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

[tomo pauk]

The 18 cylinder engine I have in mind would be of a 'broad arrow' layout, similar to the Napier Lion - 3 banks of cylinders, but, contrary to the Lion, each bank would have 6 cylinders. What would be the major engineering hurdles to achieve a reliable powerful engine - crankshaft crankpin layout possibly? What advantages disadvantages would it made vs. the V-12s of increased swept volume - more RPM due to smaller cylinders (=more HP), but for increased frontal area?
In case of timely success: where to install them 1st?

 

[Shortround6]

Several companies had already been down that road in 1930s. Formost may have been Issota-Fraschini

Granted two of the pictures are boat engines ( and the British used them in their pre-war MTBs) They used articulated rods but one of the big hang ups may have been intake and exhaust manifolding.

The French Farman and Lorraine companies dabbled with 3 bank engines although they may have stopped at the W-12.

http://www.aircraftengine.cz/Krakow/slides/Farman 12 WE (2).jpg

I have no idea what that 6 bank 24 cylinder engine is

 

[GregP]

I think they could have been produced. The issue would seem to be one of 1) design so the weight was optimal for the engines available, or 2) add engine complexity, weight, and power to make up for the lack of ability to come through in 1) above.

I think the end result would be better with the 18-cylinder unit than with an additional second V-12 added to the first, but the development time, if started in, say. 1942, might mean it would never fly during the war. So, it probably would have had to have been started in the mid to late 1930's to get operational examples in purpose-designed airframes. It might also have stimulated contra-prop development to take advantage of the added power without excessive diameter.

Another possbility is the tandem engine, as in the MC.72 and the French Latecoere Late 299A, which had the engine and transmission layout of the later Arsenal VB-10. It offers the added benefit of a second engine to get home fter one is unserviceable, but comes at a weight and length price. Probably the 18-cylinder unit would have resulted in a better fighter aircraft. Not too sure if a heavy trwin or a big bomber though.

An interesting premise that didn't get developed but WAS tested, at least in layout, before WWII. That they elected NOT to pursue it might give some indication of the complexities involved.

 

[nuuumannn]

I have no idea what that 6 bank 24 cylinder engine is

It's an Argus AS 5. I have a photo of that engine somewhere...

Argus As 5 Aircraft Engine | Old Machine Press

 

[wuzak]

It's an Argus AS 5. I have a photo of that engine somewhere...

Argus As 5 Aircraft Engine | Old Machine Press

Jumo 222 too

 

[Shortround6]

Thank you.

While looking through the website I quickly found this

http://oldmachinepress.files.wordpr...usc3a9e-de-lair-et-de-lespace.jpg?w=625&h=434



AN 18 Cylinder Hispano intended for the Schneider cup.

 

[nuuumannn]

18 Cylinder Hispano intended for the Schneider cup.

interesting, what was it going to be put in? It's the Schneider Trophy, SR; it's not a cup, see?

 

[WJPearce]

Much like Xs, there have been a number of W-18s, but not many (perhaps none) have met with success. I think the most successful broad-arrow layout would be the Lion (of course a 12-cylinder). The most successful W-18 would be the Isotta-Franschini Asso 750/1000 series that SR6 mentioned. Like the Lion, the IF engine continued on in boats long after its time in aircraft had ended (I think some IF W-18s are still running).

In the US after WWI, the US Engineering Division built a W-18 called the W-1 (Glenn Angle was the head designer I think), but it suffered from serious problems. The French developed a number of W-18s, I think more than anyone else. The Hispano-Suiza W-18 (for the Nieuport-Delage NiD-450/650 and Bernard HV140) has already been mentioned. Farman (inverted W-18 and a T-18), Lorraine, Renault, and others also made W-18s. Even Russia built up a W-18 or two (and also Y-18s).

By the early 1930s, it seems everyone moved on and there were no more W-18s. I think that tells you something right there. A number of companies tried a W-18, but none really succeeded. The W-18s seemed to fill a special moment in time when more power than what a V-12 could offer was wanted. Once V-12s made more power, there was no longer a need for W-18s. A Merlin-based W-18 would give you an engine too big to fit in a fighter, and for a bomber, why not use a R-2800 and do away with all that liquid-cooling stuff?

