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

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V-1710 seem to have the intake manifold of a different layout - one pipe/tube leading from supercharger outlet, branching into two manifolds (one per cylinder bank). How difficult/easy would it be to devise a 3-way branching from the supercharger outlet.


Quirk is that it was a rare occurrence for the UK-designed aircraft to have an engine,that would offer same or more as R-2800, in most important 'properties', in service. The Vulture was canceled, Sabre-powered planes were rare vs. other 1st line fighters (and not to be found on FAA machines, nor overseas), Centaurus was too late to matter for ww2, 2-stage Griffon was also rare in RAF, and too late for FAA ww2 needs. The 3-bank Merlin, provided it worked, would've been great for needs of FAA, and also useful for Hawker's heavy fighters. With 2-stage supercharger it should be offering about 2000 HP at 25000 ft, or around 2300 HP at 20000 ft, judging what Merlin 63/66/70 were capable for.
430 mph Typhoon, 470-480 mph Tempest?
 
Lets back up and think about this one again.

Why go to 18 cylinders?

You can't get enough power from 12?

Why?

Most designers want to use the fewest number of cylinders possible ( most, Halford was an exception

When you max out the amount of power that can be made from one cylinder then you add more (and a lot of smaller engines are somewhat modular.) Wright in late 20s/early 30s made 5, 7 and 9 Cylinder Whirlwinds all using the same 5in bore 5 1/2 stroke cylinder. 165 to 300hp. For more power Wright used bigger cylinders and went to the Cyclone R-1750 and R-1820 series engines, their smaller/more than 9 cylinder engines were pretty much failures. P&W built R-1690 and R-1860 Hornet engines but had trouble with the R-1860 version, they decided the cylinders were too big (1/8th in bigger in diameter than the Wright cylinders) and dropped the R-1860 and replaced it with the 14 cylinder R-1830.

You can only make cylinders so big without running into trouble. Gasoline burns at the same speed so big diameter cylinders either have an RPM limit or are burning fuel after it is efficient to do so ( most designers of the time wanted the fuel burn done by 20 degrees past top dead center), Big diameter cylinders also have more trouble cooling the piston (longer path for the heat to travel to the cylinder wall) which was a problem with the Big Hornet. Long stroke brings it own problems.

Reasons for bringing all this up are that the Merlin was NOT using particularly big cylinders. The Merlin used 137mm X 152mm cylinders. R-R had used 139.7mm X 190.5 mm cylinders in the Condor of 1918 and used 152.4 mm X 167.6 mm cylinders in the Buzzard, R and Griffon engines.

The Isotta W 18 used 140 mm X 170 mm cylinders and the Hispano W 18 Schneider engine used 150mm x 170mm cylinders. Obviously 12 cylinder versions of those engine would have been lacking in power at the time they were built.

The 3 bank Merlin is a 40.5 liter engine, the old Condor was a 35.02 liter, the Buzz-fon was 36.7 liters and the Vulture was only 42.47 liters. the Isotta was 47.07 liters and the Hispano was a 54.1 liter engine.

TO make a 3 bank Merlin you need new crankcase and crankshaft, new connecting rods, new pumps, new supercharger, new supercharger drive.....in fact the ONLY things you can use which are the exact same are the cylinder heads/blocks (you hope) the valve train (except you need different cams for the different firing order) and the pistons. All this for a 12.2% increase in displacement over the Buzz-fon. Now maybe you can spin the 3 bank Merlin at 3000rpm and beat the Buzz-fon that way too but maybe the heavier piston/conrod setup will limit the rpm to close the Big V-12. You have more frontal area and a two speed/1 stage Griffon went about 1790lbs while a two speed/1 stage Merlin went about 1450lbs, While the 3 bank won't weigh 50% more it will weigh over 23% more.

trying for a 3 bank Merlin seems like a lot of work for little result.
 
