Plane on a Treadmill

Started by TACP, February 15, 2010, 06:06:24 AM

0 Members and 1 Guest are viewing this topic.

Lets see where the membership stands on this question

Will Fly
13 (54.2%)
How should I know, I am on a ground team!
1 (4.2%)
Won't Fly
5 (20.8%)
Paradox in question-no answer
5 (20.8%)

Total Members Voted: 24

SarDragon

Quote from: Major Lord on February 16, 2010, 08:32:51 PM
I weep for the future of our cadets when I think who may be teaching them physics.....I remember one senior member telling cadets that a bullet shot straight up will come back to earth at the same velocity at which it was launched.

Actually, if it goes exactly straight up, and exactly straight down, that is true. Add any horizontal component, and all bets are off.

The bullet starts with a specific amount of kinetic energy when fired, and at the top of its flight it becomes potential, after having been slowed at 32 ft/(sec*sec). It is then accelerated at the same rate until it falls to Earth. Air resistance is effectively cancelled out, since it is present on both parts of the flight.
Dave Bowles
Maj, CAP
AT1, USN Retired
50 Year Member
Mitchell Award (unnumbered)
C/WO, CAP, Ret

RiverAux

Boy, I've run pretty fast on a treadmill and have yet to feel any wind on my face as I would if I was outside running around the track.

Major Lord

Lordmonar,

Right you are, but I don't think they will believe you. ( they probably still believe in man-made global warming)We might have to find an Aeronautical Engineer to convince the skeptics.

Major Lord
"The path of the righteous man is beset on all sides by the iniquities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee."

FW

Quote from: SarDragon on February 17, 2010, 01:03:54 AM
Quote from: Major Lord on February 16, 2010, 08:32:51 PM
I weep for the future of our cadets when I think who may be teaching them physics.....I remember one senior member telling cadets that a bullet shot straight up will come back to earth at the same velocity at which it was launched.

Actually, if it goes exactly straight up, and exactly straight down, that is true. Add any horizontal component, and all bets are off.

The bullet starts with a specific amount of kinetic energy when fired, and at the top of its flight it becomes potential, after having been slowed at 32 ft/(sec*sec). It is then accelerated at the same rate until it falls to Earth. Air resistance is effectively cancelled out, since it is present on both parts of the flight.
Basically, another Mythbusters Episode  ;D

Now the question is: If you add Einsteinian Theory to the equation, does it take longer for it to go up than down?  :o

Major Lord

FW, do you have bullets that go the speed of light? Send me a box.....you can't get them in California!

The science project trick of excluding air densities at various heights and calculating the velocities as if they were all in a vacuum would be great, but the earth sucks and air is thick. (unless you are a climate scientist or a witch doctor)  A bullet fired straight up weighing 120 Grains, at 3000 M/S will fall until it reaches about 300-400 M/S, its terminal velocity. ( Depending on its attitude, sectional density, coefficient of drag, and other magical influences) Still not fun to get hit with, but not the same velocity it was launched at. Okay, that one was too hard: If you put a bird in a space suit, how fast can it fly on the moon?

Major Lord

ps. Don't we have even one full fledged (pun intended) aerospace engineer on this board?
"The path of the righteous man is beset on all sides by the iniquities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee."

lordmonar

Quote from: RiverAux on February 17, 2010, 01:12:00 AM
Boy, I've run pretty fast on a treadmill and have yet to feel any wind on my face as I would if I was outside running around the track.

