mpokora wrote:
If this did work, the millitary would have started using this on aircraft carriers years ago. Just think about it.
haha, because you still dont understand it, the conveyor belt is as long as a normal airport runway.
mpokora wrote:
If this did work, the millitary would have started using this on aircraft carriers years ago. Just think about it.
haha, because you still dont understand it, the conveyor belt is as long as a normal airport runway.
mpokora wrote:
Im an aerospace major.
Since I just took my final on aerodynamics yesterday, this is still fresh in my mind and Ill put in my 2 cents.
First, lets relate this plane to our own running bodies.
The thrust from say, jet engines, is comparable to our leg muscles.
Both will exert JUST enough force/energy to keep the person/aircraft in the same location on the treadmill.
The thrust from the jet engine will keep the plane moving "forward" on the mill, but really it is in the exact same place, just as our legs keep us in the same exact place in the room (on the mill)
The thrust produced pushes the body of the aircraft forward, but a jet engine doesnt make things fly or lift up.- wings do!
Airflow OVER the wings (as so many have stated already) generates lift (low/high pressure blah blah).
Knowing a little bit about treadmills, I know that when I run on one, the air around me in the room is STAGNANT, smelly, and humid. There is no airflow blowing against me from any angle.
That plane can be sitting (and keeping up) with a treadmill spinning at Mach 5, but its not going to lift into the air. Basically, there is absolutley NO air circulation, activity, or velocity around the wings whatsoever. PERIOD.
The fact that there are 9 pages of postings about this is sad.
You are in some sense right but still wrong in your conclusion.
Surely there is no wind at your face when running on a treadmill. However propulsion during running comes from the legs. Wheels on a car if you will. A plane's wheels do not propel the aircraft. If so it will never be able to "get ahead" of the treadmill and neither can you.
Consider this (and forgive me if its been brought up)...put on some rollerblades and then get on a treadmill. You can go as fast you can but wont be able to go off the front of the treadmill. Now, have someone standing off the treadmill give you a push on the back. You'll begin to "get ahead" of the treadmill. The thrust of a jet engine works the same way. Its pushing against something else (air)...not the treadmill.
I may be generalizing but it seems the physicists think the plane will fly (theoretical) while the pilots think the plane won't (experiential). There is no bigger conundrum in life, I guess that's why we have such an issue. Can you do something without being something, or can you be something without doing something? Do be do be doo, how about doing something without thinking it can be done?
hyman shoulder wrote:
Ohio Rulz wrote:How does the plane have "speed" if it aint moving?
The same way I can be running 8 mph on a treadmill and still not be moving.
But you are stationary relative to the air around you, which is why you turn on a fan to cool you when you run on a treadmill.
The plane does not take off because it is stationary relative to the air around it. Stationary air creates no lift.
There is no better example of the decline of education in this country than this thread.
Zat0pek wrote:
hyman shoulder wrote:The same way I can be running 8 mph on a treadmill and still not be moving.
But you are stationary relative to the air around you, which is why you turn on a fan to cool you when you run on a treadmill.
The plane does not take off because it is stationary relative to the air around it. Stationary air creates no lift.
There is no better example of the decline of education in this country than this thread.
i think one of the reasons that this thread keeps going is because of the arrogance of a lot of the people who say it wont take off. do you really think the people on the other side of the argument dont know that planes dont take off without air traveling over the wings?
i really hope most of you are just messing around.
i do not see how the plane can't take off. the ground has nothing to do with the plane taking off or not.
i think the baking roller on a tread mill is a great example.
sigh....
mpokora wrote:
Im an aerospace major.
Since I just took my final on aerodynamics yesterday, this is still fresh in my mind and Ill put in my 2 cents.
First, lets relate this plane to our own running bodies.
The thrust from say, jet engines, is comparable to our leg muscles.
Both will exert JUST enough force/energy to keep the person/aircraft in the same location on the treadmill.
The thrust from the jet engine will keep the plane moving "forward" on the mill, but really it is in the exact same place, just as our legs keep us in the same exact place in the room (on the mill)
The thrust produced pushes the body of the aircraft forward, but a jet engine doesnt make things fly or lift up.- wings do!
Airflow OVER the wings (as so many have stated already) generates lift (low/high pressure blah blah).
Knowing a little bit about treadmills, I know that when I run on one, the air around me in the room is STAGNANT, smelly, and humid. There is no airflow blowing against me from any angle.
That plane can be sitting (and keeping up) with a treadmill spinning at Mach 5, but its not going to lift into the air. Basically, there is absolutley NO air circulation, activity, or velocity around the wings whatsoever. PERIOD.
The fact that there are 9 pages of postings about this is sad.
I don't know what is better about this post. The fact that the guy is a complete dumbass, or that he is a student at the University of Michigan (mpokora@umich.edu). My Ohio State engineering degree suddenly looks all that much better by comparision. Thanks!
mpokora,
Your problem is that this is not an aerodynamics question. It is more of a Statics question. There are two forces in this equation.
1. The force of the engine pushing the plane forward against the air.
2. The force of the treadmill pushing on the wheels of the plane.
1 >>>>>> 2.