trying for a 3 bank Merlin seems like a lot of work for little result.
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Depends whether we can have a ~40L engine that can turn 2850-3000 rpm, while being available early enough to matter for ww2, and while not being overly heavy and/or 'clumsy' to be installed in a functioning airplane.
If everything goes reasonably well, the 1st instance will be used on Fulmar, in service from mid 1940, with power being 25-30% greater than Merlin VIII (ie. the one with decreased reduction compressor gearing; the power for the W-18 being ~1400 HP for the take off on +6 lbs boost, 1200 HP at 10000 ft). The two-speed version, for 'Tornado', Barracuda and later Fulmars, should give 30% more than Merlin XX, meaning ~1430 HP at 18500 ft, 1800-2000 HP at lower altitudes, even with moderate boost. The 2-stage, for 'Tempest' and Firefly, looks around 2500 HP down low, 2000 at 20000 ft. Neither of those aircraft was as 'skinny' light as Spit or P-51.
The width of the I-F Asso 750 was 1060 mm, compared with Sabre's 1016 (don't know about Vulture). The smaller stroke should save somewhat on weight for the W-18 'Merlin'. Weight should be about what Sabre or Vulture weighted.
 
The Vulture's dimensions were:
(From RRHT)
Length overall: 87.625in/2225.675mm
Width overall: 35.8in/909.32mm
Height overall: 42.175in/1071.245
Weight: 2450lb/1111.3kg


Note that the cylinder banks should be nearly square across. That is, they would be about high (~35.8in/909.32mm) as it was wide. The extra height on the overall number comes, I suspect, from the accesories in the upper and lower vees and the downdraft carby.



The Vulture was a little bit heavy. Future plans for the type had the spur reduction gears (the crank drove 4 layshafts which in turn drove the cam drives, accesories and the propellor shaft) being replaced by a simpler and lighter epicyclic reduction gear system.

Early Merlins (single speed), in contrast, were:
(From Lumsden)
Length overall: 69in/1752.6mm
Width overall: 29.8in/756.92mm
Height overall: 41.2in/1046.48
Weight: 1375lb/623.7kg

Two speed engines (like the Vulture) grew by 2" in length to 71.0"/1803.4mm and 1.8" to be 43.0"/1092.2 in height, while remaining the same width. They grew to 1430lb/648.6kg weight (XX).

A broad arrow layout will probably need to push the outer banks to at least 90° spacing (not sure what angles the Lion has), so it would end up taller and wider than the Vulture.

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

Length: 57.5in/1460mm
Width: 42.0in/1067mm
Height: 43.5in/1105mm
Dry weight: 960lb/435kg

So, if we ignore the length (not enough cylinders and not supercharged) and weight (cylinders, supercharger lacking, earlier design for lower loads), the Lion is wider and taller than the Vulture.

You would also want to consider the master and slave rod arrangement, one of the areas the RR design team had the most problems with the Vulture.

The Vulture IV/V were 1950hp engines in 1940.

The bore spacing on the Vulture was similar to the Merlin's, so could theoretically take the Merlin's 5.4" bore, which would give the Vulture a total capacity of 3023ci/49.5l, but with the same frontal area as the historic Vulture.
 

Thanks for the feedback.


That would leave the Vulture being 70% heavier than 2-speed Merlin, and also 16in longer. So a W-18 'Merlin' should not be any heavier (~ 900-1000 lbs?) or longer?


.

Lion's banks were 60 deg apart, being a 12 cylinder engine, the outer banks being at 120 deg apart. The Isotta-Fraschini Asso 750 have had banks 40 deg apart, obviously outer banks being 80 deg apart, contrary to Vulture's banks being 90 deg apart. Wikipedia article about the Asso 750. An article about the W-18 engines, check out the photo gallery, too.

You would also want to consider the master and slave rod arrangement, one of the areas the RR design team had the most problems with the Vulture.
Click to expand...

Yep, seem likely that would be a deal breaker. Maybe it would be easier/faster/more reliable to expand on I-F workable engine, rather than to have an 'independent' rod arrangement intrinsic to the X engine?
The Vulture IV/V were 1950hp engines in 1940.
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Even 2000 HP was achievable on 3000 rpm at 5000 ft. Unfortunately, that power was quickly reduced once Vulture entered service use.

