which is exactally why th plane wouldn't go ANYWHERE. guarnteed.Quote:
Originally Posted by BABY J
O and last time I checked the NAVY's aircraft carriers were solid. not giant fooking treadmills.
Printable View
which is exactally why th plane wouldn't go ANYWHERE. guarnteed.Quote:
Originally Posted by BABY J
O and last time I checked the NAVY's aircraft carriers were solid. not giant fooking treadmills.
This is somewhat of a "trick" question. Not because it is phrased in a deliberately tricky way, but because people tend to have trouble thinking about the operation of other vehicles apart from cars which they know so well.
The heart of the confusion is simply these two important facts:
* cars propel themselves by pushing against the ground via friction
* airplanes propel themselves by pushing against the air
If you can let go of how cars operate and think about what an airplane
does, you'll be able to see the problem clearly.
One good way of tackling this problem is to find a good analogy. But the analogy must be a valid one else you'll just get more confused. For example, someone posted the analogy of running on a treadmill. Why is that a bad analogy? Because one runs by pushing against the ground via friction between their shoe and the ground. This is how a car propels itself! It is not how an airplane propels itself, by pushing against the air. Bad analogy.
Let's use this analogy. Instead of looking at the airplane, let's back up and go into the airport. Suppose you're walking down to your gate and pulling your carry-on bag behind you. It's a nice new bag with low friction wheels. No problem! Up ahead you see one of those moving walkways. You don't see anyone coming, so you decide to do a little experiment. You go over to the walkway that is moving TOWARDS you and place your bag on it. Meanwhile, you step off to the side of the walkway, and still holding on to the handle of your bag, you continue to walk along. In fact, you intentionally walk along at the same speed that the moving walkway is going, just in the opposite direction.
Question: does the bag move or does it remain stationary as you keep walking? Obviously it moves with you. So why does your bag move forward when you are walking at the same speed of the conveyor going in the opposite direction?
The answer to that question is also the answer to the airplane-conveyor question. To complete the analogy, the pull of your arm is analogous to the force of the airplane engines. The bag's wheels are analogous to the airplane tires. Do the nice low-friction wheels on your bag on the conveyor pull against you anymore than they do when you're just pulling your bag along normally? No, they don't. They are free-wheeling, after all. Meanwhile, you're pulling the bag with the same force in both cases. So in both cases, the bag keeps moving forward. Likewise with the airplane, the pull of the engines
doesn't change nor does the force on the airplane imparted by the tires change no matter what the ground is doing underneath the tires. You have the same force imbalance in either case, and since Force = mass x accceleration, you have the same acceleration. Remember, we are talking airplane engines which push against the AIR, not the ground. The acceleration is with respect to the AIR, thus the airplane develops a speed relative to the air and can eventually take off.
That's a long winded analogy. Here's a quicker solution. Engineers learn to draw Free Body Diagrams to understand such problems. A FBD is just a block diagram which illustrates the forces acting upon an object. The net force can be calculated from all the contributing forces. If that net force is not zero, the object accelerates in the direction of that force. Let's draw a FBD now. Represent the airplane by a simple rectangle (the shape doesn't matter). Indicate the force of the engines pulling on the plane with a large arrow, labeled "F_e" with e for engines. What force are the tires imparting to the plane? Remember, they spin freely except for bearing friction and rolling
friction, which produces forces that are quite tiny compared to the
engines Represent those forces with a small arrow, labeled F_t where t means tire. What other forces are operating? There is a drag force too. But remember this drag force is also small compared to the
propulsion of the engines at least at takeoff speeds. Label that F_d.
FREE BODY DIAGRAM
F_d |----------| F_e
<---| Plane |------------->
|----------|
<-- F_t
So what do we have here? We haven't put numerical quantities on these
forces, but instead have just been talking in terms of large and small. That's okay for the purposes of this illustration. It's enough to know that F_e is going to be much greater than F_d + F_t pulling in the opposite direction. If that's the case, we have an unbalanced force on the plane. Therefore, it accelerates. And it accelerates with respect to the AIR, since F_e is produces by the engines pushing against the air.
