Know that if you do not post in this thread today the human race may cease to exist

Moby, it's for the sake of analogy. Are you just trolling now?

The air and the water are both the media through which their respective crafts propel themselves. The conveyor is simply there, touching an innocuous part of the craft which will have no effect on how that craft gets where it's going.

That's right! The glider is now MOVING through *not calm* air. (Moving air is inherently *not* calm. The glider is still moving! But the conveyor belt is also moving backward! Why? Because the glider is being towed!

They aren't the same craft. You really can't compare them.

Again...if the plane is standing still (it is, if the conveyor is moving), then there is NO wind to give the wings lift. The wings MUST have lift to get the plane off the ground.

The plane is not being towed. So it doesn't move against the calm air. No lift.

If the plane is standing still, then the conveyor belt isn't moving, and it may as well be a parking lot.

Moby, what part of the plane has to move in order for the plane to be moving?

For your arguement to work, you would have to say the tires. But the tires on a commercial airliner are tucked up under the body, so does the plane not move, then, if the tires aren't rotating?

His example is not flawed. In it, the winch/truck/plane-not-on-a-conveyor (or on a conveyor, as it turns out) replaces a prop/turbine as a means of propulsion. None of these means are influenced by the conveyor.

Forget the plane for a second. Does a glider being towed get lift?

The bitter taste of poor quality remains long after the sweetness of low price is forgotten.

I'd rather apologize once for a higher price, than over and over for poorer quality.

Yeah, it's better to ask forgiveness than to ask for permission.

A plane does not need lift to move forward. It needs only to push air.

No, not the tires.

Assuming calm air, that means the plane has to move in relation to the air...and the ground (since it's calm). That ain't gonna happen.

Put a windsock on the tip of the wing. Start the experiment. That sock is not going to flutter at ALL. If it's not fluttering, there is no wind to provide lift for the plane.

It CAN'T move forward. It's not weightless. The conveyor belt keeps it from moving foward.

If it does move forward, the conveyor belt is failing to meet the speed.

Dude, Moby! Forget the plane for a second. Does a glider-in-tow on a conveyor belt move forward, get wind over its wings, and take off?

Not if the car is on a conveyor belt.

You're introducing an external power supply.

By the way...who's the fucker who started this thread?!

Not correct. The aircraft has weight, yet can still taxi around. It taxis by pushing air, not by turning its wheels. The conveyor cannot keep the plane from moving any more than an overhead conveyor (even with equal load-bearing, say, a weight of 500 lbs on a vessel weighing 500 lbs) can't keep a boat from moving.

The car's NOT on the conveyor belt. Yes, the power supply is EXTERNAL. But it's external to the CONVEYOR belt! The power supply is still ATTACHED TO THE GLIDER.

Moby... The plane doesn't power/move because it's wheels move. It's wheels moving is irrelevent. And whatever they're touching is irrelevent. They spin freely, providing NO resistance to the aircraft movement. Therefore, you can spin 'em any direction you want, sideways even, and it won't matter because the plane's overall movement is caused by its engines, not it's wheels.

Stolen from another forum:

Since the air is calm, the plane MUST move relative to the ground to get air flowing across it's wings.

The conveyor belt prevents it from moving in relation to the ground.

If the plane is taxiing (sp?), the conveyor belt will STILL keep it from moving.

No, it really won't.

No, it won't. The tires on the plane spin freely.

It will.

Again...put a windsock on the wing. It will not flutter.

It is physically not possible for freely rotating wheels to prevent an airplane from moving.

I swear you're just trolling now. The conveyor can apply a certain amount of friction to the wheels. The prop/turbine can provide much more force (more) directly to the fuselage of the aircraft. The force applied to the bottom of the wheels/tires causes them to spin on their respective axes (axises?) but not hold the fuselage back. Greater thrust than resistance causes the plane to move forward. As the plane moves forward the conveyor speeds up, yet is only causing friction with the bottom of the spinning tires. The prop/turbine is creating greater friction with the air. The aircraft continues to move forward at a greater rate. then, of course, as air moves over the wing (because the plane is not stationary, it is moving) the effect of gravity is less and less as the plane accelerates, resulting in less friction on the tires. Eventually lift is achieved, and the plane can go look for an inverted conveyor with a boat underneath it.

Not if the plane isn't moving.

But if the conveyor belt is moving, then the plane is moving. Period. That's in the given problem statement.

And if the plane is moving, then that windsock will be flapping like all hell.

Again, you have changed it. The conveyor matches the speed in the opposite direction. The aircraft can NOT move forward at a greater rate - the conveyor will match it. It cannot move forward at ALL.

The airspeed is 0.

OK. Stand next to the plane on the side of the conveyor belt.

In relation to you (which is also in relation to the wind, since it's calm), the plane WILL NOT BUDGE.

If the plane moves at all, then it's by the thrust of its engines.

If the plane moves, then the conveyor moves in an opposite direction and speed.

The conveyor only applies rotational force to the wheels of the plane. The rotational force of the wheels is NOT then applied to the thrust of the engines; the two are not linked in any way.

Therefore, the plane moves independent of the wheel rotation, at all times. Hence the reason a plane can fly, yet the wheels are not rotating at all.

Don't make me go Newtonian on your ass...

Just because the conveyor matches the planes speed does not mean that the plane is stationary. I have changed nothing. No matter how fast the conveyor spins, as long as the prop is pushing air it will move forward.

::ETA:: The key is greater friction with the air (caused by the prop/jet turbine pushing air) than friction with the conveyor.

Mobycat, please explain how the conveyor belt applies force to the aircraft. Do you agree with the following statement?

-- The force the conveyor belt applies to the aircraft is due to friction in the wheel bearings and deformation of the tires making them not perfectly circular. --

If we agree on the above statement then the aircraft needs to extert enough force (engines pushing against the atmosphere) to overcome the conveyor belt's force before the plane can move. I think it's been established that once the plane generates enough lift via. airspeed that it can take off.

So, if you agree with the above (and please post your arguments if you don't) then the critical issue is how much force the conveyor can exert on the plane.

Since the conveyor can only exert force through friction in the bearings and wheel deformation there is no way it can extert enough force to overcome the jet's engines. If it could that would mean that jet's would never take off in the first place because they wouldn't be able to get moving, which obviously is not the case. The most that could happen would be that as the jet accellerates the wheels will be spinning at 2x the normal speed, which might cause some slight additional resistance. The only way the jet won't take off is if the wheel bearings fail because they are subjected to speeds outside of their design parameters.

