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Plane on a Conveyor Belt - Page 4

Poll Results: (See the first question) Can the plane take off?

 
  • 42% (25)
    Yes
  • 57% (34)
    No
59 Total Votes  
post #55 of 74
Quote:
Originally Posted by iacas View Post

You did, and you kind of just did it again...? The purpose of the engines is to move the plane, not to move the air.
Ah ok I see the mix up now, thanks.
post #56 of 74

Thanks everybody for your feedback, I need a bit of time to read, analyze and understand. Thanks too for simply using your own time to help me out as i am really struggling with this concept. Usually when i am outnumbered in such a discussion it becomes more likely the majority are correct and I am not. So i do respect the likely result is for me to come back on this one soon enough declaring with excitement that i am wrong and the penny has dropped. I really do enjoy being wrong like this from time to time as when it comes to the point of knowing where i am wrong then i will have learned so much more than if by chance i had chosen YES originally. So cheers!! (beer in hand) .     

post #57 of 74
Thread Starter 

Here's another possibility.

 

Imagine a subway train that was connected to overhead rails with gears of some kind. These powered the train's movement. Beneath the train, it had free-rolling wheels that just held the train up and let it roll freely instead of scraping along the ground.

 

You could put that thing on a conveyor belt, start turning the gears above to move the train forward, and the conveyor belt could begin moving backwards at whatever rate it wanted and the train would still go forward because the gears above are providing the locomotion, not the free-rolling wheels beneath.


The gears are the plane's engines or propellers.

post #58 of 74
Quote:
Originally Posted by the chopper View Post

Thanks everybody for your feedback, I need a bit of time to read, analyze and understand. Thanks too for simply using your own time to help me out as i am really struggling with this concept. Usually when i am outnumbered in such a discussion it becomes more likely the majority are correct and I am not. So i do respect the likely result is for me to come back on this one soon enough declaring with excitement that i am wrong and the penny has dropped. I really do enjoy being wrong like this from time to time as when it comes to the point of knowing where i am wrong then i will have learned so much more than if by chance i had chosen YES originally. So cheers!! (beer in hand) .     
I can appreciate this. I was in your position with that riddle they discussed in the beginning of the movie "21" about the MIT kids who took down Vegas. (It was the "lets make a deal, should you switch your door when offered" riddle). It took me weeks to come around on that one, and I totally agree that it is fun to [occasionally] be wrong on these types of things. So, cheers!
post #59 of 74
Quote:
Originally Posted by Golfingdad View Post

I can appreciate this. I was in your position with that riddle they discussed in the beginning of the movie "21" about the MIT kids who took down Vegas. (It was the "lets make a deal, should you switch your door when offered" riddle). It took me weeks to come around on that one, and I totally agree that it is fun to [occasionally] be wrong on these types of things. So, cheers!

That is a very good logic riddle as well. The pick a door scenario. Let's make a deal riddle.

If shown an empty door, and asked if you want to switch, you always should. You will win 66% of the time instead of 33%.
post #60 of 74
Quote:
Originally Posted by MyrtleBeachGolf View Post

That is a very good logic riddle as well. The pick a door scenario. Let's make a deal riddle.
If shown an empty door, and asked if you want to switch, you always should. You will win 66% of the time instead of 33%.
Exactly. But I purposely left out details so as not to lead this thread too far astray.
post #61 of 74

The only thing you have to realize about this argument is that the forward motion of the plane is driven by the thrust of the power plant not the wheels.  Be it a propeller or a jet engine.  The power plant is PULLING the plane forward regardless of what the wheels are doing.  The only thing that has to happen is that the thrust of the engine has to overcome the weight of the plane.  Once this happens the plane is GOING to move forward regardless of what the wheels are doing.  The more thrust the faster the plane will move until it eventually takes off.  The thing that the other side of the argument fails to recognize, in physics the wheels variable would have no place in the equation, it would be like multiplying the results by 1.

