[jandrese]

The crazy part is that by modern standards they aren't really developing that much power. Sure this thing puts out 2,100 HP (using 130 octane gas), but it needs a whopping 46 liters of displacement to get that.

A Veyron engine puts out about half the HP using 17% of the displacement on worse gas. You can't even buy 130 octane gas anymore. The Veyron is a notorious fuel hog, but it has nothing on a twin Wasp radial.

[bigiain]

> A Veyron engine puts out about half the HP using 17% of the displacement on worse gas.

Not at 45,000’ altitude it doesn’t.

And that Veyron engine won’t be too happy running at 80+% of its rated power level for more than a few minutes at a time.

[userbinator]

And that Veyron engine won’t be too happy running at 80+% of its rated power level for more than a few minutes at a time.

This is the part that a lot of people are unware of when it comes to engine power ratings --- aviation engines are designed to run at their rated power continuously, while most passenger car engines aren't. Even comparing a truck engine with the latter has people confused at why the power numbers seem so small both absolutely and relative to displacement. A 9L engine in a truck used for pulling semitrailers may make "only" 330HP, but it can do that continuously, and indeed will spend the majority of its life at or close to full throttle.

[czch]

But the P-47 is on fairly high power the whole time it’s running. Most Veyrons will never use 50% of their rated power.

That being said, modern metallurgy really revolutionized ICEs. Followed by computerized control.

[Gibbon1]

Not my field but the other difference is 1500 hp at 2,400 rpm. The low max rpm is because it needs to match the propeller design speed and needs to be efficient at near full power.

[lovecg]

Couldn’t you gear down?

This whole discussion makes me think what would a modern maxed out aircraft piston engine be like!

[mannykannot]

These engines were, in fact, geared down, as was common (if not ubiquitous) in large piston aero engines. This video shows an epicyclic reduction gear inside the bell-like case on the front.

https://youtu.be/EyPvpdy4dgg?t=117

IIRC, piston speed was an issue in how fast these engines could run, as, for given RPM, the piston speed is proportional to the stroke. And, for reliability and the corresponding safety reasons, aero engines are more conservatively designed than most car engines.

[Merad]

If you're really interested in the topic look up the YouTube channel Greg's Planes and Automobiles. In addition to a deep dive series on the P-47 just a few weeks ago he made a video about late WW2 "super prop" fighters. They were the pinnacle of piston engine fighter performance, but they were all canceled because they weren't needed to win the war and everyone could see that jets were the future. We'd probably struggle to beat them even with modern technology TBH.

[pbronez]

The final incremental improvement before a revolutionary change is always an interesting place to look.

[lovecg]

Yeah it’s cool to think about how some technology might have developed if the economics didn’t make the evolutionary branch obsolete. I think that’s the appeal of steampunk fiction etc.

[linsomniac]

Gearing adds a lot of weight, and soaks up some power. Additionally, that weight tends to be at the front of the engine, so it can mess with the CG. You ideally want an engine that produces good power at rotational speeds that keep the propeller tips moving sub-sonic.

At least, that's what I found in brief investigations long ago when I was interested in the idea of a wankel rotary powered plane.

[plantain]

Gearing adds weight and complexity, and complexity brings unreliability. Best avoided where possible.

Putting car engines into recreational aircraft has been popular over the years, but never really 'took off', with high failure rates from being run at consistent power levels way past their design goals. The best conversions are high displacement naturally aspirated engines that end up looking remarkably like the existing Lycoming/Continental aviation engine installations.

[usrusr]

Not maxed out, neither in terms of size nor in terms of wartime-only tradeoffs along the lines of "it's ok when two engines blow up due to low error margins if the performance gains they enable allow four boys more to return", but the RED A3 hn-famous from driving the Otto Celera is a modern aircraft piston engine. Apparently the only one, if you ignore the occasional automotive adaption.

[jabl]

The 130 octane gas you refer to is actually 100/130 lean/rich avgas. Quite similar to the 100LL still used today.

Towards the end of the war the Allies were using 115/145 in fighters for even more oomph.

As for fuel consumption, those WWII piston engines actually were quite efficient, look up BSFC numbers if interested. Fuel load and range were critical issues. It took many decades, energy crises and computer control for car engines to catch up.