Originally posted by GalaKevIt is perhaps that the planes engines are shifting the air around the plane? They drag thair towards the wings-but then they would have to be working overtime to create enough "airspeed" that way.
And where is the airspeed coming from, you would be stationary at this stage. Therfore assumming no wind, you air speed will be 0kts.
0kts = no lift.
I can't think of any other reason why the plane would take off. There is no airspeed. There is no groundspeed relative to anything but the treadmill.
*shrugs*
EDIT: As realisation sets in...it's a silly question. Imagine a "dead" treadmill, where it only moves using newtons third law. Then if we start the plane the treadmill will move...forward, with the plane...
I'm not a pilot or a physicist but heres my take on the plane / treadmill problem:
The wheels of the plane are not driven, as has been pointed out, they allow the plane to move when an external force is exerted on the plane. The plane moves when jets are in operation. The plane relies on air movement across the wing profile in order to take off. Therefore if a plane was placed stationary in a wind tunnel and air flow generated it would (theoretically) take off. So our plane is on the treadmill with the jets running so as they would propel the plane forward at a speed X if it where on a normal runway. At this point the wheels would be turning at Y RPM The treadmill is running in the opposite direction to which the plane should be moving and at a speed that would turn the plane wheels at Y RPM if the plane was fixed in position and the wheels allowed to be powered by the treadmill (none of this sounded so complicated in my head!). Now as I see it at this point the planes jets are trying to move the plane forward on the wheels, however treadmill is trying to turn the wheels in the opposite direction and as long as these two forces are exactly the same the only thing preventing the plane from moving is the friction of the wheels against the treadmill. If this friction is overcome the wheels plane will move forward with the wheels moving backwards. What then happens to the treadmill is a function of it's mechanical design. Most likely the motor will stall and burn out (so the plane moves forward on It's wheels and takes off) or the drive train fails (the plane moves forwards on it's wheels and takes off) or nothing fails, however the heat generated from the wheels moving across the treadmill surface causes a fire. There must be something preventing the plane taking off, otherwise I would thought the priciple would have been used to enable short distance take off runways somewhere.
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The earth is one big treadmill, you are either compounding its speed by traveling in the same direction as rotation or your speed is reduced traveling the opposite direction of rotation.........Does that statment have any merit? I was just making a few logical assumptions.
Originally posted by joe shmoThats exactly what you get when you launch spacecraft from an equitorial launch center. You get a free thousand MPH boost by launching in the direction of the earth's rotation and you lose a thou when you fly off in the opposite direction. Thats why spacecenters are as close to the equator as possible. You get more bang for the buck launching from cape Canaveral than you would from a site in Greenland, for instance. You don't get quite the full thou from the Cape but you get a nice boost anyway, several hundred MPH for free.
The earth is one big treadmill, you are either compounding its speed by traveling in the same direction as rotation or your speed is reduced traveling the opposite direction of rotation.........Does that statment have any merit? I was just making a few logical assumptions.
Originally posted by joe shmoI suppose that statement would be true if the atmosphere did not follow the Earth's motion. However I think it does.
The earth is one big treadmill, you are either compounding its speed by traveling in the same direction as rotation or your speed is reduced traveling the opposite direction of rotation.........Does that statment have any merit? I was just making a few logical assumptions.
Originally posted by GalaKevThis is what I first thought, sadly it's wrong.
And where is the airspeed coming from, you would be stationary at this stage. Therfore assumming no wind, you air speed will be 0kts.
0kts = no lift.
The plane engines propell the plane forward relative to the GROUND.
The treadmill does NOTHING to prevent that. The only thing the treadmill does is make the wheels of the plane rotate faster.
Since the plane is moving forward at normal speed, there IS wind and therefore the plane will take off.
Originally posted by TheMaster37The propeller propels the plane relative to the air, not the ground.
This is what I first thought, sadly it's wrong.
The plane engines propell the plane forward relative to the GROUND.
The treadmill does NOTHING to prevent that. The only thing the treadmill does is make the wheels of the plane rotate faster.
Since the plane is moving forward at normal speed, there IS wind and therefore the plane will take off.
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Originally posted by sonhouseAt the point when you fly over either the north or south pole you are actually traveling at the speed on your speedometer?
