Question about aircraft engines.

From the Wright Brothers first flyer to the pinnacle of piston-engine technology that was reached by the end of World War Two, aircraft engines advanced enormously in both absolute and power-to-weight ratio output. I was wondering why it was possible to build an internal combustion engine in 1945 that was so much more powerful than in 1905. Was it purely design driven, or were there ancillary breakthroughs such as in metallurgy, machine tooling, fuel or gasket technology that hand’t been available earlier? Was anything stopping anyone from building a Rolls Royce Merlin engine twenty years earlier?

Everything improved. Today, machining tolerances are so precise that the case halves of a Lycoming engine are mated with only 2 very thin silk threads as gaskets. And they don’t leak.

Machining and manufacturing. IIRC, the Wrights would have used whatever material was handy. Gasoline engines were still in their infancy. Between the automotive and aircraft industries, the entire field of engine design took off (so to speak) in the period 1900-1945.

Auto engines were less concerned about eight, but certainly drove (sorry again) the development of assorted technologies. Quality casting became very important. Consider every aspect of engine design - spark plugs and spark timing, fuel mixing, piston rings and sealing, bearings, balancing crankshafts for smoother running, coolant processes, etc. All these developed over the following century; auto makers have still being making advances. Fancier metallurgy allows lighter materials without sacrificing strength or reliability - but this sort of development came with experience and mass demand - a company could make its own parts economically instead of buying “good enough” off the shelf. The first engines, like the first everything, would have been over-engineered simply to ensure the risk of failure is much lower.

(I recall reading an article about - I think it was Australian - early aircraft pioneers who made their home-made combustion engine cutting sections of pipes for the cylinders, bolting them into an engine block configuration, etc. Not the optimum weight-to-power design strategy)

The engine in the Wright Flyer was quite crude. As you might gather they had a limited choice of aircraft engines available. The first useful gasoline engines were developed in the 1880s and hadn’t seem very much usage by the turn of the century. The Wright’s engine, designed by the bros. and one of their engineers wasn’t even up to the state of the art, but they were concerned with power density, they needed a lightweight engine. As md2000 states, the following demand for lightweight engines drove the industry.

The two world wars created a lot of incentive for advancement. Having the best air force meant the difference between keeping or losing your country. Without the wars the advance in engine tech might have been more sedate, though the civil market will still have driven it well enough.

So the best machine shop on the planet in 1915 couldn’t have built a Merlin, or at least not a crappy one?

The Wright Brothers had plenty of internal combustion engines to choose from, but every one that they looked at was too heavy. So they made their own.

To put it in perspective, the Wright engine was designed by two guys who owned a bicycle shop (plus a bit of help from a machinist friend), and it was basically built in their garage using nothing more than a lathe and a drill press. And even with that, it had a better horsepower to weight ratio than anything else on the market at the time.

Materials improved, designs improved, manufacturing improved, everything improved. The Wright Flyer engine was incredibly crude by modern standards, but engines of that type were in their infancy.

It’s also a really cool looking engine. I used to have a picture of it as the background of my computer at work. People would ask me what it was and I’d make them guess. Some people figured out that it was an early engine, but no one ever guessed that it was the Wright Flyer engine.

no, not easily. it’s not easy to machine an engine out of bulk material (e.g. an ingot) because of the need for complex cooling and airflow passages. and casting techniques back then were comparatively crude; castings were heavy and thick. So things like intake manifolds had straight walls and rather sharp bends like this example of the FIAT “Beast of Turin.” Airflow is crucial to engines making power* so all of those sharp bends and narrow passages just killed airflow. Plus, the Merlin had a pretty advanced two-stage centrifugal supercharger which would have been nearly impossible for people to even conceive of in 1915, nevermind build.

as an aside, the Rolls-Royce-built Merlin was a fairly crappy engine; their production methods were already pretty archaic even by then and each engine required a tremendous amount of hand-fitting by craftsmen. When Packard took out a license to build the Merlin in Detroit (as the Packard V-1640) they had to substantially re-design a lot of the engine because Rolls’s tolerances were far too loose for real mass-production.

  • as an example, the 2010 Ford Mustang had a 4.6 liter, SOHC 3-valve-per-cylinder engine which made 315 horsepower. the 2011 Ford Mustang had a revised version of the same engine, a 5.0 liter DOHC 4-valve-per-cylinder engine which made 412 horsepower. the reason? it wasn’t because it was 400cc larger; that won’t get you 100 horsepower. It was because of the cylinder heads. the 3 valve heads on the 4.6 had good intake airflow but the exhaust valve angle was shallow so the exhaust port had a rather brutal bend in it which killed airflow. the 4 valve heads on the 5.0 have a good straight shot into the cylinder, and a good straight shot out. Air flow is key. Air flow on that Modular engine gained 100+ horsepower. and the reason is pumping losses. the engine has to expend its own horsepower sucking air into and pushing air out of the cylinders. the easier you make those tasks for the engine to do, the more horsepower it can make.

