Peter Beeney Posted October 16, 2016 Share Posted October 16, 2016 I think I might argue with the same conviction that plane wouldn’t move forward, it would stand still. Relative to the observer and the surrounding air, that is. Belt moving backwards at 150 mph, that must now mean that the point of contact under the tyre is also moving backwards at 150 mph. The 150 mph worth of jet thrust is simply now holding the plane steady against that. The wheels are still turning at 150 mph. The belt is having to apply a similar worth of thrust backwards. Top kit, these Turnigy brushless motors! The post implies that the plane takes off normally regardless of any sort of movement underneath the wheels. That being so, then how is our stalwart runner on the treadmill able maintain equilibrium between himself and the backwards moving belt? Why doesn’t he simply keep running into the stand in front of himself? Eye of newt, and toe of frog, and all that… We should have a nice thick brew by Halloween… PB Quote Link to comment Share on other sites More sharing options...
John F Posted October 16, 2016 Share Posted October 16, 2016 Posted by Gary Manuel on 16/10/2016 08:56:55: Posted by John F on 16/10/2016 08:22:26: Posted by Gary Manuel on 15/10/2016 23:50:29: Sorry Ted, I'm running out of ways to explain, but I can assure you that the plane will take off. As I said right from the beginning, the question is designed to confuse and cause a debate. Sorry but the question is designed to fish for distractions it has got it in bucket loads by folk adding various factors, therefore straying from the question. If the plane wheels, and therefore, the plane moves forward and the treadmill moves backwards to negate this forwards movement how acan the aircraft ever get airflow over the wing to take off? By the wheels spinning faster - the sum of the forwards moving plane wheels and the belt. i.e. 2 x the planes speed. The wheels spinning faster? But the treadmill also moves to absorb the speed, so how does the plane get in the air if it stationary? Some have mentioned directional velocity, but that's meaningless when the treadmill absorbs that movement, 150 mph wheel speed and 150 mph treadmill speed = 0 mph actual, not 300 mph!! if the plane is static there's no airflow over the wing. Edited By John F on 16/10/2016 11:03:03 Quote Link to comment Share on other sites More sharing options...
ron evans Posted October 16, 2016 Share Posted October 16, 2016 And another thing....when the747 takes off things don't stop there. It accelerates to 570 mph,with wheels firmly attached, and so does the poor old conveyor in the opposite direction, and continues at that speed for hours until the 747 lands at its' destination ! Can't see this conveyor thingy catching on Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted October 16, 2016 Share Posted October 16, 2016 The crucial difference between the treadmill and the plane is where the opposing forces meet On a treadmill the runners legs react against the moving conveyor belt, so his forwards motion is counteracted by the belt (if the two are equal) The aircraft does not react against the conveyor its thrust reacts against the air As the engines will develop the same forwards propulsion force if the aircraft is on the conveyor or not the aircraft is forced forwards regardless of what the belt is doing The wheels of the aircraft are the only interface between the power of tge belt and the power of the plane, as they are free wheeling they are unable to prevent the aircraft moving forwards For the aircraft to remain stationary the wheels would have to absorb and disipate the entire force of the planes engines (as energy cannot be lost) how do they do that? Quote Link to comment Share on other sites More sharing options...
