A plane on a runway, how smart is r3vlimited?

[erik325i]

So the plane is moving along the treadmill that is going the same speed as the plane in the opposite direction? That makes no sense.

If the plane would be going 150 then the treadmill will be too.

Exactly, because the runway has no effect on the plane's speed. because... let me say this really slowly... The ... wheels ... are ... free-spinning... The conveyor belt cannot hold the plane stationary.

If the plane is traveling forward though the air at 150mph, the conveyor belt woul be traveling backward at 150mph, and the wheels would be spinning forward 300mph.
Think about it.

-Erik

[RobertK]

Exactly, because the runway has no effect on the plane's speed. because... let me say this really slowly... The ... wheels ... are ... free-spinning... The conveyor belt cannot hold the plane stationary.

If the plane is traveling forward though the air at 150mph, the conveyor belt woul be traveling backward at 150mph, and the wheels would be spinning forward 300mph.
Think about it.

-Erik

So where you live I gues you can simply strap on a pair of skates, stand on a rolling treadmill and you won't be pushed off the end?

Lets get something clear... There is no such thing as a "freespinning' wheel. Even if you put a wheel on a stick and spin it around it will eventually come to a stop. Nothing is perpetual in the real world.

[DarkWing6]

What would it take for the plane to stay in place with the treadmill moving?

[chucko]

The Max speed of the belt is infinite. It is not moving at infinite while the plane it taking off, but simply moving at the same speed of the plane.
For example, the plane is traveling 200mph. The conveyor belt is traveling backward 200mph, and the wheels are spinning forward 400mph.



Also, don't tell me that you can't have a speed larger than infinite. Infinite is not an accual number, so you can't directly compare it to other numbers. Please don't make me take out my old Calculous text books to show that you can have a number reach infinite faster than another. I really hated that class and really don't feel like opening that book again, so just get over it.

I'm over it. I agree that one system can reach infinity faster than another, but you still can't have a speed (meaning numerical value) larger than infinity, the speed of light is less than infinity (isn't it true that infinity + infinity = infinity?). This is the basis of my whole argument. What I'm saying is that my system has a control system which is in synch with the wheel speed of the plane, as the wheels speed up, my belt also speeds up instananteously and this continues until infinity is reached at the same time by both the belt and wheels.

It seems that you understand how everything works, except for how the plane speed is measured now...
Once again, you cannot measure the plane speed by the wheel speed.
Imagine you are in your car at a red light. You rev up the engine, drop the clutch, and hold the brake. What's happening now? You are sitting still at the red light, while your back wheels are spinning like crazy. If you look at the speedometer, it is going to say you are going very fast because it judges your speed by the wheel speed. You are traveling 0mph, but the wheels are spinning very fast.
This proves that vehicle speed is different than wheel speed.

You need to judge the speed of the plane against something that is stationary, not something that has a variable speed (like the conveyor belt). Like I said earlier, picture it this way: a state trooper is sitting in his squad car next to the conveyor belt with his radar gun pointed at the plane. The conveyor belt automaticly goes the speed that the radar gun is reading.

Here, read the original question:

You give some good examples, and I understand what you're saying. Speed=Distance/Time, if distance =0 then speed must =0. This is true, but since you're on a conveyor belt, the distance can be extracted from the wheel revolutions per unit time if the wheel diameter is known. What I'm arguing is perception vs reality. If you walk on a treadmill for an hour at some fixed rate say 5mph, to an observer not standing on the treadmill you didn't travel any distance, however in every way that matters, you did travel some distance. Your body aches as if you actually walked some distance, calories are burned as if you walked that distance, the rubber on your shoe has worn as if you walked that distance. So, for all intents and purposes you did travel that distance. That's what I'm saying here, the planes speed is a function of distance traveled relative to a fixed position on the belt. I know, you all think I'm kookey, but that's how I'm interpreting this problem.

