Will the Plane Take-Off - Merged with MythBusters Show Thread
08-18-2006, 11:38 AM
#81
Nom Nom Nom Nom
Originally Posted by BEETROOT
You are saying that the reason the plane wouldn't move forward is because the tires spinning on this treadmill would what... not get the traction they needed to move the plane forward?
Doesn't matter if it takes off or not, if you have something generating thrust that relies on air, not contact with the ground, that thing is going to move forward regardless of whether or not there are wheels spinning beneath it. In the case of a jetpack, you will shoot forward and take off due to the thrust alone. In the case of the plane, you will move forward from that same thrust, which then generates lift from the airflow, and take off. Same principle regarding your forward movement, as neither case relies on any contact with the ground to move.
Doesn't matter if it takes off or not, if you have something generating thrust that relies on air, not contact with the ground, that thing is going to move forward regardless of whether or not there are wheels spinning beneath it. In the case of a jetpack, you will shoot forward and take off due to the thrust alone. In the case of the plane, you will move forward from that same thrust, which then generates lift from the airflow, and take off. Same principle regarding your forward movement, as neither case relies on any contact with the ground to move.
08-18-2006, 11:41 AM
#82
Suzuka Master
Originally Posted by SwervinCL
But if the treadmill is matching the velocity of the thrust that the engines are producing, the plane will be stationary.
08-18-2006, 11:43 AM
#84
Nom Nom Nom Nom
Take the wheels off the plane. Put the plane on the belly. Do you think that the thrust from the engines would be enough to get the plane moving fast enough for it to take off?
08-18-2006, 11:43 AM
#85
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Originally Posted by mclarenf3387
The thrust is created on the air, not the ground. The plane creates thrust on the air so the speed of the ground is irrellavent.
Remind me not to enroll my kids in BU.
08-18-2006, 11:43 AM
#86
Interesting. Interesting.
Originally Posted by SwervinCL
^ But if the ground is moving in the oppsite direction of the plane, the plane would then be stationary.
Only if the contact between the wheels and the ground is where the thrust vector acts. This is true for a car, but not for a plane.
08-18-2006, 11:45 AM
#87
Interesting. Interesting.
Originally Posted by SwervinCL
Take the wheels off the plane. Put the plane on the belly. Do you think that the thrust from the engines would be enough to get the plane moving fast enough for it to take off?
08-18-2006, 11:48 AM
#89
Yeehaw
Originally Posted by NSXNEXT
But Brett it's sitting on a conveyor belt that prevents it from moving forward. The faster the plane goes, the faster the belt turns in the opposite direction. How is the plane going to move forward?
08-18-2006, 11:50 AM
#90
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I dont understand why this is so difficult for you guys to wrap your head around. It doesnt matter if the converybelt matches the speed of the tires on the planes if they spin freely. The plane can move foward and acheive life because of thrust provided by the propellors or turbines on the wings not the tires. even if the tires are spinning at 500mphs and the converybelt matches that speed, the plane would move foward regardless and the tire speed would just accelerate. Its kinda like, how does a plane stay flying? By the thrust of the engines not the tires on the ground same principle at work here, you dont need ground/tires to move an object foward. You can accelerate in mid air because of thrust. The tires have nothing to do with it.
going with the dyno thing, the car doesnt move because of the "convyer" type thing. but that same care would move foward if you could attach a rocket on the roof.
going with the dyno thing, the car doesnt move because of the "convyer" type thing. but that same care would move foward if you could attach a rocket on the roof.
Last edited by FuriousGeorge83; 08-18-2006 at 11:53 AM.
08-18-2006, 11:52 AM
#92
Interesting. Interesting.
Originally Posted by BEETROOT
The conveyor belt doesn't prevent it from moving forward. It just moves the wheels, which have nothing to do with the forward motion of the plane.
yep.
This is why a plane can take off on a perfectly frictionless sheet of ice, whereas your car would just spin it's wheels and not move anywhere.
08-18-2006, 11:54 AM
#93
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The plane will fly because the thrust comes from the engines interacting with the air, not the wheels.edit: also how about a plane taking off from a river, where the water is running the opposite way, it still takes off....
Last edited by RyeCL; 08-18-2006 at 11:56 AM.
