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Dear friends and followers, welcome back to my channel!

I’m sure you have seen this question/riddle before!
Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?

Watch the video to learn more!

Thank you very much for your time! I hope you enjoy this video!
Wishing you all the best!

Your "Captain" Joe

Big thank you to all other youtubers who provided me with the video material to create this video. Your content is highly appreciated. Please follow their channels:
@Stefan Drury
@National Geographic

Intro Song:
Lounge - Ehrling: svdown.info/post/video/l2eCnrGulrCHmas.html
Outro Song:
Joakim Karud & Dyalla - Wish you were here svdown.info/post/video/i4qrqaWbq2WGltk.html


Vetenskap och teknik

Publicerades den


4 mar 2021



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Kommentarer 100   
James K
James K 8 timmar sedan
Adam savage still believe the plane can fly but forgot something ,the wind ,a plane need a lot of wind to fly ,on conveyor belt the plane doesn't have a lot of wind except if the plane is rocket powered which make that a rocket not a plane
Matthias Hartge
Matthias Hartge Dag sedan
Line up and wait, conveyor belt 25L ^^
mohamed farook mohamed fazleen
i think that if you put a 747 on a conveyor belt, it'll simple crush the conveyor belt.
illokindom jhon
illokindom jhon Dag sedan
VEEAXIS Dag sedan
I don't know anything about aviation but my guess is that the plane won't be able to take off because there won't be enough air under the wings for the plane to take off, let's see how wrong I am :P
A C M Dag sedan
The rate of the wheel spin is irrelevant, as planes (including 747s) don't rely on wheel spin for forward propulsion. So the conveyor can run as fast as it wants, spinning the plane's wheels as fast as it wants, and the plane will still move forward, still accelerate past V-1 and to V-R, where it will lift off the conveyor belt runway.
Blue Lion Sage
Blue Lion Sage Dag sedan
I can't believe how many people don't believe their own eyes from Mythbusters and want to say the show's experiment was flawed. As this video explains, the thrust is from the engines. The plane will move forward. The wheels are spinning freely. They can spin as fast as they want. With no friction against the belt - as they are spinning so not applying a breaking force - the plane moves. Heck, the wheels could even spin backwards opposite the plane's thrust if the belt was moving at high speed and it wouldn't matter.
dog3y3 Dag sedan
So, the answer to the question you ask, isn't yes or no, but "It's impossible since the conveyor belt would have to spin at an infinite velocity" But I call shenanigans. It's a stupid question, pointless and has no basis at all in the real world. I don't call this a riddle. I call it stupidity. A better question would have benn: If a plane had a tailwind that matched it's take-off air-speed, could the plane still take off? Try that one.
Meme Rights Activist
Meme Rights Activist 2 dagar sedan
arturo salas
arturo salas 2 dagar sedan
the plane will always take off, independently of the conveyor belt speed
kevin Cox
kevin Cox 2 dagar sedan
People wondering about this is an indictment of our education system. A more interesting question would be " Will a seaplane take off against a fast current?" I guess it would depend on the drag of the floats.
Nate Raft
Nate Raft 2 dagar sedan
Pre answer...Answer: No it can't because the reason the plane takes off is Because air is being pushed beneath the wings which creates lift. If the plane is essential staying still on the conveyor than there is no air to be pushed under
offbeatrobotics 2 dagar sedan
Yeah, in the real world the plane will always take off, let me explain. First, let's make some assumptions outside of the riddle, for a WORST case scenario to try an prevent the plane from taking off. 1. In this real world test we've fitted some special solid metal tires, like on the fastest land speed record setting vehicles, so no practical speed limit there. 2. We're making the conveyor belt out of some monstrously strong material to be able to handle the forces involved, and we'll allow the runway conveyor to go up to the speed of sound! Ok so, let's go back to Issac Newton's third law, every action has a equal and opposite reaction, so the force applied to stop a plane from moving forward has to be equal to the thrust at takeoff. So in this scenario where would that force come from? the friction of the wheels and wheel bearings, as in the drag of the rolling system on the conveyor. So the wheel friction has to be higher than the thrust of a 747 at takeoff. It's pretty easy to see that even allowing the conveyor to go the speed of sound, which would be a miracle of engineering, the drag would be smaller than the thrust force of the jet. Now I guess in some hypothetical realm where the conveyor could have supernatural properties of infinite speed, but somehow the wheels still had friction then yeah the plane wouln't take off, but that's pretty picky on conditions for a thought experiment.
