Riddle Me This.........

[Mark351]

Originally Posted by 42.57lb

The conveyor is accelerating at the same rate as the plane in the negative direction agreed?

I think that's where most of us disagree. The conveyor matches the speed, not the acceleration. You're adding a condition to original question to produce the result you're after!

[42.57lb]

plane goes this way -----> by the explanation on the first page that would mean the conveyer is going <------ that way, so all I did was define ----> as positive and <---- as negative... that's all.

[42.57lb]

also, the conveyor would HAVE to accelerate to match the speed

[Charliewool]

Ok... Obviously none of you took the time to look at the "definitive" video?

Try this... (on your treadmill) or if you have access to a conveyor.. Put a skateboard with a fan (normal household type fan) on the deck. Turn the fan on, simultaneously activating the treadmill in the opposite direction. The skateboard will move AGAINST the rotation of the treadmill because of the fan propulsion.. Will it not? : :

[42.57lb]

the wheels of the skateboard will rotate at the same speed as the treadmill, if the force produced by the fan is enough to exactly compensate for the force applied to wheels by the treadmill, if it is GREATER the skateboard will go off the other end

[Ghiadude]

Originally Posted by SunDrifter

But i'm going to take an unpopular stab here, and suggest that if you read the question again, you see that this magical conveyer can theoretically spin fast enough to cancel the effect of planes thrust.

no it doesnt it says
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).

this means that if the plane is moving forward at 200kmh(takeoff speed) then the conveyer will be spinning the wheels at 200kmh in the oppostie direction...
these means that a speedo on the wheels will show twice that of the air speed but the air speed willstill be 200kmh enough to lift the plane..

you people are constantl;y forgetting that a planes engines move the plane through the air not on the ground!

[SunDrifter]

Don't get mad here guys, its just a bloody theoretical question. Just remember that the question assumes that the magical conveyer can inversly match the speed of the plane.

If the plane is stationary bar the wheels whipping around at a million miles an hour, the rest of the plane is still going to be stationary isn't it?

No movement, no lift.


<edit>tx3dude, thats an assumption.

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?

I read that statement as being the plane speed, and not the speed of the wheels.

Originally Posted by tx3dude

you people are constantl;y forgetting that a planes engines move the plane through the air not on the ground!

No, we are not forgetting this, but this factor is taken out of the equasion when you assume that the conveyer is able to negate any foward movement.

And sure, in reality it is impossible, (as mentioned above) in reality it would take off. But this theoretical question engenders some assumptions.

[42.57lb]

Originally Posted by tx3dude

no it doesnt it says
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).

this means that if the plane is moving forward at 200kmh(takeoff speed) then the conveyer will be spinning the wheels at 200kmh in the oppostie direction...
these means that a speedo on the wheels will show twice that of the air speed but the air speed willstill be 200kmh enough to lift the plane..

you people are constantl;y forgetting that a planes engines move the plane through the air not on the ground!

Dude, don't forget, airplanes start off being stationary! also, the wheels would only be spinning at 200kmph

[Pilch]

Originally Posted by tx3dude

no it doesnt it says
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).

this means that if the plane is moving forward at 200kmh(takeoff speed) then the conveyer will be spinning the wheels at 200kmh in the oppostie direction...
these means that a speedo on the wheels will show twice that of the air speed but the air speed willstill be 200kmh enough to lift the plane..

you people are constantl;y forgetting that a planes engines move the plane through the air not on the ground!

you are making an assumption beyond what is stated. The original question is OPEN ENDED, there are probably 1000 different results we could come up with based on different assumptions. There is NO definitive answer. Just lots of variables that we can tweak to get the result we want.

[Sourbastard]

I suggest this aircraft is capable of the launch.

[flavze]

The only ONE contributing factor as to wether an aircraft will take off is the effect of the wing moving through the air. The fuselage, engines and tyres have no direct impact on the airplane acheiving lift. They all have indirect impact in the ability for the wing to achieve momentum throught he air which in sequence causes the wing to have lift in an upwards motion carrying the wheels, fuselage and engines with it.

If the wing were to remain stationary then it would produce zero lift, and this is what would happen if a airplane was placed on a conveyer that would match the airplane for acceleration an speed.

