Why it's so hard to build a jet engine

Re:Why it's so hard to build a jet engine by russdill on Friday February 28, 2025 @07:40PM (#43214095)

The thinner the air, the more efficient your flight can be, but I never saw this as a temperature problem. My understanding is that there just isn't enough oxygen. Maybe there's an issue with the amount of heating that occurs when you try to compress enough air to get enough oxygen to run your engine?

In any case, electric engines don't need oxygen.

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Re:Why it's so hard to build a jet engine by 0manrho on Friday February 28, 2025 @08:12PM (#43214383)

> can be

Theory != Practice. If that were the only variable, then yes. Electric would be great. But it's not. It's far from the only thing in play. Lift also suffers from thinner air. Pure electric (as-in battery/solid state energy storage) could have 100% efficiency (specifically in converting prop/turbine torque to thrust of moving air), and it'd still have a terrible efficiency problem with current day tech.

Electric's primary efficiency and efficacy issue is regarding the total operating weight of the aircraft compounded by how that weight does not meaningfully decrease as the battery banks are depleted as compared to consumable fuels. Weight is your biggest enemy in flight, not power nor mechanical efficiency.

Hybrid electric (be it consumable fuel through a generator or fuel cells) is much more promising, but rarely what people mean when discussing "electric propulsion" (without the hybrid qualifier), and still has issues of it's own.

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Re:Why it's so hard to build a jet engine by zeusk on Friday February 28, 2025 @07:58PM (#43214257)

thinner the air, harder it is to generate lift as well.

Coffin corner is a real thing.

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Re:Why it's so hard to build a jet engine by mhandley on Friday February 28, 2025 @08:52PM (#43214696)

Unless you're prepared to go supersonic. Not easy to do with electric propulsion though.

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Re:Why it's so hard to build a jet engine by namibj on Saturday March 01, 2025 @12:53AM (#43216392)

Scimitar props are pretty tame, though, or what part do you mean is hard?

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Re:Why it's so hard to build a jet engine by russdill on Saturday March 01, 2025 @01:52PM (#43222340)

Pretty sure for electric aircraft to do anything useful at supersonic speeds you'd need beamed energy. Which would be a pretty cool technology

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Re:Why it's so hard to build a jet engine by jmward01 on Friday February 28, 2025 @08:54PM (#43214721)

if you stay subsonic. I hear the U-2 has like 1-2kt of leeway when it is at its max altitude because if it went faster it would be supersonic but any slower and it would fall out of the sky.

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Re:Why it's so hard to build a jet engine by tonyarkles on Friday February 28, 2025 @10:11PM (#43215343)

To the point where, if you turned too hard, you could stall one wing tip while Mach buffeting the other.

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Re:Why it's so hard to build a jet engine by FredPret on Saturday March 01, 2025 @12:21AM (#43216240)

Obligatory plug for the excellent book Skunk Works by its former director, Ben Rich.

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Re:Why it's so hard to build a jet engine by sidnb13 on Saturday March 01, 2025 @04:13PM (#43223734)

+1, immensely satisfying read for any aviation nut

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