Plane on a conveyor belt
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Everyone who have posted on here are right, unless there are proves to prove them wrong.
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I CAN prove you wrong and did with my analogy. Its not much different than if a plane flew over a moving conveyor belt that was moving the opposite direction at the same speed as the plane...only difference would be that the wheels aren't touching the conveyor belt. You could do a touch-and-go with a plane on a moving conveyor belt as well.
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Nobody gave me feedback on my rollerblades on treadmill analogy, it must not be very good
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dubbsy wrote:
Mitch, if I"m reading this right...everything about it is wrong...#1. Air travels faster over the tops of wings.. This creates a low pressure that in turns sucks the wing up (bring the plane up with it)
#2. The plane DOES have to physically move. The engines do not move enough air around the plane to create lift. ...but no matter what, when thrust is applied, the plane will move in relative space and the plane will take off just like there was no conveyor there in the first place.
alright hang on a second... the shape of a plane's wings are such that air moves over the top and accelerates downward AFTER it crosses the back right? so doesnt the air move more quickly under the bottom? it just accelerates as the air washes over tail end of the wing?
thats how i understood it?
now for shits and giggles... how does tunneling the air through a series of passages under a car hold it to the ground, because that would mean air traves more quickly over the top and would lift the car into the low pressure area created wouldnt it?
if i have this backwards id really like to know
somebody speak up cause im confused now -
Quit it guys. All this thinking hurts. I actually believe that the plane would take off and even remove itself from the conveyor because the thrust from the turbines alone would overcome the resistance of the conveyor itself. I don't believe it would take off from the very spot it was on though. Just that the conveyor wouldn't be able to keep up with the thrust.
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What a silly question. It wouldn't take off, it can't. As a few people said before, air is needed under the wings. The movement of the wheels is inconsequential and in truth the only reason we have wheels on a jet plane is because we have yet to find something better..
Jet engines are pointed backwards so downward thrust is nill. Notice that rockets point down...
As for the car/wind tunnel scenario, faster air makes for lower pressure according to simple physics. So yes, if the bottom of your car were completely flat then it would create upward lift. This is the reason for ground effects and air diffusors, as well as air spoilers (wings, lips, scoops). The reason why dragsters have a giant upsidedown wing and a front spoiler. The aero effect doesn't occur until excessive speeds that many cars will never reach.
2005 Mercedes-Benz C240 4Matic
1993 Mazda Rx-7 Twin Turbo (sold)
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you guys are looking at this all wrong. Airplanes do not accelerate using their wheels, they are used as a way to reduce friction (as opposed to dragging the belly of the plane) with the ground until the airplane has reached the speed in which it will lift. The planes jet engines/propellers/whatever provide forward thrust to get the plane to the speed at which it will build lift. The airplane doesn't care how fast its WHEELS are being driven in the other direction, just how fast the plane itself is moving. If the plane is traveling 100mph in one direction and the conveyor belt is traveling 100mph the other direction, the only thing affected are the wheels and the wheel bearings (which would be spinning at 200mph) and a tiny amount of friction. As soon as the airplane built enough thrust to counter the gravity/friction holding the plane to the conveyor belt it would start moving forward regardless of what speed the conveyor belt is moving. In other words you guys are reading the question wrong. If the question stated could a stationary airplane generate lift while not moving you would be correct, however the question asks what happens if it is placed on a belt that is moving the opposite direction of the plane at the same pace as the plane. Again, see my sidecar analogy that I posted earlier in this thread. Exact same principal....screw it, I'll post it again:
Think about it this way if you are driving a motorcycle with a side car on it at 50MPH and the conveyor is ONLY on the side car you can still drive the motorcycle at 50MPH, however the sidecars wheel(s) will be traveling 100MPH. Same principal applies here. The planes motors providing thrust would be the motorcycle in above analogy and the planes wheels would be the side car. It is very possible for the plane to take off.*
By your guys theory, the motorcycle in the above situation is not capable of moving forward either.
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AcesHigh wrote:
As for the car/wind tunnel scenario, faster air makes for lower pressure according to simple physics. So yes, if the bottom of your car were completely flat then it would create upward lift. This is the reason for ground effects and air diffusors, as well as air spoilers (wings, lips, scoops). The reason why dragsters have a giant upsidedown wing and a front spoiler. The aero effect doesn't occur until excessive speeds that many cars will never reach.see.. what you are saying, as well as I am saying.. is that the air moves more quickly under the wing to create lift, correct? That is exactly why diffusers ect are used on cars. That is why the top of the wing is shaped and the bottom is flat? the air washing over the tail accelerates and creates lift?
the plane could take off and in theory if wind was moving fast enough (either by nature or by engines) it would lift off the ground standing still regardless of what two little round pieces of rubber are doing below it. Chuck how does a a harrier (sp?) take off? it creates enough thrust or lift downward to lift it off the ground. In theory, a plane could lift off the ground if air were moving quickly enough?
