Rolls Royce Griffon question.

If it was changed for that reason then it would be the other way, Merlins rotate the same way as US engines (right hand), the Griffon goes the other way (left hand), like other British engines such as Bristol, Alvis and DH.
I thought the P-40 with the Allison was right hand rotation? The propellers appear to be right handed.

Interesting point about the crankshaft Richard, wartime Griffons have a very offset counterweight on the crank, although the G58 crank looks more conventional.

Pete

Hi, I´m Richard from Sweden and I own a RR Griffon Mk58
Very intereseting thoughts in this topic!
Griffon is one of few aero engines that are rubber mounted via a complex rubber system, or am I wrong?
This shows the had vibration problem in the first place, they also try to solve part of the problem with counterclockwise crank rotation.
I don`t really know, but I would not be surprised if they also run the engine in “odd fire” to prevent unhealthy crank vibrations. By odd fire I mean they maybe have serarate the even firing order from 60deg crank to some +/- 1 to 3deg from this (57-63deg)…

I think the crankshaft rotation was changed to standardise with US engines where the propellers all turned in the opposite direction?

Although the Allison V-1710 seems to turn the other way (normally)?

Hi, I´m Richard from Sweden and I own a RR Griffon Mk58
Very intereseting thoughts in this topic!
Griffon is one of few aero engines that are rubber mounted via a complex rubber system, or am I wrong?
This shows the had vibration problem in the first place, they also try to solve part of the problem with counterclockwise crank rotation.
I don`t really know, but I would not be surprised if they also run the engine in “odd fire” to prevent unhealthy crank vibrations.
By odd fire I mean they maybe have serarate the even firing order from 60deg crank to some +/- 1 to 3deg from this (57-63deg)
This is not easy to detect without a proper timing disc mounted on the crank and check against a ign. timing light.
Somebody with experience of regrinding Griffon crankshafts can maybe answer this question!?

Best Regards
Richard

www.griffon-engine.se

The Griffon is considerably more powerful than the Merlin ( 37 litre capacity v 27) so I must assume that power emenating from a similar exhaust would sound different. It also rotates in the opposite direction, altho’ this in itself shouldn’t cause any variation in sound. On the Shackleton, with Griffons, there are contra rotating props. so would definitely sound different.

I should have said, in comparison to a Griffon engined Spitfire. I had the pleasure of walking around one while it was running and with exhaust stubs its distinctly louder to the sides and this may affect any recording, and therefore any comparison.

Similarly a Rover Meteor in a Centurion tank sounds similar to a Merlin but not the same. A Meteor with exhaust stubs sounds near identical.

I think that is because from the front end of an engine a lot of what you’re hearing is related to the gearbox, intake valves and associated machinery. From the side and moving to the rear you’ll get more and more exhaust noise which is a lot darker in note. This effect is most pronounced on a large radial with short exhaust stubs but sure to be present on a V-12 too.

That’s right, it is manifolded, and to be fair, the sound is less pronounced, but is certainly still there. The exhaust pipes fed from each bank of 6 is 5″ diameter and 3 to 4ft long and cuts out much of the high frequency.

Minimans, yes changing the cam on the Griffon in Miss Canada IV made the engine sound different, though the Merlin cam timing and overlap sits in between these two, and both versions of the Griffon share that unique “uneven firing” effect which is absent in the Merlin

Pete

One thing I’ve noticed with the Shackleton manifold exhaust is that it changes where you can hear the sound from. Its very directed. Stand in front, and you can hear the engines, but they are muted and there’s a lot of propeller noise. Stand behind and slightly off to one side and you hear pure Griffon.

That’s right, it is manifolded, and to be fair, the sound is less pronounced, but is certainly still there. The exhaust pipes fed from each bank of 6 is 5″ diameter and 3 to 4ft long and cuts out much of the high frequency.
Pete

A similar thing happens with the Bristol F2 in that even with the long exhaust pipes on them you can still there’s a big V engine under the cowling.

Minimans Are not TempestNut post #5 and MerlinPete post #9 saying that from their experience the Griffon makes the same sound irrespective of overlap and spanning the overlap value of a Merlin, at least from the figures given, 28-43-74? I appreciate that there are also many marks of Merlin. Presumably the overlap in the Merlin’s varies so does this change the sound?
Would this not indicate that fundamentally it is not the overlap that is producing the difference in sound between a Merlin and Griffon?