One would think a W-18 engine would offer 1/3 more power than a V-12 while maintaining a fairly compact package and relative light weight. But historically speaking for aircraft, W-18s have been a developmental dead end. At least, that is the way I see it.

 

[tomo pauk]

Thanks for the feedback, gentlemen. The I-F Asso 750 was one of the rare engines to produce 900 HP on modest weight (1460 lbs (dry)) in early 1930s. Some indeed are still running - in tractor pulling In inter war period, the Asso 1000 (1800 HP in racing trim) was used in Schneider trophy in 1929.

Hi, Bill,

Once V-12s made more power, there was no longer a need for W-18s. A Merlin-based W-18 would give you an engine too big to fit in a fighter, and for a bomber, why not use a R-2800 and do away with all that liquid-cooling stuff?

One would think a W-18 engine would offer 1/3 more power than a V-12 while maintaining a fairly compact package and relative light weight. But historically speaking for aircraft, W-18s have been a developmental dead end. At least, that is the way I see it.

Quirk is that some countries never have the opportunity to use the R-2800. Many of them squandered material and human resurces (not to mention time, a crucial resource) to build anything from 24 to 42 cylinder engines that never took flight, or were used after protracted development and number of modifications.
Some might-have-beens: Jumo 211 as a basis, skip 222 and 213 - LW has a 2000 HP engine in 1943. Or similar engines based on DB-601/605 (forget the 24-cylinders).
The Merlin-based W-18 - maybe a better bet than Vulture? Or, Napier builds a W-18 after W-12 (Lion), instead of H-16 and H-24 engines? Either RR's aor Napiers, those should make fine powerplants for Hawker heavyweights, as well as for FAA needs. The R-2800 was never sought-after thing for UK-made aircraft (unfortunately, if I may add), since they have had 3-4 (more?) of their engines of 1800-2500 HP in the works even before the USA entered the war.

 

[Shortround6]

Some problems might be more theoretical, but trying to get an even firing order? what angle/s between the banks gives an even firing order? Now try to get the cylinders to fire in a pattern that puts the least stress on the crankshaft.

Engine weight will not go up by 50% but there is more than adding just a cylinder bank as the crankcase and crankshaft will need to be heavier. Intake manifolding could be a real headache depending on country and design practice. Germans with fuel injection just have to worry about getting the same amount of air to each cylinder. Americans and British have to worry about the correct mixture to each cylinder. Italians and French can wind up with NINE carburetors to deal with. Then you have the exhaust manifolds. American, British and German V-12s were fairly neat, Intakes inside the V, exhausts outside. The W-18 needs an exhaust and intake sharing the same between banks space. Not as much of a problem for the French and Italians as they usually kept both th e intake and the exhaust on the outside of the V and shared space( the better to get at the carbs ?)

The "idea" behind the DB 606/610 (and the Allison V 3420 and a few others) was to use existing crankshafts/crank cases, conrods and just have to develop the reduction gears. Turns out that it was a bit more complicated than that but compared to developing all new bottom end parts?

 

[tomo pauk]

Some problems might be more theoretical, but trying to get an even firing order? what angle/s between the banks gives an even firing order? Now try to get the cylinders to fire in a pattern that puts the least stress on the crankshaft.

The Italians seem to have the firing order and angle between the banks in good order, they were racing with W-18s in 1929, and making (attempting?) record flights in early 1930s

Engine weight will not go up by 50% but there is more than adding just a cylinder bank as the crankcase and crankshaft will need to be heavier. Intake manifolding could be a real headache depending on country and design practice. Germans with fuel injection just have to worry about getting the same amount of air to each cylinder. Americans and British have to worry about the correct mixture to each cylinder. Italians and French can wind up with NINE carburetors to deal with. Then you have the exhaust manifolds. American, British and German V-12s were fairly neat, Intakes inside the V, exhausts outside. The W-18 needs an exhaust and intake sharing the same between banks space. Not as much of a problem for the French and Italians as they usually kept both th e intake and the exhaust on the outside of the V and shared space( the better to get at the carbs ?)

