Here's a good question for discussion...

jaybs95 said:
I don't think that it will take off.

While the plane is on the ground it is no different than a jet powered car, if you move the roadway under a jet car in the opposite direction at the same identical speed, it will still stay in one spot, so why would a plane be any different. (equal and opposite forces will canel each other out)
In order to have forward movement you need a fixed point.

"J"
Click to expand...

Well put. This is an easy question. You don't have to be a :detective to figure this one out. The plane will not move forward because as Jay states the forward motion the engines would normally generate is canceled by the equal and opposing backward motion of the conveyor belt. The conveyor belt contacting the tires essentially pushes the plane backward. If the plane is not moving forward through the air then no air is moving over the wings and therefore there is no lift. Ergo, the plane will not take off.

I mean think about it. If a plane could take off this way why would they bother using slingshots on aircraft carriers????

You want a REALLY hard question wrap your brain around this one (careful it might give a few of you a headache :) . . .

You're travelling in a car at the speed of light. You turn on the headlights. Does it make a difference? :confused:
 
Mikeyc said:
You're travelling in a car at the speed of light. You turn on the headlights. Does it make a difference? :confused:
Click to expand...
No, you've exceeded the realm of Newtonian physics and we can only guess as to what happens after that.
 
tubafeak said:
It will take off, the wheels will be moving at twice the speed of the plane at all times then there is motion. The wheels are merely there to allow the plane to gain the air resistance needed to create lift, as the conveyor accelerates it accelerates the wheels which are only there to keep the plane upright, that's all that the conveyor's force is acting upon. If you think about how a plane works it acts through friction with the air to accelerate, this has nothing to do with wheel friction. Just for fun, try putting a tethered balloon car on a treadmill, if the wheels are spinning and you let the pressure out of the balloon the car moves forward.
Click to expand...
I am assuming that there is little to no friction in the wheel bearing, otherwise you're talking about a lot more calculations and whatnot.
 
tubafeak said:
It will take off, the wheels will be moving at twice the speed of the plane at all times then there is motion. The wheels are merely there to allow the plane to gain the air resistance needed to create lift, as the conveyor accelerates it accelerates the wheels which are only there to keep the plane upright, that's all that the conveyor's force is acting upon. If you think about how a plane works it acts through friction with the air to accelerate, this has nothing to do with wheel friction. Just for fun, try putting a tethered balloon car on a treadmill, if the wheels are spinning and you let the pressure out of the balloon the car moves forward.
Click to expand...

If you add the fact that the plane is tethered then it could take off. The tether essentially counteracts the backward motion of the conveyer. Adding the thrust of the engine would give the plane enough forward motion to take off. However, the length of the tether would need to be greater than half the distance the plane would normally need to take off. Otherwise, the plane would pass the furthest distance it could travel on the tether and then the tether itself would hold the plane back. Regardless, it would have to be a REALLY long tether otherwise the plane would crash shortly after it got airborne.
 
tubafeak said:
It will take off, the wheels will be moving at twice the speed of the plane at all times then there is motion. The wheels are merely there to allow the plane to gain the air resistance needed to create lift, as the conveyor accelerates it accelerates the wheels which are only there to keep the plane upright, that's all that the conveyor's force is acting upon. If you think about how a plane works it acts through friction with the air to accelerate, this has nothing to do with wheel friction. Just for fun, try putting a tethered balloon car on a treadmill, if the wheels are spinning and you let the pressure out of the balloon the car moves forward.
Click to expand...

There is no friction being created with the air. Until it manages to be airborne it will be goverend by ground rules

Using your balloon car on the treadmill example, the car is unpowered, and is generating its motion from the treadmill, then you are adding thrust (letting the air out) without increasing the speed of the treadmill, so yes there will be forward motion, but if you increased the speed of the treadmill to match it, it will stay in place.

"J"
 
^^^ Yup. Same example I used. Consider the moving walkway at the airport. Say you are standing on one end and you have roller blades on. You are holding a rope that is tied to the other end of the walkway. Your wheels are spinning at exactly the same speed as the walkway at that point and you are making no progress whatsoever. However, if you reel yourself in then your wheels will be moving faster than the walkway. A jet engine would be even better. Do you have any doubt that if you had a jet engine under each arm that you would have any problem rolling down the walkway? It would be a breeze, so to speak. The engines don't care which way the ground is moving. They only care about overcoming whatever friction is keeping them from going forward. Once that is accomplished you would speed up as if the ground was still.
 
Here's another good way to explain it...

1. Place treadmill on a downhill at 5 deg from horizontal
2. Set the treadmill to ludicrous speed and the belt is moving upwards
3. Lower plane slowly onto the higher part of the treadmill
4. The wheels starting to touch the treadmill will spin up to ludicrous speed, while the crane holds the plane in place
5. Disconnect the plane from the crane
6. The plane will accelerate downwards without any thrust from engines

Since the question has the plane at 0 degs to horizontal, gravity doesn't provide any forward force and that's where engine thrust replaces gravity.
 
The conveyor does not exert any backward force on the plane (the wheels are free spinning). The plane will fly. :yay
 
You must log in or register to reply here.
Back
Top