Gaz6002 Posted February 6, 2008 Share Posted February 6, 2008 You despair??? I'm genuinely disappointed in the level of intelligence from members, shown in this thread, and on top of that it's been around the internet for years. Thorin is spot on. If you were running at 7mph on a treadmill in a gym and had a jetpack on your back with a forward thrust capability of 100mph, bit like a plane, and whacked it up to the full 100mph suddenly, do you a) rocket off messily through the wall at 100mph, or b) note the treadmill now reads 107mph Right, while despairing, I thought up a great analogy. Don't bring into this friction or tyres exploding or minimum air speeds or anything as that's just silly side issues, it's a hypothetical thought experiment. Now, one of the best ways to think about if something behaves a certain way or not is to try the theory in different scenarios, so we'll have the plane land on a treadmill instead... Most of you state this is true: "A plane can't take off if the runway underneath acts like a treadmill, i.e. you push against it and it moves backwards. The plane will remain stationary no matter what thrust the pilot asks of the engines." I think that's a fair summing up. So the important thing here is - if the runway goes in the opposite direction at the same speed the plane will be stationary. That means if a plane flys at zero feet altitude at 300mph and touches down on a normal runway, the plane continues at 300mph and the wheels turn at 300mph. If the plane flys at zero feet altitude at 300mph and touches down on a runway going 300mph in the opposite direction, your statement about the plane's behaviour on a treadmill is that it will immediately stop dead because the treadmill cancels out the plane's forward speed Or, my theory says, the wheels just chirp almightily as spin at 600mph as the plane carries on it's merry way unaffected. If it then accelerates up to 400mph, the wheels go at 800mph as the treadmill goes 400mph backwards but the plane STILL ACCELERATES MERRILY ON ITS WAY. Other than that, I give up Watch mythbusters if you need the all-knowing telly to hammer it home. I'm frankly shocked at how this thread is panning out. -Ian PS I haven't seen the mythbusters episode, I'm that confident I'm right. I just tried to get a £1000 bet out of someone who was adamant it'd sit still, alas, they didn't have the conviction of their own argument Whilst I still don't understand, I do appreciate these statements. But you have to remember that this is hypothetical. None of this is provable as the forces involved are impossible to replicate. At the end of the day friction does come into it because the plane is on the runway, not in flight. Gravity also comes into the equation as this is what creates the lift. I agree the way the question has been put across means it's open to several interpretations but I also think that poking fun at someones intelligence because of a differing opinion on something that is not precisely quantifiable is not exactly responsible discussion. At the end of the day I remain completely un-convinced by the arguements against my opinion in this thread as far as my understanding of physics goes. I wait to be proved wrong. Quote Link to comment Share on other sites More sharing options...
Ian C Posted February 6, 2008 Share Posted February 6, 2008 I'm honestly stuggling to understand this your reasoning behind this? How can the forces be put together to create lift in this situation? You have a plane with 10,000lbs thrust behind it from a jet engine acting on the air around it. If it was on pontoons in water, on skids on ice, on wheels on a static runway, on a runway going forwards or backwards at any speed - if the plane starts stationary relative to the air around it and then goes for takeoff, it'll take off like a normal plane. Plane engine pushes against air, plane goes forward relative to air, plane gets fast enough to make a pressure differential on its wings, plane achieves controlled flight. Note in that process there is a complete lack of the word "ground". The ground is just there to stop the plane falling off the planet. Stand on a skateboard on a treadmill. Hold on to sides. Set treadmill to 10mph. Hold yourself there. Skateboard wheels are going 10mph. Pull yourself forwards via the sides at 2mph. Skateboard wheels do 12mph, you do 2mph forwards relative to the gym. If at this point the treadmill speeds up to 12mph, you emphatically do not suddenly find your speed relative to the gym cancelled out to zero. You still go forwards at 2mph when you pull. The only difference is that the skateboard wheels are doing 14mph. Ergo, treadmill speed has no influence over forward motion when the motive thrust is applied to something that isn't the treadmill - be it the static sides of it or plane engines acting on air. -Ian Quote Link to comment Share on other sites More sharing options...
grahamc Posted February 6, 2008 Share Posted February 6, 2008 hows is the lift created? by the standing air around the plane or the volume of air that is being past through the engine/propellor? Quote Link to comment Share on other sites More sharing options...
