Recent comments in /f/explainlikeimfive

JimmyTheBones t1_j699a6q wrote

So imagine the horizontal distance, not the diagonal distance.

The front foot is the equivalent of the top of a river up a mountain, and the back foot is the equivalent of the estuary at sea level.

The human's horizontal foot distance is much less, so there is a much smaller difference between the potential from one foot to the other.

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SierraTango501 t1_j698u6k wrote

Also, ramjets and scramjets don't work at the speeds that commercial airliners fly at, and turbojets are hugely fuel inefficient.

The engines powering commercial airliners are turbofans, similar in construction to a turbojet, but with a large diameter intake fan, that bypasses a lot of cold air past the compression/ignition stage and mixes it with the exhaust air to generate thrust without burning up a ton of fuel a minute.

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noopenusernames t1_j69635y wrote

Do you happen to remember the name of the type of engine that they experimented with in, I think, the 80’s, maybe early 90’s? It was kind of like a turboprop, but the it looked more like a jet engine. The defining feature was that the “propeller” blades were short and stubby and mounted on what would look like the exhaust cone of a turbine engine, and there were a lot more of of these stubby blades than you’d see on a turboprop. It basically looked like if you took one of the compressor stages off a turbine engine and rotated it inside out so the blades all stuck outward from a central ring, and then slid that ring up onto the exhaust cone of a turbine engine.

I’ve been trying to remember the name of this thing for a long time but have had a dammed hard time finding it. Apparently they were supposed to have the efficiency of something between a turboprop and a turbine, and so airlines really wanted them, but no one pursued them because they thought the general public would think they are “scary-looking” and wouldn’t want to fly on them

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noopenusernames t1_j694zl2 wrote

It’s been a while since I’ve studied this. How do they get the ramjets into a forward motion to make them work in the first place.

Also, for scramjets, what kind of changes in engine behavior result from the air being supersonic? Does the air even spend enough time in the engine to burn long enough to put any useful energy into the system? Or is it still burning on its way out (while exiting the exhaust section), kind of creating an explosion just behind the engine that pushes the engine forward?

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noopenusernames t1_j694h7c wrote

The blades do behave like a wing, except in a horizontal direction instead of a vertical direction. I’ve heard people accidentally say ‘lift’ when they mean ‘thrust’ many times, but everyone in the industry knows what they mean just because of the design.

But you are technically correct, which is the best kind of correct!

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