Mythbusters tackles the plane/treadmill

[Pitbozz]

I think it is hilarious that people get heated debating this subject. I voted no, maybe my understanding of the principles of flight are off but I thought it happened because of the following:

Lift occurs because the air moving under the wing is travelling faster than the wind going over the top of the wing.

How does a plane on a treadmill make this happen, with no wind travelling under the wing???

Using this same logic, a really powerful car on a dyno would not spin the tires on the dyno of it had a really big wing on the back

Maybe that is why ricers have those big wings, to increase the downforce, so they won't spin

Problem with the dyno comparison is a car is wheel driven. An airplane is not. Reference the guy on rollerblades on a treadmill. A rope attaches to his waist and to the handle. Turn the treadmill to 5mph or 500mph. The speed does not matter. He stays stationary (barring wheel/bearing failure). Now pull on the rope or have someone push you(this would be the engine thrust on a plane). What happens? You move up the treadmill with extremely little resistance.

The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.

 

[Pitbozz]

I understand what you are saying, but the question says it is equal speed. Lets say the treadmill will go to whatever speed it takes to match the plane. I agree that if the treadmill cant keep up then it will fly, but that is not what the question ask or states. I think to answer this we need more details on how the speed is measured. I dont disagree with you I just think if the treadmill is respondind to air speed of the plane it will fly ,but if the plane is responding too speed of the treadmill to keep up/equal it wont fly.I think everybody is getting away from the EQUAL PART, but equal to what?

The speed doesn't matter. The treadmill doesn't matter. Measure the speed any way you want to and double, triple, quadruple, multiply it by 500. It doesn't matter.

Reference my rollerblade analogy above.

And sorry, one more time:

The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.

 

[Pitbozz]

The poll is damn near at 50-50. I was not expecting that.

 

[TurboTnZ06]

This isn't going well. Then again, I done got me my degree in inginearin at an aironoticull universitee

Plane can fly, wheels don't provide thrust, the prop does, well, differential pressures do, but the plane will move and take off if the treadmill is long enough.

 

[87Jen]

You guys have made my brain hurt for two days watching this, and I have just realized I voted WRONG!

 

[hounddogs!]

Another correct vote to get us a little farther away from 50-50.


For 10 bonus points, assume:
1. Lift is developed by high speed (low pressure per Bernoulli) air above a foil and lower speed (higher pressure) under.
2. Hot air is less dense than cool air.

How long is lift-off delayed due to the fact that the wheel bearing fire warmed the air under the wings?

 

[Pablo]

Another correct vote to get us a little farther away from 50-50.


For 10 bonus points, assume:
1. Lift is developed by high speed (low pressure per Bernoulli) air above a foil and lower speed (higher pressure) under.
2. Hot air is less dense than cool air.

How long is lift-off delayed due to the fact that the wheel bearing fire warmed the air under the wings?

Hahaha, nice angle though I don't think a wheel bearing fire is plausible at only double take off speeds

I used to rebuild aircraft wheels and tires and the bearings are essentially like the ones on your car. Whats an airliner take off at, 175 or so? I think they would handle 350 mph ok.. now the tires, maybe not.. but i do recall reading that a lot of the land speed cars used aircraft tires for their records.

You are also ignoring the fact that heat can create updrafts.. :biggrin:

 

[Pitbozz]

Hahaha, nice angle though I don't think a wheel bearing fire is plausible at only double take off speeds

I used to rebuild aircraft wheels and tires and the bearings are essentially like the ones on your car. Whats an airliner take off at, 175 or so? I think they would handle 350 mph ok.. now the tires, maybe not.. but i do recall reading that a lot of the land speed cars used aircraft tires for their records.

You are also ignoring the fact that heat can create updrafts.. :biggrin:

This is the most fascinating aspect of this scenario to me. The people who are adamant that the plane won't take off always point to the bearing/tire failure issue. They don't have a problem with imagining a treadmill the length and width of a runway. Nope, that's easy! But a bearing or tire that can handle 2 or 3 hundred MPH? Ain't no way in hell that can exist!

