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Would the plane take off?

Discussion in 'General Chat' started by imported_Nigma, Mar 21, 2006.

  1. imported_hookie
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    imported_hookie Guest

    [Mar 30, 2006]
    [ QUOTE ]
    Hookie, I shall endeavor to get my professor to give you an answer too.

    [/ QUOTE ]

    Dude I've emailed bloody loads of them, this could be quite entertaining with all the replies!!!

    Professor Wilmer Anderson of the University of Wisconsin in Madison whose research area is atomic physics replied -

    [ QUOTE ]
    If the plane remains at rest relative to the earth due to the opposite moving belt then the only way the plane can take off is if the conveyor belt entrains enough air so that the relative wind speed in the plane's rest frame is high enough to provide adequate lift. For large jets this is about 150mph. The only thing that matters significantly is the relative speed of the plane and the air.

    Wilmer Anderson

    [/ QUOTE ]


    I can see we're gonna have a long long thread on this one! As the jury is still out. Gonna email a /ubbthreads/images/graemlins/swear.gif load more in a bit! Might email all my contacts in outlook too to see what other random quotes we can get too, could be entertaining....
  2. Just Plain Old
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    Just Plain Old Active Member

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    [Mar 30, 2006]
    The plane would NOT take off.
  3. imported_hookie
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    imported_hookie Guest

    [Mar 30, 2006]
    Oh I'm gonna email the replies to those that replied also to see what their take on it is too /ubbthreads/images/graemlins/smile.gif
  4. imported_hookie
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    imported_hookie Guest

    [Mar 30, 2006]
    [ QUOTE ]
    Force and .... oh never mind. (PS it will) /ubbthreads/images/graemlins/bang.gif
    Has this been put to a vote yet, i can't remember!

    Chas

    [/ QUOTE ]

    I thought it would be entertaining somewhat to get a load of people qualified to argue this to do so, what do you think.... /ubbthreads/images/graemlins/smile.gif
  5. imported_hookie
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    imported_hookie Guest

  6. neversaydie
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    neversaydie Post Whore

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    [Mar 30, 2006]
    Lmao Dan /ubbthreads/images/graemlins/smile.gif
  7. imported_hookie
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    imported_hookie Guest

    [Mar 31, 2006]
  8. imported_hookie
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    imported_hookie Guest

    [Mar 31, 2006]
    Reading all that thread and this one everyone assumes that the relation is only between the plane and the conveyor. The thing that is being totally dismissed is that this is not true, the factors involved are not just between the plane and conveyor but also between the planes angines and the air it is acting on clearly.
  9. beaker
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    beaker Member

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    [Mar 31, 2006]
    Oh my god! Its a monster on multiple forums!
  10. imported_hookie
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    imported_hookie Guest

    [Mar 31, 2006]
    A worthy explanation for those 'idiots' -


    The Pilot's Lounge #94: It's The Medium, Manfred

    There's a new aviation myth running around the Internet. It involves a conveyer-belt runway and misuse of aerodynamics and ... well, it's better if AVweb's Rick Durden explains it all himself in The Pilot's Lounge.

    By Rick Durden
    Columnist



    The Pilot's Lounge

    I heard the commotion as I started down the hall from the flight school to the Pilot's Lounge at the virtual airport. In the few moments it took to get to the door of the Lounge, individual voices became clear, split into two very vocal camps: The vehement "Yes it will!" calls being answered by an equally intense "No it won't!" I thought back to some of the stronger disagreements that had been aired here, such as the use of flaps on landing, but this one seemed a little louder and I wondered whether Old Hack and some of the bigger guys might have to separate combatants.

    I stood off to the side and tried to get a handle on the conflict. Old Hack saw me and sidled over with a silly grin on his face. "These guys spend way too much time on the Internet," he said. "Someone has just come up with what looks like a 21st-century version of the old "downwind turn" foolishness and now the engineers and the soft-science folks are having at it."


    The "Fatal" Downwind Turn

    For those who don't recall the "downwind turn" tale of the last century, it goes like this: People observed that pilots who were flying relatively low on a heading that took them into the wind had a surprisingly high rate of impact with the ground or obstructions if they rolled into a turn and proceeded to a heading that was with the wind direction, or downwind. There were those who insisted that the airplane could not accelerate fast enough in the turn to make the necessary groundspeed change so as to stay above stall speed and thus they crashed.

