Here is an easier example.

Think of a truck that sits on a street that is going slightly uphill. There is no way that you and your buddy could lift that truck straight up in the air. But you can relativily easy push it uphill. In the end the truck is going up.

Now, what’s the physics behind that and how does it relate to planes? Well, you don’t have to lift the entire car when pushing. Most of the force from gravity is resisted by the ground. You only have to push against the much smaller horizontal component that tries to push the car downhill.

With planes you basically just replace “ground” by “lift”. So instead of tires pressing against the ground, you have wings pressing against the air. And a jet engine instead of two guys pushing.

Basically a plane’s engines are pushing the plane up a hill made of air.

It’s about lift generation and gravity. Planes stay aloft because of the lift generated. So plane takes off near horizontal, with engines creating thrust in a near horizontal vector. The shape of the wing, combined with the near horizontal thrust vector creates lift, which is perpendicular to the thrust vector, and is what exceeds the pull of gravity, so you climb, while also moving forward. Depending on how you angle the wing, you change that lift force/vector so you can climb, fly level or decend.

If you angle a conventional plane vertically, it will still generate “lift” but that lift will be angled perpendicular to to gravity force. In reality, the plane “stalls” before vertical—this stalling means the wind angle has gone beyond where it can generate enough lift to keep the plane level or climbing. Simply put, most aircraft engines are completely insufficient to escape gravity on their own, they’re using a mechanical advantage via wing generated lift to stay up.

Space rockets use an immense amount of force to escape the atmosphere, they’re basically using a direct vector force to cancel out and exceed gravity, as well as friction. This requires fairly mind boggling amounts of fuel (energy) to do, which is why pounds of cargo capacity are extremely limited.

A VTOL aircraft that has thrust vectoring, can aim thrust down vertically to rise off the ground vertically for a period of time, and then rotate the thrust to the rear to enter into standard lift based flight. I don’t know this exactly, but I suspect the vertical portion of the VTOL sequence is much more energy intensive than the horizontal portion.

Helicopters are neat because they generate vertical lift, but that rotor plane is also capable of behaving like a wing, allowing them to mimic some aspects of fixed wing flight. For instance, if your engine does, you can use autorotation (basically as you fall, it spins the rotors, and you get wing lift so you can “glide” in to land safely).That said, helicopters are less efficient than a fixed wing, which is why if you fly across the country you’re in a large plane, not a helicopter.

I’m sure there are scientific details I’m missing here, but that’s my layman’s understanding of why you can’t point a standard aircraft vertically and fly straight up.

It’s because of the “lift to drag ratio”. Airplanes in level flight at ordinary speeds generate about 15x as much lift as drag meaning if the engine spends 1 unit of work moving the plan forward, the wings give 15 units of work* upwards. So flying level needs about 1/15th the engine power of going straight up. (I’m using “work” very sloppily here, not in a precise physics sense.)

You can see this in sailboats too, which can travel faster than the wind when they’re sailing at an angle to the wind. Efficient boats travel faster when they’re going almost perpendicular to the wind, not straight downwind! This is because the “lift” of the sail pulling the boat forward even more strongly than the push of the wind in the downwind direction.

While I can’t give an intuitive explanation for why this is, there’s a very easy demonstration that it’s true: kites. If a kite had a lift-to-drag ratio of 1, then it would fly at 45° up. It would fly 50 meters downwind of you when it’s 50 meters up. But any decent kite can fly at a much steeper angle than that; sometimes they look like they’re right over your head! That’s because with a lift to drag ratio of e.g. 10, the 1 unit of drag gives 10 units of lift; if it’s 10 meters downwind it will be 100 meters high.

There’s nothing wrong with your reasoning, it just doesn’t account for all of the factors involved. There is a big difference in efficiency between using the forward movement of a wing to provide lift and using direct propulsion pointed downward. There are a few planes that have a greater than 1:1 thrust to weight ratio (the F-15 being the most famous), but it is rare. Fixed wing aircraft and helicopters are all able to fly with less power because what they have is being used more efficiently.

« 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 ?