FINALLY! Mythbuster, Dec 12th, MUST WATCH!

[Xtrema]

http://community.discovery.com/eve/forums/a/tpc/f/9801967776/m/5321919039/p/1



Airplane Hour
(Weds., December 12 at 9 PM ET/PT)
Adam and Jamie find out if either of them can safely land a Boeing 747-400 on a runway in varying weather conditions. Meanwhile, Kari, Tory and Grant risk life and limb to investigate skydiving myths regularly featured in Hollywood action films. Is it possible to catch up with someone in freefall if that person jumps out a plane before you do? Can you really hold a conversation during freefall? And would you survive if you opened your parachute only a few feet off the ground? Finally, Adam and Jamie carefully navigate their way through a myth that has baffled everyone from web bloggers to pilots. If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off? Extensive small-scale testing with a super treadmill and a nearly uncontrollable model airplane don't completely resolve the myth, so our flight cadets supersize the myth with help from a willing pilot and his Ultralight flying machine.

YES!

[Mibz]

Do people seriously think that the plane won't move forward? I'm unsure of the friction between the tires and belt so perhaps it won't be able to take off but it will definitely move forward.

[buh_buh]

its about time we solved this

[Tik-Tok]

I don't understand the myth. You require airflow, and high/low pressure ranges along the airfoil to create lift, how would a conveyer belt create this?

[alloroc]

Bernoulli's Theorem people.

no forward motion relative to the surrounding air = no airflow across the wings = no flight - unless they are contemplating doing this in a wind tunnel and blowing air across the wings at take off velocity.

[natejj]

I got 5 bucks that says the plane DOESNT take off. I've seen planes take off the back of trucks, but that is different.

[benyl]

^^ is thrust applied to the ground or the air?

OMG... hahahahaha...

It really isn't a myth. The plane will take off. It is all about relative air speed.

[benyl]

Originally posted by natejj
I got 5 bucks that says the plane DOESNT take off. I've seen planes take off the back of trucks, but that is different.

I will bet you $5 it does.

[natejj]

Originally posted by benyl


I will bet you $5 it does.

Lets just clarify something. Lets say once the plane is at full thrust, in place, on the conveyor belt, does the belt suddenly stop or something, and the plane shoots forward into the air? Or is the idea that the plane can point its nose upwards and shoot off forwards?

I dont want to start this whole argument over, because I dont claim to be an expert on the subject, I do work in the tower at an airport, so I know a bit about planes. But the theory behind lift is basically when a plane flies forward, the pressure about the wing, is lower then below the wing, so the wing moves toward the lower pressure area, up. If the plane is not moving forward, its relative airspeed is 0 (unless theres a wind) so I just dont think it will fly.

We on for 5 bucks?

[Tik-Tok]

Adam and Jamie find out if either of them can safely land a Boeing 747-400 on a runway in varying weather conditions. Meanwhile, Kari, Tory and Grant risk life and limb to investigate skydiving myths regularly featured in Hollywood action films. Is it possible to catch up with someone in freefall if that person jumps out a plane before you do? Can you really hold a conversation during freefall? And would you survive if you opened your parachute only a few feet off the ground?

Wow, their really gearing the show towards kids these days, aren't they?

Without having to use any cool toys that they always use...

1) Can you safely land a 747 during adverse weather - Highly unlikely, it would be a fluke if you can. BUSTED
2) Can you catch up with someone in freefall Obviously, how else do you think aerobatic skydiving teams do what they do? 50 people all jumping out of the plane at the same time? TRUTH
3) Can you hold a conversation during freefall Why not? you can hold a conversation on a windy day can't you? TRUTH
4) Will you survive if your chute opened a few feet off the ground? Depend how many feet a "few" are, but yeah, your aren't gonna live if they mean THAT few. BUSTED
5) Can an aircraft take off from a conveyer belt No chance in hell. BUSTED

There, I just saved you guys a 2 month wait, and an hour of your life.

[natejj]

Regards to Number 4-
http://www.msnbc.msn.com/id/17113222/

Its all about where you land... this guy survived a 14,000 feet jump with no chute.

[Tik-Tok]

Originally posted by benyl

It really isn't a myth. The plane will take off. It is all about relative air speed.

you just contradicted yourself.

The plane WON'T take off because of relative air speed. There's no air going around the wings.

Will a ram air hood scope make the same power on a dynamometer as it will going 100km/h on the road?

[Tik-Tok]

Originally posted by natejj
Regards to Number 4-
http://www.msnbc.msn.com/id/17113222/

Its all about where you land... this guy survived a 14,000 feet jump with no chute.

There's always exceptions to the rules, a few people have survived, wholly by accident.

[89coupe]

Originally posted by natejj


Lets just clarify something. Lets say once the plane is at full thrust, in place, on the conveyor belt, does the belt suddenly stop or something, and the plane shoots forward into the air? Or is the idea that the plane can point its nose upwards and shoot off forwards?

I dont want to start this whole argument over, because I dont claim to be an expert on the subject, I do work in the tower at an airport, so I know a bit about planes. But the theory behind lift is basically when a plane flies forward, the pressure about the wing, is lower then below the wing, so the wing moves toward the lower pressure area, up. If the plane is not moving forward, its relative airspeed is 0 (unless theres a wind) so I just dont think it will fly.

We on for 5 bucks?

But its thrust that is moving the plane foward, not its wheels. All I would be interested to know is if the thrust of Jet engines would be enough to overcome the gravity of the plane in relation with the drag created on the moving conveyor belt.

[benyl]

Originally posted by Tik-Tok


you just contradicted yourself.

The plane WON'T take off because of relative air speed. There's no air going around the wings.

Will a ram air hood scope make the same power on a dynamometer as it will going 100km/h on the road?

Again. Is the thrust being applied to the air, or the ground?