To sum up: Yes, the airplane takes off. The motion of the surface underneath the freely-spinning tires is irrelevant to the acceleration of the aircraft since the tires cannot impart any force to the aircraft (aside from the aforementioned very small rolling and bearing friction).
PLANE TAKES OFF. Ladies and gentleman you are free to move about the cabin.
An airplane in flight is the center of a continuous tug of war between four forces: lift, gravity force or weight, thrust, and drag. Lift and Drag are considered aerodynamic forces because they exist due to the movement of the aircraft through the air. The weight pulls down on the plane opposing the lift created by air flowing over the wing. Thrust is generated by the propeller and opposes drag caused by air resistance to the frontal area of the airplane. During take off, thrust must overcome drag and lift must overcome the weight before the airplane can become airborne. In level flight at constant speed, thrust exactly equals drag and lift exactly equals the weight or gravity force. For landings thrust must be reduced below the level of drag and lift below the level of the gravity force or weight
http://www.allstar.fiu.edu/aero/fltmidfly.htm
next time I go to the airport I'll try and make my luggage fly off of the moving walk-way. that'll turn some heads.Quote:
Originally Posted by BABY J
in bold: that is the MOST RELEVANT part of the argument.Quote:
Originally Posted by BABY J
The entire point is that the "treadmill" does not have any effect on these four forces.Quote:
Originally Posted by {X}Echo419
CORRECT! in fact it negates them! :goodjob: +1 for someone with some damn sense. :cool:Quote:
Originally Posted by joecoolfreak
Yes it can.
How does the ground moving in the opposite direction affect lift, drag etc....Quote:
Originally Posted by {X}Echo419
Here...lets do another experiment... a plane is flying 3 feet over the ground and then fly's over a huge treadmill...how would that effect the plane? The answer is it wouldn't. The only purpose of a plane's wheels touching the ground is to reduce rolling resistance until the plane reaches a high enough speed to take off. It doesn't matter how fast they go or slow. The plane's speed is determained by how fast it's engines can draw air through and push it.
did you open my link? I think that explains it pretty clearly.Quote:
Originally Posted by joecoolfreak
how does the treadmill make wind pass over the wings? it doesn't! thus the plane won't fly.
the propeller dosen't "push the air over the wings of the plane. it simply "moves" the plane when the wheelz aren't touching the ground. to KEEP THE AIR FLOWING OVER & UNDER THE WINGS!
yes the planes "speed" is determined by the engine. NOT IT'S ABILITY TO FLY!
i think we are all confused.
some ppl think that the ? means the airplane is moving faster tahn the speed of the tread mill, then it would fly,
others are thinking it means the wheels are turning the same speed as the treadmill, not moving forward nor backwards (plane will not fly)
someone, anyone I don't care who.
go out and buy a remote controlled airplane. make sure not to get 1 that's TOO BIG. as it won't fit on the threadmill.
this weekend we can go to my gym crank up a threadmill put the plane on it and watch it do nothing except buzz.
and when I prove this foolish theory wrong I get to keep the airplane. But(and it's not like this is possible anyways) if I am wrong I will pay the challenger double the cost of the plane.
any challengers wanna lose some cash?
*saturday night after 9pm I will not be avaiable. UFC 61 will be on!!!*
[QUOTE=Halfwit]i think we are all confused.
some ppl think that the ? means the airplane is moving faster tahn the speed of the tread mill, then it would fly,...[QUOTE]
then what would be the point of putting it on the threadmill?
The catergorical answer is YES.
The fundamental point to appreciate is that the power from a plane for forward momentum is not through its wheels and the wheels are free to spin. The other point to appreciate is that the questions states that the treadmill is tracking the planes speed and not the other way around. (See scenario B)
I think people's yes/no answers depend largely on them ignoring these two points. To clarify, imagine the treadmill runway but with a fixed control tower at the start.
