Airplane on a Conveyor Belt...

[2bighorn]

Originally posted by eskimo2
Believe it or not, the traction requirements for this scenario are no greater than the traction needed to hold a plane on a tarmac with its engines on full power and it brakes on full – locked.

Is that why ball in second film  doesn't stick to your belt (paper, fabric or whatever it is)?

Why don't you calculate real world example, a small plane like Cessna 172?

Here, some data to start with:
# Length: 27 ft 2 in (8.28 m)
# Wingspan: 36 ft 1 in (11.0 m)
# Height: 8 ft 11 in (2.72 m)
# Wing area: 174 ft² (16.2 m²)
# Airfoil: NACA 2412 (modified)
# Empty weight: 1,620 lb (736 kg)
# Useful load: 830 lb (376 kg)
# Max takeoff weight: 2,450 lb (1,113 kg)
# Powerplant: 1× Lycoming IO-360-L2A flat-4 engine, 160 hp (120 kW) at 2,400 rpm
# * Zero-lift drag coefficient: 0.0319
# Drag area: 5.58 ft² (0.52 m²)
# Aspect ratio: 7.32
# Lift-to-drag ratio: 11.6
# Wing loading: 14.1 lb/ft² (68.8 kg/m²)
# Power/mass: 15.3 lb/hp (9.25 kg/kW)

Of course, you can chose other type, maybe jet, so you'll know amount of thrust for certain.

Let us know when you have results, I'll be happy to check them out and admit defeat if it turns out that way.

Heck I'll even say you were right about your triplets.

Until then I'm out of this thread.

[eskimo2]

#1 Hitech already did the math for a real plane.  How many do you want?

#2 If you don’t get the concept from these simpler concepts, you will certainly get lost in the more complicated math behind a RL problem.  

#3 The paper treadmill accelerates at a bit under 1G.  You’re looking at a rubber-coated mouse ball, a copper tube with rubber bands around it for traction, and a clear acrylic sphere.  Clearly the clear acrylic sphere skids; it has very little traction/coefficient of friction.  If the plane had acrylic tires and the treadmill was paper, I’d bet the wheels would slip and the plane would take off.  So what?

[john9001]

Originally posted by eskimo2
#1 Hitech already did the math for a real plane.  How many do you want?

 

whats a real plane doing on a make believe conveyor belt?

[eskimo2]

Originally posted by vorticon
or just repeat yourself until they grow weary and leave, which is more common.

That’s their choice.  A lot of folks will never get this concept, I know that.  Many folks will never really try because they assume they already know the answer.  

I’d like to point out that in the original AH BBS thread, I was the first to explain the rotational inertia/plane won’t fly answer.  Hitech was the only person who got it on the first reading.  Many others have gotten it through a variety of examples and explanations.  I repeat myself because so many people make the wrong assumptions and can’t answer the very questions that will force them to understand the concept if they just make an effort.  

AKIron, Hitech & sluggish have also given excellent explanations and examples.

[2bighorn]

Uhh, this is getting personal (ok, I lied, I have to reply this one)

Originally posted by eskimo2
#1 Hitech already did the math for a real plane.  How many do you want?

Umm no, he didn't.

Originally posted by eskimo2
#2 If you don’t get the concept from these simpler concepts, you will certainly get lost in the more complicated math behind a RL problem.  

LOL, kinda like your triplets story? No worries, my math will always (at least) match yours.

Originally posted by eskimo2
So what?

When it comes to physics, you don't say "So, what", you got to prove it, and there are few ways to do it, either to calculate, do practical experiment or both.

As far as practical experiment goes, that thing on TV beats hell outta your sander. Plane took off.

For all other (hypotetical) scenarios, which includes super conveyor, you'll have to do something more than post your films and triplets story at every possible opportunity.