 

Think of it this way.  You put a toy truck on a treadmill with a rope tied to the front bumper and you are pulling on the rope while the treadmill is spinning, the treadmill spinning the wheels of the truck will not remove your ability to pull the truck forward with the rope no matter how fast the treadmill is spinning the wheels.  Think of the powerplant being the rope and the thrust it generates would be your force pulling on the rope.  It is exactly the same thing.

post #62 of 74

Okay I have watched the mythbusters and thought about this for far too long, my answer remains NO until properly conducted scientific study proves me wrong and this is the last I will post on the matter. All you “yes” voters are wrong LOL –I think ??cowering in preparation to take some flak. But honestly I am not convinced and mythbusters crack at it is so, so, so flawed. The biggest flaw is although the tarp is being pulled in the other direction the plane' mass is most definitely in contact with the runway underneath massively negating the forces of the tarp conveyor. I am just happy golfing flight laws are not this mind-boggling.

 

The extracts below are from the company airbus. What I am drawing from them is their use of “the take off roll” its so important here. And in the second extract at the end where they indicate the importance of airflow speed etc. This has been fun and hard work for the grey matter. Extracts highlighted green.

 

VMCG (Velocity of Minimum Control on Ground)

During the takeoff roll, it is of utmost importance to know the minimum speed at which

the aircraft will remain controllable, in the event of an engine failure on ground. This is

because, in such a case, and if the takeoff is continued, only the rudder will be able to

counteract the yaw moment that is generated by asymmetric engine(s) thrust.

Per regulations, the minimum speed at which an aircraft is defined to be “controllable”

(lateral excursion lower than 30 feet) after an engine failure on ground, is referred to

as VMCG (Velocity of Minimum Control on Ground).

VMCG mainly depends on:

Engine(s) thrust

Pressure altitude.

If a failure occurs before reaching VMCG, the takeoff must be interrupted to maintain

control of the aircraft.

Note: Steering is not used during certification flight tests. However, in real life

operations, steering would be helpful in controlling the aircraft.

Figure 1

Ground Control after Engine Failure

V1: Decision Speed

V1 is the maximum speed at which a rejected takeoff can be initiated, in the event of an

emergency. Additional information on this “Go/No-Go” decision can be found in the

Flight Operations Briefing Note entitled: “Revisiting the Stop or Go Decision”.

V1 is also the minimum speed at which a pilot can continue a takeoff after an engine

failure.

If an engine failure is detected after V1, the takeoff must be continued. This implies that

the aircraft must be controllable on ground. Therefore, V1 is always greater than VMCG.

Page 2

 

 

MY REASONING “IACAS”

 

If a 747 is doing 200kph on a runway then that equates to 18 metres per second. That is 18 metres of ground passing underneath the rolling wheels.

 

If the 747 were on a conveyor belt(that actually supports the weight of an aircraft- not a tarp LOL LOL) matching that same set of conditions then the belt will only be simulating the ground at that same 18 metres per second so the wheels will be spinning at exactly the same rate.

 

Whatever the thrust would be from the 747 on the real runway, will be the same thrust required to make the conveyor travel at 18 metres per second.The mass of the aircraft is important here. As the mass of the 747 provides the resistance the thrust is required to overcome. If the conveyor slowed and eventually stopped then the plane would soon be moving forward proper at 18 metres per second again.

 

When the conveyor would be on, it is impossible for that plane to move forward because the ground is coming towards the plane exactly proportionately to the thrust and hence roll of the plane.

 

The result of the thrust on the aircraft is only rolling along the ground(pre take off). When it is the ground rolling underneath the plane then that plane is going no-where!!!!!.

 

More importantly though the laws of flight and lift require the plane actually moving forward to allow the air to create lift and flight. Otherwise wings would only be the width of the engines.

 

 

II.1 Control Speeds and associated Takeoff Speeds

The efficiency of such aerodynamic surfaces as the wings (for lift), the rudder, the

ailerons, and the elevators, depends on adequate airflow speed. This airflow speed

determines the minimum takeoff speeds.

