Can Plane Take Off

Hooby said:

That example is completely unrelated.. One of the most important facts of the airplane thing is that it is completely horizontal to the ground (gravity always goes the same direction on earth, straight down, perpendicular to the plane/conveyor belt. Other forces, however, are relative to the situation).

A bike "riding down a vertical wall" would be pushed away from wall due to natural force.


These are my own conclusions and should not be considered as fact

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No sleep last night. A 104 degree fever on Saturday fubar"d my sleep schedule... Just explaining why I"m here.



Just thought it might be an interesting aside for ya that you"re right about the bike. It would fall away from the wall unless dropped straight down, parallel to it. You even touched on the reason. Gravity accelerates downward only, so any horizontal velocity that the bike had when it started to fall would remain.

This could also make it fall toward the wall, but so long as it didn"t hit the ground first, it would wind up bouncing off the wall, and falling away from it anyway.

In physics, even basic intuitive understandings that turn out to be correct are rare. Thus, that"s a pretty good observation.

Equator.
Plane on runway going East-West. Lift-off speed 333 km/h.
Earth rotating at 40,000km/hour -> ~1666 km/h (take some, give some) direction East.
Could the plane lift off if it was trying to accelerate?

a) Yes, at 2000km/h if it headed East.
b) Yes, at 1333km/h if headed West.

Hello, meet closed system theory.
The above is bull because wind is calculated from ground speed so it is a relative 0 - planes taking off do not care if they do it headed East or West.

Try to go with this image:
You got an ice skater accelerating on in infite body of frozen water.
You are always half as fast as the ice skater.
The ice is your conveyor belt (actually it is, the aquaplaning effect is comparable to wheels turning).
The speed above ground makes you become a stationary system because both the ice skater and the starting point of the skate are always at an equal distance to your point of view.
Remember: You are always doing half ground speed of the skater.
Does the skater gain distance on your position?
If yes a plane on a conveyer belt can take off.

This is not a question of effects, it is a question of observing one system from another system.
Wheels of the plane + conveyer belt = one closed system.
Propeller drag + bernoulli effect + absolute speed = observer system.

To make it even more vivid:
Imagine you got one of those conveyer belts that most large airports have to span long terminal hallways.
A guy on a skateboard gets some speed and rolls on that conveyer belt against the heading.
He will keep on going with (almost) the same speed as before if you stand and watch him (stationary observer system) even if the wheels of his skateboard just went from ground speed to ground speed+conveyer belt speed.

What people are forgetting here: This plane is no car. The wheels attached to the gear are not used to apply a force to the ground and push the vehicle in a direction. Actually you just have to forget about relative ground speed.
Take the airport skater, throw him a rope and start pulling him - will he accelerate even if you put the conveyer belt to acceleration that equals yours?
Rope = propeller drag

Got it now?

This seems to go along the lines of if you are falling in a helicopter or elevator and jumped out of it and up before you hit the ground that you would land slower then the helicopter. Which we all know is not true, yet it is interesting to discuss.

Meh, I used to play with balsa wood airplanes all the time. Wind the fuck out of the rubber band, let it go, continue to hold onto the plane, and you fan feel the pull. Even stationary, the prop is doing it"s job. It is trying to go forward even though I"m holding it still and the second I let go it is gone.

I"ll pass on the fancy science mumbo jumbo, my college learnin is being devoted to other subjects.

Hatorade said:

This seems to go along the lines of if you are falling in a helicopter or elevator and jumped out of it and up before you hit the ground that you would land slower then the helicopter. Which we all know is not true, yet it is interesting to discuss.

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They did this on mythbusters. Jumping at the last second on an elevator going so many feet per second met when you hit the pavement you were going that many feet per second minus 5. You are still screwed.

And the helicopter is totally going to hit first as I"m going to fan out like I saw the skydivers do to increase my wind resistance. Like two skydivers who jump out at the same time can of course go very differant speeds depending on how they position themselves.

So what do we all know is not true?

Arbitrary said:

They did this on mythbusters. Jumping at the last second on an elevator going so many feet per second met when you hit the pavement you were going that many feet per second minus 5. You are still screwed.

And the helicopter is totally going to hit first as I"m going to fan out like I saw the skydivers do to increase my wind resistance. Like two skydivers who jump out at the same time can of course go very differant speeds depending on how they position themselves.

So what do we all know is not true?

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Lol let me better explain. I meant you would still die even if you did jump out. Slower as it may be it would not be slow enough.

There is no force being applied through the wheels to the ground. The force responsible for moving the plane forward in space is force from the prop or turbine acting on air. The ground is inconsequential because that is not where the force is being applied. The plane"s power plant turns a propeller that exerts force on the air and creates thrust. There is no way for the surface that the plane is sitting on to prevent this action. The plane would be able to move forward, and therefore take off normally.

Let me first state how I read the first question in the most simplified manner I can. paraphrase: The conveyor belt the plane sits on accelerates to match and counteract the speed the plane"s thrust would create.

