Let me play devils advocate here Rock....

Are you saying that a person sitting on the wing of the plane in your above scenario would feel 100MPH of wind hitting him in the face?

While sitting on the wing of that plane, he would look over his shoulder and see the observer standing there in the same position relative to his seat on the wing of the plane. The observer has no wind hitting him. His hair is not flowing in the wind. Is the person seated on the wing of this plane feeling his hair flowing back in the wind? Can we put a wind sock on that wing and observe a reaction to a 100MPH wind?

...........

Now take note... I am not taking a position any longer on this scenario. Those that argue that the plane would take off or rather should take off seem to be correct.

Also those that claim it may not take off have also offered some valid points and also seem to be correct. (I'm also not talking about those that bring the wheels or other matters of friction or groundspeed into the debate. The debate is beyond those aspects)

I have some further thoughts and questions on the subject, but it involves your answer to the above question I have asked. That answer would lead to further questions possibly regarding the effects of air viscosity and compressibility involved in this scenario. All of which are included in the NASA links and have a direct bearing on the entire subject.

Well... first of all on the balsa wood experiment it would require a lot of calculations to make it a valid experiment vs. a real world situation. You would have to calculate many things such as the torque required on the rubber band engine vs. the weight of the plane against the speed of the conveyor or treadmill, etc. ... and probably many other calculations to make it valid. You would also have to have trials of other similar experiments which would create a control group. Isn't that how scientific research is done? By doing things like that? You can't just spin up a rubber band plane and put it on any old treadmill and call it valid science.

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There is a stipulation in the carrier scenario that the plane remain in the same point in space. There is no such stipulation in the conveyor scenario. In the conveyor scenario, the aircraft can move, regardless of what the surface does.

Maybe the wording of the conveyor scenario is creating our little conundrum and the disagreements.

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Once again, in the Carrier scenario, ROck stipulated that the aircraft must stay in the same position relative to the earth and the air. Of course, if you remove this stipulation, and replace the conveyor with an "infinitely ling aircraft carrier", the answers are exactly the same. The problem with Rock's question is that there's no way the motion of the aircraft carrier could affect a plane that's trying to fly off it, other than steaming downwind.

I'll read the aircraft scenario again. I don't recall it the way you described, but you could be correct.

Can we first arrive at the correct answer to the original scenario, and let the aircraft carrier scenario be moved to its own thread(possibly in the ALR so that zuzuman03 will be happy)?

wow-that took me over an hour to read all the posts. now, what was the question?

It's different.

A harrier is only needing to overcome one force - gravity. It's wings, while the engines *are forcing the air down* don't need forward momentum to create lift.

But that cannot be possible if the conveyor *matches* the speed backwards.

If the plane moves even .1 inches forward, the conveyor belt has failed.

Shhhh....

You're not supposed to ask those type of questions.

Especially since you have already been named in the "enemies list" in this thread.

You guys are a trip. Let me start by not even pretending to have read this entire thread, so if this is old news, forgive me.

The airplane wouldn't fly, and it doesn't matter that the engines move the plane as opposed to the wheels. In the original post, it said the belt has a control system that matches the PLANE'S speed - not the WHEELS' speed. Very important distinction because if that happens, the plane's wheels can spin at any speed but the plane's speed relative to the surrounding air remains zero.

If the plane doesn't move forward, there's no airflow (so-called relative wind) over the wings. No airflow, no lift; no lift, won't fly.

It wouldn't move forward because of the old "every action has an equal and opposite reaction" and the related laws of flight: lift must overcome gravity and thrust must overcome drag.

In our scenario, the "action" of the engines still produces the usual reaction (thrust) but not the usual result because a vital element is missing: the friction of the tires against the pavement. Take away this drag and the tires are still rolling on the conveyor belt but the result is different because the surface is not stationary.

The airplane will not move forward, so no lift will be generated and so gravity wins - the plane won't fly.

Now here's a new one for you:

Assume we're talking about a fixed-wing aircraft (i.e. not a helicopter) that is not a Harrier jet.

The plane's airspeed is 60 MPH but it is flying into a 60 MPH headwind. What is its speed over the ground?

We did.....it's been stated MANY MANY times....the plane WILL TAKE OFF!

BlueSky, what would it matter if the conveyor belt reaches the speed of the plane? The plane is sitting on a set of wheels that are basically frictionless. That only means that the wheels will be spinning MUCH faster than the plane is actually moving forward. The conveyor has an acting force on the WHEELS, NOT the engine. The only thing that can act against the engine is a headwind pushing against the entire aircraft in the opposite direction and with equal speed to the plane. You people just can't grasp the fact that the wheels and the conveyor DO NOT act against the force of the airplane's engines!! WAKE UP!!!

If the airplane were to be propelled by the wheels, then yes, the plane will in fact NOT take off. BUT...that's ONLY IF it's being propelled by the wheels, and not the engines. :rolleyes:

Allright, let me try to explain it this way. You're in your car on wet, perfectly level ice. You try to accelerate, but your wheels just spin and you go nowhere (for the sake of argument). Try as you might, as your tires push against the ice, they get no friction and can't get you moving. If, however, you applied an external force to the car, like a big-ass fan, then the car would move over the ice. Why is the car moving now? I mean, isn't it impossible to apply torque to the wheels to move the car? It's moving because it's NOT pushing against the ice, it's pushing against the air.