08-18-2006, 12:00 PM
#97
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Originally Posted by SwervinCL
I give up.
Me too.....
I actually googled the correct answer back on page 1 but felt it was fun playing the other side
08-18-2006, 12:07 PM
#99
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Of course it WILL fly!
The wheels do not provide thrust, it's the Jet engine that makes it go forward.
So, no matter how fast the belt spins, the airplan will move forward. The wheels will just spin fater than the speed of the conveyer belt.
EDIT: I should've read the entire thread... I'm on BEET's side.
The wheels do not provide thrust, it's the Jet engine that makes it go forward.
So, no matter how fast the belt spins, the airplan will move forward. The wheels will just spin fater than the speed of the conveyer belt.
EDIT: I should've read the entire thread... I'm on BEET's side.
Last edited by sipark; 08-18-2006 at 12:09 PM.
08-18-2006, 12:08 PM
#100
Nom Nom Nom Nom
OK, I read the post on Jason Kottke's site about the The case of the plane and conveyor belt, and quickly concluded that the plane cannot take off.
I was shocked, SHOCKED, to find smart people like Matt Haughey and Mike Buffington believing that the plane can take off.
Let me clear this up.
For an aircraft of any type to fly, it must overcome the constant acceration downward of gravity. Flying, for the most part, has little to do with speed and everything to do with the lifting force that counteracts the pull of gravity. Got that? Lifting force is all the matter to leave the ground and fly.
The question then is how do you generate enough lifting force. With a balloon, the lifting force is based on the fact that a bag of lighter-than-normal-air gas (usually hydrogen, helium, or hot air) will rise above normal (cold) air. Make sense? A balloon has no direct thrust or "push against air", it simply has the lifitng force of the gas.
Now let's look at an airplane. How does an airplane fly? An airplane flys off the ground solely because it can generate a lifting force. An airplane generates this lifting force by air flowing over an airfoil (known as a wing). The faster the air travels over the wing, the more lift is generated.
Planes that go fast can generate a lot of speed (air moving past the wings) can generate a lot of lift. If an airplne goes too slow, it doesn't generate enough lift to counteract the force of gravity, and it falls to the ground. This is called a stall.
So, now that you are versed in the basics of aerodynamics, let's look at the question of the airplane on the conveyer belt. The airplane will sit on the conveyer belt with engines blasting, tires rolling, and to the outside observer, standing in place. While tremendous forward force is being generated, there is no increase on the airflow over the wings.
So, if there is is no increased airflow over the wing, there is no lift. Without lift, the airplane CANNOT take off and fly. Let me repeat that key part, without lift, the airplane CANNOT take off and fly. It doesn't matter how hard the engines 'push the air', there is no lift being generated in the conveyor belt scenario.
I hope you can now see clearly the correct answer to the 'question' is that the plane will not take off.
If you start to argue about the validity of the basic aerodynamic theory of lift, you might as well start arguing that the earth is flat or in creationism.
Update: After reading the comments it seems like the debate is hinging on whether the plane stays stationary or not. Obviously above I'm assuming the plane/conveyor belt contrapion is designed to hold the plane still. If that is not assumed then then the entire question is stupid and ridiculous. It's then like asking can a plane take off in the rain or snow when the wheels slip.
If that's really the point that the question poser is making then it's fucking stupid. It's like those stupid tests where the first line says "1) Read all instructions carefully before taking the test" and the last line says "57) Now that you've read all the instructions carefully, don't do 2-56, write your name in and turn in the test." Fuck that shit.
I was shocked, SHOCKED, to find smart people like Matt Haughey and Mike Buffington believing that the plane can take off.
Let me clear this up.
For an aircraft of any type to fly, it must overcome the constant acceration downward of gravity. Flying, for the most part, has little to do with speed and everything to do with the lifting force that counteracts the pull of gravity. Got that? Lifting force is all the matter to leave the ground and fly.
The question then is how do you generate enough lifting force. With a balloon, the lifting force is based on the fact that a bag of lighter-than-normal-air gas (usually hydrogen, helium, or hot air) will rise above normal (cold) air. Make sense? A balloon has no direct thrust or "push against air", it simply has the lifitng force of the gas.