 

[Pablo]

This is the most fascinating aspect of this scenario to me. The people who are adamant that the plane won't take off always point to the bearing/tire failure issue. They don't have a problem with imagining a treadmill the length and width of a runway. Nope, that's easy! But a bearing or tire that can handle 2 or 3 hundred MPH? Ain't no way in hell that can exist!

hahahaha, good point

 

[corsair231]

The Earth is a treadmill. Just like a treadmill, what goes around comes around 24 hours later. Thanks to gravity though, unlike on a treadmill, the plane will not fall off of the backside of the belt. I'm not sure how fast the rotational speed is but it rotates from west to east faster than most aircraft can fly. Take a plane facing west. It is sitting on the ground. The friction from the brakes and wheel bearings keep it sitting in one place on the treadmill, just like the plane would do if the treadmill was brought up to speed slow enough that the inertia of the plane did not overcome the friction of the bearings. So now you have a plane theoretically going backwards on the treadmill faster than it can fly forward.

Start the engine. Release the brakes. Increase the throttle and although everything including the plane is still moving backwards, from west to east including the atmosphere, the plane starts to move forward relative to the enviroment. Since the wings act in the fluid known as air when the plane "slows down" enough from it's backward direction the fluid pushes up on the wings and the plane leaves the ground. It is now doing what we call flying. Despite the planes forward motion relative to the ground where it started and the distance above that ground, until it exceeds the speed of the Earth's rotation, it is still going backwards faster than it is flying forward. But it's still flying. :tongue: :biggrin:

 

[need boost]

way I see it ok, plane on treadmill, plane starts making power, treadmill speeds up enough plane still is sitting still in place, not flying off the back of the treadmill. No matter how much power the plane makes treadmill keeps up so plane stays still. It will not fly guys, it takes air rushing over the wings to create lift to get it off the ground. The hairier [ i think thats it but not spelled right lol ] uses adjustable motors to point the thurst downward to lift the plane off the ground but a regular jet just shoots the power backwards to get it fast enough to get wind going over the wings creating lift. Thats why a plane has to run down the runway fast enough before it flys, wind over the wings.

 

[need boost]

But a bearing or tire that can handle 2 or 3 hundred MPH? Ain't no way in hell that can exist!
ps they do man, they run them out on the salt flats all the time on some of the super fast rocket stuff. The tires usually don't last to long but they do last for a while as they are multi layer stuff. Plus you got to remember that the bearing is small, the tire is say 15 in or bigger so at 300 mph on the tire the bearing is not moving near as fast as that.

 

[bobc455]

So are you saying the plane wouldn't take off because the tires would blow and and the wheels would fall off so the airplane would collapse onto the conveyor belt in a ball of flames?

-BC

 

[Pitbozz]

way I see it ok, plane on treadmill, plane starts making power, treadmill speeds up enough plane still is sitting still in place, not flying off the back of the treadmill. No matter how much power the plane makes treadmill keeps up so plane stays still. It will not fly guys, it takes air rushing over the wings to create lift to get it off the ground. The hairier [ i think thats it but not spelled right lol ] uses adjustable motors to point the thurst downward to lift the plane off the ground but a regular jet just shoots the power backwards to get it fast enough to get wind going over the wings creating lift. Thats why a plane has to run down the runway fast enough before it flys, wind over the wings.

There is absolutely nothing keeping the plane from going down the runway/treadmill just like normal. Reference the video link I posted or the rollerblade scenario.

The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.

 

[Pitbozz]

But a bearing or tire that can handle 2 or 3 hundred MPH? Ain't no way in hell that can exist!
ps they do man, they run them out on the salt flats all the time on some of the super fast rocket stuff. The tires usually don't last to long but they do last for a while as they are multi layer stuff. Plus you got to remember that the bearing is small, the tire is say 15 in or bigger so at 300 mph on the tire the bearing is not moving near as fast as that.

Of course there are bearings and wheels that can handle it. My post was sarcasm which should have been crystal clear.

