The great conveyor belt

You are evil, Jesse.

I think at this point, the main confusion is that there are two distinct problems posed, and people get mixed up between them:

Problem One: The conveyor control system is rigged so that the backwards velocity of the conveyor belt is equal and opposite to the forward velocity of the aircraft in relation to a fixed observer (aircraft moves forward at 60 knots, conveyor moves back at 60 knots, wheels spin at 120 knots but aircraft takes off just fine.

Problem two: The conveyor control system is rigged to increase speed to whatever speed is required to keep the aircraft in a fixed position relative to an outside observer. In this case, the friction in the wheels is much less than the thrust of the propeller, so the conveyor is very quickly accelerated to such a massive velocity that the wheels burst or the bearing fry and the aircraft falls onto the conveyor and can't take off.

Problem 2a: If the wheels were frictionless and rated for infinite speed, the conveyor would increase to an infinite speed. Due to the boundary layer of the conveyor belt(the air being dragged along with the conveyor belt), the aircraft would take off straight up like a helicopter.

Problem 2b: If the wheels were rated to infinite speed and fictionless and the conveyor was dragless, the conveyor would accelerate towards the speed of light and its mass would increase to infinity and time would stop for it. I'll need the help of a physicist here, but when the mass of the belt approaches infinity in the aircraft's reference frame, the gravitational attraction would also increase infinity, right? Will the conveyor turn into a long black hole (worm hole?)? If so, the aircraft can't take off.

Problem 2c: All the above and a massless conveyor so there are no relativistic effects. Aircraft takes off. Pilot sells patent for massless, dragless, conveyor belts and retires.

Chris
 
flyingcheesehead said:
I vote we lock the thread, and throw Jesse in the river at Gaston's. :yes:
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I vote we throw Jesse in the river, on general principle, film it, post it as a special-edition video Pilotcast, give him a wedgie- a power wedgie- then we make him snort green lake water out through his nose backwards while Nick Nitro piledrives him onto the canvas, administers the abdominal claw, and make him...

...ummm...

...where was I, anyway?
 
So, how can this gizmo possibly work since it is ONLY a belt... nothing more?

And, if you can't determine this, I'll settle for a dissertation on the legitimacy of... the existing weight and balance after sun visors have been replaced with lighter sun visors. Assume no other changes have been made. Does that .3 pounds less on the specified arm and overall aircraft weight make the aircraft unairworthy since the W&B is not current?
 
KennyFlys said:
So, how can this gizmo possibly work since it is ONLY a belt... nothing more?
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My understanding is that it's a belt, power for the belt, and a control system. The contol system would include sensors for aircraft movement and a crude logic system.

Tony, how'd your control's exam go? Can you design us one of these? We need to run an experiment at Gastons with a full size rig (to match Reynolds number)

Chris
 
alaskaflyer said:
I meant forward in relation to the moving conveyor belt (here we go with the wheels thing again!) not the real world :redface:
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Spin the belt at 100 mph. I will land on it. Come to a complete stop (using thrust to hold myself in place) and takeoff again. Now do you understand how you could takeoff? The air is what you use to pull yourself over this belt. The wheels don't matter.

Get me some really good bearings and some really good tires. Spin the belt at 500 mph and I'll do the same thing.
 
cwyckham said:
My understanding is that it's a belt, power for the belt, and a control system. The contol system would include sensors for aircraft movement and a crude logic system.
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But, there is nothing to account for what allows a plane to fly in the first place! I've not heard anyone mention this belt is in a wind tunnel.
 
EdFred said:
Can an airboat go upriver?
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Yep, but it doesn't take off.

Here's a question related to yours: A seaplane is on a swiftly flowing river. While traveling downstream with the current the pilot taxis carefully out to the middle, points it upstream, configures it for takeoff and applies full throttle. However, the water is flowing so fast that even at full throttle the plane eventually matches the current flow but cannot overcome it. The plane is traveling in excess of its takeoff speed in relation to the water flowing past, but in relation to the bank and the body of air immediately around the plane it is sitting still. Will it take off? Hell no.

I know that when hang gliding one needs approximately 25-30 mph to maintain a positive rate of climb (I have no idea if that is true but take it as an example.) So I strap on my hang glider, get on my stationary bike and peddle like heck until the odometer says 30 mph (I'm a very strong biker :D ) Will I suddenly rise off the saddle of my stationary bike and levitate up into the air? Hell no.

It is the same basic situation in your original scenario. Now go away boy, you bother me :mad: :P
 
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alaskaflyer said:
Here's a question related to yours: A seaplane is on a swiftly flowing river. While traveling downstream with the current the pilot taxis carefully out to the middle, points it upstream, configures it for takeoff and applies full throttle. However, the water is flowing so fast that even at full throttle the plane eventually matches the current flow but cannot overcome it. The plane is traveling in excess of its takeoff speed in relation to the water flowing past, but in relation to the bank and the body of air immediately around the plane it is sitting still. Will it take off? Hell no.
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lmfao. You've got to be kidding me...

