Plane on conveyor... Will it ever take off?

j6p

10th December 2005 - 05:39 PM

ixolas, I got them all but #3 threw me. What's the answer to that one?
Here's one for you. How far can a person walk into the woods? There's a logical no BS answer to this.
Maybe we can share some of these cool little mind benders. Someone should start a new thread entitled "mind benders" or something like that. Anything that will get rid of this plane.

Ok, I'm editing my post. I just read the answer to #3. That's lame man . . . lame.

WOW I was just ready to post this edited version and BAM there's your post. You're quick.

Got any more good ones? I like this stuff.

ixolas

10th December 2005 - 05:44 PM

half way because as soon as you reach the half way point then you are walking out of the woods.

as for #3 it is "1968 pennies" not "a 1968 penny". The trick is the word pennies is plural.

Bloy

10th December 2005 - 05:50 PM

heavy/light

ixolas

10th December 2005 - 05:55 PM

ya I got another good one:
Imagine you are in a sinking rowboat surrounded by man eating sharks. How would you survive?

as for anyone reading this post asking what happened to the original question. My posts (plural) killed it on page 57.

j6p

10th December 2005 - 07:30 PM

Surrounded by man eating sharks??? I can't figure that one out. But I've got another one for you. There are eight frogs sitting on a log and three decide to jump off. How many are left on the log.

Guest_Another_Guest

10th December 2005 - 07:54 PM

QUOTE (j6p+Dec 10 2005, 07:30 PM)

Surrounded by man eating sharks??? I can't figure that one out. But I've got another one for you. There are eight frogs sitting on a log and three decide to jump off. How many are left on the log.

8 are left

Guest_Another_Guest

10th December 2005 - 07:55 PM

QUOTE (ixolas+Dec 10 2005, 05:55 PM)

ya I got another good one:
Imagine you are in a sinking rowboat surrounded by man eating sharks. How would you survive?

as for anyone reading this post asking what happened to the original question. My posts (plural) killed it on page 57.

I would "imagine" the Coast Guard rescuing me in the nick of time

ixolas

10th December 2005 - 08:28 PM

ya.. or you could just stop imagining.

and 8 are left because just deciding to jump off isn't actually jumping off.

another guest

10th December 2005 - 09:35 PM

9 cats are in a boat, 1 cat jumps out, how many cats are left in the boat?

gmilam

10th December 2005 - 10:18 PM

QUOTE (another guest+Dec 10 2005, 03:35 PM)

9 cats are in a boat, 1 cat jumps out, how many cats are left in the boat?

If this boat is in the water, then that cat is not jumping out.

Have you ever tried to get cats anywhere near the water?

j6p

10th December 2005 - 10:38 PM

Ok time to play. Here's an oldie but goodie that I've set to lyric. Where's the dollar?

Three men who have traveled far
Came to a place of rest
They rang the bell and called out loud
Our patience do not test

The heat of day did make us sweat
we tire, suffer and swelter
Our bodies ache, our clothes are wet
We are in need of shelter

Give us room with a bath
Oh keeper of this inn
What shall we pay, the charge we ask
Do your job and hurry the task
Our patience it grows thin

The desk clerk felt annoy
To me they speak so sharp.
I'll charge them more, five dollars more
With my pride they will not toy

Thirty dollars, he blurted out
Thirty it will be
Thirty dollars to rest and wash
(he thought, Thirty to you crusty three)

And so they paid the price
laid it on the desk
laid it down and retired
To their room for wash and rest

(As time went on and night began to fall the desk clerk felt bad. He thought about what he did and decided to give the men their $5.00. So he called for the bell boy.)

Give them this and tell them that
I've erred and am sincere
In wishing them, from management,
"Enjoy your stay while here"

The bell hop took the five
and intended to return
But on his way to the room
He thought, the guests I'll burn

Burn them for it all...oh no
Only for a bit
I'll reimburse them only three
and keep the rest of it

So now that it has come to past
they paid nine dollars each
The bell hop kept two of those
Now logic goes to breach

Three times nine is twenty seven
add two in the bell hop's till
To me that adds to twenty nine
Where is that pesky bill ?

gmilam

10th December 2005 - 11:10 PM

Oooh! Oooh! I know this one!

The men paid $27
This much is true.
The desk clerk has 25 of it
While the bell hop pocketed 2.

fargo boyle

10th December 2005 - 11:31 PM

QUOTE (ixolas+Dec 10 2005, 04:42 PM)

If this question has a simple answer of "no it won't fly" then why are they asking it?

Similarly, if the question has a simple answer of "yes it can fly", then why are they asking it?

Personally, my 'simple answer' was neither.

It took quite a bit of reasoning before I arrived at my final conclusion - which was made a lot harder by the amount of people claiming that it would fly.

I've based my conclusions on what I know and what I can prove. I've still not entirely dismissed the idea that the plane would fly, but to be honest I've seen no substantial evidence to back this up.

Guest

10th December 2005 - 11:42 PM

QUOTE (fargo boyle+Dec 10 2005, 11:31 PM)

QUOTE (ixolas+Dec 10 2005, 04:42 PM)

If this question has a simple answer of "no it won't fly" then why are they asking it?

Similarly, if the question has a simple answer of "yes it can fly", then why are they asking it?

Personally, my 'simple answer' was neither.

It took quite a bit of reasoning before I arrived at my final conclusion - which was made a lot harder by the amount of people claiming that it would fly.

I've based my conclusions on what I know and what I can prove. I've still not entirely dismissed the idea that the plane would fly, but to be honest I've just ignored, for no particular reason, the evidence to back this up.

Fixed

fargo boyle

11th December 2005 - 12:03 AM

QUOTE (Guest+Dec 10 2005, 11:42 PM)

Fixed

Why would I ignore something if I know that it's the truth, and I know it can be proved?

I'll tell you the answer: I wouldn't.

Who's ignoring things, me or you?

I said that I didn't know the answer at first, and to be honest, nor did I care.

Why would I want it to be one or the other? Why would I want it to either fly or not fly? Personally I don't have the answer to that. You seem to think I do have an answer.

You have ignored the fact that I am completely open to anyone proving anything. I am still open to the fact that the plane could fly. Unlike you, who doesn't seem open to anything that doesn't agree with your own conclusion.

Like I said, I have not completely dismissed the fact that the plane might fly, but so far the only thing that's happened is people have bandied around a lot of high-school physics, which really doesn't prove anything much at all.

ixolas

11th December 2005 - 02:06 AM

so in other words you are just trying to bait people on and continue this battle of "it will" vs "it won't".

COlE

11th December 2005 - 03:26 AM

QUOTE (ixolas+Dec 5 2005, 11:49 PM)

ok let me ask you this..

If a there was a large lake and the entire bottom of the lake was a moving conveyor. Only the ground not the water! And you had a boat that can't float and is supported by legs that at the end were free turning wheels. Would the boat move when the on-board v8 turns the propellers in the water? Even if the little wheels that support it are turning in the equal opposite way?

If a plane is flying through the air at a constant 100 mph and there is a train moving in the opposite direction at 100 mph and the plane keeping a constant 100 mph flew just over it and the wheels barely touched the train would the plane come to a complete stop just by touching the wheels to the train? Why not? The train is moving at 100 mph in the exact opposite way just like the conveyor?

The fact is that most people want to picture this like a car on a conveyor and you can't. You have to think of it like yourself on a treadmill in Rollerblades pulling a rope. The air the plane pulls against (or pushes against) is completely different than the conveyor turning the little wheels it sits on.

Here's where I see most people going wrong. This quote isn't wrong, but it doesn't apply to the question. The plane is already flying, and already generating lift.

Before the plane flys, it will will act like a car, it's propulsion system is just different. IF the runway moves along, matching the speed (thus the acceleration too since it is matching instantaneous velocity) the plane never gets up to air airspeed where it generates lift. Think of it this way, once lift is generated, the tranfser of energy changes from engine to ground to engine to air. Actually, it is arguably engine to wing.

Guest

11th December 2005 - 03:32 AM

QUOTE (COlE+Dec 11 2005, 03:26 AM)

QUOTE (ixolas+Dec 5 2005, 11:49 PM)

ok let me ask you this..

If a there was a large lake and the entire bottom of the lake was a moving conveyor. Only the ground not the water! And you had a boat that can't float and is supported by legs that at the end were free turning wheels. Would the boat move when the on-board v8 turns the propellers in the water? Even if the little wheels that support it are turning in the equal opposite way?

If a plane is flying through the air at a constant 100 mph and there is a train moving in the opposite direction at 100 mph and the plane keeping a constant 100 mph flew just over it and the wheels barely touched the train would the plane come to a complete stop just by touching the wheels to the train? Why not? The train is moving at 100 mph in the exact opposite way just like the conveyor?

The fact is that most people want to picture this like a car on a conveyor and you can't. You have to think of it like yourself on a treadmill in Rollerblades pulling a rope. The air the plane pulls against (or pushes against) is completely different than the conveyor turning the little wheels it sits on.

Here's where I see most people going wrong. This quote isn't wrong, but it doesn't apply to the question. The plane is already flying, and already generating lift.

Before the plane flys, it will will act like a car, it's propulsion system is just different. IF the runway moves along, matching the speed (thus the acceleration too since it is matching instantaneous velocity) the plane never gets up to air airspeed where it generates lift. Think of it this way, once lift is generated, the tranfser of energy changes from engine to ground to engine to air. Actually, it is arguably engine to wing.

