RE: Can It Take Off??  
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RE: Can It Take Off?? - 1/12/2006 9:01:37 PM   
britbrat


 

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quote:

ORIGINAL: Rat1


quote:

ORIGINAL: britbrat


quote:

ORIGINAL: dick Hanson

what turns the wheels ?
forward motion
no forward motion=
no turning of wheels
not even a teensy bitsy bit -



Baloney -- boundary airflow alone would do it with the plane sitting there stationary staring you in the face while the belt whirls like mad.

However ---- the question said "Imagine an airplane is on the beginning of a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation. "

The assumption that it can't move is false -- there is no restriction on forward motion -- the only constraint is that the belt will match the speed of the wheels when the plane moves.

The plane will easily fly.



If so then how is it going to fly if the wheels are not rotating faster then the velocity of the counter rotating conveyor belt. The only way it is going to make airspeed is if the wheels spin at a faster velocity then the counter rotating belt.

Wheelspeed = 20 Belt speed = 10

20-10=10

Here we have a positive forward movement or airspeed of 10

Here is what we have to have according to the rules of the question

20-20=0

Now we have a forward movement or airspeed of 0. We all know that an aircraft with no airspeed is nto going to fly muchless lift off the ground.




Baloney again -- the wheels & belt move synchronously. Read the question -- there is no constraint on forward motion -- the magic belt instantly matches the wheel motion & the plane doesn't give a damn what its wheels are doing.


(in reply to Rat1)
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RE: Can It Take Off?? - 1/12/2006 9:20:45 PM   
Liberator


 

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From: Sandy, UT, USA
Status: offline 		Actually no it doesn't. When the prop creates thrust something must be done to this force. You think the conveyer will spin backwards and the plane will stand stationary. In that scenario, the plane will advance and take off. If the conveyer tries to move with the plane (the only other option), then the wheels stay still, the entire plane moves forward until it attains lift off speed.

Either way the plane flies.

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RE: Can It Take Off?? - 1/12/2006 9:37:46 PM   
Liberator


 

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Status: offline 		"Tell me how the plane ever gets any forward motion? Remember the belt is moving backwards at the the same speed the plane is rolling forward. Who cares how much thrust there is. The fact that the wheels aren't the driving force makes no difference here.The only way a real plane moves forward on a runway is because the runway is not moving under it. Without a headwind you need the groundspeed to get airborn. You can put a Merlin on a tricycle but as long as the reverse belt speed is equal to the forward motion you will always be at a standstill as you have ZERO ground speed. You only have a screaming prop and a moving belt...no more no less. Heck we did this in high school with electric motors and prop rods."

You can't ignore the thrust. I know that you want to to keep things simple, but that dog wont hunt. (no matter how big the phone booth is)

The fact that the wheels are not the driving force is makes all the difference in the world. Again the thrust monster rears its ugly head.

"The only way a real plane moves forward on a runway is because the runway is not moving under it. " What?
Actually the only way a real plane moves on a runway is if it is either getting pushed or pulled by a thrust inducing device (read motor).

"You can put a Merlin on a tricycle but as long as the reverse belt speed is equal to the forward motion you will always be at a standstill as you have ZERO ground speed. You only have a screaming prop and a moving belt...no more no less. " This only applies if the wheels are the driving force, not if there is a different thrust parameter at work. (read prop or jet) not axle and transmission.

Heck we did this in high school with electric motors and prop rods."

Uhh no ya didn't.






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RE: Can It Take Off?? - 1/12/2006 10:13:25 PM   
dick Hanson



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RE: Can It Take Off?? - 1/12/2006 10:13:40 PM   
jamieduff1981


 

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Status: offline 		That's the point. The plane WOULD fly if you tried this in real life.

The question is worded to mathematically state that the belt speed and the wheel speed must always match.

Mathematically - they are locked together. What would really happen is now irrelevant, as this question is an issue of mathematical logic.

The plane cannot move at all without it's wheels moving faster than the belt. The belt cannot move unless the wheels do. The wheels cant move unless the plane initially moves over the stationary belt . If the plane does move (and there's no physical reason why it wouldn't) then it's wheels momentarily go faster than the belt.

Thus the belt speed does not equal the wheel speed and thats it disqualified.

I know the plane would continue merrily down the runway/belt/whatever. It would gain forward speed relative to a fixed reference point. It would fly.

The point is that by now the question is over. The result doesn't matter. Nothing can move without defying the wheel speed=belt speed statement.

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RE: Can It Take Off?? - 1/12/2006 10:20:06 PM   
dick Hanson



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Status: offline 		OK now--- how many of us have said that -
do you get the idea that this is an excercize in futility?