Clay Johanson
Clay Johanson 3 dagar sedan
The explanation provided in this video is needlessly complicated. A plane does not take off because of the speed of its wheels. It takes off because of the speed of the air over and under the wing. USUALLY these are the same thing during takeoff, but not in this case. If the plane is not moving relative to the surrounding air, then there is no lift and the plane will not take off.
Nakul K Mohan
Nakul K Mohan 3 dagar sedan
this is like telling you to run 3km on a road to get to a destination and putting you on a treadmill to do it
Paul Sarjeant
Paul Sarjeant 3 dagar sedan
No. The plane will *always* take off, no matter what you do with the conveyor: frontwards or backwards at any speed, it will just spin the wheels. *And* the wheels will *always* match the speed of the conveyor belt unless they are slipping. The plane will take off because of it's airspeed: it's movement relative to the surrounding air. Watch the Mythbusters episode for best explanation: svdown.info/post/video/roejlKuLaIuAxq8.html&ab_channel=AdamSavage%E2%80%99sTested
HerrMeyer 3 dagar sedan
Wouldn't it nearly the same procedure as described with taking off from short runways? Reving up engines to full power with brakes engaged, then release brakes and accelerate as fast as possible to the point, where ground effect kicks in, then accelerate further hovering over the runway, and climb out.
Mark H
Mark H 4 dagar sedan
If you lock the wheels to conveyor and make the plane move with the conveyor, then yes you could gain lift, however if engines not running you'd crash at the end
Mark H
Mark H 4 dagar sedan
No way. Just because the wheels turn doesn't make the plane move
Aiden Losh
Aiden Losh 4 dagar sedan
This is terrible because it completely fails to take into account the physics of how airplanes actually take off and the physics of rolling friction. Airplanes do not push on the ground to speed up, they push on the air, so having the ground move underneath it would not prevent the airplane from gaining forward velocity. Then comes rolling friction. Rolling friction is a constant, so no matter how quickly the conveyor belt is moving the resistance force will be the same as if the ground were normal. The only way the airplane would be unable to take off would be if the conveyor belt were moving so quickly the landing gear melted causing the fuselage to scrape against the ground.
74360CUDA 4 dagar sedan
Put a different way, if there was a magical conveyor belt that could instantly match the wheel speed at every moment the plane would still move forward and take off. Piper Cub, F-15 or even the 747. We are talking about a flat surface and the airplanes engines would still pull the plane forward even if the belt could match the wheels to infinitely. Don't think about it as a Wheel Dyno like at the emissions station. That kind of roller would keep the plane from rolling and it wouldn't take off. But this is a belt and the plane is still held down to the ground with gravity under the conveyor belt. That's the gag. The plane still rolls normally on the flat surface with the thrust the engines are making and the plane doesn't care what the wheels are doing. Yes, you can talk about over taxing the bearings or the tires or tying it to a tree for some reason but the plane always moves forward on a flat surface. Captain Joe is not correct
dragon Fyire
dragon Fyire 4 dagar sedan
in the first part it does not matter how fast wheels are turning, the conveyor belt and wheels would exponetinaly increase in speed yet the fact that the forward momentum is not created by friction to the ground the plane would acce;erate at normal speed the conveyor and wheels are not related to forward thrust in any way shape or form.
David Thirkill
David Thirkill 5 dagar sedan
Already seen it can
DirtDiggler 5 dagar sedan
Unless the plane moves forward the wheels will not turn, if they are turning the plane must be moving forwards, if it is moving forward it will create lift if the wheels dont move neither does the belt so no take off, we assume the belt is moving with the wheels and both are stationery.
Rens 5 dagar sedan
Your 2nd example kills your first. The wheels move freely. And we use jet engines to get speed. We only use the gear to keep the fuselage from scraping on the ground during taxi.
jeff walther
jeff walther 5 dagar sedan
Captain Joe: As a teacher, you're a consummate pilot. The physics principles and sense you are attempting to convey here through the hypothetical construct is SEMANTICALLY misunderstood by what one means by a conveyor belt operating as you describe, i.e., if the belt simply is held and moves as illustrated, on two axles front and back, then it's not really conveying or carrying the airplane, thus NOT a "conveyor belt", but more like a fanbelt. If the conveyor belt is conveying the plane above stall speed with normal takeoff power and settings THEN it should fly. My point is to illustrate how easily one can be so careful, yet entirely misunderstood or wrong altogether.