Yes...but your thrust is developed from the friction between your feet and the road.  Since the road is moving away from you your net velocity becomes zero......airplanes do not develope their thrust from friction between the wheels and the ground.....but between the prop and the surounding air.  So it will still develope thrust even if the ground is going the other way.
PATRICK M. HARRIS, SMSgt, CAP

N Harmon

Please read this:
http://tinyurl.com/Stupid-Airplane-On-Treadmill-Q

Where the author of that article claims there is no physical mechanism that would cause the plane to have nonzero speed, I say there is: kinetic friction. And kinetic friction is precisely what stops the treadmill from spinning up to infinity as the thrust of the plane's engine is bounded so is the limit of the speed of the treadmill. If you want to argue against THAT portion of my argument, I would be glad to do so.
NATHAN A. HARMON, Capt, CAP
Monroe Composite Squadron

FW

Gee Maj., can't a guy have a little fun now and again.  Of course, if you want to be a little serious, timespace (yes, one word) is not dependant on the speed of light.  The further we are from the earth's surface, the more the time rate changes in space.  GPS works because we can calculate this relationship between the time rate differences between the satellites and earth.  It's kind of like "why is there gravity?" 

I know this is tangential to the thread but, I was getting tired of running this treadmill.  ;D

N Harmon

Quote from: FW on February 17, 2010, 02:19:54 AMThe further we are from the earth's surface, the more the time rate changes in space.

That isn't exactly true. It is not the distance from the earth's surface that causes time dilation, but rather differences in inertial reference frames. The reason why objects in orbit pass through time faster then people on the ground is because they are travelling at greater velocities.
NATHAN A. HARMON, Capt, CAP
Monroe Composite Squadron

Pingree1492

Quote from: TACP on February 15, 2010, 06:06:24 AM
Imagine a plane sitting on a giant conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?

Okay, while I was working out the free-body diagram to share with everyone, I realized that I was partially wrong.

Operating on the assumption that the aircraft's engine is on at full power... The plane will take off.  The wheels will not move or spin.  Let me explain.

The conveyor belt is as long as a runway- this was stated for a reason.  The only way for an aircraft's wheels to spin while the aircraft is on the ground is for the aircraft itself to actually move. 

So the plane will be sitting stationary relative to the conveyor belt, but the plane and the conveyor belt will be moving forward at an increasing velocity, until the plane takes off.
On CAP Hiatus- the U.S. Army is kindly letting me play with some of their really cool toys (helicopters) in far off, distant lands  :)

SSIAJ

Do you guys really need this explained? 

RiverAux

Quote from: lordmonar on February 17, 2010, 02:16:11 AM
Quote from: RiverAux on February 17, 2010, 01:12:00 AM
Boy, I've run pretty fast on a treadmill and have yet to feel any wind on my face as I would if I was outside running around the track.

Yes...but your thrust is developed from the friction between your feet and the road.  Since the road is moving away from you your net velocity becomes zero......airplanes do not develope their thrust from friction between the wheels and the ground.....but between the prop and the surounding air.  So it will still develope thrust even if the ground is going the other way.
The scenario did not say that the planes engine was running...

davidsinn

On the bullet tangent: a bullet fired vertical will not fall at the same velocity it was fired at. A bullets terminal velocity is well below it's muzzle velocity. My best friend and I shoot extreme long range for fun so I've got a better than average grasp on ballistics. If the theory that all the forces are equal going up as going down were true then my bullet would hit the target at 500 yds at the same velocity as I fired it. It hits the target with about half the velocity. I'd explain further but it's late and I'm on my cell phone.
Former CAP Captain
David Sinn

lordmonar

Quote from: RiverAux on February 17, 2010, 03:04:21 AM
Quote from: lordmonar on February 17, 2010, 02:16:11 AM
Quote from: RiverAux on February 17, 2010, 01:12:00 AM
Boy, I've run pretty fast on a treadmill and have yet to feel any wind on my face as I would if I was outside running around the track.

Yes...but your thrust is developed from the friction between your feet and the road.  Since the road is moving away from you your net velocity becomes zero......airplanes do not develope their thrust from friction between the wheels and the ground.....but between the prop and the surounding air.  So it will still develope thrust even if the ground is going the other way.
The scenario did not say that the planes engine was running...
Then the wheels would not be turning and the treadmill would not be moving.  That means "can a parked airplane take off?"   The answer is NO.  ;D
PATRICK M. HARRIS, SMSgt, CAP

SarDragon

Quote from: davidsinn on February 17, 2010, 03:52:44 AM
On the bullet tangent: a bullet fired vertical will not fall at the same velocity it was fired at. A bullets terminal velocity is well below it's muzzle velocity. My best friend and I shoot extreme long range for fun so I've got a better than average grasp on ballistics. If the theory that all the forces are equal going up as going down were true then my bullet would hit the target at 500 yds at the same velocity as I fired it. It hits the target with about half the velocity. I'd explain further but it's late and I'm on my cell phone.