Thats exactly what you get when you launch spacecraft from an equitorial launch center. You get a free thousand MPH boost by launching in the direction of the earth's rotation and you lose a thou when you fly off in the opposite direction. Thats why spacecenters are as close to the equator as possible. You get more bang for the buck launching from cape Cana ...[text shortened]... ite the full thou from the Cape but you get a nice boost anyway, several hundred MPH for free.
Originally posted by TheMaster37If the engines where not running and the treadmill was switched on the plane would (theoretically) stay stationary and the wheels would be rotated by the treadmill. Any force that now acts on the plane to move it forward must overcome that the friction between the wheels and the treadmill surface. The plane will then travel forwards from the thrust of the engines and the wheels will rotate backwards from the treadmill. This makes sense to me but it quite probably wrong. Just can't see why at the minute!!!
The plane engines propel the plane forward relative to the GROUND.
The treadmill does NOTHING to prevent that. The only thing the treadmill does is make the wheels of the plane rotate faster.[/b]
Originally posted by 3DDNo, you are not wrong, you have clearly thought about it in depth and have come to the correct conclusion.
If the engines where not running and the treadmill was switched on the plane would (theoretically) stay stationary and the wheels would be rotated by the treadmill. Any force that now acts on the plane to move it forward must overcome that the friction between the wheels and the treadmill surface. The plane will then travel forwards from the thrust of the engi ...[text shortened]... ill. This makes sense to me but it quite probably wrong. Just can't see why at the minute!!!
The only horizontal force acting on the plane is the thrust from the propeller.
A treadmill cannot apply any horizontal force to the plane because the wheels decouple the plane from the treadmill.
(Yes there is friction in the wheels but, as someone pointed out in a long forgotten post, the friction is easily overcome by the thrust the propeller gives.)
Therefore, as there is a net force acting on the plane, it will have a net acceleration. Therefore it takes off
PS. Minor technicality: It's not the friction between the wheels and the treadmill surface, its the friction in the bearings of the wheels we are interested in.
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The question states that the plane in MOVING forward, taking all the other useless information out of the scenario, like the treadmill, which its only obvious intention is to distort reality, I say that if the forward speed is enough for that specific aircraft to generate enough lift for takeoff, then It will.
Originally posted by joe shmoDepends on your frame of reference. If a plane goes the same speed as the rotation of the earth it can stay in the same place, so you can go 1000MPH on the equator even if you are sitting still, although everything else around you is going the same speed. If you drive north at a steady 100 KPH you are actually going in a corkscrew motion so your total velocity goes down to your actual velocity when you cross the pole. But you are still going with whatever velocity the earth is going through its yearly orb of the sun and superimposed on that the entire solar system's velocity as it orbits around the center of the milky way and the direction of travel of the entire milky way as Andromeda and the Milky way are coming together, but of course we feel none of that as we are driving north at 100KPH.
At the point when you fly over either the north or south pole you are actually traveling at the speed on your speedometer?
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Originally posted by XanthosNZYes, but....
Plane wheels are not driving in any regard. They freely rotate. Therefore the engine running will cause the plane to move forward (wrt the air) no matter what speed the treadmill runs at.
Anyone saying otherwise clearly doesn't know how a plane works.
PS. Wings don't work via the low/high pressure thing. It's the angle of attack that does it.
planes fly because of a large amount of air pushed downward. In all but a few cases the thrust produced by the plane (F-15's being an exception) is NOT nearly enough produce the amount of airflow required to lift the entire airplanes weight. It is much the larger amount air moving past the airfoil when the airplane is in flight at high enough airspeed.
And that's really the crux of the problem, there is no speed relative to the surrounding air. Hence no flight.
Originally posted by SickboyYou agreed with him( plane moving relative to air) and then totally contradicted that by saying "there is no speed relative to the surrounding air."
Yes, but....
planes fly because of a large amount of air pushed downward. In all but a few cases the thrust produced by the plane (F-15's being an exception) is NOT nearly enough produce the amount of airflow required to lift the entire airplanes weight. It is much the larger amount air moving past the airfoil when the airplane is in flight at high enou the crux of the problem, there is no speed relative to the surrounding air. Hence no flight.
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Originally posted by tomtom232Never mind. I didn't agree with him in the way you say (I did not make it clear in my post). But you (and he) are quite right... My reading of the problem was that the airplane would be kept stationary (0 speed relative to the ground). That's not so.
You agreed with him( plane moving relative to air) and then totally contradicted that by saying "there is no speed relative to the surrounding air."