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Comment by gregschlom | Hacker News Reader

Ok, but so what? Is there something bad about diesel engines?

Nothing is inherently bad but diesels tend to be heavier for the power they make. And there's a fairly well understood weight vs reliability tradeoff. Light an unreliable is bad for airplanes and so is heavy and reliable. You want light and reliable, ideally.

This is far lighter and significantly different from your usual diesel, though. It's an all-aluminum design and weighs 250-300kg. Heavier (for the same power) than competing turbine engines (like, say, the ubiquitous PT6?) Sure, absolutely. Crazy heavy? Nah. The entire thing probably weighs somewhere around 2000-3000kg (veeery roughly) if I had to guess. So the extra 100kg or so isn't a total dealbreaker, if they can make it up elsewhere.

Very interesting aircraft for sure. I'm still skeptical, but hoping it works out, and rooting for them!

Some discussion on its claims to fly at 65,000 feet here: https://www.beechtalk.com/forums/viewtopic.php?f=49&t=174467...

It is a V12. Historical military V12s had a feature of two bank redundancy. One row of 6 cylinders can be shut down along with its pumps, cooling, etc.

And I have a big suspicion that they use two of these engines inside.

V* engines share a common crankshaft with both banks, that's the V part. Please cite any specific V12 aircraft engine that can have one bank of cylinders shut down. I don't believe one exists.

>Please cite any specific V12 aircraft engine that can have one bank of cylinders shut down.

The RED A03 Engine[0], which is what this sub-thread is about.

>Two cylinder-bank redundancy concept for high safety.

>Robustness and safety are incorporated into the engine design. The two 6-cylinder banks are capable of independent operation. All critical engine sub-systems are mutually-independent.

[0] https://red-aircraft.com/

Except the crankshaft...

Oh, and any mechanical issues with pistons or valves in one side will jam the crankshaft, therefore stop the other half working...

And that crankshaft needs some kind of oil... And a pump to pressurize that oil. And if a leak forms anywhere the oil drains out and the crankshaft seizes. Pretty hard to lube one crankshaft with two redundant and isolated oil systems...

Overall, I'd call the engine 1.5x redundancy...

Agreed. Based on the documents, I also don't see any protection against metorites or the sudden loss of oxygen in the planet's atmosphere. That's not even 1x redundancy really.

Most V engines can operate this way -- obviously not at full power. GM, Daimler, Honda, and FCA do this on some of their production v6, v8, and v12 engines. It is not that difficult to skip some cylinders, engines have a lot of rotating momentum.

https://en.wikipedia.org/wiki/Multi-Displacement_System

https://en.wikipedia.org/wiki/Active_Fuel_Management

https://en.wikipedia.org/wiki/Active_Cylinder_Control

https://en.wikipedia.org/wiki/Variable_Cylinder_Management

There is a huge difference between being able to operate in a managed cylinder deactivation mode vs being able to operate when one whole bank is experiencing some kind of catastrophic failure.

True, I was addressing the question at face value.

Of course the crankshaft is shared. It is oil, fuel, and cooling that can be shut down to prevent leaks.

Although I can't find a reference to an aircraft engine, Chrysler did have a variable displacement tech on its third gen Hemi engines that could turn off one bank of the V8.

Ref: https://en.wikipedia.org/wiki/Multi-Displacement_System

I don't know much about aircraft engines, but in fact straight-6 engines are inherently balanced, and a V12 is fundamentally two straight sixes, so at least in theory it would be quite possible to stop using one bank of cylinders if some of their cylinders suffered some form of non-catastrophic failure.

Not at all, without question it's a superior fuel to leaded avgas.

It has higher energy density, higher flash point (less prone to fire or explosion), less volatile (doesn't evaporate as quickly), and less toxic.

However, it's difficult to make a diesel that gets as much power/weight or power/volume as a comparable petrol engine.

There are trade-offs. It's not a universally superior fuel.

They weigh more but have lower fuel consumption. More complex than gasoline aero engines. Usually more reliable but making them light probably impacts that. I think the lower fuel consumption compensates for the higher weight for longer flights.

Big reason for switching to them after 100 years of using gasoline is aviation gas is expensive and concerns about lead. Big picture I think refineries and distributors don't want to supply aviation gasoline anymore.

BSFC as in horsepower generated per unit of fuel tends to be better in Diesel engines, but they’re heavier because the combustion events are more violent, requiring a stronger block and pistons.

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