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#165762 - 28/12/06 12:09 PM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
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Posts: 5232
Loc: Florida
Quote:
Originally posted by GrayHam:

Lift is not created by air being directed downward towards the ground.

An airfoil, or wing, has a greater surface area on the top side of the wing as opposed to the underside.

As air rushes over the airfoil, it must move faster over the wing, as it has more distance to cover, versus the underside of the wing.

This increased velocity of airflow over the top of the wing results in a decrease in pressure on the top of the wing.
This decreased pressure generates the lift.

Greater angles of attack can therefore create greater distance differences on the top versus bottom surfaces of a wing, resulting in greater lift.
You are right.

However, getting back to the original hypothetical question posed by this thread, much of what is required for lift... or flight is not present in this hypothetical.

The only thing that exists is thrust. While this plane may achieve some lift, I tend to doubt it would achieve flight. Not any type of stable flight.

Maybe we need a mathematician, but the vector quantities that are required for flight do not seem to exist as the situation has been proposed.

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#165763 - 28/12/06 12:09 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Paul H Offline
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Registered: 23/08/01
Posts: 4757
Loc: Mt. Zion, IL
Quote:
Originally posted by Smith:
Quote:
Originally posted by RiNkY:
[b]

Stick a forward thrusting object on something that equally matches its forward thrust with rearward motion / thrust and it won't go anywhere.

My wife would disagree.[/b]
Yeah your wife mentioned that to me as well [Wave]
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#165764 - 28/12/06 12:09 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


The Plane would only not take off in the treadmill scenario if the Pilot was throttling back the thrust to match the speed of the treadmill (initial reverse accelleration). Hence stationary no air movement, no lift, no takeoff.

If the treadmill's speed is truly infinite then ya the pilot cannot overcome the reverse accelleration and take off, but in reality the takeoff speed will be the same because the plane at full throttle will advance through the air regardless of relative ground speed.

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#165765 - 28/12/06 12:14 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Quote:
Originally posted by RiNkY:
Stick the same plane on a regular runway with a constant 200mph tail wind. Accelerate the plane so it is going 200mph (Ground Speed). Will the plane fly? No - because in essence it's air speed is 0mph. The 200mph tail wind cancels out the 200mph forward speed. Airflow over the all important wings is 0mph.
I would argue that the plane could basically hover in this condition and hence be flying. This is why you land with your nose in the wind, so you can maintain a little relative ground speed with as much as possible air speed.

There were many times flying small R/C airplanes that I experienced this, lots of fun hovering an airplane in the wind. Although when the wind changed direction quickly the lift was gone and if you didn't have the altitude to gain airspeed again you crashed.

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#165766 - 28/12/06 12:18 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Both the fired bullet and the dropped one will hit the ground at the same time. That is unless you want to get extremely technical about it. I remember this from Physics in college. Try this experiment. Grab something you don't mind dropping. It shouldn't be round or able to roll easily. Now take your object and hold it to your waist. Walk as fast as you can and let the object go in mid stride. You will find that it lands right next to you feet as you are walking. This shows that horizontal movement and vertical movement are independant. While it's hard to believe, both bullets will hit at the same time.

Now, if you want to get crazy with it, you can ponder the following. Since the earth is round, the shortest distance to the earth is right where you are standing. As you move further from that point, the distance increases. For example, if you drop a ball from right in front of your nose, it will travel a shorter distance than if you dropped the same ball from th same hight, but at arms length. Not much farther, but it is indeed a longer distance to the ground. Now considering these facts, if you want to be technical; the fired bullet will hit after the dropped one, but not by that much.

If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.

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#165767 - 28/12/06 12:22 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Quote:
Originally posted by PANissanX:
If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.
Wouldn't that mean that you fired the bullet outward (UP) and not parrallel to the ground? Hence like a rocket.

