RR Merlin, Griffin and/or Vulture are 'double engines'?

If the Merlin, Griffin and/or Vulture were developed as 'double' engines along the same lines as the OTL Fairey Prince and Monarch, would this help or hinder their development?
 
If the Merlin, Griffin and/or Vulture were developed as 'double' engines along the same lines as the OTL Fairey Prince and Monarch, would this help or hinder their development?

The bigger it gets, harder it gets to find a suitable platform to use it. My pet 'project' would've been the W24 derivative of Kestrel - hopefully Typhoon and Fulmar can use it with it's ~1500 HP at 14500ft (eg. Merlin III was good for 1100 HP there, the Sabre, once debugged was at ~1800 HP there) on 87 oct fuel. A 2-speed supercharged version will do better at low altitude, and rating for 100 oct will also give exptra power. Twin Peregrine - 2000 HP on 100 oct fuel hopefully. New superchargers would've also improve power at all altitudes.
User might also be the the Fairey Battle, later the Barracuda and Firefly.
The W24 Merlin is size & weight of the DB 606 or the Allison V-3420, if not bigger if it features two crankshaft - where to install it? The 'Flugmotoren und strahltriebwerke' book is full of drawings representing W24 engines, derivatives of DB 601, 605 and 603, that is how far they got bar the He 177.

The vulture was a double engine

It was not.
 

hipper

Banned
[QUOTE="tomo pauk, post: 17553480, member: 92367]
It was not.[/QUOTE]

per wiki

The Vulture, in effect, was two Peregrines joined by a new crankcase turning a new crankshaft, producing an X engine configuration with a displacement of 42 litres (2,600 cu in). Although the Vulture used cylinders of the same bore and stroke of the Peregrine.

I’m not sure what a double engine is if the vulture is not one.
 
Sorry, double engine down separate crankshafts, rather than the single the Vulture was.
From what I understand every time this was tried it was a hopeless failure. The engines were prone to overheating and/or catching fire. The gear boxes also had a tendency to seize up as well.
 
From what I understand every time this was tried it was a hopeless failure.
From what I recall the Allison V-3420 was actually a pretty decent "double" engine of the type PMN1 described--having two crankshafts geared together to a common output. The engine itself, I think, was adequately reliable but none of the Aircraft it was intended for went into production so it was abandoned. Also, by the time it came around upgrades to the existing engines largely filled its performance gap and the early jets were becoming available to provide the next level of performance.

Still, I think the generalization of adding more complexity and moving parts to a powerplant ultimately reduces its MTBO and increases the chance of in-flight failure would apply. The idea of a Double-Merlin (etc.) is attractive but I just do not see a place for it by the time it would be developed. It would, I think, end up filling a place in history similar to the V-3420 and other late-generation Military piston engines: a promising idea that was a (half?) decade too late to be of use.
 
Double engines are a resort when a large enough engine is not to hand. Post WW2 we saw double Centaurus used in the Brabazon and Princess to get enough power until the large turboprops in planning came to production. The double Centaurus used angled shafts to separately drive the front or rear part of a contra rotating propellor. In flights they actually worked but there were not a lot of flights trialled for other reasons. Where earlier doubles fell down was in the installation, especially where the engines shared systems instead of being entirely separate.
 
Does the Rolls Royce Exe count as a double engine?

IIRC Rolls Royce made an X version of the Eagle in the 1920s. If I have remembered correctly, how successful was it?
 
'X' engines and true 'H' engines are not double engines. Otherwise we would be going down a road which made a 4 cylinder in line a quadruple engine as it is 4 one cylinder engines on the same crankshaft. 'H' engines are a trickier point. with two flat 12 engines with one crankshaft geared to one output shaft they are a single engine because all the bits always rotate together. The Monarch also had two flat 12 engines too but each had a separate output shaft to it's own propellor so worked independently and either half could be shut down at will.

The Daimler DB610 was more two separate(ish) Daimler DB605 engines in the same nacelle driving a single propellor through a shared gearbox.