Now let's look at an airplane. How does an airplane fly? An airplane flys off the ground solely because it can generate a lifting force. An airplane generates this lifting force by air flowing over an airfoil (known as a wing). The faster the air travels over the wing, the more lift is generated.
Planes that go fast can generate a lot of speed (air moving past the wings) can generate a lot of lift. If an airplne goes too slow, it doesn't generate enough lift to counteract the force of gravity, and it falls to the ground. This is called a stall.
So, now that you are versed in the basics of aerodynamics, let's look at the question of the airplane on the conveyer belt. The airplane will sit on the conveyer belt with engines blasting, tires rolling, and to the outside observer, standing in place. While tremendous forward force is being generated, there is no increase on the airflow over the wings.
So, if there is is no increased airflow over the wing, there is no lift. Without lift, the airplane CANNOT take off and fly. Let me repeat that key part, without lift, the airplane CANNOT take off and fly. It doesn't matter how hard the engines 'push the air', there is no lift being generated in the conveyor belt scenario.
I hope you can now see clearly the correct answer to the 'question' is that the plane will not take off.
If you start to argue about the validity of the basic aerodynamic theory of lift, you might as well start arguing that the earth is flat or in creationism.
Update: After reading the comments it seems like the debate is hinging on whether the plane stays stationary or not. Obviously above I'm assuming the plane/conveyor belt contrapion is designed to hold the plane still. If that is not assumed then then the entire question is stupid and ridiculous. It's then like asking can a plane take off in the rain or snow when the wheels slip.
If that's really the point that the question poser is making then it's fucking stupid. It's like those stupid tests where the first line says "1) Read all instructions carefully before taking the test" and the last line says "57) Now that you've read all the instructions carefully, don't do 2-56, write your name in and turn in the test." Fuck that shit.
08-18-2006, 12:10 PM
#101
Suzuka Master
Originally Posted by SwervinCL
Wheres F900 when you need him.
08-18-2006, 12:10 PM
#102
Interesting. Interesting.
Another way to think about it: the plane is landing on a conveyor belt that is going in the opposite direction and same speed as the plane. The plane touches down and the engines are still on. Will the plane come to a dead stop instantly?
Last edited by wstevens; 08-18-2006 at 12:14 PM.
08-18-2006, 12:10 PM
#103
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Originally Posted by NSXNEXT
But Brett it's sitting on a conveyor belt that prevents it from moving forward. The faster the plane goes, the faster the belt turns in the opposite direction. How is the plane going to move forward?
The thrust from the engines is independant of the surface that the plane sits on. Drag is the only thing that will cause the plane to not move (that - or a big cement wall...).
You can't compare it to a dyno. Planes to not generate forward momentum by driving their wheels. You strap a jet plane to a dyno - and it will read 0 hp. The force is through the movement of air through the engine.
08-18-2006, 12:15 PM
#104
Yeehaw
Originally Posted by SwervinCL
Update: After reading the comments it seems like the debate is hinging on whether the plane stays stationary or not. Obviously above I'm assuming the plane/conveyor belt contrapion is designed to hold the plane still. If that is not assumed then then the entire question is stupid and ridiculous. It's then like asking can a plane take off in the rain or snow when the wheels slip.
08-18-2006, 12:16 PM
#105
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Originally Posted by fla-tls
OK - here's another way of thinking about it. You're walking on your manual treadmill, and your friend Mr. Jet engine comes behind you and pushes or tackles you forward. Do you move forward on the treadmill? Yes - probably fall off it. Why didn't the treadmill counteract that forward motion? Your friend's force is independant of the treadmill.
The thrust from the engines is independant of the surface that the plane sits on. Drag is the only thing that will cause the plane to not move (that - or a big cement wall...).
You can't compare it to a dyno. Planes to not generate forward momentum by driving their wheels. You strap a jet plane to a dyno - and it will read 0 hp. The force is through the movement of air through the engine.
The thrust from the engines is independant of the surface that the plane sits on. Drag is the only thing that will cause the plane to not move (that - or a big cement wall...).
You can't compare it to a dyno. Planes to not generate forward momentum by driving their wheels. You strap a jet plane to a dyno - and it will read 0 hp. The force is through the movement of air through the engine.
