Plane on a conveyor belt

[Jim]

I havent read this whole thread, but the airplane would remain on the belt as lift needs to be built by the difference in air pressure above and below the airplanes wings, and that air pressure would remain the same in this situation....

[Guest]

you guys are looking at this all wrong. Airplanes do not accelerate using their wheels, they are used as a way to reduce friction (as opposed to dragging the belly of the plane) with the ground until the airplane has reached the speed in which it will lift. The planes jet engines/propellers/whatever provide forward thrust to get the plane to the speed at which it will build lift. The airplane doesn't care how fast its WHEELS are being driven in the other direction, just how fast the plane itself is moving. If the plane is traveling 100mph in one direction and the conveyor belt is traveling 100mph the other direction, the only thing affected are the wheels and the wheel bearings (which would be spinning at 200mph) and a tiny amount of friction. As soon as the airplane built enough thrust to counter the gravity/friction holding the plane to the conveyor belt it would start moving forward regardless of what speed the conveyor belt is moving. In other words you guys are reading the question wrong. If the question stated could a stationary airplane generate lift while not moving you would be correct, however the question asks what happens if it is placed on a belt that is moving the opposite direction of the plane at the same pace as the plane. Again, see my sidecar analogy that I posted earlier in this thread. Exact same principal....screw it, I'll post it again:

Think about it this way if you are driving a motorcycle with a side car on it at 50MPH and the conveyor is ONLY on the side car you can still drive the motorcycle at 50MPH, however the sidecars wheel(s) will be traveling 100MPH. Same principal applies here. The planes motors providing thrust would be the motorcycle in above analogy and the planes wheels would be the side car. It is very possible for the plane to take off.*

By your guys theory, the motorcycle in the above situation is not capable of moving forward either.

[24valvenotak]

AcesHigh wrote:
As for the car/wind tunnel scenario, faster air makes for lower pressure according to simple physics. So yes, if the bottom of your car were completely flat then it would create upward lift. This is the reason for ground effects and air diffusors, as well as air spoilers (wings, lips, scoops). The reason why dragsters have a giant upsidedown wing and a front spoiler. The aero effect doesn't occur until excessive speeds that many cars will never reach.

see.. what you are saying, as well as I am saying.. is that the air moves more quickly under the wing to create lift, correct? That is exactly why diffusers ect are used on cars. That is why the top of the wing is shaped and the bottom is flat? the air washing over the tail accelerates and creates lift?

the plane could take off and in theory if wind was moving fast enough (either by nature or by engines) it would lift off the ground standing still regardless of what two little round pieces of rubber are doing below it. Chuck how does a a harrier (sp?) take off? it creates enough thrust or lift downward to lift it off the ground. In theory, a plane could lift off the ground if air were moving quickly enough?

[51d3w4yz]

tjamz wrote:
you guys are looking at this all wrong. Airplanes do not accelerate using their wheels, they are used as a way to reduce friction (as opposed to dragging the belly of the plane) with the ground until the airplane has reached the speed in which it will lift. The planes jet engines/propellers/whatever provide forward thrust to get the plane to the speed at which it will build lift. The airplane doesn't care how fast its WHEELS are being driven in the other direction, just how fast the plane itself is moving. If the plane is traveling 100mph in one direction and the conveyor belt is traveling 100mph the other direction, the only thing affected are the wheels and the wheel bearings (which would be spinning at 200mph) and a tiny amount of friction. As soon as the airplane built enough thrust to counter the gravity/friction holding the plane to the conveyor belt it would start moving forward regardless of what speed the conveyor belt is moving. In other words you guys are reading the question wrong. If the question stated could a stationary airplane generate lift while not moving you would be correct, however the question asks what happens if it is placed on a belt that is moving the opposite direction of the plane at the same pace as the plane. Again, see my sidecar analogy that I posted earlier in this thread. Exact same principal....screw it, I'll post it again:

Think about it this way if you are driving a motorcycle with a side car on it at 50MPH and the conveyor is ONLY on the side car you can still drive the motorcycle at 50MPH, however the sidecars wheel(s) will be traveling 100MPH. Same principal applies here. The planes motors providing thrust would be the motorcycle in above analogy and the planes wheels would be the side car. It is very possible for the plane to take off.*

By your guys theory, the motorcycle in the above situation is not capable of moving forward either.

