Plane on conveyor belt

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Physics Plane on conveyor belt

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Aurora	Jun 17 2009, 12:53 AM Return to original view \| Post #1
On my way Senior Member 630 posts Joined: Jan 2003	QUOTE(SeaGates @ Jun 15 2009, 11:55 PM) This is highly controversial debate that's still raging I think. The question is that can a plane take off on a conveyor belt moving at the speed in opposite direction? Both camp of yes and no are split quite evenly. The 'Yes' camp argued that : - Plane do not use wheels to fly, so it can lift off even if the ground is moving away at the opposite direction at the same speed. The 'No' camp argued that : - If the plane remained stationary, it wouldn't have forward momentum for air to slice through to the wing to generate lift, hence it won't have lift off. Sure, Mythbuster tested the myth, but through proper observation you will notice that both model and full scale plane in the myth has some forward momentum. In my opinion, not definite fact, there's flaws in this debate. - Propeller propelled air into the wing, thus able to generate lift despite being stationary. - If plane are able to lift up without moving, why does it still need a runway? VTOL would be laughing stock since it's an invention that fixes nothing! So IMO, a plane on a conveyor belt wouldn't fly away. I am on the 'No' camp This is first time I saw this kind of topic. My answer is "YES". The plane can fly on a moving conveyor which travel at the same speed in the opposite direction. I think we need to read the statement again. Can a plane take off on a conveyor belt moving at the speed in opposite direction?. It didn't mention that the plane will be stationary. Reason why there is a large number of people in the "no camp" because they misinterpret that the airplane will be stationary when the conveyor is moving in the opposite direction. Allow me explain a bit. Cheesenium has post an extensive lift principle, so I'll skip that. For my explaination, you need to know at least the definition of newton's third law. In newton's third law, every action has a reaction in the opposite direction. On a moving conveyor, an object will remain stationary (to a third eye) if there is a force in the opposite direction reacting on the object. For example, a car. The reaction force will be driving the car at the same speed of the conveyor, in the opposite direction. Because the conveyor is moving, the car appear stationary, like a dyno machine. Agree? Now, in airplane, the reaction force comes from the thrust of the engine. When we run the engine, the engine move air from the suction to the exit. Basically it doesn't move air on top and below the wing, but across and within the engine. So there is plenty of thrust generated, but without air moving across the wings, it will never fly. Next, imagine we mount the engine on a trolley, or cart (just the engine, without the wing). The thrust generated will transfer the force to the trolley, and hence pushing the trolley forward. The same effect can also be achieved with fan on a trolley. As the trolley travel forward, air travel across it. Although trolley cuts through the air, it don't fly because there is no wing. Now, we exchange the trolley with a hull and wings, so we get an airplane. WHEN a plane travel forward (on the runway), only will, the air move across the wing, and create lift. (Hope everyone can keep up with this.) Now, we upgrade the experiment a bit. We put a conveyor at the bottom. By running the airplane on a conveyor, the engine actually create thrust onto the hull. Despite whatever the ground speed maybe, the thrust generate force onto the stationary air. If the ground travel at light speed yet the air above it remain stationary, the thrust will generate force onto the air, unlike car which generate thrust onto the ground. So, the airplane will just keep moving forward. When it gain enough speed, sufficient air movement across the wing, the airplane will take off. In fact, it will still require the same runway length disregard of whatever speed the conveyor maybe. Mythbuster is right. This post has been edited by Aurora: Jun 17 2009, 01:01 AM
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Aurora	Jun 19 2009, 10:37 PM Return to original view \| Post #2
On my way Senior Member 630 posts Joined: Jan 2003	QUOTE(Aurora @ Jun 17 2009, 12:53 AM) This is first time I saw this kind of topic. My answer is "YES". The plane can fly on a moving conveyor which travel at the same speed in the opposite direction. I think we need to read the statement again. Can a plane take off on a conveyor belt moving at the speed in opposite direction?. It didn't mention that the plane will be stationary. Reason why there is a large number of people in the "no camp" because they misinterpret that the airplane will be stationary when the conveyor is moving in the opposite direction. Allow me explain a bit. Cheesenium has post an extensive lift principle, so I'll skip that. For my explaination, you need to know at least the definition of newton's third law. In newton's third law, every action has a reaction in the opposite direction. On a moving conveyor, an object will remain stationary (to a third eye) if there is a force in the opposite direction reacting on the object. For example, a car. The reaction force will be driving the car at the same speed of the conveyor, in the opposite direction. Because the conveyor