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Re: OT Plane on a Treadmill [Re: LandRaider] #763614 11/09/06 09:22 AM
Joined: Sep 2002
Posts: 3,634
bretwalda Offline
Roll Me Over
Think of it like this Curtis.

When I jump into my 152, start it up and proceed to taxi I have to gun the throttle to get it moving.

Once its moving I can ease off the throttle because momentum has taken hold.

To overcome static rest I had to make the engine work more.

This is why terms and common agreement of the riddle is important. I am assuming zero thrust, zero wind, speed of conveyor matches GROUND SPEED of airplane (relative to a fixed point on the ground - not the conveyor), the conveyor matches precisely the moment and force of forward motion of the plane

Still with me? That is our starting point.

The plane will not move, the conveyor will hardly move. You have to think of it at the very genesis of actions and reactions taking place and freeze frame that moment in your brain i.e. thrust creates forward motion - that motion is calculated with a ground speed - that ground speed is matched with an opposite conveyor speed - at that very point ground speed is still zero.

My only guess is that the disconnect is something with the ground speed - maybe you are assuming the treadmill speed matches the wheel speed...I am saying the treadmill matches ground speed relative to a linear point in space not related to the treadmill or the speed of the wheel over the treadmill.


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Re: OT Plane on a Treadmill [Re: bretwalda] #763615 11/09/06 09:43 AM
Joined: Sep 2001
Posts: 8,557
LandRaider Offline
Forum Moderator
*****
Quote
Think of it like this Curtis.

When I jump into my 152, start it up and proceed to taxi I have to gun the throttle to get it moving.

Once its moving I can ease off the throttle because momentum has taken hold.

To overcome static rest I had to make the engine work more.

This is why terms and common agreement of the riddle is important. I am assuming zero thrust, zero wind, speed of conveyor matches GROUND SPEED of airplane (relative to a fixed point on the ground - not the conveyor), the conveyor matches precisely the moment and force of forward motion of the plane

Still with me? That is our starting point.

The plane will not move, the conveyor will hardly move. You have to think of it at the very genesis of actions and reactions taking place and freeze frame that moment in your brain i.e. thrust creates forward motion - that motion is calculated with a ground speed - that ground speed is matched with an opposite conveyor speed - at that very point ground speed is still zero.

My only guess is that the disconnect is something with the ground speed - maybe you are assuming the treadmill speed matches the wheel speed...I am saying the treadmill matches ground speed relative to a linear point in space not related to the treadmill or the speed of the wheel over the treadmill.


Are you saying the plane can't use it's engine??? If not of course it wont go anywhere!

The plane is not tethered to the treadmill man. the wheels provide almost NO resistance to it's moving foward.

The treadmill is NOT capable ot canceling out the thrust of any airplane capable of normally taking off.

Say I got on the treadmill, and PUSHED the plane. Were not going to move at all relative to that point on the earth.

NOW Say I get along side the treadmill, and push the plane. It wont matter how fast the treadmill goes in the opposite direction, I will still be able to push the plane. The engines are the exact same thing.

IF the bearings were 0 friction, then NO matter WHAT the treadmill does, or does not do, it cannot act on the airplane.


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Re: OT Plane on a Treadmill [Re: LandRaider] #763616 11/09/06 10:00 AM
Joined: Dec 2002
Posts: 1,074
Rodeo Guy Offline
Body Damage is Cool
Forget about the plane, I have an important question:


If Doc Brown puts the Delorean on the conveyor, when the speedo indicates 88 mph, will it travel through time?


Mike

"Damn the carnage! Full throttle ahead!"

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Re: OT Plane on a Treadmill [Re: Rodeo Guy] #763617 11/09/06 10:02 AM
Joined: Sep 2001
Posts: 8,557
LandRaider Offline
Forum Moderator
*****
Quote
Forget about the plane, I have an important question:
If Doc Brown puts the Delorean on the conveyor, when the speedo indicates 88 mph, will it travel through time?


Your addition is of no use to our discussion.... <img src="/forums/images/graemlins/nana.gif" alt="" />


87 Raider 4D56td v5MT1
31's..Basically Stock
Re: OT Plane on a Treadmill [Re: LandRaider] #763618 11/09/06 10:51 AM
Joined: Sep 2002
Posts: 3,634
bretwalda Offline
Roll Me Over
Quote
NOW Say I get along side the treadmill, and push the plane. It wont matter how fast the treadmill goes in the opposite direction, I will still be able to push the plane. The engines are the exact same thing.


No man! They are not the same thing. Where V=velocity... V (+) -V = 0

From another source more eloquently spoken:

Quote
However much forward force you apply with [your hand] or engines, the exact same amount of force will be applied in the opposite direction by the conveyor belt on the tires. That force will act to accelerate the spin of the wheels. And forget about bearing friction (and wheel/surface friction too). Things like that don't belong in thought problems like this. The force the conveyor belt applies to the wheels is not acting against friction. It is acting against the inertia of the wheels. It accelerates their spin. This is the factor that is ignored by the people who say that the the wheels "decouple the plane from the runway".


