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| Thread ID: 64128 | 2005-12-04 07:01:00 | Sunday night Brain Bender - Airplane Physics | miknz (3731) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 410122 | 2005-12-14 13:03:00 | I hope that this stops the fighting and solves the problem . Answer ( . avweb . com/news/columns/191034-1 . html" target="_blank">www . avweb . com) I still have a problem with his argument . After all his waffle, it still seems to comes down to: "Manfred relaxes a bit because the conveyor cannot stop him from moving forward . There is nothing on the airplane that pushes against the ground or the conveyor" Um, how about the plane's weight and something known as gravity? Then: "the medium on which it is acting is the air . The only time it could be a problem is if the wheel speed got so high that the tires blew out" Um, if what is holding the plane above the ground makes no difference, why the heck should it make any difference whether the plane has tyres or not? |
Greg (193) | ||
| 410123 | 2005-12-14 19:35:00 | Um, if what is holding the plane above the ground makes no difference, why the heck should it make any difference whether the plane has tyres or not? With any plane (on a conveyor belt or not) there is an assumption that the wheels have a minimal amount of friction to allow the propulsion force of the aircraft to have effect on the plane, and not on the support (the wheels, or whatever is providing the low friction support). It matters not if they are wheels, well lubricated skis, or any physical support as long as it has minimal friction to allow the plane to move relative to the surface it's sitting on. I see no difficulty in accepting the principles. Its basic science. |
godfather (25) | ||
| 410124 | 2005-12-14 22:04:00 | Your confusion seems to be based on some kind of assumption that because the plane's weight is pushing down on the runway, that the runway's horizontal motion is somehow able to affect the plane. It can't, because the plane is free-rolling. Yes, there's weight on the wheels but not FRICTION. between them and the plane. You're answering the question as if the brakes were on - you probably think the plane would move backward if the conveyor belt went backwards and the engines were off. Please understand that the ONLY linkage between the rotation of the wheels and motion of the plane is a bearing of negligible friction, such that the speed of the wheels (and hence that of the conveyor) has NO bearing on the plane. If you had a treadmill, for example, and decent rollerblades with low friction, if the treadmill went backwards you would still be EASILY able to pull yourself forwards using your hands. Thed plane is the same, almost exactly. The wheels are skates with low friction, and the jets are pulling it forwards independantly of the wheels. |
george12 (7) | ||
| 410125 | 2005-12-14 22:06:00 | "the medium on which it is acting is the air. The only time it could be a problem is if the wheel speed got so high that the tires blew out" Um, if what is holding the plane above the ground makes no difference, why the heck should it make any difference whether the plane has tyres or not? It doesn't make a fundamental difference if the tires blow out, just a nasty noise and lowered braking power, and more drag. Just the same as in a car really (a car that was coasting of course :p). |
george12 (7) | ||
| 410126 | 2005-12-15 00:15:00 | If you had a treadmill, for example, and decent rollerblades with low friction, if the treadmill went backwards you would still be EASILY able to pull yourself forwards using your hands. Thed plane is the same, almost exactly. The wheels are skates with low friction, and the jets are pulling it forwards independantly of the wheels. ^ Best summarisation of the issue I have seen. The wheels aren't providing the thrust, the jet engines (or arms in the above example) are. |
Jester (13) | ||
| 410127 | 2005-12-15 00:40:00 | Just to add a rider, we talked of low friction wheels and bearing friction just to help make things easier to understand. In reality of course, the bearing friction is itself only a small part of the rolling resistance of rubber tyred wheels, but in relation to engine power, the work done in overcoming rolling resistance on a hard runway is still small. | Terry Porritt (14) | ||
| 410128 | 2005-12-15 01:17:00 | Tyres blowing out can have results . Concorde proved that . But that's nothing to do with the aspect of Newton's physics we've been discussing . Greg . Buy yourself a little model aeroplane with wheels which turn (or even a car . . . Something with wheels) . Go to a supermarket which has a conveyor belt at the checkout . You are the jet engine . Try pushing the model against the direction of the conveyor from one end to the other . Try pushing with the direction of the conveyor . Try it with the conveyor stopped . Satisfy yourself that you are determining the acceleration and speed of the model . Satisfy yourself that you can move the model from one end of the conveyor to the other . The only difference the "direction" of the conveyor makes is in the rotation speed of the wheels, as the model moves from one end of the conveyor to the other . |
Graham L (2) | ||
| 410129 | 2006-02-01 22:37:00 | Of course it can take off... its a magical plane | token (9357) | ||
| 410130 | 2006-02-02 00:18:00 | Ugh, this has been discussed so many times on the net, here is the answer, in many peoples opinions, and from a pilot (who flies 747's, a friend's dad). The plane will take off. The wheels will be spinning twice as fast. No extra speed will be required to lift the plane up. There is no issue about the plane moving at the start. The only thing that will stop this plane from taking off is possibly the high amount of inertia on the wheels, causing them to become unstable, and perhaps break. |
Haze (3028) | ||
| 410131 | 2006-02-02 00:46:00 | Of course it can take off... its a magical plane Ahh, NOW I understand ;). And welcome to PF1. |
george12 (7) | ||
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