Airplane on a treadmill

[kerosene31 349]

Wheel speed is simply the speed at which the wheels are spinning around, not the speed at which the object is moving forward relative to the ground. A car on a treadmill going 30 mph but standing still has a wheel speed of 30 mph.I might be oversimplifying, but I think the wheel speed still works though. Why wouldn't it? As the airplane accelerates the treadmill and the wheels would possibly keep accelerating as well, but eventually the plane would take off. Powered up engines have to be assumed, as if the question is if the aircraft can take off, then it is going to require power. So, put the plane with engines off on the treadmill and give it power. Nothing happens, because nothing will cause the plane to move yet as stated by the original problem. It matches wheel speed which is still zero. Now, fire up the engines and mash the throttles forward. The plane moves forward. The plane starts the whole process as it moves "first". In a perfect system both would start at the exact same moment, but since the treadmill is only reacting and matching, it should still work. People think backwards, "how fast does it have to spin to stop the plane", but that has nothing to do with the original problem. The treadmill only reacts, not jumps ahead.

[Guest Mr Chips]

Whoa there Christian! :)We're going over old ground. We know the the "matching the wheels" question is borked unless you make the assumption that it is movement relative to the wheels and not the ground as per your previous post.If, and I mean if and only if, we take on board that the question was misquoted and infact means that the treadmil speed is relative to the ground speed of the aeroplane, the way the question was originally phrased over a year ago (see other thread) then my post stands. A car on a treadmill has nothing to do with this version of the interpretation, I didn't raise cars on treadmills and don't wish too!If you choose to interpret the question literally, then go back to page one and see Murmur's post or back to your post depending to which type of speed you think the treadmill is pegged to.

[michal 44]

>If friction is the stumbling block for many people, as Michel>suggests, then consider this:>>The faster the wheels rotate, the lower the friction to a>point. There are two types of friction: static and dynamic.>Static is the amount of effort needed to intially move a>stationary object. Dynamic is the effort needed to keep it>going.I fully agree with all your comments.I think this problem rests on the beauty of simple physics and not on a trick word-puzzle (and reference system) about the moving treadmill. But folks like Kevin and Christain can interpret the problem the way they want - but it is then a different problem. As a matter of fact no physics book would dare to print "The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction" since it is highly ambiguous to begin with.In fact friction is exactly where people stumble. For example given that treadmill is moving back at say 200 MPH they can't imagine that in fact according to rules of basic physics/friction pilot won't have to add any more power to roll onto this treadmill and keep stationary in relation to the ground. So imagine a 747 sitting at the end of the runway and ready to roll onto this moving treadmill. Once the plane overcomes the static friction and starts moving (slowly) they can roll onto this treadmill with no additional power and they will be stationary in relation to the ground even though their wheels will be spinning at 200 MPH. Most folks find it bizarre and incomprehensible since intuitively everyone thinks that more speed is associated with more friction. Of course we have to assume that the fast spinning wheels won't overheat and generate extra friction this way (heat expansion, etc, but in the first-degree approximation this is perfectly OK to neglect all heat related effects).Michael J.

[Guest william273]

i don't see the mention of "wings" anywhere. unless i'm missing something, air seems to be needed to be moving over them to get the plane in the air. how is this possible with a stationary aircraft and what the heck does speed, wheels and that stupid conveyor belt have to do with getting an aircraft in the air if no air or wind is moving over the wings? the aircraft won't be moving so does this theory turn the plane into a helicoptor? william

[Guest christianholmes]

>Whoa there Christian! :)>>We're going over old ground. We know the the "matching the>wheels" question is borked unless you make the assumption that>it is movement relative to the wheels and not the ground as>per your previous post.>>If, and I mean if and only if, we take on board that the>question was misquoted and infact means that the treadmil>speed is relative to the ground speed of the aeroplane, the>way the question was originally phrased over a year ago (see>other thread) then my post stands. A car on a treadmill has>nothing to do with this version of the interpretation, I>didn't raise cars on treadmills and don't wish too!>>If you choose to interpret the question literally, then go>back to page one and see Murmur's post or back to your post>depending to which type of speed you think the treadmill is>pegged to.Ok, if the question was stated that the speed of the treadmill is simply meant to match the groundspeed of the airplane, then you are correct. And in that case, of course the plane could take off. The wheels would simply spin at twice the ground speed of the plane. And since the question states "could" and not "will" you only have to satisfy a best case scenerio.However, look at the car on a treadmill in that scenerio- Now you've broken that! Instead of remaining stationary, the car would now roll down the treadmill with it's speedometer reading twice it's actual speed! I don't see why anyone would postulate the question like this- it means you are making concessions to the logic of the original question to suit your needs and make an otherwise invalid question valid. I think the question was most certainly intended as I and some others have interpreted it. The simple problem with the question is that the original creator of the question simply did not understand math and physics enough- if they did they would not have created such a invalid question. It's basically like asking what you would see if you went faster than the speed of light. To the average person that question stirs up some debate, but to someone who understands the concept the answer is simply that you can't travel faster than the speed of light so it's irrelevant. Do you have a link for the original? I would like to see it. All the versions of it I found are this one.

