[I]This is blatantly stolen from another board, but I curious as to what some of the real "minds" over here at MS have to say about the subject. [/I]

[IMG]http://img95.imageshack.us/img95/9675/airplanean1.jpg[/IMG]

A plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.

The question is, will the plane take off or not?

Re: Will it take off?

No I don't think so. You're saying the conveyor cancels out the plane's forward vector. So your plane is stationery.

If I'm not wrong the plane has to gather enough speed for the air/wind to work on those wings to lift it up.

[IMG]http://www.ueet.nasa.gov/StudentSite/images/engines/wingairflow.gif[/IMG] [URL="http://www.ueet.nasa.gov/StudentSite/dynamicsofflight.html"] Dynamics of flight[/URL]

Re: Will it take off?

Mythbusters did this, and yes it takes off

Re: Will it take off?

^ but myth busters was crap. The "treadmill" was not countering the speed of the plane as the plane is clearly acclerating forward.

[URL]http://mythbustersresults.com/episode97[/URL]

Re: Will it take off?

i've heard a bunch of different responses and i'd have to see it for myself because i don't know who to believe. i think the answer is no, the plane will not take off [I]if it is solely using the treadmill to gain momuentum and not moving forward[/I]. as soon as it goes up in the air, i would think there isn't enough resistance against the air to keep it afloat. part of the reason the planes fly is the air it distributes under and above its wings to balance itself. when it takes off, it doesn't have the force against the plane it would have if it were moving forward and i'd think it'd just come back to the ground.

Re: Will it take off?

I'm with feather, the plane is in fact stationery (conveyor canceling the forward motion of the plane) and you need airspeed to lift the wings/plane. Can't see how the plane took off.

Re: Will it take off?

[quote=threehills;621815]^ but myth busters was crap. The "treadmill" was not countering the speed of the plane as the plane is clearly acclerating forward.

[URL]http://mythbustersresults.com/episode97[/URL][/quote]

[QUOTE]This is because the thrust of the airplane engines acts on the air, not on the ground.[/QUOTE]

that doesn't sound right, even if the engines are providing the forward thrust, wont the reversing direction of the treadmill reverse the airflow (by moving the plane backward at the same speed) thereby providing nearly no "lift"

Re: Will it take off?

Actually ... if those engines are there to provide thrust from sucking air in and thus over and under the wings (I always assumed the engines were there to propel the plane forward on the runway, but Kamal makes an illuminating point or whoever he quoted), the plane might end up lifting off or hovering. But I don't think it will maintain its flight as there is no forward motion here, the conveyor has cancelled it.

Re: Will it take off?

i guess it might depend on how much thrust the engine emits. i'd think it'd take a helluva lot more thrust to keep a plane up in the air from a standstill (how much more thrust? is it possible?) than if it were already moving at normal takeoff speed.

Re: Will it take off?

[quote=Troklo;621812]Mythbusters did this, and yes it takes off[/quote]

Fucking Mythbusters! The ruin everything...Fucking assholes. :lol:

Re: Will it take off?

[quote=feather;621825]but Kamal makes an illuminating point or whoever he quoted), the plane might end up lifting off or hovering[/quote]

thats quoted from the mythbusters link that threehills posted. If the "thrust" from the engines is in fact lifting the plane, then premise of the experiment is inaccurate imo because the wind speed through the engines far exceeds the reversing speed of the treadmill.

Re: Will it take off?

if its a harrier jumpjet it will take off - no problem :)

Re: Will it take off?

[quote=Huggie Smiles;621831]if its a harrier jumpjet it will take off - no problem :)[/quote]

:lol:

Re: Will it take off?

Yes it will take off. Think of yourself running on a treadmill. The faster you run the more air resistance you have. IMO

Re: Will it take off?

[quote=srbbnd;621833]Yes it will take off. Think of yourself running on a treadmill. The faster you run the more air resistance you have. IMO[/quote]

Not so my friend. Runner's world suggests always running at a +1% incline to what you would normally do to simulate the MISSSING air resistance.

The only air resistance encounterd while on a treadmill is from your arms swinging through the air...not whole body air resistance from running normally.

Re: Will it take off?