If the plane"s wings don"t move through the air, then the plane can"t take off. I"m not talking about the wheels causing a force on the belt, the prop or jet engine of the plane doesn"t care about the belt at all. I"m talking about the belt actively counter acting the motion of the plane forward. In that case the plane is going to sit on the conveyor belt and it"s going to haul ass under the plane.

The engine (prop or jet) simply provides thrust. Just as if it were wheels on the ground, using friction between the tires and the road, the prop / jet uses the friction of the air against the blades to move the air aft and force the wing to cut through the air. The motion of the air over AND under the wing gives lift. It"s the motion of the plane that allows that lift to be created and continue. If the plane slows to a point below the airspeed that can sustain the plane"s mass with the lift generated, the plane stalls and falls out of the sky.

So, if the question is "will the conveyor belt have any affect on the thrust generated?" the answer is no. If it is, "can the conveyor affect the forward motion and therefore the lift generated by the wings?" the answer is yes.

I voted yes, I will have sex with an airplane for 1 billion dollars.

Dapopeah said:

Let me first state how I read the first question in the most simplified manner I can. paraphrase: The conveyor belt the plane sits on accelerates to match and counteract the speed the plane"s thrust would create. If the plane"s wings don"t move through the air, then the plane can"t take off. I"m not talking about the wheels causing a force on the belt, the prop or jet engine of the plane doesn"t care about the belt at all. I"m talking about the belt actively counter acting the motion of the plane forward. In that case the plane is going to sit on the conveyor belt and it"s going to haul ass under the plane.

The engine (prop or jet) simply provides thrust. Just as if it were wheels on the ground, using friction between the tires and the road, the prop / jet uses the friction of the air against the blades to move the air aft and force the wing to cut through the air. The motion of the air over AND under the wing gives lift. It"s the motion of the plane that allows that lift to be created and continue. If the plane slows to a point below the airspeed that can sustain the plane"s mass with the lift generated, the plane stalls and falls out of the sky.

So, if the question is "will the conveyor belt have any affect on the thrust generated?" the answer is no. If it is, "can the conveyor affect the forward motion and therefore the lift generated by the wings?" the answer is yes.

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I"ll buy another balsa wood rubber band plane, try a string to it, and see if it will fly or crash into the ground. I think I did this like 15 years ago and it still flew, but I can"t remember.

You make many suppositions in that reply, Wand. If the conveyor can be built, you say it can"t.. if the bearings can withstand the friction, etc etc. You didn"t give us real-world rules, and going on hypotheticals and theoreticals, you even admit that it"s possible by stating, "The ONLY way a conveyor can actually prevent or slow a plane from moving forward .. (and I do mean ONLY).. is if it can match the thrust the engine produces" This is a very true statement. IF You can counteract the thrust the plane goes nowhere. Whether or not this is a realistic world scenario is another question entirely.

This is feeling like a rickshaw...

The plane can"t take off because I"m one arming it backwards. Discussion over.

TheWand said:

If that were the case, the plane would have to be somehow held in place while the conveyor were braught up to a speed somewhere around 900 MPH (for a jet engine)..

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Better question: If a plane travelling by you is going mach 1, do you hear a sonic boom? It"s amazing how many people get THAT wrong.

Yeah ... the original question was something along the lines of: If a conveyor is going the same speed of a plane but in the opposite direction, can it take off?

Now you"re just adding in random bullshit like tires exploding.

I am so disapointed with the collective intelligence of the people involved in this thread. So disapointed.

Better question: If a plane travelling by you is going mach 1, do you hear a sonic boom? It"s amazing how many people get THAT wrong.

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You don"t hear it coming until it"s already past, basically. But yeah, I"m sure most people"s head would explode if you asked them this question.

That didn"t answer the question: Do you hear a sonic boom or not?

Eomer said:

I am so disapointed with the collective intelligence of the people involved in this thread. So disapointed.

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So has there been an actual answer posted? Or has it just been TheWand posting shit about the impossibilites of the theoretical question he posed, and Galiem flexing his physics-peen?

I still say it won"t since lift requires horizontal motion (I have no idea, I"m just assuming here), and the plane will be sitting still.

guys arguing no are forgetting ONE THING....the Wheels are exerting no force on the conveyor- they are ROLLING..

the thrust to get the plane moving in the air is NOT transferred to the conveyor-
the plane starts up , the brake Released so now the wheels are free to move.

the plane starts to move forwards - ignoring friction- the conveyor belt starts rolling,,,, the wheels just turn faster to match the conveyor speed- as the plane accellerates the wheels are just turning twice as fast as the conveyor moves at the speed of the plane. the plane - a jet takes off at ~120 miles an hr btw- will take off easily.

NOW if the thrust of the takeoff was not generated via a propellor or jet engine but via a drivetrain like a CAR, ie all movement thrust provided by the Wheels-

THEN and ONLY THEN would the plane would not take off due to the fact that the plane wouldn"t be moving but the action would be like a person running on a treadmill.

person runs but doesn"t "move"...