Plane on a conveyor belt

Emp_Fab

ICBM said:

Anyone who still doubts it, watch this: In this case the conveyor is replaced by a truck. The plane is not moving relative to the truck, just as the hypothetical 747 on a conveyor that matches its speed would not be.

Matches its speed IN THE OPPOSITE DIRECTION!!!!!!!!!!!!!!  In your example, the truck/conveyor belt is moving in the SAME direction.  In your example, there is movement of the plane relative to the (presumed still) air around it.  In the OP's example, the plane is moving forward just as fast as the conveyor is moving BACKWARDS - therefore the plane remains stationary relative to the ground (that the conveyor belt machinery is sitting on) and the air around it.

Picture yourself on a treadmill in a gym...  you are running forward, the treadmill is going backwards - you don't move relative to the rest of the gym do you ?  You don't feel a breeze in your face like you do if you were running along the road do you ?  Because on the treadmill, you don't move relative to the rest of the gym and neither does the air around you.  There is no movement between you and the air surrounding you.  It's exactly the same in the OP's scenario.

If you dispute this, explain to me how there is any airflow over the wings ?  @ICBM ;

Gassage

Point of order- on the belt, the wheels would be spinning at c. 480mph- twice their design speed. So they'd fall off.

Handsome_Chris

Gassage said:

Point of order- on the belt, the wheels would be spinning at c. 480mph- twice their design speed. So they'd fall off.

Not true.  In the example the wheels may be spinning but the speed has not been determined yet.

Sambostar

ICBM said:

Anyone who still doubts it, watch this:



In this case the conveyor is replaced by a truck. The plane is not moving relative to the truck, just as the hypothetical 747 on a conveyor that matches its speed would not be. If this plane had wheels, they would not be turning. So how does it fly?

Yeah, the truck acheivces airspeed, so what, that has nothing to do with the question, it's totally different.

You still don't understand the question. No ground speed can be achieved nor any acceleration as the forward thrust of the engines and acceleration is counteracted by the increasing backwards speed of the conveyor, effectively meaning that the plane is static so there is no airspeed.   Of course the wheels do nothing, but the wheels could spin past infinity, but as the question states the conveyor will match their speed so the plane effectively remains static without airspeed..  

No plane can take off  without any airspeed, or are you talking about a harrier?

Think about it this way, of you mounted a fan on the wing, it wouldn't spin at all because the plane remains relatively static so there is no airspeed.

It's a trick question to confuse people with their eyes set too close together.

Ravenous

Gassage said:

Point of order- on the belt, the wheels would be spinning at c. 480mph- twice their design speed. So they'd fall off.

Correct, but sadly some people don't accept the "747" in the question on page 1 is a real, operational 747 with all of the normal material properties. If they do, the plane's gear will be wrecked very quickly.

Gassage

Handsome_Chris said:

Gassage said:

Point of order- on the belt, the wheels would be spinning at c. 480mph- twice their design speed. So they'd fall off.

Not true.  In the example the wheels may be spinning but the speed has not been determined yet.

Chris- same speed as plane in opp direction

We know V2 is 185kts...so that's 430mph at take off, 422 at rotation. (VR)

CabbageCat

ICBM said:

Maynehead said:

You're just digging a hole for yourself now. I know you're not usually wrong about amp stuff but theoretical science is clearly not your forte.

lol

Do you know what I studied at University?


You're wrong. The end.

Do yourself a favour - next time you're in a plane, don't think too hard about what's holding you up there or you'll probably scare yourself to death .

Dude. Can you answer these question (without "it's irrelevant"):

Does the plane need to be moving forwards through the air to take off?
If the wheels are going round at 10mph and the conveyor is going at 10mph what speed is the plane going?
If the plane is actually moving forwards at 10mph and the conveyor is moving backwards at 10mph what speed are the wheels moving?

Sambostar

As for Mythbusters, that plane is accelerating with airspeed as the conveyer motion and acceleration isn't matching the speed of the wheels which is what the QUESTION STATES.  You can clearly see the plane accelerating with groundspeed as the conveyor is NOT matching it's ground speed and acceleration.

It's not a single speed conveyor, it always matches the ground speed of the wheels, as THE QUESTION STATES!  FFS.

Handsome_Chris

Gassage said:

Handsome_Chris said:

Gassage said:

Point of order- on the belt, the wheels would be spinning at c. 480mph- twice their design speed. So they'd fall off.

Not true.  In the example the wheels may be spinning but the speed has not been determined yet.

Chris- same speed as plane in opp direction

We know V2 is 185kts...so that's 430mph at take off, 422 at rotation. (VR)

It does not matter, as I posted earlier, if we have a theoretically indestructible conveyor belt, we have a theoretically indestructible plane.

Assume a can opener...

Sambostar

paul_c2 said:

I think that the question is more about how you analyse scenarios, than whether the plane will take off or not. Some people on here are quite happy to accept that the conveyor has magical properties which prevent the 747 from moving forwards when its engines are put at full thrust, then tie themselves in knots with what happens next. Basically, they are blindly accepting an impossible assumption made in the question.