Michael O'Connell
Michael O'Connell 5 dagar sedan
Moot. Thrust will still propel the plane forward regardless of wheelspin. The 2 are unrelated.
David McGill
David McGill 5 dagar sedan
With a conveyor belt going infinitely fast under the plane, it's not gonna matter what form of thrust the plane has. That belt is gonna be dragging a ton of wind right by those wings and throw it in the air.
kightremin 5 dagar sedan
You run on a treadmill for an hour, will you get to your girlfriend's house?
The Thrifster
The Thrifster 5 dagar sedan
Think of a plane being hauled by a rope on that conveyor belt. Will move forward regardless of the speed of the belt.
Alastair Ward
Alastair Ward 6 dagar sedan
If in doubt, think about a seaplane taking off.
Luis R
Luis R 6 dagar sedan
Late to the party and didn't read the comments so I don't know if this has been mentioned. But after just thinking about it for a minute, the scenario #1 has a major flaw. Not just because it appears almost impossible to perfectly achieve the ability to match speed of the wheels. The issue here is that regardless of wheel speed, the aircraft will still want to move forward with take-off thrust regardless of conveyor speed (Newton's third law), therefore the moment the airplane accelerates just a tiny bit and causes the wheels to move faster than the conveyor it will immediately speed up as well. But the airplane is still moving or accelerating so the wheels keep increasing speed and therefore the conveyor will increase speed too. This will turn into a runaway situation really quickly, probably exponentially the moment the aircraft starts moving.
Ken Brown
Ken Brown 6 dagar sedan
video paused: "the speed of the wheels MOVING in the opposite direction." the wheels are MOVING.
Jay Perrin
Jay Perrin 6 dagar sedan
Ground and airspeed is nice but not if there's no airflow over the wings. If you want to take off, you need lift, not simply speed. Has anyone addressed this? Mythbusters and this channel have both missed the point.
Valtteri Wikström
Valtteri Wikström 7 dagar sedan
just slam on brakes and add enough thrust to take off.
Nelson Marques
Nelson Marques 7 dagar sedan
A plane can take off without wheels, so I think they are pretty irrelevant if they are on a conveyor or not.
Koobs 7 dagar sedan
I think a better and more real world example (as far as a car is concerned) is not a conveyor belt but a dyno. If you are tuning an engine on a car or a motorcycle, you can put it on a dyno which is basically a conveyor system for the drive wheels. It allows you to measure the output of the engine at the wheels. You can go up & down through all the gears & even mimic the vehicles top speed all while remaining 100% stationary.
Dmitry Malkov
Dmitry Malkov 10 dagar sedan
You'd probably need a giant fan installed before the belt to take off
Nathan The aviation enthusiast
i thought it can too! but no.
Linda H
Linda H 10 dagar sedan
The site for the plane model doesn't work.
Linda H
Linda H 10 dagar sedan
The plane needs to reach the speed of 100 knots to lift off the ground. It needs air not wheel movement. So I say no it wouldn't work.
Ken Brown
Ken Brown 6 dagar sedan
@Linda H the point is it is a trick question. it's designed to make you think the conveyor can stop the plane from moving - which Capt. Joe was tricked by. the conveyor runs at the speed the plane is MOVING. the key here is the plane is MOVING.
Linda H
Linda H 6 dagar sedan
@Ken Brown Yes if the plane is going the same speed as the conveyor. It will not get the wind to lift the plane. How about super strong fans to give the plane the air?
Ken Brown
Ken Brown 6 dagar sedan
so you believe that despite the fact that airliner wheels can go from zero to over 100 MPH in one rotation on landing, a conveyor belt will be able to stop the engines from pushing the plane forward?
mike duncan
mike duncan 11 dagar sedan
The only time the plane would not take off is the point that the wheel bearing create too much friction to reduce the plane’s forward motion below takeoff speed
Kevin Reed
Kevin Reed 11 dagar sedan
Yes because the wheels are not driving the vehicle. The turbines are.
Jobs Jobbed
Jobs Jobbed 11 dagar sedan
I think Joe is wrong on this one. There’s no drive from the wheels.
Logan Mailandt
Logan Mailandt 11 dagar sedan
only VTOL or specifically low-takeoff/land distance planes could pull this off. But those are literally designed to not need any groundspeed.
Christopher Maserang
Christopher Maserang 11 dagar sedan
the only thing taking off here is thought bubbles.
