Imagine a plane is sitting on a treadmill

@Tom17 - explain how it is moving then. And where is it moving to. And how lift is achieved when no air is moving over the wing.
In fact I could climb onto the wing and tap-dance or cartweel on it and nothing will happen to me (unless I fall off!)

I'll take this as Eurovol admitting defeat, he clearly does not have an answer to explain where all that energy is going.

@ eurovol

If you ever feel like trying to break the first law of thermodynamics, let me know and make sure you're insured.

Not the way I see it, it hasn't.

righter... take the matchbox test.

Do i really have to repeat myself *again*. We have been giving reasons for the entire thread! Can't you just read what we said on the first couple of pages? It covers this!

Then you have an answer to his question?

Eurovol has given up. No-one else has challenged the interpretation, and if they do they will lose.

OK, it fires the core of a nuclear reactor that then converts water to steam that turns the turbine to turn the conveyor belt. Or fuck it, just use a windmill.

So... do they have Marmite in those little handy sized sachets on this flight?

The question says everything else is normal. It's no good eurovol.

Challenged what interpretation? That the "it flys because of the jets crowd" have become beligerant asses? I rather agree with that interpretation. I will say it again, it matters not where the propulsion is coming from. Even if the wheels were powered, it still doesn't matter.

This is easy and, being a duck, I am more than qualified to answer this.

When I run along the duck-treadmill, ready to take off, I am not using my legs to propel myself, but using my wings. When the treadmill goes too fast, I cannot run any faster so I fall flat on my beak before I can get any airspeed.

As aeroplanes use feet on legs to go along the runway just like people and ducks run on treadmills, any analogy with someone running is spot on.

Therefore the plane will just sit there! Its QUACKING OBVIOUS!!!

Quack

@ eurovol

What matters is not where the energy comes from, but where it goes. I have an answer - do you?

I didn't think I was being beligerent.

It's not only the jets. It's jets and free-spinning wheels. If the wheels were not free-spinning we'd have other issues.

I read them again and belligerently, I say, the plane is going nowhere! So, Tom, seems you will have to repeat yourself *again*.

*Not sure if 'TheDucks' is being serious or not, so doesn't react*... his legs are not 'free-spinning', so we get a limitation, as I said last post.

@ righter

If you can answer these questions you have an argument. If not, you've lost.

The engines provide thrust. As the wheels supply no significant resistance, the plane moves forward in relation to the non-moving ground/air. As it does so, the treadmill starts to move in the opposite direction, i.e. backwards wrt to the plane.

There

Where does the energy go when the brakes are applied and the engines are fired up? The energy is transfered to the wheels which are transfered to the 'virtual brake' of the conveyor belt, as Sin has already stated.

*matchbox car... paper...*

The scary part is that only a fraction over 50% of the people believe that the plane will take off despite the fact that it happens every day... The earth is 12000km in diameter at the equator. It rotates once every 24hours giving it a surface speed of almost 1600 km/h west to east. This is way faster than the speed of a plane at take off... So if there are airports anywhere in the world where the planes take off by taxi-ing east to west then they are effectively taking off from a giant treadmill.

It is not the jets. It is the wording of the question. The jets are irrelevant as you could even use a car to push it or pull it. Of course, it couldn't fly very well.

In a normal situation that energy is transferred to the air - it makes it (and you) go wishhhh if you are standing behind the engines - it also sucks you in to the engines if you are standing in front of them... Hence the little spiral decal to warn you that the energy is being transferred to the air and not the brakes.

And that is a premise for the 'it wont fly' argument. Lift cannot be produced in this senario.

Ok, so tell me, you are standing on an apron staring at this screaming beast that is just bursting with uncontrollable energy in front of you. At which point does the nose lift? How much energy is needed to lift the nose if all that is needed is thrust from the engines.

No, they're integral. The point is, that forward motion is not dependent on the contact with the 'ground'.

A bit of it goes into potantial energy stored as flex in the frame of the plane/suspension and the tyre carcass. The rest of it, as the system is in effect a springy/rigid body with the ground, goes to the planet. The effect of which is a small amount of change in the planets angular momentum... Not 100% sure on this but makes the most sense.

