Big Mark Posted December 12, 2016 Share Posted December 12, 2016 A plane needs to move forward so that air passes around the wings to generate lift, as the plane would effectively be stationary then it won't generate lift and therefor not take off. Simples.................. The speeds needed for takeoff are relative to the motion of the air (indicated airspeed). A headwind will reduce the ground speed needed for takeoff, as there is a greater flow of air over the wings. Typical takeoff air speeds for jetliners are in the 130–155 knot range (150–180 mph, 240–285 km/h). Light aircraft, such as a Cessna 150, take off at around 55 knots (63 mph, 100 km/h). Ultralights have even lower takeoff speeds. For a given aircraft, the takeoff speed is usually dependent on the aircraft weight; the heavier the weight, the greater the speed needed. relative to the motion of the air = i.e. this plane is stationary relative to the air so ISN'T ever going to take off Quote Link to comment Share on other sites More sharing options...
Tyson Posted December 12, 2016 Share Posted December 12, 2016 OK to save this eating up all the server space like it did last time... The question isn't really about physic at all. It is deliberately badly worded to be ambiguous and to demonstrate how people interpret things in different ways, and once they choose an interpretation, how difficult it is to convince them otherwise. The question isn't clear enough about what it means when it says the conveyor belt moves "at the same speed as the wheels". Which part of the wheels? The outer radius of the tyre (i.e. the tangential velocity of the wheel), or the forward speed of the axle? Many people assume it is the forward speed of the axle, and then assume it follows that this means the conveyor belt stops the plane moving forwards. However the question does tell us that the wheels move. If the wheels didn't move, then there would be no speed for the conveyor belt to match. If the wheels move, then the plane is moving. In reality there is no physical mechanism that can act through the wheels to decelerate the plane once it starts moving. At best the conveyor will change the reative speed between the "ground" and the plane, and therefore speed that the wheels rotate, but it cannot affect the forward speed of the plane. If the plane is moving, the wings will generate lift and the plane will take off. This is the mechanically correct answer to the question. However, if you accept the boundary conditions of the question as "the backwards motion of the conveyor cancels out the forward motion of the plane" (despite there being no practical way that this could ever happen), then no, the plane would not take off. Now you explain it like that I am now on the fence Quote Link to comment Share on other sites More sharing options...
Wez Posted December 12, 2016 Share Posted December 12, 2016 [video=youtube;IPOtDPHjW-Y] Quote Link to comment Share on other sites More sharing options...
Dnk Posted December 12, 2016 Share Posted December 12, 2016 I think that was done with a jet engine just out of shot Quote Link to comment Share on other sites More sharing options...
Digsy Posted December 12, 2016 Share Posted December 12, 2016 A plane needs to move forward so that air passes around the wings to generate lift, as the plane would effectively be stationary then it won't generate lift and therefor not take off. Simples.................. OK, no malice intended here at all, but I'll explain why I find this so funny and why its so relevant to the question The question describes a mechanical arrangement of the plane on the conveyor. As has been discussed at length in this thread by the "plane takes off followers", there is no way that the arrangement described could actually prevent the plane from moving forwards. However, the "plane doesn't take off faction" circumvent the realities of the experimental setup and jump directly to the assumption that the somewhat ambiguous wording "the conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction" means that the plane cannot move, even though there is no way this can actually be the case. No one is disputing that planes need airflow over the wings to take off, but that is one step after the fundamental question of "can the plane actually move?". The people who look at the mechanical system know that the way it is described cannot possibly stop the plane from moving forwards, even if the person who wrote the question actually intended to imply that would be the case. Therefore they interpret the wording of the question literally and conclude that the plane moves and therefore eventually takes off. However, people who focus on the statement about the conveyor moving in the opposite direction assume the plane remains stationary as a boundary condition for the question, and rigidly stick to this viewpoint regardless of the literal mechanical explanation. Therefore, the "plane doesn't take off faction" are basing their conclusion much more on an interpretation of the question that the "plane takes off followers". Substitute the word "interpretation" for "belief system" and you will see why the "try religion" meme is so ironic. Those who think the plane stays still are those following a religion, not the ones who think the plane moves and therefore takes off. So your post was precisely what this question was designed to highlight, but you pretty much hoisted yourself by your own petard. Quote Link to comment Share on other sites More sharing options...
ManwithSupra Posted December 12, 2016 Share Posted December 12, 2016 Its simple. The treadmill neutralizes the engines thrust... therefore not allowing the plane to actually move forward (although it is moving)... which means no airflow over the wing... no airflow no lift. Next there will be a thread... "If the plane is stationary and there is a 300 mph headwind ...will it take off" .. YES .. YES IT WILL http://i0.kym-cdn.com/entries/icons/original/000/000/554/facepalm.jpg Quote Link to comment Share on other sites More sharing options...
