Would the plane take off?

[slateman]

Well, my best friend happens to also be a pilot in the Air Force (F-16s, C-130s) and I work on C-130 simulators, and we both disagree with your uncle. It is obvious that he did not understand the question.

If you've never been on an airplane, it's difficult to imagine the amount of thrust that they put out. Even for a turbo-prop like a C-130.

Instead of a 747 in the example, picture a C-5 Galaxy. If you've ever seen one of those bad boys take off, I guarantee that you were amazed at how in the hell it even made it off the ground.

This is exactly what I wrote him:

A plane (747 passenger jet) is sitting on a runway
that can move (some sort of band conveyor or a giant
treadmill). The plane moves in one direction, while
the conveyor moves in the opposite direction. This
conveyor has a control system that tracks the planes
speed and tunes the speed of the conveyor to be
exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

He sent me the answer I previously stated. BTW - He DOES fly C-5s out of Dover. And I've seen them. The reason they take of is because the earth isn't moving as fast as the plane. The 4 giant engines create enough thrust to propel the plane forward. Enough speed = enough lift because of the air going under and over the wings. On a treadmill, you don't get the wind rushing by because you're not actually moving through the air.

[SlartyBartFast]

He sent me the answer I previously stated. BTW - He DOES fly C-5s out of Dover. And I've seen them. The reason they take of is because the earth isn't moving as fast as the plane. The 4 giant engines create enough thrust to propel the plane forward. Enough speed = enough lift because of the air going under and over the wings. On a treadmill, you don't get the wind rushing by because you're not actually moving through the air.

Sorry, but that just proves that even the ignorant can fly planes...

What the heck does the earth's rotation have to do with aircraft take-off?

[neppo1345]

PWNED...ALL OF YOU

"Because the conveyor cannot stop [the plane] from moving forward. There is nothing on the airplane that pushes against the ground or the conveyor in order for it to accelerate; as Karen -- one of our techies here at the Lounge -- put it, the airplane freewheels. In technical terms, there is some bearing drag on the wheels, but it's under 40 pounds, and the engine has overcome that for years; plus the drag doesn't increase significantly as the wheel speed increases. Unless Manfred applies the brakes, the conveyor cannot affect the rate at which the airplane accelerates. "

[Glickman]

He sent me the answer I previously stated. BTW - He DOES fly C-5s out of Dover. And I've seen them. The reason they take of is because the earth isn't moving as fast as the plane. The 4 giant engines create enough thrust to propel the plane forward. Enough speed = enough lift because of the air going under and over the wings. On a treadmill, you don't get the wind rushing by because you're not actually moving through the air.

yes the engines create thrust to create speed to create lift.

but going back to miscue...


that doesnt mean that you cant use thrust alone as propellant. i could do the calculation to find out how much it would need but that would involve not being lazy


all you people with "family within the airforce":

Yea, ur friends are right, but thats only considering that the only possible way to get lift off is with lift, which is not physically true. Most effecient yes, but not the only way

[bleachit]

all you people with "family within the airforce":

I wonder how many of them took a physics or engineering course while learning to fly?

very few if any. knowing how to fly and knowing why you fly are two different things.

[Lohman446]

I wonder how many of them took a physics or engineering course while learning to fly?

very few if any. knowing how to fly and knowing why you fly are two different things.

My dad's a private pilot, and I have seen the course work to get licensing, most pilots know why, or at least passed a "ground test" on it.

[beam]

This is a little off-topic, but since we've already answered the original question, here is another one. Most pilots should be able to answer this in around 4 words:

What makes an airplane turn?

**Edit - the answer is not: The pilot**

[bleachit]

My dad's a private pilot, and I have seen the course work to get licensing, most pilots know why, or at least passed a "ground test" on it.

they may know the basics, as they are taught basics. something more advanced, such as this, is not something they would normally know.

[beam]

they may know the basics, as they are taught basics. something more advanced, such as this, is not something they would normally know.

Actually, as Army has stated, bush pilots take off of moving rivers all the time. They know what the impact is of taking off of a "moving runway"

Physics, schmisics. Why does an airboat drive equally well on ice and water? The surface medium has nothing to do with it's movement. Why? It's propulsion system is not tied to that medium. It operates in a different medium...air. The air is not moving.

Here is a scenario that would not allow the 747 to fly. Add a tailwind that is equal to the plane's velocity. The plane WILL NOT FLY.