What’s the difference between a Packard Merlin and a Rolls Royce Merlin?

The Packard has the oil on the inside. :).

There’s several questions hidden in there. Not sure which one you’re asking. In order from easiest to hardest:

Could a 1915 machine shop, given a set of 1945 plans and a pile of 1945 materials, have converted the materials into a fully as-good-as-1945 engine?

Could a 1915 machine shop, given a set of 1945 plans and a pile of 1915 materials, have converted the materials into a fully as-good-as-1945 engine?

Could a 1915 machine shop, given a set of 1915 plans for an existing real engine, a vague order for a V-12 of X bore and Y stroke and a pile of 1945 materials, have converted the materials into a fully as-good-as-1945 engine?

I think there’s not much hope for any of these. The saving grace with a Merlin, as jz78817 said, is that it was actually a pretty primitive sloppy design. Not 1915 primitive, but far below 1940 state of the art for basic machinery.

yes, I’m not an engineer or mechanic, but I’ve used a wrench and stayed at a Holiday Inn Express…

This was my impression; machining, casting etc. was in its infancy. When creating an automobile engine, the assembled gizmo was going to be built on a iron or steel frame and weigh over a ton, and the goal was to build an engine that would not fail catastrophically during the next few years (and sometimes that goal was achieved). As a result, everything was grossly over-designed; castings were, say, twice as thick as necessary. Piston rods, cylinders, pistons, the heads, crankshaft and bearings - weight was not a problem. Metallurgy was a developing science, so reliable castings could be a problem. With aircraft engines, the compromise between weight and strength had to settle out differently. When nobody else had flown successfully, what was available was pretty limited.

Even today - small aircraft engines are (much as they have been for over 70 years - built with a small central crankcase and bolt-on cylinders, rather than a giant cast block. Only extremely powerful engines like the Merlin had the power to life an aircraft that included that V12, and they were purpose built for that toward the end of the OP’s time period when large aircraft created that specialized demand.

As already described, technical advances over a broad front enabled this progress. Maybe it wasn’t possible 20 years before, but this depends on the exact assumptions made.

We can see similar advances in rocket engines. In 1959 Rocketdyne test fired the F-1 engine which was later used in the Saturn V. Such an engine was simply not possible 20 years before in 1939.

There is also funding. There is typically little demand for a technology at an early stage – whether aircraft engines, rocket engines, microprocessors or cell phones. This is regardless of whether the “demand” is free market or the result of a nationalized effort. Thus there is not a developed infrastructure and supply pyramid for the components and subcomponents. Also the manufacturing tools and test instruments and maybe even the tools to make those tools & instruments do not yet exist.

So it’s not a matter of a clever inventor puttering around in his tool shed, but requires a gigantic invisible technical and supply infrastructure which in turn requires development over a broad front and years of time.

IOW the Wright brothers in 1905 – even if given 1940 plans and component materials for a Merlin engine – could probably not build and test it, nor could they afford the team to even try that.

However your question states several different dates, and the WWII-era covers a significant span during which technology was rapidly progressing. So the feasibility of earlier production of a more advanced aircraft engine depends on the exact dates and assumptions.

In a hypothetical scenario where a 1915 Apollo-scale, top-priority national effort was undertaken to build a Merlin engine within 10 years, they definitely could have built a powerful aircraft engine by 1925 – we know that because without that hypothetical scenario it had already been accomplished. In 1924 Wright Aeronautical Corp. began development of the supercharged P-2 engine which was flight tested at 500 hp.

As early as 1916 (just one year after your 1915 date) the Royal Aircraft Factory tested a 14-cylinder 300 hp radial engine. It was co-designed by Samuel Heron who invented the sodium-cooled exhaust valve: Samuel Dalziel Heron - Wikipedia

OTOH “WWII-era engines” span a wide range of sophistication. Your question was really broader then the Merlin engine – that was just a “for instance”, which drew a of of comment. The Merlin V12 engine was designed in the early 1930s and first run in 1933. So this lessens the technological leap required from, say, 1915. Given sufficient funding and priority starting in 1915, it is conceivable something close to the Merlin might have been developed by 1925 – which was only eight years earlier than the Merlin was actually first run.

However a more advanced late-WWII-era piston engine was the Pratt & Whitney R-4360 Wasp Major.

Even if provided schematics from the future, I doubt 1915 technology could have manufactured, assembled and tested that even if funded as a top national effort over 10 years from 1915 to 1925: