[rbanffy]

> I can endure buggy software but I don’t want to deal with buggy planes

A plane built for resilience against defective engine components would be very different from the airliners we fly today. I would assume more engines for redundancy, better protection against catastrophic failure, different designs to allow engines to function even if parts flew out, and so on. It’s an interesting design exercise to build from radically different expectations from the fundamental parts.

Alternatively, a far less radical redesign would be turbines running at a much more forgiving regime feeding electric motors.

[coderenegade]

The philosophy in aerospace is more to build a better engine rather than to have more engines, and this extends to every aspect of aircraft design. Engines are already built to contain catastrophic failure, and the planes themselves remain functional for all but the most extreme situations. We're at the point where essentially every lost aircraft is a compound failure, with significant human factors contributing to the event. It's likely that we're on the pareto front of what engineering can reasonably accomplish, and the only gains in safety either barely nudge the needle of what we would notice (better materials, say), or difficult for the market to accept (removing pilots altogether).

Aerospace RND has been looking into hybrid propulsion systems for a long time. If there's one thing they aren't shy about pushing, it's the ability to go higher, faster, more efficiently. Such systems aren't used because they aren't yet good enough.

[nradov]

There's no reason think that removing pilots altogether would enhance safety. Military experience has shown that mishap rates for unmanned aircraft are significantly higher than similar crewed aircraft. Routine flight operations can be automated pretty well now but where human pilots really earn their pay is with handling emergencies and other unexpected situations. The variety of potential emergencies is effectively infinite so it's simply impossible to write and test code to handle them in advance. Instead pilots have to improvise in real time based on intuition and first principles logic. Current AI technology still isn't capable of that.

[coderenegade]

When I last looked into it (admittedly a number of years ago now) this was true for remotely piloted aircraft, but there wasn't enough data on systems that pilot themselves with humans doing the navigating.

I'm not convinced that humans are particularly effective in emergency situations, especially when they're expected to go from monitoring systems that work 99.99% of the time, to suddenly aviating with alarms going off everywhere. I guess there's not really much of an alternative as it currently stands, but seeing how effective agentic AI is at chewing through data and analyzing systems makes me think that eventually, such systems will be used if they ever get to the necessary level of reliability.

[nradov]

LLM based agentic systems can never meet current FAA certification requirements for civil aircraft. The problem is that the internal logic is essentially a black box and there's no way to verify that it won't go off and do something totally bizarre in an unpredictable way. Now you could argue that human pilots are subject to the same limitation, and there have been a few cases where humans have intentionally crashed airplanes, but we have an intuitive model of how other human minds work and in an emergency you can depend on human pilots to at least try to save themselves.

[coderenegade]

It would depend on what the data says. By the time putting such systems into civil airframes is even a conversation, there will be an enormous amount of data generated by unmanned systems and military vehicles. If the data shows that a given system is acceptable, I don't see any reason it wouldn't be allowed.

That's not the same as saying that current architectures are acceptable, because clearly they aren't. But both neural net and stochastic controllers have been tested in aircraft since at least the 1990s. Probably earlier, but that's as far back as my knowledge goes, anyway. I don't know of any neural nets doing active control type tasks, but I don't see any intrinsic reason they couldn't be used as long as you can show that they're good enough.

[nradov]

No, you're missing the point. You can't demonstrate safety regulation compliance with data. The entire avionics software development process has to be structured from the start to allow for validation.

Military experience, especially with unmanned systems, is largely irrelevant. They operate on a different set of rules and are generally willing to accept a higher level of risk in order to accomplish the mission.

[mrmlz]

Lol.

Do you think todays aircraft are not designed with the idea that the engine can fail?

And if you have unreliable components do you think redundancy is going to save you?

And lets be real - there already exist a aerospace arena where you have a higher number of CAT-events - it's called the military. And they deal with it by having a parachute for each passenger..

No - in effect building jet-engines (that are commercially viable i.e. fuel and efficeny) is not a easy to disrupt business. And the cost of entering it would be - high. And the benefit, well less obvious.

[rbanffy]

> Do you think todays aircraft are not designed with the idea that the engine can fail?

Of course they are - but the engines are also designed to be extremely reliable, and that's why you get away with two engines on long flights over water, something previously only available for planes with four engines.

> No - in effect building jet-engines (that are commercially viable i.e. fuel and efficeny) is not a easy to disrupt business.

That's true. My point being that building a better jet engine might be the hardest way to disrupt the business - making a better propulsion system, which might or not include a jet engine, is a less difficult approach. If you have an electric plane with two motors, a big APU-like turbine charging a battery and powering the motors, you might get away with a cheaper turbine, running in less extreme regimes, and still have a more fuel efficient plane requiring less maintenance than a pure turboprop would.

You don't win a stacked game by playing it by the rules. You win by changing the game to another one you can actually win. China did that with cars already.

[coderenegade]

Aerospace as a discipline has tried just about every propulsion system under the sun. What you're proposing has already been flight tested on an unmanned vehicle, albeit with many smaller props for a larger effective prop disk than the two you're proposing. This is actually better, because electric motors want to use rpm control, so you need to keep the moment of inertia of the propellers low. The efficiency penalty of smaller props is overcome by having many of them arranged closely together to create a large effective prop disk.

For a hybrid system to be worth it, you need to claw back more efficiency than you lose in going from mechanical energy to electrical energy, and then back again. For cars, this is generally the case, because they're always accelerating and decelerating. Their wide operating band means that the engine will always be a game of compromises, which is why sticking a motor and battery in the loop and decoupling the engine from the wheels is beneficial. But planes aren't like that; they go from setpoint to setpoint, and they stay in a given configuration for long periods of time. They have very narrow, highly optimized operating bands, so hybridization just isn't as effective.

[rbanffy]

> For a hybrid system to be worth it, you need to claw back more efficiency than you lose in going from mechanical energy to electrical energy, and then back again.

For short-haul you spend a lot of time climbing and descending in relation to long flights, so the plane spends less time at the optimum the engines were designed for (cruise), so, if the power unit can be at the peak efficiency throughout the flight, with extra energy being supplied by the onboard battery for take-off and the power unit be shut down for descent, we might get to a point where it's economically viable, depending on battery operating costs and weight.

You are right to point out the aerospace industry has tried everything conceivable to see what sticks, but technology evolution sometimes throws us a curveball.

[coderenegade]

It's unlikely; the energy density just isn't there, even for a hybrid system. Because of the way flight profiles work, you're still talking about enough battery to provide meaningful power for half a flight, which probably isn't feasible in the near term.

And it's not like the industry has missed this possibility. I've seen papers on systems as exotic as combining high temperature fuel cells (SOFCs, PCFCs) with the Brayton cycle to achieve a hybrid powerplant. The bar for novel propulsion systems in aerospace is extraordinarily high, higher (imo) than it is for automotive. The exception is unmanned systems, which are new enough and varied enough that there's been an explosion of activity, which has been exciting to see.

[londons_explore]

> If you have an electric plane with two motors, a big APU-like turbine charging a battery and powering the motors, you might get away with a cheaper turbine, running in less extreme regimes, and still have a more fuel efficient plane r

This works for hybrid cars because the power demand when driving varies widely, as does the output speed. The 'hybrid' bit gets huge gains by always running the engine at optimal rpm+throttle, and using the battery to cover peaks and absorb troughs (regen).

A plane cruises for many hours at a fairly constant speed and throttle, which is designed to hit peak efficiency of all components. The 'hybrid' design therefore falls far behind on weight, efficiency and cost.

[rbanffy]

> A plane cruises for many hours

This is why short-haul flight will be the first to adopt hybrid propulsion.

[londons_explore]

There are already some trials with very short flights - ie. Sub 25 miles.

Used for getting between islands for example

[nradov]

That's correct to an extent. It could never work for long haul flights due to the weight penalty but there is potential for regional flights. Current airliner turbine engines are sized to deliver enough thrust to safely take off and climb even if one engine fails. In theory the necessary excess thrust could be delivered by a hybrid system during critical phases of flight. We might see that for flights like SFO to LAX in a few decades.