[Nav13]

Heres the thing though the plane will still require the same if not more room to take off on the conveyor belt. So if they are testing weather or not it will take off on a conveyor belt, the plane will simply move forward abit and then go onto normal tarmac and they might say it doesnt work? So unless they have a huge conveyor belt, like runway length size, I dont see how they are going to do this experiment? Guess I'll just have to wait and see.

[Strider]

The idea behind the myth isn't that the thrust will overcome the conveyor and allow the plane to free itself from the treadmill and take off...

The idea is that you can use a treadmill to let the plane develop the "speed" (and thus lift) that it needs to take off, which it obviously doesn't, because the plane is still in one place.


Originally posted by 89coupe


But its thrust that is moving the plane foward, not its wheels. All I would be interested to know is if the thrust of Jet engines would be enough to overcome the gravity of the plane in relation with the drag created on the moving conveyor belt.

[jibber]

The thrust from the engines move the plane through the air, and it's soley the wings that are resposible for creating the lift that opposes gravity. The plane won't take off unless the airspeed over the wing is high enough.

If the plane was held in place on a moving treadmill by a high-strength steel cable tether, with the engines off, the experiment's results would be the same. No air over the wing = no lift.

I think the desciption of the experiment isn't detailed enough. If they stop the treadmill when the plane is rolling at take-off speed, the plane would shoot forward, and it would leave the ground when the air going over the wings creates enough lift to get the plane off the ground. If they plan on holding the plane in place on a treadmill, by whatever means, it's going to go nowhere.

I'm in for $5 that the plane doesn't take-off if the experiment is as described in the OP.

[Strider]

Thrust is applied to the air, but it's the relative velocity of the air over the wing that creates the pressure difference (between the top surface of the wing and bottom surface) that causes lift.... The jets can thrust all they want, but unless there's air moving over the wing, it's not gonna fly.

I'll take your $5 bet!


Originally posted by benyl


Again. Is the thrust being applied to the air, or the ground?

[Hakkola]

Originally posted by 89coupe


But its thrust that is moving the plane foward, not its wheels. All I would be interested to know is if the thrust of Jet engines would be enough to overcome the gravity of the plane in relation with the drag created on the moving conveyor belt.

That is the logic I used when I decided the plane would take off, with enough thrust you could probably make a plane take off on blocks, which is basically the idea with the treadmill. The negative force will cause the wheels to keep from spinning, but that doesn't mean that the plane will not move forward. It will be like the plane is on skis instead of wheels.

[Tik-Tok]

Originally posted by benyl


Again. Is the thrust being applied to the air, or the ground?

Irrelevant.

The air flowing around the wings creates a low pressure zone above them, and a high pressure zone below, since nature abhores a vacuum, the high pressure "pushes" up on the wings to try to even out the low pressure zone.

No matter where the power is coming from, no airflow around the wings means no lift. So if the aircraft is on a conveyer belt it may as well be standing still.

[Lagerstatten.ca]

Thrust from the engine will give it the force needed to move forward. But the landing gears on on the conveyor belt and if the conveyor belt is moving as fast as the landing gears then the plane will stay in one stationary place.

It won't lift off as there will be equal forces going forward (engine thrust) and the conveyor going in the opposite direction.

I drew it out...on a napkin...just doesn't work.

But we'll see...only 2 months away. Haha!

-TT

[Hakkola]

Originally posted by Tik-Tok

No matter where the power is coming from, no airflow around the wings means no lift. So if the aircraft is on a conveyer belt it may as well be standing still.

What makes you think the conveyor belt will keep the plane from moving forward? All the people who say the plane won't take off assume that this is the case.

[Oldskool]

Benyl's got the right idea, the plane will take off, it will take off just like it would any other day, the only difference is the wheels will be spinning twice as fast......

I've got 5 in for TAKE OFF

[Canmorite]

Originally posted by Nav13
Heres the thing though the plane will still require the same if not more room to take off on the conveyor belt. So if they are testing weather or not it will take off on a conveyor belt, the plane will simply move forward abit and then go onto normal tarmac and they might say it doesnt work? So unless they have a huge conveyor belt, like runway length size, I dont see how they are going to do this experiment? Guess I'll just have to wait and see.

MS Paint FTW.

http://img147.imageshack.us/img147/9348/plane2kq2.jpg

[Tik-Tok]

Originally posted by Hakkola


What makes you think the conveyor belt will keep the plane from moving forward? All the people who say the plane won't take off assume that this is the case. '

the myth is that the conveyer belt is going as fast as the plane is, in the opposite direction.

[mark4091]

It will take off.

[BerserkerCatSplat]

Originally posted by natejj
I got 5 bucks that says the plane DOESNT take off. I've seen planes take off the back of trucks, but that is different.

This has been solved here already. The plane takes off.


http://forums.beyond.ca/showthread.php?s=&threadid=110387&perpage=40&highlight=&pagenumber=9

[Nav13]

Originally posted by Canmorite


MS Paint FTW.

http://img147.imageshack.us/img147/9348/plane2kq2.jpg

hahaha, love the drawing, but I already understand that the belt is running in the opposite direction to hold the plane in stationary. But I am from the school of thought that the plane will still take off. What I was trying to get at, is that once the plane starts moving forward after it breaks the speed of the belt, it will simply just move off the belt, that is unless they have a super long converyor belt system, which is just as long as the distance required for the plan to take off normaly, or a bit longer.

[benyl]

How is it irrelevant?

How does a hovercraft move forward? How does a Florida swamp boat move forward?

They apply thrust to the air. The surface friction is irrelevant.

Haha, this is the same argument everyone had last time... haha can't wait for the physics formulas to come out.

[Tik-Tok]

Originally posted by BerserkerCatSplat


This has been solved here already. The plane takes off.


http://forums.beyond.ca/showthread.php?s=&threadid=110387&perpage=40&highlight=&pagenumber=9

Ahh, after reading a few posts, I see I misunderstood the myth itself. My attention immediately turned to the physics of lift, not thrust.

