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Plane Problem

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worluk

FNG / Fresh Meat
Nov 21, 2005
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Bernouli's Principle, anyone?

Game over. Without air pressure - i.e, without air movement below and above the wings - a plane cannot physically take off.

All other factors are irrelevant.


Only the air speed matters, and the rate at which the plane is moving through the air is 0, thusly, it cannot take off.
congratulations for not reading a single post of this thread (ok, maybe you read the first one)

This is going to take some time, I can see, so please be patient. There are several things to consider when looking at the situation that this problem describes and we will need to break it down bit by bit so you can see how it all fits together.

First, let's look at the situation of a wheel attached to a rigid body which has thrust (i.e. forward force over the whole body).

The force is F in this diagram:



It is very important to understand the nature of friction - think of your own experience - you rub your hand along rough wood it opposes the motion, slowing it down.
A wheel works on the same principle - the friction is an opposing force to the main force of the moving body. As the wheel is a perfect circle (less some negligible deformation due to the plane's weight)we can say that the forward force in the wheel is centred on the axle. Two parallel forces seperated by a distance creates a couple, i.e. a rotational force.

For this couple to exist (in other words for the wheel to roll) you need to have that force of friction there. Otherwise the wheel would not spin, it would just skate over the surface.

You also need as little friction as possible at the centre of the wheel, where it joins the axle, so that the rotation of the wheel is not opposed.

That is how wheels work.

Some of you can probably see why I hesitated before introducing this part - a lot of people are going to be saying, "WTF!? You need friction for wheels to work? BS!!!" Think of this...if you are stuck on ice in your car you need to put sand or planks down for more friction/traction. Although the force in the wheel is actually rotational that doesn't matter - you need friction between the tyre and the surface for wheels to work properly (i.e. go round AND push forwards) It's just that instead of a forward linear thrust interacting witrh friction to create rotation (as in the plane) you get a rotaion interacting with friction to produce forward linear thrust (as in the stuck car).

Now I have wasted enough work time on this so far - I will put in the diagram for the moving treadmill tonight when I get home.
yep, you perfectly explained why the wheels are rotating. That doesnt say ANYTHING about the body linked to the wheel. Infact, several people here already illustrated that the rotation of the wheel DOES NOT necassarily mean there is any force acting on the body. The wheels are not pushing the plane.
It is beyond me how you can completely ignore the rollerskate/treadmill example.
 
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BuddyLee

FNG / Fresh Meat
Apr 12, 2006
2,088
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The treadmill has no effect, unless the planes parking break is on. :p The bearings cancel out the treadmill.

A planes wheels are not in gear like a car, they are free-spinning. They have nothing to do with forward motion on a plane. They are there to support the plane when it is on the ground, and to cancel out as much friction as possible so the plane can move forward. Wheels and bearings are made to cancel out friction on a plane. Which is exactly why the treadmill in irrelevant.

It Will Take Off.

My dad builds rubber-band powered balsa wood airplanes, if I had a treadmill, I could test the theory.
 
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Cuddles

FNG / Fresh Meat
Nov 2, 2006
1,507
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Area 51
How will friction get you of the ground?(helicoptars have no fricton, but hav **** load of lift)
Lift does that and what gets you lift?
The wings thats right.(4 the helicopters the props give u lift, but for planes they only give u thrust thats right they give u thrust). only thing that can hapen if u have to much friction is this
Its not science its Logic
 

stebbs

FNG / Fresh Meat
May 15, 2006
303
0
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SF Bay Area, California
i don't see how a plane can take off at all without lift. Lift is generated by air, not by thrust, that's why gliders can take off if they get enough lift but without an engine. Also, the treadmill is stationary, so there is no lift from the air resistance. I've never felt a breeze while running on a treadmill, so the plane won't feel it either. No matter how fast the wheels are spinning or the engine running, without the air to move over the wings to generate the lift it won't leave the ground.

If all you have is thrust, it would only move in the opposite direction of the thrust. Rocket cars anyone?
 

Cuddles

FNG / Fresh Meat
Nov 2, 2006
1,507
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How about if the threadmill suddenly stoped? Plane catapult?


