RDFan said:
Bingo which is why I say the question as postulated is impossible 😉 although see my later post too 😉 with different interpretations of what speed means in the question 🙂
Tony.
Well there are alot of possibilities all with various degrees of reality mixed in.
The simple fact is (since we are not talking about a VTOL) if the plane moves forward relative to the air around it and is able to accelerate to sufficient air speed then IT WILL take off. Otherwise it wont. Period. End of story.
Something not yet considered (at least I didn't see it) is that if there is less resistance to move the belt than to move the wheels then the wheels won't move (well not much) and the belt will move instead of the wheels. In this case the plane takes off.
The simple fact is (since we are not talking about a VTOL) if the plane moves forward relative to the air around it and is able to accelerate to sufficient air speed then IT WILL take off. Otherwise it wont. Period. End of story.
Something not yet considered (at least I didn't see it) is that if there is less resistance to move the belt than to move the wheels then the wheels won't move (well not much) and the belt will move instead of the wheels. In this case the plane takes off.
But..as you say....it's all irrelevant because the plane is not in any way shape or form dependant on the wheels for propulsion.
The plane is already in Paris and the passengers are laughing their ****s off at the people still arguing in outer mongolia!
The plane is already in Paris and the passengers are laughing their ****s off at the people still arguing in outer mongolia!
It seems that so many irrelevant matters are still dominating this discussion, and some quite unnecessary, and possibly inappropriate science is also confusing the issue.
eVITAERC continues to assert that rockets and planes are the same (or "equal") in their general principles of flight, but they are *not*! They are nothing like the same, and in this context, they should not even be compared.
When he checks back with his Guru, he will discover this simple fact, and perhaps he will then stop implying that this person believes this, or whatever. I can only think he misunderstood what he heard, which seems to be apparent with several other misunderstandings being obvious in his posts.
As I pointed out earlier, their basic means of flying (i.e.defying gravity) or taking off, are quite different. Rockets rely solely on thrust, which is how they can travel for millions of miles in space without *any* air being present, whereas planes cannot. As it is simply due to this thrust which enables rockets to leave the ground, their shape has no real bearing on the matter, unlike planes which rely entirely on the airfoil sections of their wings which provide the necessary 'lift' to get them (and keep them) in the air.
Planes rely on the *passage of air past their wings* for this lift, and they cannot still stay in flight when the air becomes rare or non-existent, such as in space.
Also, for what is worth, eVITAERC doesn't appear to appreciate that most of the "rolling resistance" to which he refers with plane wheels is actually due to tyre deformation which will occur whenever a loaded wheel *revolves* on whatever it is standing on, irrespective of whether that happens also to be moving. However, as already pointed out, any such resistance or friction (again in any normal situation) will be orders of magnitude below the other forces involved in planes taking off, and will not greatly affect the issue.
There was no mention in the original question of "rockets". It was a plane and its ability to take off, so maybe it would be wiser to forget rockets for now, until eVITAERC's Guru (or anyone else who understands the principles of flight relating to *aircraft*) confirms the basic differences which I have outlined above.
In post 144, further confusion has arisen by the suggestion that some forward movement of the plane is needed for take-off or sustained flight, but I have also pointed out earlier, this is not the case, either. In a wind tunnel, for example, planes are tested for their lift and certain 'flying' characteristics, and yet the planes are completely static (horizontally) relative both to the ground, and to the surface on which they rest. Indeed they need to be 'tied down' securely in order to restrain them from rising.
The only criteria here is that air (or wind) needs to be passed over and under the plane's wings at sufficient speed that the lift caused by this passage of air exceeds the gravitational pull, and the plane will rise (or take off) entirely irrespective of the ground's relative position, or any possible movement of its immediate surface.
The question states there is no wind, and there is no mention either of any restraining devices which would prevent the plane from moving forward relative to *the surrounding air*, until it finally takes off, exactly as with all aircraft during any other normal event.
eVITAERC continues to assert that rockets and planes are the same (or "equal") in their general principles of flight, but they are *not*! They are nothing like the same, and in this context, they should not even be compared.
When he checks back with his Guru, he will discover this simple fact, and perhaps he will then stop implying that this person believes this, or whatever. I can only think he misunderstood what he heard, which seems to be apparent with several other misunderstandings being obvious in his posts.
As I pointed out earlier, their basic means of flying (i.e.defying gravity) or taking off, are quite different. Rockets rely solely on thrust, which is how they can travel for millions of miles in space without *any* air being present, whereas planes cannot. As it is simply due to this thrust which enables rockets to leave the ground, their shape has no real bearing on the matter, unlike planes which rely entirely on the airfoil sections of their wings which provide the necessary 'lift' to get them (and keep them) in the air.