You are my hero, excellent explanation. PPl don't understand that the plane would still move.

[Guest]

51d3w4yz wrote:
You are my hero, excellent explanation. PPl don't understand that the plane would still move.

Tjamz=Saving the internet, one stupid topic at a time

[Guest]

92BlackTT wrote:
In theory, a plane could lift off the ground if wind were traveling fast enough over its wings while standing still on the ground.

This is true, though not likely to happen in normal situations. I was more refering to it being a windless day, in which case it would still take off. It would NOT take off however if were in an infinitely long wind tunnel with a tail wind traveling the exact same speed as the plane was traveling as that WOULD negate all lift as the person in the plane would feel no wind from the front or back (maybe a little swirling around the sides and whatnot, but not front/rear)...except a Harrier aircraft which is not affected by front/rear winds on take off (just to lift, I know wind is a concern once airborn due to stability)

[24valvenotak]

right. ok, now how about the whole wing design part that is making me tear my hair out. does air moving faster over the top of the wing or the bottom of the wing create lift. I always thought it moved faster over the bottom and accelerated as it washed over the tail end of the top?

[Guest]

I'll have to do some thinking/research on that mitch and get back to you.

[24valvenotak]

lol you dont have to research, i was just hoping i could get an/better explaination from someone after dubbsy said thats not how it worked.

I figured it worked the same way as an F1 car..

[Guest]

http://travel.howstuffworks.com/airplane6.htm

[AcesHigh]

tjamz wrote:
you guys are looking at this all wrong. Airplanes do not accelerate using their wheels, they are used as a way to reduce friction (as opposed to dragging the belly of the plane) with the ground until the airplane has reached the speed in which it will lift. The planes jet engines/propellers/whatever provide forward thrust to get the plane to the speed at which it will build lift. The airplane doesn't care how fast its WHEELS are being driven in the other direction, just how fast the plane itself is moving. If the plane is traveling 100mph in one direction and the conveyor belt is traveling 100mph the other direction, the only thing affected are the wheels and the wheel bearings (which would be spinning at 200mph) and a tiny amount of friction. As soon as the airplane built enough thrust to counter the gravity/friction holding the plane to the conveyor belt it would start moving forward regardless of what speed the conveyor belt is moving. In other words you guys are reading the question wrong. If the question stated could a stationary airplane generate lift while not moving you would be correct, however the question asks what happens if it is placed on a belt that is moving the opposite direction of the plane at the same pace as the plane. Again, see my sidecar analogy that I posted earlier in this thread. Exact same principal....screw it, I'll post it again:

Think about it this way if you are driving a motorcycle with a side car on it at 50MPH and the conveyor is ONLY on the side car you can still drive the motorcycle at 50MPH, however the sidecars wheel(s) will be traveling 100MPH. Same principal applies here. The planes motors providing thrust would be the motorcycle in above analogy and the planes wheels would be the side car. It is very possible for the plane to take off.*

By your guys theory, the motorcycle in the above situation is not capable of moving forward either.

No, you didn't listen to me. Jet engines (as they are mounted on jet planes) do NOT produce downward thrust. They aren't aimed downward.

You are making the assumption that it's the speed of the plane making it take off, and this is incorrect. Speed is all relative. When you are walking inside a moving train with it, you aren't going at 60 miles per hour. You're going at a meter a second. Same with the plane analogy. The wheels are moving, but the plane relative to its position is not. Regardless, speed does not make the plane fly.

The assumption here is that the conveyor is moving at the SAME speed as the plane, and thus a positive vector (the plane) added to a negative vector (the belt) equals zero. If the belt is moving slightly slower than the plane, then there is some positive movement here, and the plane MAY just move due to the wind that is passing under its wings.

With that said, a large gust of natural wind, as postulated earlier, may be enough to pick the plane up. Sort of like a paper plane. You need air velocity running through those wings, too, if you want it to fly.

[Guest]

http://travel.howstuffworks.com/airplane8.htm

[AcesHigh]

Plane wings create lift because air below is moving quicker than air above the wing (and according to physics faster air = lower pressure!). Mix a high and low pressure gradient, and bingo you have lift.