[flavze]

well i made that post after reading the first page but after reading the rest i reckon i'm wrong and it will take off. Like others have said it will accelerate as normal with the tyres doing twice the normal speed!

[Rodp]

Originally Posted by Malakai

Holy sh1t, you people still don't get it.

Some of you still maintain that there would be no air movement. Why? I understand how planes create lift, but tell me how the conveyor makes any difference to the air being pulled through the engines! It can't.

The belt is not driving the air in the opposite direction... it's driving the ground. Which is irrelevant. The planes engines would still be able to pull it through the air. Period.

Also your millions of analogies about cars/bikes/people on treadmills/dynos/conveyors/escalators are all false. You can't compare a plane to any of those things, they simply do not transfer force in the same way. (IE wheels vs air)

Taking that line of thinking... wouldn't this bear similarity...? I've only read this far so unsure where the conversation has gone from here.

A yacht powered solely by wind in its sail travelling against a current. For the sake of argument we'll say that the force the sail is generating is equal to the current in the opposite direction.

Using your argument you're suggesting that because there's no drive in the keel of the boat, travelling upstream in a boat with a sail negates the force of the current...?

[gtfpv]

if a fly was in a car travelling 80kms an hour and the fly was hovering between the 2 front seats how fast would the fly be flying . answer = 0 km/hr
if the fly was on the roof hovering answer = 80km/hr
if the car was on a conveyer belt
fly on roof = 0
fly inside = 0
if the fly was on a car that was popelled
by a jet engine and the wheels spun freely
and the jet was set to 80km/hr the fly would be
flying at =80kms hour on roof. and the cars wheels would be spinning at 160kms /hr.

[JAJH]

I am having lots of difficulty understanding why anyone would think the plane WILL fly. Let's not bring variables into it, it's a simple case. Wheels, friction, bearings, airspeed, groundspeed all having nothing to do with it. If the plane's forward momemtum is negated by the conveyor running in the opposite direction, you simply do NOT have any air travelling over the wings, it is a stationary object, a lead balloon if you like. NO go anywhere!

[Rodp]

After 5 pages, I'm a believer. The plane will take off for the reason most people are suggesting.

That is, the thrust is independent of the driving wheels and that as much as you speed up the conveyor it will never negate the effect of the thrust (leaving obvious physical impossibilities behind).

The engines are sucking air in and expelling air out which creates forward momentum regardless of what the wheels are doing. The driving force is the thrust created from the engines, the wheels are negligable in this case.

Forward momentum will be created by the engines sucking in and expelling air, the wheels don't factor in any equation since they're free spinning objects that have no bearing in driving the plane forward, air will flow across the wings and the jet will take off.

[Perana]

Originally Posted by RodP

Taking that line of thinking... wouldn't this bear similarity...? I've only read this far so unsure where the conversation has gone from here.

A yacht powered solely by wind in its sail travelling against a current. For the sake of argument we'll say that the force the sail is generating is equal to the current in the opposite direction.

Using your argument you're suggesting that because there's no drive in the keel of the boat, travelling upstream in a boat with a sail negates the force of the current...?

There still would be frictional forces applied on the boat as there would be with the plane.. but the wind in the sails overcome this pushing the boat forward the same as the jet engines propel the plane forward.. the principle is much the same.


The problem is... The momentum is NOT negated by the conveyor... so not taking into account durability of tyres/wheels etc it would take off.

[gtfpv]

Originally Posted by JAJH

I am having lots of difficulty understanding why anyone would think the plane WILL fly. Let's not bring variables into it, it's a simple case. Wheels, friction, bearings, airspeed, groundspeed all having nothing to do with it. If the plane's forward momemtum is negated by the conveyor running in the opposite direction, you simply do NOT have any air travelling over the wings, it is a stationary object, a lead balloon if you like. NO go anywhere!

AIR SPEED IS IRRELAVENT TO GROUND SPEED.

[zetec]

Funniest thread I've read in a long long time. It has 250 people who each KNOW they're right. Funny thing is, there's about 15 different answers so far!!!

But I know the truth, it'll fly. So the rest of you can stay sitting at the Maccas in the terminal lamenting over your cancelled conveyor flight while I'm on my way around the world with Lynx Jet... stopping by Glengarry, Pyongyang, Ponoka then Baja.

[GenesiS]

The scientific answer is no.

