Originally posted by aging blitzerNo.
Trust us.
You're nearly there.
The belt move backwards at speed x (relative to the ground)
The plane moves forwards at speed x (relative to the ground)
The wheels turn as if the plane were doing speed 2x.
If it were a car, driven by the wheels, the car would be stationary relative to the ground, but at speed x relative to the belt.
But the ...[text shortened]... he ground, regardless of what the belt does. All the belt does is make the wheels turn faster.
Not relative to the ground - each other.
Originally posted by sugiezdAre we both talking about this problem?
No.
Not relative to the ground - each other.
"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?"
Originally posted by sugiezdSo are you trying to say:
No.
Not relative to the ground - each other.
The belt is moving backwards at speed x relative to the plane.
Which implies the plane is moving forwards at speed x relative to the belt.
In which case there is no information about any speeds relative to the ground or the air.
The belt could be going backwards at 0.5x, the plane forwards at 0.5x
The belt could be going backwards at 0.2x, the plane forwards at 0.8x
etc
Maybe the problem would be better stated in a different way.
(or at least, what I think the original intent of the problem was)
Starting condition:
Plane is stationary on a conveyer belt.
Belt is stationary. (also assume the belt is infinitely long)
Plane has wheel brakes on and engines at idle.
There is no wind, air is stationary relative to the ground.
Plane needs airspeed of 100 to take off.
At full power the plane could normally achieve a speed of 150
Then, in the same instant,
conveyor belt starts running backwards at 100
plane's wheel brakes are released
plane's engines go to full power
Can the plane take off?
Originally posted by aging blitzerThen why would it be a problem? Surely the whole point was that you have to realise exactly what is happening to get the answer.
Maybe the problem would be better stated in a different way.
(or at least, what I think the original intent of the problem was)
Starting condition:
Plane is stationary on a conveyer belt.
Belt is stationary. (also assume the belt is infinitely long)
Plane has wheel brakes on and engines at idle.
There is no wind, air is stationary relative to t ...[text shortened]... plane's wheel brakes are released
plane's engines go to full power
Can the plane take off?
Originally posted by Ian68A 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?"
The question did not say 'relative' speed, you have assumed that for no logical reason. How many times do I have to point this out?
I'm afraid that you seem to have the same blind spot as do the other fly boys.
I am truly at a loss as to how you can interpret that in any other way than the plane moving relative to the belt.
Sorry - if you insist otherwise then it's an impass.
Originally posted by aging blitzerThere's a link part way down which is even better:
http://www.kottke.org/06/02/plane-conveyor-belt
http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/
My favourite bit is: "The problem here, of course, is that the poster (and Neal) cannot disengage themselves from seeing the airplane as a car."
Does that sound familiar?
Originally posted by aging blitzerNot quite - you're forgeting:
Maybe the problem would be better stated in a different way.
(or at least, what I think the original intent of the problem was)
Starting condition:
Plane is stationary on a conveyer belt.
Belt is stationary. (also assume the belt is infinitely long)
Plane has wheel brakes on and engines at idle.
There is no wind, air is stationary relative to t ...[text shortened]... plane's wheel brakes are released
plane's engines go to full power
Can the plane take off?
while the conveyer moves at the same speed but in the opposite direction.
That is to say that if the plane is moving at 100 kph on the surface of the belt (and thus relative to it) then the belt is moving at 100 kph (relative to its surroundings), thus the plane doesn't move forward.
Originally posted by Ian68Is that meant to be taken seriously?
There's a link part way down which is even better:
http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/
My favourite bit is: "The problem here, of course, is that the poster (and Neal) cannot disengage themselves from seeing the airplane as a car."
Does that sound familiar?
If the wheels of the toy car are well oiled, even light pressure will hold the car still BUT the wheels still turn. This proves nothing.
And this post is even better:
"My god people, this conversation has completely destroyed my estimation of the intelligence of my fellow man. Airplanes fly through the AIR. The engines on an airplane move AIR. Pilots use AIRspeed to calculate how fast they are going. An AIRcraft can only take off once it has reached a certain AIRspeed. It DOES NOT MATTER how fast the ground is going when you’re talking about how fast an AIRplane needs to go to fly. The only time a moving conveyor would affect an AIRplane is in how the friction is transferred to the wheels. I saw links from people who say they’re Navy pilots, people who say they’ve seen this tested with model airplanes… those people are either lying outright or just plain dumb. I’ve been flying all my life and this is really just the most rediculous aviation-related discussion I’ve ever seen. It’s a bunch of people who only have experience with boats and cars trying to apply their limited knowledge to the world of aviation which operates on a different set of rules. My God people, stay within your depth! "
Originally posted by sugiezdHow would you answer the problem as I restated it?
Not quite - you're forgeting:
while the conveyer moves at the same speed but in the opposite direction.
That is to say that if the plane is moving at 100 kph on the surface of the belt (and thus relative to it) then the belt is moving at 100 kph (relative to its surroundings), thus the plane doesn't move forward.
Forget the original for a moment.
Originally posted by Ian68What do you fly, an armchair.
And this post is even better:
"My god people, this conversation has completely destroyed my estimation of the intelligence of my fellow man. Airplanes fly through the AIR. The engines on an airplane move AIR. Pilots use AIRspeed to calculate how fast they are going. An AIRcraft can only take off once it has reached a certain AIRspeed. It DOES NOT MATTER how ...[text shortened]... aviation which operates on a different set of rules. My God people, stay within your depth! "
In still air, on the ground (and anything else you can think of being equal) AS and GS are the same.
When the plane is not actually flying, your famous rules of aviation are somewhat beside the point!
Originally posted by aging blitzerStarting condition:
How would you answer the problem as I restated it?
Forget the original for a moment.
Plane is stationary on a conveyer belt.
Belt is stationary. (also assume the belt is infinitely long)
Plane has wheel brakes on and engines at idle.
There is no wind, air is stationary relative to the ground.
Plane needs airspeed of 100 to take off.
At full power the plane could normally achieve a speed of 150
Then, in the same instant,
conveyor belt starts running backwards at 100
plane's wheel brakes are released
plane's engines go to full power
Can the plane take off?
The plane will accelerate to 150 RELATIVE to the surface of the belt (its groundspeed). As it has an airspeed of only 50 and needs 100 to become airborne, it will remain an exotic form of ground transport.