A 'proper' way to have a 24 cylinder liquid-cooled aero engine for the ww2?

[don4331]

The axis did not deploy the high octane fuels the Americans and British did. This was a huge advantage for the Americans and British. Higher boost pressures come from high octane fuel, and from methanol water injection. Extensively used WWII V-12s were anywhere from 27 to 44.5litres.

German B4 fuel - German rating of 87 octane would have a rating of 87/115 under the US/UK system; C3 fuel - German rating of octane 96 - would have a rating of 96/125 (or better) under US/UK system. Both German fuels used the same 4.4g tetraethyl lead. US/UK 100/130 octane has 4.5g tetraethyl lead. No high octane German fuel is a myth promoted a lot of places.

It does take 22 tons of coal to make 1 ton of C3, so you better need better fuel.. German aviation fuels do have higher vaporization point, compounded by fuel injection - together they don't allow vaporization to the same extent as US/UK engines which makes German aviation engines less likely to knock - therefore they don't get as great an advantage from the "rich" rating.

Higher boost pressures come from increased supercharging. But note higher densities come from more efficient compression/inter-cooling. If your compressor isn't efficient, all that boost pressure is just making things hot.

German engines used magnesium (1.7g/cm^3) compared to UK/US which heavily used aluminium (2.7g/cm^3)

tomo pauk :

I wonder what difference is historically if RR cuts Peregrine and Griffon, rather than Peregrine and Vulture.

Is uprated Vulture* in Tornado sufficient to meet the Fw.190 threat if there is no Spitfire XII.
Spitfire does just fine with Merlins to end of its lifespan; Manchester can soldier on with Vultures, but that doesn't prevent Lancaster with 4 Merlins.

Fairey Barracuda and Firefly would enjoy additional power from Vulture; allows for earlier Spearfish
Tempest/Fury have Vulture instead of Griffon as option in more of same power/weigh class as Centaurus/Sabre.
de Havilland wanted to make a follow on to Mosquito with Sabre but lack of production capacity at Napier prevented it; Vulture would allow that.

*rpms are harder on bearings than boost, Vulture could probably make 15 psi on deck, but it will need bigger supercharger/faster drive ratios to take full advantage of 100 octane fuel

 

[wuzak]

I wonder what difference is historically if RR cuts Peregrine and Griffon, rather than Peregrine and Vulture.

Is uprated Vulture* in Tornado sufficient to meet the Fw.190 threat if there is no Spitfire XII.
Spitfire does just fine with Merlins to end of its lifespan; Manchester can soldier on with Vultures, but that doesn't prevent Lancaster with 4 Merlins.

Spitfire is OK with Merlins, but better with Griffons.

The big advantage the Griffon had over the Vulture was that it could fit into the Spitfire. And that it was originally intended for FAA aircraft.

 

[wuzak]

I assume you mean radial individual rows having odd number of cylinders for firing order of 1-3-5-7-2-4-6 for 7 cylinders, i.e. every 2nd cylinder in order. There are lots of twin row radials with even number of cylinders.

Yes, odd number of cylinders per row, with every 2nd cylinder firing.

I have Vulture as being more/less 48" square (again, hand held tape measure), so it is a little greater frontal area than the "H" engines, but way smaller than radial of same power. RR has intake manifold, magnetos, carburetor, water pumps, and engine mounts filling most of the open area in the "v".

Vulture is 35.8" wide and 42.175" tall. Across the cylinder section it is roughly square, and diagonally across the cylinders might be 48" (using width and height of 35.8" gives 50.6"). So you are gaining 5"+ over a Hercules/Centaurus or R-2800/R-4360 in diameter.

Information I have on Vulture was it was making 1,800hp@3k rpm with 9psi boost. And was getting 180 hours between overhauls at that level when it was discontinued which is pretty much same as Merlin of same period. And I know it made 2,500hp in lab, but Merlin made >2,100hp in Speed Spitfire. Neither of those aren't engines you want to fly to Germany and back on daily basis.

The Speed Spitfire engine, the Merlin II (Special), was a racing engine that used special fuels to allow boost of +27psi at a time where the regular Merlin was using +6.25psi.

I'm not sure how 2,500hp was achieved with the Vulture, but probably from increased boost. It would have been using regular fuel. Its reliability at that power level would be in question.

