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Message
re: Myth Busters/Can a plane take off on a conveyor belt
Posted on 10/24/07 at 9:28 pm to penthouse
Posted on 10/24/07 at 9:28 pm to penthouse
quote:
and the plane doesn't measure speed the way a car does by measuring wheel rotation.
You just answered your own question. Think about this: why does a plane not use wheel rotation to measure speed? Because the rotation of the wheels have absolutely nothing to do with the plane's speed.
Posted on 10/24/07 at 9:28 pm to LSUBoo
I think they're gonna do it with an ultra-light.
Posted on 10/24/07 at 9:30 pm to LSUBoo
quote:
No, they're trying to prove that if the plane's airpseed is a theoretical 100kts, and the treadmill is going the opposite direction at that same 100kts, that the plane would, in fact, more forward and take off.
Well then you will need a long arse fricking treadmill if you are trying to get the plane to accelerate to the counteracted rotation speed. And then another 100kts on top of that.
I will go further to say that the tires/wheels would be spinning at TWICE their normal rotation speed and probably would exceed the max speed of the tires. An F-18 takes off at about 140-150 kts. The tires are rated for 190kts (nose gear) and 210 kts (main mounts) . So tires would shred on the treadmill long before the hypothetical 300 kts they would have to be traveling in your scenario.
I think the myth is if the planes wheels are spinning at rotation speed and the treadmill is counteracting it perfectly but the plane is remaining at the same point in space but with the engine running full blast, that it could take off. It seems like it might at first, but for the airflow issue, which has been discussed in depth.
Posted on 10/24/07 at 9:31 pm to General
quote:
It's gonna be an interesting experiment.
Yep. It's going to have to be on a small scale though. You just can't build a 2 mile long treadmill to test the experiment.
Posted on 10/24/07 at 9:32 pm to General
quote:
I think they're gonna do it with an ultra-light.
I think they have to, but it's still going to be tricky as hell to coordinate the plane's airspeed with the treadmill/conveyor belt speed.
I think they tried it with an RC plane and couldn't get it accurate enough to prove/disprove the myth. Well, one forum I read said they tried it and couldn't control the plane well enough to conclude anything.
Posted on 10/24/07 at 9:32 pm to TigersRuleTheEarth
quote:
You just answered your own question. Think about this: why does a plane not use wheel rotation to measure speed? Because the rotation of the wheels have absolutely nothing to do with the plane's speed.
Thank you I'm aware of that. I'm not saying that it does. But if the treadmill is moving at 100kts then the perception is that the plane is moving 100kts in the other direction. Its faulty but that is the perception
Posted on 10/24/07 at 9:34 pm to penthouse
quote:
I will go further to say that the tires/wheels would be spinning at TWICE their normal rotation speed and probably would exceed the max speed of the tires. An F-18 takes off at about 140-150 kts. The tires are rated for 190kts (nose gear) and 210 kts (main mounts) .
Another reason they won't be able to do this with a large passenger jet or any other conventional aircraft. This is just a thought experiment. Who in their right mind would run a plane on a treadmill?
Posted on 10/24/07 at 9:37 pm to penthouse
And I would like to thank you all for making me miss South Park. 
Posted on 10/24/07 at 9:40 pm to TigersRuleTheEarth
I didn't see what you guys said but the plane will definitely take off
The plane is going to use it's thrusters to get up to speed and it's not going to be slowed at all by the conveyer belt
The plane is going to use it's thrusters to get up to speed and it's not going to be slowed at all by the conveyer belt
Posted on 10/24/07 at 9:42 pm to Powerman
you are a complete a-hole.
Posted on 10/24/07 at 9:57 pm to penthouse
think of it this way.
"takeoff speed" = 100 knots
conveyor belt traveling -100 knots
Plane anchored in place much like you would be if you were on a treadmill wearing skates and held on to the handrail.
wheels are spinning at 100 knots worth of rpms even though ground speed is 0.
now add some thrust...enough thrust to theoretically "anchor" the plane in place. thrust is x, ground speed is 0, and wheels are spinning at 100 knots worth of rpms. Even though the wheels are turning, you have equilibrium between the deccelarating force of the friction and the accelarating force of the thrust.
now add more thrust, thus overcoming the equilibrium and creating forward movement. Once you have forward movement its only a matter of degree to achieve "takeoff" groundspeed, and flight is theoretically possible.
"takeoff speed" = 100 knots
conveyor belt traveling -100 knots
Plane anchored in place much like you would be if you were on a treadmill wearing skates and held on to the handrail.
wheels are spinning at 100 knots worth of rpms even though ground speed is 0.
now add some thrust...enough thrust to theoretically "anchor" the plane in place. thrust is x, ground speed is 0, and wheels are spinning at 100 knots worth of rpms. Even though the wheels are turning, you have equilibrium between the deccelarating force of the friction and the accelarating force of the thrust.
now add more thrust, thus overcoming the equilibrium and creating forward movement. Once you have forward movement its only a matter of degree to achieve "takeoff" groundspeed, and flight is theoretically possible.
Posted on 10/24/07 at 10:03 pm to penthouse
quote:Please tell me that you are not a pilot.
you are a complete a-hole.
No way the government lets someone as dumb as you about physics and aviation in the cockit.
Unless it's just to clean it out for a real aviator.
Posted on 10/24/07 at 10:10 pm to penthouse
quote:
you are a complete a-hole.
Maybe
But I can promise you the plane will take off with no problem
Posted on 10/24/07 at 10:14 pm to just me
This is the way I see it
The plane takes off due to the force of the engines. Planes don't get up to take off speed the same way a car gets up to speed because it isn't powered by a drive shaft turning wheels. The force of friction on the wheels is negligent when compared with the force of the thrusters.
The plane won't have a net linear velocity of zero because the conveyor belt isn't really opposing the linear motion. The wheels just spin faster and the plane should move at the same speed.
The plane takes off due to the force of the engines. Planes don't get up to take off speed the same way a car gets up to speed because it isn't powered by a drive shaft turning wheels. The force of friction on the wheels is negligent when compared with the force of the thrusters.
The plane won't have a net linear velocity of zero because the conveyor belt isn't really opposing the linear motion. The wheels just spin faster and the plane should move at the same speed.
Posted on 10/24/07 at 10:29 pm to Powerman
Yes, except for this part:
quote:And I'm sure you know where you made your error.
The force of friction on the wheels is negligent when compared with the force of the thrusters.
Posted on 10/24/07 at 10:36 pm to just me
reckless
Posted on 10/24/07 at 10:52 pm to just me
Nobody is saying that a plane can't overcome the treadmill, its the distance that it would require to overcome it and the fact that it would have to be such a long as treadmill that makes it so ridiculous.
Posted on 10/24/07 at 10:54 pm to penthouse
quote:
Nobody is saying that a plane can't overcome the treadmill
A lot of people have said that.
quote:
the distance that it would require to overcome it and the fact that it would have to be such a long as treadmill that makes it so ridiculous.
The whole premise is rather ridiculous... kind of like turning a canoe upside down and using it as a submarine. (Another myth they're going to try and bust in the new episodes)
Posted on 10/24/07 at 10:54 pm to just me
And I will probably get banned for this.
But Justme can suck my fricking cock. I've dropped to many bombs and killed way too many people to put up with shite from pissant lawyer on a message board.
Semper Fi and frick You
But Justme can suck my fricking cock. I've dropped to many bombs and killed way too many people to put up with shite from pissant lawyer on a message board.
Semper Fi and frick You
Posted on 10/24/07 at 10:54 pm to just me
quote:
And I'm sure you know where you made your error.
negligible
Took me a second to catch it
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