[Guest]

AcesHigh wrote:
No, you didn't listen to me. Jet engines (as they are mounted on jet planes) do NOT produce downward thrust. They aren't aimed downward.

You are making the assumption that it's the speed of the plane making it take off, and this is incorrect. Speed is all relative. When you are walking inside a moving train with it, you aren't going at 60 miles per hour. You're going at a meter a second. Same with the plane analogy. The wheels are moving, but the plane relative to its position is not. Regardless, speed does not make the plane fly.

The assumption here is that the conveyor is moving at the SAME speed as the plane, and thus a positive vector (the plane) added to a negative vector (the belt) equals zero. If the belt is moving slightly slower than the plane, then there is some positive movement here, and the plane MAY just move due to the wind that is passing under its wings.

With that said, a large gust of natural wind, as postulated earlier, may be enough to pick the plane up. Sort of like a paper plane. You need air velocity running through those wings, too, if you want it to fly.

I never ONCE said that the thrust was towards the ground (except harrier). I know that speed itself does not make it fly necessarily, but rather the amount of airflow at the wings. What you fail to see is that the wheels do not push the plane forward, they just provide a rolling surface. The plane does not care what speed the wheels are rolling/freewheeling as long as there is thrust moving the plane forward it will take off.

[24valvenotak]

AcesHigh wrote:
Plane wings create lift because air below is moving quicker than air above the wing (and according to physics faster air = lower pressure!). Mix a high and low pressure gradient, and bingo you have lift.

^this is what I thought

[QUOTE=dubbsy]Mitch, if I"m reading this right...everything about it is wrong...

#1. Air travels faster over the tops of wings.. This creates a low pressure that in turns sucks the wing up (bring the plane up with it)

#2. The plane DOES have to physically move. /QUOTE]

^this is where my confusion came from...

apparently he is right about the air moving more quickly over the top of the wing creating lift... now I am confused how making the air move more quickly over the top of a car will not have the same effect?

[AcesHigh]

My apologies upon rereading my statement I notice I have it backwards. Air is moving FASTER above the wing (more distance). Also to add to your question of the effect on a car; the effect is the same. We are trying to reverse the effect (greater air velocity on top, lower on the bottom) and hence the ugly aluminum wings you see are trying to "flatten out" the top of the car so to speak.

[dubbsy]

AcesHigh wrote:
My apologies upon rereading my statement I notice I have it backwards.

correct. the bottom of the wing is flat (outside of the flaps of course) while the top of the wing is curved. Air over the top of the wing moves faster -> lower pressure -> wing tries to travel to the area of the lowest pressure and therefore the plane takes off...

The number one key here that people need to realize is..

** NO MATTER WHAT, the plane's relative position will change. It WILL move forward**

[AcesHigh]

dubbsy wrote:
** NO MATTER WHAT, the plane's relative position will change. It WILL move forward**

No, it wouldn't. I just want to compile everything I've said so far here:

This scenario is based on several assumptions.

#1. That the conveyor belt is in equi-velocity with the plane and that it's continuously variable. That is no matter how much thrust the plane can create, the conveyor belt is able to match its speed.

#2. The wheels are not neutral. Plane wheels are not free moving wheels that can readily move back and forth. They have gearing, and they function like car wheels (thrust is NOT moving the plane as it's moving towards a terminal, for instance, it has its own motor). Thus if you run an infinitely fast belt underneath a plane it would not just sit still with its wheels spinning; it would go the with the belt in the other direction.

#3. There is no wind besides that which is create upon movement.

And with these assumptions we have:

• Jet engines are pointed backwards so downward thrust is nill. Notice that rockets point down...

• Air pressure gradients is what makes a wing fly. Higher pressure at the bottom from lower speeds, lower pressure at the top from higher speeds (from greater distance).

• Using simple vector addition a positive vector (the plane with thrust) added to an equally opposite vector (the belt) equals zero.

The plane will NOT move or take off. The amount of thrust being released is equal to the speed at which the belt is moving. If you fire a bullet and somehow can blast enough air the opposite way the bullet will stop in place. Equal and opposite vector addition.