Thanks for that.
The mixture distribution seem to be one of Vultures non-problematic things, that for 24 cylinders. How well it worked for the 3+ meter Chrysler V-2200, supercharger being at one end of the engine? Napier also got mixture distribution right for the 4-bank Sabre, again that being one of engine's non-problematic 'items'.
The W-18 needs a well executed exhaust of the mid bank, the side banks can do exhausts in classic layout.

The "idea" behind the DB 606/610 (and the Allison V 3420 and a few others) was to use existing crankshafts/crank cases, conrods and just have to develop the reduction gears. Turns out that it was a bit more complicated than that but compared to developing all new bottom end parts?

We can take a look at what DB was experimenting with,here; besides the V-12s in different 'flavors' (granted, the 'power' part of the engine was pretty much inchanged), there was the X-24 and V-16. The W-18 will be easier to install into in-production airframes than double V-12s for most of the countries

 

[Shortround6]

Angles varied

Sorry but I can't seem to bring over the photos from "old machine press"

The Hispano engine was planned for 2400rpm but as in installed in the Schneider trophy racers it was limited to 2000rpm. What you can get away with for imbalance or slightly out of wack firing orders at 2000rpm is NOT what you can get away with at 2700-3000rpm. A V-12 has one cylinder firing every 60 degrees of crankshaft rotation and this can easily be done with a 60 degree V and 6 crank journals even if not all engines follow the same firing order. An 18 cylinder engine needs to fire a cylinder every 40 degrees and this gets a bit harder on a W -18, you need either 40 degrees between banks or 80 degrees. You still only have 6 crank pins so firing options are limited especially as all the cylinders are in 160 degrees or less of the crankshaft rotation. In other words with a 4 degree bank angle when the first "row" of cylinders has the middle cylinder at top dead center the flanking cylinders will be at either 40 degrees before TDC or 40 degrees after TDC. Now they don't have to be on the compression or power strokes but there are limits to the options. A 40 degree bank angle makes for some congestion between the banks and the 80 degree angle makes for wiiiiide engine. Maybe OK for bombers, not so good for fighters. Trying for the 60 degree bank angle leads to some cylinders firing closer together than others as the crank rotates. Some V-12s have been built with other than 60 degree angles and worked well but the crankshaft and crankcase have to be designed accordingly to handle the greater torsional vibration (twisting effect on the crankshaft). The W-18 could use other cylinder bank angles but it is one more thing to sort out.

 

[GregP]

The race reward was variously called the Schneider Prize, Schneider Trophy and Schneider Cup with almost equal frequency. Anyone who followed the series would recognize any of the three terms. Here's film clip that calls it the Schneider Cup.


View: https://www.youtube.com/watch?v=194UlnSpBBo

There are various film clips calling it the Prize and the Trophy, too.

Technically, I think Shortround is correct in that the proper term was the Schneider Trophy, but the three terms were used intrerchangeably in newspapers, magazines, and the press of the day, so I believe we'll all know what you are talking about in here if you use any of the three terms. Since they were all used with frequency at the time, it doesn't make sense to call any of them "wrong" today.

I have seen one writeup where the author, I forget who it was, said the money was the Schneider Prize, the trophy was the Schneider Trophy, and the series was the Schneider Cup, but I only saw that once some years back ... and didn't save it, so I can't give a reference for it. I may uncover it along the way somewhere, but maybe not, too.

I'll probably stick with Schneider Trophy in here to be more proper, but won't kick if I see the other terms used.

 

[wuzak]

The mixture distribution seem to be one of Vultures non-problematic things, that for 24 cylinders. How well it worked for the 3+ meter Chrysler V-2200, supercharger being at one end of the engine? Napier also got mixture distribution right for the 4-bank Sabre, again that being one of engine's non-problematic 'items'.
The W-18 needs a well executed exhaust of the mid bank, the side banks can do exhausts in classic layout.

Basically the X-24s could be treated as a pair of V-12s. So, in that sense, the Vulture was no more challenging for mixture distribution than the Merlin. The supercharger had two outlets, feeding either the upper or lower pair of banks.