[95EagleAWD]

Can you land a 747 in adverse weather?

How adverse are we talking about here?

Of course you can, what kind of myth is that?

[Canmorite]

Originally posted by Nav13


hahaha, love the drawing, but I already understand that the belt is running in the opposite direction to hold the plane in stationary. But I am from the school of thought that the plane will still take off. What I was trying to get at, is that once the plane starts moving forward after it breaks the speed of the belt, it will simply just move off the belt, that is unless they have a super long converyor belt system, which is just as long as the distance required for the plan to take off normaly, or a bit longer.

The conveyor belt only needs to be big enough to fit the wheels of the plane on it. It spins around basically creating an artificial perpetual runway.

[Tik-Tok]

Originally posted by 95EagleAWD
Can you land a 747 in adverse weather?

How adverse are we talking about here?

Of course you can, what kind of myth is that?

They're seeing if an untrained person could, not a professional.

[Hakkola]

Originally posted by Tik-Tok

the myth is that the conveyer belt is going as fast as the plane is, in the opposite direction.

Shouldn't matter, it isn't the wheels that are going to decide the speed of the plane, it will be the thrust of the engines. Think about a boat plane, there are no wheels to spin but the plane can still create momentum with thrust.

I think a better example would be a rocket, put it on the ground and it will still launch forward, no matter what sort of friction is placed on the bottom of the rocket, short of actually strapping it down.

Just because the wheels aren't spinning, or are even rotating the wrong way, it doesn't mean that the plane won't still be moving forward. IMO. I'm not a physics expert, but even if parts of my argument are incorrect, I don't think there is even close to enough friction to keep the plane down if it is only applied to the wheels.

Edit - LOL, I started writing this response before benyl's post was up, that's why this is late, I spent some time trying to articulate my ideas.

[Tik-Tok]

^ See previous post, my mind went straight for the lift, and not as to whether or not the engines would pull the plane forward regardless of the conveyer.

[The Cosworth]

Originally posted by alloroc
Bernoulli's Theorem people.

no forward motion relative to the surrounding air = no airflow across the wings = no flight - unless they are contemplating doing this in a wind tunnel and blowing air across the wings at take off velocity.

true!


It doesn't matter how fast the wheels are spinning, it matters what the airspeed over the wings is, which the plane is relative to the ground and hence the air, has zero horizontal speed, lift will not exist

[speedracer]

Originally posted by benyl

Haha, this is the same argument everyone had last time... haha can't wait for the physics formulas to come out.

Bust out the http://mirror-au-nsw1.gallery.hd.org/_tn/std/mechanoids/abacus-1-AJHD.jpg

hahaha

It will fly.

[Hakkola]

Originally posted by bvanlankvelt
Great explanation. And Drew I commend you for accepting the fact that the plane will take off - even after your arguments against the fact. It is about Newton's law - every action has equal and opposite reaction. We have to assume the conveyor is powered or it could not match speeds, the reaction to this action is the spinning of the wheels of the plane. Now since, the wheels cancel out the spinning conveyor, what is the equal and opposite reaction to over 200000 pounds of engine thrust? The answer of course is forward motion of the airplane relative to the air. The conveyor has already been cancelled out.







Articulated much better than I.

[b_t]

Originally posted by Tik-Tok


Wow, their really gearing the show towards kids these days, aren't they?

Without having to use any cool toys that they always use...

1) Can you safely land a 747 during adverse weather - Highly unlikely, it would be a fluke if you can. BUSTED
2) Can you catch up with someone in freefall Obviously, how else do you think aerobatic skydiving teams do what they do? 50 people all jumping out of the plane at the same time? TRUTH
3) Can you hold a conversation during freefall Why not? you can hold a conversation on a windy day can't you? TRUTH
4) Will you survive if your chute opened a few feet off the ground? Depend how many feet a "few" are, but yeah, your aren't gonna live if they mean THAT few. BUSTED
5) Can an aircraft take off from a conveyer belt No chance in hell. BUSTED

There, I just saved you guys a 2 month wait, and an hour of your life.

You are a fucking idiot

1. Yes but it would be hard as hell, so that is why they don't do it. If you can land a Hercules in a warzone, you can land a Boeing at a windy, rainy, low visibility airport - you just don't do it because of the risk. I don't think you could land in icy conditions.

2. You only can if the other person is slowing themselves down or has a lower terminal velocity. If you take two equivalent people and have one jump out five seconds before the other, the second will never catch up.

3. Have you ever tried talking in a 300km/h hurricane? You fucking moron, you don't freefall at 40 or 50km/h.

4. There are documented cases of people surviving with no parachute at all. It could happen, but it is not likely. They would say plausible.

5. I am tired of this fucking argument. The speed of a plane depends on the propeller or jets, not the fucking wheels. If the wheels AREN'T locked, the plane WILL fly.

[Nav13]

Originally posted by Canmorite


The conveyor belt only needs to be big enough to fit the wheels of the plane on it. It spins around basically creating an artificial perpetual runway.

Not wanting to look like an idiot before I go any further, do you believe the plane will take off?