Power rating of the Vulture II (from correspondence with the RRHT):

(Moderate gear):
Max t/o (SL) - 1800bhp, 3200rpm, 6lb boost, 162gph;
Max climb - 1700bhp, 2850rpm, 6lb boost, 142.5gph;
Max cruise - 1480bhp, 2600rpm, 5lb boost, 0.61 pt/bhp/hr
(High gear):
Max cl - 1455bhp, 2850rpm, 6lb boost, 134.5gph;
Max cr - 1290bhp, 2600rpm, 5lb boost, 0.66 pt/bhp/hr

The max take-off power for the Vulture IV and V was 1,955hp @ +9psi boost.

Note that the max cruise of the Vulture in MS gear was similar to the maximum power of the Merlin XX at +14psi boost.

 

[wuzak]

If I were to re-think liquid cooled engines for WWII, I would look into a 40litre L-12. This would put out 2000+HP, it would reduce the frontal area of the aircraft, and it would provide a better view to the front and down.

Given that a 36.7L Griffon V-12 was over 2m long, I'd hate to think how long a 40L in-line 12 would be.

I would imagine there would be some difficulty with torsional vibrations in the crankshaft, some difficulty getting even mixture distribution across all cylinders, and the rigidity may be a problem in s/e aircraft, given that the propeller is usually directly connected to the engine.

The gain in the frontal are might not be that good in a s/e aircraft either, given that the V-12 was roughly as wide as the pilot's shoulders and the L-12 would be taller.

 

[wuzak]

Griffon peak power was at 2,750 RPM, Merlin at 3,000 RPM and Sabre 3,800 RPM. From what I know the maximum piston speed is the limiting factor and that is a function of stroke and RPM. Forces and piston speeds increase exponentially with RPM and stroke and actually producing power is limited by the speed of the flame front/ gas expansion etc.

The Jumo 213J could rev out to 3,700rpm, and make 2,800hp.

The bore and stroke of the Jumo 213J are similar to that of the Griffon, both being smaller by around 2mm.

How much power could a Griffon produce if it had an extra 500rpm (which would be similar to the speed of the R)?

 

[swampyankee]

34litres. Twelve cylinders. They used two of the engines to make the Daimler Benz DB606 with the required twenty four cylinders, and it gave nothing but trouble.

By all reports, the Allison V-3420, made by joining 2 V-1710s in a similar manner was relatively trouble-free. I don't know the detail design issues that kept the DB606 from being successful[1], and a case study comparing the development process would be interesting.

--------------------
[1] Many of the issues assigned to the DB606 in the He177 seem to be at least as much from design decisions by Heinkel as engine issues.

 

[tomo pauk]

I wonder what difference is historically if RR cuts Peregrine and Griffon, rather than Peregrine and Vulture.

Is uprated Vulture* in Tornado sufficient to meet the Fw.190 threat if there is no Spitfire XII.
Spitfire does just fine with Merlins to end of its lifespan; Manchester can soldier on with Vultures, but that doesn't prevent Lancaster with 4 Merlins.

Fairey Barracuda and Firefly would enjoy additional power from Vulture; allows for earlier Spearfish
Tempest/Fury have Vulture instead of Griffon as option in more of same power/weigh class as Centaurus/Sabre.
de Havilland wanted to make a follow on to Mosquito with Sabre but lack of production capacity at Napier prevented it; Vulture would allow that.

Griffon was installed in Spitfire only. Without the Griffon, my bet is the RR adopts water-alcohol injection for the Merlins in order to much improve the power.
Vulture on the Tornado does everything the Sabre did. The Fw 190 threat is negated with 2-stage Merlin in the nose of a Spitfire. Main advantage with a working 24 cyl engine that is available early is indeed with the naval aircraft, where practical reasons precluded 2-engined A/C so the big payload can be flown across long distances and with good/great speed. The alternative Fulmar with a 24 cyl engine would've been a sight to behold, even with a 1-stage engine and on 87 oct fuel.

 

[wuzak]

Griffon was installed in Spitfire only.

And the Firefly.

 

[Shortround6]

Thread was supposed to be about 24 cylinder engines. Not about V12s,V16s or V18s.