The bore spacing on the Vulture was similar to the Merlin's, so could theoretically take the Merlin's 5.4" bore, which would give the Vulture a total capacity of 3023ci/49.5l, but with the same frontal area as the historic Vulture.
Click to expand...

Either that, or go for a 3000 HP 'Double Merlin'?
 
tomo pauk said:
Depends whether we can have a ~40L engine that can turn 2850-3000 rpm, while being available early enough to matter for ww2, and while not being overly heavy and/or 'clumsy' to be installed in a functioning airplane.
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Point is that if you have enough design/engineering capacity to make a 3 bank Merlin you have enough to bring out the Griffon earlier.

A Griffon equivalent to the Merlin VIII would offer 1335hp on 87 octane fuel for take-off.

The Early two speed Griffons offered 1720hp for take-off, 1735hp at 1000ft and 1495hp at 14,500ft military ratings.

A bit less than the 3 bank Merlin but then the engine is smaller, lighter, cheaper to make and easier to service (2/3rds the plugs to change and valves to adjust).

Later single stage Griffons running 15lbs boost could pull 1850hp at 2000ft and 1630hp at 10,000ft.
 
The 'continuation of Buzzard' you mean? That would be a good thing, both for FAA, but also for RAF; 1st versions up to 1600 HP for BoB? Compared with what the Vulture, Centaurus and Sabre were promising prior that time (2000 HP+, already on 87 oct fuel), however, would mean the RR is throwing a towel in 2000+ HP class?
The W-18 'Merlin' will offer 10% more of swept volume and almost 10% RPM more, so its 1430 HP at 18500 ft (a Merlin XX equivalent) will beat the Sabre, the 1500 HP at 14500 ft (1-stage Grifon) will not.
 
The W-18 engine has been tried for several applications but without any great success.

Tatra built a proposed W-18 tank engine during WWII.

A few years ago, the reactivated Bugatti automobile company built a prototype sports car with a W-18 engine but it never went into production. Their car now has what they call a W-16 but it is four banks of four cylinders.

In the 1960s, Ferrari proposed a W-18 for their Formula One racing car but I don't know if one was ever built. If I recall, it would more accurately be described as an inverted-T 18.

I also believe there was a proposed W-18 engine for the Cizeta sports super car in the 1980s but I don't know that one was ever built. Instead, the car was brought out with a mere V-16.
 
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An 18 cylinder F1 engine would have sounded spine tingling. BRM built a 16 cylinder H engine to the 1.5 litre formula there is a youtube video of it running and it screams like a banshee.
 
I don't have the engineering to debate the pros and cons of a W18 but I note that, when designers wanted bigger engines in OTL, they chose H and X variants. I presume they had their reasons.
 

Seem like I'm giving too small a power for the proposed W-18. The goal-post should be within 140-150% of Merlin's power, not 125-130%. So the technological equivalent of Merlin XX should go to ~1600 HP at 18500, or ~1850 for take off. For Merlin VIII equivalent (M.VIII was used on Fulmar), the take off power should be around 1500 HP.
 
The problem is at what cost?

It was perfectly possible to make 33-40 liter V-12s. When you try going above around 40 liters you start getting into trouble. DB 603 44.5 liters with 162 X 180 cylinders and the Russian AM-35 engine 46.66 liters with 160 X 190 cylinders have real problems with RPM which limit their power in relation to smaller engines that can turn more rpm.

And no, the 3B Merlin XX will not beat a Sabre, the Sabre IIA offered 1880hp/3750rpm/15,200ft. Even 1680hp at 18500ft is going be a hard push to beat the Sabre. You are now relying on the 3B Merlin to be smaller and lighter than the Sabre. The Griffon was about 73% of the weight of the Sabre. You are betting you can get the full 3000rpm from the 3B Merlin.