Kevin John
Kevin John 12 dagar sedan
When I saw this video was from a pilot, I honestly expected that he was going to arrive at the wrong answer. Most of the pilots I've talked to about this riddle arrive at the wrong answer, because they're thinking of it like a practical question and not realizing that question itself includes a totally impossible (or at least vastly improbable) mechanism. But if you think about it like a physics problem and map out the force diagrams, you get the right answer. So, clearly, I was pleasantly surprised to see this approached with some scientific rigor.
Robert Fletcher
Robert Fletcher 12 dagar sedan
So you are proposing a scenario that breaks the laws of physics ( infinite speed, infinite energy motors to enable the infinite speed, zero friction) in order to disprove something that does actually happen and is easily explained with basic physics?
Sir Snitty
Sir Snitty 12 dagar sedan
I don't see how scenario 1 and scenario 2 are any different. The wheel speed will always be the speed of the rest of the plane. The "infinite speed" situation described in scenario 1 wouldn't happen. The belt would never go faster than the speed of the plane. There is no speed, whether slower, exact, or faster than the wheel speed, which will prevent the engine thrust from advancing the plane. If I missed something, please point it out. I hope I'm wrong about something, and can be educated
Kirk Kitchen
Kirk Kitchen 12 dagar sedan
You would have to turn the wheels on the plane dangerously fast and the bearings would fail or the wheels would explode for a large jetplane. You are putting most of the potential energy into the moment of inertia of the wheels (collectively), NONE into the body of the plane. Maybe you could sorta get it to work if you had a small plane with big wheels. Plus, prop slipstream could generate enough lift at some point to make the plane rise above the conveyer belt. Once the wheels are off the conveyer for any reason, the plane will suddenly shoot up with great acceleration. Mythbusters needs to redo the experiment where there is no potential induced lift by prop wash and perhaps a cogged belt to insure no slippage - for example, rear-mounted jet. The problem has more parameters than meet the eye.
charlie regan
charlie regan 12 dagar sedan
Your nuts, the plane would take off. The speed of the air going by would be enough, the plane would push faster and faster though the air due to the jet engines sucking air though them.
TheOtherNeutrino 12 dagar sedan
The problem I see is people’s understanding of the conveyor matching wheel speed. If wheels aren’t skidding, then the conveyor is already matching the wheel speed regardless of what the plane above is doing or where the wheels are relative to everything else. They’ll act like two fully meshed gears and the plane still takes off because it doesn’t affect the rest of the plane.
Jerry Oswald
Jerry Oswald 13 dagar sedan
If you used a Harrier Jump Jet the conveyor is irrelevant.
Iris Oscuris
Iris Oscuris 13 dagar sedan
It’s like a machine that planes through the air. I wonder what we should call it?
Shooterlot 13 dagar sedan
So, this video is proof that you can't believe everything on the internet, he is wrong, the plane will take off for both instances. I find it funny he perfectly explains the second part, without thinking about how it would apply to the first.
Kevakazii 14 dagar sedan
The plane will take off as it's using thrust in the air to move and not friction on the ground.
SandmanSpeaks Softly
SandmanSpeaks Softly 14 dagar sedan
I'm pretty sure that it is the movement of air over the wings that give the plane lift. You could have the engines going fast enough to peel the tarmac off the runway, but if there is no lift, the plane stays on the ground. That's my theory anyway.
Jason Bieber
Jason Bieber 14 dagar sedan
This is a logical fallacy. The ground speed of the wheels is irrelevant to the air speed of the plane during takeoff. What is impossible is for the speed of the conveyor to ever match the speed of the wheels during takeoff.
Jason Bieber
Jason Bieber 12 dagar sedan
In the physical world that we live in, if the conveyor moves backwards as the planes pulls itself through the air, it can never achieve the same speed as the wheels because that equilibrium requires the plane to be stationary with the ground. The plane itself will continue to accelerate because, as the video explains, the ground speed and the speed of the landing gear is irrelevant to its locomotion. Therefore, if the plane’s velocity is higher than zero, it is impossible for the conveyor belt to match the wheels. The wheels will always keep pace faster than the belt as the belt accelerates. The question is posed is a fallacy.
Kevin John
Kevin John 12 dagar sedan
You can't contradict the parameters of the scenario in your explanation of what would happen in the scenario. They say the conveyer belt exactly matches. If you change that, you're answering a different question.
Eric Bishard
Eric Bishard 14 dagar sedan
Man, how cool would it be to watch a 747 take off from a conveyor belt?
