Mizouse

i think what he is trying to is that, if an airplane could take off in this question, that the navy would be using them on their aircraft carriers so they wouldn't have to be so huge.

jupitersolo

iwant1

It would still require same distance to get enough lift, so shorter carriers, mmm no.

NetEditor

Which makes no sense. The conveyor belt doesn't lessen the need for a proper runway. The question addresses whether an airplane on such a conveyor belt would move forward in order to generate lift.

Mizouse

yea i know, i was just trying to figure out what he meant.

salvo24

I just saw something the other day that would conclude this arguement.....it was inside a KB Toy Store, it was a Superman action figure tied to a string, connected to the ceiling that flew (string allowed it to move in circles).

So, now keep that in mind, and for the sake of the plane, it does not matter if it is solid ground, a treadmill, or just a plane that can hover above ground (gravity prevents this), the engines of a plane create thrust which propels the plane forward. The wheels simply are what connects the plane to the ground. Nothing makes the wheels move, they simply move due to the force of the engines thrusting the plane forward, just like the Superman thing that was able to move through out the air because of the propulsion of the toy and air, nothing to do with the ground

Damn...this makes so much better sense in my head. I think someone should start an official poll, just a yes or a no thread, and lets see what happens after Mythbusters.

Mizouse

btw.. he has 2nd video related to the topic, and draws some free body diagrams.

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srika

anyways I guess we will have to see on Dec 12th!

AS3.0CL

can we watch the show instead of beating this dead horse......


and he's an engineer....my ass um um um though out the whole thing.

to me force is created to propel the plane turning the wheels. now if the acceleration of the treadmill is sped up equally with the acceleration of the plane the tires will rotate but will not gain any distance, thus no air flows under the wing so no lift.

the guys video he has it set up but the treadmill's speed is constant and an applied external force which is the thrust over comes the treadmill. his is flawed because the tape holds the plane in place and the treadmill is already running.

the system has to be in equilibrium. at complete rest of the tread mill and plane it is 0. the thrust is an applied force in the positive direction and the tread mill is an applied force in the negative direction. if there forces are the same then they is no horizontal translation means no air over the wings to create lift.

nywyas thats my two cents. i'm an engineer, but i hate physics. lets all get along and watch the show :-)

srika

hehe.. yeah he was like "plus I mean minus".. I was like umm... kind of a big difference there sport

AS3.0CL

his whole thing i Flawed IMHO, i'm just going to ask my physic professor, he's been doing this shit for 35+ years and had many articles published. If i'm wrong then fine, but to me how i see it and the forces applied to it, the plane will not take off.

whoever gave this guy his degree is a complete moron.

Mizouse

or maybe you're just wrong.

AS3.0CL

i said that.....i could be wrong, maybe i'm just ,missing something right now, it has been on hellish week and it still is hell and will be for one more week, and i'm completely fried. so i could very well be missing something.

idc if i'm wrong, hell it's a learning experience.

lets al get along and watch the show

Mizouse

yea i know im tired as well, finals are next week

AS3.0CL

same, i've had two presentations to prepare for this week, 3 major tests, 20+ page final on a book, and an engineering project due, which keeps getting changed because it's illegal, and 3 labs to write up and still not done with half of it. and finals next week. yay

stogie1020

Wait, what time did the Westbound train leave the station?

Billiam

Wrong. The FASTER the flow of a fluid over a surface, the lower the instantaneous pressure acting on that surface. The airflow is accelerated over the top of a wing.

fdl

You're not serious are you? The plane still has to travel over the same distance to achieve lift. So even if you had a conveyor on a ship, it would have to be as long as the current runway.

The point is that the conveyor will not stop this from happening (assuming there isn't too much friction in the bearings of the wheels).

spooky3ce

None Jet propelled aircraft which has no lift... equals no take off... regardless how hard the engines work...

Jet propelled aircraft depending the angle of the jets and the constant angle will lift by jet power alone... Even without the treadmill... to keep it up, it will still need lift from air which will only happen after the jets get up off the treadmill and change angle of the jets to generate enough forward movement creating lift from the air around the wings to keep it going or else the crash is inevitable...

This question can be compared to how much downforce would a race car generate if it ran at full speed on a treadmill??? None...

I'm 99.99% that would be the conclusion to the show... IMHO...

<~~~ has no cable or TV... so I guess i'll wait for someone to put it on youtube...

sipark

This is so tricky...