One can think of an 'X' as a single crankshaft in a single crankcase with 4 water cooled inline 6 cylinder cylinder blocks/heads. In effect a 24 cylinder 4 bank water cooled radial engine. Except in the case of the Exe which was air cooled (and remarkably reliable).

Now a double RR Crecy would be a thing to behold but the Crecy design projections went so far down the turbo exhaust road that it became, in effect, a gas producer for a jet engine and it was easier to just make a jet engine for the same power. Not as economical in the early days though.

Post war the Double Mamba worked quite well for years.
 
The bigger it gets, harder it gets to find a suitable platform to use it. My pet 'project' would've been the W24 derivative of Kestrel - hopefully Typhoon and Fulmar can use it with it's ~1500 HP at 14500ft (eg. Merlin III was good for 1100 HP there, the Sabre, once debugged was at ~1800 HP there) on 87 oct fuel. A 2-speed supercharged version will do better at low altitude, and rating for 100 oct will also give exptra power. Twin Peregrine - 2000 HP on 100 oct fuel hopefully. New superchargers would've also improve power at all altitudes.
User might also be the the Fairey Battle, later the Barracuda and Firefly.
The W24 Merlin is size & weight of the DB 606 or the Allison V-3420, if not bigger if it features two crankshaft - where to install it? The 'Flugmotoren und strahltriebwerke' book is full of drawings representing W24 engines, derivatives of DB 601, 605 and 603, that is how far they got bar the He 177.
Your W engine ideas would have similar displacement to the 1944 Rolls-Royce Eagle, the last of their 4-stroke piston engines (the Crecy was later but that was a 2-stroke). Also, looking at the Eagle's Wikipedia page gives the answer to why a W (or X, or any other engine with a single crankshaft) layout wasn't used:
The Rolls-Royce design team realised that producing a scaled-up version of their Griffon V-12 engine would lead to excessively large combustion chambers and problems with detonation. The team concluded that a larger number of small cylinders would be the answer and considered an X-24 design. This layout had previously caused unreliability with the Rolls-Royce Vulture due to the need to fasten four connecting rods in a complicated arrangement to a common big end bearing.

The designers finally settled on an 'H' layout with two crankshafts and 'blade and fork' connecting rod attachments, the crankshafts being connected through the propeller speed reduction unit. The new engine followed the layout of the Napier Sabre and similarly used sleeve valves but with a simplified drive system.

Another very important piece of information can come from the Napier Saber's Wikipedia page:
Napier followed the Lion with two new H-block designs: the H-16 (Rapier) and the H-24 (Dagger). The H-block has a compact layout, consisting of two horizontally opposed engines, lying one atop or beside another. Since the cylinders are opposed, the motion in one is balanced by the motion on the opposing side, leading to no first order vibration or second order vibration.

So that is why the H layout was chosen despite it's complexity on paper: in reality the complexity of making bearings for 4 connecting rods (almost necessitating master-and-slave rods with their attendant limitations) and handling the increasingly severe vibrations as engines became more powerful meant much more difficulty in development, negating any simplicity. It was a major engineering achievement to get these engines to work even under the less vibration-prone H engine layout; the Eagle ran at 3,500 RPM and the Sabre ran at 4,000 RPM on WEP. A regular X or W engine without the H-engine's inherent balance would probably have shaken itself to pieces at that speed, with the vibrations being beyond the engineers' ability to fix using the technology of the day.
 
per wiki

The Vulture, in effect, was two Peregrines joined by a new crankcase turning a new crankshaft, producing an X engine configuration with a displacement of 42 litres (2,600 cu in). Although the Vulture used cylinders of the same bore and stroke of the Peregrine.

I’m not sure what a double engine is if the vulture is not one.

Vulture did not used Peregrine's blocks (cylinder spacing was bigger), crankcase, crankshaft, valve gear, supercharger & it's drive, reduction gear, acessory drive(s), connecting rods, bearings etc. Angle between blocks was 90 deg, not 60. All new vibration patterns that need to be adressed separately vs. Peregrine.
What it might have used were pistons and valves.
Authors of Wikipredia articles have many times tried to over-simplicate things, nothing new there.

