- #1
jaydnul
- 558
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When ever your flying in a plane, doesn't it go by the same principles as, say, the moon orbiting the earth? Wouldnt the plane be in free fall and just accelerating forward to keep it up? I realize this is wrong but why?
So why arent you weightless when flying in a plane?
In summary, an airplane flies by different principles than the moon orbiting the earth. An airplane flies by the principles of centrifugal force and gravity. Without centrifugal force and gravity, an airplane would be in free fall. However, an airplane is kept in the air by the air pressure difference between the top and bottom of the wings. This force is transferred to your body through the seat. If the airplane were in orbit there would be no aerodynamic lift and the plane would be in free fall. However, by flying on a ballistic path, an airplane can achieve weightlessness.
- #2
cjl
Science Advisor
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Aircraft don't fly by the same principles that keep the moon in orbit - they aren't going nearly fast enough. While in theory, it would be possible (ignoring aerodynamic drag), it would require the aircraft to go about 8 km/s, while in reality, they go about 0.2-0.25 km/s. What keeps them in the air is the force from the air over the wings, and as a result, they are not in freefall, but instead are basically in equilibrium - the weight of the aircraft is balanced by the upwards force from the air, and thus when you are inside, it feels the same as if you were sitting on the ground.
- #3
mrspeedybob
- 869
- 65
The force holding the plane away from the Earth is the air pressure difference between the top and bottom of the wing. This force is transferred to your body through the seat, therefore you feel the seat pushing up on you.
If the airplane were in orbit there would be no aerodynamic lift (no air). The force holding the plane in orbit away from the ground is centrifugal force, which is another way of saying inertia. The other force affecting your space plane is gravity. Since you are in orbit you have achieved a balance between inertia and gravity. Both inertia and gravity affect the plane and your body identically. Therefore, there is no difference in acceleration between you and the plane, and therefore no need for the plane to apply any force to you.
If the airplane were in orbit there would be no aerodynamic lift (no air). The force holding the plane in orbit away from the ground is centrifugal force, which is another way of saying inertia. The other force affecting your space plane is gravity. Since you are in orbit you have achieved a balance between inertia and gravity. Both inertia and gravity affect the plane and your body identically. Therefore, there is no difference in acceleration between you and the plane, and therefore no need for the plane to apply any force to you.
- #4
Lsos
- 803
- 9
As has been said, you need to go around the Earth about 17,000 mph in order to be in free fall. Airplanes, even the fastest ones, travel at just a small fraction of that.
That said, even that small fraction has an effect on your weight. I believe you (used to) weigh 1-2% less on a Concorde at full speed, for example, than on the earth.
That said, even that small fraction has an effect on your weight. I believe you (used to) weigh 1-2% less on a Concorde at full speed, for example, than on the earth.
- #5
- 12,175
- 182
Without verifying your 1-2% values, I'll just mention that it would be less only if the plane is traveling eastward. Traveling westward should result in an increase, since then the plane would be traveling slower -- in a nonrotating frame -- than a plane that is sitting still w.r.t. the ground.Lsos said:
- #6
Lsos
- 803
- 9
I've never actually verified the 1-2% values myself (until now), and I'm not sure where I got them from. But you do bring a very good point.
So I in fact did calculate the value now, and indeed just the speed of the Concorde only brings about a ~.5% change in weight. However, due to the fact that centrifugal force is a squared function of speed, the change DOES approach 2% when flying east (at the equator, of course).
So I in fact did calculate the value now, and indeed just the speed of the Concorde only brings about a ~.5% change in weight. However, due to the fact that centrifugal force is a squared function of speed, the change DOES approach 2% when flying east (at the equator, of course).
- #7
Integral
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A plane can be flown on a ballistic path which will provide a weightless ride.
Vomit comet
Years ago I was given a brief ballistic ride in a small private plane so it does not need to be a "special" plane.
Vomit comet
Years ago I was given a brief ballistic ride in a small private plane so it does not need to be a "special" plane.