Trouble is they were not developed in a vacuum.

You had a variety of 24clinder engines from the Napier Dagger of 16.8 liters to the DB 606 of 67.86 liters and the Hispano-Suiza 24Y of 72.10 liter.
In some cases a 12 cylinder engine was a viable alterative to a 24 cylinder engine. It some cases only the larger or largest 24 cylinder engine would do.

The French had issued a specification for a transatlantic flying boat in 1936. They wanted an engine that would make 2000hp. The engine was still in development in 1938 and with the war production being a priority in 1939 big 24 cylinder was sidelined.

Of course big 24 cylinder engines were both heavy and bulky, but that is the price you pay for big power in 1938-1940.

A 24 cylinder does have some advantages over a 12 cylinder engine (or 14) IF the 24 cylinder engine uses smaller cylinders. There is supposed to be better cooling of the smaller cylinders and there is supposed to be better volumetric efficiency. This assumes the designers got their sums right. Just like the 24 cylinder engines were supposed to offer higher rpm (on the medium sized 24 cylinder engines). RR didn't get their sums right on the Vulture engine and the 3200rpm promise vanished into the night.

The rapid development of fuel on the allied side put all kinds of engine development in a state of flux. By 1941 you had 100/130 fuel which was offering the possibility of 30% higher power than 100 fuel (assuming the cylinders would stand up to the power and cylinders could handle the higher cooling loads) and since 100 octane fuel offered/promised over 30% more power than 87 octane fuel a lot of the engines that were still in development stages were put on back burners while existing engines were updated (Not all were).

If you are calling for service use (squadron use) in Sept 1939 you may have a a war winner on your hands. You might also have a mere footnote in history. If you tailor the engine design a bit too close to the 87 octane side of things the engine may be too light to take advantage of the higher combustion pressure levels and/or you may have cooling with using fuel at higher power levels.

The H-24 was supposed to be heavier and more complicated than the X-24 but the H-24 seems to have had less trouble with the crankshafts.

 

[wuzak]

The H-24 was supposed to be heavier and more complicated than the X-24 but the H-24 seems to have had less trouble with the crankshafts.

Not sure about crankshaft issues for the Vulture, but the master connecting rods were an issue, causing big end bearing problems.

RR didn't get their sums right on the Vulture engine and the 3200rpm promise vanished into the night.

It is interesting that the Peregrine, which was developed around the same time and had the same bore and stroke dimensions, was only ever rated to 3000rpm.

 

[Shortround6]

Rolls-Royce Vulture X-24 Aircraft Engine

Developed in the late 1930s, the Rolls-Royce Vulture X-24 was rushed through development and into service. As a result, the Vulture proved unreliable and was cancelled in favor of other aircraft en…

oldmachinepress.com

This seems to have been a good account.

The Bomber engines were down graded to 2850rpm at one point. But were allowed to run at 9lb to help make up for it.
Later 3000rpm and 9lb but this may have been done with 100/130 fuel?

For Tomo we have the problem that the Vulture was less than reliable even through much of 1941, Let alone Sept 1939.

A reliable X-24 in 1939 may have been a 1600-1750hp ?
And the Vulture was about 2300-2400lbs while the later Griffon was under 1800lbs (single stage)

Most (all?) of the 24 cylinder engines took 4-5 years develop and most of the short cuts (trying use existing engine parts) didn't see to work out that well.
I don't recall seeing anything that said the Peregrine upper end gave any trouble but the 'simple' idea that you could just 'graft' Peregrine cylinders and pistons to a new crankshaft and connecting rods certainly didn't turn out well.

RR never returned to the four throw crankcase preferring to use the H-24 design for any engines after the Vultures.

The American companies may have had more engineers to throw at problems.

 

[special ed]

How about Packard's X-2775?

Packard X-2775 24-Cylinder Aircraft Engine

The Packard X-2775 (1A-2775) X-24 was a light, compact, and powerful aircraft engine. Trouble with the Kirkham-Williams and Williams Mercury Racers prevented the engine from proving itself.

oldmachinepress.com

After reading about this engine used in two racers, what was the reason for lack of development? Was it the tight money in the depression? Apparently only two engines were used in aircraft while a third was used by Packard. The photos of the racers show the ability for a clean cowling while some more practical cooling design would be necessary. Was this an opportunity lost?