Page 1

 

www.airbus.com/fileadmin/media_gallery/files/safety_library_items/AirbusSafetyLib_-FLT_OPS-TOFF_DEP_SEQ07.pdf

post #63 of 74
Quote:
Originally Posted by the chopper View Post

Okay I have watched the mythbusters and thought about this for far too long, my answer remains NO until properly conducted scientific study proves me wrong and this is the last I will post on the matter. All you “yes” voters are wrong LOL –I think ??cowering in preparation to take some flak. But honestly I am not convinced and mythbusters crack at it is so, so, so flawed. The biggest flaw is although the tarp is being pulled in the other direction the plane' mass is most definitely in contact with the runway underneath massively negating the forces of the tarp conveyor. I am just happy golfing flight laws are not this mind-boggling.


The extracts below are from the company airbus. What I am drawing from them is their use of “the take off roll” its so important here. And in the second extract at the end where they indicate the importance of airflow speed etc. This has been fun and hard work for the grey matter. Extracts highlighted green.

 

Let me try this one more time.....and I'll start by saying again, I am a pilot.

The wheels of the aircraft do NOTHING more than to reduce rolling resistance to allow for easier acceleration. The thrust from the aircraft power plant, whether propeller driven or jet, will PULL the aircraft through the air regardless of what the wheels are doing. The conveyor does NOT affect that thrust in any way. The aircraft moves forward because its forward thrust is much greater than the very minimal rolling resistance of the FREE SPINNING wheels, no matter what speed they're spinning at. That forward movement causes airflow across the wings which generates lift which allows for flight.

Sorry, there is no debate. This is simple flight dynamics and the only reason it's an interesting riddle is because too many people who think they understand those dynamics get suckered into believing that just because the conveyor is spinning the wheels faster, it somehow affects the forward movement if the aircraft through the air. It does not.

You can argue all you like, but this one is fact. At this point you either understand the dynamics involved, or you do not.

post #64 of 74
Thread Starter 
Quote:
Originally Posted by the chopper View Post

Okay I have watched the mythbusters and thought about this for far too long, my answer remains NO until properly conducted scientific study proves me wrong and this is the last I will post on the matter.

 

It's still yes.

 


Quote:
Originally Posted by the chopper View Post

But honestly I am not convinced and mythbusters crack at it is so, so, so flawed. The biggest flaw is although the tarp is being pulled in the other direction the plane' mass is most definitely in contact with the runway underneath massively negating the forces of the tarp conveyor. I am just happy golfing flight laws are not this mind-boggling.

 

That's not relevant, nor is it even true. The plane's wheels are not in contact with the runway beneath. If you stand on a tablecloth and I yank it out from under you, guess what: the fact that there's a sidewalk beneath (or a table, or whatever) matters precisely zero. :P

 

It's really not a very difficult proposition.

 

Let me ask you this: could a plane (with its wheels locked) take off from a perfectly smooth sheet of ice? How about a massive runway (still locked wheels) with Crisco smeared all over it (i.e. reducing the friction to virtually nothing)?

 

The answer to both of those - and the original question - remains yes.

 

 

Quote:
Originally Posted by the chopper View Post

During the takeoff roll, it is of utmost importance to know the minimum speed at which

the aircraft will remain controllable

 

That's not relevant. I'm not even sure why you highlighted that section. The sentences after the highlight talk about why that's important to taking off, but have nothing to do with a plane on a conveyor belt. Specifically this part:

 


Quote:
Originally Posted by the chopper View Post

 

If a failure occurs before reaching VMCG, the takeoff must be interrupted to maintain

control of the aircraft.

 

Moving on...

 


Quote:
Originally Posted by the chopper View Post

MY REASONING “IACAS”

 

If a 747 is doing 200kph on a runway then that equates to 18 metres per second. That is 18 metres of ground passing underneath the rolling wheels.

 

If the 747 were on a conveyor belt(that actually supports the weight of an aircraft- not a tarp LOL LOL) matching that same set of conditions then the belt will only be simulating the ground at that same 18 metres per second so the wheels will be spinning at exactly the same rate.

 

Whatever the thrust would be from the 747 on the real runway, will be the same thrust required to make the conveyor travel at 18 metres per second.The mass of the aircraft is important here. As the mass of the 747 provides the resistance the thrust is required to overcome. If the conveyor slowed and eventually stopped then the plane would soon be moving forward proper at 18 metres per second again.

 

That's wrong.