[erik325i]

What would it take for the plane to stay in place with the treadmill moving?

It would take only enough engine thrust to overcome the friction of the bearings, which isn't much.

Imagine this airplane is sitting on a frozed lake. Even if the wheels are locked, the thrust from the jet engines will still be enough to push the plane forward and take off. Even if the ice was on a conveyor belt and moving backward, the plane would still be able to move forward and take off.

The conveyor belt is not going to keep the plane stationary.
Even Ritalin Kid will agree with this one because he knows the plane will move forward. He just doesn't think the plane will get going fast enough because of the friction in the wheel bearings.

-Erik

[chucko]

Umm in the real world.. for the plane to fly.. it means everything.

The plane must first reach the proper ground speed for take off to occur and allow airspeed to do it's job.

If you believe that an airplane engine creates air speed that caused the plane to lift then you are mistake. The engines simply push or pull the engine through the air to create lift they do not provide it.

Tell me this.. will this plane make it?



Now tell me that wheel size and weight do not matter.

I love this, that plane reminds me of a doughnut. Yummy

[Jonathan M3]

What would it take for the plane to stay in place with the treadmill moving?

If you are to take into account the friction between the wheels and the ground, then the engine needs to create a small amount of thrust to oppose this frictional force. Say, 5% of the engine's thrust capacity.

If we are assuming no friction between the wheels and the ground(as one would assume for a controlled experiment), then no forces would be acting on the plane. The plane would remain stationary.

[chucko]

What would it take for the plane to stay in place with the treadmill moving?

An equal and opposite horizontal force counteracting the jet or rocket's horizontal force. The opposing horizontal force in this case is friction of wheels in contact with the belt.

edit-darnit too late.

[RobertK]

It would take only enough engine thrust to overcome the friction of the bearings, which isn't much.

Imagine this airplane is sitting on a frozed lake. Even if the wheels are locked, the thrust from the jet engines will still be enough to push the plane forward and take off. Even if the ice was on a conveyor belt and moving backward, the plane would still be able to move forward and take off.

The conveyor belt is not going to keep the plane stationary.
Even Ritalin Kid will agree with this one because he knows the plane will move forward. He just doesn't think the plane will get going fast enough because of the friction in the wheel bearings.

-Erik

If there was an equation built that allows infinity to be achieved by both objects and friction is no a factor then yes eventually the plane will fly.

Where I work our research is based on real world scenerios so giving answers based on fictional scenerios does not make sense to me. As a matter of fact it's kinda pointeless to argue theories on scenerios based in a non-existant universe.

Here's some more depth to the point I'm trying to get across.





If I had the coefficients I needed I could tell you if a particular plane could fly.

Basically you need an engine capable of putting out a lot of thrust and a larger set of wheels but eventually if you match everything up right the fucker will take off.

As of today I doubt anyone has every built a plane capable of surviving this scenerio short of a Harrier Jet. The tires and/or wheel bearing would most likely explode before achieving the ground speed nessesary for take off.

[erik325i]

eventually if you match everything up right the fucker will take off.

Exactly. The plane will take off.

I completely understand what you are saying about the friction of the wheels though.
The problem is that most people that say the plane won't take off are also saying that the plane won't move at all...
I'm just trying to explain to people (like chucko) that the conveyor belt is not holding the plane in place.

Now that we are on the same page here, lets see you try to convince chucko and uofom3 that the plane will move forward and eventually take off...

-Erik

[Fidhle007]

I honestly think it's all in your interpretation of the original question. When I first read it I thought no, the plane could not take off it the belt were somehow able to keep the plane stationary, but I suppose in the real world (if we discount wheel speed and go entirely with plane speed,) sure, the plane will take off. If it were a car, you'd be measuring wheel speed but because it's a plane, you're measuring forward motion.

