03 Nov 06
Originally posted by sugiezdIf the question had said: "A car is moving into a head wind at the same speed as the oncoming wind", would you have assumed the car was stationary relative to the ground?
Of course it moves along the surface, through the interface of its wheels.
OK, the wheels are not powered - ok, they have low friction bearings but they do exist.
How do you measure ground-speed when the plane is on the ground?
03 Nov 06
Originally posted by Ian68Why would I assume that?
If the question had said: "A car is moving into a head wind at the same speed as the oncoming wind", would you have assumed the car was stationary relative to the ground?
Want to answer my question - how do you determine the ground-speed of a plane on the ground?
03 Nov 06
Originally posted by sugiezdWhy would you assume that a plane moving forward at the same speed as the surface its wheels are in contact with is moving backwards is stationary relative to the ground?
Why would I assume that?
Want to answer my question - how do you determine the ground-speed of a plane on the ground?
As to your question, are you asking for a definition of ground-speed or an explanation of how a pilot would determine it from his instruments?
03 Nov 06
Originally posted by Ian68Instruments wouldn't be too much use here (if based on GPS).
Why would you assume that a plane moving forward at the same speed as the surface its wheels are in contact with is moving backwards is stationary relative to the ground?
As to your question, are you asking for a definition of ground-speed or an explanation of how a pilot would determine it from his instruments?
Can you accept that it is the rotational speed of the wheels?
If so, and the indicated GS is the speed of the plane relative to the belt which is itself moving in the opposite direction at the same speed - no net progress.
03 Nov 06
1 edit
Originally posted by flyUnityThat is the original question. The question states "The plane moves", planes move through the air regardless of whether the wheels are in contact with the ground or not, therefore the plane is moving relative to a fixed point.
A plane is standing on a runway that can move (some sort of treadmill). The plane moves in one direction, while the conveyer moves at the same speed but in the opposite direction. Can the plane take off?"
(copied and pasted from another source)
Where has this discussion of ground speed come from, and what is the relevance?
And no, ground speed is not the rotational speed of the wheels.
03 Nov 06
Originally posted by Ian68"A plane is standing on a runway that can move (some sort of treadmill). The plane moves in one direction, while the conveyer moves at the same speed but in the opposite direction. Can the plane take off?"
That is the original question. The question states "The plane moves", planes move through the air regardless of whether the wheels are in contact with the ground or not, therefore the plane is moving relative to a fixed point.
Where has this discussion of ground speed come from, and what is the relevance?
And no, ground speed is not the rotational speed of the wheels.
Motion and speed are both mentioned.
When a plane is moving it has both air-speed and ground-speed.
Why is there a problemm with that?
03 Nov 06
Originally posted by sugiezdThere isn't a problem with that, but ground speed is dependent on air speed not the other way around.
"A plane is standing on a runway that can move (some sort of treadmill). The plane moves in one direction, while the conveyer moves at the same speed but in the opposite direction. Can the plane take off?"
Motion and speed are both mentioned.
When a plane is moving it has both air-speed and ground-speed.
Why is there a problemm with that?
03 Nov 06
Originally posted by mwmillerThe would be an almost immeasurably small increase in speed due to reduced friction.
If the belt is moving backwards at 5kps and the plane is moving forward at 5kps, and you stopped the belt, would the plane move forward faster, or continue at the same speed?
03 Nov 06
Originally posted by Ian68How so?
There isn't a problem with that, but ground speed is dependent on air speed not the other way around.
They do not depend on each other - when flying, a plane can have a high airpeed and a low groundspeed when flying into a headwind and vice versa when flying with a good tailwind.
03 Nov 06
Originally posted by Ian68Then basically the plane speed is not being affected by the speed of the belt. The plane will continue to move forward regardless of whether the belt is moving or not. In other words, the speed of the belt and the speed of the plane have no bearing on each other.
The would be an almost immeasurably small increase in speed due to reduced friction.
03 Nov 06
Originally posted by sugiezdYou seem to be misunderstanding what I said. The planes ground speed is determined by its air speed in relation to other forces acting on it, but the ground speed does not in any way influence the air speed.
How so?
They do not depend on each other - when flying, a plane can have a high airpeed and a low groundspeed when flying into a headwind and vice versa when flying with a good tailwind.
03 Nov 06
Originally posted by mwmillerCorrect.
Then basically the plane speed is not being affected by the speed of the belt. The plane will continue to move forward regardless of whether the belt is moving or not. In other words, the speed of the belt and the speed of the plane have no bearing on each other.
03 Nov 06
Originally posted by Ian68Is there a point or are you dissimulating?
You seem to be misunderstanding what I said. The planes ground speed is determined by its air speed in relation to other forces acting on it, but the ground speed does not in any way influence the air speed.
On the ground (not a moving belt), in still air AS and GS are the same.