    As an example, we'll take a pilot with a reputation for good stick and rudder skills, a certain Manfred. We'll magically reincarnate him from the Western Front of World War I (where he had perished) and put him in a 65-hp, Piper J-3 Cub. Its cruise speed is pretty close to the Fokker Dr-I that Manfred last flew -- call it 80 mph. (The Fokker Triplane was so maneuverable few enemy pilots ever figured out it was astonishingly slow.)

    We'll point Manfred and the J-3 northbound at 500 feet AGL into the teeth of a 40-mph headwind. His groundspeed is, therefore, 40 mph. Now we'll have him roll into a turn and change directions 180 degrees until he is headed south, directly downwind. We'll have him make the turn in 30 seconds, a twice-standard-rate turn. At that airspeed, it's not very steep and certainly not at all unsafe. The next consideration is that in those 30 seconds, Manfred's J-3 has to accelerate from a groundspeed of 40 mph to a groundspeed of 120 mph in order to still be moving through the air at 80 mph. In fact, if he does not accelerate through that needed 80 mph change in groundspeed, the airplane could stall because the airspeed would have dropped off radically.





    There were those who were convinced that it was impossible for a 65 hp J-3 to increase its groundspeed by 80 mph in 30 seconds, and therefore the airplane would stall, which was what made downwind turns so dangerous.

    Fortunately, back when this was being debated, rationality prevailed. It was pointed out that the airplane was flying through the air, its propeller was acting upon the air and its wings were moving in an airmass. Thus, when it made its turn, its airspeed didn't change. The airplane continued to move through the air at 80 mph. Its groundspeed changed solely because of the fact that the mass of air in which it was operating, the medium upon which it was acting, was moving.

    Had the air been calm, Manfred and his J-3 would have had a groundspeed that matched his airspeed.

    Interestingly enough, when the famous aviator, Jimmy Doolittle was sent by the Army to M.I.T. to study in the mid-1920s, his dissertation for his Ph.D. included some of this discussion, so the problem's been solved for some time; it just took most of the rest of the century for the understanding to trickle down. (Yeah, that air-racing, aerobatic, military pilot also had one of the first Ph.D.s awarded in aeronautical engineering.) Doolittle also hypothesized that the frequency of crashes during such turns was the visual effect of the rapidly increasing groundspeed causing pilots to believe that the airplane was suddenly going very fast and pulling back on the stick or throttle, leading to a stall or descent into the ground.

    For those who still didn't understand that the downwind turn had no effect on the airplane, all it took was a flight on a day with some wind above a solid deck of clouds. Making a few circles made it clear that the airplane and its pilot could not tell anything about the direction of the wind while turning.


    Conveyer-Belt Runway






    What I learned from Old Hack was that an updated version of a question aimed at confusing folks over relative measurements of airplane motion and the medium in which it operates had shown up on the Internet, and it was causing the fracas in the Lounge.

    The question that has been going around is not particularly artfully worded, and I think that has caused some of the disagreements, but I'll repeat it as it is shown: "On a day with absolutely calm wind, a plane is standing on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. The conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the airplane ever take off?"

    My comment: Notice that the question does not state that the conveyor's movement keeps the airplane over the starting position relative to the ground, just that it moves in the direction opposite to any movement of the airplane.

    Initially, about a third of the folks here said that the airplane could not ever takeoff, because the conveyor would overcome the speed of the airplane and it could never get any airspeed. The rest said the airplane would fly.

    The "It won't fly, Rocky" group said that the conveyor would hold back the airplane. They asked us to imagine a person running on a treadmill. As he or she sped up, the treadmill would be programmed to speed up, just as the conveyor in the problem, and the person would remain over the same locus on the earth, while running as fast as possible.

    The argument was that if the airplane started to move forward, the conveyor program was set up to move the conveyor at exactly that speed, in the opposite direction, thus, the airplane would never move relative to the ground, and, because the air was calm, it could never get any wind over its wings. One of the analogies presented was the person rowing at three mph upstream in a river on a calm day. However, the current was flowing downstream at three mph, so the resultant speed with reference to the stream bank and air was zero, and thus there was no wind on the rowboat.

    I watched and listened to the disagreement for a while and was fascinated to see that the argument seemed to split between those who had some engineering or math background, all of whom said the airplane would takeoff and fly without any problem; and those with some other background, who visualized the airplane as having to push against the conveyor in order to gain speed. Because the conveyor equaled the airplane's push against the conveyor, the airplane stayed in one place over the ground and in the calm air could not get any airspeed and fly.

