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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 | ||
| 410062 | 2005-12-05 06:24:00 | no!! the airplane needs air speed. airspeed is the speed of the air over the wing, ground speed is the speed to the airplane over the ground. if the airplane was sitting still and a head wind of 160KPH was comming at it then it could take off with no ground speed. as far as i know my answer is right. this was the first answer given, HTF did we end up wiht so many postings for a question that has been answered? |
robsonde (120) | ||
| 410063 | 2005-12-05 06:26:00 | Well then, show us how smart you are ninja. You explain it. I await your incredibly intelligent, concise and compelling arguments with bated breath. Don't spare the jiggahurtzGod you always have to be the pompous asshat don't you. The answer has been re hashed a stack of times in this thread, many of them by you. |
ninja (1671) | ||
| 410064 | 2005-12-05 06:35:00 | Graham, Billy and Terry are right. 10/10. Imagine if you will a car - a front wheel drive car. The REAR wheels are sitting on a conveyor belt going backwards at the equivilent of 50km/h, so if you slammed on the brakes the car would go flying backwards. But you don't - like the plane, the wheels are free spinning. If you apply slight forward pressure to the front wheels, it will stay STATIONARY. If you let go (put it in neutral), it might very slowly go backwards from the friction. But as soon as you apply force, IE attempt to drive away, you will be able to easily, because the force the spinning back wheels apply is NEGLIGIBLE. It is the same with the plane. The wheels are free-spinning and the friction is negligible such that we can ignore it. The runway could be going backwards at 1,000km/h and the plane would be unaffected (ignoring bearings flying apart etc). So when thrust is applied INDEPENDANTLY of the wheels, there is nothing to counter it, so the plane will move forward, relative to the man standing beside the runway (drcspy), and be able to take off. The free-spinning wheels can do nothing to stop it. Here's the process of takeoff. Initially, the plane is stationary. The brakes are OFF, so the wheels can turn freely. Because the plane is still, the runway is stationary. The pilot opens the throttle, and the jets/propellor pushes the plane forwards. The runway counters this motion (when the plane reaches 50km/h the runway goes backwards at 50km/h. But this does not affect the motion of the plane at all (if we ignore the slight friction in the imperfect bearings) or impedes it only VERY SLIGHTLY, not enough to affect the normal takeoff, if we calculate friction accurately. The plane DOES move relative to the man standing beside the runway, so it can take off. |
george12 (7) | ||
| 410065 | 2005-12-05 06:36:00 | Of course the plane will move backwards if the power is turned off.The suggestion that it will sit still with it's wheels spinning is ludicrous. Then as power is applied the backward movement will slow untill the backward speed ant the forward thrust is equal. Then what happens? In real life my guess is the wheel struts would break. The plane WILL sit still with the wheels spinning backwards. If we account for friction it might move very slowly but not enough to affect the situation. |
george12 (7) | ||
| 410066 | 2005-12-05 06:45:00 | videos.streetfire.net | ninja (1671) | ||
| 410067 | 2005-12-05 07:23:00 | Ninja FTW | roddy_boy (4115) | ||
| 410068 | 2005-12-05 07:41:00 | The situation is similar to if the plane's wheels were imbedded in concrete. They're gonna be stuck in the same place, whether they're on the conveyor or whether stuck to the ground. They'll keep the plane rooted to the spot. This plane ain't going anywhere! |
Greg (193) | ||
| 410069 | 2005-12-05 07:47:00 | Hmmm that is true, assuming coefficient of static friction between tyres and conveyor belt is 1. Which, given the impossibility of the conveyer belt, could be easily assumed. Im on the fence now. |
roddy_boy (4115) | ||
| 410070 | 2005-12-05 08:25:00 | The answer is realy simple. Without the motor running the plane would move backwards on the conveyor. THE WHEELS WOULD NOT BE TURNING. iT WOULD BE STATIONRY ON A MOVING CONVEYOR. NO MOTIVE FORCE IS BEING APPLIED TO THE PLANE. As soon as the motor is started and power applied the plane will move forward and take off in the normal manner. QED. |
JJJJJ (528) | ||
| 410071 | 2005-12-05 08:54:00 | Why would it be moving backwards? The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.If the plane isnt moving, the conveyer doesnt move. |
roddy_boy (4115) | ||
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