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Mythbusters Show Tonite


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Did anyone watch the Mythbusters show tonite where they use a model helicopter to test whether a container becomes lighter if it hovers? Actually they were testing to see if birds lighten a trailer, but they used a R/C copter as well to test the idea.

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Guest pokey
Sounds like they're grasping at straws over there at MB. Newton's 2nd anyone??

 

 

Newton's 2nd makes it wayyyyyyyyyyyy too easy to understand. I agreee w/ Fuse, there is a point where altitude comes in to play. I ddint see how they set up their test so i cant really say to much for sure.

 

I liked the original thread, a talking chicken ! :blink:

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I might be taking this too seriously....

 

If the container is hovering, it isn't lighter since lift and weight are equal and opposite. When the container is being accelerated off the ground, it's relative weight is changed because of the way we measure weight: a scale on the ground would indicate less weight ("light on the skids"), a scale inline between the RC copter and the container would show an increase in weight. This is the same as riding Judge Roy Bean's scream. On the way down, drop a penny it floats in front of you. It has no relative motion (no change in speed, forces balanced); if you throw it up, it appears to move very fast relative to your downward path, and if you throw it down (at the same velocity) it has some speed, but less relative speed to you throwing it up. To an outside observer, there is no difference between the velocity of a penny thrown up or down. Relativity light. There's a wiki on this. When I got to buoyancy I realized I was definitely taking this too seriously.

 

The other way to consider weight is from the m=F/A perspective, where weight=F and acceleration=gravitational acceleration (32 ft/s^2 if I wasn't snoozing through that part of physics). Farther from the Earth's core, F decreases, so at very high altitudes m decreases. This decrease is negligible though, even in orbit ("weightlessness" is a different phenomenon).

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Guest pokey
Of course, if you get it high enough, everything becomes weightless. Hard to hover in a vacuum, though.

 

reminds me of my hi-school daze :lol:

 

Gomer? are you not flying in the GOM anymore?

 

 

i have yet to see how the MB set up their experiment, i am thinking tho that a hovering helicopter emits it's weight in the rotor downwash?----------never mind as i havent a clue how they did it. ( i'm still thinking about a truck full of talking chickens)

 

 

officer pulls over man driving pickup truck filled w/chickens, and asks "what are you doing w/all those chickens?" Guy replied "i dont know what to do with them" Officer suggests taking them to the zoo just up the road a few miles,,,,,,,,, next day, officer pulls guy over again, only this time all the chickens have popcorn & cold drinks with them, officer says "didnt i tell you yesterday to take them chickens to the zoo?" guy replies " yes you did & we all had a wonderful time, but today they want to go to the movies"

 

:rolleyes:

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Thanks for the reply guys. I wasn't quite satisfied on how they did the test and the R/C helicopter was lifted into a ground effect hover (skids within 6-12") of the surface and the rotor diameter appeared to be in the rang eof 18-24".

 

The set up a large container with strain gauges at each corner hooked to a computer to measure weight. Then they got the tare weight of the container and R/C helicopter (along with birds in another test), the R/C was then lifted off and flown to see if the weight increased or decreased. My opinion is that because of the the downwash created bu being in ground effect, the weight would not have changed and this was shown in fact. But if the R/C could have gotten out of ground effect and flown towards the top of the container, I think the results would have been different.

 

Another side note, some professor was interviewed by the cast (from UCSF I think), and said that birds and helicopters were very similiar in how they flew. Birds "pushed" them selves through the air, and helicopters forced air down to create lift (equal and opposite reaction). If my memory serves me correctly from ground school, lift created by downwash is secondary in nature. The primary lift is created by the difference in air pressure across the airfoil (Bernoulli principle), but please correct me if I am wrong....

 

What do you guys think here?

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