wintermute said:
I think the intent of the question is to get smart people arguing over this ridiculous scenario.
Max
anatech said:
Hi Chris,
It's always interesting when you think you have thought of all possibilities for someone else to come up with something that you just hadn't even comtemplated, can be very enlightening 🙂 LOL at the 3 pages by morning 🙂 hope you don't dream about this stupid problem 😉
Tony.
anatech said:
The problem with this problem is that the plane has to start moving to get the wheels rolling. However, at the instant they start to roll, the belt beneath them moves in opposition, at the exact same speed.
True, it doesn't matter how fast the wheels spin. The belt will match that speed and the plane will be unable to make progress relative to the air/ earth.
Put the brakes on and the wheels and belt both stop.
Even if the plane comes to a dead stop in relation to the belt, it can not nose dive into the belt to take care of thrust from the engine.
This would require the wheels to rotate backwards in relation to the plane (won't happen due to locked brake). Or, with a locked brake, wheels roll forwards relative to the belt (not allowed). The belt would just roll fowards, or backwards keeping the plane level.
Max
Can everyone just do a simple experiment to verify that a conveyer can stop a moving, rolling wheel from moving forward completely?
Find a really long piece of paper, and a wide roll of tape. Set the paper on a table and put the roll of tape on one end of the sheet. Grab that end of the sheet and push the roll of tape forward.
Now the roll of tape has a forward moving momentum. If what everyone said about the conveyer not able to stop a forward moving wheel, then no matter how fast you pull the sheet out from under the tape you'll not be able make it stay in one place. After all, it already has a forward momentum and the conveyer can't apply a force to pull it backwards, so that momentum has to stay there and keep the wheel going forward. Conservation of momentum, right?
Okay so try it. While the roll of tape rolls forward, pull the long piece of paper out form underneath it. Try not to die in shock when you find out that you can indeed pull the paper out fast enough to stop the roll of tape from moving forward, making it just spin in one place.
Oh and Maxro, you rock 😀
Find a really long piece of paper, and a wide roll of tape. Set the paper on a table and put the roll of tape on one end of the sheet. Grab that end of the sheet and push the roll of tape forward.
Now the roll of tape has a forward moving momentum. If what everyone said about the conveyer not able to stop a forward moving wheel, then no matter how fast you pull the sheet out from under the tape you'll not be able make it stay in one place. After all, it already has a forward momentum and the conveyer can't apply a force to pull it backwards, so that momentum has to stay there and keep the wheel going forward. Conservation of momentum, right?
Okay so try it. While the roll of tape rolls forward, pull the long piece of paper out form underneath it. Try not to die in shock when you find out that you can indeed pull the paper out fast enough to stop the roll of tape from moving forward, making it just spin in one place.
Oh and Maxro, you rock 😀
The plane does not get off the ground.
Humour me and imagine this scenario.
Take a runway sized friction-free conveyer belt and place a F15 Eagle on the conveyer belt. Now take two Pratt and Whitney engines out of a second F15 Eagle and use them to power the conveyer belt.
Balance the weight to power ratios so that at xx% power, the engines powering the conveyer belt can accelerate the belt (and F15 on the belt) at EXACTLY the same rate as xx% of power the F15 engines would accelerate the F15.
Hook the F15 engines and the conveyer belt engines to a common control so that they alway output the same power.
Now, as the F15 powers up and starts to accelerate down the runway, the belt (with the F15 on it) accelerates at an equal rate in the opposite direction. The net result is the plane, relative to the earth, does not move. Therefore no lift is generated and the plane stays on the runway.
Humour me and imagine this scenario.
Take a runway sized friction-free conveyer belt and place a F15 Eagle on the conveyer belt. Now take two Pratt and Whitney engines out of a second F15 Eagle and use them to power the conveyer belt.
Balance the weight to power ratios so that at xx% power, the engines powering the conveyer belt can accelerate the belt (and F15 on the belt) at EXACTLY the same rate as xx% of power the F15 engines would accelerate the F15.
Hook the F15 engines and the conveyer belt engines to a common control so that they alway output the same power.
Now, as the F15 powers up and starts to accelerate down the runway, the belt (with the F15 on it) accelerates at an equal rate in the opposite direction. The net result is the plane, relative to the earth, does not move. Therefore no lift is generated and the plane stays on the runway.
Guy's, you're still over complicating this scenario...
Let's take the 'wheels cant rotate' statement on....
The belt moves in the opposite direction...think about it.....draw two circles, put the direction of rotation on them....bingo! They dont cancel each other out...the belt just becomes the ground under normal take off procedure...not faster not slower...exactly the same.
Then ask yourself, who cares? Th eplane is decoupled from the damn wheels by it's axle and bearings so it can go anywhere it wants......take off!
Stop trying to pull this thing apart and face the simple facts....we've cracked it...red herrings and all!
Let's take the 'wheels cant rotate' statement on....
The belt moves in the opposite direction...think about it.....draw two circles, put the direction of rotation on them....bingo! They dont cancel each other out...the belt just becomes the ground under normal take off procedure...not faster not slower...exactly the same.
Then ask yourself, who cares? Th eplane is decoupled from the damn wheels by it's axle and bearings so it can go anywhere it wants......take off!
Stop trying to pull this thing apart and face the simple facts....we've cracked it...red herrings and all!
RDfan....
The ground speed has absolutely nothing at all to do with the air speed....nothing at all..absolutely nothing at all.
The ground speed has absolutely nothing at all to do with the air speed....nothing at all..absolutely nothing at all.
OK I've just realised something......
This is never going to end as there is inevitably always going to be someone new who has only read the question....not the rest of the thread.......
This could go on for ever....I'm getting of this conveyor
Bye!
This is never going to end as there is inevitably always going to be someone new who has only read the question....not the rest of the thread.......
This could go on for ever....I'm getting of this conveyor
Bye!
Lostcause said:
You're joking right? There is no wind in this scenario - the ground speed of the plane is the EXACT same as the air speed.
Too bad, you are ending the debate - that's quite a statement to exit on Lostcause.
Go on then...explain to me how the airspeed going through the jets is coupled to the ground speed
airspeed is the speed of the plane relative to the air - NOT the speed of the air going though the jets.
Now you're getting it.....You need to think about the engines and the way they produce thrust. This has nothing to do with the wheels they meerly support the plane
Lostcause said:
Ground speed has everything to do with the plane when it is GROUNDED. Only airspeed matters fater you lift off, but whether the plane gets to that is related to its ground speed.
Since there is no wind, then if the plane doesn't move relative to ground then the plane would not have moving air passed over its wings. There would be no lift and ergo no takeoff.
You must at least think physical principles through before you apply them.
Meanwhile, I'm still waiting for someone to try my experiment.
Lostcause said:
lol. I guess it is testiment to a fantastically deceptive question.
It's amazing there isn't consensus one way or another after 200+ posts.
OK guy's, as I said you need to convince me and all the others that ground speed is related to wind/air speed, or at least to the point where it affects this scenario.
Imagine standing by a travelator that is moving towards you...
Now think about the air above it...
Now tell me that the air is being affected other than a bit of a draft caused by the resistance of the surface of the belt...
Now see which direction that draft is going
This can only add to the air speed not cancel it...
Imagine standing by a travelator that is moving towards you...
Now think about the air above it...
Now tell me that the air is being affected other than a bit of a draft caused by the resistance of the surface of the belt...
Now see which direction that draft is going
This can only add to the air speed not cancel it...
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