Scott Posted October 10, 2008 Share Posted October 10, 2008 The idea of the engine carrying the aircraft vertically is stupid. The harrier was built to achieve vertical flight and can only just manage it for short periods at a time. A 747 stands no chance. Only because the harrier uses thrust direction to lift it. If the engine was pointing down it could do it easily. 747 would only be a problem because of the weight, the engine could push hard enough but it would just rip the wings straight off. The lift created by the wings lifts the plane, not the thrust of the engine. Quote Link to comment Share on other sites More sharing options...
Swampy442 Posted October 10, 2008 Share Posted October 10, 2008 As above, its simple physics. Planes need air over their wings to create lift, no amount of treadmill speed will make it fly. The engines are only overcoming the drag created by the wheels on the 'mill. Bunkum Quote Link to comment Share on other sites More sharing options...
ADL Mark Posted October 10, 2008 Share Posted October 10, 2008 Quote Link to comment Share on other sites More sharing options...
SimonB Posted October 10, 2008 Share Posted October 10, 2008 As above, its simple physics. Planes need air over their wings to create lift, no amount of treadmill speed will make it fly. The engines are only overcoming the drag created by the wheels on the 'mill. Bunkum Obviously not simple enough! For anyone that still doesn't get it, can I recommend the Mythbusters episode where they explained this simply and tested it by getting a plane to take off on what was effectively a treadmill. Quote Link to comment Share on other sites More sharing options...
Jake Posted October 10, 2008 Share Posted October 10, 2008 of course it's not going to fly?! Wings need air flowing over them to produce lift and the only air flowing is that being sucked into the engines So how do you think regular planes ever get moving then? Quote Link to comment Share on other sites More sharing options...
jamesmark Posted October 10, 2008 Share Posted October 10, 2008 So how do you think regular planes ever get moving then? With a lot of will and crossed fingers? Quote Link to comment Share on other sites More sharing options...
Branners Posted October 11, 2008 Share Posted October 11, 2008 If you hold a toy plane on a treadmill and run the treadmill up to half speed the little wheels go round and round but your hand (the thrust) is enough to hold it there. Its not taking a lot of thrust, just enough to hold it there. Turn the treadmill to full speed, you still only have to hold it there, the wheels go really really quickly now but you are still holding it in position with the same small amount of force. Now move your hand forward (additional thrust), the wheels go that little bit quicker but the plane still moves forward with just a fraction more thurst. Now fling the plane forwards, the wheels go insanely quick, but it still shoots forwards. It doesnt matter what speed that treadmill is doing it could be 100mph, the wheels freewheel and pushing it forwards means it still goes forwards. Work on the basis the wheels have no bearing on this. They just hold the plane up and freewheel at the speed of the treadmill plus the forward thurst speed. Quote Link to comment Share on other sites More sharing options...
Branners Posted October 11, 2008 Share Posted October 11, 2008 one key thing, the plane has to be moving forward to get lift. The treadmill has to be long enough for it to get to take off speed, which will be the same distance as if its on normal tarmac. So a long conveyor would be needed. Quote Link to comment Share on other sites More sharing options...
Kranz Posted October 11, 2008 Share Posted October 11, 2008 So a long conveyor would be needed. I'll get building one on 026 Left ..... its quiet at the moment. Should surprise the 0500 landings Quote Link to comment Share on other sites More sharing options...
Swampy442 Posted October 11, 2008 Share Posted October 11, 2008 Obviously not simple enough! For anyone that still doesn't get it, can I recommend the Mythbusters episode where they explained this simply and tested it by getting a plane to take off on what was effectively a treadmill. Yeah fair comment but Mythbusters used a propellor powered model weighing a couple of hundred grams, the induced airflow from the prop over the wings will create some lift, not so on a 100 ton jet powered airiner Quote Link to comment Share on other sites More sharing options...
MrRalphMan Posted October 11, 2008 Share Posted October 11, 2008 Yes I am not convinced. I thought I'd explained everything clearly too. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 11, 2008 Share Posted October 11, 2008 Are there still doubters that it would take off? I think branners explanation should clarify how thrust works (in simple terms) and how it doesn't matter what the treadmill/wheels is/are doing. There is no power to the wheels at all so even if the treadmill suddenly stopped the speed of the plane moving wouldn't change. Quote Link to comment Share on other sites More sharing options...