Scenario A - Lets assume that the plane tracks the treadmill's speed:
The treadmill starts moving at whichever ludicrously high speed you care to mention and the plane's engines are running. For the plane to remain stationary relative to the control tower, the engines would only need to operate at a power to overcome the friction on the free-spinning wheels - as previously quoted by egon_spangler, about 12% for a 747 with the wrong wheels on a concrete treadmill (a whole new question, I feel?). In this instance, will the plane take off?
Answer: Absolutely not as there is no airspeed/lift (see everyone elses comments for further explanation)
Scenario B - the treadmill tracks the planes speed: The "speed" of the
plane would be it's speed relative to the control tower. If the plane
accelerates to 100mph, the treadmill would accelerate to 100mph, and
the net effect would cause the wheels to spin at 200mph. However, the
plane would still be moving forward at 100mph. (For the plane to remain stationary relative to the control tower, there would have to be no speed, and so the treadmill would not move either.) Will the plane take off?
Answer: Absolutely yes. Once it achieves the necessary speed relative
to the control tower, the airspeed would be sufficient to create the lift. Granted the plane will have to overcome more friction on the wheels than it would on a static runway as they are moving at twice the speed, but the engines would easily overcome this.
Different conditions would cause the effects that others are arguing towards, but none apply to this question:
If the treadmill was replaced by an windtunnel and the speed of the
windtunnel increased to match the thrust of the engines or vice versa, then at the necessary speed, the plane could takeoff and fly whilst remaining stationary relative to the control tower.
Alternatively, if you replaced the plane with a car with wings where its forward momentum on the ground is through the wheels, then the treadmill tracking the speed would increase until the car reached it's top speed. The car would remain stationary relative to the tower and it would never take off due to the lack of airspeed. Aside from the treadmill question, I do recognise that a winged car with no means of propulsion once in the air would be pretty rubbish.
In conclusion, given the conditions of the question, the plane will take off everytime.
[QUOTE={X}Echo419][QUOTE=Halfwit]i think we are all confused.
some ppl think that the ? means the airplane is moving faster tahn the speed of the tread mill, then it would fly,...there wouldnt be, i am saying ppl are takingthe ? two different ways. they way i took it, the plane will not fly, cause it is staying still, only tires are spinningQuote:
then what would be the point of putting it on the threadmill?
s
This is the part that you don't get....there is no power supplied to the wheels. The propeller moves the plane regardless of whether or not the wheels are touching the ground. The speed of the ground in any direction is completely moot. Let me use yet another example to prove you wrong. Lets say we are talking about a plane with skids or floaters that lands and takes off from the water. Is it possible for the plane to take off against the current? Of course. The sea plane doesn't have to find a spot where the water isn't moving... Why? because the means of thrust as your article pointed out is from the engines and ultimately from the turbine or propeller. That thrust is completely independant of the ground as it pulls air or pushes it and the treadmill isn't even part of the equation.Quote:
Originally Posted by {X}Echo419
--> Put on some skates.Quote:
Originally Posted by {X}Echo419
--> Stand on a treadmill.
--> I will tie a rope around your waste and ENSURE that it is EXACTLY parallel to the ground. (to not exert any downward force on the mill)
--> I tug on the rope... what happens between the skates and the treadmill?
Your answer here is gonna tell me a lot about your thought process (and lack therof... LOL).
moot? I don't think so.Quote:
Originally Posted by joecoolfreak
only if the plane is GOING FASTER THAN THE CURRENT! fast enough to take off!
if I'm sooo wrong. take my challenge. free $$$ for you.
now, if you're talking about making the plane go FASTER than the threadmill. then yes it could take off...if it gained enough speed. NOT if it traveled @the same speed(remain in 1 spot) as the treadmill. plain and simple
I would then be pulling myself FASTER than the treadmill. what's your point? I could go forward without the treadmill and with alot LESS effort. so why? are you trying to make it HARDER for the plane to fly?Quote:
Originally Posted by BABY J
why don't you take up my challenge?