 

[cherry blossom]

The following 24 cylinder engines actually flew: the Napier Dagger, Napier Sabre, Fairey Monarch, Lycoming XH-2470, Rolls-Royce Eagle and Arsenal 24H (all H arrangements), the Rolls-Royce Vulture and Rolls-Royce Exe (X engines like the unflown DB-604), the Junkers Jumo 222, Dobrynin VD-3TK and Dobrynin VD-4K (all hexagonal), and the Daimler-Benz DB 606, Daimler-Benz DB 610, Allison V-3420 and Aichi Ha-70 (all built by coupling two V12 engines together).

Of those, the Napier Sabre, Rolls-Royce Vulture, Daimler-Benz DB 606 and Daimler-Benz DB 610 actually made it into combat. The Sabre was far the most successful and powered one of the best fighters of WW2, the Tempest, and one of the fastest prototypes, the Sabre Fury.

The Fairey Monarch is interesting because it was designed to be safe rather than to give the maximum power to weight and power to frontal area. It was basically two independent engines, either of which could function if the other was damaged, powering contra-rotating airscrews. The idea was to give twin engined safety to an aircraft that could land on a carrier without asymmetric thrust and whose wings could be easily folded.

My take is that each arrangement, H, X or hexagonal could work if enough resources were thrown at the problem. Certainly the late war Sabres and the 1951 VD-4K were excellent engines. However, because the need for engines giving 2,500 hp was only perceived rather late, only the Sabre made a significant positive contribution to its nations effort.

Edit: Should add the Packard mentioned above.

 

[tomo pauk]

It is interesting that the Peregrine, which was developed around the same time and had the same bore and stroke dimensions, was only ever rated to 3000rpm.

Trouble is they were not developed in a vacuum.

We can start from Kestrel (and later Peregrine) as base point.
Me, I'd probably want the H or W layout for a 24 cyl engine, those seem to be much more forgivable with bearings and crankpins than the X types. If the late Kestrel is used, we're looking at 42L engine of probably 1000 kg? It should be making, on 87 oct fuel, 2x745 HP at ~15000 ft, or almost 1500 HP. Plenty enough for a 12 gun fighter that can do close to 400 mph.
A 'W' take should be easier to make, the 'H' should be narrower.
Upping the notch and going with Peregrine as base, for 1941, gives 2x885 HP at 15000 ft IIRC, or 1770 HP. Combo of low-gear S/C and 100 oct fuel = 2000+ HP. Dry engine weight of 1100 kg?

 

[GrauGeist]

After reading about this engine used in two racers, what was the reason for lack of development? Was it the tight money in the depression? Apparently only two engines were used in aircraft while a third was used by Packard. The photos of the racers show the ability for a clean cowling while some more practical cooling design would be necessary. Was this an opportunity lost?

I beleive it was a missed opportunity.

The artical touches on the fact that the engines delivered at or above expectations - the only issue was the aircraft they were installed in.

I suspect that the engine(s) fell by the wayside simply because the USN was oriented more toward radial engines.

Now had the USAAC been involved, there's no telling what could have happened.

 

[Howard Gibson]

I wonder what difference is historically if RR cuts Peregrine and Griffon, rather than Peregrine and Vulture.

Is uprated Vulture* in Tornado sufficient to meet the Fw.190 threat if there is no Spitfire XII.
Spitfire does just fine with Merlins to end of its lifespan; Manchester can soldier on with Vultures, but that doesn't prevent Lancaster with 4 Merlins.

Fairey Barracuda and Firefly would enjoy additional power from Vulture; allows for earlier Spearfish
Tempest/Fury have Vulture instead of Griffon as option in more of same power/weigh class as Centaurus/Sabre.
de Havilland wanted to make a follow on to Mosquito with Sabre but lack of production capacity at Napier prevented it; Vulture would allow that.

*rpms are harder on bearings than boost, Vulture could probably make 15 psi on deck, but it will need bigger supercharger/faster drive ratios to take full advantage of 100 octane fuel

Why cut the Griffon? It was successful, and it was not troublesome.