Planes rely on the *passage of air past their wings* for this lift, and they cannot still stay in flight when the air becomes rare or non-existent, such as in space.
Also, for what is worth, eVITAERC doesn't appear to appreciate that most of the "rolling resistance" to which he refers with plane wheels is actually due to tyre deformation which will occur whenever a loaded wheel *revolves* on whatever it is standing on, irrespective of whether that happens also to be moving. However, as already pointed out, any such resistance or friction (again in any normal situation) will be orders of magnitude below the other forces involved in planes taking off, and will not greatly affect the issue.
There was no mention in the original question of "rockets". It was a plane and its ability to take off, so maybe it would be wiser to forget rockets for now, until eVITAERC's Guru (or anyone else who understands the principles of flight relating to *aircraft*) confirms the basic differences which I have outlined above.
In post 144, further confusion has arisen by the suggestion that some forward movement of the plane is needed for take-off or sustained flight, but I have also pointed out earlier, this is not the case, either. In a wind tunnel, for example, planes are tested for their lift and certain 'flying' characteristics, and yet the planes are completely static (horizontally) relative both to the ground, and to the surface on which they rest. Indeed they need to be 'tied down' securely in order to restrain them from rising.
The only criteria here is that air (or wind) needs to be passed over and under the plane's wings at sufficient speed that the lift caused by this passage of air exceeds the gravitational pull, and the plane will rise (or take off) entirely irrespective of the ground's relative position, or any possible movement of its immediate surface.
The question states there is no wind, and there is no mention either of any restraining devices which would prevent the plane from moving forward relative to *the surrounding air*, until it finally takes off, exactly as with all aircraft during any other normal event.
I think I may be reading it differently then everyone else, but the question states that the belt matches the speed of the wheels, in the opposite direction of rotation.
So, say speed is in m/s. Since the question doesn't explicitly state angular velocity, and speed usually refers to linear travel, I assume that the question is saying that if the wheel were traveling forward at 10m/s, the conveyor would be traveling the opposite direction at 10m/s. The wheel would spin twice as fast as normal, but the plane would still take off.
Doesn't it all depend on how you interpret the question? If by exactly match the speed of the wheels the question means match them in RPM, wouldn't the plane go flying off the back of the runway?
quickshift said:
So, say speed is in m/s. Since the question doesn't explicitly state angular velocity, and speed usually refers to linear travel, I assume that the question is saying that if the wheel were traveling forward at 10m/s, the conveyor would be traveling the opposite direction at 10m/s. The wheel would spin twice as fast as normal, but the plane would still take off.
Doesn't it all depend on how you interpret the question? If by exactly match the speed of the wheels the question means match them in RPM, wouldn't the plane go flying off the back of the runway?
Please listen to what people are saying...please...the wheel thing is a red herring and totally and completely irrelevant to the movement of the plane.....please?
Imagine if you will a plane with the breaks on....eventually the thrust of the engines will drag the undercarriage along the runway...yes?....then you can now see the total irrelevance of the wheels....yes?
The plane will lift off...and that is the answer to the question..try not to get sidelined....
Imagine if you will a plane with the breaks on....eventually the thrust of the engines will drag the undercarriage along the runway...yes?....then you can now see the total irrelevance of the wheels....yes?
The plane will lift off...and that is the answer to the question..try not to get sidelined....
Mr Teal,
Regarding your last sentence, it shouldn't make any difference because the wheels on a plane are free to revolve at any (sane!) speed, unless the brakes are applied, or there is some very unusual friction somewhere, which isn't implied in the question.
Wheels and brakes on all 'normal' aircraft are designed to cope with many times any expected 'normal' speed of revolving, anyway.
Of course, as you say, it does depend on how any question is read and ultimately understood, but in this case nothing other than the fact that the 'belt' can and does revolve under the plane is mentioned (as being out of the ordinary in this case) and one needs to make some reasonable assumptions here, or the entire question becomes nonsensical.
Regarding your last sentence, it shouldn't make any difference because the wheels on a plane are free to revolve at any (sane!) speed, unless the brakes are applied, or there is some very unusual friction somewhere, which isn't implied in the question.
Wheels and brakes on all 'normal' aircraft are designed to cope with many times any expected 'normal' speed of revolving, anyway.
Of course, as you say, it does depend on how any question is read and ultimately understood, but in this case nothing other than the fact that the 'belt' can and does revolve under the plane is mentioned (as being out of the ordinary in this case) and one needs to make some reasonable assumptions here, or the entire question becomes nonsensical.
*shrug* Who knows, I could be completely offbase here. I see the question as being a fairly simple "trick" question designed to trip people up in the fact that the wheels of a plane don't power it. As it's worded, it would seem that the plane would take off while something driven by its wheels would remain motionless.