I don't think you people know what you're trying to do.
If it remained in the same spot...see Baby J's answer...ie the plane isn't going anywhere, so it's speed is 0 and therefor the treadmill wouldn't be moving. The hypothetical treadmill here matches the speed of the plane itself, not the wheels.Quote:
Originally Posted by {X}Echo419
First, you have to assume a few things.
1. The conveyor belt can react quick enough to the plane's speed so their speed stays exactly the same.
2. The engine or propeller that powers the plane can only cause the plane to go forward (or backward) but not create any lift. So the only lift generated will be from the wings.
3. The conveyor belt's speed is linked to the speed of the plane relative to the ground and therefore also to the air around it. It is not linked to the turning speed of the wheels.
4. The wheels of the plane does not power or cause the plane to go forward.
5. The wheels can turn freely and without friction, but only in reaction to the movement of the plane or the conveyor belt.
Let's start with the plane standing still. The conveyor belt is not moving because the plane is not moving. As the engines start to cause the plane to go forward, the conveyor belt starts to move at the same speed of the plane. But because the wheels are free to move, the conveyor belt has no effect on the plane, only the wheels, so the plane continues to go forward. The faster the plane goes forward, the faster the conveyor belt moves backward, but it's only affecting the wheels, not the plane.
The plane will still take off, but the wheels will turn at twice the speed because of the conveyor belt. Because the wheels are free to move and does not affect the speed of the plane, the conveyor belt has no effect on the speed of the plane.
If the plane was powered by it's wheels, like a car, and the conveyor belt speed was linked to the speed of the wheels. Then the plane will not move.
If I could take your challenge I would, but there is no possible way for you to recreate this senerio with a treadmill because you can't track the speed of the plane, nor could you increase the speed of the treadmill accordingly.
so what's your point? if you're going to make the plane go faster than the treadmill then what's the point? you're just making it harder for the plane to fly. not impossible, just harder. wtf is the point?Quote:
Originally Posted by joecoolfreak
That IS the point. IT WILL FLY!! It will just be THAT much harder for it to achieve flight!!!!Quote:
Originally Posted by {X}Echo419
itll fly if i tell it to, that is the end.
You are not making it harder, you are just making the wheels spin faster. The entire point is that people like you have a hard time grasping that there are vehicles that move by the thrust of something other than their wheels and thats why some people automatically assume that the plane won't fly. A plane's wheels are nothing more than bearings to lower the rolling resistance to taking off. It's not like anyone is suggesting that we build a runway that is a moving sidewalk. It is just an exercise for the mind to think "outside the box".Quote:
Originally Posted by {X}Echo419
WHY PUT IT ON THE TREADMILL IN THE FIRST PLACE?!?!?!?!?!?Quote:
Originally Posted by BABY J
looks like we were talking about 2 different things here.
Ruiner's orginal question(I believe) if refering to a theory(or should I say horsey poo) that a stationary plane on a treadmill maintaining the same speed as the treadmill will fly. which of course it won't. as you seem to agree.
No...and I promise that if you ask Ruiner whether or not the plane was moving when it took off, he would say yes. No one would say that the plane would stay in one place. In fact, it would be impossible for the plane to stay stationary in the senerio that was given. The only way that it would stay stationary is if the treadmill was stopped and the propellor or turbine wasn't going because the treadmill's speed is determained by the plane's speed and if the plane ain't goin anywhere, then neither is the treadmill.