On a side note, when people talk about the jet's "speed" are you talking air speed or ground (wheel) speed? If we are talking air speed then the jet would need to first move relative to the air to induce movement in the conveyor. If the argument is that the conveyor can extert enough force to stop the jet then we wind up with the jet's engines on full and neither it or the conveyor moving at all, which makes absolutely no sense.

- Matt

Moby, I'm afraid you're mistaken in this case. Your concept would have been correct if we were talking about a vehicle which is propelled down the runway by providing power to the wheels.

This is a completely different scenario. You must see that the wheels or the speed of the coveyor have absolutely no effect on the plane taking off.

It will fly.

The plane has to gain airspeed to lift off. The force of gravity keeps it on the ground when it's stationary.

For it to move forward, it would have groundspeed. The air is calm. That means the air is equal to the ground in relation to the plane. If the plane cannot move on the ground, it cannot move in the air.

It cannot move on the ground, because the conveyor is negating it's forward movement.

It wouldn't matter if the wheels had a true no-friction connection to the plane. The conveyor is STILL going to counteract it.

It WOULD matter if the wheels were locked - the jets should have enough thrust to burn the wheels off (since the conveyor then wouldn't move, since the wheels aren't moving).

The wheels move because of the jets. Which means the jets in effect move the conveyor (since it matches the speed in opposite).

Actually it's not.

What moves the wheels? (regardless of whether they are free spinning)

The plane's motion through SPACE (both on the ground and through AIR) sets the wheels in motion.

It's a given that as something that rests on the ground moves along the ground, it also moves through the air, too. It's the air that's being pushed through the engines, not the ground.

But it's not moving through the space. The air is moving at the same speed as the plane - relative to the conveyor belt.

What moves?

Conveyor belt
Wheels

What does NOT move?

Ground
Air

Since the air is not moving, it cannot provide lift to overcome the downward force of gravity.

OK.

Put one plane on one end of the conveyor belt.

Put another on the opposite end.

The conveyor belt counteracts the tires of one of them.

The other plane does not start it's engines. It will go with the conveyor belt.

Which will take off?

The one that has not started it's engines. The conveyor has pushed it through the air providing the pressure to cause lift.

Nothing moves the wheels. The wheels are simply freespinning. Yes, when the treadmill is moving backwards there's litte friection force applied to the wheels but way not enough to overcome the force of thrust delivered by the engines.

The force of thrus is completely not dependent on the speed of ground. No matter how fast the ground moves underneath, or whether it moves fast or slower, it would play no effect.

Let's say the same plane is on the same runway, BUT the direction of the runway movement would now be the same as the direction of the plane's take off.

Let's say that when the plane guns the jet engine the runway treadmill will spin at 400 mph ground speed (example). Let's assume that it would reach that speed instanteniously. Assume that there's no friction or rolling resistance.

The plane now is standing still and not moving anywhere. Engines are off. Now turn on the engines. The plane begins to take off.

Wrong. The propulsion of the jets move the wheels.

Wrong. Wheels move due to plane accelerating down the runway. But the egines do NOT apply torque to the wheels thus spinning them. That's not a car. Maybe you're not really clear on how the jet engine works.

Correct. Gravity also keeps the plane on the ground when it's moving. If it's moving at a great enough speed, gravity is counter-acted by aerodynamic lift.
It means the air is stationary, even if the conveyor moves under it. Here you are assuming that the aircraft cannot move on the ground.
Incorrect. The conveyor cannot exert enough force or friction on the tires to counteract the thrust of a jet or prop.
The very purpose of the wheels is to reduce friction with the ground (conveyor, in this case). The purpose of the prop/jet is to create friction with the air. The props/jets create immense power and lots of friction with the air, creating forward movement. The wheels make it easier to move the aircraft over the surface. The surface moves in the opposite direction of the plane, with the conveyor, at twice the normal rate.
The wheels being locked matters in another way-it is creating more friction with the conveyor/ground. This friction can still be overcome, though it is not safe. An aircraft under full power with brakes locked will move forward.
The jets do not move the wheels. The jets push the plane, and the friction with the ground causes the wheels to move. The original problem says nothing about the wheels pushing the conveyor, it says the conveyor matches the plane's speed.

ok its going to take a blond to answer the question.. If you are in the gym and there happens to be a blond on the treadmill, she is running as fast as she can, and her hair is down.. Will her hair fly back like it would if she was running on the side of the road.. NO.. There is your answer..

Then the question is flawed. If it cannot exert enough force, it cannot match the speed. The question said it can.

Well, I'm outta here. Time to go home.

I have the question sent to a couple people - 1 engineer, 1 pilot.

We'll see what their opinion is.

this is assuming that the treadmill of the plane can keep up with the top speed of the jet.

The friectional force of the conveyor belts is NOWHERE near enough to negate the Thrust force of the jet engine.

If you push/pull a wagon, are you moving the wheels, or are the wheels reacting to your kinetic energy?

When you drive your rig, the engine turns the wheels directly (through the drivetrain) creating the forward motion of the truck. When you push a radio flyer, the wheels are reactive, not active. put a radio flyer on an old-fashioned treadmill (which requires you to push it to get it going). You can roll it right off and the treadmill won't turn, because you're not exerting any force on the surface.
The speed of the aircraft and the speed of the conveyor are independant quantities. The question does not say that the plane will be kept stationary by the conveyor, it says that the conveyor will spin at the same speed in the opposite direction. Ergo- plane travels 120 KIAS, conveyor goes 120 knots, wheels spin at 240knots until liftoff.

::eta:: Speed and force are different things. The conveyor can still match the plane's speed but not be able to push the plane back. It can't push the plane back because some clever monkey put wheels on the bottom, so when the conveyor pushes against the bottom of the tire, it just spins. Meanwhile the plane is pushing air and travelling at the same speed as the conveyor, but in the opposite direction. [notice I said "travelling", not "sitting"] No matter how much the conveyor pushes, all it affects are the wheels. It cannot push on the fuselage or any other part of the plane like the prop/jet can.

Even if the conveyor spun at 100 times the speed of the aircraft, the plane would still create forward speed by pushing air the way a powerboat pushes water. The friction against the wheels is infintesmal (sp?) and is overcome by the props/jets pushing the whole plane.

OMG

OK

The Xterra on the tread mill is limited as the CF's are arguing...and could not move...the plane is not, and can move.

The engine's thrust does NOT turn the wheels...the wheels, in fact, won't move AT ALL in the given example, unless THE PLANE moves.