If you are going to jump to a more complicated engine than the V-12 it needs to offer a big jump in performance, not a small increment. The Buzz-fon offered 36% more displacement than a normal Merlin and even if you take a 10% rpm cut that is not a bad increase in power for a relatively simple engine. Please note that R-R had run the racing "R" engines at 3200rpm in 1931 and 36.7 liter 154mm X 160mm DB 605 ran at 2800 rpm and the Jumo 211 was 35 liters with 150mm X 165mm cylinders and the 213 with the same sized cylinders ran at 3250rpm.

Depending on when you try for 2000hp (87 octane fuel or early 100 octane or late fuel) may govern the choices made. A 3 bank Merlin using 87 octane fuel is only good for 1545hp at 16,250 ft so something else is need, a LOT more displacement or more RPM or both. That was the Vulture and it wasn't trying for 2000hp to begin with.

Something to think about is that Arthur Rowledge, who designed the Napair Lion went to work for R-R in 1921 and helped design the Condor, Kestrel, "R" racing engine and development work on the Merlin. Even with Rowledge on staff R-R never mad a 3 bank engine
 
 
 
fastmongrel said:
An 18 cylinder F1 engine would have sounded spine tingling. BRM built a 16 cylinder H engine to the 1.5 litre formula there is a youtube video of it running and it screams like a banshee.
Click to expand...

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.
 

Thanks for the effort to find type down the numbers. Please note that Sabre I was not used in combat Typhoons, the 1st flight test found at Williams' site has Sabre II powering the Typhoon. Could you please check out what does Lumsden says about the Sabre II (1st +7 lbs boost. later +9 lbs boost), IIA (+11 lbs boost) and IIB (3850 rpm, +11 lbs boost), the A and B were used on Tempest V.
The Sabre I used smaller gearing ratio for supercharger, esp. in 2nd gear - that would allow for greater boost (almost 8lbs, vs. 7 lbs for earlier Sabre II) and power available to the prop. The 2nd FTH would be lower for Sabre I, however, with all other particularities remaining the same.
At any rate, this Sabre IIB shows 2050 HP at 13750 ft, but at +11 lbs boost and 3850 RPM - or almost no advance over Sabre I, if we go after Lumsden's figures??
As for what source is a 'more primary' one - I won't b!tch too much about that, hopefully someone (hint, hint!) will help us out here.


I was not the one suggesting that 3B Merlin (or any other) engine need to be run at overly high RPM . 2850-2300 RPM is a conservative value for Merlin's pistons valve train.
Interestingly enough, the maximum duration for the max RPM for the Jumo-213 (3250 rpm, on 'Notleistung') was 30 minutes!


I'm okay with 49.5 liter engine beating a 40.5 liter one. The Vulture was good for 2850-3000 rpm, 3000 being the max value for a non-restricted Vulture II, according to the chart kindly provided by Neil Stirling.


Compared with W-layout engines, the X-24 was surely a more complicated thing. The Vulture have had 5% greater swept volume, ie almost nothing vs. the 3 bank. It was all-new engine, sharing maybe just pistons and valves with Peregrine, and despite that it was 1st to the market, vs. Sabre and Centaurus. A less complicated W-18 should shave some months from the Vulture's time line, too.
Saying that a 5% bigger engine will have 33% more power (on same RPM and same fuel supercharger technology) is an exaggeration.
About the engine powers - RR has the expertise in good superchargers, that just got better with Hooker's arrival. There is a difference with an engine being good at 15000 ft, and another that is good at 20000 ft.
 
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From RRHT:
The take off rating of the Vulture II is given as 1800bhp at 3200rpm and +6 lb boost: for the Mk.IV V, the 'fighter' engines, t/o power is given as 1955bhp at 3200rpm and +9lb boost.
Click to expand...
 

How is it more complicated? A few more bits?

The X engine is better balance, has more even firing intervals and is more compact (from a frontal area perspective).

Look what the air-cooled Pennine could do with Merlin sized pistons and a short stroke - 2750ci, 2800hp @ 3500rpm. Granted, it was sleeve valve, which helped its compactness (it was quite long, though).
 
wuzak said:
From RRHT:
Click to expand...

The 3200 was indeed possible, but only for take off?


 
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