You are comparing the WATER RESISTANCE of FLOATS in *extremely* fast water to the same thing as wheels on a conveyor belt. I'm sorry--they're not. There is no possible way you could provide enough FRICTION to overcome the thrust of the prop without ripping the tires and bearings into shreds.
 
Can we discuss the theory of relativity, instead?

There's no relative wind flowing over the wings so it won't fly!
 
jesse said:
lmfao. You've got to be kidding me...

You are comparing the WATER RESISTANCE of FLOATS in *extremely* fast water to the same thing as wheels on a conveyor belt. I'm sorry--they're not. There is no possible way you could provide enough FRICTION to overcome the thrust of the prop without ripping the tires and bearings into shreds.
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Well, you've obviously never flown a plane with a C-85 engine :D
 
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KennyFlys said:
Can we discuss the theory of relativity, instead?

There's no relative wind flowing over the wings so it won't fly!
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No wind tunnel required. If we assume the case where the belt is wired so that it moves backwards at the same speed that the aircraft moves forwards (relative to a fixed point): The aircraft is moving forwards at 60 knots relative to a fixed point and the belt is moving backwards relative to a fixed point at 60 knots, then the aircraft has 60 knots of relative wind and will fly. The wheels are spinning at 120 knots.

Chris
 
alaskaflyer said:
It's all about the airflow on the airfoil. The rest is smoke and mirrors.
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For your seaplane example, I like to think of it more in terms of net force. If there's a net forward force, the aircraft will accelerate forward. So if the thrust of the prop is greater than the drag against the floats due to the river running by, you go forward. If you go forward, you get airflow on the airfoil and you can take off. The difference between the stream and the conveyor, as Jesse pointed out, is that you have significant drag in a stream but very little on a conveyor.

Chris
 
But, then you're moving forward in reference to the point where the belt is supposed to be placed. Unless you get wind flow, it's not gonna fly. You can have all the ground speed you want but with no airspeed... forget it.
 
So if the plane is traveling at 60mph foward (relative to a fixed point) and the conveyer belt is running bakward at 60mph (relative to a fixed point) and the conveyer belt stopped would it sling the plane foward at 120mph?

Even if this senerio was a car and the car was moving foward at 60mph and the belt was moving backward at 60mph the speedometer would read 120mph but it would still be moving foward because if it did not move foward than the belt would not move backward.
 
jesse said:
Spin the belt at 100 mph. I will land on it. Come to a complete stop (using thrust to hold myself in place) and takeoff again. Now do you understand how you could takeoff? The air is what you use to pull yourself over this belt. The wheels don't matter.

Get me some really good bearings and some really good tires. Spin the belt at 500 mph and I'll do the same thing.
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Tires that good would be too heavy to use. All the real high speed wheeled vehicles I've dealt with had turned aluminium wheels contiguous with the contact surface, ie no rubber at all, just turned alloy.
 
KennyFlys said:
But, then you're moving forward in reference to the point where the belt is supposed to be placed. Unless you get wind flow, it's not gonna fly. You can have all the ground speed you want but with no airspeed... forget it.
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As I posted earlier today, there are two flavors of this question. They have different answers. Here's the original question for this particular thread:

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The question is:

Will the plane take off or not? Will it be able to run up and take off?
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The conveyor is the size of a runway, so you're not going to move beyond where the conveyor is. Since there's no wind mentioned, we'll assume it's zero. Therefore, groundspeed is identical to airspeed, as long as we mean actual groundspeed compared to a fixed position and not compared to conveyor speed.

The airplane goes forward at 60 knots, the conveyor goes back at 60 knots. Because there's 60 knots of wind over the wings, the airplane flys. The wheels spin faster, but that doesn't matter.

Chris
 
JRitt said:
So if the plane is traveling at 60mph foward (relative to a fixed point) and the conveyer belt is running bakward at 60mph (relative to a fixed point) and the conveyer belt stopped would it sling the plane foward at 120mph?
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The plane no. A car yes. Why? How each of them gets its forward force.

Even if this senerio was a car and the car was moving foward at 60mph and the belt was moving backward at 60mph the speedometer would read 120mph but it would still be moving foward because if it did not move foward than the belt would not move backward.
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No I can't agree here. The car would not move on the belt relative to the ground if the belt matched speeds, because the car is physically connected to the belt's momentum. The engine drives the wheels, the wheels push against the belt and the car goes forward relative to the belt, but the belt goes backwards at the same speed.

The airplane engine is not linked to the wheels, its linked to the prop. The plane pulls forward and the belt starts going backwards and the wheels, which are free spinning, simply go faster.

Its like those test wheels at the Emissions stations - you put the car on the wheels (runners? bearings?), engage them (or actually release them) and then run the car and it goes nowhere. If you put a plane on those same wheels and released them, and started up the plane, it would pull off the runners and they'd never even turn.
 