[turner112 52]

"you can't travel faster than the speed of light"Unless you're a shadow ;)(Ok, ok, I know, technically that's not "travel"...)I believe the original problem is worded poorly and needs clarification. Otherwise, the debate must remain on the topic of what the author meant rather than what actually could happen.Andrew

[Guest Mr Chips]

Hi Christian,My car analogy was not about a car on a treadmill, I just wanted to illustrate the differece between static and dynamic friction in a way most people can related to!The link to the original was on page 1: http://forums.avsim.net/dcboard.php?az=sho...ing_type=searchHave fun!

[michal 44]

> i don't see the mention of "wings" anywhere.Because you got lost in what is being discussed here ...Michael J.

[turner112 52]

"i don't see the mention of "wings" anywhere"We had Buffalo Wings for dinner.You'd think they're more of an appetizer than a meal. You'd be wrong.:)Andrew

[Guest fyrestrtr]

>"i don't see the mention of "wings" anywhere">>We had Buffalo Wings for dinner.>>You'd think they're more of an appetizer than a meal. You'd be>wrong.>>:)>>AndrewROFLThis was the best comment. I really enjoyed the physics discussion as well :)

[Guest christianholmes]

>"i don't see the mention of "wings" anywhere">>We had Buffalo Wings for dinner.>>You'd think they're more of an appetizer than a meal. You'd be>wrong.>>:)>>AndrewBuffalos have wings? I thought they were marsupials?

[Guest CowlFlapsOpen]

Air is a gas and the principles of flight, including takeoff, depend on aspects of fluid dynamics. Light aircraft are propelled through the air by the actions of the their propellers on the air mass they are in, this includes during the takeoff phase of flight. Airplanes will not fly if they are prevented from moving forward in the airmass (or the airmass is prevented from flowing past them, or is too thin, etc), such as if they are tied down, their wheels are chocked, etc. A conveyor belt under the wheels does not have this effect and would only be relevant if planes depended on their contact (friction, resistance) with the ground to accelerate, as autos do for example. They do not. Wheels simply keep the fuselage off the ground as the airplane moves forward until it had sufficient speed through the air to generate enough lift for flight. One can also use skies (skids) or anything else for this as long as it doesn't introduce too great of drag to stop the motion of the aircraft relative to the air mass.Humans are preoccupied with relation of the airplane to the ground because almost all other movement they understand intuitive depends on acting against the earth, such as walking, driving, riding, etc. This is just a psychological bias however. An exception are submarines, which most people are more familiar with and understand more intuitively. So here is a submarine equivalent: Could a submarine move forward along the sea floor if it had wheels and they were in contact with counter-rotating conveyor belt on the bottom of the sea? Of course.

[turner112 52]

"One can also use skies (skids) or anything else for this as long as it doesn't introduce too great of drag to stop the motion of the aircraft relative to the air mass."While the aircraft is in contact with the ground (treadmill), its wheel speed is the same as its speed through the air. Andrew

[michal 44]

>here is a submarine equivalent: Could a submarine move>forward along the sea floor if it had wheels and they were in>contact with counter-rotating conveyor belt on the bottom of>the sea? Of course.Yes, very nice analogy.Michael J.

[turner112 52]

Well, the submarine bit is perhaps even stranger than the original question.But after wondering what would happen if the treadmill were moving -in the same direction- as the aircraft, I fail to believe there would be enough friction in the wheels to somehow make the plane gain any significant speed...Or, for that matter, what would happen if a plane -landed- on the same treadmill.The friction in the wheels would have a measurable but insignificant effect, I think.Ack!So now I'm believing the aircraft would take off pretty easily indeed, since the wheel friction wouldn't be a factor.---Andrew