[Tik-Tok]

And you're a bigger one



Originally posted by b_t


You are a fucking idiot

1. Yes but it would be hard as hell, so that is why they don't do it. If you can land a Hercules in a warzone, you can land a Boeing at a windy, rainy, low visibility airport - you just don't do it because of the risk. I don't think you could land in icy conditions. THE QUESTION IS IF JAMIE OR ADAM CAN LAND ONE, NOT A PROFESSIONAL PILOT

2. You only can if the other person is slowing themselves down or has a lower terminal velocity. If you take two equivalent people and have one jump out five seconds before the other, the second will never catch up. EXACTLY, SO YOU CAN CATCH UP TO THE OTHER PERSON

3. Have you ever tried talking in a 300km/h hurricane? You fucking moron, you don't freefall at 40 or 50km/h. I HAVE SKYDIVED TANDEM, AND HAVE HAD A CONVERSATION WHILE DOING SO

4. There are documented cases of people surviving with no parachute at all. It could happen, but it is not likely. They would say plausible. AS I SAID, EXCEPTION TO EVERY RULE, BUT IT WOULD KILL 99.9999% OF PEOPLE

5. I am tired of this fucking argument. The speed of a plane depends on the propeller or jets, not the fucking wheels. If the wheels AREN'T locked, the plane WILL fly. READ THE WHOLE FUCKING THREAD YOU RETARD, I RETRACTED MY STATEMENTS REGARDING THIS ONE

[atomic]

lol .

so. how does the plane take off? you just turn the flaps? where is the wind built up under the wing to raise the plane?

my problem is if the plane is in one spot . there is no wind . therefore, raising and lowering the flaps doesn't do anything .

it'd be like raising and lowering the flaps when the engine is off while sitting on the runway .

because sure there is energy used to keep the plane stationary relative to the observer . but without the wind, there is nothing to push on the flaps to raise the plane .

am i missing something ?

[b_t]

Originally posted by Tik-Tok
And you're a bigger one




It looks like I zeroed in on your absolutely amazing problem solving skills before actually reading it.

Back to #1, it has an autopilot. They didn't say they couldn't use it. They can land using autopilot in anything but zero visibility conditions.

#2 they also didn't specify. In Hollywood, they make it look like even if person #1 dives out of a helicopter, and then person #2 jumps up and out, they can catch them inside of ten feet. That will never happen.

#3. Really? So were you spooning in mid-air or what?

#4 in MythBusters past if they couldn't reproduce the successful result but there are documented cases of it actually happening, they call it plausible.

[Tik-Tok]

Originally posted by b_t
...

#1, You're right, assuming it's a CAT3 airport, but you know that's not how they'll be looking at it

#2 They didn't specificy, but the answer is still yes, you can catch up with someone. The only way you wouldn't is if you are both pointing straight down.

#3. Yes, and for a mid 40's chick, she wasn't half bad, but definetly not a MILF.

#4 Conceded.

[Hakkola]

Originally posted by atomic


my problem is if the plane is in one spot . there is no wind . therefore, raising and lowering the flaps doesn't do anything .



Again, why would the plane be in one spot? The spinning wheels will negate the effect of the conveyor, and there is no opposing force to the thrust of the jet engines.

[jibber]

After re-reading the series of posts, I stand corrected. I mis-read the OP, and I agree the plane will fly.

The engine provides thrust, which moves the plane through the air and has no relation to how fast the landing gear is rotating.

The conveyor can be moving at any speed in either direction, and the plane will still take off. All that is affected is the speed of the rotation of the landing gear. The conveyor belt will not slow the plane's forward movement at all (in a perfect simulation where friction is eliminated).

The wheels of car provide the propulsion because they act on the pavement, so if this was a car, it would go nowhere. But because the engine of a plane acts on the air, it doesn't matter what's going on on the ground.

Plane takes off, see illustration as per the link posted by BerserkerCatSplat.

[euro tang]

Hakkola, don't bother arguing with these people, you'll never win because they'll never be able to contemplate it.

Anyway, I'll bet every fool who wants, $5 the plane WILL take off! :D

[BerserkerCatSplat]

Originally posted by atomic
lol .

so. how does the plane take off? you just turn the flaps? where is the wind built up under the wing to raise the plane?

my problem is if the plane is in one spot . there is no wind . therefore, raising and lowering the flaps doesn't do anything .

it'd be like raising and lowering the flaps when the engine is off while sitting on the runway .

because sure there is energy used to keep the plane stationary relative to the observer . but without the wind, there is nothing to push on the flaps to raise the plane .

am i missing something ?

You're missing a few hundred thousand pounds of forward thrust from those jet engines, to be precise. That's thrust that the conveyor belt is powerless to counteract. :)

[Tik-Tok]

Something to clear up as well, the myth is that said conveyer belt is assumed to be as long as a normal runway for the a/c being tested. If it were only the size of the a/c, it would simply move forward and fall off.

[Audio_Rookie]

ditto...the wheels will jsut spin twice as fast.

if the wheels are locked its fucked.

[BerserkerCatSplat]

Originally posted by Audio_Rookie
ditto...the wheels will jsut spin twice as fast.

if the wheels are locked its fucked.

You'd be surprised, even if the plane was sitting on its belly, the engines are so powerful it'd take off anyway!

[Nav13]

Originally posted by Tik-Tok
Something to clear up as well, the myth is that said conveyer belt is assumed to be as long as a normal runway for the a/c being tested. If it were only the size of the a/c, it would simply move forward and fall off.

Exactly, so I ask my questions again, how are they going to test this myth? I dont mean to start an arguement, just saying it will be interesting to see how they do this.

[spikerS]

not enough info for us to speculate one way or the other.

how long is the conveyor belt? 50 feet? 5000 feet?

while the thrust would propel the plane forward, in order for it to take off, either the air flow, or the thrust pushing the plane forward, would have to generate enough airflow over the airfoils to generate lift. remember that they are using a ultra lite aircraft (propeller) and not a jet aircraft to test this.

will it take off? well, if it is a smaller treadmill, no, by the time enough lift is generated, the plane will just go off the end of the treadmill. if it is a full length of the runway treadmill, yes, it can take off from the treadmill as by the end of the runway, it will take off.

I would like to think of myself as a bit more informed than most, as I am, well, was a pilot, and flew outta springbank in cesnas, piper cubs, and cherokees.