Dont forget though, the plane with brakes *off* is no longer a rigid body in the force diagrams as the wheels essentially decouple the plane from the ground/treadmill.

Uh, you might want to go talk to people flying gliders. The manner of propulsion is irrelevant.

Where in the q. does it say the brakes are on? Freely rotating wheels will not transfer any more than a tiny fraction of the engine's energy to the treadmill.

Err.. re-read what I said...


THE PLANE MOVES FORWARD IN RELATION TO THE AIR - i.e. airspeed - i.e. lift - i.e. takes off


It would lift at the point that the plane reaches its take-off speed in relation to the stationary ground/air. Duh

No, they use gravity to provide airspeed, which then provides lift. They get their initial potential energy by being towed or by launching from a high place, and then go searching for more lift in the thermals.

What? How does a glider get to a speed where there is enough lift for it to take off?

EDIT: Beaten to it.

This is where your argument is flawed. The plane doesn't move anywhere. It is fixed to the spot, fighting with the opposite motion of the conveyor belt.

Please please tell me I am not the only person to realize that the bit about the conveyor matching the plane's speed was totally irrelevant to the question, and was purposely included in the wording to throw people off. A conveyor belt working as an "opposing factor" is illogical, because the free spinning wheels completely cancel it out. Thus what we are left with is a a plane sitting on a tarmac, wheels spinning, conveyor belt moving, plane sitting still. THAT IS until you apply a separate force, in this case turbine engines, which move air and thus the plane.

not quite. the atmosphere spins with the earth which is not the case here.
i am a believer btw. the plane will takeoff.

@ righter

Why is it fighting? The conveyor rotates one way, the wheels rotate the other. Meanwhile the engines are moving the plane forward.

Edit: if it was a car, in gear, the engine would be fighting. Not if it was in neutral. Or a plane.

So in my walking-beside-the-luggage analogy are you seriously telling me that if someone sped up the conveyor belt you would encounter any resistance to pulling your luggage??

The conveyor belt does not give it anything to "fight" against. The rolling resistance of the tyres, even at twice the specified take off speed, would be insignificant compared to the thrust that the engines produce.

On the side...
Interesting tidbit I discovered while doing some background research on this thread. Rolling resistance is, apparently, not dependent upon speed. So the force due to rolling resistance at speed x is the same as the force due to rolling resistance at speed 2x. This does not seem intuitive to me right now so I will have to delve into this deeper another time. Glad I learned something in this thread though

Mental Masturbation

The act of engaging in useless yet intellectually stimulating conversation, usually as an excuse to avoid taking constructive action in your life.

Guy 1: "If only I had taken Cindy to my high school prom, I could have fucked her instead of that loser Jeff and then now she would be my girlfriend."

Guy 2: "Dude, stop that mental masturbation right now and go out and meet a new girl!"

or

Guy 1: Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyor belt is designed to match the speed of the plane exactly but moves in the opposite direction. The engines are running at take-off thrust, the brakes are off, etc. Everything is normal save for the fact the plane is on a treadmill.

Can the plane take off?

If the belt is big enough and rough enough and stays on lon enough the air in its immediate vicinity will start to move with it too.

And it's 'goodnight' from me... and it's 'goodnight' from him.

I can't believe that with the poll, we have 50 people with the correct answer, and 45 people who either think no, not enough information or just don't know. This is not very encouraging.

Lots of people have voted and then been convinced. Still not very encouraging though.

Exactly why did he choose to have sex with Jeff?

Why hasn't anyone even mentioned the wings' angle of attack?

woof.

Because


So the wings are at the normal angle of attack for a plane while gaining speed and taking off.

Take them outside and shoot them. Now. Please! We have the gene pool of the next generation to protect!

It has been resolved, there are just a few people who mis-read the question and refuse to open their minds to the truth. 1+1=2, no matter how many idiots think it's 3. True that re-reading won't help until people take a step back and question their assumptions.


I think that's scheduled for pages 75-100, we're not there yet.

And if they are as STOOOOOPID as they seem, they can read it a 1,000 times and will never get it

We haven't discussed what kind of aircraft it is yet, either. I'd suggest an F4 Phantom.