The question is ridiculous, but that is the nature of these questions, you have to take the question at face value, you can't start assuming that the conveyor maxs out at a certain speed because the question doesn't state that, it states the opposite, that basically of goes on to infinity.

11 plus FAIL!

Nobody bloody read or understood the question properly.

Sambostar

And the majority of people on here voted to stay in the EU and said that the people who voted out were thick?  I give up.

Bring back apprenticeships.

You've spent all day philosophising about and mowing the wrong person's lawn.

CabbageCat

Sambostar said:

Nobody bloody read or understood the question properly.

That's a little unfair. Maynehead did.

Emp_Fab

Myranda said:

What the FUCK were they doing ??  I'm horrified - I thought they employed logic in their programme !  It's obvious from the video that the plane is moving significantly faster than the tarpaulin is moving !  If the plane's speed was matched to the opposite speed of the tarpaulin, it would not move relative to the traffic cones !!

That is shameful !!

Sambostar

CabbageCat said:

Sambostar said:

Nobody bloody read or understood the question properly.

That's a little unfair. Maynehead did.

Yeah except for him and a very few others who learnt to read

Ravenous

Handsome_Chris said:

It does not matter, as I posted earlier, if we have a theoretically indestructible conveyor belt, we have a theoretically indestructible plane.

Assume a can opener...

Where in the original question (as posted on page 1) does it say any of the equipment is indestructible?

Handsome_Chris

Ravenous said:

Handsome_Chris said:

It does not matter, as I posted earlier, if we have a theoretically indestructible conveyor belt, we have a theoretically indestructible plane.

Assume a can opener...

Where in the original question (as posted on page 1) does it say any of the equipment is indestructible?

Where does it say that it is not?

CabbageCat

Ravenous said:

Handsome_Chris said:

It does not matter, as I posted earlier, if we have a theoretically indestructible conveyor belt, we have a theoretically indestructible plane.

Assume a can opener...

Where in the original question (as posted on page 1) does it say any of the equipment is indestructible?

It doesn't really matter unless you think a plane can take off from a rapidly reversing conveyor grinding along a conveyor on its belly. Or "exploding in a ball of jet fuel" counts as "taking off".

Sporky

ICBM said:

If the conveyor was going fast enough the wheels would actually be turning *backwards* and the plane would still fly.

That can't happen given the constraints of the original puzzle. The wheels of the plane turn at the exact same speed as the conveyor is moving.

Following the original constraints:

Plane's engines start to produce thrust. Plane therefore starts to move forwards - on this I think we are agreed?

However, the conveyor belt is currently not turning. As soon as the plane starts to move forwards the plane's wheels turn - again, I think we are agreed on this - it is after all stated in the opening premise?

As soon as the wheels start moving, the conveyor belt starts turning in the opposite direction at the same speed. Thus the plane does not move forwards. The plane's engines continue to produce thrust, which moves the plane forwards, which makes the wheels turn faster. The conveyor accelerates at the same rate, so the plane does not move forwards.

The question frames an impossible situation. If you say that the plane moves forward then you are saying that the conveyor does not turn, but the question says that the conveyor does turn.

It's all very well talking about basic physics and calling people names, but this is not a question about basic physics. The question itself discounts basic physics. Every time you talk about basic physics you are effectively saying that you have not actually understood the question, and are instead answering a different question that you prefer.

I do indeed have a scientific and engineering education, but I also love logic puzzles and hypothetical questions, particularly ones that don't quite make sense. Such as this one.

Ravenous

Sporky said:

The question frames an impossible situation. If you say that the plane moves forward then you are saying that the conveyor does not turn, but the question says that the conveyor does turn.

Actually - although I'm sure you're right (and I'm one of the "no fly" people) - I think there is real physics in this question. Because I'm including wheel bearings and rolling resistance as drag forces counteracting the engine thrust.

But I really don't want to explain that here, because it's pretty obvious I won't get taken seriously!

ICBM

Sambostar said:

You still don't understand the question. No ground speed can be achieved nor any acceleration as the forward thrust of the engines and acceleration is counteracted by the increasing backwards speed of the conveyor, effectively meaning that the plane is static so there is no airspeed.

NO IT ISN'T!!

You don't understand the basic physics of powered flight.

The wheels, their speed of rotation or its direction are IRRELEVANT. The only thing that matters is the thrust and drag, which determines the airspeed. All that happens if the conveyor moves backwards is that the wheels turn faster.

Sporky said:

I do indeed have a scientific and engineering education, but I also love logic puzzles and hypothetical questions, particularly ones that don't quite make sense. Such as this one.

No it does not. It's a perfectly valid thought experiment.

It's actually a useful one, because the answer you give determines whether you understand the problem or not.


The answer to the question I asked earlier is Astrophysics and General Physics, by the way...