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#165768 - 28/12/06 12:28 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


We don't need a mathmetician, we need someone who has a solid understanding of Newtonian physics (also called classical physics).

This is a basic question of force. Will the plane attain the force required to overcome gravity? As I stated it will.

The conveyor belt will not translate enough force to hold the plane in place. If the wheels are moving freely (indicating low friction) the force translated to the plane (through the landing gear into the main structure of the plane) will be very low. The thrust force generated is very high. The plane moves forward, the belt speeds up.

The plane will continue to gain acceleration and therefore velocity needed to attain a lift force from the wings (as stated by someone else before - it is actually the pressure differential between sides of the wing that cause lift). The conveyor belt will speed up, and will transfer more force to the plane; however, this force will be very small, and as already stated not enough to overcome the thrust). At this point the belt would be moving very fast, however the plane would continue forward relative to it's starting point. The plane will therfore reach an airspeed suitable to attain lift and take off.

I'm sorry Rinky, but you are wrong. You need to mentally disconnect the ground from the plane. Using your cue I will try it this way. If a plane is facing forward into a 200 mph wind, engines off, will it fly? Yes, straight up. The plane will attain lift and take off straight up, untill someone applies enough force to overcome the difference between lift and gravity and bring it back down.

I already tried to make a free-body diagram, but couldn't do it here. If I have to I will draw it in paint and load it into photobucket so I can link it here.

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#165769 - 28/12/06 12:36 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Quote:
Originally posted by Conundrum:
Quote:
Originally posted by PANissanX:
[b]If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.
Wouldn't that mean that you fired the bullet outward (UP) and not parrallel to the ground? Hence like a rocket.[/b]
No, horizontally. Because of the curvature of the earth, as the bullet drops at the normal speed the earth will have curved beneath it. It will continue to fall forever. Sounds crazy, but that's how orbits work.

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#165770 - 28/12/06 12:38 PM Re: Know that if you do not post in this thread today the human race may cease to exist
TravelingFool Offline
Member

Registered: 17/10/00
Posts: 6013
Loc: Prior Lake, MN
Rinky, you're a dumbass. You state:
Quote:
Yes, if it weren't for the fact that the treadmill is canceling out any actual flow against the air it would take off.
How can a treadmill cancel out air flow? All the treadmill is doing is spinning the wheels. The treadmill could spin the wheels on the plane up to a million rpm and it wouldn't make any difference.

1. put your car on a treadmill.
2. shift it into neutral.
3. turn on the treadmill.
4. The car's wheels will start spinning, but the car itself will realize ZERO forward motion.
5. Put the car in gear and mash on the gas.
6. the engine of the car turns the wheels which are fighting the treadmill. The car still doesn't go anywhere.

That's where YOUR brain stops. Lets do the same experiment with a jet engine strapped to the roof of your car.

1. put your car on a treadmill.
2. shift it into neutral.
3. turn on the treadmill.
4. The car's wheels will start spinning, but the car itself will realize ZERO forward motion.
5. Light the jet engine.
6. The jet engine doesn't turn the wheels like the car's engine would, it thrusts back into the air. The car will rocket forward because for every action, there is an equal and opposite reaction (Newton).
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#165771 - 28/12/06 12:39 PM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
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Registered: 09/05/02
Posts: 5232
Loc: Florida
Quote:
Originally posted by Branden Burden:
We don't need a mathmetician, we need someone who has a solid understanding of Newtonian physics (also called classical physics).

This is a basic question of force. Will the plane attain the force required to overcome gravity? As I stated it will.

The conveyor belt will not translate enough force to hold the plane in place. If the wheels are moving freely (indicating low friction) the force translated to the plane (through the landing gear into the main structure of the plane) will be very low. The thrust force generated is very high. The plane moves forward, the belt speeds up.

