Plane moves forward, gets airspeed, and at rotation and lift-off, the wheels are spinning exactly twice as fast as they would on a "normal" runway.

OR:

Since they are not designed for that kind of abuse, the tires will have failed and the resultant friction will then create enough drag to keep the plane from flying.

In a perfect tire world, I'd go with the first option, the plane flys.

Pop

 

I'm sure it's been said already, the jets forward motion is not controlled by the wheels, they are on free spinning bearings. they will just spin twice as fast and the plane will fly.

put a car in the conveyor and pull it with a tow-strap, doesn't matter how fast that conveyor moves, you're still gonna pul the car as far as you want, as fast as you want.

 

I think you guys are missing the point here. The conveyer is powered, and rolling in reverse. Thrust is pushing the aircraft forward, the powered conveyer is rolling in the other direction, equally. Thrust is X. Conveyer speed is -X. If they match EXACTLY, the aircraft is not going anywhere. True the wheels aren't driving the aircraft, thrust is. BUT, if you have equal reverse power applied by the conveyer, all you're going to get is a lot of noise. Wheels will be rolling madly forward, but there will be no lift generated by air moving over the wings, because the PLANE isn't moving..........JUST the wheels are, because the speed of the conveyer. moving backwards is matching the thrust of the engines trying to push the aircraft forward.

Think on it a sec.

Gunner15a

P.S. It's been demonstrated quite nicely in a film clip I had of a B29 Superfortress flying backwards over Kadena AB in Okinawa, circa Korean War. The jetstream was moving west faster than the engines could move the plane to the east. Airplane flew backwards, even though all the instruments in the aircraft told the pilot he was flying forward at 250 Knots.

 

Been thought of more than a second.........If you take a second and read the posts, you may understand. The toy car on the treadmill is the best example.

Try it and get back to us.

[hint for the hundreth time......the conveyor belt has no effect on forward motion.]


LOL!!!...........that scenario has NOTHING to do with this. Obviously the westerly wind speed exceeded over 250 MPH.... way more than enough to keep even a 747 airborne.

 

Just because the wheels aren't pushing the aircraft forward doesn't mean that something isn't. If the ground is moving backward underneath you, and the engines are trying to move your forward. You're not going to move. They cancel each other out. Just because the engines aren't linked to the wheels doesn't mean that Newtons 3rd Law is revoked.


Yeah, thats right.......that big old JET STREAM, that works like a CONVEYER BELT, moved that big old bomber backwards no matter HOW many 1.5 HP per cubic inch engines it had, because those engines couldn't put out enough THRUST to hold the plane in position or move it forward.


Gunner15a

 

So if you hold a wheeled object on a treadmill, you can't push it forward???

No matter how hard you try, the treadmill will cancel your effort???



In your off the wall comparison, the jetstream is creating airflow over the wings...........a conveyor belt is not even in the same ball park.


I'll give you points for holding out the longest......Don't think even I took this long to come around.

 

For those that don't think the plane can fly, consider this:

From the original problem: "This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same "

Plane's speed = 0 Conveyor speed = 0
Plane's speed = 100 Conveyor speed = 100 .... plane speed = 0?????

How can the plane have 2 speeds measured from the same point at the same time?

 

Hey I'm not the sharpest tack in the box but it sounds to me like I got one right!
If it wasn't 7:30 a.m. I'd have a beer.

 

True, very true. What is pushing the plane forward? The engines, be they jet or prop, doesn't matter. What to the engines react against? Not the ground. They react against the fuselage and the atmosphere.


What does the ground react against? The wheels. What are between the wheels and the fuselage? Bearings that reduce friction (in this problem statement) to zero. Meaning there is zero friction between the ground (or conveyor) and the fuselage. Still have the engines pushing on the fuselage though.

Actually Newton's 3rd law is in full effect here. "For every action, there is an equal and opposite reaction."

So what forces are in effect here.
The force of the conveyor on the wheels. Fine, that turns the wheels. Friction free bearings means that force is not transmitted to the fuselage.

The force of the engines on the fuselage. Apply a force against an object with no counter force (there is no friction between the fuselage and the conveyor) that object will move.

If the plane can move, it picks up speed and flies.

That big old JET STREAM is not like the conveyor belt. That big old JET STREAM pushes directly on the fuselage of the aircraft and is directly counter to the force the engines put on the fuselage. So absoluetly YES, the jet stream can cause a plane's ground speed to be zero. But the jet stream is NOT acting on the plane in the same way the conveyor belt is.