Terrible analogy because the treadmill belt does not control your speed. If you run faster than the treadmill is moving you will move forward.
Oh and I guess no one bothered to read my response on post #97.
08-18-2006, 12:21 PM
#107
Interesting. Interesting.
Do an experiment:
1) Go to a treadmill with a toy truck that has passive wheels.
2) Program the treadmill to go 1 MPH.
3) Place the toy truck on the treadmill and see if you can push the truck to make it go 1 MPH toward the front of the treadmill.
4) Now take the truck off the treadmill and see if you can push the truck to make it go 1 MPH on the stationary ground.
Did you have to apply more force to get the truck to move 1 MPH on a treadwill than on the stationary ground? If not, did you notice that the only difference was the truck's wheels spun with a greater RPM on the treadmill?
1) Go to a treadmill with a toy truck that has passive wheels.
2) Program the treadmill to go 1 MPH.
3) Place the toy truck on the treadmill and see if you can push the truck to make it go 1 MPH toward the front of the treadmill.
4) Now take the truck off the treadmill and see if you can push the truck to make it go 1 MPH on the stationary ground.
Did you have to apply more force to get the truck to move 1 MPH on a treadwill than on the stationary ground? If not, did you notice that the only difference was the truck's wheels spun with a greater RPM on the treadmill?
08-18-2006, 12:21 PM
#108
Senior Moderator
I think more people need to think of this as a riddle (which is what it is) instead of a practical application.
The answer is yes the plane will take off if the treadmill is the length of whatever runway length the plane needs to take off. That of course makes this whole thing a mute point, and explains why you'll never see this in real life.
It doesnt matter what speed the treadmill moves at since the wheels are just spinning freely. The spinning propeller/jet engine will still move the plane forward through the air, and it will NOT remain stationary on the treadmill.
The answer is yes the plane will take off if the treadmill is the length of whatever runway length the plane needs to take off. That of course makes this whole thing a mute point, and explains why you'll never see this in real life.
It doesnt matter what speed the treadmill moves at since the wheels are just spinning freely. The spinning propeller/jet engine will still move the plane forward through the air, and it will NOT remain stationary on the treadmill.
08-18-2006, 12:22 PM
#109
Nom Nom Nom Nom
I didnt read all the comments below. Just what I quoted.
So whats the real answer? If im wrong, ill admit it. Just logically to me anyways, the plane wont take off. I want more of an answer than just "it will take off"
So whats the real answer? If im wrong, ill admit it. Just logically to me anyways, the plane wont take off. I want more of an answer than just "it will take off"
08-18-2006, 12:23 PM
#110
Nom Nom Nom Nom
Originally Posted by Mr Hyde
I think more people need to think of this as a riddle (which is what it is) instead of a practical application.
The answer is yes the plane will take off if the treadmill is the length of whatever runway length the plane needs to take off. That of course makes this whole thing a mute point, and explains why you'll never see this in real life.
It doesnt matter what speed the treadmill moves at since the wheels are just spinning freely. The spinning propeller/jet engine will still move the plane forward through the air, and it will NOT remain stationary on the treadmill.
The answer is yes the plane will take off if the treadmill is the length of whatever runway length the plane needs to take off. That of course makes this whole thing a mute point, and explains why you'll never see this in real life.
It doesnt matter what speed the treadmill moves at since the wheels are just spinning freely. The spinning propeller/jet engine will still move the plane forward through the air, and it will NOT remain stationary on the treadmill.
08-18-2006, 12:26 PM
#111
Senior Moderator
Originally Posted by SwervinCL
Why wont the plane stay stationary if the treadmill is matching the speed of thrust that the engines are producing?
Let me ask this, and maybe you can understand a little better.
If a car driving 50mph drives into a 50mph headwind going the opposite direction, does the car stop, or continue forward?
08-18-2006, 12:26 PM
#112
Interesting. Interesting.
Originally Posted by SwervinCL
Why wont the plane stay stationary if the treadmill is matching the speed of thrust that the engines are producing?
The engine force acts directly on the plane. Because the wheels don't lock, they just spin, there is no way to transmit the force from the treadmill to the plane. It is just transmitted to the wheels.
