I have an experiment for anyone who didn't think the plane will take off

NYSpeed Automotive NYSpeed Off Topic
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I’m not talking about any image… how others want to precieve the question as an illustration is up to them. The problem with the image you posted, it ‘appears’ to show an inability to have forward motion. Change that cable to being infront of the plane…and the cable tied to a fixed point a mile up the runway.

I will say this again. The wheels are an independent stystem. The main constraint is “The wheels will match the conveyor speed”… SPEED being a key detail since “speed” doesn’t indicate any type of “acceleration” The plane WILL accelerate when under thrust. The accleration difference between the belt (contant velocity = no acceleration) will be the same in reference to the ground, which also has a constant velocity and no acceleration. As you said…ground speed has “ZERO” to do with it.

all you’re looking for…is will the PLANE accelerate? we presume accleration of the plane will = flight eventually.

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Your problem, mr engineer, is that you seem to be measuring the plane’s speed the same way you measure a car’s speed… via the rotating wheels. The definition of speed is distance/time, not “how fast my wheels are turning”. If you’re dealing with a moving surface rotating wheels are not a true indicator of speed. It is used in cars because 1, the ground under a car never moves, and 2, under most situations there is no slip between the tires and the ground.

Quick example to explain “speed”. The roads are icy, and I’m driving to work in a 30mph zone. I’m going 25 mph, not spinning my tires, and see a cop running radar. I give it some gas, my tires spin, and my speedometer says 50 mph. My true SPEED is still 25mph, as shown on the cops radar, and the fact that in 1 hour will be 25 miles from where I am now. Wheel rotational speed is just an easy way to measure distance/time in a car, but as in this example and the plane example there are times when it is NOT your actual speed.

The original question said the conveyor matches the plane’s SPEED, but in the opposite direction. If the plane is going 100 mph, it is sending 100 miles of air over the wings in an hour. The conveyor is running 100 mph in the opposite direction, but since the plane isn’t bolted to the conveyor, it is still moving forward relative to the air. The wheels are going 200 mph and may explode if they were designed for a plane that takes off at 100 mph, but that’s not a concern in hypothetical physics debates.

Lets say the plane needs 70% thrust to get airborne on a traditional runway with no wind. To counter the slight rolling friction generated by the wheels having to turn twice as fast on the moving runway it might need 75%, but it will still fly.

Here’s one you can try at home if you have any toy cars. Place a big piece of paper on your kitchen table. Place a toy car who’s wheels rotate freely in the middle of the paper. Now pull the paper out from under the car as fast as you can, in a straight line, either directly to the front or rear of the car. The car will move, but only slightly. No where near as fast as you moved the paper though because the free rolling wheels allowed the paper to move under the toy. Attach a rubber band to the car, pull it slightly taught, and tie a string to the car to hold it in place. Have a friend cut the string at the exact moment you yank out the paper in the opposite direction the rubber band is trying to pull the car. I don’t care how fast you remove the paper, the car will still move in the other direction. It is getting it’s force from the rubber band, much like a plane gets force from the prop. Now remove the rubberband and replace the car with an RC car, driven by the wheels. Since the wheels make contact with the paper you can negate it’s forward motion through the air by matching the speed of pulling out the paper.

EDIT:

And seriously, if you’re designing airplanes for Boeing, I’m going to make sure I only fly on Airbus planes from now on :wink:

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I’m in total shock that an airplane engine engineer doesn’t understand what drives a plane.

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that is why i was up so late trying to make him understand!

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holy crap this was reopened!??! GOOD GOD! The fucking plane will take off already, and if the plane was smart, it would ask to be hijacked by terrorists and crash into the stupid people that think it won’t!

The Plane is driven NOT by the wheels, but by the jets. The Wheels are merely dragging. In the case of a prop. plane, if the prop pushes enough air over the wings, it will still get off the ground, even if it is tied back with a shitty little rope. END OF STORY.

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And eventually when the plane has travelled 2 miles ( assuming) it will fall into the same trap. As long as you are anchored to a fixed point, your concern is air speed at that fixed point across the wing of the plane traveling X speed at that same point. Unless within that point it can reach the critical air speed.

I completely agree…almost. The wheels are completely independent. However what everyone seems to have forgotten is that the wheel axle is hard connected to the plane. Therefore the rotational speed of the wheel could be 50mph, 100mp, or 1000mph ( which depends on wheel diameter and such ) but the forward vector of the aircraft will be what matches the conveyor belt.

