Hi rpollock, Thankyou. You are right, it doesn't get any simpler. However, the problem here is that folk are making it more complex! I briefly referred to the possibility that the conveyor was going with the wheels [opposite direction of rotation mean the wheels and conveyor mesh, just like two gears]. I don't claim to have noticed this myself, teak360 pointed it out to me (thanks, Teak). But I did comment that it wouldn't make any difference - the plane will still fly. Cheers! Rich. Edit: Actually (screech!) I've made a mistake - the opposite direction of rotation of the conveyor means that its does try to drive the wheels at double speed after all, which is what we've been debating. Imagine a plane taxi-ing down a runway, you are looking side on to that runway (normal to it). A plane is moving right to left, so the wheels are rotating counter clockwise. Now just imagine a conveyor belt (we'll add the plane on top in a moment). Again, you are standing side on to the conveyor belt, and you can see the drive wheels inside it and all the rollers along its length. For a spot painted on the conveyor to be moving from right to left (i.e. what's needed to allow a plane to move r to l in relation to the earth without rolling its wheels), which way are the conveyors wheels going? They're still going counter clockwise... If the conveyor's wheels rotate in the 'opposite' direction of rotation to the plane's wheels, they'd be going clockwise in my example, and yes, indeed the conveyor would be trying to drag the plane backwards (the spot I marked on the conveyor would be moving left to right). This is what we have been debating for, er, quite some time now. I believed teak when he first mentioned the 'wheels don't turn' effect of the conveyor (I don't think he was trying to mislead anyone) - just shows how you should satisfy yourself that you understand stuff before you rely on it! Cheers! Rich.
the plane will take off. it will just have an extremely high tire speed, which has nothing to do with true airspeed.
Well before talking down to everyone you should realize that many of us in the not fly camp have thought of all of that. I do agree with you in that the plane will definately move and the wheels will be moving twice as fast. But As my Buddy who is a Captain for SOuthwest Airlines pointed out. The landing gear is only rated for about 200-250 mph and a plane takes off at around 170 so the whels cannot spin at 340 thus the landing gear will fail and the plane will not take off.
Yes some tires are rated for 225, and in this situation the tire speed will be WAY past the tire speed limit. But assuming that the tires will not fail, the plane will fly when it reaches it's take off airspeed. reguardless of tire speed.
You have stated exactly why the plane will not take off. Gentelman I think we have all come to agree the planes moevment is not conditional on wheel speed. But what most of you are not thinking about is what the limit of speed is on landing gear. My buddy who is a Southwest Airlines captain tells me it is about 200 mph. A commercial plane takes off anywhere from 140-180 thus the wheels would turn at around 300-360. Can the plane still take off? I don't think so and neither does he.
Alan, where in the question does it say it is a commercial airplane or jet airplane? You are making the assumptions, the problem is not restricted to high speed aircraft. Look at the other end of the spectrum, a J3 Cub flys at about 40mph, lets use it instead of the jet, the tire speed hits all of 80mph on the conveyer, this is not a constraining factor. Give it up. It flies! Rick
Actually, if you read the question closely, you will come to realize (as I did after initially reading the question incorrectly) that there will be no wheel spin at take off. Therefore, the speed rating of the tires is irrelevant. I was not trying to "talk down" to anybody. I was just merely making a point how intelligence sometimes "over powers" clear thought, leading to incorrect decisions and argumentative scenarios. I do agree that one should not assume unwritten information when making critical decisions based upon written instructions; however, I do not believe that in this case the question is meant to be that deep. If you make assumptions concerning this question, then of course the plane will not fly (i.e. the plane had no fuel, etc.). However, if you treat the quesiton in a rational sense, then the question and concept is interesting and educational. The plane will fly.
