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kerosene31

Something to think about

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>However, the question does not mention IAS. You complicate everything immensly. Forget about IAS and all the speeds. The problem is much simpler. Imagine that some very abnoxious person is standing by the runway and this person has a big control panel in front of him with many large knobs. By turning the knobs this very nasty person can control the speed of the runway/treadmill however he wants. He can make it go forward/backward and he can adjust speeds as he pleases. Now imagine that some poor 737 pilot wants to take off even though this nasty person wants to prevent him from taking off. The question is very simple: who is going to win?Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

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>>the person would still go forward?>>yes, it would.OK! Great discussion btw!So what you are saying is that the initial example is not possible, that the plane would move forward. The speed of the treadmill will not counteract the forward thrust of the plane.


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Craig from KBUF

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>>However, the question does not mention IAS. >>You complicate everything immensly. I only mentioned IAS because others have mentioned it.>The question is very simple: who is going to win?The person with the big knob, in this example. The plane cannot exceed the speed of the treadmill.

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Guest enave

>So what you are saying is that the initial example is not>possible, that the plane would move forward. AAAHHHHH!!!! PLEASE QUOTE ANY PART OF THE INITIAL EXAMPLE THAT SAYS THE PLANE WILL NOT MOVE FORWARD!!!YOU ASSUMED THAT. YOU. NOT THE PROBLEM STATEMENT. YOU!

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Yes, we are still saying the aircraft will move. You are showing a fundamental misunderstanding. The units of speed are metres/sec: the units of thrust are Newtons. They are not the same thing and can't be equated - it's the old apples and pears fallacy.

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>The plane cannot exceed the speed of the treadmill.Look at my previous diagram. It shows the aircraft moving forward at a speed V with the treadmill moving backwards at a speed V. This is consistent with the problem as stated originally. The speeds are equal but the aircraft has a ground speed and hence airspeed and so will generate lift.

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This is a trap based on assumptions. I assumed that the plane would remain stationary. I took for granted that the treadmill could stop the forward motion of the plane. This assumption is *wrong* and is the problem. One assumption we need to make is about the airplane. The original post doesn't mention what kind. We need to assume that the aircraft is powered by either some sort of jet/rocket and/or prop. Then, you have to assume that the wheels of the aircraft can spin freely, with little or no friction. Also that the wheels would not be ripped apart from all the added speed... whcih actually probably would happen and prevent the plane from flying :)Bottom line, any normal aircraft thrust will move a plane forward, treadmill or no treadmill. The treadmill will have *zero* impact on the forward motion of the plane. It is true, a plane cannot take off without forward airspeed. However, the treadmill does nothing to stop the forward airspeed. Am I getting it now? Thanks for putting up with me. I went to school for many years, but I also played hockey and got hit in the head...often (-:


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Craig from KBUF

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>This is a trap based on assumptionsNo, it is not a trap.>One assumption we need to make is about the airplane. The>original post doesn't mention what kind. We need to assume that the > aircraft is powered by either some sort of jet/rocket and/or prop. :-hmmm :-hmmmSerius?Because the original post assumes that people know how airplanes are powered. Tell me please how else an airplane can be powered if not be a prop or a jet ?>Then, you have to assume that the wheels of the aircraft can>spin freely, with little or no friction. Not so. Wheels can spin with friction and the airplane can still take off. This assumption is not needed. Mr.Hook in 17-th century already knew that friction is not dependent on rotational speed. Absolutely elementary physics.>would not be ripped apart from all the added speed...yes, the only assumption is about tires/wheels being able to take the extra rotational speed. I don't frankly think it is a big deal. There are jet-powered cars today with wheels/tires being able to withstand speeds close to the speed of sound.>Am I getting it now? Yes, you are, sort of, but if you believe in all these assumptions you still have some territory to cross ;)Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

