This week is the infamous Plane on a Treadmill episode of Mythbusters!
I’m so looking forward to this one. I see in the pics Adam is playing with a RC plane - I can’t wait to see how their experiment goes. I REALLY need to get my plane back together and in the air. That looks like some kind of GWS model they are using… the wing looks almost exactly like my Slowstick wing.
I think it’s going to take off. I don’t really see this as any different than a plane sitting on a patch of ice. The plane still moves forward as it’s pushing against the air, not the ground. But we’ll see… 
Update:
- The plane flew!!
- Kottke live blogs event and opens comments - debate continues
- Someone actually registers http://www.airplaneonatreadmill.com
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37 Comments
Can you explain what myth they’re trying to bust? I’m assuming that it’s if a plane can take off it’s on a treadmill reaching airborne speeds?
Yeah - exactly. The plane is positioned on a conveyor belt. The belt is moving in the opposite direction in theory matching the plane’s forward speed. Can the plane take off?
LOTS of opinions on this one but I don’t think anyone has ever really done it.
Surely it’s just the plane wheels that are moving at speed. The plane itself doesn’t have any air “planing” around the wing to give any lift. Elementary physics really.
Errr… But I guess I could be wrong?!
Right…I went on to read more about it on the Discovery site. I set this one to DVR. It sounds pretty interesting. I’d have to say that while I don’t know physics very well, I’d have to agree with James…the plane doesn’t have any actual forward motion and so shouldn’t have the required lift to get off the ground.
As a pilot and an airplane nut, I would bet a large sum of money that it does NOT take off. You have to provide true forward motion via some kind of thrust to force the air to flow over and around the wings. No airflow, no lift. I would agree with the previous poster’s hypothesis that the wheels are simply spinning fast enough to match the pace of the treadmill, with no real airflow over the wings.
I would be SHOCKED if it did lift off, but I am no physicist either.
Guess I will have to set the DVR for this episode as well…thanks for the heads-up!
@Troy - great to get a pilot’s opinion
I’m on the fence. My RC airplanes have a huge amount of thrust compared to the weight and I think they would fly. A real plane however… I’m not sure 
@Jim - Very true about RC planes…the Thrust-to-Weight Ratio can be very high, maybe even high enough to cause some lift. But it would be the air being forced over the wings DIRECTLY from the front prop(s) that would be responsible for any Bernoulli Effect. I am still almost certain (and growing more so by the minute) that the lack of any true forward motion and in turn, lack of airflow over the wings, will result in no true lift.
It definitely won’t take off IMO… It would be like trying to take off in a vacuum, no airflow over the wings will just leave it sitting on the ground!
Perhaps if it was on a treadmill in a wind tunnel
That could be a followup experiment, hehehe…
People who say it won’t take off are saying that because they imagine the conveyor belt holding the plane stationary, and just the wheels are moving.
People who say it WILL take off are saying that a conveyor belt CAN”T STOP the plane from forward motion.
The plane doesn’t get its thrust from the ground/tires, its engine gets its thrust from the air. You could have the conveyor belt coming at the plane at 500mph, it doesn’t matter, when the plane hits the gas, its going to move forward.
For example, picture a conveyorbelt spinning from the bottom of a hill to the top of the hill. Put a plane on it (or a car in neutral) and try to get it to the top of the hill (without using wheel chaulks, or brakes). It isn’t going to go. It will sit at the bottom with its wheels spinning, doesn’t matter how fast you spin the conveyor belt, you aren’t going to move that plane up hill. Without friction, you can’t apply any force to the plane.
Hit the throttle on the plane, and it will go up hill easily.
Same deal in this theory. You can spin the conveyor belt against the plane, or with the plane, it doesn’t matter.
Wheels on a plane are made for one thing. Reduce friction between the ground and the plane. They do a good job of it.
Should be a good episode though, I’m looking forward to it.
if the weight of the plane is on its wheels (which it is), then how could it possibly move forward if the belt is meant to match its speed in reverse?
If thrust pushes the plane forward, then the conveyor belt is NOT matching its speed.
It doesnt mean the wheels are being driven…. ANY forward motion of the plane will be null, because the planes weight is on its wheels, whose speed is being matched in reverse by the conveyor belt.
The only way I could see the plane taking off is if a whole lot of air is pushed under its wings from somewhere.