Quote:
Originally Posted by joecoolfreak
I said that earlier you dumbass. you've obviously never heard of people thinking a plane can achieve flight without actually covering any distance on a treadmill. :321:Quote:
Originally Posted by {X}Echo419
It might be easier if I simplify this...if a treadmill is running at it's top speed and you run just fast enough to not fall off, how fast are you really going? The answer is 0. The person next to the treadmill is just standing there and he is going just as fast.
no shit douch bag. go drive your Barretta off a cliff :2up:Quote:
Originally Posted by joecoolfreak
What makes the plane move is the engines acting on the ambient air. The fact that it begins to move at all has nothing to do with its form of contact with the ground - beyond overcoming negligable wheel bearing friction. It starts creeping forward, and the belt creeps backwards, making the wheels turn faster (but still slowly at this
stage, but hardly braking the advance of the plane). Since the wheels can rotate freely, the plane continues to accelerate, as does the belt, the wheels spinning even faster, much faster than in the other definition of the problem, I admit, and maybe at takeoff at some extremely high speed.
As I pointed out, the plane's propulsion by its engines can be compared with its being pulled by a cable parallel to the ground - or your pushing a roller skate forward on a treadmill or conveyor belt. You can do it, despite the counter motion of the belt.
Since we are assuming no practical problems (bearings' freezing up, tires' flying to pieces, the existence of the conveyor belt), let's take it to the extreme and assume absolutely no friction from the wheel bearings.
It this case, the belt could be flapping along the runway before the plane even starts it engines and the plane would still stand still - no bearing friction, no overcoming of the inertia of the motionless plane. The engines start, the plane moves forwards, regardless of what the wheels and belt are doing.
By assuming zero friction in this hypothetical situation, they no longer are part of the equation. If the belt were moving in the direction of takeoff, with zero bearings' friction, it would also have no effect on the plane.
I really wish I knew why this was so hard for people to understand. The plane will take off. The wheels on a plane have nothing at all to do with the movement of the plane, they might as well not even be there. They spin freely and will just spin faster and faster no matter how fast the treadmill moves. Wheels cannot hinder the forward movement of a plane.
You are getting upset over this?
1st you have to get the plane off the ground, we are afterall bound by gravity.Quote:
Originally Posted by JennB
not if the treadmill MATCHES the speed of the plane. then of course it wouldn't be going anywhere to create the drag and lift nessary for flight. as stated above.
of course if the plane goes faster, fast enough to "beat" the treadmill.
That's the part that keeps tripping you up...if plane is going 100 and the treadmill is going 100, than the wheels are going 200 and the plane is still going 100. The plane is going somewhere...it's going 100 miles per hour and there for is "beating" the treadmill although it's moving at the same speed.Quote:
Originally Posted by {X}Echo419
Listen, if you are so sure in your answer, then would you like to make a wager on it? We can put our cash in escrow and hold it there.Quote:
Originally Posted by {X}Echo419
Trust me, the plane will take off. All the treadmill will do is spin the wheels of the plane faster. Nothing more.
Don't tell me that you think that a plane uses the wheels for power?
Perhaps you can tell me how THIS takes off since it has no wheels:
http://usmbooks.com/images/DvR9.jpg
Fuck, my hope for the future intelligence of the younger generation is quicky going down the drain. Wanna know why we have so many issues with today's kids? The answer is the people that do not believe that the plane will take off. *sigh*
Ding ding ding!Quote:
Originally Posted by joecoolfreak
They will just move at the same speeds, in opposite directions with the wheels spinning like crazy in the middle.
Quote:
Originally Posted by joecoolfreak
you are contradicting yourself, DUMBASS!Quote:
Originally Posted by joecoolfreak
if the treadmill is doing 100 and the plane's propeller is doing what off of a treadmill would be 100 the plane would not be going anywhere! the plane would simply be keeping it's place on the treadmill instead of falling off the back.
sit the plane on the treadmill(OFF) start the treadmill and it will fall off of the back. there must be some sort of force on the plane(ie the propeller) ot maintain the speed of the treadmill underneath it.
post againto make yourself look even more ignorant.
http://www.allstar.fiu.edu/aero/fltmidfly.htmQuote:
Originally Posted by Ruiner
that's how.
IT IS NOT ON A TREADMILL KEEPING IT FROM GAING ACTUAL SPEED. WITHOUT SPEED NO LIFT AND DRAG CAN BE CREATED.
DID YOU FORGET ABOUT GRAVITY?