Mikia Elizabeth Storm
Mikia Elizabeth Storm 14 dagar sedan
The wheels don't matter in the riddle. It will takeoff in either case. And in the case of the riddle the wheel speed would not hit infinity before the aircraft left the ground. at the most in the case of the riddle would result is the max speed would be the same as the matched ground speed conveyor, because the number of turns of the wheels are the same over the length of the take off
Ben Li
Ben Li 14 dagar sedan
dan b
dan b 14 dagar sedan
*Sorry but WRONG!* The motion of the airplane is *NOT* coupled to the motion of the wheels but *IS* a function of the thrust and subsequent lift of the airflow over the wings, it is that lift and thrust vector that causes the forward motion and resulting lift. _Remember the third law of motion, which states that for every action (force) in nature there is an equal and opposite reaction. In other words, if object A exerts a force on object B, then object B also exerts an equal and opposite force on object A._ *The wheels have nothing to do with the thrust vector and lift of the airfoil.*
Monte Evans
Monte Evans 15 dagar sedan
I think this question was thought up to highlight the difference between how a car is propelled down the runway and how an airplane is propelled down the runway. As such it is a thought problem and would work better (less confusion) if it was explicitly idealized. My suggestion is to include in the problem statement something like "consider the wheels themselves to have no friction in their bearings, no rotational inertia, no rolling friction, and no residual drag in the brakes when they are released." (visualize them to be something like a bicycle's spoked wheels with zero mass, and no brakes at all." LOL (also utterly indestructible). The question seems to me to be, then, "how can this conveyer belt runway PULL on this idealized airplane?" My answer is "it can't" - run the conveyor belt as fast as you want, all that will happen is the wheels will spin. The inertia of the airplane (tendency to resist changes in velocity) will keep it sitting there, until the throttles are advanced. With 4 big engines attached firmly to the body of the airplane it would accelerate down the runway with no trouble at all and take off when its airspeed reached the value to start rotation. However, if the wheels are given mass, and the conveyor belt runway is given access to unlimited energy and power, then pulling on the bottom of the wheels will actually transmit some force onto the body of the airplane (as well as give the tire rotational kinetic energy) and with infinite energy and power the conveyor belt would win.
Jussi Wallinheimo
Jussi Wallinheimo 15 dagar sedan
Come on. Aircraft doesn't need wheelspeed, it need's air speed. Aircraft can takeoff even backwards if it has enough airspeed over its wings Only thing that the conveyor belt would do is heat up the wheel bearings a bit more as bearings aren't perfect and wheels would spin some percentage more than normal at take off..
On The Road with John
On The Road with John 15 dagar sedan
nope no air over the wings
Ripstop Pilot
Ripstop Pilot 15 dagar sedan
Mind blown how wrong you are. But then the pilot on myth busters was wrong too. The plane WILL take off! Full stop. Conveyor belt can do what it likes. Dont even understand your first explanation to say it wont.
blaster 0416
blaster 0416 15 dagar sedan
No one commented that the animation of the water propellor was wrong. The curve of the prop was backwards. That prop would not do very much.
Bump_In_Night37 15 dagar sedan
I dont agree. This applies to both of the situations. Wheels on a plane do not transfer power to move the vehicle, like on a car. This means they are just rolling at x speed and the locomotion is done by a propeller or the engines, which pull themselves and thus the plane with it. Adam savage's Tested did a video some weeks ago on this topic.
Timothy Robbins
Timothy Robbins 15 dagar sedan
He’s wrong. In both cases, the plane will move forward and take off. The wheels will just be spinning super fast. Airplanes move by pushing air, not pushing against the ground.
The Big N
The Big N 15 dagar sedan
J.R. Vreugdenhil
J.R. Vreugdenhil 15 dagar sedan
Another issue concerning wheels (don't know if you gave a lesson about that before): are wheels actively slowed down to zero, before fully retracted into the wheel bays? I'm sure you can make another compelling video about that, Danke Schön 😉
Pistonburner 15 dagar sedan
You are wrong. The airplane is able to take off. The airplane's wheel speed doesn't matter at all, it never stops it from accelerating relative to the ground (not conveyor belt but actual earth) and air. The airplane will start moving forward no matter what the conveyor belt does. And the conveyor belt will never reach infinite velocity, it will only reach the takeoff speed (while the wheels spin at double the normal speed at takeoff). The wheels never "try to move forward", they only ever are spun by the conveyor belt. The way the plane moves is always dictated by engine thrust pushing the air. All the runway and wheels do is keep the plane above the ground, they support its weight vertically.
