Counter-intuitive science questions.

Don't they tip it forward, Man
But I dunno what the thing looks like
Suppose oughta Google it but please Man save me the trouble

Are you asking whether tipping the engine forward would reduce lift

I'd guess so, but I'd also guess they'd speed up the engine to compensate, lat least til they had achieved adequate forward speed

my point is that theres gotta be a point that is just below "forward flight" and upward lift that the engine has got to overcome. There seems some inherent instability built in (as if HTA flight was a stable concept)

The gadget that determines the speed of the belt can sense the rotation of the wheels and tunes the speed of the conveyer to be exactly the same speed as the wheel.
Here is the answer:
Whether jet engines or propeller driven, the plane achieve flight by pulling themselves through the air, where air rushing over the wings gives it lift and enables flight. On a normal runway, the rotation of the tires results in forward movement, but has no bearing on the behavior of a plane during takeoff. With a conveyer belt, regardless of how fast the conveyor belt is counter rotate, the propeller or the jet turbines shove the air backwards and create thrust and this won't let the plane to remain stationary. Essentially, the propeller or the jet turbines would continue to provide power to move the aircraft forward, just like it does in the air and how fast the wheels are spinning is irrelevant. The wheels may be spinning at a much higher RPM in this case, but that doesn't affect the plane at all. The propellers are pushing against air as opposed to a car where the wheels push against the ground to go, and soon the engines will exert thrust and the aircraft will acquire airspeed, and will liftoff regardless of the presence of the described high powered conveyor belt.

why is a banana a berry but a strawberry is not?

Assume you are in a boat on a lake and in the boat with you is a large rock. If you throw the rock into the lake and it sinks, what happens to the level of the lake (goes up, down or stays the same)? What if the rock is made of pumice and it floats?

I think this is my favorite... it still seems wrong to me (intuitively that is).

Seems even more wrong when you do it for Jupiter and a beach ball and get the same answer.

People have invented all manner of things for flight. But we've been unable to duplicate the flight of birds. You'd think that this would have been step one.

Can you provide a better citation for this?

Even if the wheels are just rolling and not used for propulsion, there is still friction from the conveyor belt, which counteracts the propulsion.

Once the airplane starts forward motion, the conveyor belt and the wheels are no longer balanced. Per your conditions of the experiment, this is not possible.

The only way the airplane could take off is if there is a massive headwind.

Similar to Engineer's stone in a boat: Place ice in a glass, fill the glass to the rim. Some of the ice will be out of the top of the water, which means that it will be out of the top of the glass. What happens when the ice melts?

I heard this one a little differently. The question they asked was, how much string do you have to add, in order to get the string 1 meter from the ground?

Then they asked the same question about a 10-inch diameter ball.

The answer to this is a qualified yes. The answer is qualified by initial conditions. The phenomenon is known as the
Mpemba effect.

Why do mirrors appear to reverse images horizontally, but not vertically?

Why do baseball players make their bats lighter in order to make the ball fly further?

Get two pots of the same size, and put the same amount of water in them.

Bring one to where it is barely simmering. Bring the other to where it is at a roiling boil.

Is one pot hotter than the other?

Are there more rational numbers or irrational numbers?

The thing you're not taking into account is the differentiation of air speed and ground speed. The conveyor only effects the ground speed and has no control of air speed. For the force of friction to be greater the force of propulsion, the wheel brakes would have to be engaged. Since conveyor belt simply moves at an equal and opposite velocity to the plane's wheel, then the plane will take of since the force applied to the plane by the conveyor belt will never be enough to fully oppose the thrust of the engines, being that planes do not apply their thrust via their wheels, and the plane will eventually accelerate and gains movement and by Bernoulli Principle, the plane will lift off (all the while assuming that the wheels are hardy enough to not blow out before lift off).
If you don't take my word for it: Conveyer-Belt Runway, Straight Dope Analysis.
And I think Myth Busters did a sketchy real simulation on it. You'll probably be able to find the video somewhere.

No, I did take that that into account.

Maybe the way you described the experiment is incomplete, but by the terms you gave us any increase in thrust by the aircraft will be counteracted by an increase in drag (by the conveyor belt). This will result in a net acceleration of zero.

Like I said, a headwind will get the plane off the ground. (So, yes, I did take into account the difference between ground speed and air speed.)


The whole proposal is silly, but that may be the most silly of all. When the plane is at rest, the wheel has no "velocity" and is not rotating.

Either a) the conveyor belt makes sure that the net acceleration is zero, thus preventing the plane fro taking off or b) the conveyor just moves in the same direction as the airplane, making sure the wheels never have to turn.



I understand the whole point is to demonstrate the difference between ground speed and wind speed. The idea itself isn't that counter intuitive; you've just constructed a poor way to visualize it.


I think a better way to visualize it would be to ask, what is the minimum air speed required for a fixed wing aircraft to make a vertical (i.e., zero ground speed) take off or landing? As long as the wind speed is above the stall speed, then the aircraft could do so.

The reason I like the boat version better is that some people will tell you the lake level goes up, most other people including just about all engineers will tell you the lake level stays the same, but very few people will correctly say the lake level goes down.

Well your option a) can be achieved under certain parameters that lie outside the normal conditions. Because under normal conditions the effect of wheels, speed of the conveyor belt and rolling resistance together, these two effects would be less than the thrust of the engine. If the effects of air motion overcome the effects by the wheel, lift off is assured. One could consider that if the conveyor belt was very large, there will be some effect on the air above it, and it will tend to drag air backwards to create some headwind (albeit the effect on the overall plane will be low). Because these two variables can be independently controlled, putting new parameters on the plane, flight can be incapacitated, such as making the effects by the wheel overcome the effects of air motion (not lubricate the wheel bearings or engaging wheel brakes, etc.).


That maybe, but the idea of the question is to get the thinker to take into account the difference between air speed and ground speed, and consider whether or not if the plane will remains stationary relative to the earth and, more importantly, to the air under the provided parameters.

And unless they have taken a few physics courses, this concept may likely seem counterintuitive. To some it may even seem like a modern day paradox when they hear the answer.