The plane will continue to gain acceleration and therefore velocity needed to attain a lift force from the wings (as stated by someone else before - it is actually the pressure differential between sides of the wing that cause lift). The conveyor belt will speed up, and will transfer more force to the plane; however, this force will be very small, and as already stated not enough to overcome the thrust). At this point the belt would be moving very fast, however the plane would continue forward relative to it's starting point. The plane will therfore reach an airspeed suitable to attain lift and take off.
You are adding into the scenario. That is NOT what was proposed in the hypothetical.

The plane would NOT move forward according to the hypothetical. The conveyor belt and the wheels would negate each other as forces. That is the scenario as it was proposed.

Hence, many of the vector quantities required for flight do not exist.

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#165772 - 28/12/06 12:39 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Consider this: If you had a powerful enough telescope, you could go to the top of mt.everest, look through...and at just the right angle, you could see yourself looking through the telescope from behind.

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#165773 - 28/12/06 12:40 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Quote:
Originally posted by PANissanX:
Quote:
Originally posted by Conundrum:
[b]
Quote:
Originally posted by PANissanX:
[b]If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.
Wouldn't that mean that you fired the bullet outward (UP) and not parrallel to the ground? Hence like a rocket.[/b]
No, horizontally. Because of the curvature of the earth, as the bullet drops at the normal speed the earth will have curved beneath it. It will continue to fall forever. Sounds crazy, but that's how orbits work.[/b]
Sure that's how orbits work, but it's how you get into orbit that counts. You have to first overcome the friction of the atmosphere and even if you do, orbit has to be maintained by external force or it will degrade and send you burning up in the atmosphere (Mir Space Station).

Isn't this why we still have to use the shuttle? We don't have a horizontal takeoff vehicle YET. The closest that is public is the Space Ship One by that Apple Guy?

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#165774 - 28/12/06 12:44 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


man, ya'll got way to much time on your hands. when is this gona move to the ALR?

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#165775 - 28/12/06 12:46 PM Re: Know that if you do not post in this thread today the human race may cease to exist
RedX Offline

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Registered: 25/04/01
Posts: 2394
Loc: Granite Falls, NC
They would not negate each other. The force generated by the plane is via the air (air forced through the turbines)....the force generated by the conveyor belt is transferred to the wheels, which in the instance of take-off force play no part.

The air being forced through the turbines will be pushed through those turbines regardless of the conveyor belt's speed. And therefore, the plane will respond, as it does in take-off scenarios, to that force through the turbines. And it will react by moving forward through the airspace it is in, and the airspace that is being affected by the turbines' forcing of said air. The wheels' operations and reactions to the conveyor beneath them are unimportant in this hypothetical scenario.

The only way the conveyor could affect the plane's ability to lift off under take-off thrust was if the conveyor could also negatively (with relation to the plane's intended forward motion) affect the air through which the plane needs to move to achieve lift-off velocity.

cool
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#165776 - 28/12/06 12:51 PM Re: Know that if you do not post in this thread today the human race may cease to exist
RedX Offline

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Registered: 25/04/01
Posts: 2394
Loc: Granite Falls, NC
Also....think of it this way.....

Can I run forward on a treadmill and throw a balsa wood airplane forward? Will it fly. It will.....and the laws of lift apply the same to the plane on this conveyor belt.....But instead of my legs running on the treadmill, the wheels roll on the conveyor....and instead of my hand providing the propulsion for lift, the turbines move the air (independent of the conveyor remember, they are seperate forces) to provide the propulsion for lift.

smile
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#165777 - 28/12/06 12:51 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Quote:
Originally posted by Conundrum:
Quote:
Originally posted by PANissanX:
[b]
Quote:
Originally posted by Conundrum:
[b]
quote:
Originally posted by PANissanX:
If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.
Wouldn't that mean that you fired the bullet outward (UP) and not parrallel to the ground? Hence like a rocket.[/b]
No, horizontally. Because of the curvature of the earth, as the bullet drops at the normal speed the earth will have curved beneath it. It will continue to fall forever. Sounds crazy, but that's how orbits work.[/b]
Sure that's how orbits work, but it's how you get into orbit that counts. You have to first overcome the friction of the atmosphere and even if you do, orbit has to be maintained by external force or it will degrade and send you burning up in the atmosphere (Mir Space Station).