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RE: Can It Take Off?? - 1/12/2006 10:39:43 PM   
Rat1



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quote:

ORIGINAL: dick Hanson

if the plane does not go forward - what starts yer belt?
if it goes forward -- it takes off -


If it goes forward then the wheels have rotated at a velocity that is greater then what the belt is turning. Then you have this

1-0=1

This is positive movement. This breaks the rules of the stated question as the belt is supposed to exactally match the wheelspeed at all times. The conveyor has failed its job that it was designed to do.

Oh and swearing and cursing is not going to make the "Yes" answers correct.



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RE: Can It Take Off?? - 1/12/2006 11:14:17 PM   
mesae



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quote:

ORIGINAL: dick Hanson

if the plane does not go forward - what starts yer belt?
if it goes forward -- it takes off -



This is one of the best and simplest explanations of all.

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RE: Can It Take Off?? - 1/12/2006 11:46:46 PM   
dick Hanson



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Status: offline 		Did I put a curse on this gag?
It is an accursed riddle -as stated.

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RE: Can It Take Off?? - 1/13/2006 12:55:33 AM   
Rat1



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From: Grafton, ND, USA
Status: offline 		I am putting up a quick pic I made. Do not laugh OK. it took me all of 5 mins to create it.

quote:

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Can the plane take off?



Ok Now

A is our conveyor speed

B is our wheelspeed

C is our aircraft movement in relation to the world around it

D is our thrust


Ok we will start everything moving so to speak

We have the A turning at 20 RPM and the B turning at 20 RPM (I made the "A" drive so that 20 rpm would be equal to the "B" 20 rpm)

Our thrust is 20 (just an example)

What is our aircrafts movement in relation to the world around it????


If it is not moving then what numbers do we need to change or leave alone to make the aircraft move forward in relation to the world around it????

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< Message edited by Rat1 -- 1/13/2006 12:56:40 AM >


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RE: Can It Take Off?? - 1/13/2006 2:22:07 AM   
old git


 

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quote:

ORIGINAL: bentwings


Imagine an airplane is on the beginning of a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Can the plane take off?



This is a THOUGHT experiment and need not inhabit reality, to those who do not understand the concept of a thought experiment I suggest you look up "Schrodingers Cat" in your physics texts.



old git

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RE: Can It Take Off?? - 1/13/2006 2:25:17 AM   
David Cutler



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quote:

ORIGINAL: Liberator

You can't ignore thrust. At least thats what I told her.




... and did she believe you?

-D

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RE: Can It Take Off?? - 1/13/2006 4:23:22 AM   
cyclops2


 

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Status: offline 		As the Blimp races the engines to 1/2 power and lifts gracefully off of the landing wheels, a hush falls over the conveyor belt.

< Message edited by cyclops2 -- 1/13/2006 4:24:22 AM >

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RE: Can It Take Off?? - 1/13/2006 5:38:52 AM   
PowerPlay


 

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RE: Can It Take Off?? - 1/13/2006 9:51:39 AM   
Aussie Damo



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From: GeelongVictoria, AUSTRALIA
Status: offline 		LOL, great pic
quote:

As the Blimp races the engines to 1/2 power and lifts gracefully off of the landing wheels, a hush falls over the conveyor belt.

this is true, a blimp is a form of aircraft, the the a/c would fly, this is the same for any VTOL a/c like the Bell X-22

So, YES the aircraft will fly

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RE: Can It Take Off?? - 1/13/2006 10:50:08 AM   
CHassan



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quote:

ORIGINAL: Rat1

quote:

ORIGINAL: CHassan


quote:

ORIGINAL: Rat1


quote:

ORIGINAL: CHassan

SO one is rotating clockwise the other counter clockwise.


Do you still think 1= (-1)?




Why is this important???? No 1 is not equal to -1 as 1 is a greater number then -1.

Can 1-1= a number greater then 0???? For the aircraft to make forward movement on a conveyor that is spinning at a velocity in a counter clockwise direction its wheels would have to be free rolling at a velocity greater then 1 in a clockwise direction. Once this happens the the conveyor has failed to do what it was designed to do and that was to exactally match the wheel speed at all times.

As I said forward movement/Airspeed is =C in A-B=C

A is your wheelspeed in terms of velocity
B is your conveyor speed in terms of velocity
C is your airspeed/forward momentum/run out speed in terms of velocity

A-B=C





If 1 does not = -1 then you broke the rules of the question by using these measurements.





Not really. If the wheels forward rotation is clockwise and the conveyors forward rotation is counter clockwise then I have not broken the rules at all. They are both rotating in their forward rotation velocity of 1. The only difference is they are opposite of each other (clockwise vs counter clockwise). Get my drift????? Oh well everyone else understands it.



Oh so sine the absolute values are 1, then you can just throw a (-) in where ever you like? Not only that, but then pick and choose between the planes speed and the conve