Gazboy Posted October 11, 2008 Share Posted October 11, 2008 Yeah fair comment but Mythbusters used a propellor powered model weighing a couple of hundred grams, the induced airflow from the prop over the wings will create some lift, not so on a 100 ton jet powered airiner OMG How do you think a sea plane takes off? If you were right, then the reverse would be true- get a treadmill going really fast in the direction of travel and planes would need sorter runways! That'd solve Heathrows third runway problem wouldn't it! Quote Link to comment Share on other sites More sharing options...
MrRalphMan Posted October 11, 2008 Share Posted October 11, 2008 If you were right, then the reverse would be true- get a treadmill going really fast in the direction of travel and planes would need sorter runways! That'd solve Heathrows third runway problem wouldn't it! But that would work, by accelerating the plane faster then it's engines can, you get to lift off speed faster and so it takes off. Like the catapult on an Air Craft Carrier. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 11, 2008 Share Posted October 11, 2008 OMG How do you think a sea plane takes off? If you were right, then the reverse would be true- get a treadmill going really fast in the direction of travel and planes would need sorter runways! That'd solve Heathrows third runway problem wouldn't it! He's right though Gaz. If you could create enough wind you could get any plane to take off without actually moving as long as it was anchored. he didn't mention a treadmill. Quote Link to comment Share on other sites More sharing options...
tbourner Posted October 11, 2008 Share Posted October 11, 2008 Haven't we already seen all these arguments for and against in the previous thread? Is this one going to be longer before it gets locked? Does the treadmill have a fan built into the console? Maybe there's a HUUUUUGE fan at the back of the runway that blows air at the back of the plane equal to the forward wind speed, that'd make it more interesting. We'd then need to get into fluid dynamics of how the thrust from the engines disturbs the air coming from behind and with disipation to the sides we'd still get some forward air movement over the wings etc. IF that were the case, but it's not, so it will take off. Didn't you see the diagram!!!!! Quote Link to comment Share on other sites More sharing options...
Thorin Posted October 11, 2008 Author Share Posted October 11, 2008 I think the treadmill would take off. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 11, 2008 Share Posted October 11, 2008 Haven't we already seen all these arguments for and against in the previous thread? Is this one going to be longer before it gets locked? Maybe there's a HUUUUUGE fan at the back of the runway that blows air at the back of the plane equal to the forward wind speed, that'd make it more interesting. We'd then need to get into fluid dynamics of how the thrust from the engines disturbs the air coming from behind and with disipation to the sides we'd still get some forward air movement over the wings etc. IF that were the case, but it's not, so it will take off. Didn't you see the diagram!!!!! Jet engine wouldn't take off in that instance. Approx 100mph is required over the wings to generate enough lift. If there was a fan at the back, a hypothetical monster fan, then it would pretty much cancel out the wind at the front. The plane would continue to move forward at its normal rate though so would end up crashing or getting enough distance from the fan to take off. Saying that, the wind may generate extra thrust from the engine keeping the plane in front of the wind so its possible i guess. Quote Link to comment Share on other sites More sharing options...
Havard Posted October 11, 2008 Share Posted October 11, 2008 I love these type of threads....... For my own understanding I did a little experiment last night involving a conveyor belt and a plane. I get everything set up and the experiment was almost perfect. I ran the conveyor as fast as it would go. The plane just sat there and ran off the end of the conveyor belt. It fell to the floor, blunted the blade and damaged my new laminate, I may now not be able to take 3mm off the bottom of my bedroom door now.... H. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 11, 2008 Share Posted October 11, 2008 I love these type of threads....... For my own understanding I did a little experiment last night involving a conveyor belt and a plane. I get everything set up and the experiment was almost perfect. I ran the conveyor as fast as it would go. The plane just sat there and ran off the end of the conveyor belt. It fell to the floor, blunted the blade and damaged my new laminate, I may now not be able to take 3mm off the bottom of my bedroom door now.... H. I wouldn't worry about it H, by the sounds of it you shouldn't be near anything with a blade anyway Quote Link to comment Share on other sites More sharing options...