Chuckle. Snort.

Milk on keyboard, through nose.

This thread is a testament to...

...to what?

Sadism. That's it, sadistic, cruel, evil.
 
KennyFlys said:
Does that .3 pounds less on the specified arm and overall aircraft weight make the aircraft unairworthy since the W&B is not current?
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Of course it does, if you have thoroughly p***ed off the FSDO Inspector who catches you on the ramp check.

-Skip
 
Ok, I got it. Maybe this will make sense....maybe.

The conveyor belt is set at a 45º angle. A plane/wagon/rubber ball/guy-on-roller-blades, anything that rolls without power being sent to the wheels is set at the top of the conveyor belt. The conveyor belt is turned on to move upwards when the plane/wagon/rubber ball/guy-on-roller-blades is released. Will the plane/wagon/rubber ball/guy-on-roller-blades roll down the incline? If you say no, what about if the angle was 60º, or 80º ?

Gravity is an outside force (relative to the wheels/belt) acting on the plane/wagon/rubber ball/guy-on-roller-blades, just like the propellor of the plane is. Especially if the airplane has an acceleration of 32.1f/s2
 
EdFred said:
Ok, I got it. Maybe this will make sense....maybe.

The conveyor belt is set at a 45º angle. A plane/wagon/rubber ball/guy-on-roller-blades, anything that rolls without power being sent to the wheels is set at the top of the conveyor belt. The conveyor belt is turned on to move upwards when the plane/wagon/rubber ball/guy-on-roller-blades is released. Will the plane/wagon/rubber ball/guy-on-roller-blades roll down the incline? If you say no, what about if the angle was 60º, or 80º ?

Gravity is an outside force (relative to the wheels/belt) acting on the plane/wagon/rubber ball/guy-on-roller-blades, just like the propellor of the plane is. Especially if the airplane has an acceleration of 32.1f/s2
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Depends on the value of g and coefficient of static friction between wheels and conveyor, and the value of -ycos(theta).

:D

If -ycos(Theta) = g or is greater than g then the object will not go down, it may in fact go up.
 
smigaldi said:
Depends on the value of g and coefficient of static friction between wheels and conveyor, and the value of -ycos(theta).

:D

If -ycos(Theta) = g or is greater than g then the object will not go down, it may in fact go up.
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mu = .01

There, happy? LOL

On second thought it would really be the coefficient of friction between the wheels and the bearings. Even if mu =1 between the wheels and belt, and mu ~ 0 on the bearings, it would still roll down the hill.
 
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smigaldi said:
What value of g are you using?
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Well, lets say that we use metric units and g = 9.8m/s2
The ramp is a 45 degree angle, meaning we get net downward force of m * 0.707 * 9.8m/s2 correct?

Say the plane weighs 1000kg so that 1000 * .707 * 9.8m/s2 = 6928.6N

The force of gravity on the plane is 9800N, so as long as the coefficient of friction of the bearings is less than, oddly enough .707 - the thing will roll downhill.

If I get some bearings such as these:
http://www.danahermotion.com/products/product_detail.php?parent_id=245

wheel (we'll) be A-Ok for rolling down the hill.

With those bearing the belt would have to be accellerating 1000 times faster than the plane for it to stay still.
 
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Now, at what speed would the conveyer need to run to overcome gravity?
 
EdFred said:
Well, lets say that we use metric units and g = 9.8m/s2
The ramp is a 45 degree angle, meaning we get net downward force of m * 0.707 * 9.8m/s2 correct?

Say the plane weighs 1000kg so that 1000 * .707 * 9.8m/s2 = 6928.6N

The force of gravity on the plane is 9800N, so as long as the coefficient of friction of the bearings is less than, oddly enough .707 - the thing will roll downhill.

If I get some bearings such as these:
http://www.danahermotion.com/products/product_detail.php?parent_id=245

wheel (we'll) be A-Ok for rolling down the hill.

With those bearing the belt would have to be accellerating 1000 times faster than the plane for it to stay still.
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What happens if there is a tailwind of equal speed as the thrust?
 
Greebo said:
Now, at what speed would the conveyer need to run to overcome gravity?
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See above. I posted it just as you asked the question. Oddly enough it would have to accelerate at 707G or 6928.6m/s2
 
smigaldi said:
Yep. And that is the only way that this whole problem does not work.
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So if the conveyor belt was hooked to a giant fan which followed behind the plane.......

BTW, my argument was to show the plane WILL take off, just as it would roll down the incline.
 
cwyckham said:
The airplane goes forward at 60 knots, the conveyor goes back at 60 knots. Because there's 60 knots of wind over the wings, the airplane flys. The wheels spin faster, but that doesn't matter.
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The original terms seem to be changing to fit the argument. This plane, as described below, will not fly!

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The question is:

Will the plane take off or not? Will it be able to run up and take off?
Click to expand...
 
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