It doesn't matter what speed the treadmill is going. The engine will almost always be a greater force than the mill on the wheels.
Do us all a favor and take a few more courses before you start designing things for Boeing or Lockheed.
Big Ten Engineering wrote:
I don't know what is better about this post. The fact that the guy is a complete dumbass, or that he is a student at the University of Michigan (mpokora@umich.edu). My Ohio State engineering degree suddenly looks all that much better by comparision. Thanks!
14-3.
O-H!
Zat0pek - the plane is NOT stationary relative to the air around it!
The treadmill is the same length as a normal runway. The riddle states that the treadmill moves at the same speed as the plane not the wheels. The wheels spin at twice the rate they would down a "normal" runway.
Got it?
Ohio Rulz wrote:
14-3.
O-H!
I-O!
Hey Ohio State, does 28-21 ring a bell?
Lets relate this to a runner on a treadmill.
You are running on a treadmill going 10mph. Your legs turn and you stay in the same place. Now put so afterburners from a jet on your back. You are going to f-ing fly, no matter how fast the treadmill goes.
Please mpokora - tell me you're from Columbus and pretending to have a umich e-mail to make us look bad!
First losing to Appalachian State and now a umich student thinking the plane can't take off! As a Michigan fan I don't think I can take anymore!!!!!
Read the actual riddle - it states the treadmill moves at the same speed as the PLANE - not the WHEELS!
Read this
This thread is slowly killing me - but I need to say one more thing.
It is IMPOSSIBLE for a treadmill to keep a plane stationary if the engine is running and the wheels are unlocked (free spinning). The props or jet move the plane forward relative to the AIR - not the ground - as long as the place of physical contact between the ground is relatively frictionless the plane will move forward. On a treadmill wheels would provide this basically friction free contact point - on water it would be pontoons - on snow or ice it would be ski's.
Neb wrote:
Please mpokora - tell me you're from Columbus and pretending to have a umich e-mail to make us look bad!
Read this
http://www.straightdope.com/columns/060203.html
I think we've been duped. This guy is just egging the conversation on, pretending to be from Michigan.
There it is, the perfect test for you doubters -- a jet pack while roller-blading on the treadmill. Try it and see what happens.
Big Ten Engineering wrote:
Neb wrote:Please mpokora - tell me you're from Columbus and pretending to have a umich e-mail to make us look bad!
Read this
http://www.straightdope.com/columns/060203.htmlI think we've been duped. This guy is just egging the conversation on, pretending to be from Michigan.
I don't know - I just looked on the Umich directory. That e-mail does exist and it belongs to an undergraduate engineering student.
But, just as I thought - his home address listed is from Pickering, Ohio!
Michigan is a good school - but you can't blame them for kids that get off to such a "troubled" start in life.
i have a buddy who's a good phd student (nearly graduated) in aerospace engineering. I haven't read the whole thread here, but i know for a fact that roughly 75-95% of the posts are by morons who don't know what they're talking about. I'm also a phd student in another field of engineering, and i wouldn't even really know what to say about this experiment. All of the conclusions must be based on certain assumptions, though...that's for sure. and it seems people are all making different assumptions. Here's what he said just based on the general question (if anyone has specific questions and assumptions, I can carry on the conversation with him and post it):
Does the plane have an engine? The assumption is that the treadmill will speed up and slow down depending on the throttle setting of the engine so that the plane is always in a fixed horizontal position, correct?
It depends. You need to have air flow over a wing to produce lift.
If an engine is running it will induce an airflow over the wing.
Also the no slip condition on the wall of the treadmill will result in an induced flow field. The air near the treadmill will be moving at the velocity of the treadmill wall. So if the treadmill is moving fast enough and the wings are close enough to the wall, I'd expect some lift.
I'd be curious see how they set up the experiment. I think it will depend on scaling and how much thrust they get out of their engine. If the airplane is just some small model, then I can see it lifting off, but more so based on a thrust vector in the vertical direction.
A 747 on a treadmill won't take off.
There's actually wind tunnel for cars that have both a conveyor belt and the air flow over the car to simulate real driving conditions.
The people who overthink this problem more than anyone are people with fancy engineering degrees. This riddle is meant for people with maybe a highschool level knowledge of physics. There's no need to start talking about "induced flow fields".
You are right - this is completely about assumptions. Meaning that experimentation doesn't help anything because different people would set up the experiment in different ways.
The riddle says that the treadmill matches the "speed" of the "airplane" - not the thrust of the engines (how could wheels spinning on a treadmill create enough force to equal the thrust of airplane engines anyways?) - or the speed of the wheels - but the speed of the plane.
Speed must be in relation to some other object. Some people assume that the riddle means in relation to the speed of the treadmill - but that doesn't make sense to me for the following reason: plane speed is in relation to the air around it. Is the speedometer of a plane based on how fast the wheels are spinning? Of course not - airplanes have a sensor that measures air pressure (I looked this up) - so the speedometer in an airplane will not show a speed of greater than zero unless it is moving relative to the air around it.
Therefore assuming that the treadmill is as long as a normal runway the plane will fly.