Can an airplane on a conveyor belt take off? (resolved)

[Christophe]

Nothing to do with the subject, or almost, but this is the problem that is currently running on RS: will an airplane on a conveyor belt (which constantly cancels its ground speed) successfully take off?

If it is not a child's dream, it could be a problem with teenage physics (I am going to ask my son this evening ... 11 years old)!

184602837_10159636064769668_6485710110184661695_n.jpg (7.48 KB) Viewed times 10823

Sorry it's automatic translation (I understood nothing after the "more clarity" )

Most of my friends are going to roll their eyes on this.

It happens regularly but the answer is not as simple as we think. Mainly because of a wording ambiguity.
The caption reads as follows:
Imagine that a 747 is sitting on a runway length conveyor belt. The conveyor belt is designed to exactly match the speed of the wheels, going in the opposite direction. Can the plane take off?

For the sake of clarity, I will add that the plane cranks up the throttle as it would for any other take-off. This should end SOME of the confusion.

Airplane folks (and critical thinkers) realize that airplanes move by pushing air, not by straining tires, so of course the plane can take off. But think about it. We usually measure the speed of tires by converting their rotary motion to linear speed, right? Let's do that here.

--- * Speed: based on tire rotation * ---
As the aircraft moves at 1 km / h, the conveyor belt moves at 1 km / h in the other direction. This causes the tire to accelerate immediately to 2 km / h, which makes the belt go to 3 km / h, which makes the tire go to 4 km / h, which ... The speed of the tires is heading towards infinity as the plane becomes tireless at around 1 km / h depending on the traction.

--- * Speed: based on a speedometer or GPS * ---
If you measure speed with a speedometer or GPS, you would probably be fine. The plane takes off and the tire speed will be twice as fast as the takeoff speed, which is probably only damaging (exceeding the design limits of RPM
Enough of that. Back to my regular schedule ...

You have 10 minutes!

[Obamot]

Nothing to do with the subject, or almost, but this is the problem that is currently running on RS: will an airplane on a conveyor belt (which constantly cancels its ground speed) successfully take off?

It is not the reactors that keep the plane in the air (since the plane can soar without engines) but the wings and the speed.
So no, it has nothing to do with this rigging of a treadmill, the plane not moving, because there is no lift effect of the wings by the circulating air. like in a real flight. The plane would not move.

[Christophe]

That's it ! The lift is created by the relative wind ON the wings! No ground speed = no air speed = no lift!

A lot of people on fb have a hard time understanding this (I'm not even talking about the incomprehensible statement!)

In this case, 4 reactors at full throttle, there would still be, I think, a small lift by "friction" of the air flows passing through the reactors and "reaction" effect (assuming that the thrust vector reactor is tilted slightly downwards?) ...

Other answers?

[Ahmed]

Now that the good has been given, are the bad ones admitted?

[Flytox]

That's it ! The lift is created by the relative wind ON the wings! No ground speed = no air speed = no lift!

A lot of people on fb have a hard time understanding this (I'm not even talking about the incomprehensible statement!)

In this case, 4 reactors at full throttle, there would still be, I think, a small lift by "friction" of the air flows passing through the reactors and "reaction" effect (assuming that the thrust vector reactor is tilted slightly downwards?) ...

Other answers?

AMHA, the reactors push backwards, so the zinc is pushed forward in the same way (reaction). Support is done on the air "horizontally" and not on the track in one way or another. So the zinc moves forward, so there is air flow on the wings, which will create the necessary lift when the speed is sufficient, the zinc takes off as usual.
We can compare this to the operation of the hovercraft, it advances whatever its mode of support (dragging on the ground or a few cm from the ground / water etc ... The comparison stops there because after the hovercraft n is not made to take off.

[Ahmed]

Yes, the trick of the riddle is that we are inclined to consider the airplane as a rolling system (practice bias!), Whereas the relationship between the ground and the wheels is irrelevant in the matter, since the wheels are not driving.

[gildas]

Now that the good has been given, are the bad ones admitted?

If the mat is long enough, you have to climb on the mat to travel!

[Petrus]

This treadmill story reminds me of this kind of machine:

[Christophe]

Now that the good has been given, are the bad ones admitted?

Yes starting with (to me) explaining the WTF reasoning of the author and his wheels ??

[Christophe]

AMHA, the reactors push backwards, so the zinc is pushed forward in the same way (reaction). Support is done on the air "horizontally" and not on the track in one way or another. So the zinc moves on, there is therefore a flow of air on the wings, which will create the necessary lift when the speed is sufficient, the zinc takes off as usual.
We can compare this to the operation of the hovercraft, it advances whatever its mode of support (dragging on the ground or a few cm from the ground / water etc ... The comparison stops there because after the hovercraft n is not made to take off.

You make me doubt there!

And so the plane will take off at what speed over the ground for an observer on and off the conveyor belt according to you?

Wouldn't that be a way to reduce the size of the tracks? Why is it not used on aircraft carriers?

And then if he cuts his thrust, carpet moving ... he will back up ... right? Negative speed that will have to be compensated for to have a relative wind creating sufficient lift ... So from when does it "advance" according to you?

Finally, it is more complex than expected!

Wait for ABC's advice