will it take off?

[RayH]

Ok, For the non beleivers, lets try this one to prove that wheel speed has nothing to do with the plane taking off. Lets make the plane a glider, no prop. Gliders take off by being pulled by another plane. The Glider sits on the conveyor belt, the puller plane strattles the conveyor in front of the glider so its not on the conveyor. Hook the two of them together and the puller starts moving forward pulling the glider. As the glider starts moving, the conveyor starts in the opposite direction. The puller plane still pulls the glider forward even though the glider is on a conveyor and they will lift off, it doesnt matter that the glider is on a conveyor because its still being pulled forward by the other plane. All Ive done for this example replace the prop on the plane thats on the conveyor with another source of trust, ie: the puller plane. You could pull the glider with anything, a car, tractor, human power, a mule or a prop or a jet engine, the glider will move forward and lift off.

 

[NewToy]

Which makes the winch example NOT comparable to the propeller example. I agree in your scenario, the plane would fly - because it is impossible for the conveyor to make the speed of the plane zero. The winch is moving the cable so the plane HAS to move. Your example basically makes the magic conveyor null and void - it can't eliminate ground speed because the fact that the cable is shortening will mean that it can't match the speed of the planes wheels (would require the laws of physics to change)

In the propeller example, this is not necessarily true. Since the wheels represent the ground speed and since the magic conveyor is countering all ground speed, the plane is not moving. No movement = no flight

The winch pulls the plane forward at 2 MPH and the conveyor counters that going in the opposite direction. How does the winch negate the conveyor? The winch example shows exactly what will happen with the prop installed, the plane moves forward with thrust with the wheels doing double time.
John

 

[dillo99]

Ok, For the non beleivers, lets try this one to prove that wheel speed has nothing to do with the plane taking off. Lets make the plane a glider, no prop. Gliders take off by being pulled by another plane. The Glider sits on the conveyor belt, the puller plane strattles the conveyor in front of the glider so its not on the conveyor.

But again, you are fixing the plane to the ground by attaching it to a plane that is on the ground and thus taking the magic conveyor out of the equation. In your scenario, I again agree the plane would fly because the you have made the magic conveyor an impossibility. It can't match wheel speed. But in the scenario that is described, there is no attachment of the propulsion to the ground. The prop is propelling the plane BUT the magic conveyor is counter propelling it and eliminating any forward motion. If there is no forward motion, there is no airspeed (other than prop generated which is insufficient). No airspeed = no lift = no flight.

 

[RayH]

And to add to that. The radio the airplane is using is traveling at 0 velocity in relation to the pilot/passengers.

Harry K

Exactly,
That leads me to ask, if you were flying the speed of sound and someone on the ground with a megaphone yelled at you, could you hear it? Or more realistically, you are flying a jet at the speed of sound and drop a bomb. Would you hear the explosion when the bomb hits the ground?

 

[RayH]

But again, you are fixing the plane to the ground by attaching it to a plane that is on the ground and thus taking the magic conveyor out of the equation. In your scenario, I again agree the plane would fly because the you have made the magic conveyor an impossibility. It can't match wheel speed. But in the scenario that is described, there is no attachment of the propulsion to the ground. The prop is propelling the plane BUT the magic conveyor is counter propelling it and eliminating any forward motion. If there is no forward motion, there is no airspeed (other than prop generated which is insufficient). No airspeed = no lift = no flight.

Notice a trend, every example, the conveyor is removed from the equation. Thats because it doesnt matter, its not part of the "lift off" equation. A planes wheels are not a source of thrust and they arent a source of forward motion. All the wheels do is allow the plane to travel at the speed the prop, or any other source of thrust, will pull it.
Do you agree that a plane needs airspeed and not ground speed to take off?

 

[NewToy]

Exactly,
That leads me to ask, if you were flying the speed of sound and someone on the ground with a megaphone yelled at you, could you hear it? Or more realistically, you are flying a jet at the speed of sound and drop a bomb. Would you hear the explosion when the bomb hits the ground?

You would not hear anything as your plane is travelling at the speed of sound and the sound waves created by the bomb would never catch up to you.

The speed at which the sound barrier is broken fluctuates a bit due to atmospheric conditions. What is the optimum medium for conducting sound waves? What is the speed of sound on a planet with a methane atmosphere? How is pollution, greenhouse gasses and particulates affecting the speed of sound? Is that why people in NYC talk so fast?

