03 Nov 07
Originally posted by flyUnityYes, "If you would start the treadmill the plane would go backwards". And if the "winch/propeller" began to catch up to the speed of the tread certainly you would have airflow over the flight surfaces and gain lift. I do believe if the winch/propeller only matched the tread from the take off roll then everything would be null. A fun question. And thank you for your input. It is a loaded question as others have stated. This has been fun. Thanks.
Ok, lets put a winch on the front of the plane that has a cable tied to something stationary like a tree thats on the far end of the runway, now if you would start the treadmill, the plane would go backwards, however hook the winch up to the tree, start winding it up, and the airplane WILL move forward regardless what the treadmill is doing, the treadmill c ...[text shortened]...
Now replace "winch" to "propeller", and replace "stationary tree" to "stationary air".
And Marc, when did you turn into an old grouch? 😉
03 Nov 07
Originally posted by Frank BurnsOld grouch!
And Marc, when did you turn into an old grouch? 😉[/b]
Me.....????
I'm not seeing why you ask that question, Frank.
Did you feel that my post in this thread was somehow grouchy? It wasn't meant to be. I just wanted to point out that we beat this particular airplane 'puzzler' up about a year ago. It would make interesting reading for anyone if they wanted to go back through the posts from that time.
Well, maybe I am an old grouch anyway. All I know is if you're into 'flying' and Ben is also out there flying around as a commercial pilot, I'm sticking to walking or driving if I need to get somewhere.😀
15 Nov 07
Originally posted by mrstabbyNo.
Wouldn't the G-force be huge once the plane leaves the ground?
It would behave almost exactly as though it were taking off a normal concrete runway. The only minor difference is that the little wheels on the bottom would be spinning a bit faster.
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15 Nov 07
2 edits
Originally posted by MarsanNope. I'll explain.
No.
It would behave almost exactly as though it were taking off a normal concrete runway. The only minor difference is that the little wheels on the bottom would be spinning a bit faster.
The plane does not get lift from the air pushed (or pulled) from the propeller. It gets lift from the air pushing on the bottom of the entire airfoil. The propeller merely imparts an accelerative force forwards and that's all. In flight this accelerative force is counteracted by aerodynamic drag. On a treadmill that "drag' will be friction from the wheels. Since there isn't a large amount of air moving past the airfoil (the small amount provided by the propeller is not nearly enough) there will be no flight.
Don't believe me still. Ok. Let's try a little thought experiment. Let's assume the treadmill is going full bore and so is our little airplane. Whoa! suddenly there's enough lift to get the airplane off the ground! The wheels leave the treadmill and the airplane is now .... levitating?! (zero forward momentum).
Airplanes cannot do this.
If this possible then it would be possible to simply drop an airplane from a crane as long as the engines were running. Common sense tells you this won't work.
15 Nov 07
Originally posted by SickboyYou just made yourself look like a fool! Of course the plane will take off! The force that causes the plane to accelerate is the propellors which pull on the air to make the plane go forward the wheels pushing on the treadmill are not what makes the plane accelerate(if this was the case then you would be right.) so the plane would go forward like it would on a normal runway the only difference is that the wheels would be spinning twice as fast.
Nope. I'll explain.
The plane does not get lift from the air pushed (or pulled) from the propeller. It gets lift from the air pushing on the bottom of the entire airfoil. The propeller merely imparts an accelerative force forwards and that's all. In flight this accelerative force is counteracted by aerodynamic drag. On a treadmill that "drag' will be ...[text shortened]... a crane as long as the engines were running. Common sense tells you this won't work.
15 Nov 07
Originally posted by PBE6its not poorly written because by drawing a force diagram it would be easy to see that the plane is moving forward relative to the ground and the tread mill.
Of course it's poorly written. It never definitively says "the plane moves forward relative to the ground" or "the plane is stationary relative to the ground while the wheels turn". When people argue about this question, it's always about whether or not the plane is moving forward and getting air to flow over the wings. They can't agree because the question is crap. Didn't you read the other 40 million posts on this?!? 😕
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15 Nov 07
2 edits
Originally posted by tomtom232"If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?"
its not poorly written because by drawing a force diagram it would be easy to see that the plane is moving forward relative to the ground and the tread mill.