Wrong.

ixolas

11th December 2005 - 04:18 AM

This question is a trick question and the trap comes in the wording. If this question has a simple answer of "no it won't fly" then why are they asking it? If you use logic to think about why they are asking such a simple question then you would realize the first answer you come up with "no it won't fly" is incorrect because it is a trick question. That is how you have to deal with trick questions. Yes, at first even I thought the answer was no, but after I thought about it for a few seconds I realized that it was a trick and the plane would take flight. Before arguing or making a solid conclusion you will not budge from, take the time to read this entire post and think about it!!!! For all the people who still stick to there first answer of "no it won't" I'm going to break it down for you.
Take the equation step by step and not just will it fly.

A plane (excluding harriers and any other vto planes) on a day with no wind movement, will not take flight just by turning on the engines full blast without any movement. No one is auguring that.

The main physics fundamental that you have think of is that the equal opposite force (the conveyor) is not chained to the plane and not acting directly on the engine propulsion to pull the plane.

If that isn't enough physics for you then the first question is will the plane move forward. Because: If a plane can overcome the conveyor to move forward then it will continue to overcome the conveyor and continue to move forward and eventually reach the required speed to create lift and take flight.

THINK ABOUT THIS:

IF THERE IS A GIANT CONVEYOR THAT WILL MATCH THE SPEED IN THE OPPOSITE DIRECTION I'M RIDING IN MY ROLLERBLADES. WILL I MOVE IF A FLYING HELICOPTER (USING AIR TO FLY) ABOVE ME USES A ROPE TO PULL ME FORWARD?

THIS IS EXACTLY LIKE THE QUESTION!! THINK OF THE AIRPLANE AS PIECES.
A HELICOPTER TILTS ITS PROPELLERS TO PUSH AIR AGAINST AIR TO MOVE FORWARD. PULLING A MASS (ME) ROLLING ACROSS A MOVING SURFACE ON WHEELS. SINCE I AM HOLDING ON TO A ROPE ATTACHED TO THE HELICOPTER I WILL GO FORWARD AT THE SAME SPEED THE HELICOPTER WILL GO. THE HELICOPTER WOULD FEEL A LITTLE RESISTANCE FROM ME AND THE ROPE BUT NOT MUCH AT ALL. THE CONVEYOR WILL ACT DIRECTLY AGAINST THE HELICOPTER BY ROLLING RESISTANCE AGAINST ME WHICH I TRANSFER TO THE HELICOPTER BY THE ROPE. I WOULD MOVE FORWARD, THE CONVEYOR WOULD BE MOVING UNDER ME AT THE OPPOSITE SPEED BUT THAT WOULDN'T MATTER.
Unless I tripped and fell down, ouch!

IMAGINE THE PLANE ENGINE IS THE HELICOPTER, THE PLAINS ENGINE TURNS PROPELLERS AGAINST AIR TO CREATE FORCE. NOW IMAGINE THE PLANES FRAME, FUSELAGE AND WINGS ARE THE HELICOPTER FRAME FUSELAGE AND ROPE I AM HOLDING ON TO. NOW IMAGINE THE PLANES WHEELS ARE THE SAME AS MY ROLLERBLADE WHEELS. WHEN THE HELICOPTER LIFTS OFF AND MOVES FORWARD IT IS GOING TO PULL ME ALONG THAT CONVEYOR EVEN IF IT IS GOING JUST AS FAST IN THE OPPOSITE DIRECTION.

A PLAINS ENGINES, LIKE THE HELICOPTER, USES PROPELLERS TO PUSH AIR AGAINST AIR TO MOVE FORWARD. PULLING THE A MASS (THE FRAME OF THE PLANE) ACROSS A MOVING SURFACE ON WHEELS. THE PLANE WOULD MOVE FORWARD, THE CONVEYOR WOULD BE MOVING UNDER THE PLANE AT THE OPPOSITE SPEED BUT THAT WOULDN'T MATTER BECAUSE THE PLANE WOULD HAVE FORWARD MOTION RELATIVE TO THE WORLD BY PUSHING ON THE AIR LIKE THE HELICOPTER FLIES IN THE AIR.

ONCE THE PLANE HAS FORWARD MOVEMENT IT WOULD CONTINUE TO ACCELERATE UNTIL IT REACHES THE NECESSARY SPEED TO TAKE FLIGHT.

THE MAIN THING YOU HAVE TO REMEMBER IS THE MATCHING SPEED OF THE CONVEYOR ISN'T MATCHING THE THRUST THE PLAINS ENGINES PRODUCE AGAINST THE AIR. THE CONVEYOR IS ONLY MATCHING THE SPEED OF THE PLANE AND SPINNING THE WHEELS. THE THRUST AGAINST THE PLANE VIA THE WHEELS IS SO SMALL COMPARED TO WHAT THE PLANE IS PRODUCING PUSHING AGAINST THE AIR TO MOVE IT FORWARD.

QUOTE ("INCORRECT FORMULA'S PLEASE DISREGARD"+)

I found the formula's for all the people saying the wheel resistance wouldn't allow the plane to take flight.

The rolling resistance is found roughly by a formula like this: the weight in newtons (1lb = 4.45 newtons) divided by the number of wheels, times actually wheel resistance (usually below 4% or 0.04), times the speed in meters per second (1mph = .45 meters/hour), equals the resisting force.
rr=(weight/wheels)x(.04)x(speed)

The force of thrust to move a plane is found by the formula like this: mass in newtons times speed in meters/hour equals the force.
f=(weight)x(speed)

A plane weighing 1,335,000 newtons (300,000 lbs) divided by 3 wheels multiplied by the wheel resistance .04 and then multiplied by the speed of 4.5 meter/hour (10 miles/hour) has a rolling resistance of 80,100 newtons (18,000 lbs) acting against it. The conveyor moving in the opposite direction at the same speed of 4.5 meter/hour this would double the wheel speed and make it an opposing force of 160,200 newtons (36,000 lbs) acting against it.
rr=(1335000/3)x.04x(4.5+4.5)=160200

A plane weighing 1,335,000 newtons moving at 4.5 meter per seconds has a forward force of 6,007,500 newtons.
f=1335000x4.5=6007500

Therefore the forward force of 6,007,500 newtons minus the rolling resistance of the conveyor going in the oppose direction is 160,200 newtons leaving a forward force of 5,847,300 newtons.
(f=6007500)-(rr=160200)=5847300

The opposing force, on the plane will never equal the opposing force applied to the wheels. Therefore the opposing force on the plane by the conveyor will subtract from the forward force but not equal it.

And just for everyone, don't nit pick on the spelling or technicalities like "the propellers actually don't push on air... " whatever! I am just trying to get the point across.

I have come to the conclusion that there is a select group of people arguing the scientific data and laws of physics just for the fun of seeing all the people argue. If you are doing that, stop it. I can't help of think of the character in dogma who knows that god exits talking a nun out of her faith.

Illiac

11th December 2005 - 04:53 AM

QUOTE (Atl5p+Dec 9 2005, 07:39 PM)

QUOTE (Bloy+Dec 9 2005, 07:10 PM)

Ati5p:

Will you state your opinion as to whether the plane will fly ..or not.... and give a brief paragraph as to how you arrived at that conclusion?
We can go from there.....

Sure, gladly. Except I'm going to use a skateboard, fan, and an exercise treadmill.

Exp#1:
I get the skateboard and put it on the treadmill. Holding onto the skateboard, I turn the treadmill up to 5mph. Then I let go of the skateboard. The skateboard accelerates 'backwards' until it is ejected off the treadmill at no more than 5mph, no less than 5mph. (!!!)
Proven: There IS significant drag upon the wheels to cause a 'change' in motion.

Exp#2:
I stop the treadmill. I strap a fan to the top of the skateboard. I turn the fan on and let the board go on the motionless treadmill. The skateboard accelerates to 5mph, and runs off the end of the treadmill.(front this time)
Proven: The fan propells the skateboard at 5mph on the treadmill's stationary surface.

Exp#3:
I now combine all elements. I take a 5mph fan-propelled skateboard and put it on a treadmill going 5mph. I 'let go' of the skateboard. The skateboard stays 'motionless' reletive to me. It is moving at 5mph in relation to the treadmill. There is significant breeze coming off the back of the fan. If I hold a smoke stick in front of the fan, you can see the 'air' from in front of the fan being 'pulled' into the fan, and spit out the back.
The air to the side of the skateboard (where the wings would be) is STILL CALM.

Questions that you are answering incorrectly:
Q)What is preventing the skateboard from getting kicked off the back of the treadmill ala exp#1?
A)Why the thrust of the fan, of course.

Q)What is preventing the skateboard from running off the front of the treadmill?
A)Why the backwards motion of the treadmill of course (ala exp#2)

Explanation? The prop(fan) is simply displacing the air from directly in front of the fan to directly behind the fan. With all else being equal, the skateboard would move forward.

However, when we flip the switch on that belt, we are creating an opposing force in the opposite direction.

Hey, if we aren't creating an 'equal but opposite force' with the treadmill, then how on Gods earth did exp#1 work above?

Atl5p, I couldn't agree with you more. That's why I see a stationary plane that will never fly as long as the speed of the plane's movement down the conveyor/runway is matched by an equal but opposite speed of the conveyor...just like a jogger on a treadmill. There's no "freewheeling", your experiment would clearly show that but the it-will-fliers invoke this new concept every time you try to explain basic relative motion concepts.