And how the hell is this thread so popular????????????
 

Moz

FNG / Fresh Meat
Nov 21, 2005
1,773
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No it isn't - a bearing is not there to reduce friction between the tyre/wheel and the ground - it is there to reduce friction between the wheel and its axle. You actually need friction between wheel and ground for a wheel to work.

PS. I'm an idiot

NO IT DOESN'T THE ONLY FORCE THE WHEELS PUSH AGAINST IS GRAVITY.

YOU ARE TALKING OUT OF YOUR ASS.

THE REASON WHY THE PLANE WOULD TAKE OFF IS BECAUSE IT WOULD NOT BE STOPPED BY THE TREADMILL. NOT BECAUSE OF MAGIC.

SUPPORTERS OF NO BELIEVE THESE TWO UNTRUTHS:

1) THE PLANE WONT MOVE FORWARD (FALSE - THE TREADMILL CANNOT 1:1 FORCE INTO THE PLANE TO MATCH ITS THRUST VIA FRICTION ON THE WHEELS

2) THE WHEELS PROVIDE FORWARD THRUST (FALSE - YOU ARE A RETARD, GO DRINK SOME PAINT THINNER)

How about if the threadmill suddenly stoped? Plane catapult?


And how the hell is this thread so popular????????????
Because people value there opinion over the facts.

Facts like:

-Planes do not propel themselves with their wheels

-Forces entered onto the rotating wheel would not to transfered into the plane 1:1
-The plane would not be able to move forward.

Despite being proven wrong, a select few chose to ignore these facts and then cannot understand why the plane would take off.

The whole point of this question is to confuse people into thinking it is like a treadmill with a car or a person. What is the point of mentioning the it if it is anything like a car on a treadmill?

 
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SnozzFartz

FNG / Fresh Meat
Jul 20, 2006
143
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I've made up my mind about this.

The plane can't take off. The problem specifically states that the treadmill matches the speed of the plane, not the wheels or whatever. Therefore, the plane itself will always stay at 0mph or k/h.
 

BuddyLee

FNG / Fresh Meat
Apr 12, 2006
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i don't see how a plane can take off at all without lift. Lift is generated by air, not by thrust, that's why gliders can take off if they get enough lift but without an engine. Also, the treadmill is stationary, so there is no lift from the air resistance. I've never felt a breeze while running on a treadmill, so the plane won't feel it either. No matter how fast the wheels are spinning or the engine running, without the air to move over the wings to generate the lift it won't leave the ground.

If all you have is thrust, it would only move in the opposite direction of the thrust. Rocket cars anyone?
The thrust pushes the plane forward the same as on a stationary runway. There will be lift, because the plane will accelerate forward. The ground-speed is irrelevant. The airspeed necessary for liftoff will be achieved.

The gif showing the plane, was drawn by someone who flunked physics class. There is no reason the landing gear would fall apart.

The engines are pushing the plane forward through the air, no matter what speed the wheels are revolving. It is a trick question.

I think all the flunkies are giving Moz a brain hemorrhage. This may be the second greatest thread ever. :D:D
 
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Cuddles

FNG / Fresh Meat
Nov 2, 2006
1,507
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The thrust pushes the plane forward the same as on a stationary runway. There will be lift, because the plane will accelerate forward. The ground-speed is irrelevant. The airspeed necessary for liftoff will be achieved.

The gif showing the plane, was drawn by someone who flunked physics class. There is no reason the landing gear would fall apart.

The engines are pushing the plane forward through the air, no matter what speed the wheels are revolving. It is a trick question.

I think all the flunkies are giving Moz a brain hemorrhage. This may be the second greatest thread ever. :D:D

Whats THE FIRST GREATEST THREAD EVER
 

Xendance

FNG / Fresh Meat
Nov 21, 2005
4,484
572
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Newton's third law.

For every action there is an equal and opposite reaction.

Both the jet's engines, and the belt are actions[FONT=helvetica,geneva,arial]. [/FONT]The are equal, yet opposite. Therefore they neutralize each other. The jet doesn't move. It's that simple.
Fail. The plane moving forward is the opposite reaction to the engine ****ing the air.