It is worded poorly. This clearly implies that the airplane is traveling (relative to the conveyor belt) at takeoff speed and then says that the conveyor belt is moving precisely fast enough ("matching"😉 in the opposite direction. This, albeit ambiguously, implies that the plane is not moving with respect to the ground. Neither does it say in any way that the plane is being propelled forward with its thrust mechanism.
Not to mention the use of the word "tread mill" which certainly implies something the size that will fit in my living room. I know of know airplane that can take off in the amount of space in my living room.
Bottom line, IF the plane is not moving forward with respect to the ground (assuming no air movement with respect to the ground) there is no left. That's how I interpreted the question.
Clearly, if the airplanes thrust mechanism is engaged the conveyor is irrelavent.
15 Nov 07
Originally posted by SickboyThe question is not worded poorly it just assumes that you know how an airplane takes of(by pushing on the air)which clearly some people did not know and instead of acknowledging their ignorance decided to call the question poorly worded.
"If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?"
It is worded poorly. This clearly implies that the airplane is traveling (relative to the conveyor belt) at takeoff speed and then says that the conveyor belt is moving precisely fast enough ("matchi ...[text shortened]... ion.
Clearly, if the airplanes thrust mechanism is engaged the conveyor is irrelavent.
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15 Nov 07
Originally posted by tomtom232That's right. Don't _bother_ with responding to my posts actual points. The question (first post in this thread) is simply this single sentence I quoted. Here it is again for your use.
The question is not worded poorly it just assumes that you know how an airplane takes of(by pushing on the air)which clearly some people did not know and instead of acknowledging their ignorance decided to call the question poorly worded.
"If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?"
Where does that say that there is anything driving the plane forward with respect to the ground? I stand by my statement that the error most people are having (myself included, I've already admitted) is that the question is poorly worded leaving it up to the reader to interpret what is being simulated.
Instead you want most of us to believe that no one knows that airplanes fly by pushing air? You can't be serious. I guess most of us believed those propeller doo-hickeys were just for show...
15 Nov 07
Originally posted by Sickboyyou are missing the point! How can the plane be travelling at any speed if there is no driving force? And if the plane is travelling a simple force diagram will show you that the plane has to be moving relative to the ground because it pushes on the air not the tread mill.
That's right. Don't _bother_ with responding to my posts actual points. The question (first post in this thread) is simply this single sentence I quoted. Here it is again for your use.
"If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?"
Where do ...[text shortened]... be serious. I guess most of us believed those propeller doo-hickeys were just for show...
15 Nov 07
3 edits
Originally posted by SickboyOK i suspect you're making a fundamental mistake in how you're thinking about this question so to clarify things i'll ask a question.
Nope. I'll explain.
The plane does not get lift from the air pushed (or pulled) from the propeller. It gets lift from the air pushing on the bottom of the entire airfoil. The propeller merely imparts an accelerative force forwards and that's all. In flight this accelerative force is counteracted by aerodynamic drag. On a treadmill that "drag' will be a crane as long as the engines were running. Common sense tells you this won't work.
Plane is on a massive conveyor belt that can exactly match the forward speed of the plane in the opposite direction.
Pilot opens the throttle up to max. Brakes off.
What happens?
PS. It is not only air being pushed downward beneath the wings that causes lift. The stream of air flowing OVER the wing is a major (?most important?) component. Because of the shape and "angle of attack" of the wing the air on top has to travel faster, fast moving air creates low pressure (the Bernoulli principle), the low pressure above the wing pulls the wing upwards. This coupled with higher pressure below the wing is lift.
15 Nov 07
3 edits
Originally posted by tomtom232Airplane ain't pushing on any air if it ain't moving through it. It won't take off. For the wings to provide lift it must have velocity relative to the air mass around it. It's so obvious. Engines provide THRUST, not lift. (Well, they do provide a little lift from the air they move over the wings, but it's infinitesimal) The air moving across the wing surface provided by the engines will not make the plane take off if it's stationary, if it did, planes would take off like a soap bubble as soon as the engines went to full power before the plane started moving.
The question is not worded poorly it just assumes that you know how an airplane takes of(by pushing on the air)which clearly some people did not know and instead of acknowledging their ignorance decided to call the question poorly worded.
And the question is poorly worded.