Thorin Posted February 6, 2008 Share Posted February 6, 2008 Ah but what if you have a small treadmill set vertically against one of it's wheels, set to go down as fast as you try to go up? easy, the harrier can then move away from the treadmill Ah but what if the treadmill was fixed to the body of the plane in such a way so that the actual belt is against the wheel? Quote Link to comment Share on other sites More sharing options...
Matt H Posted February 6, 2008 Share Posted February 6, 2008 No air is passing over and under the wings to give lift (high/low pressures) etc, plus the engines would overheat too I'd thought. EDIT: So no it won't take off. Just ask supradibbs well put the way i understand it is forget the wheels in relation to power the engine creates the power for forward motion (wheels free spin) the movement of the treadmill is doubling the forward speed thus creating enough forward speed to obtain lift Interesting Quote Link to comment Share on other sites More sharing options...
Gaz6002 Posted February 6, 2008 Share Posted February 6, 2008 Engine Thrust pushes the plane fwd. The wheels rotate in a reaction to this thrust. The treadmill doubles the speed of the wheels. The mass of the aircraft is still thrusted fwd...upto the AIR speed necessary for the air to be passing over the wing fast enough for liftoff. The wheel speed is still doubled but cannot affect the AIR speed of the plane. The plane is moving through the air relative to the earth, not the tradmill. But surely the treadmill being the runway is seen as the earth in this case? I mean it has to move relative to the runway as thats what it is sitting on. Quote Link to comment Share on other sites More sharing options...
Ian C Posted February 6, 2008 Share Posted February 6, 2008 hows is the lift created? by the standing air around the plane or the volume of air that is being past through the engine/propellor? Plane engine pushes against air, plane goes forward relative to air, plane gets fast enough to make a pressure differential on its wings, plane achieves controlled flight. Quote Link to comment Share on other sites More sharing options...
Matt H Posted February 6, 2008 Share Posted February 6, 2008 No its to move the plane forward. The plane moves forward and the SPEED of the air moving accross the wings is what lifts it. THe greater the speed, the greater the difference in pressure above and below the wing, the lack of pressure above the wing in comparrision to below it makes the plane lift off hows is the lift created? by the standing air around the plane or the volume of air that is being past through the engine/propellor? Post 46 is your friend Quote Link to comment Share on other sites More sharing options...
grahamc Posted February 6, 2008 Share Posted February 6, 2008 Plane engine pushes against air, plane goes forward relative to air, plane gets fast enough to make a pressure differential on its wings, plane achieves controlled flight. Not that I understand your response, but I am starting to understand why the plane WOULD take off. Quote Link to comment Share on other sites More sharing options...
Alex Posted February 6, 2008 Share Posted February 6, 2008 But surely the treadmill being the runway is seen as the earth in this case? I mean it has to move relative to the runway as thats what it is sitting on. It does move relative the treadmill/runway....it moves down it Quote Link to comment Share on other sites More sharing options...
Matt H Posted February 6, 2008 Share Posted February 6, 2008 Not that I understand your response, but I am starting to understand why the plane WOULD take off. better explanation in post 46 Quote Link to comment Share on other sites More sharing options...
Thorin Posted February 6, 2008 Share Posted February 6, 2008 If a tree falls in a forest and there's nobody around to hear it, does the treadmill make any noise? Quote Link to comment Share on other sites More sharing options...
Alex Posted February 6, 2008 Share Posted February 6, 2008 Thread of the YEAR!!!! Quote Link to comment Share on other sites More sharing options...