I’m no expert of course, but thats just the way I see it, but we’ll see on the episode!!
LOL - Kottke is liveblogging this tonight:
http://www.kottke.org/08/01/my.....veyor-belt
Oh yeah - and that is a GWS Picostick model. In case anyone cares
YES! The plane flew! I knew it
The scary part is that the pilot was amazed.
I am completely disappointed at Mythbusters handling of this experiment. The science they used and the “explanations” were both completely flawed. The original myth, and ALL of the discussion, centered around one central conceit: The plane would have NO FORWARD MOTION RELATIVE TO THE GROUND because of the conveyor belt matching the speed of the plane. NOT the “speed of the WHEELS of the plane” or any other contrived version.
Of course the plane is going to take off if it has enough forward motion RELATIVE TO THE GROUND to create the Bernoulli effect required to lift the wing because of the airflow over the wing.
I really expected more “science” from MythBusters. They almost explained it properly with the “model car example”. I guess it was the original Myth that was flawed, or my understanding of the Myth. I guess in their mind the myth is that no plane on a conveyor belt can take off if the “speeds are matching in opposite directions”. That is far too simplistic to make a determination, so it is flawed from the get-go.
Those of us who claimed the plane would not take off without forward motion relative to the ground due to the laws of physics are still correct. The planes both had significant forward motion relative to the ground. I just hope everyone involved in the debate understands these distinctions, otherwise this will just dumb down the TV watching public a bit more. It sure was fun though!
Wow, I’m totally surprised that it took off! But having not seen it, it’s a bit hard to know exactly what was happening (Myth Busters usually airs months behind here in Australia)… Was the plane actually moving forward at the time or did it just lift on the spot? I don’t see how it would have had enough (any) airflow over the wings for it to lift… This is definitely a physics WTF for me, I’ll have to see if it’s on YouTube
@Justin: There was a LOT of forward movement relative to the ground, so there was plenty of airflow over the wing. The whole thing was “flawed” in a lot of ways. They did not even truly match the speed of the conveyor to that of the plane: The conveyor’s speed was based on the wheel speed of the truck pulling it, where the airplane’s speed was taken from the pitot tube, which measures relative air speed. So of course the plane is going to “move forward” and eventually lift off.
I love this question, but it amazes me to no end to see the multitude of different ways that people can misinterpret the question.
If you put a plane on a treadmill, could it take off? That’s the question, in it’s simplest form. People nitpick and so we add in all sorts of details: the treadmill moves backwards at exactly the same speed as the plane moves forwards; the treadmill is infinitely long; and of course, the most controversial addition, intended to imply that the plane does, in fact, have wheels: the treadmill matches the speed of the wheels.
We ALL agree that a plane with no forward motion relative to the air will generate no lift and thus will not fly. So the question then must be simplified to this:
Will the treadmill prevent the plane from moving forwards?
If you nitpick and claim that the speed of the treadmill must be equal to the speed of the wheels, then you are simplifying the problem to something else, which is If we prevent the plane from moving, will it take off? and we all know that the answer to that is no.
There are two common misconceptions here. The first is that the plane’s thrust is delivered via the wheels to the ground - that the wheels are what is causing the plane to move forward. This is the case when you put a car or a human on a treadmill. But an airplane doesn’t push against the ground, it pushes against the air. The engines move a mass of air backwards, Newton’s Laws of Motion dictate an equal and opposite reaction which pushes the engines forward, thus moving the plane forward.
The second misconception is that the friction in the wheels will be sufficient to transmit the force of the treadmill to the plane, thus canceling out the thrust of the engines. This is very difficult to disprove using math, at least to most people, but is actually rather easy to disprove if people would just use common sense. Watch an airplane on a normal runway. They use their engines to gain speed, then throttle down - and the plane keeps rolling for quite a substantial distance. If the friction in the wheels was so high, the plane should have come to an almost immediate stop once the engines were turned off. This should make it clear that the purpose of the wheels is to remove the friction between the plane and the ground, thus allowing it to move freely.
Once these two misconceptions are removed, most people should be able to see that the answer to the simplified question is “No” - the treadmill has almost no effect whatsoever on the plane, and cannot prevent the plane from moving. This, in turn, makes the answer to the first question “Yes” - the plane will take off.
As a fellow poster once said so eloquently:
“The plane is not magically levitating while standing still. It is moving forwards as usual, and ignoring what the ground underneath it is doing. Which is the entire point of having a plane, really.”