So, the can't fly proponents (CF'rs) are NOT saying that the wheels will spin too fast, or that the conveyor will run too fast...but, that the conveyor will not move AT all.



Pay Attention here:

If the conveyor belt rolls AT ALL...it means the plane is moving.

There is NO other way to make the conveyor move...it matches the plane's speed exactly.

Let that sink in.
_________________________________________________



OK

Now,

WHAT can make the plane move?

There's only ONE thing that makes the plane move...any guesses?



The thrust from the engines.

Can we all agree that a planes engines can make it move?

I mean...its worked for deacdes so far...that's how they do it every day at Newark Airport at least.



Fine - we have the ability to make a plane move using thrust from the engines...agreed?

(We all ALSO agree that if the plane could power its tires, that THAT would NOT make the plane move...as THAT motion is the same as the XTERRA's motion...)

Now - here's the part where all the CF's trip up on the logic...

The thrust will push the plane forward...and, the conveyor will roll along under it...

Hold that thought...

Here's the moment of truth...

Can a runway that rolls towards you, keep you from ever rolling forward?

NOT matching you...actually rolling towards you...so you would actually be carried backwards if you didn't move forward.

Could you take off then, using the same logic, it should be a lot harder, right?

Not only are you not already going forward, or accelerating from a stand still as normal, you have momentum carrying you backwards.

___________________________________-

Can thrust overcome momentum in the opposite direction?

________________________________________

I hope so, its how a retro rocket, etc, works.

_________________________________

Its also how a Jump Jet Lands, etc.

________________________________________-

OK - so we have the principle that thrust from a jet engine can over come actually travelling in the wrong direction.

_____________________________________

We also know that the runway is not going to change that....or the conveyor belt...

As, its the plane's motion relative to the planet, not the the belt, that makes a difference.

The belt is a Red Herring (A diversion for you CF'rs...)

The belt merely acts to support the weight of the plane....

The tires merely roll along under the plane...the landing gear supports the plane, the thrust pushes the plane...and the plane moves forward...

Now, when I say forward...I mean across the planet some distance, whatever, a foot, an inch a meter, whatever it is...

The belt just goes faster...even if it went FASTER than the plane's speed...it would be irrelevent...all THAT would do is increase the TIRE'S rotational speed...the attached landing gear would continue, as would te attached plane, to move across the planets surface, further down the belt's length.

_________________________________

One last analogy:

I kneel down next to my tread mill as it rolls along...I have a toy xterra...I put it on the tread mill...and hold it there, with its wheels spinning on the belt...I'm using one finger to hold on the back of the little X, to keep it in one spot on the belt.

Got that...?

One finger on the back of the X, holding it in position against the rolling tread mill belt...

OK...here' where I blow your CF mind...

Ready?

OK - I push my finger against the X a bit more....it can now MOVE AGAINST THE DIRECTION OF THE ROLLING BELT!!!!!!!!!!!!!!

How is that POSSIBLE you ask?

OK - its because the thrust from my finger is what's moving the little X...NOT THE LITTLE X'S TIRES.
________________________________________

Instead of a little X, I grab a toy RC plane, and do the same thing...

I use a finger to hold the plane against the on rushing belt, exactly as I did the little X...

The belt rushes along under the plane's tires...and, IT STAYS IN ONE SPOT!!!!!!!!

How is that POSSIBLE you ask?

OK - its because the thrust from my finger is what's moving the little plane...NOT THE LITTLE Plane's TIRES.



____________________________________

OK -

NOW, I still have the little plane on the tread mill, miraculously able to maintain its position through the magic of rolling tires and thrust from my finger.

I take the remote, and start the engine of the RC plane...the propeller spins, and pulls the plane forward, off of my finger and AWAY...

How is this POSSIBLE, you ask?

OK - its because the thrust from the propeller is what's moving the little plane...NOT THE LITTLE plane's TIRES.



________________________________-

So my finger can be the thrust...

There isn't a tread mill made that I could not roll my little X forward on by merely applying an external force to the X...

The tread mill CAN'T roll fast enough to keep me from doing it either...at the same speed, or at double the speed of my finger...the little X's tires will just spin faster..

...but, my FINGER will push the little X against the spinning belt.

_______________________________

As a jet engine can provide the same external force to the plane...

...perhaps even MORE force than my finger...

...the real plane will be pushed forward on the INITIALLY NOT spinning belt..MAKING it spin...

...but, just like my finger just keeps pushing the little X further along the tread mill belt...

....he real plane will ALSO be pushed IN THE SAME WAY...along the giant belt.

As the conveyor belt DOES NOT have its OWN ATMOSPHERE...the air that the plane is moving forward through, is the SAME air it would NORMALLY move forward through.

So - as the thrust independently pushes the plane like a giant finger, along the belt...through the air...eventually, the air rushing OVER THE WING, creates enough pressure differential to create lift.

(A wing does not lift the plane, or a bird, etc...by pushing air down...it creates lift by basically making the air on top of the wing take a longer path...which makes it less dense than the air below the wing...so it essentially PULLS the WING UP, rather than pushing the WIND DOWN)

I did see at least one reference to the above misconception, referred to as one reason WHY the conveyor belt would prevent air flow from creating lift...so, of course, that's not going to make any difference...because its not how a wing works, etc.

________________________________________-

sigh.

I HOPE some of this sinks in.

Then it's an infinite acceleration.

The plane is not travelling at 240 knots in air speed (assuming that's what KIAS is). It's travelling at ground speed relative to the conveyor belt. It's not moving in airspeed.

At some point it WILL hit it's limit. Engines don't have an infinite speed.

Nicely done, TJ. But I know someone's not going to read the whole thing and say something like "but there's no finger holding the plane in place, stupid!"

I thought about becoming a teacher when I retire. I'll probably think about it a little less.

For the LOVE OF GOD! PLEASE!

The air speed has NOTHING to do with the conveyor belt...

Every one HAS to absorb this.

Ground speed of the plane is not different on a conveyor belt, any more than it would be different taking off from an aircraft carrier, or a train, or launched from a B1, etc.

Ground speed is relative to the planet...not things running about under you.

Otherwise...a plane's ground speed would be different if flew over a river ...but it ISN'T.



A Plane's AIR SPEED DOES change if there's a head wind, or a tail wind...as the AIR its flying through IS the relative baseline.

For ground speed, the relative baseline would be the planet, say by GPS coordinates.

We have GOT TO absorb this if we are to one day have every XOC member know if the damn plane can take off.