- #8
davenn
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Integral said:
I'm pleased you brought that one up... saved me doing so.
Lsos forgot about that easily attained situation ...
one doesn't need to be traveling at 17,000mph to attain weightlessness
Dave
- #9
Lsos
- 803
- 9
davenn said:
I didn't forget. In fact, I live on the 3rd floor so weightlessness is literally right outside my window (for a few moments). No need for airplanes whatsoever.
I wanted to discuss what happens to an airplane in steady-state flight, which is what I understood OP to be asking.
- #10
- 12,175
- 182
That was my understooding too, if by steady-state you meant constant speed and altitude, i.e. a circular trajectory centered on the center of Earth.Lsos said:
Hmm, post number 1 of the thread said:
When ever your flying in a plane,..."
- #11
russ_watters
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Sure, but I rather suspect that none of us have ever been in a vomit comet. In either case, that sentence is written as an affirmative declaration. Paraphrase: we are NOT weightless when we fly in planes. Why not?
- #12
Jupiter6
- 131
- 0
If the plane and passenger had no weight, it wouldn't be able to fly. The Earth is ultimately what foots the load of an airfoil and it's passengers.
Apparent weight during a red-out in an airplane(while much more noticeable) is the same feeling you get while on roller coaster or speeding over a hump in a vehicle, or in an fast elevator that starts to descend or come to a stop while moving upwards.
Apparent weight during a red-out in an airplane(while much more noticeable) is the same feeling you get while on roller coaster or speeding over a hump in a vehicle, or in an fast elevator that starts to descend or come to a stop while moving upwards.
- #13
- 12,175
- 182
Russ: yes, put that way, that was surely the OP's intent. And it was answered in posts 2 and 3; the rest of the thread is just discussing nuances or related phenomena.
Jupiter6: Most (hopefully all?) of us do mean zero apparent weight when we say "weightless". It's pretty standard usage of that term.
Jupiter6: Most (hopefully all?) of us do mean zero apparent weight when we say "weightless". It's pretty standard usage of that term.
- #14
Jupiter6
- 131
- 0
Redbelly98 said:
I know. I just never cared for the term because it confuses people.
- #15
- 12,175
- 182
No argument here.Jupiter6 said:
1. Why do you feel heavy when flying in a plane?
Despite the sensation of weightlessness that many people experience when flying in a plane, the truth is that you are not actually weightless. The feeling of weightlessness is due to the plane's speed and the forces acting on your body. The plane is constantly accelerating downward due to gravity, and your body is accelerating at the same rate, which creates the feeling of weightlessness.
2. How does gravity affect you when flying in a plane?
Gravity is constantly acting on your body, regardless of whether you are on the ground or in the air. When flying in a plane, you are still subject to the Earth's gravitational pull, but the plane is able to counteract this force by generating lift from its wings. This allows the plane to stay in the air and give the illusion of weightlessness.
3. Can you float inside a plane like astronauts do in space?
No, you cannot float inside a plane like astronauts do in space. While the plane's speed and motion may give the sensation of weightlessness, there is still gravity acting on your body, preventing you from floating. In order to achieve true weightlessness, you would need to travel far enough away from Earth's gravity or experience microgravity in orbit.
4. Do you weigh less at higher altitudes in a plane?
Yes, you do weigh slightly less at higher altitudes in a plane. This is due to the decrease in gravitational force as you move further away from the Earth's surface. However, the change in weight is minimal and may not even be noticeable. Additionally, the decrease in weight is not due to being weightless, but rather the change in the strength of gravity at higher altitudes.
5. How does weightlessness in a plane compare to weightlessness in space?
The weightlessness experienced in a plane is very different from the weightlessness experienced in space. While the sensation may be similar, the forces and conditions are very different. In a plane, weightlessness is achieved through constant acceleration and the effects of gravity. In space, weightlessness is achieved through the absence of gravitational forces, allowing objects and people to float freely.
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