And also:

Quote
You might ask: "what if I put the plane on the conveyor belt, and then [push] it along at 10 meters per second with [my hand]?" Well, that is a logical impossiblity. You cannot have the wheel speed match the conveyor speed, no wheel slippage, and still move at 10 meters per second. It is like asking what happens if you're tied to an immovable wall with an unbreakable rope, and you start to walk away from the wall at 10 m/s. You can't even start to answer, because the question itself is impossible. All the conditions of the question cannot possibly hold true. In the airplane question, this problem arises if you specify that the wheels are massless, because it doesn't take any force to spin a massless wheel, and so the conveyor belt cannot apply a backward force to the plane. In this case, the question is logically inconsistent.


Read this post - all of it - and I think you will change your mind:

http://forum.physorg.com/index.php?showtopic=2417&st=1155&#entry42611


concreteprinter.com
Re: OT Plane on a Treadmill [Re: bretwalda] #763619 11/09/06 02:03 PM
Joined: Feb 2004
Posts: 10,238
FrankR Offline
Web Wheeler
****
Phil -

The amount of force that can be applied by the treadmill to the airplane is limited to the amount of friction in the plane's wheel bearings. The airplane's thrust easily counters it. You'd still need to rev the engine to get the plane moving, but move, it would.

Imagine yourself on roller skates and standing on a treadmill with side rails. Don't you think you could pull yourself forward against the direction of the treadmill?

Frank


'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum
Re: OT Plane on a Treadmill [Re: FrankR] #763620 11/09/06 04:55 PM
Joined: Mar 2006
Posts: 6,950
cmonty72 Offline
Trail Leader
****
I'm swimming against a current that is equal my swim speed.(conveyor) Im going nowhere. But if I grab a branch of a tree(prop aganst air) and pull forward I can make headway. But if the current increased just as I pulled forward. It would come down to strength over friction. If the current speed was increased enough to over power me(friction of wheel bearings) I would never "fly".

Now we can interpret how the riddle is worded to make both scenarios possible.

Obviously an airplane can overcome its wheelbearing friction. And the riddle said the conveyor would just match the planes speed. It did not say it would run a milliion RPMs and sieze the wheel bearings . If the plane is achieving "airspeed" Meaning just that, air speed over the wing,. Then I know it will fly.


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Re: OT Plane on a Treadmill [Re: cmonty72] #763621 11/09/06 05:12 PM
Joined: Nov 2003
Posts: 5,690
87Montero Offline
Trail Leader
***
It's all about THRUST guys!

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Re: OT Plane on a Treadmill [Re: bretwalda] #763622 11/09/06 05:17 PM
Joined: Nov 2001
Posts: 3,272
Oyaji_Jon Offline
Roll Me Over
***
Quote
Think of it like this Curtis.

When I jump into my 152, start it up and proceed to taxi I have to gun the throttle to get it moving.

Once its moving I can ease off the throttle because momentum has taken hold.

To overcome static rest I had to make the engine work more.

This is why terms and common agreement of the riddle is important. I am assuming zero thrust, zero wind, speed of conveyor matches GROUND SPEED of airplane (relative to a fixed point on the ground - not the conveyor), the conveyor matches precisely the moment and force of forward motion of the plane

Still with me? That is our starting point.

The plane will not move, the conveyor will hardly move. You have to think of it at the very genesis of actions and reactions taking place and freeze frame that moment in your brain i.e. thrust creates forward motion - that motion is calculated with a ground speed - that ground speed is matched with an opposite conveyor speed - at that very point ground speed is still zero.

My only guess is that the disconnect is something with the ground speed - maybe you are assuming the treadmill speed matches the wheel speed...I am saying the treadmill matches ground speed relative to a linear point in space not related to the treadmill or the speed of the wheel over the treadmill.


I am 100% at the same starting point that you are. The thing that you are overlooking is that the treadmill CANNOT exert FORCE on the plane because there is no friction between the treadmill and the plane. I never discounted gravity, and yes, it is holding the plane down so the wheels make contact with the treadmill. However, gravity is limited to verical influence because of the wheels' frictionless bearings.

The treadmill exerts horizontal force on the wheels which exert no horizontal force on the fuselage because the bearings lack friction.

Gravity exerts "downward" force on the airplane assy. The wheels transfer the force equal to gravity from the ground to the airplane assy via FRICTIONLESS bearings.

The airplane engine exerts horizontal force on the airplane assy and moves it forward (establishes speed over ground) regardless of how fast the treadmill is moving. The treadmill could be infinitely long in which case the airplane would take off and fly over the top of it forever.


73
-Jon
KJ6GVM

As seen on Expedition with TX plates: VEGETARIAN - An old Indian word for poor hunter

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1987 FJ60
Re: OT Plane on a Treadmill [Re: Oyaji_Jon] #763623 11/09/06 05:29 PM
Joined: Sep 2002
Posts: 3,634
bretwalda Offline
Roll Me Over
I give up guys. If you dont read the link in my last post and argue from there there is no hope for this discussion.

No, this is not the same as a car wheel. Obviously. <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> What you are failing to see is that anytime and outside force makes more work to move the plane foward, the conveyor matches that force with equal and opposite work. It'll never go anywhere no matter how far your ignorance leads you to believe otherwise. From static rest the plane and conveyor will hardly move.

Again - read the more eloquent link I just posted. I'm done - too much work to do today <img src="/forums/images/graemlins/drunk.gif" alt="" />


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