I thought you were going home. Short commute, huh? Nice

You're partially correct, then totally wrong. The plane is travelling at 120 knots indicated arispeed. Therefore, relative to the ground (not on the conveyor) it is travelling at 120 knots (ground speed) at sea level. Relative to the surface of the conveyor, the plane IS TRAVELLING at 240 knots.

Here it is again, as the plane travels:

Airspeed-120 knots

Groundspeed (at sea level in no wind)-120 knots

Speed relative to conveyor surface- 240 knots

Read TJ's post again, thoroughly.

::eta:: Lizz, I'm glad you think so. Thanks for indirectly getting this going.

TJ, that was your damn longest post to date...

Hahaha. 18+ pages of nonsense trying to convince the unconvincible that a plane on a conveyor belt can actually get off the ground.

I think all humans CAN apply logic...but its like playing a new sport, or writing with your other hand, for some...it just requires practice.



Sometimes...its like pointing at where you want your dog to go....trying to tell your dog to go "OVER THERE...The Ducks OVER THERE...Go get the duck!!!"

And the dog just keeps looking at your finger, not where its pointing.

Of course, some dogs don't even get that there might be a duck, and just fall asleep.

sigh...I gotta go home...someone with more time...go through the posters, and sort them by Fly or Can't Fly...I'd like to have a record of who was in which camp so if I have to explain OTHER things later, I can take it into account.



If a reader, post if you are an F'r (Fly) or a CF'r (Can't Fly).



Remember, be honest, this is for posterity.

No one answered Smith's question...

Is this a smoking or a non-smoking flight?

Attach the plane to another plane with a short length of chain and have both planes attempt to take off in opposite directions....

neither plane will take off

LOL

I think some people are smoking snakes.

Neither! The plane's not flying, remember?

If they are serving chicken for dinner, the plane will definitely fly.

If that horible airline vegetable lasagna is on the menu, it will not take off.

Here's another one to ponder

An airplane is on an infinately long Aircraft carrier. As this airplane attempts to take off in one direction, the aircraft carrier moves in the exact same speed in the opposite direction (so that the plane appears to be staying in the same spot to a impartial observer who is not on the aircraft carrier)....

Does the plane take off?

Not true. The plane is flying while standing still, with snakes on board with people using treadmills on the plane in order for the frictional forces to prevent them from taking off.

Yeah... The plane takes off.

Man oh man!!! I posted this question not quite expecting this kind of response. It's rather funny that some of you people can't seem to get your mind off the wheels. They are not a determining factor on whether the plane can or cannot fly. Cmon people!! Think!!!

I've said it a few times now....those that said that the plane WILL take off can sleep easy tonight. It will in fact be able to take off.

It doesn't matter if the conveyor is going backwards at 1000mph. It's not pulling against the force of the engines. It's pulling at the wheels. Therefore, the engines will not be effected AT ALL by the conveyor belt causing the plane to eventually get enough speed to take off.

ok i can't be bothered to read 19 pages of stuff, but for a plane to become airborne, you need to have air moving over the wings to create lift. so if the plane has zero ground speed (engines are only making the plane keep up with the conveyor), then it doesn't fly.

aerodynamics 101

I dunnoooooo..... people here beg to differ!!!!

Great, now this is gonna go another 10 pages.

TJ, I hope this helps you. Listed below in reverse appearing order are our "Special" XOC members:

JayZ
Mobycat
far west x
RiNky
NY Madman
Paul H
Mostly_Harmless
MarGinJoey

This doesn't include those that thought the bullet that was dropped would hit the ground first... I didn't have the patience to track 2 things at once.

You obviously haven't read the entire thread.

I am no longer dedicated to the position that it will not fly.

It seems alot of people are stuck on the preconception that the wheels will be propelling the plane and therefore will just stand still on the treadmill.

Its been said 100 times already, but the engines do the propelling, thus negating any effect the treadmill would have.

If the plane always appears to be in the same spot, then it's not moving through space, it's not moving through air, so it's not gonna take off. In order for the plane not to move through air, its means of propulsion must not be coming from the plane, it must come from the carrier (i.e. the infinitely long catapult).

This problem differs in that you specifically stated that the plane does not move absolutely, whereas the original scenario only mentions motion of the plane and the conveyor belt. Your plane may be in motion relative to the carrier, but in your scenario, the plane is not in motion relative to the air (or to the rest of the world).

So, again, no, your plane won't take off.

You don't have to recant your original position:

If the Jaguars could get a few receivers and an accurate QB, we might be good next year.

Everybody sinnnnnnnggggg

The Jags still suck, the jags still suck.......

but damn can Jones-Drew run.

Given calm winds, no. The plane does not take off. It will be at the same point relative to the air surrounding it, and thereby have attained a net of zero airspeed. However, the proposed scenario is even more unlikely than the conveyor the size of a runway. An aircraft carrier achieving speeds at which an aircraft could obtain lift would take such immense power as to be just about unthinkable. Besides which, the resulting movement of the flight deck would preclude a safe launch. But I'm just spitballin here.

ok, i might as well chime in on the bullet gun thing too.

they both hit the ground at the same time. gravity affects them equally, but the one fired from the gun also has a forward motion component to it. i could get into vectors and all the scientific crap but i wont.

edit: here is a link explaining lift. note the final paragraph titled 'no motion, no lift'.

http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html

OK, from a pilot:

DING DING DING!!!

That's the EXACT same scenario as the conveyor belt!

Just because it's coming from a pilot, doesn't mean it's right. I'm an air traffic controller, I tell pilots what to do all day, but that doesn't mean a damn. Go ahead and try the balsa-plane-with-a-rubber-band-powered-prop trick on the treadmill at your local gym. See if it works, then try to figure it out.

Of course, it's been done. You've read the whole thread, right?

That rubber band plane has almost no weight. It's wheels obviously moved faster than the treadmill.

If the jet is weightless, all bets are off...then yes, it could take off.

BZZZZZZ! Sorry, you are incorrect. The scenario is not the same. Examine, if you will, scenario #1:
Nothing in this scenario says that the plane must remain stationary. In fact, it states with certainty that the plane must move (otherwise no speed at all. Now for scenario #2:
Given the stipulation that the aircraft remains in the same point in space (as was described in the parenthesis in the above quote), no airspeed at all could be generated, except what was necessary to counterract the minimal friction of the flight deck under the wheels. If the carrier and plane were free to move to any point in space, yet the only stipulation being that their speed must be equal in opposite directions, the aircraft would still take off.

We have weightless aircraft. Blimps and hot-air balloons. But they're not relevant to this discussion.