Do you see it now?

[SlartyBartFast]

Add a tailwind that is equal to the plane's velocity. The plane WILL NOT FLY.

And when that happens while you're in the air, it called "dead" air. Been there, 767, done that, not pleasant.

[ScatterPlot]

This is a little off-topic, but since we've already answered the original question, here is another one. Most pilots should be able to answer this in around 4 words:

What makes an airplane turn?

**Edit - the answer is not: The pilot**

I'm not pilot here, and unless this is a trick question, could it be "aelerons, rudder, and elevators"?
Cause from what I know of planes and stuff, there's a bunch of ways it could "turn." If you mean like the yaw, then just the rudder could do it, or you could pitch to one side and use the elevators to do it, or I guess if you had engines on each side of the plane controlled separately (like not a Cessna) then that could do it, or maybe the answer is "the wind" or something... Am I overanalyzing this?


Anywho, back to you who don't get the question and whoever that was with the uncle and whatnot. You seem to think the plane will not move. The plane will not take off if it is not moving, but the issue here is that the conveyor belt will not impede movement. Think of it this way- with frictionless wheels and a belt going a hundred thousand miles an hour, will the plane be moving? No, because the wheels are frictionless. Now add a teensie bit of thrust to that, the plane will move a teensie bit. Add a lot of thrust, and the plane will take off.

Your uncle might be a pilot, but the question here is not whether or not there can be lift at zero speed. Obviously no. Tell him some of the responses seen here, he will probably hit himself in the forehead with a resounding "duh" like I did when I figured it out.

[slade]

after looking over the question, i realized its not worded that clearly and there are multiple ways of looking at it. we dont know much about the "tracking system". To hopefully clear everything up, i decided to post this.

method 1: it tracks the wheel RPM, and uses the wheel diameter to calculate the MPH of the wheels, and sets the belt to rotate at this speed. if this is the method used, when the plane starts and moves forward, its wheels will begin to rotate, and the belt will begin to move. the belt will speed up the wheels, and will soon far exceed their mas RPM, break, and the plane will fall down and crash. since the belt speed matches the wheel RPM, the plane CANNOT move forward. the belt just keeps increasing rapidly until the wheels break.

method 2: the potential speed of the plane is tracked. the speed the plane would go if on a normal track is recorded and the belt moves at the same speed (relative to time) in the opposite direction in the actual trial. the wheels just spin at twice the RPM and the plane takes off. this is how most people are looking at the question.

*forget method 3. for all practical purposes its almost the same as 2*

[SlartyBartFast]

To hopefully clear everything up, i decided to post this.

method 1: ...
method 2: ...
method 3: ...

Clear things up?!?

You realise that each of those methods is exactly the same, right?

RPM of wheels at take-off speed, speed compared to a normal take-off, or actual speed from a radar gun.

ALL result in the wheels doing twice the RPMs that they would without the moving surface.

[slade]

Clear things up?!?

You realise that each of those methods is exactly the same, right?

RPM of wheels at take-off speed, speed compared to a normal take-off, or actual speed from a radar gun.

ALL result in the wheels doing twice the RPMs that they would without the moving surface.

re-read my post slowly...

the first method is the speed of the wheels. the speed of the wheels will be increased by the belt rotating. if the linear speed of the wheels exactly matches that of the belt, the wheels CANNOT move forward and thus the plane cannot move forward. note i did NOT say RPM of the wheels at takeoff speed. i said the actual linear speed of the wheels in the experiment.

the second method is the belt spins at the speed of the plane in a normal takeoff. this results in the wheels rotating at about twice their normal rate.

the third method is the belt speed adjusts to match the actual forward speed of the plane, as compared to the ground. the friction from the belt will slow the plane down somewhat, although not much, so it wont be exactly the same. it will be close to method 2... ehh, maybe i should have just not mentioned it. although it is a different interpretation of the question, they all are valid interpretations.

[ntn4502]

I be pilot...

its kind of tricky, but this is what would happen:

as the jets increase their thrust the plane would speed further down the conveyor belt until it reaches its Vr speed, or speed in which the plane will take off

/the belt has no effect on creating the lift
//tires would be doubling in speed...possible failure
/// would need a conveyor belt as long as the normal runway
////picture a kid wearing a jet pack and roller blades on a treadmill