[Hakkola]

Originally posted by Nav13


Exactly, so I ask my questions again, how are they going to test this myth? I dont mean to start an arguement, just saying it will be interesting to see how they do this.

You don't need a full length belt to test the myth, if the plane makes any forward movement the myth would be busted.

[Weapon_R]

Originally posted by Nav13


Exactly, so I ask my questions again, how are they going to test this myth? I dont mean to start an arguement, just saying it will be interesting to see how they do this.

could also be a scale model, or a small airplane. It didn't say they were going to test a 747

[black13]

Wait, isn't this pretty much exactly like a car dyno test?
http://www.torqueperformance.co.nz/images/dynotorque/dynotorqueDynoWithCar.jpg

The engine runs and the belt moves with it. While sure the car doesn't have wings but you see that it stays in the same place and there is no air flow around it.

So therefore the plane would be the same and wouldn't take off either.

Seems simple for me but all this talking has gotten me a little confused so we'll see at the show.

[robpark]

RE: Airplane on conveyor...

My vote is the force applied is not via the ground, so the plane will take off. The push force is acting independently of the frictional force...

[BerserkerCatSplat]

Originally posted by black13
Wait, isn't this pretty much exactly like a car dyno test?
http://www.torqueperformance.co.nz/images/dynotorque/dynotorqueDynoWithCar.jpg

The engine runs and the belt moves with it. While sure the car doesn't have wings but you see that it stays in the same place and there is no air flow around it.

So therefore the plane would be the same and wouldn't take off either.

Seems simple for me but all this talking has gotten me a little confused so we'll see at the show.

No, the difference is that cars are powered by their wheels pushing on the ground, while airplanes are powered by jet engines pushing on the air behind them. If you put an airplane on a dyno, what would happen?

[GreyFox]

By no means do I intend to provoke further argument, and I do understand everybody's side that the plane can and will still move forward and fly given enough space....however...

I just re-read the original question in the first post of this thread, and it is basically asking if the plane will still take off if the conveyer is going just as fast as the plane is at takeoff speed. In other words, if the plane applies more trust and tries to move forward, isn't the conveyer belt just going to go faster to negate that forward movement?

Or does the speed of the conveyer belt stay constant and the plane is allowed to apply as much trust as it wants? If that's the case, of course the plane will fly, but I'm unclear of all of the specifications of the experiment.

[Hakkola]

Originally posted by black13
Wait, isn't this pretty much exactly like a car dyno test?
http://www.torqueperformance.co.nz/images/dynotorque/dynotorqueDynoWithCar.jpg

The engine runs and the belt moves with it. While sure the car doesn't have wings but you see that it stays in the same place and there is no air flow around it.

So therefore the plane would be the same and wouldn't take off either.


Strap a rocket to the roof of the car, wings or not, that bitch is going to fly off the dyno. The turbines of a plane don't turn the wheels, they push the jet. You can't compare a plane and a car.

[sneek]

Originally posted by GreyFox
By no means do I intend to provoke further argument, and I do understand everybody's side that the plane can and will still move forward and fly given enough space....however...

I just re-read the original question in the first post of this thread, and it is basically asking if the plane will still take off if the conveyer is going just as fast as the plane is at takeoff speed. In other words, if the plane applies more trust and tries to move forward, isn't the conveyer belt just going to go faster to negate that forward movement?

Or does the speed of the conveyer belt stay constant and the plane is allowed to apply as much trust as it wants? If that's the case, of course the plane will fly, but I'm unclear of all of the specifications of the experiment.

:werd: :werd:

[Hakkola]

Originally posted by GreyFox


I just re-read the original question in the first post of this thread, and it is basically asking if the plane will still take off if the conveyer is going just as fast as the plane is at takeoff speed. In other words, if the plane applies more trust and tries to move forward, isn't the conveyer belt just going to go faster to negate that forward movement?

Or does the speed of the conveyer belt stay constant and the plane is allowed to apply as much trust as it wants? If that's the case, of course the plane will fly, but I'm unclear of all of the specifications of the experiment.

It doesn't matter, either way, the plane will take off, the rotation of the wheels has no bearing on the directionality or speed of the plane when turbine thrust is brought into the equation.

[b_t]

People seem to have a LOT of trouble grasping that a plane does not move with its wheels but is actually pulled through the air by a propeller or pushed by a jet ... pulled THROUGH the AIR ...

[Hakkola]

Originally posted by b_t
People seem to have a LOT of trouble grasping that a plane does not move with its wheels but is actually pulled through the air by a propeller or pushed by a jet ... pulled THROUGH the AIR ...

It's annoying, but funny. :rofl:

Here, I've got another one, if the plane is flying at 200km/h at an elevation of 2000 feet, and the landing gear is brought down, and the wheels start turning the opposite direction at 200km/h, will the plane fall out of the sky?

[black13]

Originally posted by BerserkerCatSplat


No, the difference is that cars are powered by their wheels pushing on the ground, while airplanes are powered by jet engines pushing on the air behind them. If you put an airplane on a dyno, what would happen?

yeah i got that part but the way I see it, the plane's jet is working exactly in oppostie direction of the belt.

[Hakkola]

Originally posted by black13


yeah i got that part but the way I see it, the plane's jet is working exactly in oppostie direction of the belt.

Which doesn't matter, because the belt is only in contact with the wheels, which are going to have an incredibly small impact on the movement of the airplane.

[Darkane]

Very very interesting. I've thought this through and Yes it will fly. Question: In happy magical no laws of physics land, IF and a BIG IF, could a plane generate FULL thrust with out moving and then "Let go" would it immediatly start to go up? yes.

[Super_Geo]

Originally posted by Darkane
Very very interesting. I've thought this through and Yes it will fly. Question: In happy magical no laws of physics land, IF and a BIG IF, could a plane generate FULL thrust with out moving and then "Let go" would it immediatly start to go up? yes.