is moving, the car appear stationary, like a dyno machine. Agree? Now, in airplane, the reaction force comes from the thrust of the engine. When we run the engine, the engine move air from the suction to the exit. Basically it doesn't move air on top and below the wing, but across and within the engine. So there is plenty of thrust generated, but without air moving across the wings, it will never fly. Next, imagine we mount the engine on a trolley, or cart (just the engine, without the wing). The thrust generated will transfer the force to the trolley, and hence pushing the trolley forward. The same effect can also be achieved with fan on a trolley. As the trolley travel forward, air travel across it. Although trolley cuts through the air, it don't fly because there is no wing. Now, we exchange the trolley with a hull and wings, so we get an airplane. WHEN a plane travel forward (on the runway), only will, the air move across the wing, and create lift. (Hope everyone can keep up with this.) Now, we upgrade the experiment a bit. We put a conveyor at the bottom. By running the airplane on a conveyor, the engine actually create thrust onto the hull. Despite whatever the ground speed maybe, the thrust generate force onto the stationary air. If the ground travel at light speed yet the air above it remain stationary, the thrust will generate force onto the air, unlike car which generate thrust onto the ground. So, the airplane will just keep moving forward. When it gain enough speed, sufficient air movement across the wing, the airplane will take off. In fact, it will still require the same runway length disregard of whatever speed the conveyor maybe. Mythbuster is right. Hate to quote myself. The correct answer is in my post. I take it some of the reader is from various background and age group, so I ignore all the physic equations, assuming an ideal case. QUOTE(wKkaY @ Jun 17 2009, 05:48 AM) If it generates thrust towards the hull, doesn't that create drag and result in force going in the backwards direction, working against the airplane? And besides, the point of the conveyor is to match the airplane's forward speed but in the opposite direction, so "keep moving forward" won't happen unless the wheels loose frictional contact with the belt. Yup, the hull is actually holding the engine from moving forward. However given enough thrust, it will overcome this resistance and start moving forward. If you take a close look at Boeing, you will notice a "lump" at the bottom of the hull, which connect to the wing. The point of the discussion is conveyor belt and take-off. Friction is secondary. In fact, if there is zero friction and resistance, the plane will move with a household fan!!! Of course, if we were to discuss about extreme case, secondary factor will become big enough and will have significant effect. But that is not the point here. Mythbuster target audience is general public, hence they try to make it less technical. bgeh pointed the friction, which would just bored the viewer if mythbuster broadcast this much.
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Aurora	Jun 25 2009, 09:55 PM Return to original view \| Post #3
On my way Senior Member 630 posts Joined: Jan 2003	QUOTE(Thinkingfox @ Jun 22 2009, 02:46 PM) So, since many of us here agree that the plane can take-off even when it is on the conveyor belt, can we use this to decrease the length of the runway? *Let's assume that we can manufacture a conveyor belt that is strong enough Nope, it wouldn't help the plane to take off earlier. We will still need a conveyor as long as the runway. QUOTE(mylife4nerzhul @ Jun 24 2009, 03:28 PM) To those who actually support the 'YES' answer, what are you guys thinking? I'm am not a scientist. In fact, I'm pretty ignorant when it comes to science. But even I know that most airplanes, in this case, a 747, need to have wind pass it's wings in order for it to fly. If a plane is on a conveyor belt that is moving backwards as fast as the plane is moving forward, then the plane is actually just staying still. If the plane stays still, then there is no wind passing it's wings. And if you think a plane, with enough propulsion, can take off while staying still, then you are right, but those planes are called VTOLs (Vertical Take Off and Landing), and they use very powerful thrusters to lift them UPWARDS when taking off. Other, more traditional planes have thrusters (propeller, jet turbine, etc) that move the plane FORWARD so the wind will do the job of lifting the aircraft. UPDATE: Okay, I've seen the Mythbuster episode, and I am now in doubt about my own answer. But that doesn't mean I fully accept the other camp, though. The plane flown was just a light, propeller based plane, not a huge jet turbined behemoth like a 747. UPDATE: Okay, I changed my mind. Actually it is possible to take off, even for a 747. Glad that you change your mind. The thrust is acting on the stationary air, not on the conveyor. If we have wind traveling backward that fast, the airplane will take off vertically. That is how scientist did the simulation in wind tunnel.
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Aurora	Jun 29 2009, 05:51 PM Return to original view \| Post #4
On my way Senior Member 630 posts Joined: Jan 2003	Try read before posting. For godsake, it's only 5 pages. We don't have that much amount of patience to type it over and over again. fantagero: try look up mythbuster member profile before making a fool of yourself.