Despite your stamina for staying in the game, they still only see a powerful engine and nothing but a little friction in the wheels so... (remove all other physics here)...off we go flying. What they fail to grasp is relative motion is what this is all about.

Put two skateboarders on adjacent conveyors of equal surface friction one moving and the other stationary. The length of the conveyors is longer than the distance that a force of X would push the skateboarder on the stationary conveyor. If both skateboarders weigh the same and are pushed down the surfaces by the same force of X, the one on the moving surface will stop nearer the start point. They both are exposed to similar friction on the surface so it will affect both skateboarders. The force of X was sufficient to overcome the relatively small force of friction in both cases (just like the powerful engine vs the wheels of the plane) but without additional force, both will stop. Force must continually be applied to overcome the force of friction. Now in both cases a similar mass was moved a distance. Why is that distance apparently less in the case of the moving conveyor? Because the backward motion of the conveyor was not counted. If you counted the length of the conveyor that passed under the one on the moving surface, the distance traveled would be identical, hence a given force will move a given mass a given distance....what a beautiful thing. If the relative motion of the conveyor is considered, everything is accounted for and Newton would be happy.

Obviously, we can continue to apply the force to overcome the gradual slow down of friction but if we want to accelerate we have to apply more force. Faster, even more force...that's where that powerful engine comes in handy. But what does the backward moving conveyor do? It provides an infinite distance to travel down so all the available force from the engine is consumed not only by countering relatively small amounts of friction, but by continually moving mass of the plane the distance down the conveyor, JUST LIKE a JOGGER on a TREADMILL. Match the speeds and you remain stationary, no airspeed, no takeoff. The jogger isn't burning up a lot of energy associated with friction but he's burning up a LOT, MOVING down the surface of the treadmill. So that powerful engine is not working to overcome friction so much as it is moving the mass plane down the conveyor surface...and remember, we can make the conveyor act like an infinite surface.

ixolas

11th December 2005 - 05:13 AM

QUOTE (Illiac+Dec 11 2005, 04:53 AM)

Put two skateboarders on adjacent conveyors of equal surface friction one moving and the other stationary. The length of the conveyors is longer than the distance that a force of X would push the skateboarder on the stationary conveyor. If both skateboarders weigh the same and are pushed down the surfaces by the same force of X, the one on the moving surface will stop nearer the start point. They both are exposed to similar friction on the surface so it will affect both skateboarders. The force of X was sufficient to overcome the relatively small force of friction in both cases (just like the powerful engine vs the wheels of the plane) but without additional force, both will stop. Force must continually be applied to overcome the force of friction. Now in both cases a similar mass was moved a distance. Why is that distance apparently less in the case of the moving conveyor? Because the backward motion of the conveyor was not counted. If you counted the length of the conveyor that passed under the one on the moving surface, the distance traveled would be identical, hence a given force will move a given mass a given distance....what a beautiful thing. If the relative motion of the conveyor is considered, everything is accounted for and Newton would be happy.

wow.. you are so close to understanding.. ok lets just use your skate board analogy if given force of x was continuously applied to skateboarder (running next to him on pavement pushing him allong the treadmill) then he would have forward movement and even with the moving conveyor moving the opposite direction under him providing a little bit of friction. But what you have to add into the equation is with the amount of x force applied the skateboarder a fraction of weight will be subtracted and with less weight comes less resistance by the wheel. Less resistance of the wheel means the same force x applied to the skateboarder will move him forward faster but will also subtract more weight and subtract more resistance. Little by little his weight will become lighter and lighter and the resistance becomes less and less until weight is zero and the resistance is zero and he will have lifted off, even with the same force x appied.

By the formula's provided above you should be able to do the math and realize that at 4.5 meters per hour (10 miles/hour) the resistance is fractional to the force by the engine to get the mass to move that much. Admitiedally during low speeds the acting weight on the wheel is greater than the resistance applied and at high speeds the acting resistance on the wheel is greater than the weight acting on the wheel but both forces acting together is still only a fraction of the resistance the plane feels. Those formula's also don't take any consideration to the application of lift to the plane.

another guest

11th December 2005 - 05:28 AM

QUOTE (Guest+Dec 11 2005, 03:32 AM)

QUOTE (COlE+Dec 11 2005, 03:26 AM)

QUOTE (ixolas+Dec 5 2005, 11:49 PM)

ok let me ask you this..

If a there was a large lake and the entire bottom of the lake was a moving conveyor. Only the ground not the water! And you had a boat that can't float and is supported by legs that at the end were free turning wheels. Would the boat move when the on-board v8 turns the propellers in the water? Even if the little wheels that support it are turning in the equal opposite way?

If a plane is flying through the air at a constant 100 mph and there is a train moving in the opposite direction at 100 mph and the plane keeping a constant 100 mph flew just over it and the wheels barely touched the train would the plane come to a complete stop just by touching the wheels to the train? Why not? The train is moving at 100 mph in the exact opposite way just like the conveyor?

The fact is that most people want to picture this like a car on a conveyor and you can't. You have to think of it like yourself on a treadmill in Rollerblades pulling a rope. The air the plane pulls against (or pushes against) is completely different than the conveyor turning the little wheels it sits on.

Here's where I see most people going wrong. This quote isn't wrong, but it doesn't apply to the question. The plane is already flying, and already generating lift.

Before the plane flys, it will will act like a car, it's propulsion system is just different. IF the runway moves along, matching the speed (thus the acceleration too since it is matching instantaneous velocity) the plane never gets up to air airspeed where it generates lift. Think of it this way, once lift is generated, the tranfser of energy changes from engine to ground to engine to air. Actually, it is arguably engine to wing.

Wrong.

very wrong

The plane never acts like a car.The thrust the plane produces acts against the air,never the wheels, the fact that the wheels are touching the ground changes nothing.Therefore the ground has no influence on the forward movement of the plane, so therefore it does not matter what the ground is doing, it can stay still,move forward or backwards and have no effect on the plane.

another guest

11th December 2005 - 05:50 AM

QUOTE (Illiac+Dec 11 2005, 04:53 AM)

QUOTE (Atl5p+Dec 9 2005, 07:39 PM)

QUOTE (Bloy+Dec 9 2005, 07:10 PM)

Ati5p:

Will you state your opinion as to whether the plane will fly ..or not.... and give a brief paragraph as to how you arrived at that conclusion?
We can go from there.....

Sure, gladly. Except I'm going to use a skateboard, fan, and an exercise treadmill.

Exp#1:
I get the skateboard and put it on the treadmill. Holding onto the skateboard, I turn the treadmill up to 5mph. Then I let go of the skateboard. The skateboard accelerates 'backwards' until it is ejected off the treadmill at no more than 5mph, no less than 5mph. (!!!)
Proven: There IS significant drag upon the wheels to cause a 'change' in motion.

Exp#2:
I stop the treadmill. I strap a fan to the top of the skateboard. I turn the fan on and let the board go on the motionless treadmill. The skateboard accelerates to 5mph, and runs off the end of the treadmill.(front this time)
Proven: The fan propells the skateboard at 5mph on the treadmill's stationary surface.

Exp#3:
I now combine all elements. I take a 5mph fan-propelled skateboard and put it on a treadmill going 5mph. I 'let go' of the skateboard. The skateboard stays 'motionless' reletive to me. It is moving at 5mph in relation to the treadmill. There is significant breeze coming off the back of the fan. If I hold a smoke stick in front of the fan, you can see the 'air' from in front of the fan being 'pulled' into the fan, and spit out the back.
The air to the side of the skateboard (where the wings would be) is STILL CALM.

Questions that you are answering incorrectly:
Q)What is preventing the skateboard from getting kicked off the back of the treadmill ala exp#1?
A)Why the thrust of the fan, of course.

Q)What is preventing the skateboard from running off the front of the treadmill?
A)Why the backwards motion of the treadmill of course (ala exp#2)

Explanation? The prop(fan) is simply displacing the air from directly in front of the fan to directly behind the fan. With all else being equal, the skateboard would move forward.

However, when we flip the switch on that belt, we are creating an opposing force in the opposite direction.

Hey, if we aren't creating an 'equal but opposite force' with the treadmill, then how on Gods earth did exp#1 work above?

Atl5p, I couldn't agree with you more. That's why I see a stationary plane that will never fly as long as the speed of the plane's movement down the conveyor/runway is matched by an equal but opposite speed of the conveyor...just like a jogger on a treadmill. There's no "freewheeling", your experiment would clearly show that but the it-will-fliers invoke this new concept every time you try to explain basic relative motion concepts.

Despite your stamina for staying in the game, they still only see a powerful engine and nothing but a little friction in the wheels so... (remove all other physics here)...off we go flying. What they fail to grasp is relative motion is what this is all about.