From what I understand every time this was tried it was a hopeless failure. The engines were prone to overheating and/or catching fire. The gear boxes also had a tendency to seize up as well.

DB 606 was problematic, motly due to the exausts being too close to where excess oil will drip down. DB 610 was not due to improved installation, the Allison V-3420 was also okay.
 
The Daimler DB610 was more two separate(ish) Daimler DB605 engines in the same nacelle driving a single propellor through a shared gearbox.

One can think of an 'X' as a single crankshaft in a single crankcase with 4 water cooled inline 6 cylinder cylinder blocks/heads. In effect a 24 cylinder 4 bank water cooled radial engine. Except in the case of the Exe which was air cooled (and remarkably reliable).

Either half of the DB 606 or 610 could be run separately.
Lumsden notes that Exe 'suffered from a formidable rate of oil consumption'; FWIW.

Your W engine ideas would have similar displacement to the 1944 Rolls-Royce Eagle, the last of their 4-stroke piston engines (the Crecy was later but that was a 2-stroke). Also, looking at the Eagle's Wikipedia page gives the answer to why a W (or X, or any other engine with a single crankshaft) layout wasn't used:


Another very important piece of information can come from the Napier Saber's Wikipedia page:


So that is why the H layout was chosen despite it's complexity on paper: in reality the complexity of making bearings for 4 connecting rods (almost necessitating master-and-slave rods with their attendant limitations) and handling the increasingly severe vibrations as engines became more powerful meant much more difficulty in development, negating any simplicity. It was a major engineering achievement to get these engines to work even under the less vibration-prone H engine layout; the Eagle ran at 3,500 RPM and the Sabre ran at 4,000 RPM on WEP. A regular X or W engine without the H-engine's inherent balance would probably have shaken itself to pieces at that speed, with the vibrations being beyond the engineers' ability to fix using the technology of the day.

Both R and Napier used the same trick from the book - short stroke, and many cylinders per displacement. Gives high RPM without pushing piston speed to high. More RPM = more power. A 'W' engine with short stroke will run just fine. On the other hand, Germans managed with then-new, long-stroke Jumo 213 V12 turning 3250 RPM (allowed for 30 min in service) in 1944, while testing the Jumo 213J to 3700 rpm, while latest Allisons V-1710s were allowed for 3200 rpm on what is almost a legacy engine by 1944.
The Dagger went even higher with RPM - 4400, being a 16.8 liter 24 cyl engine, 3.75 in stroke. Before the ww2. Exe - 4200 rpm, X engine, 4 in stroke. Perhaps it was too bad that Napier didn't designed the Sabre with poppet valves instead of sleeve valves, so it's initial service use is more trouble-free than historically.

With that said, the H24 layout does look like a less of a hussle than X24.
 
More RPM = more power
True, but it also usually means higher fuel consumption from an engine with a given efficiency. Then again, it can be partially offset with a properly designed exhaust stack to gain intermittent jet thrust which can improve the Net Thrust Specific Fuel Consumption and gains more as the RPM increases (due to the increase thrust incidence) but designing effective jet stacks for a W, X, or H may prove to be more than a little problematic.

Of course, I have a solution, but that is a discussion for an entirely different thread and one which I belabored to death over the past six months elsewhere.
 
Twinned engines would be great for transports, bombers and maritime patrol. Use all cylinders for takeoff and climb. As fuel burns off, start shutting down half-engines to conserve fuel.
Restart all engines - as you return to base - in case you miss on your first approach.
 
Twinned engines would be great for transports, bombers and maritime patrol. Use all cylinders for takeoff and climb. As fuel burns off, start shutting down half-engines to conserve fuel.
Restart all engines - as you return to base - in case you miss on your first approach.
You could do a similar trick with a standard 4 engine plane though. The Avro Shackleton patrol aircraft could be flown on one engine with the other three props feathered. Maybe you get a bit more drag from four sets of props not two, but you also get a far simple installation, probably cheaper/faster maintenance and a bit more redundancy - if something goes seriously wrong in a 'twin' engine it probably takes out both halves.
 
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