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?
« 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 ?
Yes you’re correct this wasn’t what I meant.
I should have said air to push behind you (but same misunderstanding, the air needs to be coming from the front before being pushed), or pull, or something like that, but my English is from video games and Internet so not the most useful technical terms are in my vocabulary :)
The « pull push » airflow is really well seenable on schematics of newer by-pass engines.
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.
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.
You basically already answered it yourself. The wings provide the lift needed to overcome gravity. The wings can provide this lift because the plane is moving through the air, which it does via the engines propelling it forward. At a certain velocity enough lift is generated to overcome gravity and the plane can take off.