**

Now for TT's car question, the overall shape of a typical car is very much like the wing of a plane. We have rounded tops with flattened bottoms for the most part. If you want to travel at +100mph all the time it is ideal to do the opposite -- rounded bottom and flattened top. Remember that more distance => greater velocity => lower pressure. You want the high pressure area (lower velocity) to be at the top to push you down, and wings do that.

[dubbsy]

AcesHigh wrote:
No, it wouldn't. I just want to compile everything I've said so far here:

This scenario is based on several assumptions.

#1. That the conveyor belt is in equi-velocity with the plane and that it's continuously variable. That is no matter how much thrust the plane can create, the conveyor belt is able to match its speed.

#2. The wheels are not neutral. Plane wheels are not free moving wheels that can readily move back and forth. They have gearing, and they function like car wheels (thrust is NOT moving the plane as it's moving towards a terminal, for instance, it has its own motor). Thus if you run an infinitely fast belt underneath a plane it would not just sit still with its wheels spinning; it would go the with the belt in the other direction.

#3. There is no wind besides that which is create upon movement.

yes, it will..

#1. Yes.. I will not argue that the conveyor will match the speed of the plane. it's matching the speed of the plane thoug, NOT THE SPEED OF THE WHEELS!

#2. Umm... I don't agree there. Without doing some more research (although everything I've seen thus far agrees), the wheels do no driving of the plane. Hence the use of tow vehicles. Prop planes do not use wheel power on the ground, and this scenario will apply the exact same to a prop plane.. besides, if landing gear was geared it'd destroy everything when it touched down.

#3. No, there is no wind.. However like I've said, the plane will move forward in relative space creating lift.

The plane will NOT move or take off. The amount of thrust being released is equal to the speed at which the belt is moving. If you fire a bullet and somehow can blast enough air the opposite way the bullet will stop in place. Equal and opposite vector addition.
my god, every time someone posts this I want to bash my head into the desk!

If the plane is not moving, then it's speed is zero!!!!!!! Therefore the conveyor is not moving either!!!!

Equal opposite blah blah blah.. The AIR that the engines are acting against is NOT MOVING! Therefore there is no opposite force!
And the wheels are free to roll (I still disagree with the gearing stuff)....

meh...

[dubbsy]

"I watched and listened to the disagreement for a while and was fascinated to see that the argument seemed to split between those who had some engineering or math background, all of whom said the airplane would takeoff and fly without any problem; and those with some other background, who visualized the airplane as having to push against the conveyor in order to gain speed. Because the conveyor equaled the airplane's push against the conveyor, the airplane stayed in one place over the ground and in the calm air could not get any airspeed and fly.

It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards."

http://videos.streetfire.net/player.aspx?fileid=35E964D9-38DB-4EFD-BE8D-D6BA1A43A06B

Try looking at it another way. Lets pretend a jet plane is flying at 200mph and comes in for a touch-n-go. It does it's touch-n-go on this hypothetical conveyor that is moving 200mph in the opposite direction. When the jet touches down it will not cease to move forward. Instead the wheels of the jet will be moving roughtly 400mph. If the jet touched down on a normal runway then the wheels would be moving at 200mph. According to the "no fly" people, as soon as the jet touched the moving conveyor it would simply stop moving.

What's up for debate is how the wheels affect the plane when they are on the conveyor.

Nope, no debate.

Let me try this another way.

First, image you have a conveyor belt moving at -1 mph.

Next, put a free standing wheel on it spinning at 2 mph. Nothing is wrong with this so far.

The wheel would be moving relative to the air around it at 1 mph opposite the conveyor.

Just attach a plane to the wheel and you're good to go.

The thrust of the plane now accelerates it to 5 mph. The conveyor now is moving at -5 mph.

The wheels are forced to speed up to 10 mph. Once again everything is fine.

Go back to just the conveyor, spinning at -5 mph. You can put a wheel on it spinning at 10 mph no problem right? The wheel would be moving along the conveyor at a relative speed to the air at 5 mph. Just have a plane sitting on top of the wheels, and once again you've got no problem, the plane is moving at 5 mph as well.

As far as the body of the plane is concerned, the conveyor doesn't even exist.