Megawatt Posted October 16, 2016 Share Posted October 16, 2016 Posted by Peter Beeney on 16/10/2016 10:49:22: I think I might argue with the same conviction that plane wouldn’t move forward, it would stand still. Relative to the observer and the surrounding air, that is. Belt moving backwards at 150 mph, that must now mean that the point of contact under the tyre is also moving backwards at 150 mph. The 150 mph worth of jet thrust is simply now holding the plane steady against that. The wheels are still turning at 150 mph. The belt is having to apply a similar worth of thrust backwards. Top kit, these Turnigy brushless motors! The post implies that the plane takes off normally regardless of any sort of movement underneath the wheels. That being so, then how is our stalwart runner on the treadmill able maintain equilibrium between himself and the backwards moving belt? Why doesn’t he simply keep running into the stand in front of himself? Eye of newt, and toe of frog, and all that… We should have a nice thick brew by Halloween… PB Ok One last time (this time I mean it) Yes the bottom of the wheel is in contact with the belt and is moving back at 150mph relative to the air No the axle is not stationary it is moving relative to the air at 150mph - and 300mph relative to the belt - it is revolving twice as fast as on a stationary runway remember The top of the wheel is moving at 300 mph relative to the air and 450 mph relative to the belt Draw it out if you want to - I did Once again your man on the treadmill can only derive his thrust from the belt which reacts to his movement such as to keep him there - the 747 has no such constraint. A final example - not that it will do any good if you do not believe your own eyes watching the mythbusters video - Consider a car, in neutral on a rolling road with the brakes off. The road is moving at 30mph and the car is held stationary by a rope attached to something off the rolling road in front of it. Now then the something it is attached to is a winch which begins to shorten the rope at 5mph - the rolling road compensates by increasing its speed to 35mph. Are you really saying that the car will not be winched off the road! That really is it for me - I'm off back to lurking. Edited By Megawatt on 16/10/2016 11:14:44 Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by ron evans on 16/10/2016 11:06:31: And another thing....when the747 takes off things don't stop there. It accelerates to 570 mph,with wheels firmly attached, and so does the poor old conveyor in the opposite direction, and continues at that speed for hours until the 747 lands at its' destination ! Can't see this conveyor thingy catching on No but wouldn't that be great? Other planes could drive onto the the moving belt using the thrust from their engines and then apply their brakes and achieve a take off speed of 570mph in the the opposite direction to the first plane and all powered by the first plane that is still in flight Quote Link to comment Share on other sites More sharing options...
bouncebounce crunch Posted October 16, 2016 Share Posted October 16, 2016 well you lot have lost your marbles. you must take wind direction, curvature of the earth, thermals, noise restrictions and global warming into the equations. what brand of tyre? some are terrible others great. Is the pilot's Mother in law sitting in the flight engineers seat? was the pilot reading RCM&E when he should have been watching wheel speed? Quote Link to comment Share on other sites More sharing options...
Mike Phillips 4 Posted October 16, 2016 Share Posted October 16, 2016 The aircraft would take off. Jet engines work by the thrust of the efflux . Newton states that for every action ,ie thrust , there is an equal but opposite reaction. The aircraft, complete with engines is effectively pushing against the air, (which is independent of the moving conveyor belt.) The wheels would rotate at twice their normal takeoff speed (assuming the bearings/tyres would stand it!) The wheel drag would naturally be increased (tyre and bearing) but this is minimal compared with the several tens of thousands of pounds thrust the engines produce. As has been said before, takeoff would occur. Quote Link to comment Share on other sites More sharing options...
bouncebounce crunch Posted October 16, 2016 Share Posted October 16, 2016 Mythbusters usa had a conveyer belt takeoff with a kitfox type aeroplane. Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 A thought accurred to me while I was watching the Sunday Politics show, which was ironically about new runways at Gatwick and Heathrow. Imagine our 747 had different sized front wheels to the rear wheels (they are actually all the same). Lets say the main tyres are 56 inches diameter and the front tyres are 40 inches diameter. If our plane accellerated to 150mph, would both sets of wheels be moving at the same speed or at different speeds? Bare in mind that they are all attached to the plane and all in contact with the belt. This is actually the crux of the argument and both camps will give a different answer, but it will highlight where the difference of opinion comes from. Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by bouncebounce crunch on 16/10/2016 11:50:39: Mythbusters usa had a conveyer belt takeoff with a kitfox type aeroplane. Yes there's a link to it a couple of pages back. Quote Link to comment Share on other sites More sharing options...
bouncebounce crunch Posted October 16, 2016 Share Posted October 16, 2016 https://youtu.be/YORCk1BN7QY try this link for the experiment video. Edited By bouncebounce crunch on 16/10/2016 11:59:06 Quote Link to comment Share on other sites More sharing options...
