Helicopter Hovering: Solving the Mystery of Earth's Rotation

In summary, the conversation discusses why a helicopter, which can theoretically hover in one spot for hours, does not end up in a different part of the world due to the Earth's rotation. The atmosphere rotating with the Earth and the helicopter's horizontal momentum are identified as factors that keep it in the same place and at the same velocity. The effects of altitude and the atmosphere are also mentioned.
  • #1
pr1de
9
0
Question that was always bugging me.

Why doesn't a helicopter which could theoretically hover on the spot for hours doesn't end up in another part of the world. Since it's off from the ground doesn't it lose the velocity of Earth's rotation? What keeps it in the same place/at same velocity all the time? I would assume that it's the atmosphere that's rotating along with the planet right?
 
Physics news on Phys.org
  • #2
Welcome to PF!

Hi pr1de! Welcome to PF! :wink:
pr1de said:
… Since it's off from the ground doesn't it lose the velocity of Earth's rotation?

No … imagine a hovercraft on the Moon (obviously, a helicopter wouldn't work there … no air! :biggrin:) …

it'll still hover! :smile:

The helicopter has horizontal momentum when it's on the ground.

When it lifts off, the only force is vertical, so it still has the same horizontal momentum: its horizontal speed still perfectly matches that of the Earth's surface. :wink:
 
  • #3
If the 'copter was hovering at 100m above the Earth, to a rough approximation it would only need to move at about 0.01 mph to "keep up with" the rotation beneath it.
 
  • #4


tiny-tim said:
Hi pr1de! Welcome to PF! :wink:


No … imagine a hovercraft on the Moon (obviously, a helicopter wouldn't work there … no air! :biggrin:) …

it'll still hover! :smile:

The helicopter has horizontal momentum when it's on the ground.

When it lifts off, the only force is vertical, so it still has the same horizontal momentum: its horizontal speed still perfectly matches that of the Earth's surface. :wink:

Increasing its distance from the centre means that its horizontal velocity (or angular velocity) must be less if its angular momentum remains the same.
 
  • #5
I think Galileo tested that assumption by dropping balls from the mast of a ship and found they dropped straight down relative to the ship, not the earth. Newton explained it by saying that objects tend to remain as they are, either in motion or stationary. This he called inertia. The helicopter has the same velocity as the surface of the Earth and will keep that velocity unless something causes that velocity to change.
 
  • #6
Stonebridge said:
If the 'copter was hovering at 100m above the Earth, to a rough approximation it would only need to move at about 0.01 mph to "keep up with" the rotation beneath it.

Well, yes but first it would have to keep its rotation imparted to it from the Earth, which is 1000mph at the equator and ~707mph up near the the great Lakes.

The OP's question is a bit vague so it's hard to tell why he thinks the helicopter would not stay stationary wrt the ground.
 
  • #7
DaveC426913 said:
Well, yes but first it would have to keep its rotation imparted to it from the Earth, which is 1000mph at the equator and ~707mph up near the the great Lakes.

The OP's question is a bit vague so it's hard to tell why he thinks the helicopter would not stay stationary wrt the ground.

Yes, 1000mph at the equator, and approx 1000.01 mph at a height of 100m would be necessary to keep up with the Earth below.
ie, to maintain the same angular velocity.
 
  • #8
So, the total answer is:
1] While parked, the helicopter has momentum imparted to it from the ground. At the equator, this is 1000mph.
2] When it lifts off, it retains this momentum, and continues moving at 1000mph.
3] If the helicopter were to lift high enough off the ground that the curvature of the Earth became a factor, then the Earth would be able to move under the copter slightly faster and the copter would fall behind (just like a race car one curve in the outside lane will fall behind). The copter would have to move very slightly to "keep pace" with the Earth.
4] This assumes we ignore the effect of the atmosphere. The atmo is carried along with the Earth, even at altitude. Which means as the copter rises, the atmo will overwhelm this tiny force of angular momentum.
 
  • #9
Thank you guys, it all makes sense to me now. It's always good to have someone confirm your thoughts :D
 
  • #10
One word answer: wind.
 

1. What is helicopter hovering?

Helicopter hovering refers to the ability of a helicopter to remain stationary in mid-air, without moving forward, backward, or sideways. This is achieved by balancing the forces of lift, weight, thrust, and drag.

2. How does helicopter hovering solve the mystery of Earth's rotation?

Helicopter hovering is a key tool used by scientists to study Earth's rotation. By hovering in one spot, scientists can measure the Coriolis force, which is caused by the Earth's rotation and affects objects moving in a straight line on the surface. This helps us understand the direction and speed of Earth's rotation.

3. What factors affect a helicopter's ability to hover?

There are several factors that affect a helicopter's ability to hover, including weight, altitude, wind speed and direction, and temperature. The helicopter's design and rotor system also play a significant role in its hovering ability.

4. How is helicopter hovering different from other forms of flight?

Unlike fixed-wing aircraft, which require forward motion to generate lift, helicopters are able to generate lift through the rotation of their rotor blades. This allows them to hover in one spot and perform vertical takeoffs and landings. Helicopters also have the ability to hover at varying altitudes and can fly in any direction.

5. What are the practical applications of studying helicopter hovering and Earth's rotation?

Studying helicopter hovering and Earth's rotation has numerous practical applications, including improving weather forecasting and navigation systems, understanding the Earth's climate and weather patterns, and developing more efficient modes of transportation. It also allows us to gain a deeper understanding of the forces that shape our planet and the universe.

Similar threads

  • Other Physics Topics
Replies
3
Views
2K
  • Classical Physics
Replies
19
Views
2K
  • Other Physics Topics
Replies
2
Views
6K
  • Astronomy and Astrophysics
Replies
27
Views
2K
Replies
38
Views
2K
Replies
2
Views
971
Replies
12
Views
5K
Replies
69
Views
10K
  • Other Physics Topics
Replies
12
Views
2K
Back
Top