So the balsa plane takes off because it's light. Get a bigger balsa plane, and try it again. then try it again with a larger, heavier RC plane. Then with an even larger one. If the plane's propulsion system can push enough AIR to move its own weight fast enough to achieve lift, is certainly will not sit still because something's turning its wheels.

There is nothing that can get me to go back and read the whole thread but I would love to throw my hat into the ring:

Why is a Harrier jet able to take off from what is basically a stable position while hovering? The plane achieves flight through propultion rather than wind speed and there is no need for a runway or wheels for that matter.

I have to throw my lot in with the "it flys" crowd since a plane achieves flight through propultion at a certain level regardless of the land speed.

But I still wonder: why does it take X hundreds of feet for a plane to take off when all a pilot could do is set the throttle wide open and slingshopt the plane.

So who the hell knows....

Welcome, SCPX. To your question-

what you've described is done frequently. The thing is, it must gain momentum to achieve airspeed. Airspeed is not created by sitting still and pushing air, you must travel through air to have airspeed.

So while a plane spools up with the brakes on, it's like a boat at 3/4ths throttle tied to a pier. Get free of the line, and it's off like a shot. If the boat is a hydrafoil, it will still need to gain momentum and speed through the water to be raised up on it's foils. Do I make any sense, ever?

::ETA:: While the engine is turning, air flows only through the turbine/prop path/both. In order to achieve lift, you must create airflow over the entire wing. This is why forward motion is required.

20 pages and still in the club house? come on, lets take this to the ALR.

Fuck you queer

Matt ...

The rubber band powered balsa wood plane experiment is not a good test of the scenario that is being discussed in this thread. No where near a good test. I think you know that.

I also have a question for you....

You seem to think the plane on the aircraft carrier would not take off and you are using virtually the same argument that people are using against the plane on the conveyor belt. Why is that?

Maybe you should have read the paragraph and not just the title
One problem is that people are assuming that ground speed and air speed are one and the same, when in fact they are not.

Take my Kites, for example, which fly based on the same principles as an airplane - only they have no groundspeed...which means they rely on the air moving past the kite to generate lift.

Again, it makes no difference whether the object moves through a static fluid, or the fluid moves past a static solid object. In either case, lift is acheived.

Taht's the other problem, people are assuming that lift only occurs if the plane is moving in relation to the ground, as they assume the ground and air move together - which is compltely false.

If I run 5 mph towards the east on a calm, windless day, I will feel a 5 mph breeze coming from the west - the difference between my velocity (5mph east) and the airs velocity (omph).
That is my groundspeed is 5mph, my windspeed is 5mph.

If I run 5mph towards the east with a tailwind at 5mph, I will feel no wind - because now there is no difference between my velocity (5mph east) and the airs velocity (5 mph east)
that is my groundspeed is 5mph, but my windspeed is 0mph.

This is important, because as the NASA link states in the "no motion, no lift" paragraph
Taking the conveyor belt -
Remember you have to use vector addition, and everything has to equal out.
If the plane is moving at 100mph, the Belt is also moving at 100mph in the opposite direction (add them together, you get 0 mph)
A person (impartial observer) standing off of the belt sees the plane staying in a stationary spot, and feels no windspeed (0mph). They see a person on the belt moving with the belt (away from the plane) at a speed of 100mph.

The person on the belt sees the plane moving away at a rate of 200mph (the combined speeds of the person and plane), and feels a windspeed of 100mph (the difference between speed the person is travelling on the belt and the speed of the air (omph) felt by the observer). The person on the belt sees the observer moving away from them at a rate of 100 mph.
The plane sees the person on the belt moving away at 200mph. The plane sees the observer as not moving in relation to it. The Plane also feels a windspeed of 100mph.

Now the vector addition -
The plane is moving at 100mph in one direction, the belt/person at 100mph in the opposite direction - they cancel each other out (0mph total movement)
The observer and the person on the belt see each other moving away at 100 mph (in opposite directions) so that cancels each other out. (0 mph)
The person on the belt and the airplane see each other moving away at 200 mph in opposite directions, so that cancels each other out. (0mph)
The airplane and the observer do not see any change in distance between them - they cancel out (0mph)
The person on the belt feels a windspeed of 100mph (because they are moving in relation to the wind at 100mph)- since the observer feels no windspeed, the airplane must cancel the person on the belts windspeed of 100mph out by feeling a windspeed of 100mph in the opposite direction (which would be going from head to tail on the plane).

Oh, ands to those who think that groundspeed and airspeed are one and the same....

When the air moves (wind), does the ground move with the air?

Explain to me, madman, why the balsa plane experiment is not a "good test."

There is a stipulation in the carrier scenario that the plane remain in the same point in space. There is no such stipulation in the conveyor scenario. In the conveyor scenario, the aircraft can move, regardless of what the surface does.

Once again, in the Carrier scenario, ROck stipulated that the aircraft must stay in the same position relative to the earth and the air. Of course, if you remove this stipulation, and replace the conveyor with an "infinitely ling aircraft carrier", the answers are exactly the same. The problem with Rock's question is that there's no way the motion of the aircraft carrier could affect a plane that's trying to fly off it, other than steaming downwind.

Let me play devils advocate here Rock....

Are you saying that a person sitting on the wing of the plane in your above scenario would feel 100MPH of wind hitting him in the face?

While sitting on the wing of that plane, he would look over his shoulder and see the observer standing there in the same position relative to his seat on the wing of the plane. The observer has no wind hitting him. His hair is not flowing in the wind. Is the person seated on the wing of this plane feeling his hair flowing back in the wind? Can we put a wind sock on that wing and observe a reaction to a 100MPH wind?

...........

Now take note... I am not taking a position any longer on this scenario. Those that argue that the plane would take off or rather should take off seem to be correct.

Also those that claim it may not take off have also offered some valid points and also seem to be correct. (I'm also not talking about those that bring the wheels or other matters of friction or groundspeed into the debate. The debate is beyond those aspects)

I have some further thoughts and questions on the subject, but it involves your answer to the above question I have asked. That answer would lead to further questions possibly regarding the effects of air viscosity and compressibility involved in this scenario. All of which are included in the NASA links and have a direct bearing on the entire subject.

Well... first of all on the balsa wood experiment it would require a lot of calculations to make it a valid experiment vs. a real world situation. You would have to calculate many things such as the torque required on the rubber band engine vs. the weight of the plane against the speed of the conveyor or treadmill, etc. ... and probably many other calculations to make it valid. You would also have to have trials of other similar experiments which would create a control group. Isn't that how scientific research is done? By doing things like that? You can't just spin up a rubber band plane and put it on any old treadmill and call it valid science.