 

For those that do not see it, I did not until I thought about it, remember the following items:

1. The wheels of aircraft have no drive mechanism

2. The treadmill is simply a distracter for the question/Thus there is no force being put into the treadmill.

3. The engine (either prop, jet or turbo fan) is what is propelling the plane and not the wheels.

4. Conventional wisdom/conventional logic states it will not work, but remember that the treadmill is a non-viable variable.

If this does not help think of this example. A fly is in a car on the freeway going 65mph. The fly is in the air, so how fast is the fly flying? It is all relative to the situation. The fly is going 65mph, but it is not expending energy to fly this fast. The cabin of the car is like the treadmill, it has not effect on the speed.

PS. My father landed a plane with a 3 foot rool out. He was flying a O-1 Bird dog and there was a 37 mph crosswing (Plane stalls at 45).

 

I wonder how many pages this thread is going to take? Ok,you need to answer a few more questions before I can answer.First,Is this plane filled with commuters on their way home for a holiday?Then no,it will not fly.Second,who owns this plane?Are the baggage handlers on strike?Again,it aint flyin! Third,What is the weather like?And last,what airport is it at,If it is metro in Detroit,then it might take off,tomorrow,the day after tomorrow,the day after the day after tomorrow,the day after the day after the day after tomorrow,the day after the,,,,,OK I`LL QUIT! But to answer the question,I have to agree that the speed of the conveyor or the wheels is irrelevant,forward motion is created by thrust.So,unless this conveyor is a bagillion(an old word I just made up) miles long,the forward motion from thrust would push the plane off of the belt and down the runway

P.S.Do I get extra points for such an imaginative answer?Rep points can be sent via Pony Express, that way I will be sure to get them in case this plane never gets off the ground!

 

I have to give Gunner props for thinking exactly like I was thinking when this thread was on it's first page.

However, I think the easiest way to explain is like this:
If the airplane's wheels have perfect "frictionless" bearings, then the conveyor CANNOT provide any force on the airplane other than vertical. Forget airspeed, ground speed and thrust for a second. Just focus on the wheels, Bearings and Conveyor. Once you have that correct in your head, everything else falls into place.

Good luck!

 

Everyone in favor of it staying on the ground ignore key factors in physics.

To gain forward motion thrust must exceed drag (in the case of wheels, this drag is friction).

The thrust force generated by the engines exceeds the drag (friction) generated by the wheels. If it did not, the plane would not be able to move forward, regardless of whether the ground is stationary or in motion (conveyor).

Does drag from the tires equal or exceed thrust? No, not even close, not for several orders of magnitude. A plane, whether it uses wheels, skids, floats or whatever, must be able to generate more force than the drag created by them in order to gain speed and generate lift.

To the doubters, please tell me how drag in the wheels can possibly equal or exceed thrust, yet we still have a vehicle capable of lift-off?

Its a very simple formula. Wrap your mind around it. A 747 generates 62,100 lbs of thrust per engine! And it has 4 of these. Who can possibly justify that the wheels are going to create the 248,400 lbs of drag required to keep it stationary, at any speed? The drag of the wheels, at best, is going to be a few thousand pounds at take-off and flight speeds.

Comparing this to the jet stream is way off. Speed relative to air speed is what lifts a plane. It doesn't matter if the jet stream where 5 or 500 mph, so long as relative to that speed the plane has speed to lift.

 

The wheels are a platform for the airframe. The plane moves on the wheels.
The thrust from the engines move the plane which in turn makes the wheels turn.
If the conveyor is matching the speed of the wheels there is no foreward motion of the plane.
If the conveyor and wheels will stand up to any speed whatsoever the plane will not gain airspeed to achieve lift.
The friction of the wheels is offset by the conveyor belt
A plane will take off on ice because the ice is not moveing. A float plane is designed to skim across the top of the water gaining speed to produce lift. I doubt it would takeoff going up a rocky waterfall.
There is no other scenereo as the one of the conveyor belt moveing the same speed as the wheels. Not even the car on the treadmill.

Pray that I don't get stuck on a jury where everyone thinks someone is guilty
and I think they are innocent.

 

And he still doesn't get it - awesome. You are one stubborn man, my friend.

You still haven't answered my question - where is this backward force holding the airplane back coming from? If the wheels were locked, it would be coming from the conveyor belt - but the wheels are free to spin!

You are overwhelmingly in the minority here - has it occurred to you that dozens of intelligent FTE'ers aren't wrong, and neither is the physics behind what we are saying?