In a debate with someone who thinks the earth could be flat, not smart enough to despute a point they are making plz help.
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The same reason as a boat on plane. As your pull back the power the boat settles down into the water.
Overcoming air resistance takes power, and climbing altitude takes power. If power is constant, then you can’t keep climbing. The plane has to fall back to where the amount of power is correct.
If analogy helps, it’s the exact same reason that a boat going in a straight line doesn’t start to float higher and higher in the water as it travels. The plane isn’t a machine that just goes in the direction you point it, it’s a vehicle that’s lifted up and supported by the matter that it’s travelling through. As the earth “slopes” away from it, that matter gets thinner and doesn’t have the mass to support it, and so it sinks down a little to stay at a consistent level.
Which might just confuse the issue because the mechanism by which air flow over a plane’s wings produces lift is really nothing like buoyancy…
It takes energy to pick up an item off the ground. It takes energy to move an object further away from the Earth. If you only give the plane enough energy to stay at the same height that is what it is going to do. If you give it less energy from the engines it will eventually come down to the surface.
not Eli5…
If the plane was to go in an exact straight line and thus increase its distance from the center of the earth that would require added propulsion as the move away from the earth creates a greater gravitational potential. As in Newton’s first law there is a force (gravity) acting on the object so it does not stay in a straight line unless you give it enough force to increase altitude.
Planes do not inherently fly straight, a trim tab on the elevator (the control surface that pitches the plane up and down) is adjusted so that the plane flys level so that it neither gains or loses altitude while the controls are in the neutral position. If the plane was flying straight it would leave the atmosphere, but it’s not flying straight it’s flying level.
The autopilot uses GPS height above ground so it constantly corrects the tiny amount of pitch needed to follow the curvature of the earth.
You could fly in a “straight line” in a Cessna 152 – for a certain amount of time – just like in a BlackBird you have pitch control and trim. However your instruments won’t help you fly that trajectory, they are intended to help you fly level and maintain altitude. I’m not sure how you’d find and maintain “straight”. At some point, you’ll be too high for your aircraft to maintain that course, and the pilot’s life …
Higher altitude means less air density means less aerodynamic lift means the super fast plane will track the curvature of the earth rather than an astronomical “straight line”.
So…the plane really isn’t flying in a perfectly straight line…it’s flying at an altitude. If the plane goes away from it a bit the pilot or autopilot corrects it and brings it back to that altitude. The altitude is defined by air pressure as you get higher that pressure goes down as you go down the pressure goes up. If you were flying in a perfectly straight line from your reference all indications would be that you are in a climb. The artificial horizon gyro is self correcting…for example, if you are in a turn for a while they pick up a slight bank when you roll back to level that slowly corrects to show wings level.
Source am pilot who routinely flies in the 40,000 feet range.
Pilot here. When we fly at a constant altitude we are in fact flying in a curved path the entire time.
If the Earth was much smaller it would be more obvious.
Gravity pulls down.
But the plane goes forward, away from the center of the Earth, which means ‘going up’.
When you are the pilot, you set the controls so that these two movements ‘balance out’, and you stay at the same height.
By the way, proving the Earth is round – this is a ‘low earth orbit’. The Moon is constantly falling downward, and constantly moving away from the Earth’s center.
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