Quote:

There is a stipulation in the carrier scenario that the plane remain in the same point in space. There is no such stipulation in the conveyor scenario. In the conveyor scenario, the aircraft can move, regardless of what the surface does.

Maybe the wording of the conveyor scenario is creating our little conundrum and the disagreements.

Quote:

Once again, in the Carrier scenario, ROck stipulated that the aircraft must stay in the same position relative to the earth and the air. Of course, if you remove this stipulation, and replace the conveyor with an "infinitely ling aircraft carrier", the answers are exactly the same. The problem with Rock's question is that there's no way the motion of the aircraft carrier could affect a plane that's trying to fly off it, other than steaming downwind.

I'll read the aircraft scenario again. I don't recall it the way you described, but you could be correct.

Can we first arrive at the correct answer to the original scenario, and let the aircraft carrier scenario be moved to its own thread(possibly in the ALR so that zuzuman03 will be happy)?

wow-that took me over an hour to read all the posts. now, what was the question?

It's different.

A harrier is only needing to overcome one force - gravity. It's wings, while the engines *are forcing the air down* don't need forward momentum to create lift.

But that cannot be possible if the conveyor *matches* the speed backwards.

If the plane moves even .1 inches forward, the conveyor belt has failed.

Shhhh....

You're not supposed to ask those type of questions.

Especially since you have already been named in the "enemies list" in this thread.

You guys are a trip. Let me start by not even pretending to have read this entire thread, so if this is old news, forgive me.

The airplane wouldn't fly, and it doesn't matter that the engines move the plane as opposed to the wheels. In the original post, it said the belt has a control system that matches the PLANE'S speed - not the WHEELS' speed. Very important distinction because if that happens, the plane's wheels can spin at any speed but the plane's speed relative to the surrounding air remains zero.

If the plane doesn't move forward, there's no airflow (so-called relative wind) over the wings. No airflow, no lift; no lift, won't fly.

It wouldn't move forward because of the old "every action has an equal and opposite reaction" and the related laws of flight: lift must overcome gravity and thrust must overcome drag.

In our scenario, the "action" of the engines still produces the usual reaction (thrust) but not the usual result because a vital element is missing: the friction of the tires against the pavement. Take away this drag and the tires are still rolling on the conveyor belt but the result is different because the surface is not stationary.

The airplane will not move forward, so no lift will be generated and so gravity wins - the plane won't fly.

Now here's a new one for you:

Assume we're talking about a fixed-wing aircraft (i.e. not a helicopter) that is not a Harrier jet.

The plane's airspeed is 60 MPH but it is flying into a 60 MPH headwind. What is its speed over the ground?

We did.....it's been stated MANY MANY times....the plane WILL TAKE OFF!

BlueSky, what would it matter if the conveyor belt reaches the speed of the plane? The plane is sitting on a set of wheels that are basically frictionless. That only means that the wheels will be spinning MUCH faster than the plane is actually moving forward. The conveyor has an acting force on the WHEELS, NOT the engine. The only thing that can act against the engine is a headwind pushing against the entire aircraft in the opposite direction and with equal speed to the plane. You people just can't grasp the fact that the wheels and the conveyor DO NOT act against the force of the airplane's engines!! WAKE UP!!!

If the airplane were to be propelled by the wheels, then yes, the plane will in fact NOT take off. BUT...that's ONLY IF it's being propelled by the wheels, and not the engines. :rolleyes:

Allright, let me try to explain it this way. You're in your car on wet, perfectly level ice. You try to accelerate, but your wheels just spin and you go nowhere (for the sake of argument). Try as you might, as your tires push against the ice, they get no friction and can't get you moving. If, however, you applied an external force to the car, like a big-ass fan, then the car would move over the ice. Why is the car moving now? I mean, isn't it impossible to apply torque to the wheels to move the car? It's moving because it's NOT pushing against the ice, it's pushing against the air.

Does that convert anybody? I doubt it.

::edited for clarity::

Here's the thing, Moby. If the plane doesn't move, it has no speed. If it sits still with its wheels turning, it's not moving, and therefore, has no speed.

The conveyor matches the *speed* of the aircraft, not the movement.

Dude, you don't have to publish the results of the balsa plane test. There's no Nobel for re-proving basic physics. You're saying it's bad science because it isn't measured first? Accept this for any self-propelled fixed wing aircraft- balsa, canvas, aluminum or whatever- is can generate enough friction with (nothing else but) the air to move forward at a rate of speed great enough to achieve lift. Contact with the surface is incidental.

But they are NOT frictionless.

You have just added a second power source.

The plane does NOT have a second power source.

You're so very close here, until you conclude that the plane's speed is zero. If the conveyor could *magically* keep the plane in a single position, the plane would have no speed. But wait- if the plane has no speed, then the conveyor must also have no speed, as stipulated by the problem.
Whoa-hold up here. Wheels are a means of reducing friction while attempting to move an object-yes? The tires-on-pavement do extraordinarily little to create friction without brakes applied. The plane still moves because it moves air, and there's nothing the conveyor can do about that.
The plane on the conveyor will create forward motion and achieve lift, because it's using friction against something that has nothing to do with the conveyor.

Imagine roller skating on a long treadmill that matches your speed exactly. There's a taut rope directly overhead within easy reach. As you move forward, the treadmill acts to keep you in the same place. If you grab the rope and start using it to push yourself forward, hand over hand, and your wheels are just touching the treadmill, will the treadmill be able to stop you from propelling yourself forward using the rope? No, because you're applying force to the rope and your wheels are reducing friction with the treadmill.

Of course an aircraft with a 60 knot headwind and 60 KIAS will have a groundspeed of zero. I've seen a plane with a 140 knot headwind remain motionless 6000 feet over an airport for about five minutes before I asked him if he thought he was going anywhere. When he realized he wasn't, he turned around and got home in a hurry.

Right, but the plane does not create its movement by pushing against the ice/ground. Put a plane on that same frictionless ice and it will still move whenever it wants to, because it moves by pushing the air, not the surface.

Ugh.

A rope is NOT fluid. The air IS.

The rope is tied to something. The air is NOT.

The wheels are NOT frictionless.

Heck, even ice has *some* friction. If it didn't, you wouldn't slow down on ice skates.

OH. MY. GOD.