    It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards.


    Manfred In The 21st Century





    OK, let's figure out why the airplane will fly.

    We'll use Manfred again. Although we're bringing him forward into the 21st Century, we'll still let him use the 65 hp J-3. It doesn't really matter what airplane he flies, but he got used to the J-3 while he was demonstrating downwind turns and this one happens to have lifting rings on the top of the fuselage. It's also been modified with a starter so no one has to swing the prop.

    Manfred's in the airplane. Old Hack has the Army-surplus crane fired up and he's picking up the J-3 and Manfred and carrying them over to Runway 27, which has been transformed into a 3,000-foot conveyor belt. It is a calm day. The conveyor drive is programmed so that if Manfred can start to move in the J-3, if he can generate any airspeed or groundspeed, the conveyor will move toward the east (remember Manfred and the J-3 are facing west) at exactly the speed of the air/groundspeed. Because the wind is calm, if Manfred can generate any indicated airspeed, he will also be generating precisely the same groundspeed. Groundspeed, of course being relative to the ground of the airport surrounding the conveyor belt runway. So, the speed of the conveyor belt eastbound will be the same as Manfred's indicated airspeed, westbound.

    Manfred does his prestart checklist, holds the heel brakes, hits the starter and the little Continental up front clatters to life. Oil pressure comes up and stabilizes and Manfred tries to look busy because the eyes of the world are upon him, but all he can do is make sure the fuel is on and the altimeter and trim are set, then do a quick runup to check the mags and the carb heat. He moves the controls through their full travel and glares at the ailerons, doing his best to look heroic, then holds the stick aft in the slipstream to pin the tail and lets go of the brakes.


    Baron of the Belt

    So far the J-3 has not moved, nor has the conveyor. At idle power, there's not enough thrust to move the J-3 forward on a level surface, so Manfred starts to bring up the power, intending to take off. The propeller rpm increases and the prop shoves air aft, as it does on every takeoff, causing the airplane to move forward through the air, and as a consequence, forward with regard to the ground. Simultaneously the conveyor creaks to life, moving east, under the tires of the J-3. As the J-3 thrusts its way through the air, driven by its propeller, the airspeed indicator comes off the peg at about 10 mph. At that moment the conveyor is moving at 10 mph to the east and the tires are whirling around at 20 mph because the prop has pulled it to an airspeed, and groundspeed, of 10 mph, westbound. The airplane is moving relative to the still air and the ground at 10 mph, but with regard to the conveyor, which is going the other way at 10 mph, the relative speed is 20 mph.

    Manfred relaxes a bit because the conveyor cannot stop him from moving forward. There is nothing on the airplane that pushes against the ground or the conveyor in order for it to accelerate; as Karen -- one of our techies here at the Lounge -- put it, the airplane freewheels. In technical terms, there is some bearing drag on the wheels, but it's under 40 pounds, and the engine has overcome that for years; plus the drag doesn't increase significantly as the wheel speed increases. Unless Manfred applies the brakes, the conveyor cannot affect the rate at which the airplane accelerates.

    A few moments later, the roaring Continental, spinning that wooden Sensenich prop, has accelerated the J-3 and Manfred to 25 mph indicated airspeed. He and the airplane are cruising past the cheering spectators at 25 mph, while the conveyor has accelerated to 25 mph eastbound, yet it still has no way of stopping the airplane's movement through the air. The wheels are spinning at 50 mph, so the noise level is a little high, but otherwise, the J-3 is making a normal, calm-wind takeoff.

    As the indicated airspeed passes 45 mph, groundspeed -- you know, relative to where all those spectators are standing beside the conveyor belt -- is also 45 mph. (At least that's what it says on Manfred's GPS. Being brought back to life seemed to create an insatiable desire for electronic stuff.) The conveyor is also at 45 mph, and the wheels are whizzing around at 90 -- the groundspeed plus the speed of the conveyor in the opposite direction.

    Manfred breaks ground, climbs a few hundred feet, then makes a low pass to see if he can terrify the spectators because they are Americans, descendants of those who defeated his countrymen back in 1918.


    It's All About Airspeed



    (Don't try this at home!)