"Thrust Basics

The goal of a turbofan engine is to produce thrust to drive the airplane forward. Thrust is generally measured in pounds in the United States (the metric system uses Newtons, where 4.45 Newtons equals 1 pound of thrust). A "pound of thrust" is equal to a force able to accelerate 1 pound of material 32 feet per second per second (32 feet per second per second happens to be equivalent to the acceleration provided by gravity). Therefore, if you have a jet engine capable of producing 1 pound of thrust, it could hold 1 pound of material suspended in the air if the jet were pointed straight down. Likewise, a jet engine producing 5,000 pounds of thrust could hold 5,000 pounds of material suspended in the air. And if a rocket engine produced 5,000 pounds of thrust applied to a 5,000-pound object floating in space, the 5,000-pound object would accelerate at a rate of 32 feet per second per second.

Thrust is generated under Newton's principle that "every action has an equal and opposite reaction." For example, imagine that you are floating in space and you weigh 100 pounds on Earth. In your hand you have a baseball that weighs 1 pound on Earth. If you throw the baseball away from you at a speed of 32 feet per second (21 mph / 34 kph), your body will move in the opposite direction (it will react) at a speed of 0.32 feet per second. If you were to continuously throw baseballs in that way at a rate of one per second, your baseballs would be generating 1 pound of continuous thrust. Keep in mind that to generate that 1 pound of thrust for an hour you would need to be holding 3,600 pounds of baseballs at the beginning of the hour. If you wanted to do better, the thing to do is to throw the baseballs harder. By "throwing" them (with of a gun, say) at 3,200 feet per second, you would generate 100 pounds of thrust.

Jet Engine Thrust

In a turbofan engine, the baseballs that the engine is throwing out are air molecules. The air molecules are already there, so the airplane does not have to carry them around at least. An individual air molecule does not weigh very much, but the engine is throwing a lot of them and it is throwing them at very high speed. Thrust is coming from two components in the turbofan:
The gas turbine itself - Generally a nozzle is formed at the exhaust end of the gas turbine (not shown in this figure) to generate a high-speed jet of exhaust gas. A typical speed for air molecules exiting the engine is 1,300 mph (2,092 kph).
The bypass air generated by the fan - This bypass air moves at a slower speed than the exhaust from the turbine, but the fan moves a lot of air.

As you can see, gas turbine engines are quite common. They are also quite complicated, and they stretch the limits of both fluid dynamics and materials sciences. If you want to learn more, one worthwhile place to go would be the library of a university with a good engineering department. Books on the subject tend to be expensive, but two well-known texts include "Aircraft Gas Turbine Engine Technology" and "Elements of Gas Turbine Propulsion."

There is a surprising amount of activity in the home-built gas-turbine arena, and you can find other people interested in the same topic by participating in newsgroups or mailing lists on the subject.

For more information on gas turbine engines and related topics, check out the links on the following page."

From http://science.howstuffworks.com/turbine7.htm

And because the wheels/tyres/whatever are completely irrelevant because of the ball bearings, the plane will move forward and eventually take off.
 
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REZ

FNG / Fresh Meat
Nov 21, 2005
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Would you all agree that you need the ground in some fashion to take off (water included)?

Ok, then if the ground is matching your forward speed in the opposite direction, how do you get moving forward to create enough air causing lift?

Plane is at a full stop. Applies thrust, starts to creep forward. At the exact same instant the treadmill moves with equal speed in the opposite direction. The plane is never allowed to move forward or gain momentum due to the treadmill matching the speed made by the plane's thrust - in the opposite direction. Where does the force of the air come from in an example that has the plane, in effect, standing still?
 

Moz

FNG / Fresh Meat
Nov 21, 2005
1,773
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I always love taking an opportunity to make a massive as out of myself.

especially when am backed up by science.

I'm considering redoing my video... with you know... a script... and fact checking. And maybe I can find myself a treadmill, a rocket kit and a model airplane some time in the next week or so.