You've been fucking with me this whole time, haven't you? Do you mean to say that an aircraft cannot move itself forward using fluid air?

That's the bad assumption of everybody who thinks the plane doesn't move.

The ONLY rearward force on the system is a nominal amount of friction on the wheels (which spin FREELY!). This will NEVER be enough to prevent forward motion against thousands of pounds of thrust.

Go back in the thread and look at the free-body diagram (FBD). Also look at my t= scenario which explains how the conveyor belt will affect the system.

As I said before. This is not rocket science or an aerospace engineering problem. This is a 9th-grade Physics problem that requires the person to understand how an airplane propels itself (the wheels aren't involved in propulsion). If people don't, at least, have that background, they should refrain from comment.

There is one recognized correct answer to this problem. Look at the FBD, stop getting hung up on the conveyor belt, and disregard rockaholics invalid scenario. ONLY THEN will you be able to come to terms with the recognized correct answer.

The plane flies.

Good luck!

Yea, it was a hypothetical. Maybe I should have said "magical frictionless surface" instead. Regardless, the plane would move on the ice, even if its brakes were locked and a car couldn't get rolling in any direction.

I'm saying it is a bad scientific experiment to use as proof of the hypothetical scenario in this discussion of the aircraft and the conveyor belt.

With the way you are proposing the balsa wood plane experiment, you are moving away and beyond the conditions set in the original hypothetical scenario.

You keep forgetting that in the original scenario the conveyor matches the aircraft's speed. Without the numerous calculations I mentioned in my earlier post you are not duplicating the conditions for the hypothetical scenario by just spinning any rubber band plane over any treadmill.

So if the conveyor/treadmill had greater speed to begin with and the balsa plane still took off, the result would somehow be different if you could make the treadmill accelerate at the same rate as the plane?

I don't know how fast traditional treadmills go, but I'm fairly sure balsa planes cannot go faster than 10 MPH (being generous to the plane). So supe up a treadmill, set it for 20 MPH, and try it again. I guarantee you the balsa plane would take off.

I don't care about the speed of either.

We are talking about the hypothetical scenario. If you wish to create an experiment to use as proof... you would need to calculate all of the numbers and match the speeds of each.

Otherwise we are no longer talking about the hypothetical scenario.

If this is being discussed all over the internet, why hasn't anyone tried to do a scale model experiment with a remote controlled aircraft?

People have. There are all kinds of videos on YouTube, but none of them really show much of anything. Someone needs to do this experiment with a radio controlled jetliner on a conveyor system a-la Mythbusters.....Hopefully they'll reply to the email sent to them...

I just don't understand how it is so difficult for people to understand the forces being acted upon and the forces at work here....I've said it many many times.....

The conveyor belt puts a force on the wheels, NOT the engines. The engines are completely indepentant of the conveyor. The conveyor WILL NOT provide any resistance to the engines and the engines will continue to pull the airplane forward, thus creating lift, thus allowing the plane to take off. What's so difficult about that?!?

Moby, you just contradicted your position, and you don't even know it...

The plane doesn't have a "second" power source. It has 1 power source. And it's not connected to the wheels. The wheels provide 0 propulsion or resistance of the plane's movement, at any time. So no matter how fast the wheels move, the plane's motion is NOT controlled by their movement.

Look, are we all in agreement that on the aircraft carrier, it would not take off?

Put the aircraft carrier on the conveyor belt.

The conveyor belt now moves the boat (instead of the boat's engines - they are connected, so it doesn't matter).

The exact same scenario!

The air around the wings does NOT move - there is nothing to provide lift.

Imagine a hamster on a wheel. The hamster runs, the wheel turns, and the hamster moves across the surface of the wheel but stays in the same relative position so like the plane, there's no airflow over the hamster.

Now on the same wheel (maybe bigger), put the hamster on "nearly frictionless" skates and strap a tiny jet engine on its back. Guess what? The wheel still turns (just faster) and the hamster still maintains a stationary position at the usual place on the wheel. It doesn't travel around the inside of the wheel.

Where Hawk seems hung up is on the relative position. Though air is moving through the engines, generating thrust, the plane itself must be moving forward to generate lift. According to the scenario, the more thrust applied, the faster the belt goes, so the moving treadmill prevents forward motion by in effect giving the wheels nowhere to go.

If the belt moves faster as the plane moves faster, the plane's RELATIVE position doesn't move forward, so again, there's no airflow over the wings. In the scenario given, even with the engines at full power, if you raise the landing gear the plane will collapse to the ground.

Wow-it took me over an hour late last night to read all these pages. Then I forgot what the post was about. If I have repeated any one else's post-it was not done deliberately. My two cents. Ground speed and air speed are not independent of each other. Air speed is created by thrust. Thrust in this case is created by the engines. Not the spinning wheels. If you take a balloon, and blow it up-then release it. It will essentially fly away until it has no more foreword thrust (escaping air). If that same balloon is let go into a head wind of equal thrust/speed-the balloon will stay where it is....mid air. Not counting on how un-aerodynamic a balloon is. Still flying-but going no where. If the thrust of the plane going foreword is less then the treadmills speed, then the plane will go backward. If the thrust is greater, the plane will fly away. If the thrust is equal to the tread mill-the plane will still fly. But will not take off as quickly because ground speed and air speed is the same. But the plane will fly away. Do you guys remember the old WWII Naval pictures of naval aircraft taking off from carriers? This was before catapults. The carriers would turn into the wind and go full steam ahead. Back then, they could muster maybe 20 or so knots of foreword speed. The planes would lumber into the air and would either crash into the ocean or fly away-very slowly until their air speed was much greater than ground speed. So, to all you can't fly mother fuckers, your wrong. Now, that last sentence was meant for the ALR. As you quote me and may be flame me-remember, I am a very delicate flower. Bruise easy. Have a nice New Years.

EXACTLY. The car by itself would not have a secondary power source. It won't move.

Put the fan on it - it has a secondary power source.

Again - try the rope example. The rope is not fluid, and it is taught - meaning it's connected to something else.

The jet has to overcome it's weight to move forward.

So the friction of the wheels IS relevant.

If it weren't, you could walk up to a plane and push it with your own force.

You cannot agree on anything about the Aircraft carrier scenario.

It is INVALID. It does not have anything holding the plane back yet it states the plane does not move.

That ridiculous scenario has done nothing but confuse the issue further.

Read above and please come to terms with the correct answer.

Bottom line:

Jet engines push (F = ma ==> a =F/m)

Wheels roll, and don't push back.

You know...

