Mythbusters - airplane on a conveyor belt

Physics professor wrote:

1. The argument that the plane takes off is predicated upon the plane moving forward through the air.

2. For the plane to move forward through the air, it is necessary for the plane's wheels to be moving faster than the treadmill.

3. If the treadmill's speed matches the plane's wheels, the plane does not move forward through the air and the plane does not take off.

Show me where I am wrong.

I think you're missing the point. The thrust will come from the engine or propellers against the static air. This thrust will push the plane forward, regardless of how fast the wheels are spinning. Translation: The plane's wheels will always be spinning faster than the treadmill, no matter what speed it is moving.

The plane will take off. From an outsider's point of view, you will be unable to tell that the plane is even on a treadmill! It will move down the runway no matter how fast you turn the treadmill up! Unless of course the treadmill can go thousands of miles an hour, which will then slow the plane due to the friction in the wheels.

Ohio Rulz: I think you are right in that if this was ACTUALLY conducted, the plane would bounce and take a messy, noisy, screechy "flight".

Ying Yang Twins: you said, "The plane's wheels will always be spinning faster than the treadmill"

This is NOT what the riddle states. It states that the treadmill speed ALWAYS equals wheel speed. IF this is the case, then the thrust cannot push the plane forward through the air.

Then the riddle is impossible phrased because it first requires that the planes engines are off (wheel speed=treadmill speed) and then says that they are turned on. whatever sick bastard wrote this thing is laughing at us now.

If the conveyor belt is like a manual treadmill then it is unlikely for the plane to take off as the plane speed will always be matched by the treadmill speed and the plane will not move through the air thus it will not take off.

Now, it is also unlikely that you can create a belt like that without the plane's wheels creating enough friction to overcome a manual conveyor belt. The weight of the plane would likely push down enough to overcome the belt.

If the belt is a normal treadmill type of automatic belt then what will happen is that the belt will be turned on at whatever speed and the wheels will be turning at whatever speed, but once the engines are turned on the shit will hit the fan and the plane will move forward and IF the engines produce enough thrust to move forward faster than the treadmill and the belt is long enough the plane will take off.

Now, a problem may occur with the air speed generated by the belt itself. If you move a conveyor belt at 50mph it is going to move a lot of air. How much air and at what speed is the problem. Taking out the air movement of the belt let's say you have a plane with a takeoff speed of 50mph and the belt is moving at 50mph, the plane would have to move at 100mph to takeoff under those circumstances. The problem comes with the air moved by the belt. The movement of air due to the belt let's say drops the actual take-off speed by 10mph. Then the plane only has to go 90mph to take off....but what happens when it leaves the air space of the treadmill, what happens when it leaves that assistance?

Using the above numbers a plane's engines are creating enough thrust to move at 90mph, but because of the conveyor belt moving at 50mph the actual speed through the air of the plane is 40mph, still enough to take off given the air being pushed by the conveyor belt. Once the wheels leave the belt the plane will be thrown forward at 90mph and likely crash.

I say given the above situation the plane will leave the ground, but not for long...:) In fact, if the plane's take-off speed is 50mph that means it simply needs to move through an airspeed of 50mph. If you can create a conveyor belt that can move air at that speed you should be able to takeoff regardless of what kind of conveyor belt it is.

Alan

You are making this waaaay too difficult. The riddle doesn't say that the treadmill matches the speed of the WHEELS - it says the treadmill matches the speed of the PLANE.

According to the riddle, if the plane is standing still than the treadmill isn't moving. The treadmill only moves if the "plane" is moving forward (relative to the air and the unmoving ground next to the treadmill). People get stuck on the point that they picture this plane taking off without any air flowing over it's wings - of course a plane can't take off without air flowing over it's wings.

But, this plane is barreling down this treadmill runway at exactly the same speed that the treadmill is moving - the WHEELS are moving twice the speed of the plane and twice the speed of the treadmill.

Do you get it yet?

Ying Yang Twins: you said, "The plane's wheels will always be spinning faster than the treadmill"

This is NOT what the riddle states. It states that the treadmill speed ALWAYS equals wheel speed. IF this is the case, then the thrust cannot push the plane forward through the air.

This is the part of the myth that is incorrect! I am saying that this is impossible to do! You simply could not crank up the treadmill speed to match the wheel speed. Because of the engines / propeller, the wheel speed will always be greater than the treadmill speed.

In order for the wheel speed to match the treadmill speed, it would require you to have a PHYSICAL BOND between the wheels and the treadmill! It would have to be a strong physical bond, because the plane's engine will always be pushing the tires to spin faster than the treadmill.

You guys are missing the most important point...

Kari is a hotie

http://images.google.com/imgres?imgurl=http://saturn5.com/darwin/beef/images/38-MythBusters_Girl_Kary_Byron_Large.jpg&imgrefurl=http://www.nuclearbeef.com/stupid_stuff/&h=600&w=800&sz=162&hl=en&start=8&um=1&tbnid=BvuDh_Iay8q9rM:&tbnh=107&tbnw=143&prev=/images%3Fq%3Dmyth%2Bbusters%2Bkari%26svnum%3D10%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26channel%3Ds%26rls%3Dorg.mozilla:en-US:official%26hs%3Dx8v%26sa%3DN

opps, try this

http://saturn5.com/darwin/beef/images/kari/06-kari_byron_shark_bikini_radio_belly_800x600.jpg

I think part of the problem is that the riddle has been stated in two different ways.