As far as I’m aware the valvetrain geometry stayed the same in all marks of merlin until the advent of the 100 series engines, my comment was perhaps not to well thought out more a musing after a morning bacon buttie!! But a cam timing with lots of overlap does produce a more crackling growl sound than a cam with less overlap and the Merlin has far less overlap than the Griffon which was the basis for my comment.

minimans : I know from tuning Subaru boxer engines that the headers also contribute a huge difference to the sound with a marked difference between equal and unequal length headers.

If the growl is there irrespective of manifolds, stubs or ejectors and exists throughout the rev range it must to be the firing order as per Beermat #45 giving uneven pulses and harmonics that produce the growl.

While we are pondering the meaning of life and where the growl comes from I thought those that haven’t already seen it might like to watch the whirly bits of a Packard Merlin 266 for 30 secs or so.

(function(d, s, id) { var js, fjs = d.getElementsByTagName(s)[0]; if (d.getElementById(id)) return; js = d.createElement(s); js.id = id; js.src = “//connect.facebook.net/en_US/all.js#xfbml=1”; fjs.parentNode.insertBefore(js, fjs); }(document, ‘script’, ‘facebook-jssdk’));
Post by Battle of Britain Memorial Flight (Official).

As MerlinPete says it is the unique and distinctive sound that the Merlin and Griffon makes that we are discussing. I think we would all agree that many factors such as exhaust systems and overlap etc will change the overall sound but that distinctive characteristic underlying sound is still always there making the engine clearly identifiable.

Minimans Are not TempestNut post #5 and MerlinPete post #9 saying that from their experience the Griffon makes the same sound irrespective of overlap and spanning the overlap value of a Merlin, at least from the figures given, 28-43-74? I appreciate that there are also many marks of Merlin. Presumably the overlap in the Merlins varies so does this change the sound?
Would this not indicate that fundamentally it is not the overlap that is producing the difference in sound between a Merlin and Griffon?

Merlinpete From what I can see on the Shackleton manifold each bank combine into a single pipe. Is that correct? Would you say that the “pulses” coming from these pipes would still be basically the same as stubs added together such that Beermats theory in #45 could still work.?

That’s right, it is manifolded, and to be fair, the sound is less pronounced, but is certainly still there. The exhaust pipes fed from each bank of 6 is 5″ diameter and 3 to 4ft long and cuts out much of the high frequency.

Minimans, yes changing the cam on the Griffon in Miss Canada IV made the engine sound different, though the Merlin cam timing and overlap sits in between these two, and both versions of the Griffon share that unique “uneven firing” effect which is absent in the Merlin

Pete

I would venture to say that its the valve overlap that creates the different “sound” having been building engines of an automotive nature for 40 odd years for road and race cars it’s quite startling to hear the difference in sound between a Std cam and a racy cam with lots of overlap……………..

Merlinpete From what I can see on the Shackleton manifold each bank combine into a single pipe. Is that correct? Would you say that the “pulses” coming from these pipes would still be basically the same as stubs added together such that Beermats theory in #45 could still work.?

Mike Yes I did but you have put it better.

Beermat I think you could well have it here! Interference would give you the pulse effect you can hear. Comparison with light is perfectly valid and obviously clearly visualised with Moire Patterns clearly showing the pulse effect. I have to say that’s a brilliant correlation bringing the firing sequence together with interference patterns, well thought of. And as Mike called it the PRF gives it that gruff sound.

Though I agree high frequency pulses probably produces a gruff sound. By which I mean frequent pulses.

Ah what you meant was PRF (pulse repetition frequency) rather than pitch then. I can definitely understand that.

My brain is starting to overheat, but something struck me – the bangs are so close together in time that the physical distance between them becomes crucial.

As the bangs move up and down left and right banks in opposition, the sound waves generated by them may well move in and out of phase as the distance between consecutive bangs changes from more-or-less the width of the block to more-or-less the length of it. Moving in and out of phase rapidly could create the rapid amplitude variation seen (through constructive and destructive interference), which translates to a growl.

Edit Ref. Young’s double slit experiment – imagine rapidly bringing the slits closer together and apart again, and observing the brightness from a given spot as you do so. Not entirely analogous, but it helps me!

The idea put forward by Spartabus and Beermat sounds the most plausible to me.
Different exhaust stubs do have a marked effect on the sound of these engines, but the distinctive Griffon roughness is there on the test bed regardless of whether it has stubs, Shackleton manifolds or none at all, or those pipes the tractor pullers use. Similarly, it doesn’t matter if there is a prop fitted either.

Pete

Is it to do with the Ejector exhausts that the Merlin has?

Yes.It is the same as why the P51 Packard Merlin sounds different to the Spitfire RR version.