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tjamz wrote:
you guys are looking at this all wrong. Airplanes do not accelerate using their wheels, they are used as a way to reduce friction (as opposed to dragging the belly of the plane) with the ground until the airplane has reached the speed in which it will lift. The planes jet engines/propellers/whatever provide forward thrust to get the plane to the speed at which it will build lift. The airplane doesn't care how fast its WHEELS are being driven in the other direction, just how fast the plane itself is moving. If the plane is traveling 100mph in one direction and the conveyor belt is traveling 100mph the other direction, the only thing affected are the wheels and the wheel bearings (which would be spinning at 200mph) and a tiny amount of friction. As soon as the airplane built enough thrust to counter the gravity/friction holding the plane to the conveyor belt it would start moving forward regardless of what speed the conveyor belt is moving. In other words you guys are reading the question wrong. If the question stated could a stationary airplane generate lift while not moving you would be correct, however the question asks what happens if it is placed on a belt that is moving the opposite direction of the plane at the same pace as the plane. Again, see my sidecar analogy that I posted earlier in this thread. Exact same principal....screw it, I'll post it again:Think about it this way if you are driving a motorcycle with a side car on it at 50MPH and the conveyor is ONLY on the side car you can still drive the motorcycle at 50MPH, however the sidecars wheel(s) will be traveling 100MPH. Same principal applies here. The planes motors providing thrust would be the motorcycle in above analogy and the planes wheels would be the side car. It is very possible for the plane to take off.*
By your guys theory, the motorcycle in the above situation is not capable of moving forward either.
You are my hero, excellent explanation. PPl don't understand that the plane would still move.
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51d3w4yz wrote:
You are my hero, excellent explanation. PPl don't understand that the plane would still move.Tjamz=Saving the internet, one stupid topic at a time
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92BlackTT wrote:
In theory, a plane could lift off the ground if wind were traveling fast enough over its wings while standing still on the ground.This is true, though not likely to happen in normal situations. I was more refering to it being a windless day, in which case it would still take off. It would NOT take off however if were in an infinitely long wind tunnel with a tail wind traveling the exact same speed as the plane was traveling as that WOULD negate all lift as the person in the plane would feel no wind from the front or back (maybe a little swirling around the sides and whatnot, but not front/rear)...except a Harrier aircraft which is not affected by front/rear winds on take off (just to lift, I know wind is a concern once airborn due to stability)
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right. ok, now how about the whole wing design part that is making me tear my hair out. does air moving faster over the top of the wing or the bottom of the wing create lift. I always thought it moved faster over the bottom and accelerated as it washed over the tail end of the top?
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I'll have to do some thinking/research on that mitch and get back to you.
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lol you dont have to research, i was just hoping i could get an/better explaination from someone after dubbsy said thats not how it worked.
I figured it worked the same way as an F1 car..
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tjamz wrote:
you guys are looking at this all wrong. Airplanes do not accelerate using their wheels, they are used as a way to reduce friction (as opposed to dragging the belly of the plane) with the ground until the airplane has reached the speed in which it will lift. The planes jet engines/propellers/whatever provide forward thrust to get the plane to the speed at which it will build lift. The airplane doesn't care how fast its WHEELS are being driven in the other direction, just how fast the plane itself is moving. If the plane is traveling 100mph in one direction and the conveyor belt is traveling 100mph the other direction, the only thing affected are the wheels and the wheel bearings (which would be spinning at 200mph) and a tiny amount of friction. As soon as the airplane built enough thrust to counter the gravity/friction holding the plane to the conveyor belt it would start moving forward regardless of what speed the conveyor belt is moving. In other words you guys are reading the question wrong. If the question stated could a stationary airplane generate lift while not moving you would be correct, however the question asks what happens if it is placed on a belt that is moving the opposite direction of the plane at the same pace as the plane. Again, see my sidecar analogy that I posted earlier in this thread. Exact same principal....screw it, I'll post it again:Think about it this way if you are driving a motorcycle with a side car on it at 50MPH and the conveyor is ONLY on the side car you can still drive the motorcycle at 50MPH, however the sidecars wheel(s) will be traveling 100MPH. Same principal applies here. The planes motors providing thrust would be the motorcycle in above analogy and the planes wheels would be the side car. It is very possible for the plane to take off.*
By your guys theory, the motorcycle in the above situation is not capable of moving forward either.
No, you didn't listen to me. Jet engines (as they are mounted on jet planes) do NOT produce downward thrust. They aren't aimed downward.
You are making the assumption that it's the speed of the plane making it take off, and this is incorrect. Speed is all relative. When you are walking inside a moving train with it, you aren't going at 60 miles per hour. You're going at a meter a second. Same with the plane analogy. The wheels are moving, but the plane relative to its position is not. Regardless, speed does not make the plane fly.
The assumption here is that the conveyor is moving at the SAME speed as the plane, and thus a positive vector (the plane) added to a negative vector (the belt) equals zero. If the belt is moving slightly slower than the plane, then there is some positive movement here, and the plane MAY just move due to the wind that is passing under its wings.
With that said, a large gust of natural wind, as postulated earlier, may be enough to pick the plane up. Sort of like a paper plane. You need air velocity running through those wings, too, if you want it to fly.
2005 Mercedes-Benz C240 4Matic
1993 Mazda Rx-7 Twin Turbo (sold)
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