Almost... Almost everything stated is right. The wheels will spin at twice the air speed, the engines will suck air though and cause air propulsion at the rate of the belt etc etc...

HOWEVER the aircraft displacement is ZERO. Ever noticed that when your in a gym and on a treadmill you tend to sweat more than when you are out running along the road???

That is because your moving and when you're actually moving you have a displacement and the wind is flowing around you and causing evaporation. When you're on a treadmill this effect doesn’t occur.

HOW does this relate you ask? Simple, a plane requires more than just thrust from the engines to take off. It is aerodynamically designed, and its wings require airflow due to displacement to actually gain enough lift to push the aircraft off the ground.
IF the plane is on a treadmill, this doesn’t occur so either you have a infinite loop and the plane just keeps on kicking with the treadmill, or you have a plane on its belly because as it pushed off the treadmill the air around the wings wasn’t pushing at the rate flowing through the thrusters and it simply falls as physics doesn’t allow it to gain lift.

Don't believe me… go ask a physicist... wait, that’s me!!! :

[rodderz]

...imagine this convo down the pub...it'd end up an all-in!

If the conveyor belt is matching the speed of the forward movement of the plane, obviously as the plane thrusts foreward under power, the conveyor will go forward too! The pilot can push as hard as he can on the throttle to get more thrust, which will only make the wheels turn faster, which will makew the runway turn faster!

And you have the drama of no airspeed to create the lower pressure unde the wings to lift it!

One of the posts said that the wheel bearings will explode before takeoff....i'm going with that one!

[zetec]

Originally Posted by GenesiS

The scientific answer is no.

Almost... Almost everything stated is right. The wheels will spin at twice the air speed, the engines will suck air though and cause air propulsion at the rate of the belt etc etc...

HOWEVER the aircraft displacement is ZERO. Ever noticed that when your in a gym and on a treadmill you tend to sweat more than when you are out running along the road???

That is because your moving and when you're actually moving you have a displacement and the wind is flowing around you and causing evaporation. When you're on a treadmill this effect doesn’t occur.

HOW does this relate you ask? Simple, a plane requires more than just thrust from the engines to take off. It is aerodynamically designed, and its wings require airflow due to displacement to actually gain enough lift to push the aircraft off the ground.
IF the plane is on a treadmill, this doesn’t occur so either you have a infinite loop and the plane just keeps on kicking with the treadmill, or you have a plane on its belly because as it pushed off the treadmill the air around the wings wasn’t pushing at the rate flowing through the thrusters and it simply falls as physics doesn’t allow it to gain lift.

Don't believe me… go ask a physicist... wait, that’s me!!! :

Some people NEVER give up!! We have physicists, pilots, brain surgeons (perhaps) and we still can't get it right!!!! All I want to say is I'll never fly, never have brain surgery and never need physics tutoring with experts like this!!!! :the_finge

[JAJH]

Originally Posted by gtfpv

AIR SPEED IS IRRELAVENT TO GROUND SPEED.

Your point is what? I said the same thing that airspeed, groundspeed, friction,thrust, etc, etc is all irelevant, not forward movement, no air over the wings, no lift.

[GenesiS]

Originally Posted by zetec

Some people NEVER give up!! We have physicists, pilots, brain surgeons (perhaps) and we still can't get it right!!!! All I want to say is I'll never fly, never have brain surgery and never need physics tutoring with experts like this!!!! :the_finge

Sorry mate, but after reading the first two pages of garbage I decided to write a relpy and not read the rest. My bad, I don't claim to be an expert, but I have spent the last 5 years now studying physics at University in an Applied Science degree, out of interest, how do YOU know what is right and wrong... just curious is all

[Rodp]

Originally Posted by zetec

Funniest thread I've read in a long long time. It has 250 people who each KNOW they're right. Funny thing is, there's about 15 different answers so far!!!

But I know the truth, it'll fly. So the rest of you can stay sitting at the Maccas in the terminal lamenting over your cancelled conveyor flight while I'm on my way around the world with Lynx Jet... stopping by Glengarry, Pyongyang, Ponoka then Baja.

One way ticket to Ponoka thanks...

[rodderz]

I've finished a beer or 3, and I'm stuffed if i can agree with the "take off" theories...