Have a good one  

[SaburoS]

Originally posted by eskimo2
Imagine that “exactly matches” really means that YOU have a big acceleration control dial for the conveyor and your job is to keep it in place. The plane fires up and begins to inch forward; you see this and crank the acceleration dial.  (Or are you going to say, "I give up" the instant you see the plane budge?) You go too far, however, so the plane drifts back behind its starting point. Seeing this you back off on the acceleration dial and adjust it to keep the plane pretty much where it started.

Look at the concept; don’t get caught up in the semantics of the word “exactly”.

But at no point is the concept to keep the plane's airspeed at zero.
The job of the conveyor belt is to match wheel speed, not counter the plane's forward movement. That is your mistake (If I read your post(s) correctly).
If the job was to keep the plane in one place, then you'd be right.
The moment you try to make the plane go back to its starting point, you are exceeding the wheel's speed.

The plane's wheel isn't doing a thing until the plane starts rolling forward. At each point of adjustment, the conveyor belt is reacting to match the wheel's speed.

The wheels turn because of the plane's forward movement, not the other way around. The plane has to move forward to get the wheels to rotate. The conveyor won't do a thing until it senses wheel rotation.
The wheel won't start rotating until the plane moves forward.

[SaburoS]

Originally posted by eskimo2
That’s their choice.  A lot of folks will never get this concept, I know that.  Many folks will never really try because they assume they already know the answer.  

I’d like to point out that in the original AH BBS thread, I was the first to explain the rotational inertia/plane won’t fly answer.  Hitech was the only person who got it on the first reading.  Many others have gotten it through a variety of examples and explanations.  I repeat myself because so many people make the wrong assumptions and can’t answer the very questions that will force them to understand the concept if they just make an effort.  

AKIron, Hitech & sluggish have also given excellent explanations and examples.

Actually I do hope you continue with the subject as I'm no expert. I know we all are thinking within our own box and I know I'm doing the same. I enjoy discovering new things outside of 'my box' as that never hurts. Right now I am not seeing the same as you.

[Donzo]

Originally posted by SaburoS
But at no point is the concept to keep the plane's airspeed at zero.
The job of the conveyor belt is to match wheel speed, not counter the plane's forward movement. That is your mistake (If I read your post(s) correctly).
If the job was to keep the plane in one place, then you'd be right.
The moment you try to make the plane go back to its starting point, you are exceeding the wheel's speed.

The plane's wheel isn't doing a thing until the plane starts rolling forward. At each point of adjustment, the conveyor belt is reacting to match the wheel's speed.

The wheels turn because of the plane's forward movement, not the other way around. The plane has to move forward to get the wheels to rotate. The conveyor won't do a thing until it senses wheel rotation.
The wheel won't start rotating until the plane moves forward.

Good points...this makes sense to me.


I'd like to know what would happen if we pulled the plane forward with a cable attached to a winch.  With all this talk of rotational inertia, what would happen?  Would the cable simply snap or the winch motor burn out trying to pull the plane that's being held back by the conveyor?

[sluggish]

Originally posted by Donzo
Good points...this makes sense to me.


I'd like to know what would happen if we pulled the plane forward with a cable attached to a winch.  With all this talk of rotational inertia, what would happen?  Would the cable simply snap or the winch motor burn out trying to pull the plane that's being held back by the conveyor?

Theoretically yes if we are using an infinately powerful conveyor belt.  We are attempting to use constant acceleration to create enough rotational inertia to prevent the plane from moving forward.  Even a winch would be unable to move the plane unless it was powerful enough to drag the plane even with it's wheels locked.




edit-even

[john9001]

why would the wheels be locked?

[eskimo2]

Originally posted by SaburoS
But at no point is the concept to keep the plane's airspeed at zero.
The job of the conveyor belt is to match wheel speed, not counter the plane's forward movement. That is your mistake (If I read your post(s) correctly).
If the job was to keep the plane in one place, then you'd be right.
The moment you try to make the plane go back to its starting point, you are exceeding the wheel's speed.

The plane's wheel isn't doing a thing until the plane starts rolling forward. At each point of adjustment, the conveyor belt is reacting to match the wheel's speed.