I stated a very (almost impossible) narrow case. ANY horizontal component will change the result greatly.
Dave Bowles
Maj, CAP
AT1, USN Retired
50 Year Member
Mitchell Award (unnumbered)
C/WO, CAP, Ret

davidsinn

Quote from: SarDragon on February 17, 2010, 08:51:51 AM
Quote from: davidsinn on February 17, 2010, 03:52:44 AM
On the bullet tangent: a bullet fired vertical will not fall at the same velocity it was fired at. A bullets terminal velocity is well below it's muzzle velocity. My best friend and I shoot extreme long range for fun so I've got a better than average grasp on ballistics. If the theory that all the forces are equal going up as going down were true then my bullet would hit the target at 500 yds at the same velocity as I fired it. It hits the target with about half the velocity. I'd explain further but it's late and I'm on my cell phone.

I stated a very (almost impossible) narrow case. ANY horizontal component will change the result greatly.

Even pure vertical it would not impact at the same velocity it was fired at. Drag increases exponentially while velocity increases linearly. The bullet will not exceed it's terminal velocity on the way down. That velocity is much lower than muzzle velocity.
Former CAP Captain
David Sinn

N Harmon

Quote from: davidsinn on February 17, 2010, 11:19:12 AM
Even pure vertical it would not impact at the same velocity it was fired at. Drag increases exponentially while velocity increases linearly. The bullet will not exceed it's terminal velocity on the way down. That velocity is much lower than muzzle velocity.

Agreed. The resistance force of atmospheric drag will keep the bullet from returning with muzzle velocity. I might also mention that in a vacuum, even a horizontal component wouldn't really matter. The bullet would travel parabolically and return to the surface with muzzle velocity.
NATHAN A. HARMON, Capt, CAP
Monroe Composite Squadron

davidsinn

Quote from: N Harmon on February 17, 2010, 01:32:13 PM
Quote from: davidsinn on February 17, 2010, 11:19:12 AM
Even pure vertical it would not impact at the same velocity it was fired at. Drag increases exponentially while velocity increases linearly. The bullet will not exceed it's terminal velocity on the way down. That velocity is much lower than muzzle velocity.

Agreed. The resistance force of atmospheric drag will keep the bullet from returning with muzzle velocity. I might also mention that in a vacuum, even a horizontal component wouldn't really matter. The bullet would travel parabolically and return to the surface with muzzle velocity.

Yup. Most people never get past kinematics in a vacuum and so can't fully grasp this stuff. I never had any actual training past that point myself. All I know about ballistics is self taught. I must be doing something right because I spot for my friend and he can hit a 19" gong at 730 yds with a .308 in squirrelly winds. I myself can hit the same gong just past 500 yds with an AR chambered for 5.56 but shooting .223.
Former CAP Captain
David Sinn

DG

I have an engineering degree (Last year I couldn't even spell engineer, and now I are one.)

All you need to know is two things.

F=MA

and

You can't push on a string.

CadetProgramGuy

THE PLANE WILL NOT FLY.

Presuming the treadmill was the only equipment and it was touching the wheels only.  It don't make a split of difference if the wheels are rotating at 110kts, 50kts otr 500kts.

Unless the aircraft has enough revative wind flowing over the airfoil the aircraft will not fly.

Airfcraft speed had nothing to do with the equation, only speed of the relative wind over the airfoil.

The treadmill theory is BUSTED.

Remember relative wind over the airfoil creates lift unless you exceed the angle of attack of the airfoil in which timeyou will stall the lift of the wing.