Megawatt Posted October 16, 2016 Share Posted October 16, 2016 Posted by Gary Manuel on 16/10/2016 11:51:15: A thought accurred to me while I was watching the Sunday Politics show, which was ironically about new runways at Gatwick and Heathrow. Imagine our 747 had different sized front wheels to the rear wheels (they are actually all the same). Lets say the main tyres are 56 inches diameter and the front tyres are 40 inches diameter. If our plane accellerated to 150mph, would both sets of wheels be moving at the same speed or at different speeds? Bare in mind that they are all attached to the plane and all in contact with the belt. This is actually the crux of the argument and both camps will give a different answer, but it will highlight where the difference of opinion comes from. Ok I'll start the ball rolling Both will have the same linear speeds but will have to rotate at different RPM to achieve them Quote Link to comment Share on other sites More sharing options...
john kennedy 4 Posted October 16, 2016 Share Posted October 16, 2016 A definite NO. An aircraft wing needs lift produced from airspeed. Groundspeed makes no difference. Haven't read all the posts so might have already been said. Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted October 16, 2016 Share Posted October 16, 2016 Ok, lets try again I wear roller skates and stand on the conveyor belt there is a rope running up the length of the belt attached to something not on the belt. I hold the rope and start to pull myself along it allowing the roller skate wheels to rotate as they wish The belt speeds up in response to my movement as per the original question Now what is stopping me working my way up the rope hand over hand? Nothing at all..... The rope equates to the engine thrust acting on the surrounding air...... hence the belt will have no effect on take off which will occur normally Quote Link to comment Share on other sites More sharing options...
WolstonFlyer Posted October 16, 2016 Author Share Posted October 16, 2016 Spot on Dave, thank you 😊 Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by Megawatt on 16/10/2016 12:00:21: Posted by Gary Manuel on 16/10/2016 11:51:15: A thought accurred to me while I was watching the Sunday Politics show, which was ironically about new runways at Gatwick and Heathrow. Imagine our 747 had different sized front wheels to the rear wheels (they are actually all the same). Lets say the main tyres are 56 inches diameter and the front tyres are 40 inches diameter. If our plane accellerated to 150mph, would both sets of wheels be moving at the same speed or at different speeds? Bare in mind that they are all attached to the plane and all in contact with the belt. This is actually the crux of the argument and both camps will give a different answer, but it will highlight where the difference of opinion comes from. Ok I'll start the ball rolling Both will have the same linear speeds but will have to rotate at different RPM to achieve them Yep - that's right. There is actually enough information within my question to be able to calculate the linear and rotational speeds of all wheels and the belt. Note that the belt speed is measured in MPH. The speed of whatever the belt is matching must also be in MPH. I would be interested to hear an explanation of how the belt could match the rotation speed of a wheel which is measured in RPM. Quote Link to comment Share on other sites More sharing options...
J D 8 Posted October 16, 2016 Share Posted October 16, 2016 If you know the rolling circumference of the wheel and its rpm then you can work out what mph that vehicle would be doing.It's how speedometers in cars work. Quote Link to comment Share on other sites More sharing options...
Tim Kearsley Posted October 16, 2016 Share Posted October 16, 2016 Posted by Gary Manuel on 16/10/2016 09:20:34: Apologies - just woke up and I've been listening to Andrew Marr talking about momentum. Notwithstanding my slipup, the other facts remain true. I'll go back and edit my post to avoid confusion. No problem, it's very easy to confuse the two - I always have to think twice! Cheers, Tim. Quote Link to comment Share on other sites More sharing options...