Theoretically the pilot could be punting the thing flat stick, but the conveyor would notice the increase in wheel speed and move faster backward. In effect, the whole thing is on rollers. Even with thrust the wheels need to move foreward so that the appropriate wind speed can be achieved, but this will be cancelled out by the treadmill effect

The plane needs to move foreward to get lift, which is impossible with the bloody treadmill working overtime!

[rodderz]

Originally Posted by Malakai

Now I am completely astonished...

BTW the lower air pressure is required ABOVE the wings for lift to be created.

read post above for beer comment! :1syellow1

I knew what i meant! lol

[flappist]

Originally Posted by GenesiS

Sorry mate, but after reading the first two pages of garbage I decided to write a relpy and not read the rest. My bad, I don't claim to be an expert, but I have spent the last 5 years now studying physics at University in an Applied Science degree, out of interest, how do YOU know what is right and wrong... just curious is all

While you were busy at school studying, I was busy flying aircraft.
I bounced the same question of a few buddys.

1) QANTAS Captain 747
2) Ex QANTAS Captain (ret) chief check & training 747, 707, constellation
3) Commercial pilot, ex chief pilot for turbine charter organisation
4) Commercial pilot, line check & ground school for major freight organisation
5) LAME
6) AME

Between us over 30,000 hours (mostly them)

All say it will fly, but then we all left school a long time ago....

[GenesiS]

Originally Posted by flappist

While you were busy at school studying, I was busy flying aircraft.
I bounced the same question of a few buddys.

1) QANTAS Captain 747
2) Ex QANTAS Captain (ret) chief check & training 747, 707, constellation
3) Commercial pilot, ex chief pilot for turbine charter organisation
4) Commercial pilot, line check & ground school for major freight organisation
5) LAME
6) AME

Between us over 30,000 hours (mostly them)

All say it will fly, but then we all left school a long time ago....

Fair enough, but I would like to know how it would fly. Everything that I have been taught about aerodynamics and how a plane actaually lifts off the ground (creating low pressure and atempting to cause equilibrium etc etc) basically, as far as i can tell would have to be ignored.

I can't see how the lift and drag would be simulated on a treadmill... Although I may be missing something, so I would love for you and your buddies, and the person to whom that comment was actually directed at to actually tell me how it works, within reason, I mean because I say so really counts for , there's no reason behind it.

I mean last time I checked the way a plane operated... basic theory is that, the engine creates thrust, allowing forward direction and travel (effectively pulling the aircraft through the air as it sucks then pushes), while the air which it is travelling around the aircraft (not apparent on a treadmill) travels over and under the wing span. due to the shape of the wings and the calculated area, low pressure is created and the factors of lift and drag occur, allowing the plane to actually lift of the ground. The flaps, when correctly positioned allow for equillibrium, say when flat at 30,000 feet...

That is my basic, dumb downed idea of the actual operation of an airplane, the basics of the physics and aerodynamics...

I can't see how all of that occurs on a treadmill, as the treadmill effectively renders the dissplacement zero and thus the aircraft stationary... Which means the air is being sucked directly into the engines, no airflow around the wings and thus no low pressure...
same as when you're on a treadmill at the gym, you sweat because air doesn't circulate the body and evaporate the sweat.

So now I want to know!!!! Fill me in!

[Casper]

Originally Posted by GenesiS

I can't see how all of that occurs on a treadmill, as the treadmill effectively renders the dissplacement zero and thus the aircraft stationary... Which means the air is being sucked directly into the engines, no airflow around the wings and thus no low pressure...
same as when you're on a treadmill at the gym, you sweat because air doesn't circulate the body and evaporate the sweat.

So now I want to know!!!! Fill me in!

Its Different to being on a treadmill at a gym. The difference being that a plane is not powered forward by forces pushing into the goround (treadmill). To use the same theory go to the gym, stand on a skateboard on a treadmill and turn it on flatout. Then pull yourself forward with your arms (the equ of a prop or jet thrust into the atmosphere creating forces to move forward). Now, regardless of how fast the treadmil is going... your going to go forward. Why? Because the wheels on the skateboard are just there to hold you off the ground.. your arms are the "thrust" and no matter how fast the treadmil is going it has absoulutly no effect on your arms pulling you forward on a treadmill. Unless the treadmill can manipulate the atmosphere around it.. the plane is going forward and will create lift with the airflow.. and take off.