Let's have an argument - Argh it keeps recurring! - The Bear and Badger

davyK

If the plane moves forward at sufficient speed to generate lift from its wings it will fly.

The question is reduced to "Will it get enough speed?".

RamSteelwood

i still think it's a bit of trick question, because something being on a treadmill implies (to me anyway) that it's not moving forward. This is all just a bit of a fudge around planes being 'propelled' by moving air rather than the wheels on the ground turning, and is basically 'will a plane take off if it's wheels are spinning a bit faster than normal?'

Is this the same question/answer: a plane is on a big long (ie infinite) straight train that is basically a mobile runway, and the train is moving at the top speed of the plane. the plane is facing the opposite direction that the train is moving, and the plane is initially not moving itself (so it is moving with the train). Can it take off in the opposite direction to the train?

Bonus question, could it do an instant/vertical take off in the direction the train is heading?

Facewon

I'm with monkey around the implied question. Other than that, pretty cool thread.

New question:
If you put a plane on a conveyer belt will it be able to run cyberpunk77?

hylian_elf

Only just saw this and read first page... will wait to see answer but my guess is that the belt moving backwards actually moves the wheels forwards so plane moves and takes off?

Edit: nope, stupid. Just saw answer. Forget the wheels, my head is now spinning

hylian_elf

I'm so glad I'm not clever enough for this kinda shit otherwise I'd probably get pissed off and also get headaches and collapse or something

Yossarian

Facewon wrote:

I'm with monkey around the implied question. Other than that, pretty cool thread.

New question:
If you put a plane on a conveyer belt will it be able to run cyberpunk77?

Don’t risk it, it’ll probably crash.

GurtTractor

RamSteelwood wrote:

i still think it's a bit of trick question, because something being on a treadmill implies (to me anyway) that it's not moving forward. This is all just a bit of a fudge around planes being 'propelled' by moving air rather than the wheels on the ground turning, and is basically 'will a plane take off if it's wheels are spinning a bit faster than normal?'

Is this the same question/answer: a plane is on a big long (ie infinite) straight train that is basically a mobile runway, and the train is moving at the top speed of the plane. the plane is facing the opposite direction that the train is moving, and the plane is initially not moving itself (so it is moving with the train). Can it take off in the opposite direction to the train?

Bonus question, could it do an instant/vertical take off in the direction the train is heading?

It's not a trick question, it's just that people trick themselves into seeing nonexistant presuppositions about it. Pilots and the like seem particularly susceptible to it, it seems like one of these things that the more you understand about the physics and the cleverer you are the easier it is to trap yourself into the wrong answer.

For the train question; my guess is that yes it will eventually take off, I'm not sure exactly what effect the initial backwards moving airflow would have on the plane, it would essentially be like a very strong tailwind. I think that should subside rapidly though as the plane applies thrust and starts to roll down the length of the train, it would hit a point of being stationary relative to the ground and then continue to accelerate until takeoff speed.

For the bonus question; it could probably take off because of the sufficient airflow under the wings, however I think when something like a train moves through the air it creates it's own series of vortexes and airflows, so it might be that the train would have to travel some percentage faster than the typical takeoff speed.

Yossarian

I think it’s almost impossible to phrase the question in such a way as to not make it feel like a bit of a trick question. In order to do so, it needs to be clear in the phrasing of the question that the speed that the conveyor belt is moving isn’t necessarily going to match the speed at which the plane can move.

You could ask something like “if a plane was facing the wrong way on a conveyor belt that was programmed to match standard take-off speeds, would the plane be able to take off?”, that at least points to the answer within the question (yes, as the plane can go faster than standard take-off speed), but this almost seems to be intentionally confusingly worded, so it feels like a trick question.

poprock

I’m gonna repeat this for the hard of thinking.

Spoiler:

Ignore the bloody conveyor belt. It doesn’t matter. Ever. At all. It’s the trick part of the trick question.

poprock wrote:

The plane’s engines pull it forwards through the air, regardless of what its wheels and the conveyor belt are doing.

The conveyor is a distraction. Ignore it. The plane moves forward, accelerates and takes off just as it normally would.

GurtTractor

I think you might be missing something here Yoss, the plane doesn't need to 'go faster than standard take-off speed', it can apply the same amount of power/thrust as it would normally and it would take off.

I've been thinking about it and I don't think I actually fucked up the question, though I could be wrong. As I've said it's describing a possible physics experiment, and it has a simple answer, so I'm not sure it's really necessary to make it totally watertight to pedantry.

