Can the airplane take off?

[smack Down]

Originally posted by: bsobel

Even if you assume relitive to ground if you take the limit of moving forward for adjusting the speed of the treadmill the airplane wouldn't move.

Sorry smilin, gotta try.

Ok, imagine that I am in a plane doing 200mph flying 5 feet over a treadmill running in the other direction at 200mph. I lower my landing gear. What occurs:

a) The wheels spin at 400mph (200mph forward plane motion + 200mph treadmill motion in the other direction)

b) The plane comes to an immediate halt killme as my body flies foward at 200mph (if so, please explain the physics involved)

c) Dogs and cats live together

Once you realize the answer is 'a' the problem is the same as originally stated.

Bill

The quote was taken out of contect and that isn't really what I'm trying to say. I was just saying with that just because there is forward motion doesn't mean the plane will move any noticeable amount. I was talking about the treadmill at all.

 

[smack Down]

Originally posted by: brikis98

Originally posted by: smack Down

Originally posted by: sao123
I've got it... the perfect understandable analogy.


you're on a raft, free floating on the water.
Now a current starts pulling your raft down river towards a waterfall. So you start moving in that direction.

Theoretically... If I were to throw you a rope and you tied it your raft, and I pulled it with a winch.

Do you die, or will the winch pull you through the water?

HINT: you cant stay stationary. You either move forward or backwards.
If you move forward your safe...and the plane takes off.
If you move backwards the rope broke and you died.
If you stay stationary, the rope breaks, and you still die.

either way the point is... there is no balance between the planes engines and the treadmill which will keep the plane perfectly still moving in place on the treadmill.
And because the wheels of the plane are free spinning, this eliminates movign backwards.
therefore you must move forward.

This totally depends on how you read the question. If you read it the treadmill matches the speed of the plane relitive to the treadmill surface then what you said is simply wrong. If you read it as the treadmill matches the speed ground speed then it is correct.

that interpretation MAKES NO SENSE. any reasonable interpretation of the problem will obviously assume that the treadmill matches the speed of the plane with respect to the ground. why? because other than the trivial case of a stand-still, the treadmill CANNOT match the speed of the airplane relative to the treadmill. this is paradoxical and has been explained to you MANY times.

Just because a lot of people who failed physics think that it is a paradoxical doesn't make it so.

The total kinetic energy of the plane is given by
E_t = 1/2 m*V^2 + 1/2I*w^2
Where m is mass, V is velocity of the plane relitive to ground, I is moment of inertia, and W is the angular velocity.

W is porportional to (speed of the treadmill + the ground speed of airplane) ie the speed of the airplane relitive to treadmill. Let ignore the 1/2 m *V^ because it is basicly a constant.
E_t = 1/2I*w^2

Just as an example lets assume the plane needs w = 1 for take off and I = 1
E_t = 1/2 J

Ok now imagine that the plane has it engine off and is on a treadmill going backwards at 2. For simplicity assume the treadmill applies zero force to the plane. The plane is going forward at 2 relitive to the treadmill surface thus w = 2.
E_t = 1/2 * 1 * 2^2
E_t = 2 J
For the plane to take off it will require a wheel speed of 3, 2 to overcome the backwards motion of the tires due to the treadmill and 1 to reach the required ground speed.
E_t = 1/2 1 * 3^2
E_t = 4.5 J

Even with no loss to friction it still requires 4.5 times the amount of energy to take off. The wheel doesn't need to apply any force to the plane to make take off more challenging.

If the treadmill tracks the speed of the plane relitive to the treadmill it will just sit there burning its fueal until the wheels have all the kentic energy

 

[AeroEngy]

I stayed out of this discussion for awhile and I am probably stupid for jumping back in but. Here is a new FBD of the senario New FBD Link I used real aircraft data and acounted for the angular acceleration of the tires and rollign friction. Previously I ignored the required force to impart an angular acceleration on the tires and only considered friction and smackdown called me on it. However, after accounting for this as seen in the FBD the airplane still takes off with just a slightly lower acceleration. If I made a mathmatical error or implemented an equation incorrectly I will consider your input because I am not always perfect *just most of the time* and it was been a few years since my kinematics and dynamics courses.

 

[Netopia]

Originally posted by: Smilin

Originally posted by: Netopia
You sir, committed the same sin I did by not reading the whole thread. Had you done that, you would have seen that I have already voluntarily eaten a well earned and healthy portion of humble pie, talkng with mouth full only enough to admit arrogance and incorrectness.
Joe

You are quite correct. I have not read the entire thread. Pretty much just the first page then last few. If you have expressed the courage to admit a mistake of any magnitude I applaud you. It is not an easy thing to do.

