WolstonFlyer Posted October 15, 2016 Author Share Posted October 15, 2016 I would just like to say how civilised everyone is, what a fun thread this has been, some very interesting points of discussion have been explored Edited By WolstonFlyer on 15/10/2016 17:24:18 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted October 15, 2016 Share Posted October 15, 2016 Posted by Rich2 on 15/10/2016 17:06:18: Posted by Erfolg on 15/10/2016 16:34:30: We are seeing the issues quite differently. As far as i am concerned there is a fixed relationship between the wheels velocity and the air craft. The question tells me that the linear velocity of the wheel at the point of contact is identical and opposite to the linear velocity of the conveyor belt. The question does not tell me explicitly how the aircraft is powered, it is by inference that it is the jet engines. Yet for me it does not matter. I am told if the airframe increases its velocity, there is an instant reaction of equal and opposite velocity. As far as I am concerned it is just like going on an airport travelator, walking in the wrong direction, or even on my roller skates. If my wheels rotate at the same linear velocity, i stay put. Stop the wheels I go backwards. To go forward my wheels have to have a greater linear velocity, than the linear velocity of the conveyor. Our question tells us that the wheels and the conveyor have an equal and opposite linear velocity. No, no, no! The aircraft is driven completely independent of the wheels. The wheels will merely turn faster. I asked my wife this question last night, and to my amazement she said that the aircraft would take off of course, because the wheels aren't driven - I was gobsmacked ! That's a good woman you have their Rich - hang on to her! BEB Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted October 15, 2016 Share Posted October 15, 2016 PB. BEB is right. The point is that the wheels can rotate at a rate faster or lower than the speed of the conveyor by either advancing or retreating on it. If that wasn't the case a plane would stand still on a runway and couldn't move. The runway is a stationary conveyor belt. Quote Link to comment Share on other sites More sharing options...
Rich too Posted October 15, 2016 Share Posted October 15, 2016 Posted by WolstonFlyer on 15/10/2016 17:08:51: That's a good lady you have there. Ok my personal answer is that the plane will take off. Has everyone had enough yet? Quote Link to comment Share on other sites More sharing options...
Rich too Posted October 15, 2016 Share Posted October 15, 2016 Posted by Biggles' Elder Brother - Moderator on 15/10/2016 17:27:19: Posted by Rich2 on 15/10/2016 17:06:18: Posted by Erfolg on 15/10/2016 16:34:30: We are seeing the issues quite differently. As far as i am concerned there is a fixed relationship between the wheels velocity and the air craft. The question tells me that the linear velocity of the wheel at the point of contact is identical and opposite to the linear velocity of the conveyor belt. The question does not tell me explicitly how the aircraft is powered, it is by inference that it is the jet engines. Yet for me it does not matter. I am told if the airframe increases its velocity, there is an instant reaction of equal and opposite velocity. As far as I am concerned it is just like going on an airport travelator, walking in the wrong direction, or even on my roller skates. If my wheels rotate at the same linear velocity, i stay put. Stop the wheels I go backwards. To go forward my wheels have to have a greater linear velocity, than the linear velocity of the conveyor. Our question tells us that the wheels and the conveyor have an equal and opposite linear velocity. No, no, no! The aircraft is driven completely independent of the wheels. The wheels will merely turn faster. I asked my wife this question last night, and to my amazement she said that the aircraft would take off of course, because the wheels aren't driven - I was gobsmacked ! That's a good woman you have their Rich - hang on to her! BEB I intend to Quote Link to comment Share on other sites More sharing options...
Bob Burton Posted October 15, 2016 Share Posted October 15, 2016 "The point is that the wheels can rotate at a rate faster or lower than the speed of the conveyor by either advancing or retreating on it." Not according to the original post. Quote Link to comment Share on other sites More sharing options...
Megawatt Posted October 15, 2016 Share Posted October 15, 2016 Erfolg - please put me out of my misery and admit this is a wind up. It is so blindingly obvious that if I run alongside and push you on your skates on the travelator that you would have a linear velocity equal to mine that I can only conclude that your answer was just to keep the thread rolling. I call Troll and suggest that if you want to indicate that I am wrong you reply to the simple direct closed questions I have asked without introducing yet more technobabble to obfuscate the issue. Sorry Erfolg I read Andy48's reply as yours on my phone please ignore the Troll call above I can see now you have yet to reply Edited By Megawatt on 15/10/2016 18:50:09 Quote Link to comment Share on other sites More sharing options...
ted hughes Posted October 15, 2016 Share Posted October 15, 2016 It seems everyone has a theory and a different answer, how can we reach a consensus? Quote Link to comment Share on other sites More sharing options...