    While the speed of the conveyor belt in the opposite direction is superficially attractive in saying the airplane cannot accelerate, it truly is irrelevant to what is happening with the airplane, because the medium on which it is acting is the air. The only time it could be a problem is if the wheel speed got so high that the tires blew out.

    Put another way, consider the problem with the J-3 mounted on a hovercraft body (yes, similar things were tried about 30 years ago). The hovercraft lifts the airplane a fraction of an inch above the conveyor belt, and so no matter how fast the conveyor spins, it cannot prevent the propeller -- acting on the air -- from accelerating the airplane to takeoff speed. It's the same with wheels rolling on the conveyor belt. Those wheels are not powered and thus do not push against the belt to accelerate the airplane. Were that the case, the vehicle could not reach an airspeed needed to fly, because then the conveyor, the medium acted upon by the propulsive force, would be able to negate the acceleration relative to the air and ground.

    I'm reminded of the New York Times editorial when Robert Goddard's rocket experiments were first being publicized. The author of the editorial said that rockets can't work in space because they have nothing to push against. It was laughably wrong, ignoring one of Sir Isaac's laws of physics that for every action there is an equal and opposite reaction. Here the propeller is pushing against the air, as it does every time an airplane takes off. How fast the airplane is moving over the surface on which its wheels rest is irrelevant; the medium is the magic. On a normal takeoff -- no conveyor involved -- if there is a 20 mph headwind, Manfred and the J-3 will lift off at 45 mph indicated airspeed; but relative to the ground, it is only 25 mph. Should the wind increase to 45 mph and if Manfred can get to the runway, he can take off without rolling an inch. His airspeed is 45 and groundspeed is zero. It is not necessary to have any groundspeed to fly, just airspeed. Conversely, if Manfred has a lot of runway and nothing to hit, and takes off downwind in a 25 mph tailwind, the propeller will have to accelerate the airplane to a zero airspeed, which will be a 25 mph groundspeed, and then on to a 45 mph airspeed, which will have him humming across the ground at 70 mph. The speed over the ground, or a conveyor belt, when an airplane takes off is irrelevant; all that matters is its speed through the air, and unless the pilot sets the brakes, a moving conveyor belt -- under the freely turning wheels -- cannot stop the process of acceleration.

    Things eventually calmed down as the number of "it won't fly" folks dwindled as they began to understand that the airplane would take off. Old Hack looked at me and suggested we depart as the few holdouts showed no sign of changing their position. So, we headed out into the night to watch the guys take the conveyor out and reinstall the runway.
  11. pwnorman
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    pwnorman Member

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    [Mar 31, 2006]
    This must be some sort of record by now, hookie have all your 60 odd posts been on this thread dont know what the last one said i've lost the will to live or ever fly again as there's to many planes and conveyor belts at airports i may just have a mental breakdown.
  12. pwnorman
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    pwnorman Member

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    [Mar 31, 2006]
    Whilst im on how in the name of god did that french plane get like that must have been faulty belt system then they wonder why the french crashed concorde.
  13. TDI-line
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    TDI-line Uber Post Whore

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    [Mar 31, 2006]
    [ QUOTE ]
    Lmao Dan /ubbthreads/images/graemlins/smile.gif

    [/ QUOTE ]

    Thanks mate. /ubbthreads/images/graemlins/beerchug.gif
  14. bircham
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    bircham New Member

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    [Mar 31, 2006]
    The plane would take off! As has been repeatedly said the speed that the wheels are travelling at have no relation to the airspeed of the aircraft.
    The only thing that would stop the plane taking off would be the wheels overheating, exploding and the plane would then not be able to take off because the aircraft can't generate enough thrust to overcome the friction of the non-moving wheel gear. Analogies to cars ar completely misleading as cars are driven by their wheels and planes are driven by massive jet engines. Groundspeed and airspeed are two totlly differnt things.
  15. imported_hookie
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    imported_hookie Guest

    [Mar 31, 2006]
    [ QUOTE ]
    This must be some sort of record by now, hookie have all your 60 odd posts been on this thread dont know what the last one said i've lost the will to live or ever fly again as there's to many planes and conveyor belts at airports i may just have a mental breakdown.

    [/ QUOTE ]

    I used to have a post count of about 3500 on here......