Put two skateboarders on adjacent conveyors of equal surface friction one moving and the other stationary. The length of the conveyors is longer than the distance that a force of X would push the skateboarder on the stationary conveyor. If both skateboarders weigh the same and are pushed down the surfaces by the same force of X, the one on the moving surface will stop nearer the start point. They both are exposed to similar friction on the surface so it will affect both skateboarders. The force of X was sufficient to overcome the relatively small force of friction in both cases (just like the powerful engine vs the wheels of the plane) but without additional force, both will stop. Force must continually be applied to overcome the force of friction. Now in both cases a similar mass was moved a distance. Why is that distance apparently less in the case of the moving conveyor? Because the backward motion of the conveyor was not counted. If you counted the length of the conveyor that passed under the one on the moving surface, the distance traveled would be identical, hence a given force will move a given mass a given distance....what a beautiful thing. If the relative motion of the conveyor is considered, everything is accounted for and Newton would be happy.

Obviously, we can continue to apply the force to overcome the gradual slow down of friction but if we want to accelerate we have to apply more force. Faster, even more force...that's where that powerful engine comes in handy. But what does the backward moving conveyor do? It provides an infinite distance to travel down so all the available force from the engine is consumed not only by countering relatively small amounts of friction, but by continually moving mass of the plane the distance down the conveyor, JUST LIKE a JOGGER on a TREADMILL. Match the speeds and you remain stationary, no airspeed, no takeoff. The jogger isn't burning up a lot of energy associated with friction but he's burning up a LOT, MOVING down the surface of the treadmill. So that powerful engine is not working to overcome friction so much as it is moving the mass plane down the conveyor surface...and remember, we can make the conveyor act like an infinite surface.

"What they fail to grasp is relative motion is what this is all about."

The "it-will-flyers" understand that the plane needs to move relative to the gorund and air (which are the same in this case because there is no wind) in order to fly.
And we understand that Exp#1 and Exp#2 are correct. What YOU'RE FAILING TO GRASP is the fact that EXP#3 is incorrect and the plane WILL move forward relative to the air and ground. Because it is NOT like running on a treadmill, the runner is exerting his force on the the treadmill and the plane (or the fan on the skateboard) exerts it's force on the AIR.

Bloy

11th December 2005 - 07:44 AM

vacuum/pressure

Atl5p

11th December 2005 - 09:30 AM

QUOTE (Bloy+Dec 11 2005, 07:44 AM)

Ati5p said:

Exp#1:
I get the skateboard and put it on the treadmill. Holding onto the skateboard, I turn the treadmill up to 5mph. Then I let go of the skateboard. The skateboard accelerates 'backwards' until it is ejected off the treadmill at no more than 5mph, no less than 5mph. (!!!)
Proven: There IS significant drag upon the wheels to cause a 'change' in motion.
-------------------------------------------

Here he states that the skateboard will be ejected off the end of the treadmill at no MORE than 5mph... this would be true....
BUT, he makes the MISTAKE of saying that it will be NO LESS THAN 5mph. It definitely COULD be less than 5mph as the skateboard gradually accelerates while moving towards the end(ejection point) of the belt. So example one is rejected as INCORRECT, and the drag becomes less significant.

========================================
Ati5p also said:

Exp#3:
I now combine all elements. I take a 5mph fan-propelled skateboard and put it on a treadmill going 5mph. I 'let go' of the skateboard. The skateboard stays 'motionless' reletive to me. It is moving at 5mph in relation to the treadmill. There is significant breeze coming off the back of the fan. If I hold a smoke stick in front of the fan, you can see the 'air' from in front of the fan being 'pulled' into the fan, and spit out the back.
The air to the side of the skateboard (where the wings would be) is STILL CALM.
------------------------------------------------

In this example, he states that the treadmill is going 5mph, but fails to say in relation to what, but he is using a reference that is not the skateboard. There is no skateboard at this time. NOW he puts the skateboard on the treadmill and states "IN RELATION TO THE TREADMILL". He now has two references. This is a MISTAKE in that one would have to say in
ACCORDANCE WITH HIS TERMS:
Two planes are sitting on a runway. They move oppositely at equal speeds. One begins to move at 5mph. To meet his terms, the other stands still because it is already moving at 5mph "IN RELATION TO THE OTHER".

..Go figure..... he continually fails to grasp the idea of a SINGLE reference.

Fine Bloy, you're obviously grasping at straws here, so I'll piece it together for you again...

Ex1 OK, sure, if the treadmill is short, the skateboard might go off at less than 5mph. But last night, I took a skateboard, put it on a treadmill with a digital speedo set at 5mph. I knelt down next to the treadmill. I was kneeling on the ground. It was the same God made earth that the treadmill was sitting on. The treadmill was making alot of noise. The treadmill's belt was whirring away in front of me at 5 mph in relation to me, the ground, the control panel on the treadmill...OK?!?! The treadmill was moving at 5mph!!

I then put the skateboard on the treadmill. I held it steady. By that I mean I held the skateboard steady reletive to me...reletive to the actual earth beneath the treadmill. The wheels of the skateboard were spinning. They were spinning just as fast as the treadmill. This is because the wheels were in direct contact with the treadmill, using the skateboard's full weight.

OK?...OK??? DO YOU GET IT?

THEN I 'let go' of the skateboard. It began to move backwards in relation to me. The wheels of the skateboard began to slow down in relation to the treadmill's belt (indicating that 'friction' was slowing the skateboard down, in relation to the treadmill's belt)

Then, just before the skateboard ran off the back of the treadmill, the wheels of the skateboard stopped moving, in relation to the treadmill's belt. I could read the writing on the wheels now. The wheels had 'Stopped' moving. That means the skateboard, at that time, was 'stopped' on the treadmill. Since we know the treadmill is 'going' 5mph, we can now infer that the skateboard is now moving at 5mph away from me, as it is 'stopped' reletive to the treadmill.

Ex2 Hey, why didn't you chime in here? It IS a necessary piece of this puzzle you know...or are you ignoring on purpose?

Ex3 In order to keep from repeating myself, we'll assume the same conditions as Ex1 above. The treadmill is 'set' to 5mph..it's down there spinning, you ninnie! I crank up the fan, you silly! I hold that fan laden skateboard down on that treadmill belt that is spinning at 5mph in relation to a freaking oak tree that's been in the same spot for 100 freaking years. I'm holding that skateboard 'steady' in relation to that same damn tree. The skateboard's wheels are spinning. They are spinning the same speed as the treadmill...this is because, WHY?? They are both in direct contact with each other.
Now, I let go of the fan laden skateboard. That sucker will remain motionless in relation to the oak tree. That skateboard will be going 5mph in relation to the treadmill's belt.
This fan laden skateboard will do 5mph in relation to the treadmill's belt, just like it will move 5mph down a static road, in relation to the oak tree.

Better now?
Bloy, tell me it wasn't you who faked my user name?

Allnighte

11th December 2005 - 09:31 AM

I think the question was just worded wrong, not that it's a trick question. (i didnt read the entire thread, but another forum asked the same thing and google brought me here)

it seems to me like the question is trying to convey that airspeed is only what matters for lift. a better example would be if the plane had some blocks in front of the wheels and cranked up the throttle, or if it would "take off" if a 200mph hurricane blew straight at it while it was parked.

otherwise, the question is just kindof a technicality, not a trick. i could picture a high school physics/math class asking a correct version of this question, because some students im sure would believe that a plane with its engines up can fly

Atl5p

11th December 2005 - 09:40 AM

QUOTE (ixolas+Dec 10 2005, 12:20 AM)

Take the equation step by step and not just will it fly.
I'm going to break it down for everyone.
Yes, at first even I thought the answer was no, but after I thought about it for a few seconds I realized that it would take flight. Before arguing or making a solid conclusion you will not budge from, take the time to read this entire post and think about it!!!!

A plane (excluding harriers and any other vto planes) on a day with no wind movement, will not take flight just by turning on the engines full blast without any movement. That is idiotic to think that anyone posting on this site would think that.

The first question and main question is will the plane move forward. Because: If a plane can overcome the conveyor to move forward then it will continue to overcome the conveyor and continue to move forward and eventually reach the required speed to create lift and take flight.

THINK ABOUT THIS:

IF THERE IS A GIANT CONVEYOR THAT WILL MATCH THE SPEED IN THE OPPOSITE DIRECTION I'M RIDING IN MY ROLLERBLADES. WILL I MOVE IF A FLYING HELICOPTER (USING AIR TO FLY) ABOVE ME USES A ROPE TO PULL ME FORWARD?

THIS IS EXACTLY LIKE THE QUESTION!! THINK OF THE AIRPLANE AS PIECES.
A HELICOPTER TILTS ITS PROPELLERS TO PUSH AIR AGAINST AIR TO MOVE FORWARD. PULLING A MASS (ME) ROLLING ACROSS A MOVING SURFACE ON WHEELS. SINCE I AM HOLDING ON TO A ROPE ATTACHED TO THE HELICOPTER I WILL GO FORWARD AT THE SAME SPEED THE HELICOPTER WILL GO. THE HELICOPTER WOULD FEEL A LITTLE RESISTANCE FROM ME AND THE ROPE BUT NOT MUCH AT ALL. THE CONVEYOR WILL ACT DIRECTLY AGAINST THE HELICOPTER BY ROLLING RESISTANCE AGAINST ME WHICH I TRANSFER TO THE HELICOPTER BY THE ROPE. I WOULD MOVE FORWARD, THE CONVEYOR WOULD BE MOVING UNDER ME AT THE OPPOSITE SPEED BUT THAT WOULDN'T MATTER.
Unless I tripped and fell down, ouch!