You could imagine a conveyor belt runway with a plane on it, there is a RADAR/LIDAR sensor at the far end on the ground that measures the forward speed of the approaching plane and sends that speed to the control system of the conveyor. As the plane moves forward the belt moves backwards under the craft as controlled by the sensor. In this scenario the plane will take off almost entirely normally.

There's another form of this question where the belt tries to match the rotation of the wheels, but because there is thrust from the plane the wheels will always be moving faster than the belt, leading to a feedback loop where the belt will go infinitely fast. If you were to attempt this in practice however with an RPM sensor on the wheel controlling the belt, and built it all as best as you could with our current technology, I think it's likely that most planes would still take off. The tires might burst or the bearings would catch fire or something, but I would wager that a plane with a decent amount of thrust would overcome the scraping and take off. Jets in particular have an obscene amount of thrust.

Yossarian

GurtTractor wrote:

I think you might be missing something here Yoss, the plane doesn't need to 'go faster than standard take-off speed', it can apply the same amount of power/thrust as it would normally and it would take off.

Only if friction doesn’t exist, otherwise it would need the thrust required for takeoff plus the thrust required to overcome the friction.

GooberTheHat

The thrust required to overcome the friction and comensate for the backward motion of the conveyor belt is much less than the trust required to propel the aircraft forwards.

It's still a silly question.

GurtTractor

Basically any decent plane will have more than enough thrust for takeoff in usual conditions, to account for tailwinds and extra cargo etc. The wheels are there to keep the plane off of the ground and minimise friction with the ground, the turning of the wheels offers very little resistance to prevent the plane from moving forward when thrust is applied.

GurtTractor

b0r1s

He sounds like one the flat earthers.

nick_md

Has no one thought to just build a giant conveyor and find out once and for all?

GurtTractor

nick_md wrote:

Has no one thought to just build a giant conveyor and find out once and for all?

b0r1s

I’m not convinced by that “experiment”. You see the plane undulating over the “belt” and aren’t they just hitting the ground underneath and getting purchase there to allow the plane to accelerate.

GurtTractor

No. The material is in between the rubber of the wheels and the tarmac of the runway. As has been explained planes have thrust against the air rather than torque through the wheels.

b0r1s

I know that planes take off from airflow and lift. But traction against the ground is needed to get that initial small amount of movement.

So if the planes weight is enough for it to push the belt against the ground, are the wheels actually pinning the belt and then jumping off from that to get the initial acceleration needed?

Yossarian

There’s no traction on the ground, the wheels aren’t powered.

GurtTractor

b0r1s wrote:

But traction against the ground is needed to get that initial small amount of movement.

This is incorrect.

poprock

Seaplanes work fine without wheels. Imagine a seaplane taking off upstream. There you go, same situation as your wheels and conveyor belt.

GurtTractor

More or less, yeah that is a perfectly good analogy. That would be a fun experimet actually as the drag from the flow of the water is probably quite a lot more than with wheels on hard surface, so you could figure out how fast a river would have to be to prevent takeoff. Not sure if that flow speed exists on the planet but it may do. If I was proper clever like I would do the maths on it.

b0r1s

poprock wrote:

Seaplanes work fine without wheels. Imagine a seaplane taking off upstream. There you go, same situation as your wheels and conveyor belt.

Ok this makes sense.

Lurch666

you need to do the monty hall puzzle next for max arguing........

GurtTractor

I just had a look at that one and it's absolutely hell on earth. I've no idea how to get an intuition of why the answer is what it is. Maybe one of you lot's brains can manage it -

Suppose you're on a game show, and you're given the choice of three doors: Behind one door is a car; behind the others, goats. You pick a door, say No. 1, and the host, who knows what's behind the doors, opens another door, say No. 3, which has a goat. He then says to you, "Do you want to pick door No. 2?" Is it to your advantage to switch your choice?

After the problem appeared in Parade, approximately 10,000 readers, including nearly 1,000 with PhDs, wrote to the magazine, most of them claiming vos Savant was wrong. Even when given explanations, simulations, and formal mathematical proofs, many people still do not accept that [redacted] is the best strategy. Paul Erdős, one of the most prolific mathematicians in history, remained unconvinced until he was shown a computer simulation demonstrating vos Savant's predicted result.

....

poprock

Yes, it’s to your advantage to switch.

You have better odds of being right this time than you had of being right the first time.

Yossarian

Yeah, I know that one. It’s one of those things that, as I’m reading an explanation of it, starts to make some fuzzy kind of sense, like a vague memory of someone’s face slowly forming in my mind, but as soon as I stop reading, the logic immediately dissipates.

GurtTractor

I start to feel a dull ache emanating from a point somewhere behind the centre of my forehead.

Plane on a conveyor belt was a piece of fucking piss.

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