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Comment by baybal2 | Hacker News Reader

> no complex turbomachinery.

The turbomachinery is by far more simpler than high performance piston engines.

A car engine of 200kw only needs to give peak power for a few seconds of acceleration, and can be electronically safeguarded from outside of envelope operation.

An avia engine of 200kw needs to be able to operate on its full rated power continuously, for longer continuous periods of operation, be many times as reliable as a car engine, be lighter than a car engine, be engineered to accommodate, and survive failures, and be engineered free of governor mechanisms of any kind that may fail on take off (engine governor having to deliver demanded performance even if it has to waste the engine)

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There are 200kw car engines that in reality can be pushed to ~600kw with minimal modification. I'm sure you could run a 2JZ at 80% for thousands of hours.

I wouldn't bet on it. The safety record of auto engines converted for aircraft use (generally in homebuilt/experimentals) is not very favorable. Auto engines are designed to cruise at 10% power or less with brief excursions to higher power. An aircraft engine runs at 75% power for hours continuously, and even with modifications, auto engines historically have not delivered the reliability of the essentially 1930s designs of aircraft piston engines.

Sure, and a 2JZ can run at over 100% for 10 hours non stop (in endurance races, at 300% with a duty cycle over 30%)

Most car engines are engineered for weight savings and efficiency instead of reliability. Not all.

When we’re in the realm of aircraft engines, I’d like to imagine continuous rated power isn’t also peak power?

Is this not the case?

I can’t speak to helicopters, but light aircraft engines tend to run at 80% of peak; peak is only used for takeoff and go around, to my knowledge. (Not a pilot)

Depends on the aircraft and engine. Some (like my little Rotax 912ULS) has a peak power at which I can only operate at for 1 minute during takeoff. I typically cruise around 70% peak.

I believe in Helicopters you're often running at 90%+ max rated power, but on an engine that's derated from its true maximum power.

Your Rotax is limited to 5 continuous min. at 5800 rpm, or a max continuous RPM of 5500. There's no setting at which you are limited to only 1 min.

Ah yes you're correct. I use 1 minute as my personal limit so I don't grow accustomed to running it too hard for too long, but the operator's manual indeed states 5 minutes above 5500. I have a fixed pitch prop, which means I typically can only spin the prop at those speeds during cruise anyhow.

Generally speaking on combustion (piston) engines the max torque (and efficiency) is at revs between 2/3 and 3/4, sometime 4/5 of power peak revs, and in "static" applications (i.e. when you don't have an accelerator that you use continuously) such as aviation but also power generators, hydraulic loaders and excavators, etc. they normally are operated (continuously) at those levels range (around max torque).

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