It lets you run comparatively higher manifold pressures than an otherwise identical but unleaded fuel.
Like, Mazda is running 14:1 compression ratios in gasoline engines, but 7:1 is considered normal for a naturally aspirated Lycoming and it'll often dip into the 6's for turbocharged versions.
Cessna has the best selling model of airplane of all time, the 172, which has sold around 45K units since its introduction in 1956.
Mazda sells that many cars in a typical 2 month period. It’s no surprise that there’s more non-recurring engineering investment in car engines than airplane engines.
There have been tons of advances in general aviation, look at panel technology between now and 15 years ago. That's awesome! Let's do the same thing but for engines now. But it isn't going to happen as long as no one is pushing for it; we have the efficiency in automobiles we do now because regulators have been pushing for better fuel consumption and lower emissions for decades. It'd be great if there was similar pressure applied to aviation.
I'd love to have a 172 that had no mixture knob and no issues with hot starts. Man, wouldn't that be awesome? This is what we should be asking for, not apologizing for why we're stuck with mechanical FI, carb heat, and shock cooling worries.
If Lycoming or Continental spend $25M on a new engine program and sell them for 15 years in all 172s, it’s around $22K per airplane or around 550 basis points. When investments in engine development are over 180x more expensive on a percent of sales basis and over 2000x as expensive on a per-unit basis, it’s unsurprising that few companies are stepping up to do that development.
I don’t mind at all if you want to lobby for it; I think there are improvements that could be made, but I think you’ll find the economics daunting and the current engine tech to be pretty well matched to the application.
_Certifying_ them is hilariously expensive for the manufacturers and users.
One can certainly fix that, but that's how it is. Main reason why the planes that consume automotive gas the most are in the 'experimental' category.
Plenty of 100+ octane unleaded fuels out there.