The youtube guy's theory is that thrust will overcome the force of friction.
But, you could alway spin the treadmill faster to increase the friction to even out the thrust.
But, then you could also increase the thrust so it's greater than the friction.
But, then you could also increase the speed of the treadmill to increase the friction to even out the thrust.
etc, etc, etc.


Let's say it takes 10 mph increase of treadmill to generate the friction that is equivalent of 1 mph thrust. As long as you spin the treadmill 10 times faster than the thrust, it'll alway even out. (I'm mixing up the units, I know.. hope you get the idea)


This is assuming there is no limit on the frictional force wheel bearings can generate. In reality, I think there is, so eventually thrust will overcome the friction and the airplane will take off.

Bearcat94

I'm stumped.

Everytime I get if figured one way, I think of something that makes me think its the other way.

fdl

Speeding up the treadmill doesn't increase the friction, or the necessary force. Let's say you were on a treadmill with roller skates. I was behind you with my hand on your back to keep you from rolling back. Speeding up the treadmill wont require me to push harder to keep you from moving back. It would take (more or less) the same force. The only difference is your rollerskate wheels would turn faster.

Now this is just a theoretical discussion. There is a limit to what the bearings in a wheel can handle, so in practice at some point they wouldn't be able to spin fast enough and that would require extra force. But in our theoretical discussion, we assume the wheels can turn at the speed of the treadmill.

fdl

wrong. The race cars forward "thrust" is reliant on it pushing against/off the ground, which is moving backwards in a treadmill scenario. The plane on the other hand doest push against the ground to move forward. it pushes against the air. This is why we have planes that can take off from water, with no wheels at all.

Whiskers

Lets make a public poll and then ban whoever is wrong after the show...

Osamu

at first I thought the question was if you just put the plane on a moving conveyor belt, would the plane take off without the plane using any of it's own force? And obviously that is a stupid question, but I think that's what people were thinking with the whole air craft carrier thing.

but if you're asking if the converyor belt will impeed the plane from taking off, since the plane forces on the the stationary air, the only backwards force would be the friction on the wheel bearings, and the plane should go fine (although probably a bit slower) but the wheels would be turning faster.

is300eater

totally agree... I hate that video...

and I'm going to my stance... NO FLIGHT

Mizouse

cibs

I love how no one addresses the simplest solutions - they'd rather try to make it more complicated than it is.

No one has still addressed the rope theory. Strap on some roller blades stand on a treadmill moving 100,000 miles an hour while holding on to a rope anchored in the wall infront of you.

Now, the tread mill is moving faster against you than you could ever POSSIBLY hope to move forward, but now start pulling on the rope and what happens? You start moving closer towards the wall. EGAD - is this possible? yes.

I'm curious to see if anyone has a different view on THIS example instead of just ignoring it like most people have...

The engines push against AIR and don't turn the tires to provide forward momentum.

I stand by the plane WILL take off. - although it might take more thrust than usually required...

However I doubt they will be able to use this in real scale as they'd need a hell of a long ass treadmill and knowing the trouble they had even being able to use the engines of a cargo plane for that thrust test they'll probably end up using a cessna or something.

dom

sipark

I don't think so.. If the treadmill moves at 0.01 mph, it will be require much less force to keep you still than if the treadmill were to move at 100 mph.

CGTSX2004

iTrader: (1)

Assuming a totally perfect system where the bearing are completely friction free and there is no traction limit, the force is completely placed upon the rotation of the wheels and should not affect the object that those wheels are attached to.

In reality though, we have to deal with friction and traction limits.

I still say this entire plane on treadmill scenario is going to be dependent upon the traction that the tires of the plane will have against the treadmill. Once that traction has been exceeded and the tires slip, the plane will be able to more forward and will eventually take off.

Bearcat94

No .... not on wheels. Regardless of treadmill speed, you only need a "pushing" force equal to the rest inertia of the wheels --> and that is a constant.

fdl

Nope, you're wrong. Assuming that the bearings in the wheels can handle the speed, it will require exactly the same force.

I really don't understand why people are having such a hard time grasping this. A planes forward thrust on takeoff has nothing to do with power from the wheels. It pushes against the air, which is not moving backwards. There is no resistance from the treadmill, because the wheels of the plane simple turn at whatever speed they need to.

NetEditor

FDL's example of a seaplane is good. If the water is flowing in the opposite direction, it in no way prevents a seaplane from taking off. The trick part of the question is the wheels. People think the wheels of a plane are like a car; they're not.

dom

I'll say again.