On letsrun it was stated that the treadmill moves at the same speed as the PLANE. On that boing website it states the treadmill moves at the same speed as the WHEELS.

I think the boing website is NOT the original riddle. The plane couldn't take off if the treadmill was at the same speed as the wheels - it could take off if it was the same speed as the plane.

So the plane eventually takes off because the wheels slip on the treadmill? (If I understand the discussion so far.) Thus, if you made a treadmill that was some sort of drive belt or chain and replaced the wheels of the plane with the complementary gear you could force the wheels of the plane to travel at the same speed as the treadmill. In this case, I think it is pretty obvious that the plane will not take off though.

Additionally, how much of a role do you think the airflow produced by the treadmill plays. (This is probably either a massive machine or consider a scaled down scenario with a hyper lightweight plane)

The real question is how will they end the experiment? Of course the plane will not take off. Now you have a plane going full bore and a treadmill matching that speed. Which do you turn off first?

Ohio Rulz wrote:

[quote]Physics professor wrote:

2. For the plane to move forward through the air, it is necessary for the plane's wheels to be moving faster than the treadmill.

quote]

NO! The plane's wheels don't need to be moving faster. You're assuming they'll always remain interlocked - in contact - with one another.

The vastly overwhelming force of the engine will cause jumps or disconnects between treadmill and tire. The plane will slowly accelerate, with its spinning wheels unable to absorb the force. Screeching galore.

AND, it's not like the plane immediately goes airborn, like a helicopter and zips right into a 300MPH flight. It's not like liftoff would be immediate. The plane has to get moving (not talking wheel spin rate here) fast enough to generate lift.

For the wheels to be moving at the same speed as the treadmill, and the plane to be moving forward, you have to overcome the friction between the wheels and the treadmill - like if the wheels are locked on a normal runway. I say a plane will not take off with locked wheels.

Ohio Rulz wrote:

For the wheels to be moving at the same speed as the treadmill, and the plane to be moving forward, you have to overcome the friction between the wheels and the treadmill - like if the wheels are locked on a normal runway. I say a plane will not take off with locked wheels.

Ohio Rulz wrote:

For the wheels to be moving at the same speed as the treadmill, and the plane to be moving forward, you have to overcome the friction between the wheels and the treadmill - like if the wheels are locked on a normal runway. I say a plane will not take off with locked wheels.

Of course a plane will take off with locked wheels. It just takes more thrust. Planes have taken off on carriers even though the pilot has forgotten to unlock the wheels. The catapult doesn't care if the wheels are locked or not, you're still going to get shot off the deck.

.................... wrote:

Ohio Rulz wrote:

For the wheels to be moving at the same speed as the treadmill, and the plane to be moving forward, you have to overcome the friction between the wheels and the treadmill - like if the wheels are locked on a normal runway. I say a plane will not take off with locked wheels.

Of course a plane will take off with locked wheels. It just takes more thrust. Planes have taken off on carriers even though the pilot has forgotten to unlock the wheels. The catapult doesn't care if the wheels are locked or not, you're still going to get shot off the deck.

Interesting. Did we add a catapult to the treadmill? Sweet. In that case, I say a bowling ball will take off.

wheel wrote:I say a plane will not take off with locked wheels.

Really? If a plane sitting on a (stationary) runway with it's wheels locked slowly cranked up it's engines to full blast, you think the plane would just sit there? I'm pretty sure the force created by the engines would overcome the friction at some point. I could be wrong, I suppose it would depend on the mass of the plane and on the power of the engines, but I still think any commercially made/mass produced plane would be able too.

Or use a windtunnel.

Or a stationary plane with its engines off and a big 150mph headwind comes along.

Terminator X wrote:

Really? If a plane sitting on a (stationary) runway with it's wheels locked slowly cranked up it's engines to full blast, you think the plane would just sit there? I'm pretty sure the force created by the engines would overcome the friction at some point. I could be wrong, I suppose it would depend on the mass of the plane and on the power of the engines, but I still think any commercially made/mass produced plane would be able too.

true, but with the wheels sliding rather than rolling down the runway, i'm pretty sure the friction would melt/shred/otherwise destroy the wheels and landing gear before takeoff

Terminator X wrote:

wheel wrote:I say a plane will not take off with locked wheels.

Really? If a plane sitting on a (stationary) runway with it's wheels locked slowly cranked up it's engines to full blast, you think the plane would just sit there? I'm pretty sure the force created by the engines would overcome the friction at some point. I could be wrong, I suppose it would depend on the mass of the plane and on the power of the engines, but I still think any commercially made/mass produced plane would be able too.

I don't think the plane would just sit there. But would it move in a straight line? Would the tires catch on fire and blow up the whole plane? I'm still saying the plane doesn't take off. Probably a better chance of exploding with some really exciting movement.