Plane on conveyor belt !!!
- Thread starter SRB-TEAM
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WaGoNowner
New member
La portance de l'avion dans tout ca? T'as beau avoir un moteur qui te pousse, si tu fais du "sur-place" et que y'a aucune force d'air sour les ailes, tu lèvera pas ben ben.
Ca serait comme de dire que ton aileron te donne du downforce sur le dyno...
Ca serait comme de dire que ton aileron te donne du downforce sur le dyno...
BoxsterBoy
Administrator
Tu l'as ta portance, l'avion avance grâce à son moteur (hélice ou turbine) et même si les roues ne tournent pas, il va décoller.
Les roues de l'avion semblent faire du "sur place" sur le belt, mais l'avion elle, elle avance... Le power est pas aux roues...
C'est pas un char là... Avion = free spin aux roues.
MrSpace
Legacy Member
L'avion avancerait et decollerait.
Même si le convoyeur allait à 1000kmh... l'avion avance par l'air qui sort des moteurs aucunement par ses roues. C'est pour ça qu'un avion décolle aussi sur la neige avec des skis pis sur l'eau avec des flotteurs.
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BoxsterBoy
Administrator
^^ Ben oui, on s’entend, si le convoyeur est assez long pour lui offrir de la portance.
WaGoNowner
New member
Edit mais on peut me lire en quote de BoxsterBoy
Last edited:
BoxsterBoy
Administrator
Ciboire, les moteurs sont full throttle, on s'en sacre du tapis, l'avion va avancer, c'est pas un char.
BoxsterBoy
Administrator
Eh boboi.
Pkoi l'avion avancerait pas? C'est quoi la relation être le tapis et la force appliquée par les moteurs?
Spaceman Spiff
Well-known member
https://blog.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/The problem is as follows:
Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?
The practical answer is “yes”. A 747’s engines produce a quarter of a million pounds of thrust. That is, each engine is powerful enough to launch a brachiosaurus straight up (see diagram). With that kind of force, no matter what’s happening to the treadmill and wheels, the plane is going to move forward and take off.
But there’s a problem. Let’s take a look at the statement “The conveyor belt is designed to exactly match the speed of the wheels”. What does that mean?
Well, as I see it, there are three possible interpretations. Let’s consider each one based on this diagram:
1. vB=vC: The belt always moves at the same speed as the bottom of the wheel. This is always true if the wheels aren’t sliding, and could simply describe a treadmill with no motor. I haven’t seen many people subscribe to this interpretation.
2. vC=vW: That is, if the axle is moving forward (relative to the ground, not the treadmill) at 5 m/s, the treadmill moves backward at 5 m/s. This is physically plausible. All it means is that the wheels will spin twice as fast as normal, but that won’t stop the plane from taking off. People who subscribe to this interpretation tend to assume the people who disagree with them think airplanes are powered by their wheels.
3. vC=vW+vB: What if we hook up a speedometer to the wheel, and make the treadmill spin backward as fast as the speedometer says the plane is going forward? Then the “speedometer speed” would be vW+vB — the relative speed of the wheel over the treadmill. This is, for example, how a car-on–a-treadmill setup would work. This is the assumption that most of the ‘stationary plane’ people subscribe to. The problem with this is that it’s an ill-defined system. For non-slip tires, vB=vC. So vC=vW+vC. If we make vW positive, there is no value vC can take to make the equation true. (For those stubbornly clinging to vestiges of reality, in a system where the treadmill responds via a PID controller, the result would be the treadmill quickly spinning up to infinity.) So, in this system, the plane cannot have a nonzero speed. (We’ll call this the “JetBlue” scenario.)
But if we push with the engines, what happens? The terms of the problem tell us that the plane cannot have a nonzero speed, but there’s no physical mechanism that would plausibly make this happen. The treadmill could spin the wheels, but the acceleration would destroy them before it stopped the plane. The problem is basically asking “what happens if you take a plane that can’t move and move it?” It might intrigue literary critics, but it’s a poor physics question.
So, people who go with interpretation #3 notice immediately that the plane cannot move and keep trying to condescendingly explain to the #2 crowd that nothing they say changes the basic facts of the problem. The #2 crowd is busy explaining to the #3 crowd that planes aren’t driven by their wheels. Of course, this being the internet, there’s also a #4 crowd loudly arguing that even if the plane was able to move, it couldn’t have been what hit the Pentagon.
All in all, it’s a lovely recipe for an internet argument, and it’s been had too many times. So let’s see if we can avoid that. I suggest posting stories about something that happened to you recently, and post nice things about other peoples’ stories. If you’re desperate to tell me that I’m wrong on the internet, don’t bother. I’ve snuck onto the plane into first class with the #5 crowd and we’re busy finding out how many cocktails they’ll serve while we’re waiting for the treadmill to start. God help us if, after the fourth round of drinks, someone brings up the two envelopes paradox.
BoxsterBoy
Administrator
^^ On s'en fout des histoire de détruire les roues, le problème à la base ne va pas dans les problèmes mécaniques potentiels mais valide la simple logique de la force appliquée par les moteurs versus le convoyeur qui ne change rien au fait que l'avion va avancer...
BoxsterBoy
Administrator
Surement dû à l'extraction de ma molaire à 6pm pis le fait que je suis pomal sur la codeine en ce moment. Will read again.
CuddlyJen
Multi Field Esssspert
lavion ne flotte pas. Il avance grace aux roues.
Ca dit que le tapis roule a la vitesse des roues alors si les moteurs "poussent" lavion, ca veut dire les roues tournent plus vite que le tapis, ce qui ne peut etre le cas dans cet exemple. Donc il fait du surplace en tout temps sans air pour le soulever.
Non il volera pas.
End thread.
Ca dit que le tapis roule a la vitesse des roues alors si les moteurs "poussent" lavion, ca veut dire les roues tournent plus vite que le tapis, ce qui ne peut etre le cas dans cet exemple. Donc il fait du surplace en tout temps sans air pour le soulever.
Non il volera pas.
End thread.
Quick599
Well-known member
Oublie les criss de roues. Elles n'ont aucune importance. Le tapis pourrait avancer à 10,000x la "vitesse" de l'avion qu'elle avancerait quand même.
On parle de trust ici et non de horsepower aux roues. ROFL
Les réacteurs ou l'hélice de l'avion pouce l'air. L'avion va avancer et créer du lift peut importe ce qui se passe avec les roues.