Isn't this why we still have to use the shuttle? We don't have a horizontal takeoff vehicle YET. The closest that is public is the Space Ship One by that Apple Guy?

Right...at 27,000KMPH the bullet (fired horizontally) would leave our atmosphere and go into orbit. If we had a plane that would go that fast, we could fly horizontaly out of our atmosphere.

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#165778 - 28/12/06 12:54 PM Re: Know that if you do not post in this thread today the human race may cease to exist
TravelingFool Offline
Member

Registered: 17/10/00
Posts: 6013
Loc: Prior Lake, MN
Wow, this thread brings back memories. I used to work part time at Houston Raceway Park, a drag strip about 40 miles out of downtown. Some nights, they would race jet cars vs. top fuel dragsters... Lots of noise and fire, etc, to rev up the crowd.

Anyway, the Top-Fuel dragster would always do a burnout to heat up the tires and thus get better traction. Obviously, the jet car had no need... and yet; someone would ALWAYS shout out, "DO A BURN!"

Even better, people would make excuses for the jet car, "That jet car COULDN'T do a burnout cuz if'n it did, it would melt the tires!" etc.

Oh well. Its what makes America "great," I suppose...

- Thousands of Americans shot at their local water towers after Orson Wells read the story of the "War of the Worlds" on the radio...

- MILLIONS of lemmings bought thigh masters...

- Tens of thousands of people use the flash on their cameras at sporting events, even though they only illiminate about 10 feet of area in front of the camera...

We (as a nation) aren't that smart, I guess frown MAKE your kids take science classes, please?
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#165779 - 28/12/06 12:56 PM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
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Registered: 09/05/02
Posts: 5232
Loc: Florida
Quote:
Originally posted by RedX:
They would not negate each other. The force generated by the plane is via the air (air forced through the turbines)....the force generated by the conveyor belt is transferred to the wheels, which in the instance of take-off force play no part.

The air being forced through the turbines will be pushed through those turbines regardless of the conveyor belt's speed. And therefore, the plane will respond, as it does in take-off scenarios, to that force through the turbines. And it will react by moving forward through the airspace it is in, and the airspace that is being affected by the turbines' forcing of said air. The wheels' operations and reactions to the conveyor beneath them are unimportant in this hypothetical scenario.

The only way the conveyor could affect the plane's ability to lift off under take-off thrust was if the conveyor could also negatively (with relation to the plane's intended forward motion) affect the air through which the plane needs to move to achieve lift-off velocity.

cool
You are falsely treating the plane's jet engines as if it were moving through the air. It is NOT moving forward through the air.

The forward motion of moving through the fluid of air must be removed from your thinking regarding this hypothetical.

In the hypothetical the plane is stationary to it's relative position on the ground.

There is no air being forced through the turbines as there would be if it was moving forward through fluid air. The fuel from the plane at this point is what is moving the turbines of the jet.

There is no forward motion of this plane in the hypothetical.

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#165780 - 28/12/06 12:58 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


someone call Mythbusters for chrissakes.. :rolleyes:

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#165781 - 28/12/06 01:06 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


NY - the question said nothing about the plane's ability/inability to move forward relative a point off of the belt.

If it was anchored and unable to move forward (again, relative to a point off of the belt), then you are right - try as you might if you don't move you won't fly.

If it is able to move relative to a point off the belt, then it would be moving thru the air, and able to attain lift. It would be moving down the conveyor belt runway away from the plane's starting point and toward the belt's "head pulley"; therefor the fluid air will be moving over the wings, and able to attain lift. This is the assumption I made, and as it was not stated otherwise, the assumption I will follow.