Well it would start to accelerate (really quickly) until it hit 290km/hr, then it would start to go up. It won't be immediate though... (unless you point the turbines at the ground).

[kertejud]

This really depends on how the wheels move. If the wheels move the plane backwards as fast as the conveyor belt moves, then it wont take off because the thrust would only counteract the conveyor leaving the plane motionless.

However, if the wheels don't move as fast as the conveyor, then it just increases the amount of distance the plane needs to take off.

That being said, the plane will still need to reach a certain speed in order to take off, if the conveyor's effect on the wheels could negate that because the plane's max speed isn't high enough it probably wouldn't take off either.

Based on the experiment I imagine Mythbusters will set up, the plane will take off (or at least fly off the conveyor before going out of control). It does need a large runway sized conveyor to really answer the question.

[Darkane]

Originally posted by Super_Geo


Well it would start to accelerate (really quickly) until it hit 290km/hr, then it would start to go up. It won't be immediate though... (unless you point the turbines at the ground).

No.. If all Static energy is converted to Kinetic It would instantaniously<sp> start ascending at it's directed setpoint.

IE: In the air the engines are moving the plane at 800kmh, enough for flight. If on the ground the engines could produce the same THRUST not moving, once it was let go it would go up.

The point of the conveyer is to keep it Static

[Super_Geo]

Originally posted by Darkane


No.. If all Static energy is converted to Kinetic It would instantaniously&lt;sp&gt; start ascending at it's directed setpoint.

IE: In the air the engines are moving the plane at 800kmh, enough for flight. If on the ground the engines could produce the same THRUST not moving, once it was let go it would go up.

The point of the conveyer is to keep it Static

What is static energy?

I think I know what you're saying though: say you had a cable attached to the plane that was holding it back. At max thrust, the tension in the cable is equal to the thrust. If you were to cut the cable, would the plane instantly take off? I'm pretty sure the answer's still no.

[BerserkerCatSplat]

Originally posted by Darkane


No.. If all Static energy is converted to Kinetic It would instantaniously&lt;sp&gt; start ascending at it's directed setpoint.

IE: In the air the engines are moving the plane at 800kmh, enough for flight. If on the ground the engines could produce the same THRUST not moving, once it was let go it would go up.

The point of the conveyer is to keep it Static

No. For Bernoulli's Principle work, and thus the wings to provide lift, there has to be a minimum airspeed. The plane cannot "jump", it must be moving in relation to the surrounding air.

[jibber]

Okay, I'm getting frustrated reading all of this, so let me expand the example.

Most people are getting caught on the premise that the conveyor belt moving at the same speed in the opposide direction to the plane will cause the plane to have no movement in relation to the air.

Let's use the same example, but now the conveyor belt is move 8 times as fast as the plane, but in the oppposite direction. The plane will still take off as it normally would, but the wheels would be spinning 9 times faster than they normally would when the plane takes off from a normal runway.

How about this: The conveyor belt is moving twice as fast as the plane, but this time in the same direction as the plane. The plane will still take off like usual, but the wheels will be spinning the same speed they normally are at takeoff, but in the opposite direction.

The belt does exert a force on the plane, but that force pales in comparison to the force by the thrust of the engines on the air. So the plane goes wherever the engines make it go, regardless of anything making the wheels spin more or less. The plane will fly whether or not the wheels are touching the ground, right? So why worry about what's going on with the landing gear?

/rant

[Hakkola]

Originally posted by kertejud
It does need a large runway sized conveyor to really answer the question.

No, it doesn't. :D

If the plane accelerates at all, it proves that the conveyor is not sufficient to keep the thrust of the airplane in check. There are no stipulations on the length of the conveyor belt, if it is 10km, or 1km makes no difference to the question. If the plane moves forward it will take off, proving that the conveyor does little to hinder the take off.

[Mazstyle]

I didnt read all the posts but the treadmill thing is retarded. You need airspeed.

With enough airspeed (wind) you could realistically lift off while remaining in the same spot on the ground. Also with enough wind you could land the plane at almost a complete stop.

[Darkane]

Originally posted by Super_Geo


What is static energy?

I think I know what you're saying though: say you had a cable attached to the plane that was holding it back. At max thrust, the tension in the cable is equal to the thrust. If you were to cut the cable, would the plane instantly take off? I'm pretty sure the answer's still no.

Yes that is basically the example I'm portraying. Assuming G's and everything had nothing to do with it theoritically, if you can accelerate from static to kinetic instantly, you're flying.

[Darkane]

Originally posted by BerserkerCatSplat


No. For Bernoulli's Principle work, and thus the wings to provide lift, there has to be a minimum airspeed. The plane cannot &quot;jump&quot;, it must be moving in relation to the surrounding air.

It wouldn't jump instantly it would be on the ascend of Whatever, 8degrees I don't know what it is.

Check this out.. Car vs plane. If a car had wings and theoretically could reach lift speed, how high would it get? :)

Answer is nothing. Once the wheel leaves the ground Speed is lost where as a car with THRUST and wings could fly. If there is Thrust energy available you're moving the air regardless of velocity as we know it.

[arian_ma]

The myth is very vague.

If a plane is traveling at takeoff speed on a conveyor belt...

So...is the plane actually moving or not?
Seems like a pretty simple question which they worded awfully to confuse people.

[Strider]

Giving it a second thought, I'll change my answer... The plane will take off.

[Lagerstatten.ca]

Let's take the actual question as saying that the plane is positioned on top of the large conveyor belt. Nothing is moving: no engine thrust, no wheels spinning and the conveyor belt isn't rotating in the opposite direction.

Now the plane begins to increase thrust produced from the engines. The plane has a mass of X and this creates a downward force on the conveyor belt that is translated through the point of contact (ie, the landing gear).

Force = mass x gravity

So there's a constant downforce in the whole equation.