I try to avoid making things more complicated than they need to be, and since the question doesn't appear to be implying any more complexity than that, I think people are just trying too hard. Unfortunetly, the original questioner is not here, so we can't ask for clarification.
I try to avoid making things more complicated than they need to be, and since the question doesn't appear to be implying any more complexity than that, I think people are just trying too hard. Unfortunetly, the original questioner is not here, so we can't ask for clarification.
Bobken said:
Given that the question stated no wind then the only other way to get upto the required air speed is indeed forward movement. But yes I agree, the original question is very poorly formed and is more or less irrelevant to any semblance of reality.
And yes thinking logically, my guess is that the wheels (if they turn at all) will turn at twice the normal speed and the plane move forward, accellerating until it takes off... otherwise, (if the wheels don't move) the belt will move forward instead of backwards and the plane will still take off. There are more red herrings in this thread than should be legal.
Hi all,
That is exactly been my point all along. The wheels are thrown in to confuse the issue. By their very design, they are free to rotate. Therefore, the plane is free to move in response to the force applied to the surrounding air by it's engines.
It takes off. I don't care if the wheels rotate at 2X speed, or not at all. To argue otherwise indicates a belief that powered flight has not been invented.
Ask yourself but one question. Is the friction in the wheel system high enough to stop the aircraft?
-Chris
That is exactly been my point all along. The wheels are thrown in to confuse the issue. By their very design, they are free to rotate. Therefore, the plane is free to move in response to the force applied to the surrounding air by it's engines.
It takes off. I don't care if the wheels rotate at 2X speed, or not at all. To argue otherwise indicates a belief that powered flight has not been invented.
Ask yourself but one question. Is the friction in the wheel system high enough to stop the aircraft?
-Chris
Hi Dan,
You were quite right to comment on my wording here, as I have no wish to add to any existing confusion.
I was simply trying to point out that several inaccurate and 'generalised' statements had recently been made, and many of them appeared to be giving others a 'bum steer'.
The statement here also seemed potentially confusing at the time of reading it, because it appeared to me to be another 'generalisation' relating to 'lift' of planes, including perhaps under other circumstances. Having just looked at this post again, I now think I was mistaken in this view, but too many posters are getting hung up on 'the ground', and whether it is apparently moving under the plane, or whatever else, although this is entirely irrelevant to the real issue here.
Factually, it is not speed relative to the ground which governs any plane's ability to take-off, but speed in relation to the surrounding air, but, if, as I acknowledged in my following sentence there was no wind on this occasion, then 'wind-speed' and 'ground-speed' will be the same, of course.
You were quite right to comment on my wording here, as I have no wish to add to any existing confusion.
I was simply trying to point out that several inaccurate and 'generalised' statements had recently been made, and many of them appeared to be giving others a 'bum steer'.
The statement here also seemed potentially confusing at the time of reading it, because it appeared to me to be another 'generalisation' relating to 'lift' of planes, including perhaps under other circumstances. Having just looked at this post again, I now think I was mistaken in this view, but too many posters are getting hung up on 'the ground', and whether it is apparently moving under the plane, or whatever else, although this is entirely irrelevant to the real issue here.
Factually, it is not speed relative to the ground which governs any plane's ability to take-off, but speed in relation to the surrounding air, but, if, as I acknowledged in my following sentence there was no wind on this occasion, then 'wind-speed' and 'ground-speed' will be the same, of course.
I have put my thinking cap on again.
If we hypothetically assume that there is no friction in the bearings to create a drag in the "free wheeling" wheels, and that there is no delay in the reaction speed of the belt, then I believe the following to be true:
The plane will take off and the wheel speed will be the same as under regular takeoff.
I made the statement and then tried very hard to disprove it. I cannot
If we hypothetically assume that there is no friction in the bearings to create a drag in the "free wheeling" wheels, and that there is no delay in the reaction speed of the belt, then I believe the following to be true:
The plane will take off and the wheel speed will be the same as under regular takeoff.
I made the statement and then tried very hard to disprove it. I cannot
To all the people who think the plane will fly:
Can you please tell me how the plane will traverse up the conveyer belt runway?
Personally, I think this is the main issue. The wheels are not free - they must move at the same speed as the conveyer belt.
I also think wintermute (and others) are right when they say the problem is in the question. This is not a scenario that could ever happen in real life. Since the belt can 'magically and instantainiously' match the speed of the wheels at all times, the plane can not travel forward up the conveyer belt runway. Since there is also no wind, ground speed is equal to wind speed. Since you can not travel up the belt runway, you can not achieve any ground speed. Therefor no lift.