 

If the plane is traveling 18m/s, the belt will be traveling 18m/s in the opposite direction, and thus, the wheels will be rolling at 36m/s.

 

The plane only needs to generate enough thrust to travel 18 m/s.

 

You're still stuck on the idea that the conveyor belt can keep the plane from moving. IT CANNOT.

 


Quote:
Originally Posted by the chopper View Post

When the conveyor would be on, it is impossible for that plane to move forward because the ground is coming towards the plane exactly proportionately to the thrust and hence roll of the plane.

 

The plane could not care less how fast the ground is moving - the wheels are happy to spin. That's the whole freakin' point of having wheels to begin with.

 

Quote:

Originally Posted by the chopper View Post

The result of the thrust on the aircraft is only rolling along the ground(pre take off). When it is the ground rolling underneath the plane then that plane is going no-where!!!!!.

 

Wrong.

 

The thrust is not applied to the ground.

 

The thrust is applied TO THE AIR. Just because you can't see the air doesn't mean it doesn't matter.

 

Get it? That's a pun. c5_banana.gifa3_biggrin.gif

 

 


Quote:
Originally Posted by the chopper View Post

More importantly though the laws of flight and lift require the plane actually moving forward to allow the air to create lift and flight. Otherwise wings would only be the width of the engines.

 

Good thing the plane moves forward. It takes off normally.

post #65 of 74
Quote:

Originally Posted by the chopper View Post

 

When the conveyor would be on, it is impossible for that plane to move forward because the ground is coming towards the plane exactly proportionately to the thrust and hence roll of the plane.

 

The result of the thrust on the aircraft is only rolling along the ground(pre take off). When it is the ground rolling underneath the plane then that plane is going no-where!!!!!.

 

 

In addition to the information in these previous two posts from Iacas and David, consider what you are suggesting in the part I have quoted. You say the ground is rolling (by which I understand you to mean the conveyor belt), and yet at the same time you say the plane is going nowhere (by which I understand you to mean that ground speed is zero). But if ground speed is zero, the conveyor belt is not moving.

 

So which do you envision happening on takeoff: (1) the conveyor belt moving or (2) the plane standing still?

Both can't happen at the same time (by the defined conditions of this thought experiment). You've got a logical inconsistency that can't be resolved, the way you're looking at the problem.

post #66 of 74

Not to pick on Chopper here (just having a little fun) but this conversation is starting to remind me of this:

 

post #67 of 74
Quote:
Originally Posted by Missouri Swede View Post

 

In addition to the information in these previous two posts from Iacas and David, consider what you are suggesting in the part I have quoted. You say the ground is rolling (by which I understand you to mean the conveyor belt), and yet at the same time you say the plane is going nowhere (by which I understand you to mean that ground speed is zero). But if ground speed is zero, the conveyor belt is not moving.

 

So which do you envision happening on takeoff: (1) the conveyor belt moving or (2) the plane standing still?

Both can't happen at the same time (by the defined conditions of this thought experiment). You've got a logical inconsistency that can't be resolved, the way you're looking at the problem.

 

In the spirit of fun!!! You guys have asked a few questions, i do not mean to be rude but i may not answer them all, but i am not gonna ignore you, so i am posting!. Plus it would be too easy to pretend "hey you are all correct and i get it". And rest assured i understand what you are all saying.I do not agree with it all. All i am saying is i am not convinced.No proof of this is available. As i have said before i recognize you guys are probably right , i expect this and welcome it. But i would feel pretty stupid and lacking if i concurred with something i cannot perceive and accept as being factually true, I get the plane being  able to take off on ice, i get planes taking off from water and i get planes taking off from runways. It would be also fair to say i have very little knowledge about aircraft and flight, these are not my chosen subjects in study(formal or personal) so i do remain respectful of those with greater knowledge. However i cannot insult my intelligence (the teeny weeny  amount that i have LOL) by accepting this yet, when i do not. but thanks anyway!