Yes I think certain planes will lift off but not all. I guess we'll have to agree it depends on the plane.
another hypothetical example with the same similarities. one person is wearing roller skates. this person with the skates steps onto the rear of a treadmill. while the treadmill is operating at the same exact wheel speed of the skates, ANOTHER person pushes the person with the skates forward towards the front of the treadmill. as you can see in this example forward thrust is achieved regardless of wheel speed.
well, if the plane will move it's because it's accelerating. therefore it will eventually reach it's takeoff airspeed.
Ok so you seem to think the plane will fly. Can you answer my question: Does the plane in your "will fly" scenario have the rear wheel AT the start point(horizontally speaking) when it lifts off the ground? Image Unavailable, Please Login
Hi Folks, Good to see some debate on reading extra things into the question. There are always two participants in any question/answer session - the poser of the question and the respondent(s). Here we have a few different types of respondents. If you asked the question to some seasoned jet airline pilots, who know how planes work and know what tyres are rated for, they'll see that the conveyor doesn't drag the plane back but will reckon the tyres will explode. This is what Alan has done and I agree that a normal airliner type plane with tyres rated for 200max would explode before they reached the 360 they'd be doing for a take off speed of 180. Even though I'm in the plane will fly camp, I agree that the tyres of a real jet airliner would be blown to bits and I wouldn't want to be on that plane. If you asked the question to a pilot of a J3 Cub that can take off at really low speeds and has tyres that won't explode if they turn twice as fast as usual (as rpollock states), he'll say there's no problem. If you asked the question to my six year old god-daughter, she'd say 'What's a plane? Can I have ice-cream now?' As for me, I too am reading just one extra thing into the question, that the question is hypothetical (unburstable tyres and perfect wheel bearings) as that's how I see the question - that's because I'm affected by my background of having lots of questions (even regarding real things) being posed in a hypothetical way. I support my 'take' on the question because the building of such a conveyor in the real world would be highly expensive and serve no practical purpose, that's why I treat the question as hypothetical. With a nod towards the real world, though, what if Alan posed to his pilot friends that the ground crew replaced the wheels with those from Thrust SSC, which can do in excess of 700mph rotationally. I hope they'd agree that the plane, even an airliner with 180mph take-off speed, would be OK to fly. Best regards, Rich. Edit: forgot to credit rpollock for the info on the J3 Cub... sorry!
Alan, you admit that the plane will move, and hopefully now understand (based on how the question is worded - conveyor belt moving in the opposite direction of rotation) that the wheels/tires will have no spin (therefore no failure); then what position are you taking that says the plane will not fly?
Assume a plane needs 60 feet in 3 seconds (best case) to get off the ground and has some sort of acceleration to get there. Now the conveyor belt is preprogrammed to match that 'best case' in the opposing direction. So the plane at the end of 3 seconds will still have it's rear wheels at the start point. To those saying the plane will fly, are they saying that the plane's rear wheel has lifted vertically off the start point for a moment before it took flight horizontally/diagnally? In other words for some split moment, will the rear wheel be DIRECTLY over the starting point?
Hi MHWC4S, Sadly, acehole's diagram is not correct. I appreciate him producing it, but if you look at the left/green side and imagine which way the roller that makes the conveyor turn would be turning, it is in fact the same way as the aircraft wheel but he has labelled that side as correct. Likewise the red/right side he has labelled as 'same rotation', when in fact the roller that moves the conveyor would be rotating in the opposite direction to the aircraft wheel. The aircraft has to drive on the top of the conveyor belt, so the rollers that drive the conveyor are underneath the horizontal line he has drawn. Of course, if the conveyor belt was arranged such that the plane was **inside** it - we'd have a whole different kettle of fish! (The question doesn't state the plane is on top of the conveyor - we all just assumed it because it's 'obvious'). Arrgh!! Best, Rich.
Hi Murcielago, You said you hadn't read the whole thread (and by now I don't blame you!!), so I'll summarise: The point we're making in the 'it will fly' camp is that the freely spinning wheels of the plane don't allow the conveyor to hold the plane back. It moves forward, thrusting against the air/engine exhaust gases and the backwards motion of the conveyor just makes the wheels spin faster than usual. Hope that helps! Rich
