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Why can't all planes fly straight up? (lemmy.ca)

submitted 1 year ago by [email protected] to c/[email protected]

16 comments fedilink hide all child comments

I'm not great at physics and have no knowledge of aeronautics, so this whole chain of reasoning might be wrong.

A plane stays in the air because air is moving over the wings, which generates lift. However, that air is moving because the engine is moving the plane forward. There is no other source of energy. Therefore, some of the engine's energy is going into keeping the plane in the air, and some is going into accelerating it forwards, or keeping it at the same speed (fighting air resistance).

Therefore, if the plane points straight up, the engine should be able to support it hovering in the air. If it didn't have enough power to fight gravity when pointing straight up, it wouldn't have enough power to fight gravity when moving horizontally, either.

(Okay, some older engines only worked in certain orientations, but I don't think that's a problem for jet aircraft, or any aircraft built after WWII.)

So why can only certain planes fly vertically?

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[–] [email protected] 5 points 1 year ago* (last edited 1 year ago) (1 children)

« Therefore, if the plane points straight up, the engine should be able to support it hovering in the air. If it didn't have enough power to fight gravity when pointing straight up, it wouldn't have enough power to fight gravity when moving horizontally, either »

Well no, even if some engines are able to climb almost straight up (F-16 I believe) it is only for a few military aircrafts in specific configuration (light load) and not for a very long time. As you climb higher the air is less dense so the engine have less air to push.

Helicopters somewhat do that but they fly lower altitude and doesn’t have the same rotor size.

Even if such engines would exist, the power needed to achieve that thrust would be always around 100%, so very bad for fuel consumption, noise and engine life.

But more simply, imagine it that way : It’s easier for you to climb on a small incline instead of 90 degrees up on a rope. And if you are able to climb straight on a rope, how long can you do it in comparison with a nice uphill walk ?