:p
 

Ruprecht

FNG / Fresh Meat
Aug 29, 2006
211
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Ulm
Code:
void PlaneTakeoff(bool TakeOff)
{
 if (TakeOff == TRUE) {cout<<"A miracle..  *swish*.";}
}


void WeelsBroken(bool Broken)
{
 if (Broken == TRUE) {cout<<"Too bad, the weels broke..";}
}



void main()
{
 int PlaneMinTakeOffSpeed = 600;
 float WeelCircumferential = 0,1;
 int AmountWeels = 4;
 int PlaneThrust = 10000;
 int PlaneIntertia = 100;
 int WindBlow = 10;
 float FrictionPerRotation = 0,0001;
 float PlaneActualSpeed = 0;
 int WeelsBreakFriction = 1000;
 float WeelSpeed;
 int NegWindblow = 0;


 gotoxy(1,1);
 cout << "Input the speed the plane needs to take off: ";
 cin >> PlaneMinTakeOffSpeed;

 gotoxy(1,2);
 cout << "Input the weels cirumferential: ";
 cin >> WeelCircumferential;

 gotoxy(1,3);
 cout << "Input the amount of weels: ";
 cin >> AmountWeels;

 gotoxy(1,4);
 cout << "Input the trust the plane can generate: ";
 cin >> PlaneThrust;

 gotoxy(1,5);
 cout << "Input the planes Intertia: ";
 cin >> PlaneIntertia;
 
 gotoxy(1,6);
 cout << "Input how strong the wind blows: ";
 cin >> WindBlow;

 gotoxy(1,7);
 cout << "Input the weels friction per rotation: ";
 cin >> FrictionPerRotation;


 while(1)
 { 
   clrscr();

   if (WindBlow >= PlaneMinTakeOffSpeed) {cout<<"Plane flys allready"; break;}

   if (WindBlow <= 0) {NegWindblow = WindBlow;}
        else {PlaneMinTakeOffSpeed = PlaneMinTakeOffSpeed - WindBlow;}

   WeelSpeed = PlaneActualSpeed + PlaneActualSpeed;

   WeelSpin = WeelSpeed / WeelCircumferential;
 
   WeelFriction = (FrictionPerRotation * WeelSpin) * AmountWeels;

   if ((WeelFriction / AmountWeels) >= WeelsBreakFriction) {WeelsBroken(1); break;}
   
   if (NegWindBlow == 0)
    {PlaneAcceleration = PlaneThrust - ((WeelFriction + PlaneIntertia) + WindBlow);}
   else
    {PlaneAcceleration = (PlaneThrust - (WeelFriction + PlaneIntertia)) + NegWindBlow;}

   if (PlaneAcceleration <= 0)
    {cout<<"Windblow, Friction and Intertia are biger or equal as the planes thrust. You may wait for better weather or reduce the amount of weels / unload cargo."; break;}

   if (PlaneAcceleration <= PlaneThrust)
           {PlaneActualSpeed = PlaneActualSpeed + PlaneAcceleration;}
   
   if (PlaneActualSpeed >= PlaneMinTakeOffSpeed) {PlaneTakeOff(TRUE); break;}

   gotoxy(1,1);
   cout<<"Weelfriction over all: "<<WeelFriction;

   gotoxy(1,2)
   cout<<"Single weel friction: "<<(WeelFriction / AmountWeels);

   gotoxy(1,3)
   cout<<"Weels speed: "<<WeelSpeed;
   
   gotoxy(1,4)
   cout<<"Thrust generated: "<<PlaneThrust;

   gotoxy(1,5)
   cout<<"Plane acceleration: "<<PlaneAcceleration;

   gotoxy(1,6)
   cout<<"Windblow :"<<WindBlow;

   gotoxy(1,7)
   cout<<"Treadmill speed / actual plane speed: "<<PlaneActualSpeed;

   gotoxy(1,8)
   cout<<"Plane minimum speed to take off: "<<PlaneMinTakeOffSpeed;
   
   sleep(1000);
 }
}
think thats it, too bad i have no compiler here.
 
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spraduke

FNG / Fresh Meat
Nov 21, 2005
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www.spraduke.co.uk
Ok time to way in !!!


Now it all depends how you interpret the question!

Lets state some truths first.