MrRalphMan Posted February 6, 2008 Author Share Posted February 6, 2008 Ah but what if the treadmill was fixed to the body of the plane in such a way so that the actual belt is against the wheel? Couldn't find the tut tut tut smily.. Quote Link to comment Share on other sites More sharing options...
Ric Posted February 6, 2008 Share Posted February 6, 2008 If a tree falls in a forest and there's nobody around to hear it, does the treadmill make any noise? No because your talking about a tree falling over, why would a treadmill make a noise? Quote Link to comment Share on other sites More sharing options...
Guest CoolsBlue Posted February 6, 2008 Share Posted February 6, 2008 i think it cant, although it picks up speed in one spot there is not enough air rushing into the engine and against the plane for the nose to lift up and to press agaisnt the flaps Quote Link to comment Share on other sites More sharing options...
grahamc Posted February 6, 2008 Share Posted February 6, 2008 Post 46 is your friend yes, Im getting there Quote Link to comment Share on other sites More sharing options...
Gaz6002 Posted February 6, 2008 Share Posted February 6, 2008 It does move relative the treadmill/runway....it moves down it I still maintain - the wheels move but the plane doesn't. How can the plane move if the speed being generated by the engines is cancelled out by the speed of the runway in the opposite direction? Quote Link to comment Share on other sites More sharing options...
tbourner Posted February 6, 2008 Share Posted February 6, 2008 I put no, but then realised I'm an idiot!!! If you think the plane won't move, then the treadmill wouldn't move anyway (because the plane is going 0mph), so then it would start to move, then the conveyer would stop it, etc. etc. Quote Link to comment Share on other sites More sharing options...
Ian C Posted February 6, 2008 Share Posted February 6, 2008 Whilst I still don't understand, I do appreciate these statements. But you have to remember that this is hypothetical. None of this is provable as the forces involved are impossible to replicate. Actually I think there is a mythbusters episode readily viewable on youtube that does in fact discuss, quantify, and downright prove the treadmill has no effect at all on the plane taking off. Someone must have a link to it? At the end of the day friction does come into it because the plane is on the runway, not in flight. The only increased effect is bearing and tyre friction on the wheels, the speed doubles so these will go up. Negligible in the scheme of things compared to the power required to get a 777 up in the air. Gravity also comes into the equation as this is what creates the lift. Er. Wow. Can't even begin to start on that one in this thread At the end of the day I remain completely un-convinced by the arguements against my opinion in this thread as far as my understanding of physics goes. Well, see above re understanding of physics Your unconvincedness is to be admired. I'm certainly not going to turn that around with mere text - find the mythbuster thang, or failing that, a jetpack and a treadmill now that'd be a youtube hit -Ian, entertained at work at last Quote Link to comment Share on other sites More sharing options...
Ian C Posted February 6, 2008 Share Posted February 6, 2008 i think it cant, although it picks up speed in one spot there is not enough air rushing into the engine and against the plane for the nose to lift up and to press agaisnt the flaps Please tell me all that is deliberate for comedy reasons. Quote Link to comment Share on other sites More sharing options...
grahamc Posted February 6, 2008 Share Posted February 6, 2008 http://www.youtube.com/watch?v=IbRcg3ji_Pc however it is not 100% correct Quote Link to comment Share on other sites More sharing options...
CJ Posted February 6, 2008 Share Posted February 6, 2008 Please tell me all that is deliberate for comedy reasons. For what it's worth, I agree with those that say yes, it would take off. Quote Link to comment Share on other sites More sharing options...
grahamc Posted February 6, 2008 Share Posted February 6, 2008 For what it's worth, I agree with those that say yes, it would take off. not worth a thing Quote Link to comment Share on other sites More sharing options...
Alex Posted February 6, 2008 Share Posted February 6, 2008 Does this help? http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html Quote Link to comment Share on other sites More sharing options...
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