Why HASN'T someone actually gone through the trouble of a computer model of this?

I wouldn't count on Mythbusters.

Rinky linked to a physics forum with 500 pages on this topic. Someone on one of the first pages said they emailed Mythbusters and that was over a year ago. I'm sure they have received hundreds if not thousands of emails on this topic.

Quote:

The conveyor belt puts a force on the wheels, NOT the engines. The engines are completely indepentant of the conveyor. The conveyor WILL NOT provide any resistance to the engines and the engines will continue to pull the airplane forward, thus creating lift, thus allowing the plane to take off. What's so difficult about that?!?

You are correct in stating the conveyor provides no resistance to the aircraft's engines.

The conveyor is matching the speed of the plane.

Let me ask you this question.... Does a person sitting on the wing of that plane feel the wind? If the conveyor is moving 200MPH in one direction and the plane's engines are throttled down and it's instruments say it is traveling at 200MPH in the other direction -- does a person sitting on the wing of that plane feel that wind?

Bad analogy with the hamster. If the hamster were atop the wheel, it would be better. In the wheel, there is always something in front of the hamster keeping it inside the wheel, regardless of means of propulsion. However, if atop the wheel, the hamster with rockets will not be contained and will be propelled forward. Still not a good analogy, but it doesn't have the containment. Inside the wheel, depending on the thrust of the jet/rocket whatever, and the hamster's grip on the wheel, the wheel would whip around backwards like a firework pinwheel.

Hawk is not hung up, you are. The wheels cannot keep the plane from taking off, no matter how fast they spin.

The plane's instruments would not indicate any speed at all if it was throttled down (no power) and the plane was stationairy. If the plane was throttled up (powered) then the plane would move forward (relative to the ground, not the conveyor) and the "wing passenger" would feel wind.

Instead of trying to convince everybody that the wrong answer is right, read the UNBELIEVIABLY simple physics of the situation.

Coefficient of dynamic friction:

Force of friction:

F(f) = -uN

(negative because it opposes motion)

u = coefficient of static friction

N = weight of plane

Notice velocity is not included!

That means that the velocity of the conveyor belt is irrelevant for all practical purposes.

F(t) is force of thrust

a = (F(t)+F(f))/m

You won't find a scenario where |F(f)| is greater than |F(t)|. Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.

Please stop being so bloody indignant and pause long enough to understand why the correct answer is correct.

Exactly. Two questions to the "plane doesn't care what the wheels are doing" group:

1. You think the wheel friction doesn't enter into it? Stick your head under one of them, since they're bearing the entire weight of the aircraft, and see what happens.

2. If what's going on with the wheels doesn't matter, try reducing their speed to zero and see what happens, even with full thrust. Trust me, you won't fly.

You guys are confusing the issue of what counteracts what to achieve flight.

Lift overcomes gravity.
Thrust overcomes drag.

BOTH must occur for flight. The wheels turning on a stationary surface allows the thrust to overcome gravity (the aircraft's weight).

Think of the law that says an object at rest tends to remain at rest unless an outside force is applied. The outside force here is engine thrust, but it's negated by the moving belt, so the object remains at rest and gravity thus is NOT overcome by lift.

The plane WILL NOT FLY.

Moby, the car on ice (magic frictionless surface) Is in park with the E-brake on, and you put the big-ass fan on it, it will still move.

It doesn't matter that the rope is taut, it is an external means of propulsion, just like air. Air is connected to something else-other air. For real, if you think that an aircraft cannot move by manipulating air, then I don't know if anyone will be able to make this scenario clear to you.

I disagree about the hamster because as stated in the original post here, the wheel would keep increasing in speed.

Throttle up/down... whatever. You knew what I was getting at.

Now -- We have already established that an outside observer viewing the plane on the conveyor belt would see it as a stationary object because of the matching speeds between the conveyor belt and the plane.

Are you absolutely sure that a person sitting on that wing would feel the rushing wind on their face... even though the observer is experiencing no wind on what is otherwise a non-windy day?

I ask because that is the key to the entire scenario and the flight of the aircraft in this hypothetical situation. None of the other peripheral issues being added to the discussion matter. That is the entire key.

OK, I'll try again. Wheels are simple tools designed to minimize friction. Propellors and jet turbines are relatively simple machines designed to MOVE whatever vehicle they're mounted on. No matter what the surface beneath the wheels does, as long as the wheels can perform their function and reduce friction (spin freely) the prop/turbine will power the craft forward.

Unless the surface they're on is moving in the opposite direction.

So by your statement, if the surface is moving sideways, the craft will go forward?

We have established no such thing. The plane will travel forward relative to the ground, relative to the air, and at twice that rate relative to the conveyor.
The key here is what I said above. The plane is not stationary, it moves forward relative to everything around it.

No it won't.

The WHEELS will travel at twice the rate relative to the conveyor.

The conveyor matches the PLANE'S speed.

Jet says it's doing 60knots.

Conveyor is going -60 knots.

Wheels are going 120 knots relative to the conveyor.

The original question:

I think you need to read the thread again.

Since the conveyor is matching the speed of the plane, once those speeds have been matched, an outside observer most certainly does view the plane as being stationary.

Not exactly.

The wheels will rotate at twice their normal rate.

This is giving me a headache.

What if the question was a similar conveyor on a downward slope with a vehicle on it with free-spinning wheels? No matter how fast the conveyor went, gravity would pull the vehicle downhill, right?

That's causing me to rethink my position though all my previous arguments still seem valid.

Good grief.

No, if the surface is moving sideways it would create friction with the wheels which are designed to move longitudinally, not laterally. A plane with landing gear mounted sideways would be able to create forward motion with the props/jets, but would have a hard time overcoming the additional friction. That's why the smart fellas over at lockheed and boeing like to put the wheels on longitudinally. However, if the surface was ice (or the magical friction-free or friction-light surface) and the plane could have four sets of sideways landing gear and still move forward and take off.

Yeah, I know. That was a rhetorical question meant to annoy. Did it work? :p

Yeah, I thought about that after I typed it.

Guess what, Moby? You can do exactly that.

BWAHAHAHAHA.

Go try.

They do a plane pull at Dulles every year.

It takes at least 20 people to pull a plane. They have to overcome the friction.

Maybe I should be more specific - under your scenario, you could tap the plane with your finger and it would roll foward.

If the conveyor is fast enough to overcome gravity, then yes, it would stay put, even on a downhill slope (however, it would have to travel faster than the plane at that point).

Gravity was already equalized in the horizontal position - the force pushing up on the landing assembly.