Pete B Posted October 15, 2016 Share Posted October 15, 2016 Posted by Megawatt on 15/10/2016 18:25:30: Erfolg - please put me out of my misery and admit this is a wind up. I call Troll and suggest that if you want to indicate that I am wrong you reply to the simple direct closed questions I have asked without introducing yet more technobabble to obfuscate the issue. No, Erf's his normal self - once you've read a thousand or two of his posts you'll realise that.... Besides, we all love him and wouldn't want it any different.... Pete Quote Link to comment Share on other sites More sharing options...
Josip Vrandecic -Mes Posted October 15, 2016 Share Posted October 15, 2016 So far, I always thought that the plane must have a buoyancy that would rise, which means that it needs to achieve the necessary speed for take-off. If something interferes to achieve takeoff speed, the plane will never ...airborne... You brought me into a doubt, because here, on the forum, has trained aero-engineer.. so I will wait for the outcome to the right answer ... hopefully soon ... Thanks for your time. Quote Link to comment Share on other sites More sharing options...
Rich too Posted October 15, 2016 Share Posted October 15, 2016 How many examples do we need? If the drive is independent of the wheels and conveyor belt, it will take off. A glider tug (not on a conveyor belt) towing a glider that is placed on a conveyor belt whose speed equals the gliders main wheel. Will the tug take off while the glider remains stationery on the conveyor belt? Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 15, 2016 Share Posted October 15, 2016 Well I've had a great day flying. All planes managed to take off without sliding backwards, so I'm a happy bunny. Glad to see you are still at it. I'm guessing this thread will reach 20 pages before the penny finally drops on the remaining "No" campaigners. I hope none of them take offence at being eventually proved wrong. The question was designed to get people wound up because it exploits the different perspective people have of the scenario. It can be very difficult to change the way you see something in your "minds eye". Until they finally see the relationship between the thrust acting on the plane and the belt force acting on the WHEELS, they will continue to see it the same way and be convinced that they are right. Quote Link to comment Share on other sites More sharing options...
Megawatt Posted October 15, 2016 Share Posted October 15, 2016 Posted by Pete B - Moderator on 15/10/2016 18:50:17: Posted by Megawatt on 15/10/2016 18:25:30: Erfolg - please put me out of my misery and admit this is a wind up. I call Troll and suggest that if you want to indicate that I am wrong you reply to the simple direct closed questions I have asked without introducing yet more technobabble to obfuscate the issue. No, Erf's his normal self - once you've read a thousand or two of his posts you'll realise that.... Besides, we all love him and wouldn't want it any different.... Pete Indeed -that is what makes the debate worthwhile Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted October 15, 2016 Share Posted October 15, 2016 Colin, Bob Burton’s little sentence says it all, really. Keeping to the rules of the original question, which is - The conveyor is designed to exactly match the speed of the wheels, moving in the opposite direction. So the statement - "The point is that the wheels can rotate at a rate faster or lower than the speed of the conveyor by either advancing or retreating on it." is rather totally nullified as far as I’m concerned, I’m afraid. If I accepted that then I’d have to accept any statement about anything. There is another little statement in another post - When the aircraft reaches 5mph the conveyor will be going in the opposite direction at 5 mph resulting in the wheels moving at 10mph relative to the belt so we have movement of the aircraft while the original statement is still true. This seems to be a common theme. Taking a closer look; ‘When the aircraft reaches 5mph the conveyor will be going in the opposite direction at 5 mph’ I have have difficulty with this for a start. The aircraft will have to have accelerated from zero through 1 - 2 - 3 - 4 up to 5 mph. What has the belt been doing meantime though? The question says that too has been accelerating at exactly the same speed and at the same time but in the opposite direction. Had this not been so, as in standard runway, then the plane would’ve accelerated normally but because it’s trying to move forward on a surface that’s moving backward at the same magnitude then the nett result must surely be that the plane’s still standing there and not going anywhere soon. The real clue must be that the wheels are in contact with the surface all the time and their rotation is strictly controlled by what the plane and the surface are doing; they cannot turn freely on their own. But I have to emphasise that this is only my view. Now this part - ‘resulting in the wheels moving at 10mph relative to the belt’. If I can go back for a moment to the microlight powered car at the oak tree, we left them moving at 50 mph in opposite directions. So are the wheels now turning at 100 mph? Not so, I’m afraid, it’s a mere 50 mph, the car is stationary relative to the tree and the road is moving underneath them at 50 mph. Thus they can only turn at this 50 mph. The saga continues… PB Quote Link to comment Share on other sites More sharing options...
