do planes have to keep tilting down for long flights to make up for the earth’s curvature?

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this is a common argument made by flat-earhters, I want to be able to refute it

In: Physics

No. Gravity is pulling them down while the lift from the wings is pushing them up. They stay at a constant height above the surface of the planet.

The simple answer is yes. If you maintained the same angle with respect to space you would be pitching up relative to earth and that would initially cause a gain in altitude which is not desirable in the long term.

The proper answer is that it happens so slowly you can’t feel it.

At a typical airliner speed of 450 knots (nautical miles per hour) you would be doing 7.5 nautical miles per minute (450/60).

If you fly at that speed you will cover the equivalent of 1 degree of latitude (60 nautical miles) every 8 minutes (60/7.5).

So at 450 knots you would have to pitch down 1/8th of a degree every minute.

Blowing this up to a bigger scale, it’s 10,800 miles from pole to pole and that would mean 180 degrees of pitch change, @450kts that would take 24 hours (10800/450) or 1440 minutes. 180 degrees / 1440 minutes = 0.125 degrees per minute or 1/8th of a degree.

This is like asking an ant walking around the surface of an inflated balloon if he has to look down as he crawls forward. He is just going in a straight line forwards from his perspective.

>ELI5: do planes have to keep tilting down for long flights to make up for the earth’s curvature?

>this is a common argument made by flat-earhters, I want to be able to refute it

You can’t refute it. It is true. However, the angle of tilt is so slight it is drowned out by the noise of normal flight variances. Updrafts, winds, turbulence, movement of the center of mass as passengers move about and as fuel is expended, even the trembling of the pilot’s hands, and the thermal expansion and contraction of parts of the plane – all of these swamp and overwhelm the minor correction needed to compensate for the Earth’s curvature. The pilot continuously and subconsciously compensates for it as she continuously compensates for a thousand other factors.

It’s like a car on a straight, level, road. The road surface is not flat, but tilts away from the center to drain away rainwater. A car travelling along the road will naturally drift off the road because of that tilt, yet the driver continuously and subconsciously compensates for it.