Jet engines do not move air over the wing they work in a similar manner to a rocket engine by pushing faster air out the back than originaly came in.

A prop engine does the same thing but being located at the front of a plane (in most cases) it also forces air over the wing adding to the relative air speed to the wing.

We must assume that the wheels are frictionless in their rotation (just for simplification)

Assume that the treadmill is magical and can exist ;).

Now this all depends how you interpret the question.

If you interpret it to say "The plane is not moving relative to the air" the plane will never ever take off! No air speed over the wing means no difference in the pressure above/below the wing and thus no lift.

However if their was a strong wind (or propeller/hairdryer pushing the air) going at 60mph (lets say the speed to "take off" is 60mph in a "normal" situation) and the plane was stood still on tarmac at an airport it would gain vertical lift but no forward momentum thus when the wind stopped it would fall directly back where it started.

Air speed is hugely important to lift and thats the reason aircraft carriers turn into the wind to reduce the forward velocity (relative to earth) required by the plane to gain lift

Now if you interpret the question to say that the treadmill matches a certain speed (say 100mph).

As others have stated the wheels will simply spin faster and as theyre frictionless they provide no of the plane the plane will simply use the engines to push of the AIR and thus go faster than the treadmill achieve speed for lift and of you go into normal flight.

In summation the question is badly (wrongly) worded and would be crucified by any of my physics lecturers :p.
 

Deeival

FNG / Fresh Meat
Sep 4, 2006
674
1
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Moz, next time you use BIG WORDS please use proper punctuation, which will make your BIG WORDS much easier to read!

Quick question from 1st year physics: Friction doe not depend on the rotation speed of the wheels, does it?
 

stebbs

FNG / Fresh Meat
May 15, 2006
303
0
0
SF Bay Area, California
The thrust pushes the plane forward the same as on a stationary runway. There will be lift, because the plane will accelerate forward. The ground-speed is irrelevant. The airspeed necessary for liftoff will be achieved.

The gif showing the plane, was drawn by someone who flunked physics class. There is no reason the landing gear would fall apart.

The engines are pushing the plane forward through the air, no matter what speed the wheels are revolving. It is a trick question.

I think all the flunkies are giving Moz a brain hemorrhage. This may be the second greatest thread ever. :D:D
lol, nice response. But 2 questions: how is the plane getting pushed through the air if the treadmill is stationary? if the treadmill exactly matches the speed of the plane then there is no airspeed.

how can the plane accelerate forward without actually moving forward?

BTW, after watching the video again I think they guy shoots himself in the foot. He said lift is irrelevant for this example, but any pilot will tell you that lift is REQUIRED for an airplane to get airborne. Just because an engine creates thrust does not mean it will generate any actual speed or lift. He also contradicts himself by saying that somehow the wheels move faster than the treadmill. "if the jet is moving at 200 kph forward and the treadmill is moving at 200 kph in the other direction, then the wheels are moving at 400 kph." ????
If there were no treadmill then the wheels would be moving at 200kph?

I just don't see any airspeed with this example or explanation. Airspeed is the motion of moving through the air, and a treadmill negates that motion. The treadmill merely moves the ground under the plane, not the airspeed around the wings. So....where is the airspeed being created?

So thrust creates motion, we all know that, and the motion is what creates the lift through air resistance, it doesn't just suddenly appear because you have thrust. the air needs to move around things to create lift. Consider putting your hand out of a window of a moving car, boat, plane, whatever. as you move your hand around, you fill the resistance, i.e. lift, acting on your hand. Take that same car and put it on a dyno. The same amount of forward motion is being generated but if you put you hand out the window, there is no air resistance, i.e. lift. I don't think where the thrust is generated makes a difference, it's the forward motion that creates lift. Even race cars will get airborne without their downforce, but it will never happen on a dyno because there is no air resistance being created.


Sorry for the book, :D
 

REZ

FNG / Fresh Meat
Nov 21, 2005
3,534
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Exactly.. if the plane cant move forward, than no lift will occur. The question is poorly worded. The plane cannot move faster than the treadmill according to the question. So without forward movement through the air... lift cannot be generated.
 
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