IMAGINE THE PLANE ENGINE IS THE HELICOPTER, THE PLAINS ENGINE TURNS PROPELLERS AGAINST AIR TO CREATE FORCE. NOW IMAGINE THE PLANES FRAME, FUSELAGE AND WINGS ARE THE HELICOPTER FRAME FUSELAGE AND ROPE I AM HOLDING ON TO. NOW IMAGINE THE PLANES WHEELS ARE THE SAME AS MY ROLLERBLADE WHEELS. WHEN THE HELICOPTER LIFTS OFF AND MOVES FORWARD IT IS GOING TO PULL ME ALONG THAT CONVEYOR EVEN IF IT IS GOING JUST AS FAST IN THE OPPOSITE DIRECTION.

A PLAINS ENGINES, LIKE THE HELICOPTER, USES PROPELLERS TO PUSH AIR AGAINST AIR TO MOVE FORWARD. PULLING THE A MASS (THE FRAME OF THE PLANE) ACROSS A MOVING SURFACE ON WHEELS. THE PLANE WOULD MOVE FORWARD, THE CONVEYOR WOULD BE MOVING UNDER THE PLANE AT THE OPPOSITE SPEED BUT THAT WOULDN'T MATTER BECAUSE THE PLANE WOULD HAVE FORWARD MOTION RELATIVE TO THE WORLD BY PUSHING ON THE AIR LIKE THE HELICOPTER FLIES IN THE AIR.

ONCE THE PLANE HAS FORWARD MOVEMENT IT WOULD CONTINUE TO ACCELERATE UNTIL IT REACHES THE NECESSARY SPEED TO TAKE FLIGHT.

THE MAIN THING YOU HAVE TO REMEMBER IS THE MATCHING SPEED OF THE CONVEYOR ISN'T MATCHING THE THRUST THE PLAINS ENGINES PRODUCE AGAINST THE AIR. THE CONVEYOR IS ONLY MATCHING THE SPEED OF THE PLANE AND SPINNING THE WHEELS. THE THRUST AGAINST THE PLANE VIA THE WHEELS IS SO SMALL COMPARED TO WHAT THE PLANE IS PRODUCING PUSHING AGAINST THE AIR TO MOVE IT FORWARD.

I found the formula's for all the people saying the wheel resistance wouldn't allow the plane to take flight.

The resistance of a wheel is found roughly by a formula like this: the weight in newtons (1lb = 4.45 newtons) divided by the number of wheels, times actually wheel resistance (usually below 4% or 0.04), times the speed in meters per second (1mph = .45 meters/hour), equals the resisting force.
rr=(weight/wheels)x(.04)x(speed)

The force of thrust to move a plane is found by the formula like this: mass in newtons times speed in meters/hour equals the force.
f=(weight)x(speed)

A plane weighing 1,335,000 newtons (300,000 lbs) divided by 3 wheels multiplied by the wheel resistance .04 and then multiplied by the speed of 4.5 meter/hour (10 miles/hour) has a rolling resistance of 80,100 newtons (18,000 lbs) acting against it. The conveyor moving in the opposite direction at the same speed of 4.5 meter/hour this would double the wheel speed and make it an opposing force of 160,200 newtons (36,000 lbs) acting against it.
rr=(1335000/3)x.04x(4.5+4.5)=160200

A plane weighing 1,335,000 newtons moving at 4.5 meter per seconds has a forward force of 6,007,500 newtons.
f=1335000x4.5=6007500

Therefore the forward force of 6,007,500 newtons minus the rolling resistance of the conveyor going in the oppose direction is 160,200 newtons leaving a forward force of 5,847,300 newtons.
(f=6007500)-(rr=160200)=5847300

The opposing force, on the plane will never equal the opposing force applied to the wheels. Therefore the opposing force on the plane by the conveyor will subtract from the forward force but not equal it.

And just for everyone, don't nit pick on the spelling or technicalities like "the propellers actually don't push on air... " whatever! I am just trying to get the point across.

Let me ask all you people who think the plane wouldn't take off, and please voice this in your reply.. how about a variation: if the conveyor is already going an opposing direction of 10 mph and will stay 10 mph faster than the plane and then the plane with the engines going full throttle was then released on the conveyor (no forward movement just straight down by a crane or something then unattached) would it move backwards or move forwards? I mean the conveyor is already going in an opposite direction faster than the plane since it has no forward movement. Since the conveyor is moving faster than the plane (no forward motion) would it roll the plane straight back and off the conveyor since it isn't equal speed. Why not is what we are trying to get you to understand. the wheels don't act on the plane with the same force of the conveyor so therefor the "equal speed in opposite direction" doesn't matter cause it just spins them.

I'm going to get a rubber band powered plane and get a treadmill and turn the treadmill up to 10 mph then set the rubber band plane on it to prove it would take flight, and you know the rubber band plane won't go as fast as 10 mph, and will still move foreword. I will post a link after I do it. Will this quite you people saying it won't fly?

The reason why the "it will fly" group is a settlement is because once the people figure it out they are going to settle in and not budge. For everyone who agrees with this analogy please copy and paste then repost it!!!!!!!!!!!!!!!!!!!

Alll righty then....just got the home connection fixed and was able to absorb your EXCELLENT research...I did what you asked, I took my time, I wrapped my head around your theory. Your's was by far the very best post thus far on this subject!! Much props!

However, there are just a couple of fatal flaws, whereby you prove the plane will NOT FLY! I appreciate all your hard work...what I will now do is quote you directly, but in the correct contexts, and everything should make sence.

I only ask that you provide me the same courtesy that I provided you, in really reading the following message to the world. If you take the time to understand, as I did for you, you too will come to a greater understanding of the world we live in.

You said:

QUOTE

The force of thrust to move a plane is found by the formula like this: mass in newtons times speed in meters/hour equals the force.
f=(weight)x(speed)

A plane weighing 1,335,000 newtons moving at 4.5 meter per seconds has a forward force of 6,007,500 newtons.
f=1335000x4.5=6007500

Ok, that’s fine, you just described a 300,000 lb plane propelled with 6,007,500 newtons of force will move at 4.5 m/s WITH NO OTHER FRICTION….This plane is NOT moving on a runway, OR a treadmill’s moving belt! (a little light should be coming to life right about now, hint hint…)

You continued with:

QUOTE (->

QUOTE

The force of thrust to move a plane is found by the formula like this: mass in newtons times speed in meters/hour equals the force.
f=(weight)x(speed)

A plane weighing 1,335,000 newtons moving at 4.5 meter per seconds has a forward force of 6,007,500 newtons.
f=1335000x4.5=6007500

Ok, that’s fine, you just described a 300,000 lb plane propelled with 6,007,500 newtons of force will move at 4.5 m/s WITH NO OTHER FRICTION….This plane is NOT moving on a runway, OR a treadmill’s moving belt! (a little light should be coming to life right about now, hint hint…)

You continued with:
The resistance of a wheel is found roughly by a formula like this: the weight in newtons (1lb = 4.45 newtons) divided by the number of wheels, times actually wheel resistance (usually below 4% or 0.04), times the speed in meters per second (1mph = .45 meters/hour), equals the resisting force.
rr=(weight/wheels)x(.04)x(speed)

A plane weighing 1,335,000 newtons (300,000 lbs) divided by 3 wheels multiplied by the wheel resistance .04 and then multiplied by the speed of 4.5 meter/hour (10 miles/hour) has a rolling resistance of 80,100 newtons (18,000 lbs) acting against it.

Great, you just came up with the friction created by by EACH of 3 Wheels due to the force of the runway when that plane is taxing down a normal runway. Out of 3 wheels, each wheel is creating 80,100 newtons of friction, when a 300,000 lb plane moves over the ground with 6,007,500 newtons of thrust behind it. Super! I'm so glad you've come up with these numbers!

Below is where you are actually showing the plane taxing on a normal runway with the engines producing their thrust and the wheels creating their friction.

QUOTE

Therefore the forward force of 6,007,500 newtons minus the rolling resistance of the conveyor going in the oppose direction is 160,200 newtons leaving a forward force of 5,847,300 newtons.
(f=6007500)-(rr=160200)=5847300

Your math was a little off there…didn’t you say 3 wheels earlier? So 80,100 x 3 = 240,300 newtons of wheel friction instead of 160,200? Doesn’t matter too much so don’t worry…I just wanted everything to be totally accurate from your earlier calculation where you said the plane had 3 wheels….so if you will:
(f=6,007,500)-(rr=240,300)=5,767,200 (Fair enough?...I agree, it doesn’t change the end result of this calculation much...but anyway)

I'll put everything we've covered so far into illustration, but first we must take a trip to the Bonneville Salt Flats....think loooong runway here:

What is happening here, is this: This plane moving through the air with 6,007,500 newtons of force will be traveling 4.5 m/s. BUT, when it hits the runway, that same plane, with that same 6,007,500 newtons of force (keep the engines fired just the same), will be slowed down by 240,300 newtons of wheel friction, which will result in 5,767,200 newtons (or 4.32 m/s) of forward motion. Keep those engines up, and you'll stay at 4.32 m/s for miles...now, magically 'take-off' again into the air, and when the wheel's friction is gone, you'll resume your former 4.5 m/s!

So basically, your 6,007,500 newtons of force will taxi this plane on a RUNWAY at 4.32 m/s, NOT 4.5 m/s.

THE SOLUTION
Now, move the plane onto the treadmill runway. Crank up the engines, and I'll get the treadmill ready.