John

 

[BillyP]

Exactly,
That leads me to ask, if you were flying the speed of sound and someone on the ground with a megaphone yelled at you, could you hear it? Or more realistically, you are flying a jet at the speed of sound and drop a bomb. Would you hear the explosion when the bomb hits the ground?

On the megaphone deal. Only if you were flying towards it. If you were flying away, the sound waves wouldn't be able to reach you.

The bomb deal. Nope. Even if you slowed below the speed of sound, the bomb would have already hit long before you hear the sound.

Same as if you were to shoot and immediately kill a deer at say 300 yards, with a 30-06. The deer would never hear the sound of the shot.

 

[dillo99]

Notice a trend, every example, the conveyor is removed from the equation. Thats because it doesnt matter, its not part of the "lift off" equation. A planes wheels are not a source of thrust and they arent a source of forward motion. All the wheels do is allow the plane to travel at the speed the prop, or any other source of thrust, will pull it.
Do you agree that a plane needs airspeed and not ground speed to take off?

Yes, I agree that the plane needs airspeed and not ground speed to take off and yes I understand that the wheels are not a source of thrust - they have nothing to do with POWERING the plane to take off. BUT the wheels do represent the speed of the plane while it is on the ground. So if the wheel is turning 5 rotations per second then the plane is moving forward at 5 rotations per second. If, you somehow magically counter that and move the plane backwards at an identical rate (5 rotations per second) then you effectively cancel out any movement of the plane. It is not moving. Yes, the propeller provided thrust to move it forward, but the ground moved the plane backwards an equal distance thus taking airspeed to zero.

To me, the conveyor is identical to the scenario of the brakes being locked. If the breaks are locked and thus the plane does not move, can it take off? No because it can't generate air speed. You point out that "all the wheels do is allow the plane to travel at the speed of the prop" - AGREED. And in this case, I interpret the conveyor to be preventing that movement. I guess it depends on your interpretation of the conveyor. If it truly can match the speed of the wheels instantly, then to me it is the same as the wheels not spinning which is the same as the brake being on. no movement = no airspeed = no flight

 

[RayH]

You would not hear anything as your plane is travelling at the speed of sound and the sound waves created by the bomb would never catch up to you.

The speed at which the sound barrier is broken fluctuates a bit due to atmospheric conditions. What is the optimum medium for conducting sound waves? What is the speed of sound on a planet with a methane atmosphere? How is pollution, greenhouse gasses and particulates affecting the speed of sound? Is that why people in NYC talk so fast?

John

The speed of sound is proporsional to the density of the medium that it is travlling through. Example; water transmits sound faster than air and as you go further up in our atmoshere, the speed of sound gets slower as the atmoshere gets thinner until eventually sound will not travel in the vacuum of outerspace. I believe methane is a heavy gas ,more dense, so sound would travel faster, the same goes for smoggy NYC.

 

[NewToy]

But again, you are fixing the plane to the ground by attaching it to a plane that is on the ground and thus taking the magic conveyor out of the equation. In your scenario, I again agree the plane would fly because the you have made the magic conveyor an impossibility. It can't match wheel speed. But in the scenario that is described, there is no attachment of the propulsion to the ground. The prop is propelling the plane BUT the magic conveyor is counter propelling it and eliminating any forward motion. If there is no forward motion, there is no airspeed (other than prop generated which is insufficient). No airspeed = no lift = no flight.

You are failing to see that the thrust from the engine IS the same thing as a cable pulling the plane, you just can't see it. Why can't the conveyor match wheel speed if being pulled by a cable? It can, and will result in the wheels turning 2x at liftoff. The rearward force created by the thrust must result in the plane moving forward. Say the plane had a magnetic levitation (ala bullet train) landing gear. The thrust moves the plane forward an inch above the conveyor which is moving the opposite direction the plane is at the same speed, time etc. The conveyor isn't impeding the movement of the plane just like the wheels freely spinning would have no effect other than the negligible amount of energy lost in bearing and tire friction. Where do you propose all the thrust energy is going? It must propel the plane forward, just the wheels will be going twice as fast at LIFTOFF!
John