AHB Gaming
AHB Gaming 16 dagar sedan
I think no
Ben Millen
Ben Millen 16 dagar sedan
Without watching this... No, the wings won't be generating lift, if we are presuming the conveyor accelerates to match the forward thrust then it will simply stay in place
Ben Millen
Ben Millen 16 dagar sedan
...aaaand I just watched the video, well that was an exercise in stating the obvious and deviation into non relevant points, hey if I ignore the rules of the riddle I can take off.....great.....well done
Amani Gaula
Amani Gaula 16 dagar sedan
I don’t think the plane would take of don’t you need wind to put pressure on the wings for lift! Now if the wings aren’t getting enough wind for lift then the plane shouldn’t be able to take off!
Eddie Olsson
Eddie Olsson 14 dagar sedan
Indeed, but the airplane does not accelerate by pushing on the ground through its wheels, so the conveyer belt doesn't change the airplane's speed through air in any way. The jet engines will accelerate the plane in exactly the same way as it would without the conveyor belt.
MaxAMillion1961 16 dagar sedan
Wow, I used to think you were kind of smart, not anymore, it is to bad you do not understand the physics of this issue. Sad.
Petteri Laine
Petteri Laine 16 dagar sedan
The riddle is impossible to begin with. It is not possible that to conveyor belt could match the speed of the wheels becaus the wheel spin freely and the engines of the plane will push the plane forward regardless of the speed of the wheels or the belt. When the plane starts moving forward the tires start to spin and if the conveyor belt could match their speed the speed would jump to infinite instantly. There is no way the belt could prevent the plane from moving because of the thrust of the motors being applied to the air above the belt not to the belt.
Petteri Laine
Petteri Laine 16 dagar sedan
Petteri Laine
Petteri Laine 16 dagar sedan
Of course some planes can take of without ground speed. In fact all planes can if air speed is enough. Some small planes can take off with a strong head wind and a passenger plane needs about 150 knots of wind, but in theory they could get airborn.
NitrowolfUT 16 dagar sedan
Wow how can Capitan Joe not know how a plane flies? The wheels of a plane serve to reduce the friction of the plane during takeoff. IE they are there to prevent the belly from scraping along the ground, nothing more. The conveyor belt can spin as fast as it wants and it will have zero effect on the plane moving forward. It doesn't matter if the belt instantly matches speed exactly, the wheels will spin or not spin. The plane will move forward. You'd think a pilot would know this. Lost a lot of respect for this guy. Sheesh.
Michael-Dario Obermaier
First 3 minutes in the Video...im done. Sorry M8, that is just bullshit ur are talking and i dont even bother watching the (hopefully) "real" answers. it doesnt matter if its "exactly" or if there is a "delay" in matching the speed. Here is why: The wheels of the Airplane are free-spinning, there is not engine causing them to spin and there is no noteworthy friction in the bearings of the wheels. There is ONLY ONE Scenario where the Plane couldnt take off. If the Brakes are at Full and are strong enough to hold the Airplane in place at full throttle, so the plane would move backwards and the load on the coveyerbelt increases by the thrust of the airplane. In EVERY OTHER Scenario the Wheel of the plane are rotating matching the relative speed of Airplane to Coveyerbelt, either 0 or up to factor 2 of the takeoff speed, but there is no horzontal motiontransmission and only a normalforce to counter the gravity of the airplane up to point where aerodynamic uplift carries off of the gravityforce. And yes if the Airplane is engaging thrust after the conveyer is already moving it totally would moving backwards until thrust takes effect, doesnt affect the ability to takeoff tho, it would just take a bit longer to overcome the additional difference to reaching takeoffspeed. Long story short: basicly the rotation of the wheel and thus the speed of the conveyerbelt are completly unrelated to the neccesary takeoffspeed of the plane.