 


Thrust from a planes engine is not applied to the ground , it is applied to the air "yes" but the sum total physical result of that thrust is the plane rollinge4_tumbleweed.gif

 

Need to go now , i will finish off after, bye y'all

post #68 of 74

Nice  banana, this is a bit of a slippery subject right enough a3_biggrin.gif anyhoo  i am maybe getting closer to conceptualizing whats going on by imaginig a calm river and hovercraft doing it' full speed of say 50 knots. the next day incredibly the river is flowing smoothly at 50 knots (thus minimizing resistance on the hull). the hovercraft heads upstream no problem but not at 50 knots. Is this similar to what you guys are saying about the nature of thrust with the plane. Where i still struggle is that we are dealing with land and not water or ice. But i think i get it. good puzzle.

post #69 of 74
Thread Starter 
Quote:
Originally Posted by the chopper View Post

I do not agree with it all. All i am saying is i am not convinced.No proof of this is available.

 

You are wrong - proof of this is readily available - both real-world testing AND theoretical "proofs."

 

Goodness, in the show they put a literal plane on a literal treadmill (it was a miniature sized plane) and the plane accelerated forward.

 

The cows understand why a plane can take off at this point! :D

 

 

 

^^^^^^^^

(Practically a direct quote from the funny video clip. Lighten up. It's funny.)

b3_huh.gif


Quote:
Originally Posted by the chopper View Post

Thrust from a planes engine is not applied to the ground , it is applied to the air "yes" but the sum total physical result of that thrust is the plane rolling

 

No.. The sum total physical result is the plane moving within the air column or the air space or the air. It's the same principle that lets the plane move forward while it's airborne - the airplane is pushed or pulled AGAINST THE AIR. Air has mass and matter.

 

The airplane works just like a boat propeller.

 

One MORE example (to the great annoyance of the cows):

I've rigged up a boat to have four wheels sticking straight up from it towards the sky. The boat itself is sitting in a lake. As the boat engine turns the propellers, I measure its speed relative to a series of unmoving poles stuck in the bottom of the lake and that speed is matched by a large, stationary conveyor belt* which rests upon the wheels attached to the boat.

 

Bingo: the airplane situation flipped 100% upside down and replacing the air with water. Everything else is the same.

 

* (The entire conveyor belt contraption is stationary - the conveyor BELT itself is moving.)

 

Quote:
Originally Posted by the chopper View Post

Nice  banana, this is a bit of a slippery subject right enough a3_biggrin.gif anyhoo  i am maybe getting closer to conceptualizing whats going on by imaginig a calm river and hovercraft doing it' full speed of say 50 knots. the next day incredibly the river is flowing smoothly at 50 knots (thus minimizing resistance on the hull). the hovercraft heads upstream no problem but not at 50 knots. Is this similar to what you guys are saying about the nature of thrust with the plane. Where i still struggle is that we are dealing with land and not water or ice. But i think i get it. good puzzle.

 

Water provides MORE FRICTION than the wheels on a plane. The plane will face more resistance to take off against a 50 knot current than it will taking off with wheels "against" a conveyor belt going as fast, or even four times as fast, as the plane. The friction of wheels spinning twice as fast is negligible.

post #70 of 74

chopper, let's try this: imagine a plane with its wheels down, flying at 350mph just a foot above a conveyer belt moving backwards at 350mph (it's gotta be a pretty long conveyer, but whatever, this is a thought experiment). Now, the plane descends that one foot so the wheels touch the conveyer. By your reasoning the plane should instantly stop. You should see now that it won't, just, the wheels will suddenly start spinning at a rate equal to 700mph, get it? (Actually the plane will slow a bit due to energy being expended to overcome the inertial resistance to acceleration in the wheels as well as the friction of the wheel bearings.)

post #71 of 74
Thread Starter 
Quote:
Originally Posted by dak4n6 View Post

(Actually the plane will slow a bit due to energy being expended to overcome the inertial resistance to acceleration in the wheels as well as the friction of the wheel bearings.)

 

Yes, roughly 0.13 MPH. a3_biggrin.gif

 

I'm giving up on chopper. If he can't sort it out in his mind given the countless examples given to him, he'll never record one TV show and watch another at the same time.

 

 

^^^^^^^^

(Poking fun - lighten up, dude.)

b3_huh.gif

post #72 of 74

are you trying to isult me !!!!!!!!!!!!!!!!!!!!!!!1

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