I ask you guys this though:

If a CAR were to be traveling at 60 mph, on a conveyor belt that's also moving at 60 mph in the OPPOSITE direction, will the car ever move forward? And if it would and the conveyor belt was 30 miles long, how long would it take before it hit solid ground? And if it ever did hit solid ground, how fast would it me traveling?

I'm tempted to post this as another thread just to see what peoples answers will be.

~Brendan

[chucko]

Edit - Tell me why the plane will not move forward if the only thrust it creates is from a propeller or jet which obviously pushes air to move the whole contraption forward, no thrust or force intended to drive the wheels is exerted on the wheels in either direction besides mechanically being forced to follow the plane. The belt can only move when the plane moves,and at the same speed the plane moves, the planes engine will create enough thrust with the surrounding air, as any airplane does, to move. It will have a little bit more drag from the wheels spinning more once the plane lurches forward and the belt backwards, but thats about where your logic runs out of "road" ha ha get it? funny huh. sorry.

Ok, I've finally decided to read your earlier posts as you suggested. The plane will not move forward if the frictional forces acting on the plane provide a force equal and opposite to the thrust provided by the jet or propellor or rocket. If I throw out my scenario of plane speed=wheel speed (which I still believe is valid), then I do get your understanding of the conveyor belt and plane moving 1/2 of the wheel speed. The more I think about it, the more I can see that the frictional forces acting on the wheels may not be enough to counter the thrust from the engine. In this case I would agree that the plane would move forward while the belt is spinning backward (See I can agree with you). This does not mean the plane will take off before it runs out of runway though. How much time does it take for your plane to reach a sufficient speed to achieve lift? You need specific coefficient of friction values, plane weight, and thrust values.

[chucko]

Exactly. The plane will take off.

I completely understand what you are saying about the friction of the wheels though.
The problem is that most people that say the plane won't take off are also saying that the plane won't move at all...
I'm just trying to explain to people (like chucko) that the conveyor belt is not holding the plane in place.

Now that we are on the same page here, lets see you try to convince chucko and uofom3 that the plane will move forward and eventually take off...

-Erik

haha Dude, why are you singleing me out?
In my fictional scenario the plane will not take off. In a more realistic scenario, then yes the plane should accelerate and take off eventually. Don't know how long that would take though.

[RobertK]

I honestly think it's all in your interpretation of the original question. When I first read it I thought no, the plane could not take off it the belt were somehow able to keep the plane stationary, but I suppose in the real world (if we discount wheel speed and go entirely with plane speed,) sure, the plane will take off. If it were a car, you'd be measuring wheel speed but because it's a plane, you're measuring forward motion.

I ask you guys this though:

If a CAR were to be traveling at 60 mph, on a conveyor belt that's also moving at 60 mph in the OPPOSITE direction, will the car ever move forward? And if it would and the conveyor belt was 30 miles long, how long would it take before it hit solid ground? And if it ever did hit solid ground, how fast would it me traveling?

I'm tempted to post this as another thread just to see what peoples answers will be.

~Brendan

Since the wheel is powered the car would stand still at 0mph. At 61mph the car would be moving 1 mph. After it drops off the conveyor engine would die because it would be the equivlant of doing 1mph in 4th gear. In a car's transmission inertia is it's friend. We've already been over this.

[Fidhle007]

You are right, sort of. I said the car was TRAVELING at 60, not that the speedo was reading 60. And hence I think I illustrate where the discrepancy in the answers to the original question lie. In my scenario, if the the speed of the car were being calculated but a police officer with a laser gun the vehicles forward velocity would be 60 mph but the speedo would read 120.

So lets apply this to the plane scenario and fill in some of the details a bit: The plane is a Piper Cub and the conveyor is moving at 70 mph. If the Cub's foward speed is also 70 mph then the plane will certainly lift off, despite the fact that the wheel speed is somewhere's around 140 mph. I picked a Piper because their takeoff speed is not much over 60 mph and they only need a few hundred feet of runway. Keep everything small and the liftoff argument makes sense I think.