Now let's say that the conveyor is rotating at a speed that is equal to that of the plane, when said plane is travelling on tarmac. So if the plane is travelling at say 400km/hr on the tarmac before it lifts off...then we can say that the conveyor belt is travelling at the same speed but in the opposite direction. For our sake, let's say the plane is trying to travel to the left and the conveyor belt is trying to move the airplane to the right. They cancel each other out.

The thrust from the engine of the plane is typically translated to speed on the ground. It has to achieve a minimium velocity before it's able to achieve the lift necessary to counteract with the force of gravity (which has always been there). So if it can't achieve a moving velocity that is greater than the force of gravity, it'll just continue to sit there on the conveyor belt, spinning it's wheels and stay stationary.

I think everyone just forgot about good ol' gravity that's all. Now does this make sense to you?

If not another good example is the dryland/stationary skating system they have at The Talisman Center. The skater can push all they want, but as the conveyor belt is moving in the opposite direction at the exact same speed as the skater...the skater remains in the same position. Otherwise we'd have a lot of injured atheletes using that machine.

-TT

[HondaRice]

they should do a show on if jetliner actually hits a building how does the building implode or would it cause it implode. maybe use a wtc scale or something they can figure it out. but i guess it wont be politically correct and all the lemmings will boycott the show, you know the ones who put up american flags on their car antenna right after that 2001 incident where 2 buildings were on fire and they imploded.

[BerserkerCatSplat]

Originally posted by Darkane


Yes that is basically the example I'm portraying. Assuming G's and everything had nothing to do with it theoritically, if you can accelerate from static to kinetic instantly, you're flying.

Well, yeah, I guess if you could have infinite acceleration (instant change from stasis to flight speed) it would theoretically work. However, the plane is far too heavy and the engines far too weak to even approach the idea of infinite acceleration, and thus it would never even come close to happening in reality.



Originally posted by HondaRice
they should do a show on if jetliner actually hits a building how does the building implode or would it cause it implode. maybe use a wtc scale or something they can figure it out. but i guess it wont be politically correct and all the lemmings will boycott the show, you know the ones who put up american flags on their car antenna right after that 2001 incident where 2 buildings were on fire and they imploded.

I guess that must have sounded really intelligent in your head.

[doublepostwhore]

well. I guess mythbusters was right, you guys have spent 3 days discussing it, only to come to an impass hahaha.

Definitive answer t-minus 2 months!

[BerserkerCatSplat]

Originally posted by doublepostwhore
well. I guess mythbusters was right, you guys have spent 3 days discussing it, only to come to an impass hahaha.

Definitive answer t-minus 2 months!

Impasse? We've proved rather definitively that it will take off on a runway-length conveyor belt, Darkane has posed a different scenario altogether.

[rage2]

Originally posted by Lagerstatten.ca
If not another good example is the dryland/stationary skating system they have at The Talisman Center. The skater can push all they want, but as the conveyor belt is moving in the opposite direction at the exact same speed as the skater...the skater remains in the same position. Otherwise we'd have a lot of injured atheletes using that machine.
Strap a jet engine on the back of that skater and see what happens :D.

I can't believe this argument is still going on. It's not a myth, it's simple physics. This is why not everyone is an engineer I guess lol!

It's funny to see that in the original debate, there are more wrong answers than correct haha.

[googe]

Originally posted by Lagerstatten.ca
Let's take the actual question as saying that the plane is positioned on top of the large conveyor belt. Nothing is moving: no engine thrust, no wheels spinning and the conveyor belt isn't rotating in the opposite direction.

Now the plane begins to increase thrust produced from the engines. The plane has a mass of X and this creates a downward force on the conveyor belt that is translated through the point of contact (ie, the landing gear).

Force = mass x gravity

So there's a constant downforce in the whole equation.

Now let's say that the conveyor is rotating at a speed that is equal to that of the plane, when said plane is travelling on tarmac. So if the plane is travelling at say 400km/hr on the tarmac before it lifts off...then we can say that the conveyor belt is travelling at the same speed but in the opposite direction. For our sake, let's say the plane is trying to travel to the left and the conveyor belt is trying to move the airplane to the right. They cancel each other out.

The thrust from the engine of the plane is typically translated to speed on the ground. It has to achieve a minimium velocity before it's able to achieve the lift necessary to counteract with the force of gravity (which has always been there). So if it can't achieve a moving velocity that is greater than the force of gravity, it'll just continue to sit there on the conveyor belt, spinning it's wheels and stay stationary.

I think everyone just forgot about good ol' gravity that's all. Now does this make sense to you?

If not another good example is the dryland/stationary skating system they have at The Talisman Center. The skater can push all they want, but as the conveyor belt is moving in the opposite direction at the exact same speed as the skater...the skater remains in the same position. Otherwise we'd have a lot of injured atheletes using that machine.

-TT

http://web.mit.edu/mokang/Public/fail.jpg

[Lagerstatten.ca]

rage2: what I'm saying is that the skaters leg muscles is equivalent to the jet engine.

Edit: Looks like I'll have to do an mini-experiment of my own using an r/c model airplane and a belt sander this weekend...

-TT

[rage2]

Originally posted by Lagerstatten.ca
rage2: what I'm saying is that the skaters leg muscles is equivalent to the jet engine.
And that's where everyone makes the mistake. A skaters leg muscle is equivilent to driving force on the wheels. A plane doesn't move forward from driving force from the wheels.

[googe]

What he (and the other correct people) are saying is, you're making the critical mistake of not recognizing the difference between applying force to the ground and applying force to the air.

Legs push off ground. Wheels in jet are not pushing. Not the same.

Edit: Bah, beat me :P

Edit 2: To make your skater analogy valid, have a skater tie a rope to the wall. No matter the speed of the belt, if they hold on to the rope and pull themselves forward, they will make it. No matter what speed that belt goes, its not going to change the fact that you using a force being applied to something other than the ground (hands on rope) is going to allow you to create forward movement.