What feather said is exactly right. Airspeed that is higher over the top than the bottom of the wing is what gives a plane lift. A conveyor belt serves no purpose because you need the air over the wings to be at rotation speeds, not just have the wheels move really fast.

Re: Will it take off?

[quote=srbbnd;621833]Yes it will take off. Think of yourself running on a treadmill. The faster you run the more air resistance you have. IMO[/quote]

You aren't much of a runner or a thinker, are ya?

Re: Will it take off?

^ lmao. someone had to say it :lol:

Re: Will it take off?

[quote=feather;621811]No I don't think so. You're saying the conveyor cancels out the plane's forward vector. So your plane is stationery.

If I'm not wrong the plane has to gather enough speed for the air/wind to work on those wings to lift it up.

[IMG]http://www.ueet.nasa.gov/StudentSite/images/engines/wingairflow.gif[/IMG] [URL="http://www.ueet.nasa.gov/StudentSite/dynamicsofflight.html"] Dynamics of flight[/URL][/quote]

^ the reason why It won´t take off...

Re: Will it take off?

[quote=threehills;621836]Not so my friend. Runner's world suggests always running at a +1% incline to what you would normally do to simulate the MISSSING air resistance.

The only air resistance encounterd while on a treadmill is from your arms swinging through the air...not whole body air resistance from running normally.[/quote]

The only difference is wind. The air resistance would be the same outside if there was no wind. I think...

Re: Will it take off?

the aeroplane can still take off, it just needs an adequate runway length treadmill, and its wheels will simply spin twice as fast as normal matching the aeroplanes speed x 2 due to the treadmill (disregarding all friction forces etc).

The thrust comes from jet engines, not from the wheels, if it did then aeroplanes wouldn't be able to fly very far.

Its a funny psychological trick because it has two garden paths:

-One is that due to the conveyer belt, the plane can take off vertically relative to a static observer - wrong -The other is that it cant take off because the plane can't generate any thrust due to the belt -wrong too.

Re: Will it take off?

^^^ but isnt the point of this being the fact that the plane ISNT moving forward just stationary on a "conveyor belt"? so having a runway length treadmill would defeat the purpose.

Re: Will it take off?

[quote=Kamal;621820]I'm with feather, the plane is in fact stationery (conveyor canceling the forward motion of the plane) and you need airspeed to lift the wings/plane. Can't see how the plane took off.[/quote]

doesnt meen everything around it is stationary i.e. air etc

Re: Will it take off?

in which case the plane wouldn't be able to take off simply because the runway length is too small, so not enough upward force is generated from airflow to counterat gravity (I guess the problem could be read like that) lol

another way of looking at it is that if you fired wind towards the nose of the plane at a speed that matched the jetengines, the aeroplane then could rise directly up to a static observer

Re: Will it take off?

[quote=red1;621898]doesnt meen everything around it is stationary i.e. air etc[/quote]

so if you're standing stationary, a wind blows against you, you open your shirt and hold it apart like a set of wings, you're betting you're gonna take off ?

Re: Will it take off?

erm tbh it was a bit of a dum answer, crazy question...i,m gonna loose sleep over this one tonight lmao...

Re: Will it take off?

[quote=jamesalvarez;621895]the aeroplane can still take off, it just needs an adequate runway length treadmill, and its wheels will simply spin twice as fast as normal matching the aeroplanes speed x 2 due to the treadmill (disregarding all friction forces etc).

The thrust comes from jet engines, not from the wheels, if it did then aeroplanes wouldn't be able to fly very far.

Its a funny psychological trick because it has two garden paths:

-One is that due to the conveyer belt, the plane can take off vertically relative to a static observer - wrong -The other is that it cant take off because the plane can't generate any thrust due to the belt -wrong too.[/quote]

I understand your arguement, I do..really. But the problems states that [I]the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction[/I]. I think about it like this...imagine the treadmill starts up fist. Natually the place moves backwards relative to the viewer as the friction between the wheels and treadmill holds the plane fast to the tread. Now the jets fire, providing thrust that is equal to the friction (static initially, kinetic once the wheels start to roll), but opposite in direction. Now, the plane is rolling along the tread, in a "forward" direction, but remaining stationary to the observer (a fixed point on the ground). The obsever/fixed point could also be considered to be the air. So.....relative to the air, the plane is not moving. No air is sliding over the wings and no lift is generated so the plane remains firms on the treadmill.

