Flight Altitude and Sphericity of the Earth

So, there was a flat-earther who took a spirit level on a flight. His intention was to determine whether the plane periodically adjust its angle in order to make it level in relation to the surface of the Earth. According to him, if the Earth were really spherical, then the plane would need to make these periodic adjustments; otherwise it would fly away straight into space!

His video became viral, and predictably, the plane did not make these periodic adjustments. The conclusion, surely, is not that the Earth is flat. The following are some explanations why the plane doesn’t have to make those periodic adjustments, and still reaches its destination.

  1. The density of air decreases with altitude; and thus the lift generated by the wings of the aircraft also decreases with altitude. At some point, the amount of lift is no longer sufficient to counteract the weight of the aircraft.
  2. Commercial aircrafts are engineered to have longitudinal static stability. It will restore its orientation in relation to its center of gravity, when there’s no input from pilot.
  3. The steeper the angle, the smaller the component of lift that counteracts gravity.
  4. With constant flight parameters, an airplane will fly along the density altitude.
  5. In most aircrafts, thrust generated by the engines is lower than the weight of the aircraft. The force from thrust by itself will not be sufficient in order to bring the aircraft into space.
  6. Engines works by combustion and require oxygen, and oxygen itself becomes more scarce as the altitude increases. As altitude increases, at some point engines will cease to work and no longer generating thrust.

Because of the above reasons, an aircraft will follow the curvature of the Earth, and will never fly away into space. Flying into space is not that easy: you will not be able to fly into space ‘by accident’. It will require a significant amount of energy and is far more expensive than any commercial flight.

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