Chuck Plains Posted October 16, 2016 Share Posted October 16, 2016 LOLLLL!!! The question, if it was copied directly from Facebook was not correctly phrased. When I first saw this on the web, about 8 years ago it was phrased like this: If an airplane is on a conveyor belt runway and the runway moves backwards at exactly the same speed as the plane moves forwards, can the plane take off. And the answer is clearly yes. And yes, it is definitely a question that can ONLY BE ANSWERED BY PHYSICS. The solution. Boeing 747-8 = 266,000 lbs of thrust applied on take off surface moving backwards = one planet's worth of thrust connection of surface to the aircraft = the wheel bearings reverse thrust applied through wheel bearings = 5 lbs per wheel (guesstimated worst case) For every action there is an equal and opposite reaction. Therefore the thrust from the engines pushes the plane forwards and it WILL reach rotation speed. Any connection to the ground is eliminated by the wheels. ---------- Teehee. I work for an aerospace components maker and I asked quezzy this to a few guys at work about a month ago. 3 machine setters and one engineering manager. 2 setters in my department decided the answer was no "because the ground". One setter from the lathe turning dept said no, initially, but wait a minute, yes it can, there's no effect. He has flown RC in the past. The engineering manager? "Yes it can, there's nothing to stop it." So now we know why he's a manager. So, if you're already a manager and already answered no . . . Quote Link to comment Share on other sites More sharing options...
Chuck Plains Posted October 16, 2016 Share Posted October 16, 2016 Posted by Dave Hopkin on 16/10/2016 12:10:02: Ok, lets try again I wear roller skates and stand on the conveyor belt there is a rope running up the length of the belt attached to something not on the belt. I hold the rope and start to pull myself along it allowing the roller skate wheels to rotate as they wish The belt speeds up in response to my movement as per the original question Now what is stopping me working my way up the rope hand over hand? Nothing at all..... The rope equates to the engine thrust acting on the surrounding air...... hence the belt will have no effect on take off which will occur normally Unless you have very cheap bearings. Then you'd have t ogive an extra pound or so of pull before your skates will take off. Quote Link to comment Share on other sites More sharing options...
Chuck Plains Posted October 16, 2016 Share Posted October 16, 2016 Posted by John F on 16/10/2016 08:22:26: Posted by Gary Manuel on 15/10/2016 23:50:29: Sorry Ted, I'm running out of ways to explain, but I can assure you that the plane will take off. As I said right from the beginning, the question is designed to confuse and cause a debate. Sorry but the question is designed to fish for distractions it has got it in bucket loads by folk adding various factors, therefore straying from the question. If the plane wheels, and therefore, the plane moves forward and the treadmill moves backwards to negate this forwards movement how can the aircraft ever get airflow over the wing to take off? Ah, but it's only the imagination that says 'negate'. Even the wrongly worded question on Facebook didn't say negate. Don't explain it to yourself that way just use scientific calculation. Quote Link to comment Share on other sites More sharing options...
Chuck Plains Posted October 16, 2016 Share Posted October 16, 2016 https://www.youtube.com/watch?v=XESlDuXb_Ho If these guys, using skates without wheels can maintain speed against a tread mill, it's obvious that if the had wheels (zero friction) they could easily move forwards instantly even if the belt speeded up. Quote Link to comment Share on other sites More sharing options...
WolstonFlyer Posted October 16, 2016 Author Share Posted October 16, 2016 There are two versions of the question Chuck, neither are 'wrong' they are just worded differently. The one I posted seems to be the first google search result for '747 on a conveyor belt', sorry about wording of the title of the link, I am sure the 'big man upstairs' is not offended. **LINK** Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 16, 2016 Share Posted October 16, 2016 Gary You missed my point. What happens if the car moved the belt backwards very fast indeed. At some point the force required to stop the plane moving backward would become significant and in the extreme would equal to its thrust. Only if the wheels were frictionless (both the bearings & rolling resistance) would the belt speed have absolutely no impact on the plane and it would take off normally - actually slightly better than normal! In the real world the take off will be 'impaired' to a degree proportional to belt speed. Quote Link to comment Share on other sites More sharing options...
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