    New account you see /ubbthreads/images/graemlins/wink.gif

    Just wanted to clear this argument up, and when I know I'm right I'm like a dog with a bone /ubbthreads/images/graemlins/tongue.gif
  16. god_thats_quick
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    god_thats_quick Numptie of the highest order

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    [Mar 31, 2006]
    I think the one reply on here from the astrophysics chap, is a result of either not reading the question correctly or not realising that the plane isn't driven by it's wheels although there are many different wordings of the question I think I'm solidly in the it will take off camp now.

    I think someone needs to try the fan on skatebord on a treadmill or even better a conveyor in a airport and film it!
  17. imported_hookie
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    imported_hookie Guest

    [Mar 31, 2006]
    Remote control airplane on a conveyor belt at tesco's checkout???
  18. robthehungrymonkey
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    robthehungrymonkey Member

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    [Mar 31, 2006]
    [ QUOTE ]
    I think the one reply on here from the astrophysics chap, is a result of either not reading the question correctly or not realising that the plane isn't driven by it's wheels although there are many different wordings of the question I think I'm solidly in the it will take off camp now.

    I think someone needs to try the fan on skatebord on a treadmill or even better a conveyor in a airport and film it!

    [/ QUOTE ]

    I'm actually going to cause lots of controversy here and say that I could have been wrong all along!!/ubbthreads/images/graemlins/bang.gif

    I don't think the question works.

    The plane would take off, no question. But, the wheels could not increase speed without the conveyor belt going the opposite way, this would mean that the weels woould never accelerate, if the conveyor belt always maintained the same speed as the wheels the plane would remain stationary.

    But the plane wouldn't remain stationary because of the thrust from the engines have to push it somewhere.

    So my new answer is that the conveyor belt could not "sense" the wheel speed and instantly go the opposite direction at that speed.

    So, I believe that this is not just impossible in the real world but impossible theoretically too.

    I.e. the engines would definitely push the plane forwards, but the wheels and conveyor belt by definition could not allow the plane to move.


    Am I missing something? or is this just an impossible question. /ubbthreads/images/graemlins/confused.gif /ubbthreads/images/graemlins/bang.gif
  19. god_thats_quick
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    god_thats_quick Numptie of the highest order

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    [Mar 31, 2006]
    [ QUOTE ]
    [ QUOTE ]
    I think the one reply on here from the astrophysics chap, is a result of either not reading the question correctly or not realising that the plane isn't driven by it's wheels although there are many different wordings of the question I think I'm solidly in the it will take off camp now.

    I think someone needs to try the fan on skatebord on a treadmill or even better a conveyor in a airport and film it!

    [/ QUOTE ]

    I'm actually going to cause lots of controversy here and say that I could have been wrong all along!!/ubbthreads/images/graemlins/bang.gif

    I don't think the question works.

    The plane would take off, no question. But, the wheels could not increase speed without the conveyor belt going the opposite way, this would mean that the weels woould never accelerate, if the conveyor belt always maintained the same speed as the wheels the plane would remain stationary.

    But the plane wouldn't remain stationary because of the thrust from the engines have to push it somewhere.

    So my new answer is that the conveyor belt could not "sense" the wheel speed and instantly go the opposite direction at that speed.

    So, I believe that this is not just impossible in the real world but impossible theoretically too.

    I.e. the engines would definitely push the plane forwards, but the wheels and conveyor belt by definition could not allow the plane to move.


    Am I missing something? or is this just an impossible question. /ubbthreads/images/graemlins/confused.gif /ubbthreads/images/graemlins/bang.gif

    [/ QUOTE ]

    Similar to me then hey... can't make your mind up! /ubbthreads/images/graemlins/laugh_roll.gif

    It's all in the wording of the question, but I think that the wheels would spin faster and faster as in the question that started this it suggested that the plane moves forwards first so the converyor would always be trying to catch up... I think!
  20. robthehungrymonkey
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    [Mar 31, 2006]
    [ QUOTE ]

    Similar to me then hey... can't make your mind up! /ubbthreads/images/graemlins/laugh_roll.gif

    It's all in the wording of the question, but I think that the wheels would spin faster and faster as in the question that started this it suggested that the plane moves forwards first so the converyor would always be trying to catch up... I think!

    [/ QUOTE ]

    I think i've decided that the scenario just is an impossibility, even theoretically. As the plane would definitely go forwards.
    The question doesn't allow for the belt to "catch up" as it said it would always be moving at exactly opposite speeds.

    I think...

