Imagine a plane is sitting on a conveyor belt, can it take off?

[DWarrior]

Originally Posted by Grapist

I will grant you this as a possibility based on ideal versus realistic circumstances. But an airplane doesn't achieve lift due to it's speed, as much as it achieves lift due to the speed of the wind moving over the wings.

Propellers, jet engines, etc are designed to move air across wings and the wings are designed in such a way that lift is achieved if you move enough air over the wing. It doesn't matter if the wheels of the plane are actually causing the plane to move forward. If the jet engines/propellers pull enough air over the wing, lift will be created and the plane will take flight.

You may very well be right. Physics works in seemingly strange ways sometimes if you don't understand it (which I don't). I'll give it to you guys.

[phooey]

Originally Posted by Grapist

I will grant you this as a possibility based on ideal versus realistic circumstances. But an airplane doesn't achieve lift due to it's speed, as much as it achieves lift due to the speed of the wind moving over the wings.

Propellers, jet engines, etc are designed to move air across wings and the wings are designed in such a way that lift is achieved if you move enough air over the wing. It doesn't matter if the wheels of the plane are actually causing the plane to move forward. If the jet engines/propellers pull enough air over the wing, lift will be created and the plane will take flight.

if there is no wind, even if the treadmill is travelling at 200 miles an hour, the wheels will just be moving that fast... of course there will be resistance and the plan will be pulled backwards.. not because it is flying but because the wheels won't be able to spin that fast.. if the wings were turned around.. maybe it would fly off the back of the treadmill as it is thrown that way, but if it is facing forward it won't fly.

[golgi body]

From what I remember from my physics class and a fifth grade science project is that wind traveling over the top of a plane's wing has a longer distance to cover than the wind on the bottom . This creates a difference in pressure which in turn creates lift. Or at least something along those lines. So I say no it won't work.

EDIT: I just checked out what I thought was true and came across a "BAD PHYSICS" website which says what I learned and is commonly taught is incorrect. It's not far off but has to do with the wing forcing the air downwards to create lift. I still say it won't work though since the plane is stationary relative to the ground.

EDIT 2: here's the link if anyone's interested http://www.eskimo.com/~billb/miscon/miscon4.html#wing

[Grapist]

Originally Posted by Rye

ummm plane needs the lift which needs the forward momentum etc... now i think the plane will move forward regardless of belt speed.

Ooooh but there's the trick now isn't it? No one said how the plane would react on a treadmill other than taking off.

They are jet engines, they are DESIGNED to move a vehicle by a means that has nothing to do with friction.

Wheels in this context mean nothing other than they can roll. Yes, the plane will move down the giant treadmill runway, yes, it will take off. It's not the same as your car.

And if you want more details as to why I am more than happy to share but only upon request.



When is this episode airing, I so want to watch it and all of us be online, right, wrong, whatever, I love that show.

[DoctorRon]

Hello there,

I am so fucking sick to death of this rumor!!!

I am a pilot recreationally, and also have a degree in Physics from the State U. Let's remember Newton's Third Law people: for every action there is an equal and opposite reaction.

An airplane flies by using what's called the "Bernoulli Effect." An airplane wing is curved (an airfoil). It takes air longer to pass over an airfoil than under it. This creates a zone of low pressure air over the wing. Hence, the airfoil is literally "sucked" into the air--producing the miracle of flight.

Now, the purpose of an aircraft engine is to push the airfoil (hence the airplane) through the air, creating a low-pressure zone that pulls the airfoil surface into the air. Here's where Sir Newton comes in: an airplane's engine, whether jet or piston driving a propeller, generates a reactive force. This force is countered by an equal and opposite force. So, what I'm saying is that the engines on, say, a 767, output thrust--which is pressure (hence force) against the static air around the engine. The air acts back on the engine with an equal and opposite counterforce, pushing the airfoil (wing) through the air. This generates airspeed, which LIFT is a function of.

In an airplane's case, LIFT is a direct consequence of THRUST, because THRUST produces AIRSPEED due to the Third Law. Hence: if a wing is allowed to fly without any control input and you add thrust the plane goes up. Physics do not care what the hell is under the plane, or what the wheels are doing. Pilots know that airspeed and lift are two sides of the same coin; you can trade one for another--at least while your engines keep spinning--or you keep hitting thermals and gliding. Eventually you run out of airspeed, in which case lift ceases, producing a STALL. The nose of the plane drops, and if you try to keep it up without that crucial airspeed (by adding elevator, for instance), you enter a SPIN. This will soon degenerate into a FLAT SPIN, which, without power, isn't really possible to recover from. This is followed by AUGERING IN, BUYING THE FARM, KISSING ONE'S ASS GOODBYE, or many other ugly flight attitudes.

