Do we have to do the plane thing again?

But if the propeller is at max speed and pushing air past it at 80mph then the plane would move on its wheels 80mph forwards. And then obtain lift.

But if on conveyer belt then it would not. Because it would need to pull 160mph air past it. But the engine was at max when doing 80mph.?

The prop will propel the plane forward, but the movement is being cancelled by the conveyor belt. There's is no process for moving the wings through an air mass.

Yeah if you throw it forward. i know that.

Im talking about throwing it backwards, the opposite way of the train.

I think i understand this now though.

No and no. We've already been over this a million times! They even proved it on Mythbusters. The aeroplane WOULD take off!

Damn, you replied before I did my edit.

Actually, now that I think about it, I'm guilty of what I was advising against in the first place.

Edit: My apologies for not being part of the conversation the million times prior to this.

hmm well i still don't fully understand it. Because the plane requires the wheels to be connected with the ground to get up to a speed where it can create its own lift and take off and not require the ground anymore. So how does it go faster than the conveyer belt when it is still dependent on being in contact with it to get up to speed ?

arghhhhhhhh. I just want to get my head round how.

I understand that the prop would be pushing air back, but that would not be going over the wings? therefore i cant see how it can leave the ground.

The conveyor belt would be unable to cancel the forward movement because the prop propels the airplane forward, not the wheels. As I now understand it.

Edit: It's kind of a trick question because the average person assumes that the conveyor belt IS able to cancel the forward movement.

Because it's not. The wheels do not provide the propulsion - it's as simple as that.

Think about the speed of the wheels when the plane takes off of stationary ground, then add the additional speed of the conveyor belt moving. The wheels do no work therefor the plane still moves forward, the wheels are simply just compensating (moving faster) for the belt.

Ok ive got it i think.

Because i thought if you pushed a toy car along with your hand on a conveyer belt, it takes the same effort as it would to push it forward you if are non moving ground. You dont have to move your hand any faster to make the car go the same speed. because it is not driven by the wheels?

And to hold the car stationary you dont need to push it at the same speed of the belt. you simply just put your finger behind it.

So take that over to the plane and i get..

The planes thrust would still be the same, and would displace the same amount of air and pull its self forward at the same speed regardless of if the ground was moving. Ive got it now :D


Now it would be a different story if you had a 80mph thrust and a 80mph wind from behind the plane. The plane could then not take off i assume :D

Yep.

Now it would be a different story if you had a 80mph thrust and a 80mph wind from behind the plane. The plane could then not take off i assume :D If you meant the wind blowing towards the front of the plane, then yes the plane would not take off

No i meant a back wind. Because moving forward at 80mph with a 80mph back wind coming from behind the plane. Then the effective wind over the wings would be 0mph. so no lift.

Its same as the car on a conveyer belt principle as far as i can see. i think :/

If the wind's coming from the rear of the plane it would be pushing the plane forward.

hmmmm

But if the plane was going/being pushed at 80mph with wind behind it going at 80mph, then the plane would not have any air flow over the wings. Because the speed of the plane minus the speed of the wind in the same direction would mean no air would be going over the wings?

the air at the wing area would effectively be 0mph i think.


Where as if the plane had a head wind from the front it would be able to take off even easier because of the speed of the plane PLUS the wind, would create more air speed over the wings and thus more lift.

Well pilots always take off and land in a headwind for this reason. The runway at airports always directs planes into a headwind. If that wind changes then they close the end that was open and open the other end for a head wind takeoff/landing. http://www.discussworldissues.com/fo...lies/wink1.gif

I get ya.

So we know what can stop a plane from taking off, a back wind of the same speed.
And we know a conveyer belt as the same speed as a car will stop it from moving.

So what stops a rocket ? Another rocket of the same power would be the only thing im guessing then ? Or a concrete cloud :D

EDIT: nm, Obviously a rockets opposite force is gravity thinking about it. duh

A plane going 100mph isn't going to stop dead if it hits a 100mph headwind. It depends on the wind resistance of the plane etc. It's not quite that simple.

Here is an easier way too look at the same problem. Replace wheels with skis, and cover the conveyer belt with ky-jelly. Will the plane take off? Yes.

Good old air is pretty good if the rocket is going fast enough. The space shuttle has to throttle down to something like 70% about a minute after launch to prevent it from building up too much speed as the density of air is high enough to knacker it.