Just view the problem from the standpoint of what the wheels have to do to get ground speed (and then what they are limited to do from the scenario) and you'll see the conundrum.
Can you please tell me how the plane will traverse up the conveyer belt runway?
anatech said:
Personally, I think this is the main issue. The wheels are not free - they must move at the same speed as the conveyer belt.
I also think wintermute (and others) are right when they say the problem is in the question. This is not a scenario that could ever happen in real life. Since the belt can 'magically and instantainiously' match the speed of the wheels at all times, the plane can not travel forward up the conveyer belt runway. Since there is also no wind, ground speed is equal to wind speed. Since you can not travel up the belt runway, you can not achieve any ground speed. Therefor no lift.
Just view the problem from the standpoint of what the wheels have to do to get ground speed (and then what they are limited to do from the scenario) and you'll see the conundrum.
Hi RDFan,
Please consider the following. The belt speed has no relation to the ground speed at all.
The rotational velocity of the wheels does not matter at all either.
Accept that there is little resistance to rotation in the wheels, and with the belt with respect to ground.
Are we okay so far?
Now, given that the wheel assemblies are designed to not impede the motion of the plane, the motion of the belt becomes completely unimportant within reason. Also, since the propulsion acts on the surrounding air, and not the wheels, the plane must accelerate forward. At some point the airflow across the wings generate enough lift to leave the belt. Just like on a real runway. We don't care if the wheels go one way and the other even. It really does not matter.
-Chris
Please consider the following. The belt speed has no relation to the ground speed at all.
The rotational velocity of the wheels does not matter at all either.
Accept that there is little resistance to rotation in the wheels, and with the belt with respect to ground.
Are we okay so far?
Now, given that the wheel assemblies are designed to not impede the motion of the plane, the motion of the belt becomes completely unimportant within reason. Also, since the propulsion acts on the surrounding air, and not the wheels, the plane must accelerate forward. At some point the airflow across the wings generate enough lift to leave the belt. Just like on a real runway. We don't care if the wheels go one way and the other even. It really does not matter.
-Chris
Let's try this:
The engines begin to rev up, the plane begins to move through the AIR not over the ground (I believe this to be the biggest stumbling block in this thread) because it is not coupled to the ground it is simply supported from the ground by the landing gear. So it begins to move at let's say 1 unit of speed.
The wheels as a REACTION to this, move at the same speed as the plane through the AIR. 1 unit of speed.
The belt reacts and moves in the opposite direction at 1 unit of speed. The plane is moving forward because it is not coupled to the ground it is being pushed through the AIR.
This cycle repeats it self until the plane reaches it's takeoff speed of say 200 units, the wheels as a REACTION will be moving at 200 units and so will the belt.
The other and really easy way is to think of it is well, if the wheels and belt are decoupled and reactionary, the thrust has to go somewhere, and if it's comin' out the back then I guess the planes moving forward.
The engines begin to rev up, the plane begins to move through the AIR not over the ground (I believe this to be the biggest stumbling block in this thread) because it is not coupled to the ground it is simply supported from the ground by the landing gear. So it begins to move at let's say 1 unit of speed.
The wheels as a REACTION to this, move at the same speed as the plane through the AIR. 1 unit of speed.
The belt reacts and moves in the opposite direction at 1 unit of speed. The plane is moving forward because it is not coupled to the ground it is being pushed through the AIR.
This cycle repeats it self until the plane reaches it's takeoff speed of say 200 units, the wheels as a REACTION will be moving at 200 units and so will the belt.
The other and really easy way is to think of it is well, if the wheels and belt are decoupled and reactionary, the thrust has to go somewhere, and if it's comin' out the back then I guess the planes moving forward.
Ok lets try this:
replace "speed" with "RPM".
replace wheels and belt with meshed gears of equal size.
Now, if you pull with an outside force (airplane engine, rope, whatever) on the upper gear, it will want to roll over the lower gear. We're not driving the gear, just pulling on it.
But the stipulation is that the whell speed must match belt speed.
So, substitute gears at same RPM:
The upper gear can not climb the lower one without rotating faster than the lower.
Stipulation violated.
No progress is made, plane remains grounded.
Max
replace "speed" with "RPM".
replace wheels and belt with meshed gears of equal size.
Now, if you pull with an outside force (airplane engine, rope, whatever) on the upper gear, it will want to roll over the lower gear. We're not driving the gear, just pulling on it.
But the stipulation is that the whell speed must match belt speed.
So, substitute gears at same RPM:
The upper gear can not climb the lower one without rotating faster than the lower.
Stipulation violated.
No progress is made, plane remains grounded.
Max
maxro said:
It appears you have now coupled the wheels with the motion of the plane which we know is incorrect.
EDIT:
I reread and realize that is not what you were saying
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