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>>This is a trap based on assumptions>>No, it is not a trap.>>>One assumption we need to make is about the airplane. The>>original post doesn't mention what kind. We need to assume>that the > aircraft is powered by either some sort of>jet/rocket and/or prop. >>:-hmmm :-hmmm>>Serius?>>Because the original post assumes that people know how>airplanes are powered. Tell me please how else an airplane can>be powered if not be a prop or a jet ?>>>Then, you have to assume that the wheels of the aircraft can>>spin freely, with little or no friction. >>Not so. Wheels can spin with friction and the airplane can>still take off. This assumption is not needed. Mr.Hook in>17-th century already knew that friction is not dependent on>rotational speed. Absolutely elementary physics.>>>would not be ripped apart from all the added speed...>>yes, the only assumption is about tires/wheels being able to>take the extra rotational speed. I don't frankly think it is a>big deal. There are jet-powered cars today with wheels/tires>being able to withstand speeds close to the speed of sound.>>>Am I getting it now? >>Yes, you are, sort of, but if you believe in all these>assumptions you still have some territory to cross ;)Wow, no need to attack my intelligence... I already admitted to being wrong. Am I too stupid to talk to the big bad men in the forum? The power of the airplane is an assumption. I'm not saying it is an unreasonable one...As for the tires, I would assume doubling the speed on them might put a little extra strain on them. Forgive me, as I don't work for Goodyear.


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Craig from KBUF

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Guest R1200RT

HAHAHA...I've been sitting back and watching this! We argue about this at my office as well - all frikken day. I say we all write Mythbusters and let them solve it.(I still think she'll fly...BTW)Don

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The wings aren't the only difference between an automobile and an aircraft.The automobile creates a rearward force against the pavement it rests upon. The reaction to this force is the forward motion of the automobile. The same holds true for people and animals. Pavement and vehicle/person/animal are propeled in opposite direction with velocity changes in inverse proportion to mass. In most cases the pavement is attached to the ground and the MUCH heavier planet isn't accelerated a noticeable amount. If a treadmill or roller is substituted for the ground the upper surface of the treadmill or roller could move rearward MUCH easier than the planet, greatly reduceing the velocity change imparted on the car. Add a small additional force to the treadmill from another source and the auto engine merely rotates the machine it rests upon.A fixed wing powered aircraft creates a force against the air in it's propeller disk, the air and combustion gases in its jet or, in rare cases, the gasses in its rocket motor. These gases aren't attached to the ground. In our hypthetical case these gases aren't attached to the treadmill either. The gases (includeing air flowing through any propeller or Fanjet houseing) and engine, with attached aircraft, are thrust in opposite directions with velocity change in inverse proportion to mass. Unless there's some incredably rapid breakdown, with wheel bearings siezing up with frictional heating or tires bursting with the rolling friction, the wheels and treadmill are going to be a MINOR impediment. The plane WILL move forward. There WILL be airflow over the wing. The plane WILL be able to fly.An aircraft imparts forces upon the surrounding air with every maneuver. Downward forces are imparted on the air by lift. Some of those forces are are angled to the side when the aircraft banks in turns. Air is forced rearward by the engines. Large air transports leave a violent wake behind them. Gliders are, relative to the air mass that surrounds them, ussally nosed downward slightly; their long wings directing the air towards the rear.A jet propelled automobile would move forward too. The jet propulsion makes the same difference in that case. The difference between the jet automobile and the airplane is the WING. The wing allows the plane to lift off of our outrageiously long treadmill. The jet propelled automoble would be limited to running off it's distant end.

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You're assuming the treadmill will be imperfect.During thought experiments it is assumed the situation IS perfect and therefore the force exerted by the treadmill on the aircraft will counter the force exerted by the aircraft perfectly causing the aircraft to remain stationary.If such were not the case the treadmill would be pointless, it would serve the same purpose as a wet or icy runway in that it slows down rather than halts accelleration and thus the buildup of airspeed.

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