    What happened to the physics teacher!?
  21. imported_hookie
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    imported_hookie Guest

    [Mar 31, 2006]

    [ QUOTE ]

    Professor Wilmer Anderson of the University of Wisconsin in Madison whose research area is atomic physics replied -

    If the plane remains at rest relative to the earth due to the opposite moving belt then the only way the plane can take off is if the conveyor belt entrains enough air so that the relative wind speed in the plane's rest frame is high enough to provide adequate lift. For large jets this is about 150mph. The only thing that matters significantly is the relative speed of the plane and the air.

    Wilmer Anderson

    [/ QUOTE ]

    Mark Birkinshaw replied to this-
    [ QUOTE ]
    This is misguided. The plane doesn't remain at rest relative to the Earth. The moving conveyor belt can't move the plane since it isn't coupled to the plane's mass (c.f. the frictionless bearings on the wheels).

    MB

    [/ QUOTE ]

    I don't think I'll send his reply to her! lol
  22. rickquattro
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    rickquattro Member

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    [Mar 31, 2006]
    [ QUOTE ]
    the engines would definitely push the plane forwards, but the wheels and conveyor belt by definition could not allow the plane to move.


    Am I missing something?

    [/ QUOTE ]

    In a word..... I think that you are absolutely missing the whole argument and explaination given in the long text from the pilots...keep drinking the absinthe from the above statement !

    Seems a bit easy this after reading the article

    School physics, Newton's laws of motion. Every action has an equal and opposite reaction.

    There is no mechanical connection applying power from the aircraft, via the wheels. They just spin freely. The belt moves the wheels, the wheels spin. Full stop.

    The engines apply force on the air just behind the engine to move. More force more movement. Aircraft dont stop flying when the wheels leave the ground, do they?

    Is the aircraft driven by the wheels? No.
    Are the aircraft engines pushing the aircraft along by exerting force on the air directly behind the engines. Yes.
    Is the air directly behind the engines in any way mechanically linked to the conveyor. No

    All together now....

    "I believe I can fly"

    Great thread Gromitt ! /ubbthreads/images/graemlins/ok.gif
  23. audi5e
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    audi5e Member

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    [Mar 31, 2006]
    Pretend there is no plane, only a wheel driven by some unknown power/force. As the wheel starts to rotate so the conveyor counters that rotation by moving under the wheel. Every time the wheel speed increases the conveyor speed instantly increases to an EQUAL but OPPOSITE speed. If the wheel rotation slows then the conveyor slows. At all times during this process the wheel axle remains stationary while the circumference rotates on the moving conveyor.

    Now attach wings and a power source (be it a jet, turbine, nuclear, does not matter) to the axles and perhaps a few more wheels to give stability. You still have the same thing happening, equilibrium.

    It actually does not matter what power source is used or what resistance is measured, the axles remain stationary while the rotation and conveyor speed remain equal.
    Remember the question:
    "the conveyor belt senses the speed of the plane's wheels and moves at exactly the same speed in the opposite direction"

    Since the plane body is stationary, it is not moving forward or backward, hence not enough airflow over the wings and no flight. The aircraft is unable to translate true ground speed (not conveyor speed) into airspeed and is therefore not able to fly...
  24. Just Plain Old
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    Just Plain Old Active Member

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    [Mar 31, 2006]
    OK.

    Everybody's right.............. sort of! /ubbthreads/images/graemlins/crazy.gif

    In the 'hypothetical' world, if the conveyer belt runway could 'actually' stop the plane from moving forward then it would have zero airspeed and NOT be able to take off.

    However in the 'real' world, the conveyor belt would not 'actually' be able to stop the plane from moving forward, therefore 'in the real world' it WOULD take off.
  25. chazzy
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    chazzy Member

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    [Mar 31, 2006]
    The physics teacher is still here, some great explanations of why it would take off, vectors, forces, thrust . WOW its great language wish you were all in my class, but as i'm a real teacher (at the mo) and not a viirtual facilitator i need to wave my hands a lot and draw squiggles on the board to explain it any better than before apart from if you replaced the wheels with blocks of ice and the conveyor still moved the plane would still take off!
    Chas (where the plane smiley!)
  26. imported_hookie
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    imported_hookie Guest

    [Mar 31, 2006]
    [ QUOTE ]
    OK.

    Everybody's right.............. sort of! /ubbthreads/images/graemlins/crazy.gif

    In the 'hypothetical' world, if the conveyer belt runway could 'actually' stop the plane from moving forward then it would have zero airspeed and NOT be able to take off.