Now, I will readily admit the sin of not reading the entire thread, but I am not yet ready to admit I am wrong about the original question.

The airplane WILL take off. See my thrice quoted explanation that involves the "three speedometers" for my view on the matter.

I agree that it will, now comprehending the free spinning wheels. Hey... I've got a little of this humble pie left if you want a bite for your transgressions... tastes like crap but it's good for keeping the ego in check!

Joe

 

[Netopia]

Ok, how about this... at a certain speed, the bearings in the wheel will melt, causing them to seize. The wheels will come to a halt and the combination of the rearward movement of the belt and the forward thrust of the engines might cause the plane to tip up on it's nose and then be dragged to the back of the belt where it falls of and is destroyed, killing the crew. We all feel horrible and go out and have a beer and commiserate!

Joe

 

[Oblivionaire]

Originally posted by: Netopia
Ok, how about this... at a certain speed, the bearings in the wheel will melt, causing them to seize. The wheels will come to a halt and the combination of the rearward movement of the belt and the forward thrust of the engines might cause the plane to tip up on it's nose and then be dragged to the back of the belt where it falls of and is destroyed, killing the crew. We all feel horrible and go out and have a beer and commiserate!

Joe

What certain speed would that be? Hint: Real scientists use quantitative analysis. Charlatans fear numbers and babble about hypothetical situations while avoiding math.

But ok I'll bite anyway, what if the bearings can handle twice the top speed of the aircraft? This is a hypothetical situation anyway so now you'll have to prove how fast the bearing can go before it breaks down. Have you climaxed yet? Or are you still mentally masturbating today? Microsofts tagline: Where do you want to go today? ATOT's should be, where do you want to mentally masturbate today?

 

[Netopia]

The real point of the post was having the beer and chilling. You missed the point that Real Humans use.



Joe

 

[smack Down]

Originally posted by: AeroEngy
I stayed out of this discussion for awhile and I am probably stupid for jumping back in but. Here is a new FBD of the senario New FBD Link I used real aircraft data and acounted for the angular acceleration of the tires and rollign friction. Previously I ignored the required force to impart an angular acceleration on the tires and only considered friction and smackdown called me on it. However, after accounting for this as seen in the FBD the airplane still takes off with just a slightly lower acceleration. If I made a mathmatical error or implemented an equation incorrectly I will consider your input because I am not always perfect *just most of the time* and it was been a few years since my kinematics and dynamics courses.

Again you FBD is only valid if you read the problem as the treadmill tracks the ground speed of the plane. If it tracks the speed of the plane relitive to the treadmill surface then dw/dt = 2a / r is just wrong. The plane wouldn't be a constant torque on the tires there would be an ever increasing torque on the tires.

 

[Agent11]

Originally posted by: BrownTown
just a sort of "hypothetical" question, but if I start curssing alot will that get this thread closed, or simply get my post deleted and me banned? I'm trying to find someone of getting this idiotic thread closed, but I'm not sure how to do it without getting banned?

Anyone want to randomly get in a flame war full of personal attacks in order to get this thread closed.

Ill start:

Dear <insert name here>, your mother is fat, and furthermore I question your sexuality.

LOL





After reading through this thread your post gave me a much needed laugh. Thank you



The plane takes off.

Get a hotwheels car. get a belt sander.
have someone hold the belt sander or put it belt up on the ground.
start it up. hold the hotwheel in place, it will not be hard. then move it forward. it will not be hard.

you moving the hotwheel forward = jet engine


If you grind your fingertips off it's not my fault.

 

[DrPizza]

Hey, I was just thinking... maybe I will have one of the physics students at my school video tape me wearing roller blades on a treadmill (abec 5's); and I can use a force scale to measure how much backwards force the treadmill exerts on me. Then, I can increase the speed of the treadmill, and ("I believe in physics!") the scale should read the same.

Think that'd help?

 

[smack Down]

Originally posted by: DrPizza
Hey, I was just thinking... maybe I will have one of the physics students at my school video tape me wearing roller blades on a treadmill (abec 5's); and I can use a force scale to measure how much backwards force the treadmill exerts on me. Then, I can increase the speed of the treadmill, and ("I believe in physics!") the scale should read the same.

Think that'd help?

Only if you video tape it while the rate of acceleration is increasing. I which case the force reading will increase.

 

[sao123]

Originally posted by: DrPizza
Hey, I was just thinking... maybe I will have one of the physics students at my school video tape me wearing roller blades on a treadmill (abec 5's); and I can use a force scale to measure how much backwards force the treadmill exerts on me. Then, I can increase the speed of the treadmill, and ("I believe in physics!") the scale should read the same.

