the conveyer belt will not drag air. if it does disturb the air at all. it will be such a small effect that you can effectivley ignore it. if there was a system in place to keep the plane from moving horizontally, it would not take off. such a system exists actually, its the brake on the wheel. put the brake on, plane wont move. The sole purpose of the engine, is to move air backwards. and there is a law of physics that states that for every action (in this case the propeller pushing on the air) there is an eaqule and opposite reaction (in this case the air is also pushing on the propeller in the opposite direction.) if you stood behind a plane with its engine going full power the wind would be enough to blow you over. that much air pushing back on the propeller is enough to push hard enough on the propeller that it moves the plane forwards. If you dont understand that concept, picture yourself standing on ice with skates on. a friend of yours is infront of you. he also has skates on. you push him, but its not just him that moves, you will also be pushing yourself away. the action is you pushing on him, the reaction is in effect, he also pushes on you, the result is that you both move. As the aircraft starts to move forward due to the propeller pushing on the air (and the air pushing back in the opposite direction) it will gain speed. as it gains speed a pressure differental will start to build above and below the wing. this is mainly due to the shape of the wing, but there are other factors. the bottom of the wing will have a high pressure, the top a low pressure. the high pressure pushes up, the low pressure pulls up. This causes lift. Lift has a value, as does weight. say for example the plane weighs 1000lbs. When the value of lift hits 1000lbs, it will be eaquel and opposite to weight. remember that weight is due to gravity and pulls down. the result of the pressure differental around the wing will pull the plane up. once the value of lift is more than the value of weight, the plane will be able to leave the ground and become airborne. On a side note. there a lot of variables that I left out. things that you would consider and be tought if you were to persue a career in aviation. But for the sake of my sanity, and my fingers, I have made this fairly simple. if you need farther clarification, let me know. On a second side note, the pilot who flew me home today was one of my old flight instructors. Its amazing where you meet people from your past when you least expect it.
The problem with that is as soon as you factor the word 'infinite' in, all common-sense flies out the window as it moves all arguments into the absurd... you could argue a 747 could never land because a random bee flying at infinite velocity could impact it when landing... Anyway back to the problem at hand: there are several forces acting on the aircraft at takeoff: 1-forward thrust from engines 2-upwards thrust from wings from airspeed mainly from engine thrust 3-resistance from landing gear acting apon ground... Now i'd be incredibly surprised if #3 has any bearing whatsoever at all apon anything unless the pilot forgets to take the handbrake off... Again back to my first point: i cannot understand how anyone can think that a plane on an treadmill cannot take off... it just cannot make any difference unless you go to absurd situations like the treadmill going so fast the landing gear melts and the plane crashes... any other situation will mean the plane takes off... It's just basic physics people And in case people are still confused: PLANES DO NOT SPIN THE WHEELS ON THE LANDING GEAR TO TAKE OFF THE ENGINES ARE NOT CONNECTED TO THE WHEELS IN ANY WAY
hurray for captain oblivious, and his loud parrot. i am not among the people that are confused, i was only talking about an hypothetical improbable system were the drag from the wheels would not help the plane take off.... i was thinking of what is possible with physics and then insert mathematics into it. and yes, in the real world a plane on a conveyor will fly, there is no way a conveyor can go that fast and wheel drag that high.
that video doesn't explain anything at all! I always thought it was a black guy singing that, no way is that voice coming out of that little redhead Wouldn't it be easier instead of getting a big conveyor, to chain the plane to the ground, go full power, lift gets so strong the plane starts to rise, release chain and off she goes, or just get a harrier or other vtol.
I may be being dumb here but I've read this thread and still don't understand it. If the conveyor belt was going the same speed backwards as the plane is going forward then surely the plane can't take off as there's no air moving around the wings. The Mythbusters plane was moving forward though so what does that prove. Obviously if the plane can move forward it will take off. What exactly does any of this prove? Edit: Infact after thinking about it a bit more. The whole debate doesn't seem to be about if it wil take off. It's whether or not a plane will move forward on a conveyor belt. Is that right?
That's exactly right, if a plane can move it can take off (if it can reach a high enough speed). Too many people are looking at the question and thinking that the plane can't move because the treadmill is going backwards at the same speed as the wheels. Since the plane "can't move", it can't take off. People are correct about that, but they have the fundamental bit of the problem completely wrong, the plane will move, the rollerblade explains exactly why the plane will move. People saying the experiment was wrong because the plane moved have got the wrong end of the stick.
I can't believe that people are still debating this, even after the fact Mythbusters (and physics) proved it is possible! It's so darn simple.
Ok I get it now. I was confused before because I thought the idea was that the plane was meant to be held stationary by the conveyor belt.
I know how a plane works (even if I did ask a stupid question earlier because I got confused after reading all of this), and am planning to try to get a licence to fly a Cessna. I mean I was not expecting the answer to be the plane still fly because he can move compared to the ground because the wheels allow the plane to move independently to the speed of the conveyer belt. If like in the start of the thread someone specified all the parameters to take in account I guess we would be less confused =/ It is almost like a trick question Ditto : ), I thought that the wheels were considered not perfect and the treadmill would have to go at some speed Y, to force the plane to not move at all compared to the ground.