But we are no longer talking about flight dynamics and lift, we are talking basic physics principles.

If there is no friction on either the wheel bearing of the plane or on the rotational bearings of the conveyor belt and the only force being applied in this closed system is propulsion on the plane ( regardless of type or location ), then any force applied as a vector to the wheel center, will cause a rotation of the wheel ( forward movement ) due to the friction between the belt and the tire, but it will immediately be counter acted by the movement of the conveyor belt. Net result = 0 velocity of the aircraft in relation to surriounding air even though the wheels and conveyor could be going 1000mph and 500mph respectively.

In order for there to be forward motion, there has to be a force applied that will overcome the resisting forces. In the case of aircraft flight, lift overcomes gravity and the plane rises. If gravity overcomes lift, then the plane drops like a rock. There is no difference to lateral movement except the normal force ( the earth “pushing up”) isn’t a factor and can be ignored.

On the road, your car applies a force to the wheel. The friction of the tire to the road moves you forward in relation to mass ( and the earth a little bit back but its incredibly tiny that its not worth mentioning ). So 99.9999999% of the force moves the car forward.

So in this case, the force is applied by an engine ( jet or otherwise ), the wheel turns due to the friction of the belt but this time, the motion is split between 2 evenly distributed entitites ( remember no friction to load balance one over the other ). So now for each foot of travel the wheel turns ( regardless of diameter), the conveyor will travel 1 foot. Net movement of the plane = 0 feet. This doesn’t exclude that the wheel could be moving twice as fast as the conveyor. In fact I would count on it unless the belt of the conveyor is exactly the same diameter as the wheel.

Net result? Plane won’t go anywhere and no air speed will be generated directly from the propulsion meaning the plane won’t fly.

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For some reason I can’t resist looking at this thread and its posts.

SOMEONE PLEEEEZE PUT A BULLET IN MY HEAD!

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:word: :banghead:

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The prop doesn’t push any air. The prop pulls the plane fast enough to get the right speed of air flow. IF the plane doesn’t move in relation to the air, it take off regardless of how much propulsion, prop or otherwises, exists.

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If a single engined turboprop plane like the one you drew in your image was used, wouldn’t it force the air over and under the wings therefore creating lift?

Just a counterpoint.

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I believe that if there is no lift - the plane will not take off.

a plane sitting on a belt that matches it speed for speed will not have any air flowing over/under the wing.

planes need lift.

end of story.

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:biglaugh: I am sooooo going to kick your ass when i see you next.

you’re right…you need lift… the conveyor won’t restrict it.

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NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOo.

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i guess i’m with howie on this one…i don’t see how if the plane is at a standstill no matter how much the jet engines are “pushing”, how is there going to be lift?

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See my post at the end of the last page about speed. There is no way the plane would be at a standstill.

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omg y is this back again

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It’s not at standstill. The treadmill is acting on freely spinning wheels, thus exerting no force on the plane itself. The turbines DO exert force on the plane itself, thus creating motion and thus creating lift.

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Nevermind - the conveyor is unable to hold the plane back, I’m retarded.

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I was thinking of some anchor point

Think of it this way -

a plane is on a runway - going 50 MPH

half the runway is normal pavement - the second half is a conveyor belt moving at 50MPH

as soon as the plane hits the belt, it would still be going 50MPH, but the wheels would register 100MPH

I like, explained that to myself while on the phone with lafengas and realized I shot myself in the foot, focusing on something that cannot happen.

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REWORDING THIS QUESTION:… THIS IS MY LAST POST TO GIVE INSIGHT OR SHED LIGHT ON THE SUBJECT

disclaimer: all remaining posts by me in this thread will be to make fun of people.

IF you have a plane on a FRICTIONLESS SURFACE, NO FRICTION. (i.e wheels on a conveyor belt… if there was friction, the plane would be pulled backwards. This question assumes the plane is stationary… I.E. NO FRICTION IS ACTING ON THE PLAN IN THE OPPOSITE DIRECTION!!! this is a theoretical, non real world scenerio, i know…but so is a huge conveyor runway.

HOW could the conveyor all of a sudden hold be able to hold the plane back when it tries to accelerate?

REWORDED QUESTION: Can a plane take off on a frictionless surface?