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Aurora	Jun 29 2009, 07:17 PM Return to original view \| Post #5
On my way Senior Member 630 posts Joined: Jan 2003	QUOTE(fantagero @ Jun 29 2009, 06:33 PM) did i wrote something wrong? i know mythbusterr are professional. what i meant was, the experiment they did is experiment (where the plane take off). of coz the result gonna be different if u talking in term of simple physics. where assumption could be made. No offense bro The thrust from the running engine is acting on stationary air. Did the conveyor movement affect or disturb the air? Hate to repeat the post. Hereby I repost my explaination again. » Click to show Spoiler - click again to hide... « QUOTE(Aurora @ Jun 17 2009, 12:53 AM) This is first time I saw this kind of topic. My answer is "YES". The plane can fly on a moving conveyor which travel at the same speed in the opposite direction. I think we need to read the statement again. Can a plane take off on a conveyor belt moving at the speed in opposite direction?. It didn't mention that the plane will be stationary. Reason why there is a large number of people in the "no camp" because they misinterpret that the airplane will be stationary when the conveyor is moving in the opposite direction. Allow me explain a bit. Cheesenium has post an extensive lift principle, so I'll skip that. For my explaination, you need to know at least the definition of newton's third law. In newton's third law, every action has a reaction in the opposite direction. On a moving conveyor, an object will remain stationary (to a third eye) if there is a force in the opposite direction reacting on the object. For example, a car. The reaction force will be driving the car at the same speed of the conveyor, in the opposite direction. Because the conveyor is moving, the car appear stationary, like a dyno machine. Agree? Now, in airplane, the reaction force comes from the thrust of the engine. When we run the engine, the engine move air from the suction to the exit. Basically it doesn't move air on top and below the wing, but across and within the engine. So there is plenty of thrust generated, but without air moving across the wings, it will never fly. Next, imagine we mount the engine on a trolley, or cart (just the engine, without the wing). The thrust generated will transfer the force to the trolley, and hence pushing the trolley forward. The same effect can also be achieved with fan on a trolley. As the trolley travel forward, air travel across it. Although trolley cuts through the air, it don't fly because there is no wing. Now, we exchange the trolley with a hull and wings, so we get an airplane. WHEN a plane travel forward (on the runway), only will, the air move across the wing, and create lift. (Hope everyone can keep up with this.) Now, we upgrade the experiment a bit. We put a conveyor at the bottom. By running the airplane on a conveyor, the engine actually create thrust onto the hull. Despite whatever the ground speed maybe, the thrust generate force onto the stationary air. If the ground travel at light speed yet the air above it remain stationary, the thrust will generate force onto the air, unlike car which generate thrust onto the ground. So, the airplane will just keep moving forward. When it gain enough speed, sufficient air movement across the wing, the airplane will take off. In fact, it will still require the same runway length disregard of whatever speed the conveyor maybe. Mythbuster is right. This post has been edited by Aurora: Jun 29 2009, 07:22 PM
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Aurora	Jun 30 2009, 12:54 PM Return to original view \| Post #6
On my way Senior Member 630 posts Joined: Jan 2003	QUOTE(fantagero @ Jun 30 2009, 09:50 AM) QUOTE Now, we upgrade the experiment a bit. We put a conveyor at the bottom. By running the airplane on a conveyor, the engine actually create thrust onto the hull. Despite whatever the ground speed maybe, the thrust generate force onto the stationary air. If the ground travel at light speed yet the air above it remain stationary, the thrust will generate force onto the air, unlike car which generate thrust onto the ground. So, the airplane will just keep moving forward. would u mind transfer it to a diagram like what i did please? or probably just use mine. I'll begin with 1 sentence at a time: Despite whatever the ground speed maybe, the thrust generate force onto the stationary air. This is self-explanatory. Airplane engine moves air, air exit from the engine and act onto the stationary air, then it become thrust. If the ground travel at light speed yet the air above it remain stationary, the thrust will generate force onto the air Ground speed doesn't matter here, engine thrust only acts on air. unlike car which generate thrust onto the ground. So, the airplane will just keep moving forward. Explaination on why we should not confuse with car. WE must remember, mythbuster did the experiment at relatively low speed. Therefore most of the high speed assumption are negligible (like friction, crosswind). The point of argument here is about plane and conveyor, and not about discussion of secondary factor. A lot of things come into play when high speed is consider. In reality, the airplane will be bound to higher resistance when it try to takeoff from a moving conveyor. It's not part of this discussion to argue about these resistance, but simply the logic of can an airplane takeoff from a moving conveyor. bgeh: I think you try too hard. Forget about the assumption. Anyone who came in trying to argue about secondary factor and resistance obviously don't understand the question.