Last edited by wstevens; 08-18-2006 at 12:30 PM.
08-18-2006, 12:28 PM
#113
Yeehaw
Originally Posted by SwervinCL
Why wont the plane stay stationary if the treadmill is matching the speed of thrust that the engines are producing?
So this conveyor belt situation would stop a car from moving forward, since the spinning treadmill would counter the force generated from the spinning of the wheels. To stop a plane from moving forward, you would need something to counter the thrust of a jet/propeller engine, like another jet/propeller engine pushing in the opposite direction.
08-18-2006, 12:33 PM
#114
Nom Nom Nom Nom
Im wrong... I read it. It makes sense now. 
This is what I just read.
http://www.straightdope.com/columns/060203.html
This is what I just read.
http://www.straightdope.com/columns/060203.html
08-18-2006, 12:34 PM
#115
Senior Moderator
If the plane accelerated using its wheels, it would be stuck in one spot, and not generate the lift needed to take off, but since it uses its prop/jet engine to accelerate, the prop/jet will pull the plane forward while its wheels spin freely on the runway length treadmill.
08-18-2006, 12:39 PM
#116
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Originally Posted by NSXNEXT
Terrible analogy because the treadmill belt does not control your speed. If you run faster than the treadmill is moving you will move forward.
Oh and I guess no one bothered to read my response on post #97.
Oh and I guess no one bothered to read my response on post #97.
l
i
f
t
<-thrust-+-drag->
g
r
a
v
i
t
y
v
Those are the 4 forces that act on a plane. The treadmill will not affect any of them. A treadmill that keeps moving forward will not affect thrust or it's affect on aircraft motion & resulting lift in any way (ok - the rolling resistance of the tires would be there). The treadmill could be moving 1000mph. If there's enough thrust, the plane will still move forward through the air and take off.
I give up...
Last edited by fla-tls; 08-18-2006 at 12:42 PM.
08-18-2006, 12:44 PM
#117
Senior Moderator
Originally Posted by fla-tls
I give up...
Originally Posted by NSXNEXT
Me too.....
I actually googled the correct answer back on page 1 but felt it was fun playing the other side
I actually googled the correct answer back on page 1 but felt it was fun playing the other side
Sorry Neil, I could tell you were torturing him, had to break it to him
08-18-2006, 12:47 PM
#118
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OK now that we've all had our fun...
The plane generates thrust by accelerating air opposite the desired direction of travel, it blows air backwards to move forward. Unlike a car that generates motion by pushing against the ground. So as long as the forward motion of the plane causes airflow over the wing to generate sufficient lift it will fly. The effect of the conveyer to exactly counter the detected motion of the plane should only serve to cause the wheels to rotate at twice the actual speed. The wheels are not the source of any thrust so countering their motion has no effect on forward motion. This assumes that the entire runway remains fixed in location although the surface is moving in a conveyer fashion.
The plane generates thrust by accelerating air opposite the desired direction of travel, it blows air backwards to move forward. Unlike a car that generates motion by pushing against the ground. So as long as the forward motion of the plane causes airflow over the wing to generate sufficient lift it will fly. The effect of the conveyer to exactly counter the detected motion of the plane should only serve to cause the wheels to rotate at twice the actual speed. The wheels are not the source of any thrust so countering their motion has no effect on forward motion. This assumes that the entire runway remains fixed in location although the surface is moving in a conveyer fashion.
08-18-2006, 12:48 PM
#119
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Originally Posted by Mr Hyde
LOL, Let me help here. In post 97, if you highlight the whole thing, this is what you will find. After Me too...., the rest of the this text is in white font.
Sorry Neil, I could tell you were torturing him, had to break it to him
Sorry Neil, I could tell you were torturing him, had to break it to him
Funny, after a while I started to believe what I was saying. It's pretty interesting the answers people gave for why it would or would not fly.
08-18-2006, 12:49 PM
#120
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Originally Posted by NSXNEXT
Me too.....
I actually googled the correct answer back on page 1 but felt it was fun playing the other side
I actually googled the correct answer back on page 1 but felt it was fun playing the other side
We need a fish hook smiley - because I fell for that one big time!