My Head Hurts,,,,,, I'm Taking A Bus!!!!

 

Then you're not understanding the problem correctly. Watch the video I linked to. It shows an experiment that demonstrates this problem perfectly. It shows by means of engine thrust the object on the conveyor can move forward. Since it can move forward, it generates airflow over the wing and lift.

The conveyor is only acting on the wheels of the landing gear, not the body of the plane. Since the wheels can spin freely and are not given any limitations in the problem statement, the conveyor cannot stop the forward motion of the plane. The only thing the conveyor contributes is an APPARENT ground speed double that of normal takeoff speed.

 

[QUOTE=76supercab2]

The conveyor is only acting on the wheels of the landing gear, not the body of the plane. Since the wheels can spin freely and are not given any limitations in the problem statement,


the conveyor cannot stop the forward motion of the plane.

Thank you 76 supercab2,, this statement right here set me straight!

All the other smarts made my head hurt!

 

The more I think about it, the more I think you're right. The only thing the conveyor belt can do is make the wheels spin faster. It can't stop the forward motion of the plane.

*thinks some more*

I change my mind. The plane will fly.

 

I do not believe the video in the link is an accurate test. In order to reproduce the concept, a true treadmill must be used. If you watch the video, the skateboard picks up speed (speed over ground) only when the experimenter is reaching for another handful of paper or whatever the "conveyor" is in this instance.

If the plane is sitting on a conveyor and th conveyor is relying on the friction of the plane's wheels to turn the belt, then the plane will take off. If the belt is "self-powered" and is able to turn at the same rate of speed as the wheels, forward motion will be negated thus resulting in zero airflow over the wings and zero lift.

BTW, I have a very good friend who has over 15,000 hours in commericial jets (757, 767) and he says no way. Take it for what it's worth.

 

Not to blow my own horn but check out my reply from page 3.....

 

I don't know. I keep re-watching that video and the skateboard seems to accelerate in smooth manner. The paper however, starts and stops several times. It might occasionally be moving faster than the board. Just the fact that the board continues to move so smoothly while the paper doesn't, indicates to me that the motion of the paper (conveyor) has no effect on the motion of the skateboard (plane).

I would love to see a video of the same setup on a treadmill. I don't expect the results would be any different.

 

I'm pretty sure that pilot school doesn't cover what happens to a plane when you put it on a giant conveyor belt. So I'm not sure why you're dragging your friend into this.

It has to do with where the power is being applied to the plane. If the plane's power was being applied at the wheels, it would not fly. But it's not - the power is being applied to the chassis of the plane. The only way to negate the power is to apply an equal and opposite force to the chassis of the plane, making the net force on the plane zero. You can't apply that equal and opposite force on a plane through the wheels, because they move freely and independently.

 

Not sure where page three is, because everyone's settings are different. This thread is on two pages for me.

But yeah, I already switched sides. The plane will fly.

 

Then your friend did not understand the question. Because if there were any commercial airline pilots that did understand the question, and said the plane would not fly....well, it wouldn't happen because pilots know the physics of powered flight. I can't believe people are still debating this. WHEEL SPEED HAS NO BEARING ON AIRSPEED. A turbine engine is pushing against the airframe of the aircraft. Not the wheels. Envision an airplane taking off from a frozen sheet of ice, a frozen lake. Heck, C-130's even have SKIS for landing on snow, and taking off from it.

 

DITTO, end of discussion - schools out. Only conclusion possible from info given.

 

Honestly, if you don't believe the plane will move forward and take off, do an internet search on Newton's Three Laws of Motion. Paying particular attention to his third law. If you still don't believe the plane will move forward and take-off, then by all means, come back and explain to us why Newton was wrong, and that the law should be disregarded.

 

[IMG]<img src="http://xf2.xanga.com/76a86a3470d3021949390/w15614562.jpg" alt="plane" style="width:400px" />[/IMG]

I thought a little diagram might help. The red arrows indicate the direction of travel for the belt. The green indicates the direction of travel for the wheels. The blue---indicates THRUST.

Belt is moving---say, 30 knots.
Take off requires 60 knots (by the way---don't get technical on me, I'm no pilot by any means---I don't have a clue as to just how fast 60 knots is... or how many 'knots' are required for take-off, but this is THEORY).

If the wheels are free-rolling (no brakes applied), they will roll with the conveyor belt, which, assuming the plane were somehow held from the top, the wheels would spin at 30 knots. Once the belt and wheels have reached their speed, kick on the thrust---which will have a magnitude of 60 knots. Here's the thing, assuming that the wheels are free-rolling, the wheels will not hold back the thrust what-so-ever. The motor (consequently the plane) will be moving at 60 knots.
Where does the extra 30 knots go???? To the wheels, they are spinning at 90 knots.
Plane moves 60 knots to the left, belt moves 30 to the right, and top of the wheels spin 90 knots (the bottom technically is 0 knots, but that's another argument) counter-clockwise (according to the picture).

If however, you were to lock the brakes up, and assuming there is perfect friction between the wheel and the road, given the same magnitudes, the plane will still move forward at 30 knots, but will drag the conveyor belt with it.

Anyways, chew on that for a little while. See what you thing---I think it's a fairly good example. Not to mention, I'm kinda proud of my picture.

To me, this is one of those "if you're driving in your car at night at the speed of light and turn your lights on, will your lights be effective???".

STan

 

We have a vector, Victor.

 

Now you've gone and done it. We were having a nice, polite conversation in Classical physics and you had to bring up a trick question in Modern physics. For shame.

(BTW. The answer is, the lights can do whatever you want them to, because that car couldn't exist in our universe. So the laws of relativity don't apply.)