Re: Will it take off?

[quote=threehills;621916]I understand your arguement, I do..really. But the problems states that [I]the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction[/I]. I think about it like this...imagine the treadmill starts up fist. Natually the place moves backwards relative to the viewer as the friction between the wheels and treadmill holds the plane fast to the tread. Now the jets fire, providing thrust that is equal to the friction (static initially, kinetic once the wheels start to roll), but opposite in direction. Now, the plane is rolling along the tread, in a "forward" direction, but remaining stationary to the observer (a fixed point on the ground). The obsever/fixed point could also be considered to be the air. So.....relative to the air, the plane is not moving. No air is sliding over the wings and no lift is generated so the plane remains firms on the treadmill.[/quote]

Exactly

Re: Will it take off?

it wont take off. the premise of drag and lift on the wing is absent when the wing is not moving through a medium (air).

the wheels are rotating around thier core, however, there is nothing happening to the wing.

Re: Will it take off?

Let me bring my piloting expertise into this one (yes I'm a private pilot).

Say you were about to take off and you had a wind that was going parallel to the runway. Conventional wisdom would say that you would want to take off with the wind, no? But conventional wisdom doesn't apply to aerodynamics. You want to take off into the wind (a headwind) because air resistance is what gets the airplane off the ground. Since there is more wind/air coming over the leading edge of the wing (i.e. what creates lift), even though you're technically not going as fast with relation to ground speed, [U][B]the air speed is all that matters[/B][/U]. So if you were to takeoff with the wind (a tailwind), you would need to be going much faster ground speed wise to get the same amount of air over the leading edge of the wings, and unless you're taking off on the space shuttle landing strip, you would probably run out of runway before you got to rotation speed (speed the airplane can lift off the ground and climb).

So going back to this "conveyor belt" idea, there is no way that this would work with any conventional aircraft because while your wheels may be spinning like you're going 150 knots, your airspeed is essentially 0. The engine does provide some air over the wings (in a propeller plane for example) but nowhere near the amount and speed of air that is needed to get the plane off the ground. You need forward motion.

Re: Will it take off?

^ very well put. i don't know how many times it needs to be repeated in different ways before people start understanding. i have a hard time believing this is such a popular argument on the internet.

Re: Will it take off?

And something else for people to consider if they still don't understand that: if you hold the brakes and put the engine to full throttle, you're not taking off the ground. The only thing that is different between holding the brakes and being on a conveyor belt is the wheels moving. Moving wheels do absolutely nothing.

Re: Will it take off?

[quote=Garrick;621946]^ very well put. i don't know how many times it needs to be repeated in different ways before people start understanding. i have a hard time believing this is such a popular argument on the internet.[/quote]

Cause mythbusters shows the plane taking off. But its a crock because they don't set up the experiment correctly.

Re: Will it take off?

[quote=MJDub;621944]Let me bring my piloting expertise into this one (yes I'm a private pilot).

Say you were about to take off and you had a wind that was going parallel to the runway. Conventional wisdom would say that you would want to take off with the wind, no? But conventional wisdom doesn't apply to aerodynamics. You want to take off into the wind (a headwind) because air resistance is what gets the airplane off the ground. Since there is more wind/air coming over the leading edge of the wing (i.e. what creates lift), even though you're technically not going as fast with relation to ground speed, [U][B]the air speed is all the matters[/B][/U]. So if you were to takeoff with the wind (a tailwind), you would need to be going much faster ground speed wise to get the same amount of air over the leading edge of the wings, and unless you're taking off on the space shuttle landing strip, you would probably run out of runway before you got to rotation speed (speed the airplane can lift off the ground and climb).

So going back to this "conveyor belt" idea, there is no way that this would work with any conventional aircraft because while your wheels may be spinning like you're going 150 knots, your airspeed is essentially 0. The engine does provide some air over the wings (in a propeller plane for example) but nowhere near the amount and speed of air that is needed to get the plane off the ground. You need forward motion.[/quote]

the expert has spoken...nuff said

Re: Will it take off?