Actually, the plane doesn not have to be moving to take off. What makes a plane fly is not it's speed relative to the ground, but it's speed relative to the air. This is why aircraft take off and land going into the wind. Doing so increases their speed relative to the wind but decreases their speed relative to the ground. This also means that if the wind blows hard enough an airplane can lift off even though it's stationary relative to the ground. If you visit an airport you'll notice that the planes are tied down for exactly this reason. In extreme circumstances a plane can actually fly backward relative to the ground because it's forward motion relative to the wind is less than the wind's motion relative to the ground. The part that really matters is the wings motion through the air, the rest is just drag.
Yeah I was working for Snecma for 1 year prior to join a bank (a company making engines used for aerospace and normal planes). We effectively use alot of machinery blowing air to test aerodynamism of new crafted parts. You can imagine that if you want to test aerodynamism for some hours at various speed, you will not throw it along a rail but instead blow air on it ... It was just that when I read the replies I really got confused, for some reason, I thought that the conveyor speed had to go at a very high speed to maintain the plane in place using the residual friction of the wheels (which would be supposed not perfect), and thought that maybe at that speed it would drag some air under the wings (since it would be very high). Did not understand the test from mythbusters since I was thinking that a car would not even be close to enough fast for the friction to be equal to the thrust. I think the easy way to answer so everybody understand is to say that: The plane will be moving compared to the ground, and that is the ONLY reason it will be taking off If you do not agree you misunderstood We suppose the wheels to have no or few friction The converyor will be moving with a relative speed of X the plane will be using the same motor thrust than the one to reach X if the plane was hang to the ground by a system which would allow it to move only vertically it would not take off This is the problem as written in the link provided in the first link Well if you re-read it, this is very badly written. It tries to trick you into thinking that the plane is not moving. Of course if the plane is moving, it is taking off ... In fact I doubt that the problem was correctly explained to the guy holding the flight center because I am quite sure that he would get it right if asked correctly =/
Not no but yes, because the lift from a non-VTOL aircraft is a function of the velocity of the air relative to the wings, not the ground. It's all about windspeed. If you've got powerfull motors moving air fast enough over the wings, the plane will rise/fly. Release the chain, and it will start to fly away. If you had a ridiculously huge headwind then the motors can be turned off and the plane will rise. For those that don't get the conveyor, the only hope the conveyor has to keep the plane still is a large amount of friction in the wheels, cos lets say a certain little plane needs to travel at 100kmh to take off. We sit this plane on a long conveyor doing 100kmh backwards. The plane doesn't care, it needs 100km/h of airspeed to take off. So the plane powers ahead like normal, and once it has 100kmh of airspeed, it takes off. If there is no wind, then this will be 100km/h relative to the ground, so the wheels are actually doing 200km/h relative to the conveyor belt! - this is where the friction aspect comes in, because the wheels are having to spin at double the rate! The plane moves forward because it is the propellor "grabbing" or "pulling" or "sucking" the air that makes the plane move forward. Think of a seaplane - seaplanes move forward because of the propellors, they don't care about the speed of the current (ignoring big crashing waves of course!) Now, lets say there is a huge 50km/h headwind, so the plane only needs to travel at 50km/h relative to the ground, to achieve the same 100km/h airspeed, and it takes off at 50km/h relative to the ground, and the wheels are doing 150km/h relative to the conveyor belt! Now pretend the little plane has a couple of powerfull motors, that can move the air at 50km/h past the wings, and we have a big 50km/h headwind. In this case, the plane can be stationary relative to the ground, the wheels are doing 100km/h and the plane rises. Once the plane rises the plane will start moving forward of course, unless we weren't using a conveyor belt but a chain to keep the plane still, in which case it just hovers until we release it.
Actually that is a very important part, planes can be held stationary to the ground sometimes until the wind changes direction or stops.
I can't resist chiming in, even this late in the game. Mythbusters proved absolutely nothing. They did not meet the terms of the problem as I heard it. I first heard the myth where the conveyor must match the plane tires rotational speed, and not forward speed of the plane. If it is to match the Forward velocity of the plane it will of course take off. If it is to match the wheels rotational velocity it will not take off PERIOD. Hopefully everyone will see the difference, and how one or two words rearranged or changed can change a scenario from guaranteed, to impossible. EDIT: forgot to include the simple formula as to why it cannot take off by matching wheel speed. V1 = V2 = V2+V1 where V1 equals the rotation speed of the wheels and V2 equals the velocity of the conveyor and where the value of both is greater than zero (impossible, I know). Ex: The wheel rotates at 1MPH relative to the conveyor surface. This means that the conveyor instantly accelerates to 1 MPH relative to the ground in the SAME direction, and increases the rotational speed of the wheels to 2 MPH. This all happens instantly (according to the terms of the problem). This means that the conveyor belt attains an instant velocity of c (speed of light). Even if the plane and it's gear were indestructible, the resistance is simply too great. This scenario is impossible of course and cannot be tested.