Dalle Samllhals
Dalle Samllhals 16 dagar sedan
Baaah! THIS will ALL change when we get our own flying "CAR" ;-P
Jeff Rath
Jeff Rath 16 dagar sedan
air speed ... not wheel speed
Really Next
Really Next 16 dagar sedan
Airflow somewhere? Maybe? )
Michael Fairhurst
Michael Fairhurst 17 dagar sedan
Don't agree hardly at all with the analysis of the *original* wording of the question. I'm glad Captain Joe admits that it's impossible, but, even that isn't really the right way to look at it. If the wheels accelerate to 1mph, and the treadmill matches it, that will *speed up the wheels* to 2mph. This *isn't* because the treadmill is reacting slowly. you can take the limit, for any non-zero ∆v the same thing applies, the wheels speed becomes ∆v and accelerating the conveyor belt to ∆v accelerates the plane to 2∆v. For the plane to *not* pick up speed, an additional force must act on it. That force in this example is clearly friction. Simply speaking, the energy lost to friction must match the energy created by the engines. Conveyer belt speed is not going to necessarily match wheel speed at this balance point. For instance, a plane with a high enough thrust to weight ratio could take off on skids on a normal runway, and the skids aren't ever rolling. But perhaps a fast enough treadmill could still stop such a plane. And if you deliberately designed a plane to have the worse axle bearings you can imagine while still allowing the plane to take off on a normal runway, then it would only take a slowly moving treadmill to increase the friction sufficiently to prevent takeoff. So in some extreme scenarios, a conveyer belt must move faster than the wheels to prevent takeoff, and in others it can go slower than the where and prevent takeoff. But all of these examples are absurd and require absurd amounts of friction to work, you may as well just bolt the plane onto the runway, and nobody would disagree. It's also worth noting that the plane does not necessarily stay in the same spot in my examples. Captain Joe says the plane can't take off because it can't move, but that's not necessarily true. It's just that with enough friction the plane can at some point be stopped from accelerating to takeoff speed.
Barefoot 17 dagar sedan
My problem with the riddle is that it's not _quite_ defined well enough. Specifically, what _exactly_ does "designed to move at precisely the speed of the wheels in the opposite direction" mean? I see two main, and somewhat ambiguous, interpretations: 1. If it means that the conveyor's velocity is always equal and opposite to the average velocity of the wheels, i.e. the velocity of the central hub (which is the same as the velocity of the plane itself), then yes, it can probably take off. This would effectively simply double the radial velocity of the wheels, and as long as that is something that's within the tolerances of the tires and hubs to not explode and overheat, respectively (which I suspect it is, since a no-flaps landing in a tailwind could come pretty close to that ground speed), then there should be no problem taking off, since the plane doesn't rely on ground friction for its thrust and acceleration. Yes, there'd be a little more friction from the hubs and rolling resistance of the tires, due to the increased apparent wheel speed, but compared to the power of a passenger jet's engines, my head-napkin math says that should be negligible. 2. If it means that the conveyor's absolute velocity relative to an inertial observer is equal and opposite to the tangential velocity of the tires as they spin, then... probably not, but it still might be possible. This definition is recursive, so the wheels' speed and the conveyor's speed, which are each defined by each other, would create a positive feedback loop that would exponentially ramp the speed up toward infinity. Of course, you could never actually build an infinitely fast conveyor belt, so it would depend on whether the conveyor can go fast enough to over-speed the wheel assemblies before the plane has enough lift to take off. Edit: Cool, that's pretty much exactly the conclusion you came to. If you ever _do_ find yourself taking off on a conveyor belt in either scenario, I recommend the most extreme possible short-take-off setup... brakes on full as long as possible until engines spool up as fully as possible, for starters. I might even consider starting in a clean configuration for the initial acceleration, then dump flaps/slats approximately one cycle time before rotation speed (the earliest rotation speed possible given the load parameters, with engines running at absolute max power). Could you even spool up most of the way with reverse thrust selected, so that the reversers would be closing just as thrust passed maybe the 60% mark, and finish the transition just as the thrust pushed the mechanical limits of the hydraulics? In any case, since you'd be doing so in real reality instead of spherical cow thought experiment land, I think you could put your faith in the safety factor the engineers of the tires and wheels designed into them, over the bizarre possibility of an infinite-velocity, infinite-acceleration conveyor belt. That is, assuming the take-off is super-important, like to escape the massive volcano island on the verge of erupting that the supervillain who built the conveyor belt anti-takeoff system triggered, or something. If it's just, like, to go to another city for business, I'd just ... Actually, scratch that. If you ever find yourself facing a conveyor runway, just take off on the longest taxiway instead.
garrnk 17 dagar sedan
Yes it will the airplane doesn't use its tires to generate thrust. They freespin.
garrnk 17 dagar sedan
The tires will remain stationary while the aircraft moves forward
Lexor888 17 dagar sedan
Well I have seen the Mythbusters episode this topic is based on and even there I knew the answer in advance, so hypothetically speaking yes the 747 won't have any difficulties taking off - but I still have doubts this would work with a 747. At takeoff speed the wheels would roughly run at 320 knots, I do not believe they are designed to withstand such abuse and may explode/disintegrade.
