# If an airplane is.......

…Travelling at 100mph and it encounters a headwind also of 100mph what happens?

The drink cart doesn’t make its rounds.

Its ground speed is 0 but its air speed is still 100. If it hits a headwind of 200mph, it would actually travel backwards, but still have an air speed of 100.

It’s gonna be another delayed flight. Did you pack an extra pair of clean undies in your carryon?

You mean backwards and downwards surely

It remains airborne, but stationary relative to the ground.

If the plane has 100mph winds passing over its wings, it will stay aloft, just like if it was traveling at 100mph through calm air. Its the speed of the wind over the wings that creates lift.

Why would it go downwards?

ETA: To be less obtuse, and to emphasis the point previous posters have made, it doesn’t matter if the fluid is going over the object or if the object is going through the fluid. That’s why wind tunnels can be used to model a still object moving through air.

It it’s travelling backwards it’ll probably fall out of the sky. (Would it?)

No, because it is the speed of the wind across the wings that makes it stay in the air.

With a 200 mph headwind, it is still travelling at 100 mph forwards, relative to the wind, but 100 mph backwards relative to the ground - but its groundspeed is irrelevant (except for making your onward connecting flight).

Imagine it this way. You’re on a train, facing opposite the direction. The train is going 20 mph. You are running towards the back of it, running at 10 mph. Do you fall down, just because you’re going “backwards”?

Now, if the plane was on a treadmill… :smack:

Excuse a question from the physics ignoramus, but does a headwind of 100 mph automatically mean a 100 mph reduction in ground speed? Wouldn’t the aerodynamic design of the plane counter wind resistance to some extent?

I’m all confused :smack:

That is precisely what he does not mean.

A 100 mph head wind against an aircraft travelling at 100mph does not bring the aircraft to zero.
The air drag will increase a little due to the stronger headwind, and given a constant output from the engines, the aircraft will slow down a little.

A plane stays aloft because moving air creates a lifting force on the wings. Normally, this is achieved by the plane moving. Thus, on takeoff, a plane accelerates along a runway and lifts off when it has reached sufficient speed so that the lifting force exceeds the force of gravity that’s pulling it down.

However, as noted by other posters, it doesn’t matter whether the plane is moving or the air is moving - a lifting force is still created on the wings.

This is where the consideration of air vs ground speed are important. Our plane doesn’t care how fast it’s moving relative to the ground, only how fast it’s moving relative to the air that’s holding it aloft.

In calm air, the engines have the power to push the aircraft (of whatever aerodynamics) past air at 100mph. The power of the engines does not change when the wind picks up and they still have the power to pust the plane past the air at 100mph. (Imagine there is NO ground.) But if that mass of air is moving past the earth at 100mph eastward, and your engines are pushing the plane past the air mass at 100mph westward, then the ground and the plane will be going at the same speed and the plane will look to be stationary relative to the ground.

If the aircraft is -traveling- at 100mph, then you’re right. But if the aircraft -has a wind speed of- 100mph, then it does, in fact, have a -ground speed- of zero.

Yeah, but can a plane fly backwards? If you flipped the engines around (nothing else, just the engines), could it fly backwards?

For what is worth I´ve flown my model airplanes backwards many, many times; if the wing is strong enough I can either hover them or make them go crawling back.

A plane in flight doesn´t give a rats ass about the ground, its frame of reference is the air mass it´s moving through. I´ve also flown plenty of Free Flight model planes, they are trimmed to flight in circles but they drift away with the wind, like a fish in a fishbowl, its taken wherever its medium goes… and let me tell you, chasing one of those suckers 3 kilometers down a field is not all that easy.