You will move the plane with 6,007,500 newtons of force.
What I am proposing is moving the treadmill with 6,007,500 newtons of force from the motors.
The crushing weight of the plane and resulting friction of the wheels due to the 6M newton force will prevent treadmill's BELT from moving faster than to 240,300 newtons.
The friction from the tires on the belt will slow the plane down to 5,767,200 newtons.
(you have a complete equation up there now!)

Treadmill:
6,007,500n (from motors) - 5,767,200n (plane's net force after frictional loss) = 240,300n (the 'light' belt's resulting movement is 4.32 m/s at 240,300n)

Plane :
6,007,500n (from jets) - 240,300n (belt's friction upon the wheels) = 5,767,200n (the 'heavy' plane's resulting forward movement is 4.32 m/s at 5,767,200n )

The treadmill is now moving at 4.32 m/s.
The plane is now moving over the treadmill at 4.32 m/s.
The wheels are now moving at 4.32 m/s.
The plane appears stationary to us in the tower.
The plane appears stationary to the molecule of air over the wing.
The wings do not produce lift.
The plane does not fly.

6,007,500n from treadmill's motors.
vs.
6,007,500n from plane's jet engines.
factor in
240,300n from wheels slow's the plane down to 5,767,200n, which at 300,000lbs is 4.32 m/s.
results in
5,767,200n of plane's remaining 'net' force acts on the treadmill's 6,007,500n, slowing the belt down to 240,300n. The belt itself is reletivlely light compared to the plane, so this also equals 4.32 m/s.

You can raise the force of the plane all day long...as long as you match those newtons on the treadmill, that plane won't go nowhere!!

(for this example, mechanical losses within the treadmill itself and the weight of the actual belt are ignored, since this is not important in this illustration.)

Or look at it a different way...the touch and go landing...
Fly the plane in at 6,007,500 newtons of force (I know this is 4.5 m/s or 10mph, and planes can't fly that slow, but just bear with it for a second...what's important is what happens upon 'landing')

The treadmill is moving with a force of 6,007,500 newtons. And NO It is NOT spinning at 10mph BEFORE the plane lands, as was previously thought!! Who knows how fast it's spinning??, but with a 300,000 lbs plane comming in to land, that thing had better be 'freewheeling' pretty darn fast, huh?
Since the belt is relatevly light, let's just say 6,007,500 newtons spins the belt at say...., I don't know -- 250mph, before the weight of the plane comes down. (BEFORE the plane lands)
Now the plane lands.
The plane's crushing 300,000 lbs comes lumbering in at 4.5 m/s with 6,007,500 newtons of force behind it. It is met with the high speed shrill of the treadmill's screaming 6,007,500 newton motor spinning the belt at 250mph! We'll pretend it's a veeeery slow 747 landing on a modified carrier that has this huge nuclear powered treadmill belt instead of arrestor cables. What a sight to behold!!!

What happens at the treadmill?
The crushing weight of the plane and the 6,007,500 newtons of force begins to slow the belt very rapidly. Though the plane is comming in at 6,007,500n, remember it's wheels are going to 'give up' 240,300 to friction. This results in a net force of only 5,767,200 newtons of the plane's force acting upon the treadmill's full 6,007,500n. Do the math, the result is 240,300 newtons of belt speed. This slows the belt's actual speed down to 4.32 m/s. So the belt slows, but does not stop. It dosn't stop, because the belt's motor is still excerting 6,007,500 newtons of force against the plane.

What happens on the plane?
At the same time, the friction from the belt slows the plane very rapidly as well. Since the plane's 6,007,500 newtons have been met by the treadmill's 6,007,500 newtons, the now fully-loaded wheels produce 240,300 of friction on the plane's progress, causing it to slow down rapidly. Since this amount of friction is reletivly slight, the rapid deceleration is short lived as the plane slows from 4.5 m/s to a measly 4.32 m/s in a flash. The passengers in the plane feel a slight 'jerk'.

And remember, the throttles on the plane are held in place...the plane is still excerting 6,007,500 newtons of force, just like the treadmill's motors...they are balancing each other out, except for the small 240,300n friction caused by the wheels. It is this friction that is allowing the tires on the plane to move at 4.32 m/s. That movement in the tires is what is allowing the treadmill to move at 4.32m/s.

In fact, if you go ahead and apply the bakes, the tires will stop, and the treadmill will stop. Keep the 6,007,500 newtons kicking from the plane....keep the 6,007,500 newtons coming from the treadmill. When the brakes are applied, and the wheels locked up, that jet will scream all day and won't go anywhere. (kinda exactly reminds me of what I do before takeoff...lock the brakes and throttle up the engine...we don't move until I release the brakes). IT's just the plane's engines against the treadmill's motors at this point, right? Yup! That's right folks...you just stopped the treadmill from moving just by applying your brakes (in this example). Assuming the treadmill is manually operated and 'set' at 6,007,500n, and the plane is likewise 'set' to the same 6,007,500n, you can modulate the motion of both the tires AND the treadmill's belt JUST BY APPLING THE BRAKES!!! HAHAHA!!

Anyway, go ahead and release the brakes. What happens? If you said the wheels will start to roll at 4.32 m/s, you are right! Next, since that 'give' from the wheels has releved the treadmill of 240,300n, it will start to move at 4.32 m/s.

There you have it. A 300,000 lb plane, with 6,007,500 newtons of force is met by a treadmill excerting 6,007,500 newtons of force. When the wheels are locked, the treadmill and wheels won't move. When the brakes are released, both will move in opposite directions from each other at a speed of 4.32 m/s. To us in the tower the plane will 'stand still', as well as the molecule of air over the wings. No Lift, No Flight, pay me my money!

Lessons in Gravity
What the 'Fly Boys' were forgetting was the tremendous effect of GRAVITY. The Aero-knowlegable people will get it wrong every time, because they spend all their time 'in the clouds' where gravity has been overcome. Once you have lift, gravity, and it's frictional losses over the ground, are just not in your day to day vocabulary. Most of your calculations would probably factor neutral lift as a given, in all but the most dangerous recovery manuvers.

It is the 'Educated Lay Person' who will get this one right. We live and think within the confines of gravity most every day. It is more natural for us think about gravity and the ground, just as it is more natural for 'you' to think up in the sky.

But that is the reason for the descrepancy between the two camps backgrounds. The Aero buffs think it will fly, because they are trained to make that thing fly. The Edu-Lay's know in their heart of hearts that it wont fly, and that's because our feet are on the ground.

This is the CLASSIC example of book learning gone bad. So much brain power, but not enough sence to get in out of the rain...Can't see the forrest from the trees, you're just to close to the math....call it what you will. We got it, you helped us prove it, all that's left now is to make a few points, try to knock some holes, and eventually agree, 'This Is Right'.

OH, I almost forgot your last request:

QUOTE (->

QUOTE

Therefore the forward force of 6,007,500 newtons minus the rolling resistance of the conveyor going in the oppose direction is 160,200 newtons leaving a forward force of 5,847,300 newtons.
(f=6007500)-(rr=160200)=5847300

Your math was a little off there…didn’t you say 3 wheels earlier? So 80,100 x 3 = 240,300 newtons of wheel friction instead of 160,200? Doesn’t matter too much so don’t worry…I just wanted everything to be totally accurate from your earlier calculation where you said the plane had 3 wheels….so if you will:
(f=6,007,500)-(rr=240,300)=5,767,200 (Fair enough?...I agree, it doesn’t change the end result of this calculation much...but anyway)

I'll put everything we've covered so far into illustration, but first we must take a trip to the Bonneville Salt Flats....think loooong runway here:

What is happening here, is this: This plane moving through the air with 6,007,500 newtons of force will be traveling 4.5 m/s. BUT, when it hits the runway, that same plane, with that same 6,007,500 newtons of force (keep the engines fired just the same), will be slowed down by 240,300 newtons of wheel friction, which will result in 5,767,200 newtons (or 4.32 m/s) of forward motion. Keep those engines up, and you'll stay at 4.32 m/s for miles...now, magically 'take-off' again into the air, and when the wheel's friction is gone, you'll resume your former 4.5 m/s!

So basically, your 6,007,500 newtons of force will taxi this plane on a RUNWAY at 4.32 m/s, NOT 4.5 m/s.

THE SOLUTION
Now, move the plane onto the treadmill runway. Crank up the engines, and I'll get the treadmill ready.

You will move the plane with 6,007,500 newtons of force.
What I am proposing is moving the treadmill with 6,007,500 newtons of force from the motors.
The crushing weight of the plane and resulting friction of the wheels due to the 6M newton force will prevent treadmill's BELT from moving faster than to 240,300 newtons.
The friction from the tires on the belt will slow the plane down to 5,767,200 newtons.
(you have a complete equation up there now!)

Treadmill:
6,007,500n (from motors) - 5,767,200n (plane's net force after frictional loss) = 240,300n (the 'light' belt's resulting movement is 4.32 m/s at 240,300n)

Plane :
6,007,500n (from jets) - 240,300n (belt's friction upon the wheels) = 5,767,200n (the 'heavy' plane's resulting forward movement is 4.32 m/s at 5,767,200n )

The treadmill is now moving at 4.32 m/s.
The plane is now moving over the treadmill at 4.32 m/s.
The wheels are now moving at 4.32 m/s.
The plane appears stationary to us in the tower.
The plane appears stationary to the molecule of air over the wing.
The wings do not produce lift.
The plane does not fly.