The wheels turn because of the plane's forward movement, not the other way around. The plane has to move forward to get the wheels to rotate. The conveyor won't do a thing until it senses wheel rotation.
The wheel won't start rotating until the plane moves forward.

The conveyor’s job is to match the wheel’s speed.  If the plane to moves forward, the wheel must be moving faster than the treadmill.  The treadmill’s job is to match the speed of the wheel; if it start’s “losing ground” the only thing that it can do is speed up.  (It certainly wouldn’t just give up.)  But how much?  To the speed of the plane?  No, it’s supposed to match the wheel speed.  So it speeds up to whatever speed/acceleration-rate it takes to keep the plane in place.  When the plane is in place the conveyor is doing its job!  Be it taxi power or full throttle.

[eskimo2]

Originally posted by john9001
why would the wheels be locked?

Only to illustrate that most planes’ tires have enough traction to hold the plane still at full power.  A plane with enough power to skid on full locked brakes and take off on a normal runway would also have enough power to skid its wheels on the wheel-speed treadmill as well.  I don’t think normal planes can do that however.

[SaburoS]

Originally posted by eskimo2
Snip~ So it speeds up to whatever speed/acceleration-rate it takes to keep the plane in place.  When the plane is in place the conveyor is doing its job!  Be it taxi power or full throttle.

Sorry but its job is not to keep the plane in place but to match the wheel speed.
Therein lies the difference in our school's of thought. If its job was to keep the plane in one place then I'd say you'd be right as it could exceed the wheel's speed to bring the plane back to its starting point. The losing battle of our conveyor belt is that it has to forever react to the wheel speed which is the result of the plane moving forward. The moment you stop the plane's forward acceleration/movement, you are now exceeding the wheel's speed forcing the plane to react accordingly.

We're not talking an immediate wheel speed of 200knts but a gradual increase from zero. The conveyor has to react to a plane that is in motion for that is the only way the wheels start rotating.

Try your sander experiment but starting at a crawl and moving it faster slowly. What happens to the wheel then? Keep in mind that is without additional thrust acting on the wheel's forward movement.

[eskimo2]

Originally posted by SaburoS
Sorry but its job is not to keep the plane in place but to match the wheel speed.
Therein lies the difference in our school's of thought. If its job was to keep the plane in one place then I'd say you'd be right as it could exceed the wheel's speed to bring the plane back to its starting point. The losing battle of our conveyor belt is that it has to forever react to the wheel speed which is the result of the plane moving forward. The moment you stop the plane's forward acceleration/movement, you are now exceeding the wheel's speed forcing the plane to react accordingly.

We're not talking an immediate wheel speed of 200knts but a gradual increase from zero. The conveyor has to react to a plane that is in motion for that is the only way the wheels start rotating.

Try your sander experiment but starting at a crawl and moving it faster slowly. What happens to the wheel then? Keep in mind that is without additional thrust acting on the wheel's forward movement.

Suppose the wheel is only rolling 2 mph on the treadmill, but its center/axle is not moving down the runway.  The treadmill also must be going 2 mph…  In this case the treadmill is matching the wheel’s speed.


Now imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph.  The treadmill must be going only 1 mph…  In this case the treadmill is not matching the wheel’s speed.

Now imagine the wheel is rolling 1,002 mph on the treadmill, and its center/axle is moving down the runway at 1 mph.  The treadmill must be going only 1,001 mph…  In this case also, the treadmill is not matching the wheel’s speed.

When the treadmill is matching the wheel’s speed, the plane is stationary.

[john9001]

Originally posted by eskimo2
Only to illustrate that most planes’ tires have enough traction to hold the plane still at full power.  A plane with enough power to skid on full locked brakes and take off on a normal runway would also have enough power to skid its wheels on the wheel-speed treadmill as well.  I don’t think normal planes can do that however.

that does not answer the question, why do you want the wheels locked when a wench cable is attached to the plane?

lets try this, put a sail plane on the belt and the tow plane off the belt, when the tow plane takes off will the sailplane take off or will the belt hold both planes at 0 mph ground speed.