Edit to add: (Just thought of this) If the plane was anchored the belt would never start moving, because the plane would never start moving, because the wheels would never start turning, because they are obviously not driven by jet engines.

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#165782 - 28/12/06 01:10 PM Re: Know that if you do not post in this thread today the human race may cease to exist
GrayHam Offline
Member

Registered: 17/04/01
Posts: 8849
Quote:
Originally posted by NY Madman:
The conveyor belt and the wheels would negate each other as forces. That is the scenario as it was proposed.
Agreed.

The wheels and conveyor belt would battle each other incessantly, ad nauseum.

Unfortunately, wheels on a plane play zero role in the actual forces of flight.

Even if the treadmill was able to spin the wheels backwards, against the direction of thrust, at a bazillion RPMs, the thrust propulsion is independant of the little battle the wheels are involved in.
The wheels are immaterial to the forces of flight (lift, gravity, thrust and drag).

-------------------------------------
EDIT:
That's not quite correct.
Wheels, if they are stuck, or break off, or are otherwise damaged, could generate drag by dragging against the ground or causing damage to the airframe.

But as I understand the scenario, the conveyor belt is spinning the wheels freely, creating zero drag.

I am assuming a zero-drag scenario, as the conveyor belt is not damaging the wheels, merely spinning them in an attempt to negatively affect the aircraft's groundspeed.
-----------------------------------------

In essence, the plane does not give a fuck what the wheels are doing.

So yes, the tradmill and the wheels would cancel each other out. At 100 RPM, at 1,000 RPM, and at 1,000,000 RPM.

And the thrust from the propulsion would launch the plane quite handily.
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#165783 - 28/12/06 01:11 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Well, I'd need to consider all the variables.

Such as, are there motherfuckin' snakes on this motherfuckin' plane?

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#165784 - 28/12/06 01:14 PM Re: Know that if you do not post in this thread today the human race may cease to exist
RedX Offline

Member
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Registered: 25/04/01
Posts: 2394
Loc: Granite Falls, NC
Quote:
Originally posted by NY Madman:
The forward motion of moving through the fluid of air must be removed from your thinking regarding this hypothetical.

In the hypothetical the plane is stationary to it's relative position on the ground.

There is no air being forced through the turbines as there would be if it was moving forward through fluid air. The fuel from the plane at this point is what is moving the turbines of the jet.

There is no forward motion of this plane in the hypothetical.
So......how does the air interact with the turbines? The only way your scenario makes sense is if there is a mechanical bond between the conveyor and airplane.....interlocking the rearward motion of the conveyor to rearward travel by the airplane.

I think the plane will initially react as a ball will on a treadmill.....It will counter-roll to the treadmill's direction, until laws of inertia play into the equation and pull the ball back with the treadmill.....until the friction between the ball and mill overrule the law of inertia, the ball will stay in its original spot and roll backwards.

I suppose the questions are......How quickly does the conveyor get up to speed? Does it accelerate at the same rate as the plane's turbines? What is the coeficiant of friction between the wheels and conveyor (and likewise, internally in the wheels' structuring)?

I still believe the turbines' thrust will overpower the inertial and friction related actions between the wheels and conveyor.
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#165785 - 28/12/06 01:18 PM Re: Know that if you do not post in this thread today the human race may cease to exist
XPLORx4 Offline
Member

Registered: 23/03/01
Posts: 1906
Loc: San Jose, CA
Quote:
Originally posted by NY Madman:
There is no forward motion of this plane in the hypothetical.
Yes, there is. The plane is not bolted to the ground. Therefore, it moves forward because a plane's engines push against AIR, not the GROUND. Planes achieve lift via airspeed, not groundspeed.

Unless that conveyor somehow manages to prevent the engines from moving air through them, the plane is gonna take off.
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#165786 - 28/12/06 01:18 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


smile I wish people added this much the the phat chicks thread! smile

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