    [/ QUOTE ]

    No but it couldn't stop it moving, only way it could would be if the belt was stationary and the plane was bolted down to it!
  27. imported_hookie
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    imported_hookie Guest

    [Mar 31, 2006]
    So I've had a reply from Wilmer commentting on Prof Birkinshaw's reply, hope this helps clarify our correctness and convert those doubters /ubbthreads/images/graemlins/wink.gif

    [ QUOTE ]
    Dear John,

    I think that Birkinshaw is closer to correct than I was. Of course there must be a force on the wheels to produce the torque that makes them spin, but if the moment of inertia of the wheels is small this force is small. While this force pushes backward on the plane and must be included in calculating the motion of the plane (it is not a frictional force in the wheels) it is likely unimportant and I believe that Birkinshaw is basicaly correct and that I was not correct in my first e-mail to you.

    Wilmer

    [/ QUOTE ]
  28. audi5e
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    audi5e Member

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    [Mar 31, 2006]
    Consider that the wheel and the conveyor are moving at exactly the same speed all the times, just in opposite directions. This is true because it has been stated in the question. The only time there will be a forward motion of the plane is when equilibrium ceases and the wheel is allowed to spin faster than the conveyor thus setting up a forward movement of the aircraft, and that would mean that the stated condition of the question is no longer true.

    If you were to place a stake in the ground in line with the axle of the wheel just beyond the conveyor, and you kept with the question that the wheel and conveyor are in equilibrium at all times, then it would be true that there would be no axle movement relative to the stake. The wheel and the conveyor on the other hand would continue to accelarate to higher speeds until the power source reached a peak, or until the wheel bearings conked in, the conveyor stopped moving, the landing gear collapsed, the aircraft fell on it's belly, slamming the engines into the ground which then tear the plane apart sending lots of dumb arse passengers into the sky. So there you go, the aircraft may well not have become airborne but at least the passengers did.....
  29. NEiLS3LK51
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    NEiLS3LK51 Member

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    [Mar 31, 2006]
    audi5e, you need to come to England, it seems we are in short supply of engineers and physicists!
  30. TDI-line
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    TDI-line Uber Post Whore

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    [Apr 1, 2006]
    [ QUOTE ]
    audi5e, you need to come to England, it seems we are in short supply of engineers and physicists!

    [/ QUOTE ]

    No, please don't or new threads like this will spring up. /ubbthreads/images/graemlins/bang.gif
  31. imported_hookie
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    imported_hookie Guest

    [Apr 1, 2006]
    The plane would have taken off along time before any bearings would have failed etc....

    What will it take you doubters to beleive it? I can't quite understand why, it's been quite simply explained.
  32. scoTTy
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    scoTTy Active Member

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    [Apr 1, 2006]
    Why don't people just ignore the wheels and the conveyor belt. Imagine it was a sea plane with skates on....if it was going with the tide or away from the tide it wouldn't make any difference.

    It would flt regardless or what the wheels ground were doing.
  33. Beerzo
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    Beerzo Masa'warty 3200... Talk To Me!

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    [Apr 1, 2006]
    Lets look at the facts...

    An aircraft wing needs air passing over it to provide lift to take off.

    If the conveyer belt is traveling at the exact same speed but in the opposite direction then the plane WILL stay stationary. Although on full power via the engines.

    Think of it like you running on a tread mill when you are running at say 7 mph and the belt is turning at the same speed you do not move. You also do not feel the wind in your face because you are not moving.

    This is the exact same as the aircraft just on a bigger scale. Hence no air passing over the wing so no lift.

    If the plane could take off (which it cant) air craft carriers would most certainly use them to shorten take offs. Hell if it worked you could have 3 or 4 planes taking off at a time as you would only need about 35 feet or so of "conveyor belt". This could also be stuck on the back of a truck so a jet could take off practically anywhere.

    So i am affraid if you think the plane would take off your sadly mistaken.

    /ubbthreads/images/graemlins/groovy.gif /ubbthreads/images/graemlins/bravo.gif
  34. audi5e
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    audi5e Member

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    [Apr 1, 2006]
    [ QUOTE ]
    [ QUOTE ]
    audi5e, you need to come to England, it seems we are in short supply of engineers and physicists!

