That Merlin Crackle… Or Not?

… but could it simply be that fuel is more precisely purified these days?

Interesting thought. The wartime 100/130 grade fuel was different from the AVGAS 100LL available today. The latter having only a fraction of the lead contents which, I assume, reduces the anti knocking values, preventing the highest boost levels. Maybe someone with actual flying experience can tell which boost levels are possible with AVGAS 100LL?

Daft question(s), but could it simply be that fuel is more precisely purified these days? On top of that, engines are maybe maintained to a better standard and, when overhauled, are put back together with closer tolerances etc?

I’m thinking generally along the lines of the fact that a lot of historic fighters now look a lot cleaner, and are maintained to a lot higher standard, than when they were ever used in action. I don’t know when ‘childhood’ was for Adrian Gray, so he could be talking about Spitfires used in anger or the very early days of the preservation movement?

I’ll throw this one into the mix, they do sound really good when they power back at touchdown. Boise Bee with its -9 Merlin sounds awesome!!

Jason

THANK YOU FOR NOT ADDING MUSIC ,Lovely video 🙂

I’ll throw this one into the mix, they do sound really good when they power back at touchdown. Boise Bee with its -9 Merlin sounds awesome!!
Jason

Not to mention the Allisons(?) crackling…..

I’ll throw this one into the mix, they do sound really good when they power back at touchdown. Boise Bee with its -9 Merlin sounds awesome!!

Jason

3+ years ago I visited Old Warden for their first of the year display & the commentator remarked on the different sounds of the Merlins in the different aircraft that day. Now I have’nt heard a Merlin for donkeys years, but his comment explained why I thought some of the pilots were not using full power. He said that the different exhaust stubs were to blame!
I cannot remember exactly the aircraft that day, possibly the Spit , Hurricane & a Mustang.

I know exactly where you’re cominng from and agree with you 100%. I think it’s just conserving engines.

I can see I am going to have to do some explaining here. I grew up at Cornish Hall End – look it up on Gurgle Maps – under the flight path to Stansted (lovely – Britannias. Heavy Lift’s Belslows, and even the occasional Dak back then) – so anything heading for DX came underneath it, nice and low.

So… unless the fields around Cornish Hall End conceal a secret Spitfire landing ground. I am not talking about the crackling as the pilot throttles back for landing!!!!!

You can hear an approximation of it (I suspect the mike is the limiting factor) in the Col Pays video (thanks, bearoutwest!) between 5 & 6 minutes in and again just after 10 minutes. It’s a very distinctive noise, a real crackle, and it made the hairs on the back of my neck stand up. I fear that powerandpasddsion may have nailed the reasons it has gone in post #15, which made me laugh like a drain.

I’ll write this in bold again:

As they passed over, there was an awe-inspiring crackling sound. I wonder if it has anything to do with the change in diretcion of the sound relative to the pipes?

Make what you will of that.

Adrian

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

Anon.

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

There might be some Merlin sounds in this video: https://www.youtube.com/watch?v=6Ev29gcUAk0

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.

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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

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.

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.

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.

Fantastic videos.

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

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.