Billiam

New question: what would the wheel speed be at takeoff? 2x airspeed?

curls

Yes, absolutely. (assuming the magic conveyor can exactly, simultaneously match the wing speed of the plane... which is the assumption of this myth to begin with).

spooky3ce

Correct... The forward thrust is reliant on it pushing against/off the ground... but so that the tires obtain the maximum grip at high speeds there is something called down force. Down force is produced from the air traveling around the car pushing the car down to the ground at high speeds. That is what canards in front of the car are for and the wing on the rear. Without wind; which is produced when a vehicle is moving forward, the car will not create/obtain any down force. Analogy: Down force to a car is like Lift to a Plane... The more lift the higher it flies and the more down force more grip for quicker speed... (The only difference is too much down force can also create a lot of drag holding your maximum speed back).

So you are correct in the aspect that a plane pushes against the wind which creates lift, but on a treadmill there will be no wind pushing against the plane creating no lift... Regardless of how fast the wheels are spinning, the plane will never be able to push against the wind...

Run on an indoor treadmill and feel the air blow through your hair... Impossible... because your body is at a standstill but the floor below you is moving backwards...

Since the wings on a plane are the opposite of a car's wing (spoiler), lift is created instead of down force... Without the wind moving around the vehicle or the plane there will be no down force nor lift...

The wheels of the plane serve for one purpose only, and that is so that the plane can roll freely without it bottoming out (summarizes landing, and/or rolling to the strip).



If the plane was on one end of the treadmill and it was slingshot to the front of the treadmill of vice-versa... the plane will take off and soar for a while. It would need the engines to keep it moving forward so that the wind keeps lift on the wings... Kind of like a paper plane... the treadmill will act like your hand and the speed at which the plane is moving pushes against the air creating lift allowing it to soar... but keep your hand still holding that paper plane (you running = the wheels of the plane) and run on a treadmill and let the plane go, it will just drop to the ground... 100% sure that once you drop the paper plane the wings of the plane will push against the air as it drops straight down and then it will create lift... you'll see it kind of float a bit before it hits the ground...

spooky3ce

Forgot to mention about planes that take off from water...

If a plane is at a stand still but the water is rushing under the plane... the plane will be pushed backwards... If the speed of the water pushing the plane backwards is equal to the speed of the plane moving forward the plane will be at a stand still in the water... Once the plane exceeds the speed of the water pushing it backwards and pushes agains the wind to creat lift, then the plane can take off... This is why planes that take off from water try to find a way to go towards the curent and not against the curent... because the speed of the water plus the speed of the plane plus the wind pushing againts the plane equals a shorter run and easier lift...

curls

Pretty much everything you just said is correct, except that you aren't taking into account how the fuselage/wings of the plane are isolated from the conveyor belt by nature fo the free-spinning wheels.

A car, or a person, on a treadmill is NOT like a plane on a treadmill. Why? Because the car and person rely on pushing off of the ground to move, and if the ground is moving, they can't get forward motion relative to something standing off of the treadmill. However, a plane pushes on the air to move, and simply rolls along the runway, skiis along the snow, or floats along the water as a means of keeping it as isolated as possible from the ground.

Think of it this way, if you will: Stand on a treadmill with rollerblades on. Set the treadmill to 5mph. Skate at an effort of 5mph. Net result: You are skating at 5mph but going nowhere relative to the wall next to you. This is how a car, or anything propelled by contact with the ground, would react -- it would stay stationary relative to a stationary object. Now, new scenario: You are on a treadmill, wearing rollerblades, but also have a rope attached to your waist on one end, and a friend in front of (but not on) the treadmill is holding the other end. Set the treadmill to 5mph. Skate at 5mph so your new speed relative to the wall next to you is 0mph (ie: typical treadmill...). Now, have your friend pull the rope at a speed of 3mph. What happens?

- you'd still only be skating at an effort of 5mph (or you could stop skating and glide with NO change in the result)
and
- the wheels on your rollerblades will be rotating at a speed of (5+3=) 8mph. (or in the case of you stopping the skating and simply gliding, the wheel speed is still 8mph!)
and
- You'd be moving forward, relative to the stationarty wall (and the air around you!) at a speed of 3mph.

Apply this principle to the plane whose thrust is NOT generated from contact with the runway/conveyor, but the interaction with the air around it. Net result? The plane DOES move forward with no extra effort(*). And since the plane moves forward, it DOES have air moving over the wings, and as such, WILL FLY.

* The "no extra effort" ignores the very minute increase in rolling friction and bearing efficiency. Thrust requirement will NOT double with every doubling of the conveyor speed, as rolling resistance is almost constant in most circumstances!