The Chosen One
The Chosen One 17 dagar sedan
Airspeed is the answer.
J. Sin.
J. Sin. 17 dagar sedan
Wheel speed is independent or air speed and thrust therefore even scenario one the plan would take off
Greg McQueen
Greg McQueen 17 dagar sedan
As the aircraft is not propelled by the wheels, they will only rotate when the jet moves forward. The aircraft moves forward independently of the wheels. Mythbusters showed there was absolutely no difference in take off speed and distance when taking off from a conveyor.
LeDerpLegend 18 dagar sedan
Fun Fact: Mythbusters tested this. Very interesting episode.
Adarsh Patil
Adarsh Patil 18 dagar sedan
The wheels are rotating but the plane is not moving, so the plane will not be able to takeoff.
jefrhi 18 dagar sedan
Think of it another way... Replace thrust with a rope. If the rope is reeled in, it doesn't matter how fast the wheels or conveyor are moving, the plane WILL move forward because the mode of locomotion is disconnected from the wheels.
Tony Montana
Tony Montana 18 dagar sedan
05:30 "The power your engine must therefore provide equals the power it would need to accelerate you from 150 to 300 km/h ground speed." Sorry, but this is not true. Of course the exact numbers will vary from car to car, but at such speeds with a conventional car, most of the power you need to only keep your speed are due to the friction with air. The power you need to overcome friction with air grows *cubicly* with the speed: twice the speed needs 8 times the power (to overcome friction with air, not total power). Therefore, it makes a huge difference in power need if you drive 300 km/h on a conveyor belt with -150 km/h speed (i.e. effective headwind of 150 km/h) or 300 km/h on a normal street (i.e. 300 km/h of headwind): even if your car could never make it to 300 km/h on ze German autobahn because of a lack of engine power, it could reach it on a conveyor belt. Additionally, as power is energy per time, the *power* you need to increase your speed from 150 to 300 km/h is obviously dependent on how *fast* you want this increase to happen.
bcreason 18 dagar sedan
This doesn’t make sense. The wheels would never spin faster than twice the take off speed. The plane should take off regardless of the speed of the conveyer belt.
bcreason 18 dagar sedan
Yes but a little slower unless the tires explode due to centrifugal force. There will be slightly more friction in the wheel hubs as the wheels will be spinning twice as fast. There would also be some energy loss from inertia due to having the tires rotation brought up to double the speed.
Justa Youtuber
Justa Youtuber 18 dagar sedan
I think the flaw might be thinking that the wind speed equals the conveyor belt speed. At full thrust the wind speed moving over the wings would be greater than the tire rotation speed. This is how you can lift off into an extreme headwind with very little forward ground speed. Right?
Travis Ross
Travis Ross 18 dagar sedan
Doesn't a seaplane moving on water simulate a conveyer belt moving at a potentially infinite speed becuase it is essentially a frictionless surface?
Rod Bennett
Rod Bennett 19 dagar sedan
Captains Joe's restriction of the conveyor belt matching the wheel speed is not possible. Lets take a frictionless system. As soon as the engines have enough thrust to move the plane ordinarily it will move in this scenario as well - breaking the restriction. In a system with friction, the plane will move backwards if the conveyor belt starts up first, but that instantly breaks the restriction. So the restriction is something of a tautology as it means the only possible speed of the conveyor is zero unless there is no friction and the plane does not use its engine. There is no scenario which a plane can stay stationary on a conveyor if it is using its engine.
Zxore 19 dagar sedan
Wouldn't the plane take off in both instances? In the 1st instance we are talking about the conveyor canceling the speed of the wheels. So as the wheels tried to spin, the conveyor would go in the opposite direction to make it so the wheels would not spin. Effectively the plane would take off from a conveyor traveling in the same direction, at the same speed (the conveyor and planes speed would match). It seems like everybody thinks wheel speed but then keeps the conveyor moving as if we were trying to influence plane speed. All this does is create a positive feedback loop. As soon as you moved forward at all the wheels and conveyor would increase in speed to infinity (or until they were destroyed). The question states wheel speed, and to cancel wheel speed, the conveyor would move with the plane.
Jessica Hall
Jessica Hall 19 dagar sedan
Mythbusters proved that a plane can indeed take off. In fact it didn't even effect the performance of the take off.
Ritupan Sarmah
Ritupan Sarmah 19 dagar sedan
No it will not bcz since the conveyor speed is same as plane speed, it will remain stationary, though the tyres will spin......it's like a car or bike on a dyno ....
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