The Sabre had 4 outlets to it supercharger, feeding each of the banks.

 

[tomo pauk]

Thanks for the Vulture tidbit. My point was - divert the mixture from supercharger into 3 inlet manifolds instead in 2 or 4.

 

[wuzak]

To add to what I said earlier, the Vulture's supercharger discharges were 180° apart, pointing, more or less, directly to where the mixture had to go. In teh Sabre they were 90° apart, pointing, again, to where they needed to go.

With a "broad arrow" layout, I am not sure that the three supercharger outlets can be placed so that they point, basically, where they need to go. And if that was done, it would, without doubt, place an inbalance on the discharger pressure/mass flow between the pipes because of the different flow path lengths in the supercharger. But if you place them equally you are going to have at least one pipe facing in completely the wrong direction, requiring longer intake piping and, thus, an impact on the mixture distribution.

 

[Shortround6]

And on the center bank off a W-18 you are dodging an exhaust manifold. The Hispano and Isotta engines used a design were the outer banks had both the intake and exhaust on the out side of the engine. Perhaps teh center bank had both on one side or not, photos are hard to see. But taking an existing V-12 with ports on opposite sides of the head and trying for the 40 degree angle seems difficult.

 

[WJPearce]

Hello Tomo and all,

I referenced the R-2800 because I figured it would have the same power output as my imaginary three-bank Merlin. My point was that by the time you design another bank onto a V-12, you may find that there are existing power plants (or those in the advanced stages of development) that would have the same output.

There are a great number of developmental dead ends in engine design. The fact that high-power piston aircraft engines are almost exclusively Vs or radials is not because nothing else was tired. I think two-crank Hs and also some Xs were the next step and did not present some of the issues that Ws had.

Both of the I-F Asso 1000-powered M.67s did not finish the 1929 Schneider race. While the engine was not 100% of the reason they dropped out, it did have issues. The official name of the Schneider deal was "Coupe d'Aviation Maritime Jacques Schneider." While you get a trophy, the "Cup" part comes from "Coupe." In addition to the three names GregP mentioned, it has been regularly called the Schneider Contest and Race. Trophy, Prize, Cup, Contest, Race.... as long as it has "Schneider" in front, I think we all know what we are talking about.

By the way and a bit off topic, have you ever thought about how Napier never built a "conventional" aircraft engine? They made W, X, Hs, opposed piston, two-stroke diesel and used sleeve valves and a form of turbo compounding. Napier makes everyone else look conservative.

 

[wuzak]

Napier Javelin!

A 3 bank Merlin may only be as powerful, or only slightly more powerful than an R-2800. It could, possibly, be heavier than an R-2800.

A 4 bank Merlin (H or X) should comfortably exceed the power of the R-2800.

A developed Vulture would certainly out-power an R-2800. In 1941 the Vulture was testing at 2500hp, and it was far from sorted at that point. Meanwhile, the R-2800 was an 1850hp engine at that point (may have been testing to 2000hp).

 

[Shortround6]

The trouble with test numbers is that the test conditions have to be spelled out. A P&W development engineer pushed an R-2800 "B" series development engine to 3500hp (or more?) briefly in 1944/45, A "friendly" rivalry with the R-4360 development team may have been involved. The engine didn't 'blow' but P&W changed just about everything in the engine (already well in progress when this 'stunt' was pulled) in order to provide service ratings ( non War emergency) over 2000hp. We know R-R ran the 'speed' Merlin at 1800hp in 1938 (or 1600hp for 10-15 hours?) yet beefed up crankcases and other parts before approving significantly lower power levels for service use.

The idea behind the H engines (either vertical or horizontal )was they made the most use of 'common' parts and going from a 60 degree crankshaft to a 180 degree crankshaft posed less difficulty ( in theory) than putting 3 or 4 cylinders on each crankpin. Most H 24s proposed during or after the war ( French were big on H 24s , both Hispano Suiza and using Junkers 213 cylinder blocks) used two 12 cylinder superchargers further cutting down on development risk.