@Troy: They measured the plane’s take-off speed with the plane on a normal runway, and then drove the truck at that speed. They never actually measured the plane’s speed while the plane was on the treadmill.
@Justin: The plane was moving forwards, not sitting still at that one spot. Read my post above as to why.
@Duff: Nice clarifications. I do understand that this has all become convoluded. But if you boil it down to the simple question that you clarified, then I think it becomes a big “duh” that it will take off. I honestly got the impression from everything I read that the myth was implying the plane would be stationary relative to the ground because of the conveyor belt. I know that is crazy, but if you do not make that assumption, there really is no debate is there? All of the animations on the show even showed the plane stationary, and then “magically lift off”. I guess it is just a lame myth or “question” in the first place.
In regards to your reply to me:
“They measured the plane’s take-off speed with the plane on a normal runway, and then drove the truck at that speed. They never actually measured the plane’s speed while the plane was on the treadmill.”
The problem with that is the take-off speed was measured using a camera pointing at the air speed indicator in the plane. That is based on a reading from the pitot tube. They should have used a radar gun from the ground to measure the speed at take off. It really does not matter though…like I said, this whole thing was flawed from the beginning. If you keep it simple, there really is no “myth to bust”. If you start make qualifications, it just gets more and more convoluted. But I know that the VAST MAJORITY of people discussing this all over the web were envisioning the plane being stationary relative to the ground, and were debating if lift would be created in that instance.
I have a feeling they will be revisiting this show one way or the other…
I’ll agree with you that they should have measured the plane’s take off speed with a radar gun instead of using its airspeed measurement.
The whole reason this riddle exists is because people (incorrectly) assume that the treadmill/conveyor will prevent the plane from moving. And I agree that the VAST MAJORITY of people make this assumption. However, once that assumption is dropped, and the problem is analyzed without any preconception, then yes, it becomes a “Duh” question. It’s getting people to realize that the riddle doesn’t say the plane doesn’t move that’s the trick.
For all who are disapointed with the way they tested.
The MYTH, was “Could the conveyor belt prevent the plane from taking off” Answer, NO !!.
Read my above quote before the show aired.
That was the “riddle” Would a conveyor belt have ANY affect on a plane. Answer, NO.
No one thought that the plane was going to majically rise straight up in the sky because a conveyor belt was under it.
We said a conveyor belt CAN”T STOP THE PLANE. Its going to move forward and get lift from the wings just like it always does.
You could have the conveyor belt spinning at 500mph it doesn’t change anything, the plane will just go forward like always.
If you tie a rope around the tail, then hit the gas, then it will stay in one place and never get off the ground. (I agree)
But its not going to be revisited. Why would it be?
Browsing the Mythbusters wiki, it’s amazing to see how many people think that the myth is “If you keep the plane from moving, can it take off” instead of “can the treadmill keep the plane from moving”.
I really need to get over this and get back to work
Here is a questiong then, in the episode the plane needed 20mph to get airborne, and Jamie drove the druck in the opposite direction pulling the treadmill at 20mph, does it then mean that the plane is actually getting up to 40mph to still take off?
@Duff: The problem is that any mention of “matched” speeds leads people to assume that the plane isn’t allowed to try to accelerate any further… Of course if it’s stationary relative to the ground it’s not going to take off, which is why we were so surprised that this was even a myth!…
Its all what you measure your speed by.
The conveyor “relative to the ground” was going 25mph.
The Plane, “relative to the ground or air” was going 25mph.
The wheels on the plane were spinning roughly 50mph “relative to the conveyor”.
If I’m rolling at 10mph on a skateboard and coast onto a moving sidewalk (like in the airports) thats moving against me at 10mph, the wheels would instantly jump to 20mph.
Did I just magically accelerate with no effort? or am I going the same speed, but my wheels are spinning faster now.
I guess its just how you look at it.
I have never seen the myth worded in a way that it would make sense to assume the plane remains stationary. In fact, I think that is the real value of the myth in that otherwise smart people for some reason think that a conveyor belt will have the same effect on a plane that it does on a car or human.
I am curious to hear from the NoFlys or former NoFlys why they thought it was reasonable to assume the plane would remain stationary?
