airplane on convayor

[jbuckl]

But Kev, what colour are the planes in the black hole? Red or yellow?


I suppose it depends on which end of the black hole you are looking down?


There are no ends to a black hole ..... how can we set up sketcher without a normal?


( datum on the fly?.....cant get off the ground! not without a conveyer any way)


Heck its going to be a long day..... ooh it is the longest day (summer solstice)


I know, lets all go to stonehenge..... too late the suns already risen ahh.... need to do some time travel down a black hole oops.... its all crashed..... too many questions I think....by the way when is the Vulcan going to take off? (XH558)


Too many parent child circular references here now, better start a new model / thread.

 

[goosemonster]

I just can

 

[SW]

Where did it say the plane isn't moving?

Sam

 

[pjw]

The amount of air sucked into and expelled from the engine is irrelevant.

 

[pjw]

Surely the amount of air 'sucked' into an engine determines how much fuel can be burnt for stoichiometric combustion and hence how much thrust the airplane can produce?


How is it irrelevant goosemonster?

 

[farmerpat]

A detailed free body diagram would explain it all!


I think the wheels are going to spin 2x speed and the plane will fly away. There is no thrust from the wheels.

 

[verge]

I love it! Your first post, and you're calling for a detailed free body diagram! The chutzpah of it!

Of course, I wouldn't mind seeing that myself. I'll just tell my family that I'll be busy in the evenings figuring out an airplane on conveyor problem...that should go over well.

 

[prohammy]

I love it! Your first post, and you're calling for a detailed free body diagram! The chutzpah of it!

Of course, I wouldn't mind seeing that myself. I'll just tell my family that I'll be busy in the evenings figuring out an airplane on conveyor problem...that should go over well.

Easy solution to the problem.....Ditch the family

(Course that's a very expensive way to solve a very simplistic problem that the answer is already out there for)


Kev

 

[verge]

Easier solution - do it on company time!

 

[phoxeoy]

I'm just picturing a plane on a conveyor. The conveyor starts to move. The plane's wheels start spinning the other direction but the plane is still stationary. The plane starts it's engines. The plane thrusts and the conveyor spins faster but the plane starts moving anyway and all that the conveyor is doing is spinning the plane's tires faster than normal. There is nothing preventing the plane from moving forward, the tires are free to spin. The plane's thrust is pulling the air to make the plane move. It does not move because the engine drives the tires. End result, a plane in the air with very fast spinning tires.

 

[Rbrgr83]

I just can

 

[prohammy]

I also think that we can all agree that having a self powered mini black hole in the back of your car for a subwoofer would be totaly kickass. "Oh, I know you can't hear or feel the bass, but that's just because it's 58 times below the audible frequency range. Trust me it's there"

Rb,


Gotta say that if you go down your local ASDA (KMART in US) with such a system late in the night, this is bound to impress the natives


Kev
Edited by: prohammy

 

[goosemonster]

OK the wheels aren

 

[jraquet]

OK the wheels aren

 

[goosemonster]

JRAQUET WROTE -No, the conveyor moves backwards spinning the wheels twice as fast


what makes you think that? If a 1m dia wheel turning at 100 rpm is on a treadmill type thingy moving at approx 314 meters/min the other way, the wheel will not move in relation to a fixed point.


Why would the wheel acc to 200rpm???

 

[jraquet]

Yes, if you are holding the wheel in place on the treadmill. If you move or "walk" with the wheel (with your feet on the ground not on the treadmill) the wheel will move, but will spin faster regardless of the speed of the treadmill.


You are providing the thrust to the wheel assembly (the wheel axle/suspension) just as the engines are providing thrust to the body of the plane. (There is no motor driving the wheels, they are free to rotate).

 

[Rbrgr83]

I hate to throw another analogy out there, but here we go.


Same example as jraquet. We have a roller skate on a treadmill. If the treadmill is off and you pull the shoe string @ 1m/s then the skate will move forward at 1 m/s


If you turn the treadmill on and hold the string, the skate will be stationary with the wheels rolling. However, if you pull the skate at the same 1m/s, the skate will move forward at the same 1m/s.