Does that convert anybody? I doubt it.

::edited for clarity::

Here's the thing, Moby. If the plane doesn't move, it has no speed. If it sits still with its wheels turning, it's not moving, and therefore, has no speed.

The conveyor matches the *speed* of the aircraft, not the movement.

Dude, you don't have to publish the results of the balsa plane test. There's no Nobel for re-proving basic physics. You're saying it's bad science because it isn't measured first? Accept this for any self-propelled fixed wing aircraft- balsa, canvas, aluminum or whatever- is can generate enough friction with (nothing else but) the air to move forward at a rate of speed great enough to achieve lift. Contact with the surface is incidental.

But they are NOT frictionless.

You have just added a second power source.

The plane does NOT have a second power source.

You're so very close here, until you conclude that the plane's speed is zero. If the conveyor could *magically* keep the plane in a single position, the plane would have no speed. But wait- if the plane has no speed, then the conveyor must also have no speed, as stipulated by the problem.
Whoa-hold up here. Wheels are a means of reducing friction while attempting to move an object-yes? The tires-on-pavement do extraordinarily little to create friction without brakes applied. The plane still moves because it moves air, and there's nothing the conveyor can do about that.
The plane on the conveyor will create forward motion and achieve lift, because it's using friction against something that has nothing to do with the conveyor.

Imagine roller skating on a long treadmill that matches your speed exactly. There's a taut rope directly overhead within easy reach. As you move forward, the treadmill acts to keep you in the same place. If you grab the rope and start using it to push yourself forward, hand over hand, and your wheels are just touching the treadmill, will the treadmill be able to stop you from propelling yourself forward using the rope? No, because you're applying force to the rope and your wheels are reducing friction with the treadmill.

Of course an aircraft with a 60 knot headwind and 60 KIAS will have a groundspeed of zero. I've seen a plane with a 140 knot headwind remain motionless 6000 feet over an airport for about five minutes before I asked him if he thought he was going anywhere. When he realized he wasn't, he turned around and got home in a hurry.

Right, but the plane does not create its movement by pushing against the ice/ground. Put a plane on that same frictionless ice and it will still move whenever it wants to, because it moves by pushing the air, not the surface.

Ugh.

A rope is NOT fluid. The air IS.

The rope is tied to something. The air is NOT.

The wheels are NOT frictionless.

Heck, even ice has *some* friction. If it didn't, you wouldn't slow down on ice skates.

OH. MY. GOD.

You've been fucking with me this whole time, haven't you? Do you mean to say that an aircraft cannot move itself forward using fluid air?

That's the bad assumption of everybody who thinks the plane doesn't move.

The ONLY rearward force on the system is a nominal amount of friction on the wheels (which spin FREELY!). This will NEVER be enough to prevent forward motion against thousands of pounds of thrust.

Go back in the thread and look at the free-body diagram (FBD). Also look at my t= scenario which explains how the conveyor belt will affect the system.

As I said before. This is not rocket science or an aerospace engineering problem. This is a 9th-grade Physics problem that requires the person to understand how an airplane propels itself (the wheels aren't involved in propulsion). If people don't, at least, have that background, they should refrain from comment.

There is one recognized correct answer to this problem. Look at the FBD, stop getting hung up on the conveyor belt, and disregard rockaholics invalid scenario. ONLY THEN will you be able to come to terms with the recognized correct answer.

The plane flies.

Good luck!

Yea, it was a hypothetical. Maybe I should have said "magical frictionless surface" instead. Regardless, the plane would move on the ice, even if its brakes were locked and a car couldn't get rolling in any direction.

I'm saying it is a bad scientific experiment to use as proof of the hypothetical scenario in this discussion of the aircraft and the conveyor belt.

With the way you are proposing the balsa wood plane experiment, you are moving away and beyond the conditions set in the original hypothetical scenario.

You keep forgetting that in the original scenario the conveyor matches the aircraft's speed. Without the numerous calculations I mentioned in my earlier post you are not duplicating the conditions for the hypothetical scenario by just spinning any rubber band plane over any treadmill.

So if the conveyor/treadmill had greater speed to begin with and the balsa plane still took off, the result would somehow be different if you could make the treadmill accelerate at the same rate as the plane?

I don't know how fast traditional treadmills go, but I'm fairly sure balsa planes cannot go faster than 10 MPH (being generous to the plane). So supe up a treadmill, set it for 20 MPH, and try it again. I guarantee you the balsa plane would take off.

I don't care about the speed of either.

We are talking about the hypothetical scenario. If you wish to create an experiment to use as proof... you would need to calculate all of the numbers and match the speeds of each.

Otherwise we are no longer talking about the hypothetical scenario.

If this is being discussed all over the internet, why hasn't anyone tried to do a scale model experiment with a remote controlled aircraft?