6,007,500n from treadmill's motors.
vs.
6,007,500n from plane's jet engines.
factor in
240,300n from wheels slow's the plane down to 5,767,200n, which at 300,000lbs is 4.32 m/s.
results in
5,767,200n of plane's remaining 'net' force acts on the treadmill's 6,007,500n, slowing the belt down to 240,300n. The belt itself is reletivlely light compared to the plane, so this also equals 4.32 m/s.

You can raise the force of the plane all day long...as long as you match those newtons on the treadmill, that plane won't go nowhere!!

(for this example, mechanical losses within the treadmill itself and the weight of the actual belt are ignored, since this is not important in this illustration.)

Or look at it a different way...the touch and go landing...
Fly the plane in at 6,007,500 newtons of force (I know this is 4.5 m/s or 10mph, and planes can't fly that slow, but just bear with it for a second...what's important is what happens upon 'landing')

The treadmill is moving with a force of 6,007,500 newtons. And NO It is NOT spinning at 10mph BEFORE the plane lands, as was previously thought!! Who knows how fast it's spinning??, but with a 300,000 lbs plane comming in to land, that thing had better be 'freewheeling' pretty darn fast, huh?
Since the belt is relatevly light, let's just say 6,007,500 newtons spins the belt at say...., I don't know -- 250mph, before the weight of the plane comes down. (BEFORE the plane lands)
Now the plane lands.
The plane's crushing 300,000 lbs comes lumbering in at 4.5 m/s with 6,007,500 newtons of force behind it. It is met with the high speed shrill of the treadmill's screaming 6,007,500 newton motor spinning the belt at 250mph! We'll pretend it's a veeeery slow 747 landing on a modified carrier that has this huge nuclear powered treadmill belt instead of arrestor cables. What a sight to behold!!!

What happens at the treadmill?
The crushing weight of the plane and the 6,007,500 newtons of force begins to slow the belt very rapidly. Though the plane is comming in at 6,007,500n, remember it's wheels are going to 'give up' 240,300 to friction. This results in a net force of only 5,767,200 newtons of the plane's force acting upon the treadmill's full 6,007,500n. Do the math, the result is 240,300 newtons of belt speed. This slows the belt's actual speed down to 4.32 m/s. So the belt slows, but does not stop. It dosn't stop, because the belt's motor is still excerting 6,007,500 newtons of force against the plane.

What happens on the plane?
At the same time, the friction from the belt slows the plane very rapidly as well. Since the plane's 6,007,500 newtons have been met by the treadmill's 6,007,500 newtons, the now fully-loaded wheels produce 240,300 of friction on the plane's progress, causing it to slow down rapidly. Since this amount of friction is reletivly slight, the rapid deceleration is short lived as the plane slows from 4.5 m/s to a measly 4.32 m/s in a flash. The passengers in the plane feel a slight 'jerk'.

And remember, the throttles on the plane are held in place...the plane is still excerting 6,007,500 newtons of force, just like the treadmill's motors...they are balancing each other out, except for the small 240,300n friction caused by the wheels. It is this friction that is allowing the tires on the plane to move at 4.32 m/s. That movement in the tires is what is allowing the treadmill to move at 4.32m/s.

In fact, if you go ahead and apply the bakes, the tires will stop, and the treadmill will stop. Keep the 6,007,500 newtons kicking from the plane....keep the 6,007,500 newtons coming from the treadmill. When the brakes are applied, and the wheels locked up, that jet will scream all day and won't go anywhere. (kinda exactly reminds me of what I do before takeoff...lock the brakes and throttle up the engine...we don't move until I release the brakes). IT's just the plane's engines against the treadmill's motors at this point, right? Yup! That's right folks...you just stopped the treadmill from moving just by applying your brakes (in this example). Assuming the treadmill is manually operated and 'set' at 6,007,500n, and the plane is likewise 'set' to the same 6,007,500n, you can modulate the motion of both the tires AND the treadmill's belt JUST BY APPLING THE BRAKES!!! HAHAHA!!

Anyway, go ahead and release the brakes. What happens? If you said the wheels will start to roll at 4.32 m/s, you are right! Next, since that 'give' from the wheels has releved the treadmill of 240,300n, it will start to move at 4.32 m/s.

There you have it. A 300,000 lb plane, with 6,007,500 newtons of force is met by a treadmill excerting 6,007,500 newtons of force. When the wheels are locked, the treadmill and wheels won't move. When the brakes are released, both will move in opposite directions from each other at a speed of 4.32 m/s. To us in the tower the plane will 'stand still', as well as the molecule of air over the wings. No Lift, No Flight, pay me my money!

Lessons in Gravity
What the 'Fly Boys' were forgetting was the tremendous effect of GRAVITY. The Aero-knowlegable people will get it wrong every time, because they spend all their time 'in the clouds' where gravity has been overcome. Once you have lift, gravity, and it's frictional losses over the ground, are just not in your day to day vocabulary. Most of your calculations would probably factor neutral lift as a given, in all but the most dangerous recovery manuvers.

It is the 'Educated Lay Person' who will get this one right. We live and think within the confines of gravity most every day. It is more natural for us think about gravity and the ground, just as it is more natural for 'you' to think up in the sky.

But that is the reason for the descrepancy between the two camps backgrounds. The Aero buffs think it will fly, because they are trained to make that thing fly. The Edu-Lay's know in their heart of hearts that it wont fly, and that's because our feet are on the ground.

This is the CLASSIC example of book learning gone bad. So much brain power, but not enough sence to get in out of the rain...Can't see the forrest from the trees, you're just to close to the math....call it what you will. We got it, you helped us prove it, all that's left now is to make a few points, try to knock some holes, and eventually agree, 'This Is Right'.

OH, I almost forgot your last request:
Let me ask all you people who think the plane wouldn't take off, and please voice this in your reply.. how about a variation: if the conveyor is already going an opposing direction of 10 mph and will stay 10 mph faster than the plane and then the plane with the engines going full throttle was then released on the conveyor (no forward movement just straight down by a crane or something then unattached) would it move backwards or move forwards? I mean the conveyor is already going in an opposite direction faster than the plane since it has no forward movement. Since the conveyor is moving faster than the plane (no forward motion) would it roll the plane straight back and off the conveyor since it isn't equal speed. Why not is what we are trying to get you to understand. the wheels don't act on the plane with the same force of the conveyor so therefor the "equal speed in opposite direction" doesn't matter cause it just spins them.

What you need to realize here is this. When the treadmill is 'freewheeling' at only 10mph, it is producing very very few newtons. Then you drop a 'plane' on it (I'll assume it's the same 747 as before weighing 300,000 lbs). As soon as the plane hits the deck, the motors in the treadmill are going to need to put out a TON more juice to match the newtons it has just encountered.
But once that happens, it will be right back up to 10mph again, just like the plane.
Now, raise the treadmill another 10mph you say? The plane's engines are maxed out? You want me to send the plane off the back of the treadmill? You Sure? OK, Fine. Here goes.
Since we know 240,300n on the belt is about 10mph (4.32 m/s), and we want to raise the speed by another 10mph, we just need to add about another 240,300n to the speed of the belt. So, what was that treadmill equation again? Oh, here it is:
6,007,500n - 5,767,200n = 240,300n

Just add 240,300n to both sides of the eqation, and you get the following
6,247,800 - 5,767,200n = 480,600

There, easy as pie. Simply increase the treadmill's motor output to 6,247,800, and that 300,000 lb plane will shoot off the back of your treadmill at a speed of 8.64 m/s. Now I realize this is going a little less than your 10mph, but just give turn the knob a little more, and you'll have it. Shoot, go ahead and make it an even 6,300,000 newtons at the treadmill...we've got power to spare...your plane will start to go backwards, in relation to the tower, until it rolls off the back of the treadmill. (hopefully we aren't on the aircraft carrier for this one).

Now remember once again...we're assuming above that 'this' particular plane is 'maxed out' at 6,007,500n. 10mph is full throttle on that plane. If you want to go for 'real thrust' of a 747 that's fine...I'll just match it with my nuclear powered treadmill, so no problem. As much thrust as your plane can dish out, my treadmill can counter it. That's key to the question. Your plane can never out-power my treadmill. That'd be cheating.

As long as we match Newtons, then the wheelspeed will match the belt speed.

And if you set both plane and treadmill to the same newtons, we can actually regulate the speed of the belt and wheels via our brake pedal. Think about it...it'll make your brain feel good when you understand it!!

I have the treadmill....I'm getting a wheeled, air-propelled vehicle...I will prove it.
My treadmill goes 10mph according to the digital speedo. I'm sure your's wont go much faster. Make SURE you time that rubber band plane of yours at 4.5 meters per second!! That's 10mph, remember? At least we won't have to factor in the weight for a rubber band plane. Just make sure it goes 10mph on the ground, then set it up on a 10mph treadmill...It'll work, TRUST ME!! Please let me know what you find out...this isn't about getting back, this is about solving this problem the RIGHT way.

(What I haven't mentioned is that I am a professional Quality Assurance Engineer...yeah, I'm the guy that finds all the smelly 'bugs' that you 'know it all' engineers leave behind)...THIS IS my JOB! I'm pretty good at it too...

And just a little note for author of this vicious attack upon me:
http://forum.physorg.com/index.php?showtop...indpost&p=41340
I would recomend that you think deeply on this post, and be prompt in your retractions....