@PWB: For me, I joined the conversation at the 11th hour via this blog. So I had not really read “the original myth” per se. But I just thought that if there WAS forward movement relative to the ground, it would be clear that there would be lift. So I thought the “myth” was centered around the plane being stationary relative to the ground because of the conveyor. It appears now that was the whole point to the riddle — and they should have called this a RIDDLE. There is no prevailing myth out there about this (at least not one I had ever heard of, and I am what you would call an aviation nut). But I guess then they could not have had it on a show called Myth Busters.
A quote from Adam, of the actual myth.
Adam: “Let me spell it out for you, normally a plane sits on the runway, spins up its engines, moves forwards gets enough air over its wings and takes off. But in this case, the plane is sitting not on the runway, but a huge conveyor belt that is matching the planes forward speed in reverse, and the grand question is can the plane take off? The myth is that it can’t”.
Answer….. it flys. The conveyor belt is simply matching the speed of the plane, not stopping forward motion.
If the plane was stationary, the conveyorbelt would never move in the first place because it has no “speed” for the conveyor to “match” in the first place.
1. everyone knows a stationary plane can’t fly. No myth or argument about it.
2. Everyone SHOULD know, that a conveyorbelt can’t stop a plane because the means of propulsion are not related.
The conflict
1. “no flys”, thought the “will flys” were expecting it to just rise up like a harrier magically because the wheels were spinning.
Obviously the “no flys” thought the “will flys” were morons.
But the “no flys” just misunderstood the question.
2. many “no flys” are still convinced that a conveyorbelt spinning in the opposite direction can affect the forward movement of the plane.
If you have hours of spare time to kill, go to the mythbusters forum. They are on about 90+ pages since the show still arguing.
Duff is absolutely correct. Here’s a more detailed explanation, with a little bit of high school physics. It’s not really that difficult to understand if you take it slowly.
If you consider all of the forces on the plane, you’ll know why it had to fly. I’ll oversimplify to save time and confusion for those who don’t have a physics background.
1) The vertical forces start out as the weight of the plane downward and the force of the earth upward. Those cancel out so the plane stays on the ground. We also have a very slight, and insignificant, amount of lift created by the slipstream from the propeller over the wings, which creates a trivial amount of vertical lift (not enough to do anything, so it can be ignored).
2) Horizontally, we have the treadmill pulling backwards with the friction of the wheels opposing that. We also have the forward force generated by the propellers (too complicated to explain here how that works), opposed by the friction of the wheels. Let’s ignore air resistance for simplicity’s sake since it doesn’t play a significant role.
3)The key point is that, once the torque (rotational force) on the wheels is great enough, they will start to spin and the friction will become essentially irrelevant. That torque is created by the force from the treadmill plus the force from the propeller transmitted through the body of the plane. They both act in the same direction on the wheels, causing them to spin. Once the wheels start spinning, the backwards force acting on the plane from the treadmill will be so small relative to the forward force from the propeller that the plane will start to move forward. THIS IS THE KEY POINT!!! The fact that the wheels will spin at twice the rate as during a “normal” takeoff is essentially irrelevant.
4) Once the plane starts moving forward relative to the earth (and air), it will take off as if the treadmill were not there, following the usual laws of physics whereby the vertical lift is generated by the flow of the air over the wing (not so much from the propeller as from the forward movement of the plane through the air).
If that causes your head to spin, just think of it this way: All the treadmill does is cause the wheels to spin faster; it doesn’t move the plane backwards once the propeller starts moving it forwards.
If there was a separate treadmill under each wheel and a vertical pole through the aircraft so that it could not move forward but only up and down, no matter how fast the treadmill was going or the propeller spinning, the a/c would not take off. Air must flow over the wing to create a negative pressure on top and a positive pressure on the bottom to give it lift. The a/c would remain stationery although the wheels would be spinning which have nothing to do with the a/c flying.
