The 18 cylinder spin-offs from known V-12s: worth pursuing?

[wuzak]

More compact the X-24/Vulture is not. The width of the Asso 750 was 1060 mm on the widest point, due to the stroke of 170 mm. Vulture was 910 mm, with small stroke - 140 mm? 3B Merlin would be closer to Vulture, not just because of modest stroke (152 mm), but because the outboard banks will be set 80 deg apart vs. Vulture's 90 deg. The lower end of the engine will be narrower than of X-24, since there is only crankcase present there, not 2 additional banks of cylinders. The Vulture was higher than Asso 750, despite having 30 mm less stroke, again because of 2 banks under crankcase. The 3B Merlin should save further 20 mm in height.

The length of the con-rods compared to the stroke are also important, and if the ratio is too low the rpm ability of the engine is restriicted.

The Merlin XX is already taller than the Vulture.

Sticking a vertical cylinder bank up the middle will only make it more so.

How/why do you get 80° for the outer banks? Have you laid out the cylinder banks graphically to see if they can still mount the same distance from the crank centreline?

 

[fastmongrel]

No, no.

The H-16 was for the 3 litre formula in the mid 1960s, and was a dismal failure (replaced by a V-12).

The 1.5l engine was a V-16 and had air supplied by a Rolls-Royce designed 2 stage centrifugal supercharger - yes, it was a min Merlin supercharger. That is teh engine that you hear al over youtube.

Got my Vs and Hs mixed up. The sound of the V16 warming up turn the speakers up loud


View: https://www.youtube.com/watch?v=anVAkHP4BgQ

Dont you just love the sound of internal combustion

 

[wuzak]

Got my Vs and Hs mixed up. The sound of the V16 warming up turn the speakers up loud


View: https://www.youtube.com/watch?v=anVAkHP4BgQ

Dont you just love the sound of internal combustion

Indeed!

 

[Jugman]

This is a nitpick but the early Merlin was 75" long INCLUDING the propeller shaft. the 69" figure is measured only to the rear propeller cone. This is true for most Griffon length figures as well.

 

[wuzak]

More compact the X-24/Vulture is not. The width of the Asso 750 was 1060 mm on the widest point, due to the stroke of 170 mm. Vulture was 910 mm, with small stroke - 140 mm? 3B Merlin would be closer to Vulture, not just because of modest stroke (152 mm), but because the outboard banks will be set 80 deg apart vs. Vulture's 90 deg. The lower end of the engine will be narrower than of X-24, since there is only crankcase present there, not 2 additional banks of cylinders. The Vulture was higher than Asso 750, despite having 30 mm less stroke, again because of 2 banks under crankcase. The 3B Merlin should save further 20 mm in height.

The Lion, a broad arrow or W type engine, was wider and taller than the Vulture, despite having smaller cylinders than the Vulture.

The Vulture's dimensions were:
(From RRHT)
Width overall: 35.8in/909.32mm
Height overall: 42.175in/1071.245

The Lion II's dimensions were:
(from Napier Lion Aircraft Engine Pictures, Information and Specifications)

Width: 42.0in/1067mm
Height: 43.5in/1105mm

 

[fastmongrel]

If you want sheer gut twisting noise the Honda 125 5 cylinder RC146 I have heard this warm up and it genuinely makes you feel ill.


View: https://www.youtube.com/watch?v=Xuvx15DLDmc

 

[stan reid]

If you want sheer gut twisting noise the Honda 125 5 cylinder RC146 I have heard this warm up and it genuinely makes you feel ill.

Sounds good to me. Before the cylinder limit, Honda was supposedly developing both 24 cylinder and 32 cylinder 3 liter Formula One engines. I don't know the configuration but I think "X" would probably be my best guess. The engines may have had oval pistons so the term "cylinder" might be a bit of a misnomer.

Edit: The Wiki article on X Engines says the Honda 32 was an X configuration so maybe the 24 was a W configuration, in which case, each engine would be based on banks of 8 cylinders.

 

[wuzak]

A 3 bank Merlin with the outer banks 80° apart.

Looks a little crowded.

If the two banks that share the intake side were the same as for the Vee the outer banks would be 120° apart.

 

[Shortround6]

It does have an extra bank of cylinders, that would amount to 20-25% more parts?

True

More compact the X-24/Vulture is not. The width of the Asso 750 was 1060 mm on the widest point, due to the stroke of 170 mm. Vulture was 910 mm, with small stroke - 140 mm? 3B Merlin would be closer to Vulture, not just because of modest stroke (152 mm), but because the outboard banks will be set 80 deg apart vs. Vulture's 90 deg.

Perhaps, it depends on the layout, Outer banks 40 degrees from center bank for compactness (80 degrees total spread) or outer banks 80 degrees from center bank (160 degrees total spread) ? with the 40 degree spread you have a lot less volume to fit intake and exhaust. Getting a good firing order may be a bit trickier than with the wider spread.