OhGod Posted October 11, 2008 Share Posted October 11, 2008 I'm still not convinced it'd take off either! From what I can see the "it would take off" group assume a completely frictionless, free spinning set of wheels with their "it'd take off as normal, the wheels would just spin twice as fast" theory. As in, treadmill goes backwards at a speed of -10, plane produces thrust for a forward speed of +10, plane moves forward at +10 while wheels spin at +20. What if, while keeping everything else the same, the plane drops it's thrust to 7? Forward speed of +7, wheel speed of +17? Now drop the thrust to 3...forward speed of +3, wheel speed of +13? Now drop the thrust to 0, forward speed of +0, wheel speed of 10? See, the "it's not a car, the wheels don't power it/matter" seemed logical until that last step. From the "it would take off" argument you should be able to set the treadmill to any speed and the plane will remain stationary as the wheels free wheel to compensate. I can't see this being the case, so the treadmill via the wheels does produce a backward force on the plane, meaning you have to produce a little bit more thrust to get to take off speed. But each time you try to do this, the treadmill increases speed to counter. This of course relies on this theoretical treadmill being able to counter the speed instantly of course. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 11, 2008 Share Posted October 11, 2008 I'm still not convinced it'd take off either! From what I can see the "it would take off" group assume a completely frictionless, free spinning set of wheels with their "it'd take off as normal, the wheels would just spin twice as fast" theory. As in, treadmill goes backwards at a speed of -10, plane produces thrust for a forward speed of +10, plane moves forward at +10 while wheels spin at +20. What if, while keeping everything else the same, the plane drops it's thrust to 7? Forward speed of +7, wheel speed of +17? Now drop the thrust to 3...forward speed of +3, wheel speed of +13? Now drop the thrust to 0, forward speed of +0, wheel speed of 10? See, the "it's not a car, the wheels don't power it/matter" seemed logical until that last step. From the "it would take off" argument you should be able to set the treadmill to any speed and the plane will remain stationary as the wheels free wheel to compensate. I can't see this being the case, so the treadmill via the wheels does produce a backward force on the plane, meaning you have to produce a little bit more thrust to get to take off speed. But each time you try to do this, the treadmill increases speed to counter. This of course relies on this theoretical treadmill being able to counter the speed instantly of course. I would think the same if i had absolutely no understanding of what thrust is and how it has absolutely nothing to do with the wheels Edit: I can't see this being the case, so the treadmill via the wheels does produce a backward force on the plane, meaning you have to produce a little bit more thrust to get to take off speed. But each time you try to do this, the treadmill increases speed to counter. This of course relies on this theoretical treadmill being able to counter the speed instantly of course. This is correct but, it would be impossible to create this amount of friction through the wheels. They would not be able to withstand that amount of force and the tyres would shred etc etc etc etc. Its theoretically possible but practically impossible. Quote Link to comment Share on other sites More sharing options...
Thorin Posted October 11, 2008 Author Share Posted October 11, 2008 There is no spoon. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 11, 2008 Share Posted October 11, 2008 Think of it like a boat in the ocean. If you put a boat into a current it will move the boat the way the current is going. If you raise the sail and the wind is blowing the other way all you need is the amount of force created from the wind (thrust) to be greater than the amount of force created by the ocean (friction) and the boat will move forward. With the plane, the only thing that would hold back the plane would be the friction created by the wheels and the friction created by the air. Using a treadmill would increase the amount of friction in the wheels but nowhere near enough to cause the plane any problem when it comes to moving forward. The friction created by the air would be exactly the same as it always was so it would cause no problem. You have to understand just how much thrust these engines produce. Quote Link to comment Share on other sites More sharing options...
miko_supra Posted October 11, 2008 Share Posted October 11, 2008 So how do you think regular planes ever get moving then? By not sitting on the spot on a treadmill? This thread is gonna turn into a long one Quote Link to comment Share on other sites More sharing options...
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