The Vulture effectively was two Peregrine engines. I would assume that many parts were common to both engines. Problems certainly were too. You make both or neither. The Peregrine was too small for a WWII single engined fighter.

The British just loved Merlin engines, setting up plants in Derby (32,377), Crewe (26,065) and Glasgow (23,647). Ford of England made 30,428 in Manchester, and of course Packard Motor Car Company made another 55,523 in the USA. Around 5,000 Napier Sabres were built, at two sites, it appears. All sorts of aircraft were proposed as being suitable for Napier Sabres, but the engines were not available. My reference claims that the cost per horsepower of a Sabre was four or five times that of a Merlin. This makes it not very good for multi-engined aircraft like Mosquitos and Vickers Warwicks.

Old Machine Press: Napier H-24 Sabre Aircraft Engine

Would the Vultures be manufactured as rapidly as the Merlins? It was 42.5litres displacement, and its mass was 1210kg. I have it doing 1780HP at 2850RPM, for a BMEP of 1320kPa. 1320kPa is high for 87 octane, and low for 100 octane. I don't see this thing being as good as a Rolls Royce Griffon, or fitting in a Spitfire.

 

[don4331]

And I believe we have missed the, Hispano-Suiza 24Y and Arsenal 24H Arsenal missed the war, but it is a H-24 that flew.

Does the Fiat AS.6 count? The mid mounted supercharger supplies both engines.

 

[swampyankee]

Does the Fiat AS.6 count? The mid mounted supercharge supplies both engines.

Yes.

 

[don4331]

Why cut the Griffon? It was successful, and it was not troublesome.

The Vulture effectively was two Peregrine engines. I would assume that many parts were common to both engines. Problems certainly were too. You make both or neither. The Peregrine was too small for a WWII single engined fighter.

Because RR may only develop 2 engines. Kestrel doesn't need development and training aircraft don't need the Peregrine. Merlin or Vulture address every requirement of the Griffon.

Not sure if you are in the misguided camp which believes that the Vulture uses 4 Peregrine cylinder camp, or if you have been following W wuzak and my discussion on how the Vulture as almost but not quite the same bore spacing as a Merlin (so, Vulture cylinder block is about 2½" longer than Peregrine). The only parts from the Peregrine which might work in the Vulture are: sleeves, pistons and rings, intake and exhaust valves* and maybe some assorted bolts. Crankcase, cylinder blocks, crank, cams, reduction gear, magnetos, supercharger, carburetor are all unique to each engine. Peregrine has lots in common with the Kestrel, but it isn't identical.

*Ford 300 I-6 and 400 V-8 both have 4" bore and 4" stroke, but pistons have different compression heights/domes, rods are different lengths, valves are different sizes. So, nothing swaps between them. But they both bolt up to the same transmission.

 

[Spindash64]

I'm certainly no expert on mechanics, but a single crankshaft isn't all that and a bag of chips. You are attempting to fit twice as many piston connections per unit length as with a V-12. It's certainly possible, but the complexity of such an arrangement is arguably a bigger headache than it is worth

It seems safe to say the H-24 is the most practical way to get more power in a liquid cooled piston engine. While the Saber was not without its share of pains, it was still in production aircraft by 1943, which only German attempts at double engines can boast on the He 177, and the difference in weight and reliability heavily favors the H-block example here.


However, I'd argue this is a bit of a moot point: I'm not convinced that the monster engines offered enough of a power vs weight benefit over V-12s, or power vs frontal area vs radials, to justify much more development effort than they received in WWII. The Saber, the most successful of these engines, was around the same weight as the R-2800, which was also boasting equal or greater power late in the war on equivalent fuel. On the flip side, the Rolls Royce Griffon and Merlin 60 series, while not as powerful, were much lighter to install (the Griffon was a heavy engine by dry weight still, but had an advantage in wet weight, making it more practical to design a fighter plane to use than to use the Saber).

By the time 24 cylinder engines and 3+ row radial engines became feasible, Turbine engines had already made reciprocating engines obsolete for military aviation purposes, and I'm not simply referring to turbojets: the engine in the Westland Wyvern offered more then 3,500hp at a weight not significantly greater than a Sabre or "Big Cheese" radial, and this was a generation 1 or 2 Turboprop, roughly analogous to a J47 at most.