Bloy

11th December 2005 - 09:45 AM

early/late

Allnighte

11th December 2005 - 09:49 AM

QUOTE (Bloy+Dec 11 2005, 09:45 AM)

I think the question was worded just fine....all you have to do is follow what it says....
both the plane is MOVING forward at an equal speed that the conveyor is moving opposite. using the ground as a single reference, and the prop of the plane for the thrust, you move the plane forward while the belt moves backward. the speed between the two is double....so simple.....nothing that a good wheel assembly can't handle.

yes, but what is the point of the question then? it's not very "oh, how neat! physics sure is interesting!" the way it's currently worded.

just imagine yourself being in high school again. wouldn't this question be better if it was trying to illustrate that planes only fly if wind is moving over the wings? instead of this stupid treadmill that just makes the wheels turn faster for the plane.

Atl5p

11th December 2005 - 09:57 AM

QUOTE (Bloy+Dec 11 2005, 09:45 AM)

I think the question was worded just fine....all you have to do is follow what it says....
The plane is MOVING forward at an equal speed that the conveyor is moving opposite. Using the ground as a single reference, and the prop of the plane for the thrust, you move the plane forward while the belt moves backward. The speed between the two is double....so simple.....nothing that a good wheel assembly can't handle.

You are reading too much into the question. The whole purpose is to see whether or not the treadmill can keep the plane from flying. The 'ground' has nothing to do with it, except for providing refrence to the calm air, which we cannot see.

QUOTE

A plane is standing on runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The question is:

Will the plane take off or not? Will it be able to run up and take off?

"The conveyor has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

The conveyor is tracking the speed of the plane in relation to ITSELF! The treadmill. When the plane is moving at 5mph, that is in relation to the treadmill's BELT.

We wouldn't have all these issues with friction and drag, if it were as simple as being a 'trick question'. Read it for what it is, and see my 'Solution' post for all your answers.
The Solution...by Atl5p and ixolas

Bloy

11th December 2005 - 10:02 AM

new/old

Bloy

11th December 2005 - 10:19 AM

wide/narrow

Allnighte

11th December 2005 - 10:21 AM

QUOTE (Bloy+Dec 11 2005, 10:02 AM)

QUOTE (Allnighte+Dec 11 2005, 09:49 AM)

QUOTE (Bloy+Dec 11 2005, 09:45 AM)

I think the question was worded just fine....all you have to do is follow what it says....
both the plane is MOVING forward at an equal speed that the conveyor is moving opposite. using the ground as a single reference, and the prop of the plane for the thrust, you move the plane forward while the belt moves backward. the speed between the two is double....so simple.....nothing that a good wheel assembly can't handle.

yes, but what is the point of the question then? it's not very "oh, how neat! physics sure is interesting!" the way it's currently worded.

just imagine yourself being in high school again. wouldn't this question be better if it was trying to illustrate that planes only fly if wind is moving over the wings? instead of this stupid treadmill that just makes the wheels turn faster for the plane.

The point of the question is moreso for individuals that haven't developed their logic and exactness ..... some keep placing the plane's speed relative to the conveyor....this is contrived maybe for argument's sake.
when the plane relative to the ground is moving 5mph(or whatever) then that is what it is doing. It can't be standing still just because the conveyor is moving opposite. The planes throttle(prop speed) controls the plane...not the conveyor(of any significance). Sure you may have to push in the throttle a little more to compensate for the wheel assembly's friction, but we already know that.
Unless you want to take the numbers to extremes to where man cannot technologically produce a flying vehicle with supporting wheel assemblies, then I think things will be just fine.

i see what you're saying, but there are better ways of doing logic questions. this one seems more like a technicality.

reminds me of one of my old favorites: A man builds a house with all 4 sides facing south. A bear walks past the house. What color is the bear?

while the technical answer is "black" (since a polar bear has black skin and transparent fur), the answer that fits the problem better is "white", since most people only know of one kind of white bear.
the question is much better illustrated by an answer of "white", and only those few who have read/heard that a polar bear is actually black will get it technically correct.

that's why i think the question should be reworded so that either the treadmill prevents any forward motion of the entire plane, or that the plane is glued to the ground. then the answer of "no, it wont fly" (assuming no hurricane force winds are blowing at it) illustrates the general properties of airplanes better than frictionless wheels and treadmills

Guest_atl5p

11th December 2005 - 10:26 AM

QUOTE (Bloy+Dec 11 2005, 10:19 AM)

QUOTE (Bloy+Dec 4 2005, 11:35 PM)

So I say... without adding any elements to the posed question.

Will the airprop driven plane reach liftoff speed? Yes
Will the winged wheel driven car/plane reach liftoff speed? yes

Will the airprop driven plane fly?: Yes, because it can continue to accelerate.

Will the winged wheel driven car/plane fly?: NO, because it will lose thrust when friction to the runway is lost at liftoff speed, thus never being able to accelerate beyond the liftoff speed.

That's my final answer and I'm sticking to it.

Since we're bringing up past posts, I thought I restate my position.
Tell me why this isn't so so I can point out through your negations why it IS so.

Please reffer to The Solution...Thanks! Everyone is forgetting GRAVITY mashing the plane into the treadmill.

If the treadmill is making 10,000,000 newtons of force, and the plane is making 10,000,000 newtons of force, then the two WILL balance each other out...no?

The Solution

Bloy

11th December 2005 - 10:38 AM

full/empty

Bloy

11th December 2005 - 10:41 AM

push/pull

Bloy

11th December 2005 - 10:44 AM

take/give

Bloy

11th December 2005 - 11:44 AM

over/under

Guest

11th December 2005 - 12:30 PM

QUOTE (Guest_atl5p+Dec 11 2005, 10:26 AM)

Please reffer to The Solution...Thanks! Everyone is forgetting GRAVITY mashing the plane into the treadmill.

If the treadmill is making 10,000,000 newtons of force, and the plane is making 10,000,000 newtons of force, then the two WILL balance each other out...no?

Just for the record, it wasn't Bloy who did that excellent impersonation of you. It was just a passer by that was amused...you've shown more ignorance than anybody else on here.

No one is forgetting gravity. Where does the rolling resistance come from? It's because of "GRAVITY mashing the plane into the treadmill"? That is indeed present in at least one of the two examples earlier showing that the force of the planes engines easily overcomes the rolling resistance of the wheels. Those that are ignoring rolling resistance as if it doesn't exist aren't technically right, but the force from that is small enough that the plane can still accelerate relative to the ground and the air.

And how does the treadmill apply 10,000,000 newtons of force to the plane? You think that doubling the rotation rate of the wheels on the conveyor takes the rolling resistance force from some value, low enough to normally allow that plane to accelerate to (and past) the take off speed, to 10,000,000 newtons? That's some funny stuff. The rolling resistance for this plane in the problem will simply double. Its already been show why and how.

You need to realize that Speed DNE Force.

essdee

11th December 2005 - 12:35 PM

Hi,

This is the first time I'm posting here; just happened to swing by. The question caught my eye and I spent the next 30 minutes reading the various posts and solutions. I am not a trained engineer or a pilot but can realistically visualise scenarios. My preferred method is to replace factors I know little about with things I am familiar with till I solve the "equation" and then slowly bring in the stuff I don't understand.

Despite the compelling scientific arguments both for and against the plane taking off, here's what I did to decide.

Stick a pinwheel to a car's bonnet. Stick the car on a giant treadmill (or at a testing facility where they have rollers in the floor for the car's wheels to turn). In my mind's eye, no matter how fast the car's wheels turn, it is not moving relative to the air and the pinwheel will not turn.

An airplane creates lift by forcing air to pass over its wings at high speed. This is why it needs a long runway to generate this AIR SPEED regardless of its groundspeed. An airplane stuck on a treadmill could have all its engines at full throttle moving it forward but the treadmill would move it backward and its net movement relative to the air would be zero.

The plane will not fly. It can't unless it can generate enough AIR SPEED over its wings and it can't do that unless it physically moves through the air.

Maybe I'm missing something crucial and will sit corrected. As for the plane landing on a moving treadway (treadmill+runway) I lack the engineering to decide for sure but using my car again, I visualise it landing on a spinning treadway. The engine's off and the wheels are free. The car's momentum pushes it forward and it will do so regardless of where it lands. However, if the treadway can absorb the impact of the landing and can quickly speed up to more than the car's forward speed it will eventually be able to slow down as the momentum dissipates.

Of course, the time can be shortened by applying the brakes; but this would mean someone sitting inside the car and I'll pass. Interestingly, I project that the pinwheel in this scenario (assuming it survived the impact) will ultimately stop spinning long before the car comes to rest because relative air speed will be zero as soon as the car's forward motion is matched by the treadway.

While the treadway scenario won't work for take-offs, it sounds like it might just work for temporary landing strips. These could come in handy during disaster relief operations and so forth where getting help in fast is vital. The only problem is: How the hell do the relief C-130s take off once they're done?

So maybe the idea won't work in real life. If any of the readers here can fix this minor glitch, they may want to post the idea at the www.halfbakery.com for evaluation.

Regards,
essdee

Bloy

11th December 2005 - 12:49 PM

thick/thin

another guest

11th December 2005 - 01:00 PM

QUOTE (Atl5p+Dec 11 2005, 09:40 AM)