This difference is
a) The wheels will spin faster to compensate for the conveyor
b) You have to pull with more force to compensate for the added friction.


So, while it may require more thrust to achieve takeoff, it will still happen (and the frictionto overcome on the airplane will be reletively minute) The only other difference will be the speed of the wheels. And as jraquet said, the speed of the wheel is dependant on the speed of the conveyor and the plane, not vice versa. The wheels are free rotating, not driven.

 

[goosemonster]

<DIV =comment-content>


This guy goes fishing with the priest from his church. They're relaxing and enjoying the day when suddenly the priest snags a giant fish. He reels it in, and his amazed companion says "Whoa, look at that son of a bitch!"


"My son," says the priest, "you shouldn't use language like that; the Lord is watching."


The guy, trying to cover his mistake, says, "Oh, Father, you don't understand; the name of this type of fish is 'son of a bitch.'" The priest buys it and is pleased to have learned something. He decides to take the fish home for the dinner that night with the archbishop. He returns to the church and finds a nun. He gives her the fish and says, "Sister, look at this huge son of a bitch I caught! Would you please cook it for our dinner with the archbishop?"


"Father!" the sister gasps, horrified. "You're in the house of the Lord; how can you use such language?"


"Oh, Sister, you don't understand; this type of fish is called a 'son of a bitch.'" The nun is also amazed at this fact, and takes the fish to prepare it.


The archbishop comes over and the three sit down to enjoy their meal. They're just about done, and the archbishop says, "My, this fish was excellent."


The priest says, "Yep, I caught the son of a bitch myself!"
The nun says, "And I cooked the son of a bitch myself!"


The archbishop looks confused for a moment, then leans back in his chair, smiles, and says, "You know, you fu*#ers are all right."</DIV>

 

[slacender26]

enough of your fight


now after so much experimentation i have found a answer to it .


so plz see it and dont talk on it futher.


Here's the original question: "A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"


The implicit assumption is that if the conveyor belt's speed backward exactly counteracts the airplane's "speed" (whatever that means) forward, the plane remains stationary relative to the earth and, more importantly, to the air. (We assume the winds are calm.) With no wind moving past its wings, the plane generates no lift and can't take off.


But the assumption is false. While the conveyor does exert some modest backward force on the plane, that force is easily overcome by the thrust of the engines pulling the plane ahead. The plane moves forward at roughly its usual speed relative to the ground and air, generates lift, and takes off. Many people have a hard time grasping this (although it can be easily demonstrated in the lab), but eventually they do, smack their foreheads, and move on. We'll call this Basic Realization #1.





The answer is yes. Understanding why is Basic Realization #2.


The conveyor doesn't exert much backward force on the plane, but it does exert some. if you're standing on a treadmill wearing rollerblades while holding a rope attached to the wall in front of you, and the treadmill is switched on, your feet will initially be tugged backwards. Partly this is due to friction in the rollerblade wheel bearings, but partly--this is key--it's because the treadmill is accelerating the rollerblade wheels and in the process imparting some angular (rotary) but some linear (backward) momentum to them. You experience the latter as backward force. Eventually the treadmill reaches a constant speed and the rollerblade wheels cease to accelerate. At this point you can easily haul in the rope and pull yourself forward.


But what if the treadmill continues to accelerate? Different story. In principle it's possible to accelerate the treadmill at a rate that will exactly counteract any forward force you care to apply. (This is a departure from the original question, which said the conveyor belt compensated for the plane's speed,, not its force.) The only mathematics needed to demonstrate this is the well-known physics axiom F = ma--that is, force equals mass times acceleration. Given that the conveyor exerts some backward force F on the plane, we simply crank up the acceleration as much as necessary to equal any forward force F generated by its engines. Result: The plane stands still and doesn't take off.

 

[bobb]

Did anyone see Mythbusters last night (30Jan08)? The plane took off!!! They pulled a long tarp down the runway with their truck while the plane went the other way and took off with no problem!!!


Bob