Stuart C Posted October 15, 2016 Share Posted October 15, 2016 It all depends on the interpretation of "wheel speed" and "opposite direction". It is easy to think of wheel speed as being the axel translation speed - in which case we have a completely different scenario. The conveyor must now go ever faster to give the wheel mass the necessary acceleration to balance the a/c engine thrust via the reactive component through the axel. This is enhanced as the wheel mass increases near the speed of light, and the plane disappears into a black hole without ever taking off! Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted October 15, 2016 Share Posted October 15, 2016 I've had a re-think............... I am now sure the plane stays perfectly still but the conveyor belt takes off............... Quote Link to comment Share on other sites More sharing options...
Megawatt Posted October 15, 2016 Share Posted October 15, 2016 Ok what does the original question not say - it does not say that the conveyor moves in the opposite direction so as to render the plane stationary - because that would be impossible the conveyor has no means to achieve that. What it says is that it will travel at an equal speed (note this implies that the 747 is moving, speed being distance moved over time) in the opposite direction, So the original question allows for the 747 to be moving in one direction whilst the conveyer moves in the other resulting in the rotation of the wheels at the correct rpm to result in no skidding. I really can't see why this is so difficult to grasp. Quote Link to comment Share on other sites More sharing options...
Geoff S Posted October 15, 2016 Share Posted October 15, 2016 A few years ago this same question cropped up on the RCMF web site and generated an equally big response. Now when someone asks a question that starts to get complicated eventually the conveyor belt gets mentioned and everyone has a good laugh. Geoff Quote Link to comment Share on other sites More sharing options...
Tony Bennett Posted October 15, 2016 Share Posted October 15, 2016 **LINK** Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 15, 2016 Share Posted October 15, 2016 ALL Please don't ignore Tony's link above. It is NOT the old toy Mythbuster video. It is a full size plane and the findings back up the physics. Please watch it. Edited By Gary Manuel on 15/10/2016 20:51:41 Quote Link to comment Share on other sites More sharing options...
Stuart C Posted October 15, 2016 Share Posted October 15, 2016 If the wheel rolls forward at 1 mph, and I now make the conveyor move back at 1mph, the wheel speed is now 2 mph. I must now make the conveyor do 2 mph. Oh no! This is a divergent series with no end ( unlike the tortoise, which was convergent). Quote Link to comment Share on other sites More sharing options...
ted hughes Posted October 15, 2016 Share Posted October 15, 2016 Posted by Dave Hopkin on 15/10/2016 20:07:12: I've had a re-think............... I am now sure the plane stays perfectly still but the conveyor belt takes off............... Best post in the thread! Made me splutter and spill my drink! Quote Link to comment Share on other sites More sharing options...
ted hughes Posted October 15, 2016 Share Posted October 15, 2016 Posted by Gary Manuel on 15/10/2016 20:50:34: ALL Please don't ignore Tony's link above. It is NOT the old toy Mythbuster video. It is a full size plane and the findings back up the physics. Please watch it. Edited By Gary Manuel on 15/10/2016 20:51:41 The trouble with this, is that it is a different experiment. They are matchihg the speed of the plane, not the speed of the wheels. In our problem the belt matches the speed of the wheels.The plane is not moving. Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 15, 2016 Share Posted October 15, 2016 But the wheels are travelling at the same speed as the plane. If they weren't the plane would have to wait for the wheels to catch up when it got to it's destination. This is the critical bit you are missing. Think about it before you answer. Quote Link to comment Share on other sites More sharing options...
flight1 Posted October 15, 2016 Share Posted October 15, 2016 I think some people must just be related to this woman when it comes to this Quote Link to comment Share on other sites More sharing options...
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