[alloroc]

Originally posted by 89coupe


But its thrust that is moving the plane foward, not its wheels. All I would be interested to know is if the thrust of Jet engines would be enough to overcome the gravity of the plane in relation with the drag created on the moving conveyor belt.

The plane isn't moving forward.

It will be stationary.

The only thrust required would be that to overcome the friction of the wheels and bearings on the rotating belt to get the wheels turning at 20 - 30MPH or so (ultralight's stall speed).

In fact there would be more air across the wings if they deleted the conveyor belt, the pilot puts on the brakes and wfo's the throttle. Would the plane take off then? Engine at full power? No! of course not. The only way this could work conveyor or not is if they do it indoors and circulate air around the building - inducing a wind tunnel effect.

Unless the Ultralight is capable of VTOL it isn't going anywhere. Even a cf-18 which has a greater than 1:1 thrust to weight ratio is not going to take off if it is stationary.

There are only three operational airplanes that I have ever heard of that are capable of doing this - Osprey, Harrier, F-35, (Yes I know of the experimental models like the Canadair Dynavert etc.)

No flight
Bernouli wins.

[googe]

^None of the rest of your post matters because your first sentence is already incorrect. Again, read :) No need to explain why a stationary plane can't take off, because this plane will not be stationary.

[natejj]

Can we just lock this and wait for the gosh darn episode?:dunno:

[BerserkerCatSplat]

Originally posted by natejj
Can we just lock this and wait for the gosh darn episode?:dunno:

No, because the longer the thread is open, the more people reveal they don't understand basic physics. :poosie:

[rage2]

Originally posted by BerserkerCatSplat
No, because the longer the thread is open, the more people reveal they don't understand basic physics. :poosie:
haha no doubt. It's pretty funny how many ppl fail at elementary physics.

[alloroc]

Originally posted by googe
^None of the rest of your post matters because your first sentence is already incorrect. Again, read :) No need to explain why a stationary plane can't take off, because this plane will not be stationary.

Well then its fucking stupid question. The plane will fly as there is air moving across the wings equal to or greater than stall speed but the wheels will be turning twice the normal rotational velocity. Big whoop.

However I still think my perception of the question is the correct one. Forward motion of the plane in relation to the conveyor belt ... not the ground = no flight.

[natejj]

:banghead:

I think the main problem here, is that people are imagining different setups. Some people imagine a runway length conveyor, some imagine a plane size conveyor, and to be honest, I dont know which they will use. So I MS Painted a few scenarios.

A. The conveyor is the size of the plane, The plane once at full speed on the conveyor, pulls back on the flaps, and shoots straight into the air. This would not work for obvious reasons. Correct?

B. The plane is on a giant Conveyor.... The conveyor is the length of a runway. Once the plane gets enough speed to overtake the conveyor, it starts to move forward, and assuming it can gather enough speed before it reaches the end. Takes off. Am I missing anything?

C. The plane at full throttle, once the throttle increases past a certain point, shoots off the conveyor, rolls for a while on a runway, THEN shoots into the air. I dont see why this wouldnt work, so the plane would take off.
http://img87.imageshack.us/img87/7868/airplaneow3.jpg

[em2ab]

I think I can explain this a way people will understand.

Will the plane take off if the pilot can use the thruster as much as he wants?
The answer is yes and here is why. The plane's wheels are causing it to go X miles per hour. And the conveyor belt is moving in the opposite direction at X miles per hour so if you stood next to the plane it wouldn't be moving anywhere......it'd be stationary. But then as the pilot turns on the thrusters or jet engines and creates a force independent of the wheels, the plane will move forward, eventually get up to a speed to create lift and take off. The reason for this is Newton's third law of motion, every action has an equal and opposite reaction. Think of it this way......you're standing on a treadmill with rollerblades on. The treadmill is on speed 5/10 and you're simply holding your arms out against the wall so you're not moving anywhere. In this scenario, your wheels are travel at X miles per hour in one direction while the belt is moving at X miles her hour in the opposite direction, thus you're standing still. If you push against the wall, exerting a force independent of the belt, you will roll on the treadmill before it creates enough friction to bring you back to the wall again. So to counteract this, you just bring the treadmill speed up to 10/10 right? Wrong. Even at a higher speed, if you push on the wall with the same force, you'll still move up the belt. This is because the energy required to keep you stationary needs to be equal. So the force created by you pushing on the wall has to be matched by the friction imposed on your wheels by the belt. And since there is almost no friction on a spinning wheel, this is impossible.

So the basic principle is that the belt cannot create enough friction to match the force exerted by the jet engines pushing against the air behind it.

[kertejud]

It all depends on how fast the conveyor moves the plane backwards. If a plane needs to be travelling at 100km/hr in order to take off, and it has say 200km of thrust, but the conveyor is able to move the plane backwards at 110km/h, it will never take off (barring of course a strong enough headwind).

But if the conveyor can only move the plane backwards 10km/hr, it will take off rather easily, it would just need slightly more runway than usual.

The latter would of course be the case in most (if not all) planes.

[em2ab]

Originally posted by kertejud
It all depends on how fast the conveyor moves the plane backwards. If a plane needs to be travelling at 100km/hr in order to take off, and it has say 200km of thrust, but the conveyor is able to move the plane backwards at 110km/h, it will never take off (barring of course a strong enough headwind).

But if the conveyor can only move the plane backwards 10km/hr, it will take off rather easily, it would just need slightly more runway than usual.

The latter would of course be the case in most (if not all) planes.
No, you're missing the point. The conveyor belt can only negate forces applied by the plane's wheels. It cannot negate any force applied by the plane's propellers or jet engines. So once the engine is fired up, the conveyor belt doesn't have a chance at holding it still.