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Aurora	Jul 31 2009, 10:58 PM Return to original view \| Post #7
On my way Senior Member 630 posts Joined: Jan 2003	QUOTE(DeniseLau @ Jul 27 2009, 04:52 PM) » Click to show Spoiler - click again to hide... « Hmm... read a couple of explanations here, doesn't explain the fundamentals. I’ll try to explain here why an aeroplane can take off from a coveyor belt and do a comparison with cars on a coveyor belt. Here are the steps we'll take towards understanding the concept: Step 1 = How a car moves forward ("gains forward momentum" in TS's words) on a normal road Step 2 = How an aeroplane moves forward ("gains forward momentum" in TS's words) on a normal runway Step 3 = How a car reacts on a conveyor belt Step 4 = How an aeroplane reacts on a conveyor belt But before we get into all that, let me first describe how a car works and how an aeroplane works in a normal scenario... meaning like normal lah, without coveyor belt and all that. The Car First let’s take a look at the car. A car is able to move forward because it has an engine which is connected to a gear box which in turn is connected to the wheels. When you pay money to Petronas, they’ll give you petrol which when poured into your engine will cause the engine to rotate and spin the gears in the gearbox which will then cause your wheels to spin. The rotation from the wheels then cause the tires to push backwards against the road surface and move the car forwards, thus making you spend more money and making Petronas richer. But also making your car go forwards at the same time. So at this point, I'd like to introduce a new term just to make the explanations easier. The term is "Medium-of-motion". For a car, the petrol gives power to the engine which gives power to the gearbox which then gives power to the wheels and then finally the wheels push against the "medium-of-motion" which is the road surface. One important thing to note here in this scenario, is that the "medium-of-motion" (ie. the road surface) is not moving and is fixed. The Aeroplane Okay now let's look at how the aeroplane moves forward. Forget about the whole thing about "aerofoil" and "lift" and all that stuff, we don't really care about that, let's just look at how an aeroplane moves forward on the ground at an airport runway. Click to see how aeroplane moves on ground: » Click to show Spoiler - click again to hide... « Lol... but seriously though, an aeroplane moves forward both on ground and on air by using massive engines that suck in air from the front and blows it out the back. If you're wondering how something can move forwards by blowing air out the back, try inflating a balloon and then letting it go with the end untied. It flies forwards doesn't it? Same thing with the aeroplane, just that instead of keeping a tank full of air to blow backwards, it simply sucks in the air from the front and blows it out backwards. At this point, let's stop for a while and look at the "medium-of-motion" for aeroplanes. Again, Petronas's petrol gives power to the engines which give power to the propeller which then sucks in the air from the front and blows it out the back really fast causing the high speed air to push against the stationary air behind the propeller causing the plane to move forward. So the "medium-of-motion" here in this case is the air. So now we begin to see that the wheels of the airplane serves no purpose at all, except to hold the aeroplane up. That's why aeroplanes can also use skis or floaters instead of wheels. Introducing the conveyor belt! Okay, now that we understand the fundamental difference between how a car moves forward and an air-plane moves forward, let's bring in the problem... the conveyor belt! Before looking further into this problem, let's make a few assumptions: 1. The conveyor belt is very long, longer than the distance required for an air-plane to take off. 2. The conveyor belt is going 'backward' (i.e. opposing the direction we want to go). 3. The conveyor belt, aeroplane and car speeds can be controlled very accurately. 4. The car and the aeroplane has a GPS receiver that reads out the coordinates of it's current location. 5. The aeroplane has an additional speedometer that is connected to the aeroplane's wheels So now, we put the car on the conveyor belt. Let's see what happens. So we put the car on the belt, turn on the conveyor belt at 35KM/h. At the same time, we on the engine and start driving forwards at car-speedometer's 35KM/h in the opposite direction. Guess what? The car doesn't move forward or backward! It stays in the same spot although the wheels are spinning furiously. The GPS reading too doesn't change and it shows the same coordinates and a speed of 0KM/h! But why? Well, when you burn your petrol to make the wheels spin, normally the wheels will push against the road surface to go forwards. But this time, since the conveyor belt too is going backwards, the pushing action of the wheels is negated. It's like driving on a normal road, but instead of you going forwards, the whole world is going backwards! Because of this, all the force that the wheels