20mm of height isn't worth worrying about.

continued: They also have Centaurus ready, the Griffon will soon produce 2500 HP etc. What I'm after is a 1700-1800 HP engine for early war, 2000 HP mid-war, up to 2500 HP for late war, that would use some existing engine parts, hence cutting on risk time to develop.

trouble is the parts you are saving are actually the easy parts. The parts you need new are the hard ones. Once RR drops the ramp heads and goes back to the scaled Kestrel heads the cylinder head and valve problems are about over.

connecting rods for Lion.

With a 60 degree V-12 the cylinders on each crank pin fire about 300 and 420 degrees of crankshaft revolution apart, but one piston follows the other by 60 degrees. One cylinder is firing every 60 degrees of crankshaft rotation. This is the firing order for a Merlin--- 1A-6B-4A-3B-2A-5B-6A-1B-3A-4B-5A-2B

With an X-24 you have a cylinder firing every 30 degrees and have the cylinders on crank pin giving two firing pulses per crankshaft revolution but not evenly, you do have an even movement of the reciprocating parts. When upper right cylinder is at TDC the bottom left cylinder is at BDC and the other two cylinders are at mid travel, one going up and one gong down. Opposing pistons will fire at at 180 and 540 degrees from each other.

With the 3 bank if you have the 40 degree bank (80 total) you can have all three pistons ascending or descending at the same time although briefly. I haven't tried figuring out the firing order (it makes my head hurt

edit: with a 40 degree spread you can have the cylinders on one crank pin fire 40 degrees apart and then 640 degrees of crank rotation before they fire gain or left hand cylinder fires (assuming clockwise rotation facing away) , center skips, right had fires 80 degrees later, middle fires 320 degrees after that and then another 320 degrees before left cylinder fires again, repeat. Or right hand cylinder fires, 280 degrees later left hand cylinder fires with middle cylinder firing 400 degrees after that but then the right hand cylinder fires the 2nd time just 40 degrees after the center cylinder.

in theory you can have one cylinder firing every 40 degrees of crankshaft rotation, getting it to work with the cylinder bank angles gets a bit tricky.

Now IF you built a 18 cylinder Y engine with 120 degrees between each bank figuring out a firing order and piston movement would be a lot easier although it would be one wacking BIG engine

This is the challenge/hard part. Getting the crankshaft to live at high RPM with the higher out of balance forces and and trying to squeeze as even a firing order out of it as you can given the limitations of piston movement. Torsional vibration can be a real problem here. the twisting (or loading) of the crankshaft along it's length as the cylinders fire. It gets worse with higher pressure (boost) in the cylinders.

Strangely this was an advantage for the Napair Lion over the contemporary V-12s. For a 12 cylinder engine of about equal power the shorter crankshaft of the Lion had less problems and could be lighter than a V-12 crankshaft and crank case. Now if you were trying to build a 3 bank 18 to compete with a V-16 or V-18 (?) you may have the same shorter crankshaft advantage but if your crankshaft is as long (or close) to the V-12 the advantage doesn't exist. Each blow to the crankshaft is a bit smaller than a big V-12 but weight of the reciprocating parts thrashing around may cancel that out.

This is were you will spend your development time, crankshaft, crankcase and con rod design and development (the same things that killed the Vulture) plus supercharger and reduction gear ( needed for any 1500-2000hp engine at the time). As I said before the ONLY stuff you are saving is the easy stuff.

 

[wuzak]

A Merlin X

 

[stan reid]

Ah, then that's a master rod with two slave rods like a radial engine - that's how it appears to me at least.

 

[GregP]

Yes.

The problem wouldn't really be the rods; it would be the balance, timing, and the manifolds (intake and exhaust).

Honda came up with a formula that allows perfect primary balance many years ago, but I don't know if it applies to 18 cylinder engines. It certainly works for 1, 2, 4, and 6 cylinder engines though (all motorcycle engines). It would be interesting to apply it to WWII V-12 and maybe V-18's. I'd also like to see it applied to radials, but is seems the day of the air-cooled radial is almost over ... except for maybe general aviation.

 

[wuzak]

A V-12 is ineherently perfectly balanced in the primary mode. IIRC in the secondary mode as well. The bank angle does not matter for balance, only in terms of even firing intervals. 6 cylinder in-lines are also well balanced.

The rod length will have an impact on the size of the engine as well as the rpm capability.

 

[tomo pauk]

Pennine - 37.5in/952.5mm x 39in/990.6mm - 106in/2692mm long.

Thanks. More about Exe and Pennine can be read here.

The length of the con-rods compared to the stroke are also important, and if the ratio is too low the rpm ability of the engine is restriicted.

Okay.

The Merlin XX is already taller than the Vulture.

Interestingly enough, seem like the Merlin 61 was 2 inches lower? (Wikipedia = corrections welcomed).