    [/ QUOTE ]

    No, please don't or new threads like this will spring up. /ubbthreads/images/graemlins/bang.gif

    [/ QUOTE ]

    We have internet, I can torment remotely..... /ubbthreads/images/graemlins/dancing.gif
  35. chazzy
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    chazzy Member

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    [Apr 1, 2006]
    [ QUOTE ]
    Think of it like you running on a tread mill when you are running at say 7 mph and the belt is turning at the same speed you do not move. You also do not feel the wind in your face because you are not moving.


    [/ QUOTE ]

    when you run your feet provide a backwards force on the ground, which results in a forwards force on YOU. granted this would not work eg bicycle with wings on type plane. BUT a real plane exerts a force backwards on the air, so it experiences a force forwards from the air (Newt .3rd law)) if it pushes air backwards it will be pushed forwards, if the push is bigger than any friction it will accelerate, all that happens is that the conveyor belt also accelerates.
    I don't think anyone is saying the plane will stay still and take off, but that it will move forwards and hence create lift etc.

    Imagine a rocket strapped to a toy car on a very fast shopping conveyor belt. it. if placed on the belt after the rocket is lit it will mmove forwards.
    Chas
  36. neversaydie
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    neversaydie Post Whore

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    [Apr 1, 2006]
    cough cough
  37. TDI-line
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    TDI-line Uber Post Whore

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    [Apr 1, 2006]
    [ QUOTE ]
    [ QUOTE ]
    [ QUOTE ]
    audi5e, you need to come to England, it seems we are in short supply of engineers and physicists!

    [/ QUOTE ]

    No, please don't or new threads like this will spring up. /ubbthreads/images/graemlins/bang.gif

    [/ QUOTE ]

    We have internet, I can torment remotely..... /ubbthreads/images/graemlins/dancing.gif

    [/ QUOTE ]

    Bugger.

    God damm internet. /ubbthreads/images/graemlins/swear.gif
  38. TDI-line
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    TDI-line Uber Post Whore

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    [Apr 1, 2006]
    [ QUOTE ]
    cough cough

    [/ QUOTE ]

    Idiots. /ubbthreads/images/graemlins/laugh_2.gif
  39. dummi
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    dummi smoking a6

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    [Apr 1, 2006]
    haha that skate board video is funny, how can a several thousand horse power jet engine be compared to thrust of a 30 watt fan, the friction in the bearings of the skate board would hardly be overcome its like the old magician pulling the table cloth from under dinning set

    there is no friction between the plane and the belt, the wheels may burn up or skid with the conveyer belt moving to match speed but wouldn't do anything, the sheer thrust of the jets would push the plane forward, then as we know with bunoulis principle generated lift on the wings moving forward

    this thread needs to die now, we have the answer from professors listed, anyone disagreeing is for the sake of it /ubbthreads/images/graemlins/laugh.gif
  40. audi5e
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    audi5e Member

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    [Apr 1, 2006]
    [ QUOTE ]
    [ QUOTE ]
    Think of it like you running on a tread mill when you are running at say 7 mph and the belt is turning at the same speed you do not move. You also do not feel the wind in your face because you are not moving.


    [/ QUOTE ]

    when you run your feet provide a backwards force on the ground, which results in a forwards force on YOU. granted this would not work eg bicycle with wings on type plane. BUT a real plane exerts a force backwards on the air, so it experiences a force forwards from the air (Newt .3rd law)) if it pushes air backwards it will be pushed forwards, if the push is bigger than any friction it will accelerate, all that happens is that the conveyor belt also accelerates.
    I don't think anyone is saying the plane will stay still and take off, but that it will move forwards and hence create lift etc.

    Imagine a rocket strapped to a toy car on a very fast shopping conveyor belt. it. if placed on the belt after the rocket is lit it will mmove forwards.
    Chas

    [/ QUOTE ]

    Sure, it will work, IF you are prepared to ignore the condition stated in the question. If you change the question to read that the wheel is allowed to overcome the rearward motion of the conveyor then you no longer have equilibrium and the plane will take off, since it is no longer constrained.... In effect you now have the same effect as a normal runway with the exception that the aircraft's power source consumes more energy to propel the aircraft against the direction of the conveyor. An interesting point is that because of this the effective ground speed (conveyor speed) has to be higher to achieve enough air speed...so a normal aircraft needs to be doing say 160km/h to get enough lift on the wing, whereas if it were travelling on a conveyor it would have to add the rearward speed of the conveyor to the airspeed to achieve enough airspeed.... :)

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