Can the airplane take off?

[beansbaxter]

Alright, this is NOT a homework question. In another thread on the Anandtech forums, I saw this mentioned deep within a thread but it was never addressed. I am still curious so I ask it here:

You have an airplane on a conveyor belt - when the airplane moves forward, the conveyor matches its speed in reverse. Can the airplane take off?

 

[Toastedlightly]

Yes.

 

[Shaftatplanetquake]

It would depend upon the airplane.

F35 aircraft is capable of hovering in place, so that one would not be affected.

Forward motion is not was causes the airplane to be able to "take off". Thrust is what causes this.

 

[Howard]

Originally posted by: Shaftatplanetquake
It would depend upon the airplane.

F35 aircraft is capable of hovering in place, so that one would not be affected.

Forward motion is not was causes the airplane to be able to "take off". Thrust is what causes this.

Not thrust, but lift. How do you get lift from a motionless plane?

 

[Shaftatplanetquake]

Like I said, the F35 can pull straight up. I think the thrusters just point down and can make the plane move only vertically, if the pilot should choose.

I'm basing this knowledge on Battlefield 2.

 

[kpb]

That question doesn't make sense. A car which moves it's self foward using the wheels would be stationary relative to the ground if the conveyor was moving in the opposite direction at the same speed as the car is according to the speedometer. This is actually how they do a number of things on cars like testing horsepower and torque or how they figure out estimated mpg.

The problem with a plane is that the movement is generated by the jet engine or propeller and is not dependant on the wheels at all. They just support it and allow it to move foward until lift allows it to take off. So even if the conveyor belt was moving backwords the plane would still end up moving forwards and gaining speed. The wheels would just be turning twice as fast. The plane would either reach then end of the conveyor belt and crash or what ever or take off once it got enough speed. The conveyor belt wouldn't effect things at all really. The type of plane wouldn't change this at all because all planes must generate thier forward motion using an engine and not the wheels or they'd start loosing speed as soon as they took off =)

 

[Gibsons]

Originally posted by: Shaftatplanetquake
Like I said, the F35 can pull straight up. I think the thrusters just point down and can make the plane move only vertically, if the pilot should choose.

I'm basing this knowledge on Battlefield 2.

It doesn't need to take off vertically in this situation though. Assuming the wheels are in good working order, any airplane should be able to take off.

 

[Shaftatplanetquake]

Originally posted by: kpb
The problem with a plane is that the movement is generated by the jet engine or propeller and is not dependant on the wheels at all.

I disagree. Unless the plane doesn't have wheels (one of those crafts that is stored on a body of water) then the plane is completely dependent on the wheels for moving forward if it is grounded. If you take the wheels off the plane either doesn't move at all or moves completely unpredictably.

Thats like saying that cars don't rely on brakes to stop.

 

[kpb]

Originally posted by: Howard

Originally posted by: Shaftatplanetquake
It would depend upon the airplane.

F35 aircraft is capable of hovering in place, so that one would not be affected.

Forward motion is not was causes the airplane to be able to "take off". Thrust is what causes this.

Not thrust, but lift. How do you get lift from a motionless plane?

You don't typically but it doesn't matter because the theoretical plane wouldn't be motionless =)

 

[Shaftatplanetquake]

Originally posted by: Gibsons

Originally posted by: Shaftatplanetquake
Like I said, the F35 can pull straight up. I think the thrusters just point down and can make the plane move only vertically, if the pilot should choose.

I'm basing this knowledge on Battlefield 2.

It doesn't need to take off vertically in this situation though. Assuming the wheels are in good working order, any airplane should be able to take off.

I don't think so. A regular commerical jet actually needs the speed it generates on the ground to get into the air. Without the speed, it would be like trying to launch a rocket into outer space with a fraction of the fuel required for blastoff.

 

[Howard]

Originally posted by: kpb

Originally posted by: Howard

Originally posted by: Shaftatplanetquake
It would depend upon the airplane.

F35 aircraft is capable of hovering in place, so that one would not be affected.

Forward motion is not was causes the airplane to be able to "take off". Thrust is what causes this.

Not thrust, but lift. How do you get lift from a motionless plane?

You don't typically but it doesn't matter because the theoretical plane wouldn't be motionless =)

What does it mean when the conveyor matches its speed in reverse?

 

[kpb]

Originally posted by: Shaftatplanetquake

Originally posted by: kpb
The problem with a plane is that the movement is generated by the jet engine or propeller and is not dependant on the wheels at all.

I disagree. Unless the plane doesn't have wheels (one of those crafts that is stored on a body of water) then the plane is completely dependent on the wheels for moving forward if it is grounded. If you take the wheels off the plane either doesn't move at all or moves completely unpredictably.

No it's accurate to say that they don't depend on the wheels for movement. The fact that you can use skys, or floats or what ever just proves that. The wheels on a plane are like the wheels on a roller skate. They are not hooked up to any motor and can not move the plane forward on thier own. They do allow it to easily roll but it's the jet engine that actually causes the motion to occur.