Sticking a vertical cylinder bank up the middle will only make it more so.

Agreed -though still not as high as Griffon (46 in)?

How/why do you get 80° for the outer banks? Have you laid out the cylinder banks graphically to see if they can still mount the same distance from the crank centreline?

I've took SR6's word for it, and seem like the people here agree:
"Un posto di rilievo spetta alla Isotta Fraschini con il suo Asso 750, prodotto a partire dal 1927 su progetto di Giustino Cattaneo. Si trattava di un eccellente 18 cilindri a W di 40° con distribuzione bialbero a quattro valvole che, con una cilindrata di 47 litri, erogava 850 cavalli."

(basically: I-F developed the Asso 750, design work started in 1927 by G. Cattaneo. The excellent 18 cylinder in 'W' with 40°, with DOHC and 4 valves, capacity of 47L and capable for 850 HP)
That would mean that 80 deg is the 'span' between outer banks, and the drawing seem to agree with that figure.

The Lion, a broad arrow or W type engine, was wider and taller than the Vulture, despite having smaller cylinders than the Vulture.

As for the width - the Lion have had the 120°between outer banks, so there was no way that it was to be a narrow engine. As for the height - Lion seem to be of even greater height than a long-stroke Asso 750; was there a difference in oil sumps technology or application of same?

 

[tomo pauk]

The W-18 engine with 80 deg span between central and outer banks can have the outer banks faired in with wings, as it was in Bernard aircraft (from here):

The installation in the Nieuport-Delage aircraft does not seem remotely as tidy streamlined as in the Bernards (from here):

Of course, the engine could use the raised, external spur reduction gear, so the prop would be raised too and undercarriage legs would be kept reasonably short, esp. in case the engine is installed in a fighter.

 

[Jugman]

Now IF you built a 18 cylinder Y engine with 120 degrees between each bank figuring out a firing order and piston movement would be a lot easier although it would be one wacking BIG engine

How and why would a Y be whacking big?

 

[Shortround6]

Because it would have 3 banks of cylinders spaced at 120 degrees from each other. Like this:

Granted these are 3 cylinder radials but you get the idea. Flip the engine over (two banks up and out the sides and one hanging vertical) and you have an engine almost has tall and wide as an H-24. The Bristol Lucifer was an attempt to cut development time an d tooling cost by using already existing parts. Three cylinder radials work "ok" at 30-50hp but at 120hp and up??? a 2.66 liter 40hp cylinder firing every 240 degrees of crankshaft rotation?

The 3 bank engines best shot at an even firing order (and balance crankshaft/rotating parts) is the Y or inverted Y configuration. While you can squeeze the banks closer together the balance and firing order get more difficult. Since the idea that started this thread was to get more power quickly and easily we have a problem. The more compact you make the engine the more time it may need to develop.

 

[Jugman]

Yes I know what a Y would look like. I would think an inverted Y would have less frontal area than broad-arrow arrangement. You can somewhat hide the coolant pump(s), scavenging pumps in side the lower V. A close fitting cowl would look rather awkward and ugly. (It's a wonder the French didn't try it! )


On firing order You're mistaken. At least with 120° bank angle with a symmetrical 120° crankshaft. At any point 1/3rd (six) of the cylinders will be at TDC. There will be three simultaneous power pulses every 120° instead of one every 40°. By contrast a 40°+40° or 80°+80° broad-arrow well have only two cylinders at TDC at any point in time. Thus giving one power pulse every 40°.

One could use an offset crank or a helix arrangement to achieve even firing in a Y. The former would negate the advantages of a six throw 120° crank while the later negates any frontal area advantage.

 

[tomo pauk]

The designers have had the way to streamline the engine's outer banks that were 120 and 160 deg apart. Mitchell with Supermarine S4 managed to streamline the Napier Lion installation (120 deg between outer cylinders); picture from here:

Another Bernard's aircraft, the V4 (160 deg between outer banks):

http://richard.ferriere.free.fr/3vues/bernard_v4_3v.jpg

So if one goes for an Y engine layout, it would be better to have it as an inverted Y, actually, so the wings can 'follow' after the outer banks, the wings mounted low on the fuselage. And, again, the prop shaft need to be raised, via external spur reduction gear, to allow shorter sturdier U/C legs.

 

[Shortround6]

Before you get too clever just remember that all those racing seaplanes used surface radiators, had truly abysmal views from cockpit, More than one pilot crashed due to exhaust fumes in the cockpit ( a real problem with the center bank solvable by good exhaust ducts at the expense of exhaust thrust and wearing an oxygen mask at all times the engine is running.

And in the end the 18 cylinder 3 bank engine doesn't do a lot for the British because the British designers had NOT maxed out the size of their cylinders like the Italians and French had. Their engines went to the third bank because they were already using cylinders about the same volume as the Griffon cylinders.