I work at a University just called the aviation department. They said there is no way this would work. There is no indicated air speed and no angle of attack was the terminology they used. However, if there was a giant fan in front of the plane this could work...

Re: Will it take off?

[QUOTE=MJDub;621944]Let me bring my piloting expertise into this one (yes I'm a private pilot).

Say you were about to take off and you had a wind that was going parallel to the runway. Conventional wisdom would say that you would want to take off with the wind, no? But conventional wisdom doesn't apply to aerodynamics. You want to take off into the wind (a headwind) because air resistance is what gets the airplane off the ground. Since there is more wind/air coming over the leading edge of the wing (i.e. what creates lift), even though you're technically not going as fast with relation to ground speed, [U][B]the air speed is all the matters[/B][/U]. So if you were to takeoff with the wind (a tailwind), you would need to be going much faster ground speed wise to get the same amount of air over the leading edge of the wings, and unless you're taking off on the space shuttle landing strip, you would probably run out of runway before you got to rotation speed (speed the airplane can lift off the ground and climb).

So going back to this "conveyor belt" idea, there is no way that this would work with any conventional aircraft because while your wheels may be spinning like you're going 150 knots, your airspeed is essentially 0. The engine does provide some air over the wings (in a propeller plane for example) but nowhere near the amount and speed of air that is needed to get the plane off the ground. You need forward motion.[/QUOTE]

Well, I'm satisfied with that answer. Thanks. :Bingo:

Re: Will it take off?

Surely the two would just cancel each other out and the plane would be stationery going neither forwards or backwards and certainly not anywhere near flying!

Re: Will it take off?

[QUOTE=MJDub;621944]Let me bring my piloting expertise into this one (yes I'm a private pilot).

Say you were about to take off and you had a wind that was going parallel to the runway. Conventional wisdom would say that you would want to take off with the wind, no? But conventional wisdom doesn't apply to aerodynamics. You want to take off into the wind (a headwind) because air resistance is what gets the airplane off the ground. Since there is more wind/air coming over the leading edge of the wing (i.e. what creates lift), even though you're technically not going as fast with relation to ground speed, [U][B]the air speed is all the matters[/B][/U]. So if you were to takeoff with the wind (a tailwind), you would need to be going much faster ground speed wise to get the same amount of air over the leading edge of the wings, and unless you're taking off on the space shuttle landing strip, you would probably run out of runway before you got to rotation speed (speed the airplane can lift off the ground and climb).

So going back to this "conveyor belt" idea, there is no way that this would work with any conventional aircraft because while your wheels may be spinning like you're going 150 knots, your airspeed is essentially 0. The engine does provide some air over the wings (in a propeller plane for example) but nowhere near the amount and speed of air that is needed to get the plane off the ground. You need forward motion.[/QUOTE]

lol - air speed does matter, it is confusing but if you have a long enough runway then the plane can take off. The conveyor belt will only cause a tiny amount of extra friction due to the increased wheel rotation in contact with the ground.

forget what the wheels are doing its what's confusing. the jet engines creates a pressure difference in the -air- which causes them to pull the plane forward due to -air- friction. like a submarine uses a turbine in water. the forward motion is created from a force on the air not the ground. so a forward motion would be generated and the plane can rise.

think of the behaviour of wheels that are not connected to an engine, if you lift the airplane up, set the conveyor on full and put it down again, for a second the wheels will just spin with the airplane still, (then friction as a force on the wheels would slowly cause cause the plane to accelerate backwards). This what would happen without a jet engine on. If you put the engines on full, the plane would start moving forward.

the wheels on an airplane are just there to support the plane and lower friction for taking off and landing and maybe they drive it slowly round the airport? dunno but they are not used for flying!

if the aviation department got it wrong then they probably didn't get the question. it is pretty confusing and i would certainly not blame anyone for not getting it at first

Re: Will it take off?

Edit to my post:

"...the air speed is all [U][B]that[/B][/U] matters."

Re: Will it take off?

[QUOTE=MJDub;622025]Edit to my post:

"...the air speed is all [U][B]that[/B][/U] matters."[/QUOTE]

yeah, and whatever the conveyor belt does , it doesn't effect the air speed the airplane can -still- generate!