Guest Budz86 Posted December 12, 2016 Share Posted December 12, 2016 Everyone says the wheels serve no purpose as they are not driven by the engine but I don't see how that is the case? As it is agreed, lift is created by a wing varying the pressure above it, creating lift below it. The flaps are there to create additional lift (used at slow air speeds to stop the engines stalling). The wheels simple allow the plane to move along the ground, thereby creating enough speed (and therefore pressure difference over the wing, creating lift). By this reasoning, the wheels are essential for take off. A seaplane replaces the wheels with pontoons or skids, but the effect is the same. My question is this; ditch the belt and replace the landing gear with concrete blocks; this will greatly hinder the plane from building any ground speed (as the conveyor scenario is designed to replicate) due to the increased friction. Can the plane take off? Yes, but it has a much harder job as it needs to overcome the friction created by the block. Chain that block to a building with 10ft thick chains and a foundation that runs a mile deep. Will it take off then? No as it is can't move and can't create lift, same as if you gave a normal plane a normal take off with a 5 mile chain attached to it (that hypothetically can't break). What happens when the plane reaches the end of its tether? Also, if the above were possible why do we not have this setup anywhere in the world!? It would save miles of tarmac and so much space! I'm a fan of myth busters but there is no way to recreate this myth easily Quote Link to comment Share on other sites More sharing options...
ManwithSupra Posted December 12, 2016 Share Posted December 12, 2016 Everyone says the wheels serve no purpose as they are not driven by the engine I dont get that.. of course they are Just not directly... I cant help but think this "physics problem" was made by members of the flat earth society .. evidence staring at them in the face but wont believe it. Quote Link to comment Share on other sites More sharing options...
pedrosixfour Posted December 12, 2016 Share Posted December 12, 2016 Budz. It wouldn't save any runway space. See my earlier post about the conveyor needing to be long enough for the plane to reach take off speed. The only difference between the plane taking off from a runway and from a conveyor is that the wheels will be spinning much MUCH faster as the plane takes off from the conveyor. The plane still needs to travel the exact same distance and speed on either platform to achieve take-off. But being on a conveyor does not hinder the forward movement of the plane, it simply cannot affect it. And Richard Stock, I am dismayed, simply dismayed. Quote Link to comment Share on other sites More sharing options...
ManwithSupra Posted December 12, 2016 Share Posted December 12, 2016 And Richard Stock, I am dismayed, simply dismayed. LOL I see both sides of the argument and the other side has good theories but... I cant agree with you on it I would agree with you if the conveyor was at a constant speed. However the argument is the conveyor matches the speed of the wheels at all times. So If the conveyor was set at 100mph then yes for the plane to achieve 200 mph the wheels would need to be moving effectively at 300mph. The engines in a normal situation would provide a forward motion to the whole aircraft and therefore the wheels would rotate allowing the plane to move, so effectively "driving" the wheels in that direction through forward thrust provided by the engines. If you have an equal opposite action of the wheels rotational motion then the plane will sit still but at full thrust as the converted rotational forward energy (at the wheels) would be neutralized by the opposite direction of the conveyor. Quote Link to comment Share on other sites More sharing options...
ManwithSupra Posted December 12, 2016 Share Posted December 12, 2016 Nope... I get it now... Yep it will take off... What an idiot lol Quote Link to comment Share on other sites More sharing options...
Guest Budz86 Posted December 12, 2016 Share Posted December 12, 2016 It wouldn't save any runway space. See my earlier post about the conveyor needing to be long enough for the plane to reach take off speed. If it were as long as a normal runway, or indeed any significant length longer than the plane, the conveyor would not be matching the forward movement of the wheels and the original statement would not be true. In essence, the scenario is "can a plane take off with its engines at full thrust if it were to hypothetically remain stationary." I agree that the scenario defies the laws of physics in that it is almost impossible to keep that amount of thrust stationary; it moves a 300 tonne object at over 500mph, half a mile in the air! BUT, if there were a way of keeping it stationary, even with the engines at full thrust, what is generating the lift? It's not the engine otherwise there would be no need for wings Quote Link to comment Share on other sites More sharing options...
pedrosixfour Posted December 12, 2016 Share Posted December 12, 2016 But, on the conveyor, the wheels are free to turn at whatever speed the conveyor is doing at that instant. It still has no bearing on the engines using thrust to push the plane forward through the unaffected (still/unmoving) air, causing the wings to generate lift and so enabling take-off. And it is the wheel speed that the conveyor is (theoretically) being used to match. It says nothing about the forward momentum of the plane, which is determined by engine thrust, not power transferred from the wheels to the runway or conveyor. But as I've already said, even the claim that the conveyor can match the wheel speed exactly is impossible. The instant the conveyor starts to move in order to match the wheel's rotational speed, produced from the plane's forward movement, the belt instantly alters the wheel speed again which requires the conveyor to increase speed, which causes the wheel speed to increase again, and so on and so forth until the wheels or conveyor explodes from the stresses! But if the wheels and belt are capable of these ever increasing speeds or take off can be achieved prior to a catastrophic failure then no conveyor speed can alter the effect that the thrust produced by the engines has on the plane. Quote Link to comment Share on other sites More sharing options...
Gaz6002 Posted December 12, 2016 Share Posted December 12, 2016 This again Quote Link to comment Share on other sites More sharing options...
pedrosixfour Posted December 12, 2016 Share Posted December 12, 2016 This again Never again! Quote Link to comment Share on other sites More sharing options...
Pixelfill Posted December 18, 2016 Share Posted December 18, 2016 Also, if the above were possible why do we not have this setup anywhere in the world!? It would save miles of tarmac even if it were possible. Have you thought about landing? I wouldn't want to be on the first aircraft trying to land on a small conveyor belt runway system Quote Link to comment Share on other sites More sharing options...
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