In the Mythbuster’s experiment, the a/c flew because it moved forward creating a laminar flow of air over the wing. The wheels would be revolving faster but would have no effect on the plane taking off. They did not mention the distance at which the plane took off which should have been the same as it was without the treadmoill
Having just watched the episode on Discovey in Australia, I was amazed that both Adam and Jamie were able to state emphatically that they had Busted the myth. It has been pointed out by a few other keen observers that the full scale test clearly showed the aircraft moving forward relative to the ground giving it airflow over the wings and thus providing lift. By their assesment, a plane could stand on its brakes, run up full power and take off simultaneously when brakes are released because forward movement is not a factor in gaining flight. Other than using the lightest aircraft they had available and pointing it into wind (giving it a localised air speed anyway), the actual airspeed over the wing to gain flight is not solely able to be produced by the propellor alone. Maybe the Navy should install conveyor belts on aircraft carriers given that it is such an effective means of inducing flight in aircraft. Honestly though, I would hope that the Mythbusters revisit this Myth in future and review the following,
1. The aircraft should remain stationary relative to the ground in order for the true basis of the myth to proved-disproved.
2. The aircraft should not be capable of being registered as an Ultra Light. CAA regulations in Australia do permit for two aircraft registration types. Aircraft to a certain specification can be registered as an Ultra Light and as such do not have the same restrictions and requirements on use and user as an aircraft on the General Aviation register. Gross weight, Engine capacity and maximum Take Off Weight are all governing figures in determining what constitutes an Ultra Light. Ultra Lights can be registered on General Aviation registers. Some kit and pre fab aircraft (Caloundra Sky Fox) meet the requirements for both.
3. The conveyor belt if possible needs to be at speed at the same time as the aircraft applies power so forward momentum is not a factor.
I know Jamie said that there was heated discussion on this, however given my very basic knowledge of flight principles, I am certain that a propellor alone is not capable of providing sufficient airspeed over a wing to produce sufficient lift without the addition of forward motion over the wings to supplement the thrust developed by the propellor. Looking at a Helicoptor which is a rotary wing design, they require the blades to be turning at a significant rate before lift is generated, thrust from a plane is developed in the same way but lift is only provided by the differential pressures of air over the wing, the whole length too I might add as the rate of lift produced by a wing varies along its length depending on thickness (camber) and the chord (the distance from leading to trailing edge). Other factors like Aspect Ratio and the whole Co-Efficient of Lift will also play a role in determinig the optimum conditions for flight, height above sea level, air pressure and density as well as humidity and temperature.
Good luck to all in relation to this myth, I know where I stand in relation to these results and it will be a very good experiment that would cause me to change my mind.
David,
The myth is NOT can a stationary plane just lift into the sky majically because the wheels are spinning. Everyone knows if you tie a rope to the plane, or put the plane on a pole (mentioned above ha ha) that the plane isn’t going to take off. Theres no argument.
The MYTH is can a Converyor Belt, keep an airplane stationary. Answer NO it Can’t !!
FACT. You cannot stop a planes forward motion with a conveyorbelt.
Think of it as more of a riddle.
Here is another for you. If a car is going 100mph west but the wind is blowing 100mph east, is the car still moving.
Yes, of course it is. You can’t really stop a car with wind, thats not where its propulsion comes from.
Its the same question as the plane, just reversed.
Its not that complicated guys.
I’ve forgotten who the pilot was that flew the plane for the Mythbusters, but at first he said it wouldn’t take off but then was astonished when he did!! I would suggest that he needs to go back to flight school and restudy the “Basics of Flight!”
The only thing that made the plane take off was the thrust of the propeller moving the plane forward which would then have laminar flow of air over the wings.
One way to completely put this myth to rest and be busted is to place a glider on the treadmill. Tie a rope to the nose to stop it from moving backward and start up the treadmill. It wouldn’t move in a vertical direction one iota no matter how fast the treadmill went. QED.
I’d like to see what the Mythbusters have to say in response to all of us who have shot down their findings.
But it is different for a car as the wheels provide forward momentum whereas the wheels on a plane have no power and simply turn freely.
Nowhere in the myth does it say the plane will remain stationary.
Thats the “assumption” of the person hearing the myth.
Its not that I think the “no fly” people are morons, you just have to admit you “didn’t think of it that way”
Its a no brainer.
watch them explain it again. http://youtube.com/watch?v=KSBFQOfas60
Tape a handheld GPS to the belt on the treadmill, tape a handheld gps on the plane.
have them both going the same speed in opposite directions.
The plane will move forward and fly.
The planes GPS will show the same speed needed to take off everytime, doesn’t matter if a treadmill is under it or not.
You could have the conveyor belt doing 10 times the speed of the plane, it doesn’t matter. They are not connected.
Since the caveman invention of the wheel, its only purpose was to eliminate friction between the ground and the object sitting on the wheel.
Its not that hard.