 

[BLACK6PACK]

way I see it ok, plane on treadmill, plane starts making power, treadmill speeds up enough plane still is sitting still in place, not flying off the back of the treadmill. No matter how much power the plane makes treadmill keeps up so plane stays still. It will not fly guys, it takes air rushing over the wings to create lift to get it off the ground. The hairier [ i think thats it but not spelled right lol ] uses adjustable motors to point the thurst downward to lift the plane off the ground but a regular jet just shoots the power backwards to get it fast enough to get wind going over the wings creating lift. Thats why a plane has to run down the runway fast enough before it flys, wind over the wings.

The question says nothing about the plane setting still. The question states that the belt matches the speed of the plane. The plane moves forward at 10 mph the belt moves backwards at 10mph. If you look right out of the plane while sitting in the pilot's seat, you'll see trees going by just like you would if you were driving 10mph in a car. You get up to 100mph (take off speed) you look to your right, the trees are now going by at 100 mph. The conveyor belt is moving backwards at 100mph. The tires are turning at 200 mph. You take off.

The speed of the plane is measured by an air speed indicator. Lets just say its a little windmill on the windshield, and it has a transmitter that signals the air speed of the plane to the conveyor belt. When the air speed indicator reaches 100mph the conveyor will be going 100 mph in the opposite direction.

The problem with your scenario is that if the plane isn't moving forward, the belt doesn't move either, so they both sit there doing nothing.

 

[BLACK6PACK]

Another way to look at it is a water plane. A plane with floats instead of wheels is tied up in the middle of a river that flows at 30mph. The plane has a take off speed of 30 mph. The plane, with its given power, can easily reach 60mph on water if needed. The plane powers up enough so that when its untied it sits still in the river (looking out the window to the right, the trees aren't moving). In relation to the water its moving at 30 mph, say you had a paddlewheel on one of the floats measuring water speed. The plane gives it full throttle and starts moving forward on the river. Once it hits 30mph forward motion it takes off. At that time the paddle wheel is measuring 60mph.

 

[noslo6]

way I see it ok, plane on treadmill, plane starts making power, treadmill speeds up enough plane still is sitting still in place, not flying off the back of the treadmill. No matter how much power the plane makes treadmill keeps up so plane stays still. It will not fly guys, it takes air rushing over the wings to create lift to get it off the ground. The hairier [ i think thats it but not spelled right lol ] uses adjustable motors to point the thurst downward to lift the plane off the ground but a regular jet just shoots the power backwards to get it fast enough to get wind going over the wings creating lift. Thats why a plane has to run down the runway fast enough before it flys, wind over the wings.

The treadmill will not keep the plane from moving in relation to the air and earth. The treadmill simply will spin the plane's wheels nothing more...nothing less. The treadmill is irrelevant... again, the treadmill is irrelevant. I think that has been stated at least once.

 

[acoen]

The treadmill will not keep the plane from moving in relation to the air and earth. The treadmill simply will spin the plane's wheels nothing more...nothing less. The treadmill is irrelevant... again, the treadmill is irrelevant. I think that has been stated at least once.

Exactly, All that needs to be done is a simple test. place a Hot Wheel on a moving treadmill. Holding it in place, the wheels just spin, increase the speed of the treadmill, same thing.....wheels spin faster. Your hand acts like thrust holding the car in one place overcoming gravity and friction (or the Hot Wheel or plane would race backwards off the treadmill). Increase thrust by moving your hand forward. Increase the speed of the treadmill all you want. As thrust from your hand increases or in the case of the airplane the thrust from the prop increases the plane moves forward until take off speed is reached.

Simple as that!

 

[jpratt]

Exactly, All that needs to be done is a simple test. place a Hot Wheel on a moving treadmill. Holding it in place, the wheels just spin, increase the speed of the treadmill, same thing.....wheels spin faster. Your hand acts like thrust holding the car in one place overcoming gravity and friction (or the Hot Wheel or plane would race backwards off the treadmill). Increase thrust by moving your hand forward. Increase the speed of the treadmill all you want. As thrust from your hand increases or in the case of the airplane the thrust from the prop increases the plane moves forward until take off speed is reached.

Simple as that!

I should not post after lunch, much too sleepy.