Sorry for the overly long post; I'm quite loquacious and, as I said, I'm just sick of this rumor. Stick with physics folks; it will generally never let you down.

Love you all,

DOKTOR R

[phooey]

Originally Posted by Grapist

Ooooh but there's the trick now isn't it? No one said how the plane would react on a treadmill other than taking off.

They are jet engines, they are DESIGNED to move a vehicle by a means that has nothing to do with friction.

Wheels in this context mean nothing other than they can roll. Yes, the plane will move down the giant treadmill runway, yes, it will take off. It's not the same as your car.

And if you want more details as to why I am more than happy to share but only upon request.



When is this episode airing, I so want to watch it and all of us be online, right, wrong, whatever, I love that show.

I see what you are saying... if the treadmill is used like a slingshot than sure, if you push the plane forward it will take off but I think the question is... what if there is no friction on the wheels and the wheels spin and spin? and the plane does not move forward? will it take off? i think that is the question

[Grapist]

Originally Posted by DoctorRon

Hello there,

I am so fucking sick to death of this rumor!!!

I am a pilot recreationally, and also have a degree in Physics from the State U. Let's remember Newton's Third Law people: for every action there is an equal and opposite reaction.

An airplane flies by using what's called the "Bernoulli Effect." An airplane wing is curved (an airfoil). It takes air longer to pass over an airfoil than under it. This creates a zone of low pressure air over the wing. Hence, the airfoil is literally "sucked" into the air--producing the miracle of flight.

Now, the purpose of an aircraft engine is to push the airfoil (hence the airplane) through the air, creating a low-pressure zone that pulls the airfoil surface into the air. Here's where Sir Newton comes in: an airplane's engine, whether jet or piston driving a propeller, generates a reactive force. This force is countered by an equal and opposite force. So, what I'm saying is that the engines on, say, a 767, output thrust--which is pressure (hence force) against the static air around the engine. The air acts back on the engine with an equal and opposite counterforce, pushing the airfoil (wing) through the air. This generates airspeed, which LIFT is a function of.

In an airplane's case, LIFT is a direct consequence of THRUST, because THRUST produces AIRSPEED due to the Third Law. Hence: if a wing is allowed to fly without any control input and you add thrust the plane goes up. Physics do not care what the hell is under the plane, or what the wheels are doing. Pilots know that airspeed and lift are two sides of the same coin; you can trade one for another--at least while your engines keep spinning--or you keep hitting thermals and gliding. Eventually you run out of airspeed, in which case lift ceases, producing a STALL. The nose of the plane drops, and if you try to keep it up without that crucial airspeed (by adding elevator, for instance), you enter a SPIN. This will soon degenerate into a FLAT SPIN, which, without power, isn't really possible to recover from. This is followed by AUGERING IN, BUYING THE FARM, KISSING ONE'S ASS GOODBYE, or many other ugly flight attitudes.

Sorry for the overly long post; I'm quite loquacious and, as I said, I'm just sick of this rumor. Stick with physics folks; it will generally never let you down.

Love you all,

DOKTOR R

Okay, I haz a pretty good idea of what you are saying, but can we some it up for those of us who don't speak "Newton"?

[Grapist]

Originally Posted by phooey

I see what you are saying... if the treadmill is used like a slingshot than sure, if you push the plane forward it will take off but I think the question is...

Nope, not used as a slingshot. The point of this "riddle", is that the wheels/mph/etc have nothing to do with lift.

what if there is no friction on the wheels and the wheels spin and spin? and the plane does not move forward? will it take off? i think that is the question

The airplane will move forward due to the thrust. Motion of a plane is not analagous to motion of your car/bus/train etc. Physically they work on different principles.

[DWarrior]

Originally Posted by Grapist

Okay, I haz a pretty good idea of what you are saying, but can we some it up for those of us who don't speak "Newton"?

I think he sums it up pretty well: "no"

But yeah, I really gotta learn Physics already, I'm tired of not understanding stuff.

[Diana]

Originally Posted by DoctorRon

stuff

And why didn't you take my physics regents for me last year??