Think that'd help?

The physics God has spoken... and now we observe a moment of silence to absorb and meditate on his statements of absolute truth.


Ooooooooooohhhm. Ooooooooohhhm.
Amen.

 

[DrPizza]

Originally posted by: smack Down

Originally posted by: DrPizza
Hey, I was just thinking... maybe I will have one of the physics students at my school video tape me wearing roller blades on a treadmill (abec 5's); and I can use a force scale to measure how much backwards force the treadmill exerts on me. Then, I can increase the speed of the treadmill, and ("I believe in physics!") the scale should read the same.

Think that'd help?

Only if you video tape it while the rate of acceleration is increasing. I which case the force reading will increase.

It's unfortunate that you've never taken a physics class. Because, if you had, there's a chance that you could have typed a sentence that meant what you think you meant. What on earth do you mean by "rate of acceleration is increasing?"

Acceleration is a rate; it's the time rate of change of velocity. Do you mean that the rate at which the rate of change of velocity is changing? Or, did you simply mean "only if you video tape it while the speed is increasing."

If you meant the latter, you are not going to see any significant effect on the force caused by increasing the speed of the treadmill. But, you've convinced me... apparently, this is an experiment that I'll have to do with my physics class this week.

 

[DrPizza]

Originally posted by: sao123

Originally posted by: DrPizza
Hey, I was just thinking... maybe I will have one of the physics students at my school video tape me wearing roller blades on a treadmill (abec 5's); and I can use a force scale to measure how much backwards force the treadmill exerts on me. Then, I can increase the speed of the treadmill, and ("I believe in physics!") the scale should read the same.

Think that'd help?

The physics God has spoken... and now we observe a moment of silence to absorb and meditate on his statements of absolute truth.


Ooooooooooohhhm. Ooooooooohhhm.
Amen.

Nooooo, far from "the physics God." The physics Gods are all over at physicsforums

 

[smack Down]

Originally posted by: DrPizza

Originally posted by: smack Down

Originally posted by: DrPizza
Hey, I was just thinking... maybe I will have one of the physics students at my school video tape me wearing roller blades on a treadmill (abec 5's); and I can use a force scale to measure how much backwards force the treadmill exerts on me. Then, I can increase the speed of the treadmill, and ("I believe in physics!") the scale should read the same.

Think that'd help?

Only if you video tape it while the rate of acceleration is increasing. In which case the force reading will increase.

It's unfortunate that you've never taken a physics class. Because, if you had, there's a chance that you could have typed a sentence that meant what you think you meant. What on earth do you mean by "rate of acceleration is increasing?"

Acceleration is a rate; it's the time rate of change of velocity. Do you mean that the rate at which the rate of change of velocity is changing? Or, did you simply mean "only if you video tape it while the speed is increasing."

If you meant the latter, you are not going to see any significant effect on the force caused by increasing the speed of the treadmill. But, you've convinced me... apparently, this is an experiment that I'll have to do with my physics class this week.

Sorry I must have missed an 'n' while typing "In" I have now fixxed it.

Yes I mean the "that the rate at which the rate of change of velocity is changing"
Where da/dt > 0 for the treadmill.

 

[bsobel]

Sorry I must have missed an 'n' while typing "In" I have now fixxed it.

Really is it fixxed now?

 

[Zolty]

so the plane takes off right, I mean there is air flowing over the wing caused by the prop.

 

[bobsmith1492]

No, it takes off because the engines provide forward thrust=forward movement through the air = air flow over the wing... so, yeah, but indirectly

 

[gamefreakgcb]

All you guys saying it wont take-off should stop, and ponder over this, why on earth will the wheels hold the plane back? The example with the roller-skates or the hot wheels can be applied here. So lets see now, you throttle the planes engine up and it starts moving forward, so far so good, now the treadmill comes into play and starts to spin backwards to try to keep the plance stationary, but, now get this, the plane continues to move forward, unhindered by the treadmill, ofcourse the treadmill can try and counter as much as it wants but there is no effect on the plane itself since the wheels of the plane will just spin faster and faster staying ahead of the treadmill becasue the wheels are in free spin, and the plane will move forward and finally take-off due to the air being pulled through the engines, which is the direct result of the throttling we did in the first step, and act as "the rope". You cant just cancel a reaction by acting on some other variable here, ie. the air is pulled but I apply some counteraction to the wheels which have nothing whatsoever to do with the air and keep the plane stationary. Have you seen those wind-tunnel tests with the jet-engines? the engine has to be tied to something, in addition to being on some sort of a trolley, so it doesn't blow through the walls.

