col Pay's Spitfire VIII display in 1998. The first few minutes are a landing sequence with the "throttling-back" engine crackle. About 4 minutes in to the video, there's a fly-by at speed and there is a distinct crackle as the Spitfire goes past and is heading away from the camera. Perhaps the crackle is a distortion of the exhaust exiting the exhaust nozzles. Anyway, enjoy the video and the sound....as a homage to a "departed Spitfire pilot". ...geoff https://www.youtube.com/watch?v=SVdYb_otTwc
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Fantastic videos.

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3 years 6 months

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May I suggest that the considerable variations in exhaust stub arrangements would have an impact on the sound of a Merlin flying overhead. Some engines with six tubular shaped stubs on each side have a more distinct "crackle" than say a two into one pipe shape, or even the two into one with the flattened fishtail outlet. I've always been amazed how a Spitfire with a Merlin can sound so very different from a Hurricane with the same engine. Still the sweetest sound though in my humble opinion.
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I have to agree that Merlins do seem to be run more conservatively (and therefore more quietly) these days, it would be great if someone with first-hand knowledge could confirm or deny. The sound is obviously more muffled on the earlier engines with the fishtail exhausts but even the twelve-stub Merlins seem quieter than they used to.
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For a while you could purchase on EB old BBC sound affects records - one had fly-bys of various Merlined apparatus during WW2. These sound NOTHING like ANY Merlined device I have ever heard in my life. Basically the doppler sound/engine affect, if you close your eyes, makes you see a 20 year old, tongue hanging out the side of the mouth, wind blown dribble running across the cheek, flogging an aircraft at FULL BOOST, FULL THROTTLE past the sound recordist. It's like a jet, in terms of doppler speed and the engine is SCREAMING. If I were a Boche on a French seawall HEARING a Rhubarb Mosquito coming in the gaulise would fall out of my mouth as my chin grew slack. Sound is a form of energy. More sound, more energy. More boost, more energy, more sound. So I would suspect that the modern display pilot, seated in a portable before an airshow, is shown a range of medieval thumb screws, and informed that the engine management system records boost, and more boost equals application of thumb screw to gonads, after they have paid the USD250,000 to rebuild an overboosted engine. More display pilots today are airline pilots, screened and trained not to make passengers vomit up nuts and beer or hit the luggage racks, selected for maturity, nothing like the 20 year olds in WW2. Probably if you heard a Merlin roar in the 70s or 80's, it was the same 20 year WW2 old pilot trapped in a 60 year old body doing what was 'normal', and if the engine failed, you just went down to the scrap yard and bought another three. So forget about hearing a Merlin at full throat, it's gone. Never going to happen to an engine that costs as much as running Venezuela for a year. Unless the Russians get some Hurricanes dug up out of swamps and the vodka flows, then all you have to worry about is not being hit by a piece of something falling out of the sky, but it will sound good, and historically correct.
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6 years 9 months

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This isn't a Spitfire, sorry, but if you want to hear a Merlin at full giddy-up like P&P just described go to the 05:00 minute mark of this video. https://www.youtube.com/watch?v=EE9re9BqSIo

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Video unavailable This video contains content from SME, who has blocked it in your country on copyright grounds.
Profile picture for user DH82EH

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6 years 9 months

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Sorry. Just google P-51 Voodoo speed record run and you should get an assortment of runs at full bore. (either that or you could move countries :) :) ) These unlimiteds still get run at full tilt.
Profile picture for user Dave Hadfield

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At any reasonably high power setting the Merlin roars, or at least pulls steadily. It's only when you pull it back to idle that it crackles. It's hard on the engine to pull it back that far in normal flight. It's generally better to have the engine driving the propeller than the propeller driving the engine. So most pilots try to arrange their flight so that the only hard-back-idle is during the flare for landing. The power settings during this airshow display are rather low. But no crackle. You can hear it though, during the landing. https://www.youtube.com/watch?v=rHcq4v_tP3E
Profile picture for user Anon

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So, post number 20 says just about the same as post number 9 - except using different words! Anon.