 

[kpb]

Originally posted by: Howard

Originally posted by: kpb

Originally posted by: Howard

Originally posted by: Shaftatplanetquake
It would depend upon the airplane.

F35 aircraft is capable of hovering in place, so that one would not be affected.

Forward motion is not was causes the airplane to be able to "take off". Thrust is what causes this.

Not thrust, but lift. How do you get lift from a motionless plane?

You don't typically but it doesn't matter because the theoretical plane wouldn't be motionless =)

What does it mean when the conveyor matches its speed in reverse?

Nothing because the plane doesn't use the wheels to generate forward motion. It just means the wheels are spinning faster because the plane is moving twice as fast relative to the belt but the plane still moving forward relative to someone standing on the ground next to the belt.

 

[Horus]

The aircraft (let's say it's a conventional, non VTOL aircraft) will have no forward motion relative to the ground. Therefore, no lift will be developed over the wings and it will not fly!

 

[dkozloski]

The conveyor belt is of little consequence. It's just noise in the problem. The only way it would come in to play is if it's too short for the aircraft to reach flying speed. The velocity of the aircraft relative to the ground is of no consequence. The only thing that matters is the speed of the aircraft relative to the air. The wheels and/or tires may be oversped and fly apart by contact with the belt. This is no different from an aircraft being launched from an aircraft carrier except for the relative speed of the belt. There really is no serious question here.

 

[Ika]

Originally posted by: dkozloski
The conveyor belt is of little consequence. It's just noise in the problem. The only way it would come in to play is if it's too short for the aircraft to reach flying speed. The velocity of the aircraft relative to the ground is of no consequence. The only thing that matters is the speed of the aircraft relative to the air. The wheels and/or tires may be oversped and fly apart by contact with the belt. This is no different from an aircraft being launched from an aircraft carrier except for the relative speed of the belt. There really is no serious question here.

Excellent answer.

Think of this situation in another form: you're standing on a treadmill, wearing roller skates, while holding onto a rope attached to a far wall in front of you. Ignoring friction, while you're standing on the treadmill, the wheels counteract the pull of the treadmill itself, so that you stay in place. But when you start pulling on the rope, you begin moving forward. This is akin to the airplane's engines "grabbing" ahold of the air and pulling the plane forward. The conveyor belt has no way to counteract this force and thus the plane will move forward, allowing it to take off.

It is erroneous to assume that the plane does not move just because there is a conveyor belt in the equation.

 

[enwar3]

I can't believe we're still discussing this.

A plane takes off because of the lift of air passing under its wings. If it's taxiing on a conveyor belt like you said, it's motionless - air does not pass under the wings and there is no lift.

 

[Howard]

I forgot that the wheels are free-spinning...

 

[SociallyChallenged]

Originally posted by: enwar3
I can't believe we're still discussing this.

A plane takes off because of the lift of air passing under its wings. If it's taxiing on a conveyor belt like you said, it's motionless - air does not pass under the wings and there is no lift.

Ding ding ding.

 

[Kelemvor]

Oh god. People are still talking about this? THere are tons of sites on the internet that explain why he airplane WILL take off. Anything else is just plain wrong.

 

[her209]

The obvious answer is that it does not take off otherwise it would have been done already!!!

 

[Ika]

Originally posted by: her209
The obvious answer is that it does not take off otherwise it would have been done already!!!

The obvious response to your statement is that friction exists, so you're a fool.

No offense, but I wanted to say it

 

[her209]

Originally posted by: Aflac

Originally posted by: her209
The obvious answer is that it does not take off otherwise it would have been done already!!!

The obvious response to your statement is that friction exists, so you're a fool.

No offense, but I wanted to say it

Obviously friction has to exist in order for the conveyor belt to match the speed of the wheels (in the opposite direction), idiot!

If friction did not exist, a spinning wheel would not move horizontally... think of it this way. If no friction exists, and the conveyor belt was moving underneath the wheels, do you think the wheels would rotate?

 

[kpb]

Originally posted by: enwar3
I can't believe we're still discussing this.

A plane takes off because of the lift of air passing under its wings. If it's taxiing on a conveyor belt like you said, it's motionless - air does not pass under the wings and there is no lift.

Thats the thing. The wheels aren't what is generating the forward motion it's the jet engines. It will still be moving threw the air and will still generat lift.

 

[her209]

Originally posted by: kpb

Originally posted by: enwar3
I can't believe we're still discussing this.

A plane takes off because of the lift of air passing under its wings. If it's taxiing on a conveyor belt like you said, it's motionless - air does not pass under the wings and there is no lift.

Thats the thing. The wheels aren't what is generating the forward motion it's the jet engines. It will still be moving threw the air and will still generat lift.

The engine isn't what moves the air under the airplane's wings. The engine moves the plane forward which in turn moves air underneath the plane's wings causing lift.