Edit: Damn, too much rambling and lost sentence structure, I need to sleep

 

[Smilin]

Originally posted by: smack Down

Originally posted by: AeroEngy
I stayed out of this discussion for awhile and I am probably stupid for jumping back in but. Here is a new FBD of the senario New FBD Link I used real aircraft data and acounted for the angular acceleration of the tires and rollign friction. Previously I ignored the required force to impart an angular acceleration on the tires and only considered friction and smackdown called me on it. However, after accounting for this as seen in the FBD the airplane still takes off with just a slightly lower acceleration. If I made a mathmatical error or implemented an equation incorrectly I will consider your input because I am not always perfect *just most of the time* and it was been a few years since my kinematics and dynamics courses.

Again you FBD is only valid if you read the problem as the treadmill tracks the ground speed of the plane. If it tracks the speed of the plane relitive to the treadmill surface then dw/dt = 2a / r is just wrong. The plane wouldn't be a constant torque on the tires there would be an ever increasing torque on the tires.

Look, monkey, aircraft measure their forward motion with an airspeed indicator not a speedometer attached to some magical treadmill they happen to be on. The original question said as a GIVEN that the aircraft moved forward.

I have a question for YOU. How far are you willing to take all this just to avoid admitting you are both wrong and thought a fool?

 

[gsellis]

Based on all 6 pages, it is then possible to stand that treadmill on end and prevent the airplane from smacking into the ground just by speeding up the treadmill. Cool trick. Anybody want to buy a bridge? A bit over 100years old in the NYC area...

 

[Smilin]

Originally posted by: gsellis
Based on all 6 pages, it is then possible to stand that treadmill on end and prevent the airplane from smacking into the ground just by speeding up the treadmill. Cool trick. Anybody want to buy a bridge? A bit over 100years old in the NYC area...

According to smackdown, yes it would be quite possible to stand the treadmill vertical then simply increase the spead of the treadmill. It would allow the plane to stand perfectly still and defy gravity in such the same way it would stand still and defy the thrust of it's engines when horizontal.

 

[Cerpin Taxt]

Originally posted by: smack Down

Again you FBD is only valid if you read the problem as the treadmill tracks the ground speed of the plane.

There is no other coherent interpretation of the problem.

If it tracks the speed of the plane relitive to the treadmill surface

Depending on what you mean, this is either a meaningless tautology, or it is an impossibility.

If you mean that the treadmill surface moves at a rate relative to the plane that is equal to the plane's rate relative to the treadmill surface, you have stated a tautology. At any speed this must be true, so it means nothing.

If you mean that the treadmill surface moves at a rate relative to the ground that is equal to the plane's rate relative to the treadmill surface, you have stated an impossibility. In order for the treadmill surface to register a change in motion from zero velocity to a state of motion, the plane must accelerate. When the plane accelerates relative to the treadmill surface, then the treadmill surface accelerates relative to the ground. The acceleration of the treadmill surface relative to the ground necessarily increases the acceleration of the plane relative to the treadmill surface, however. Therefore there is no way that the two relative rates (plane to treadmill and treadmill to ground) can be simultaneously equal, so that interpretation is incoherent.

You, sir, have failed utterly.

 

[darkhorror]

Assuming the wheels are free moving and the plane is moving due to jets then the plane will take off.

If you have a car you put an extra wheel on it that doesn't have any power and just is free moving. Then you drive your car with only that wheel on a convayer belt now move the belt backwards at the same speed as the car moves forward. Moving the convayer belt backwards isn't going to do anything. Your car will still move forwards as the wheels with power are on the ground moving forward. that free moving wheel has nothing to do with how fast the car will go. This is the same thing as a plane, the jets are like the powerwheels on a car. The wheels on plane are like the free wheel.

 

[randay]

DrPizza I dub thee "HT Trollslayer".

This smack down guy is just trolling, plain and simple. I pointed out that for his scenario to work the treadmill would be accelerating infinitely. At the time he thought that the treadmills speed would become constant. Now he is going back on that thought and his answer now involves a treadmill that continuously accelerates at a rate which imparts enough torque on the airplanes wheels to counter the thrust from its jet engines, while giving no real word numbers or measurements. He is just trolling for some reason and getting a kick out of you all telling him how dumb he is. Maybe he is some kind of weirdo of the "dance puppets dance" variety. We would be all better off just ignoring him. Please stop feeding the troll.

Also smackdown is wrong no matter how he interprets the question. In his interpretation the airplane would end up moving backwards, infinitely, and just take off backwards. Who cares if it crashes a few seconds later or resembles a bad crash at a Nascar event? It takes off regardless. Sorry to let you down smacky, but youre wrong no matter what.

The plane takes off.