is trying to apply to the ground to make the car go forwards is instead being used to stop the car from going backwards. In other words the forward momentum that the car is generating is being cancelled by the backward momentum of the conveyor belt. What does this mean? Well let's jam on the breaks!! Suddenly when you jam on the breaks, you realise that you're hurtling backwards at 35KM/h. Your GPS reader shows your previously stationary coordinates now moving backwards and your speed as 35KM/h!! So you press the fuel again all the way until your speedometer shows 35KM/h. Look now at your GPS reader and you see that your coordinates are stationary again and you're going at 0KM/h. Therefore, when your car says you're moving at 35KM/h, this is the speed of your car relative to the "medium-of-motion (ie. conveyor belt), it's not the true speed of the car. The true speed - relative to the Earth - of the car is given by the GPS receiver, which is 0KM/h. This happens to the car, because the "medium-of-motion" for the car is the road surface and this scenario, the conveyor belt simulates the road surface moving in the opposite direction. Now let's do it again, this time with an air-plane! Since air-planes move faster, we're going to set the conveyor to 100km/h! Also remember that we have connected an extra speedometer to the aeroplane's wheels, we'll be monitoring this as we do the experiment. Okay, first lets turn on the conveyor belt at 100KM/h. Immediately we see that the aeroplane is hurtling back at 100KM/h. Let's check the meters: GPS: 100KM/h -- going backwards Aeroplane's speed indicator: 0KM/h Speedometer connected to the wheels: 0KM/h Okay now we turn on the engines, and start pressing the fuel just a little. Look at the meters! GPS: 1KM/h -- going forwards Aeroplane's speed indicator: 1KM/h Speedometer connected to the wheels: 101KM/h Notice how fast the speedometer readings jumped? Why? To understand why we notice such a huge difference in the speedometer reading, we need to look again at the "medium-of-motion" idea. Remember that the speedometer is connected to the tires of the aeroplane, so it measures the velocity of the aeroplane relative to the conveyor belt. When the propellers of the aeroplane starts spinning, they begin to suck the air from the front and blow it backwards, this creates a forward momentum for the air-plane. Now this is where the magic happens: Because the "medium-of-motion" that the aeroplane uses is air and not the road surface, the conveyor belt cannot cancel off the forward momentum of the aeroplane! So almost immediately when you press the fuel, the air-plane will start moving forwards relative to the Earth! That's why your GPS will start showing you that you're moving forwards at a certain velocity. Now let's go full throttle!! GPS: 100KM/h Aeroplane's speed indicator: 100KM/h Speedometer connected to the wheels: 200KM/h So now we see that as we really start burning the petrol and making Petronas richer, we continue moving forwards relative to the Earth really fast! And since we are now moving forwards relative to the Earth really fast, it's exactly like taking off from a normal runway! But wait! Let's try something extra here. Let's maintain the aeroplane throttle but now pump up the conveyor belt speed to 300KM/h!!! Look at the meters!! GPS: 100KM/h Aeroplane's speed indicator: 100KM/h Speedometer connected to the wheels: 400KM/h Now the speed of the aeroplane - relative to the conveyor belt - increases to 400KM/h but the aeroplane's true speed relative to the Earth is unaffected! This is because the conveyor belt - which simulates the road as "medium-of-motion" - does not affect the aeroplane which uses the air as "medium-of-motion". Conclusions 1. Yes, an aeroplane can gain forward momentum while on a conveyor belt regardless of the speed of the conveyor belt. 2. Yes, an aeroplane can take off from a conveyor belt, because of #1. 3. No, taking off on a conveyor belt will not result in the aeroplane needing a shorter runway, it will still need the same length of runway to take off. 4. It's almost impossible to make an aeroplane stay stationary with it's engines on on a conveyor belt, unless you put the whole experiment inside a wind-tunnel. A wind-tunnel is to an air-plane what a conveyor belt is to a car. Alternative way to look at it Another way to look at this is through seeing humans running on a treadmill. In the first scenario depicted below, the man has to run faster than the treadmill if he wants to reach the wall. His legs are representative of the engines, gearbox and wheels of the car. In the second scenario depicted below, the man needs just to pull himself with the string to reach the wall. The string is representative of the air as the medium-of-motion while the hands are representative of the engines of an air-plane and it's propellers. Hope this helps you understand the concepts. » Click to show Spoiler - click again to hide... « Lol... took me a few hours just to write this one post! Need to rest Hey bro... Very detail explaination with all the diagrams.
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