Why "Balloon Boy" Never Could Have Been

October 18, 2009 1:17 AM

Why "Balloon Boy" Never Could Have Been
I've written a very short paper which explains the physics behind helium lifting balloons and why nobody should ever have been worried about "Balloon Boy" Falcon Heene.
posted by alby (13 comments total)

I *love* the idea of fighting silly news stories with math and physics.
posted by mathowie at 1:18 AM on October 18

So you're telling me that little Timmy never fell into the well after all? Why do so few of us ever see that coming!?

The real kicker in this paper, and one which can be handily explained without layman bamboozling equations, is your teardrop observation. That should have been immediately obvious to anyone, amazing how 99% of brains turn off when a really good drama starts to unfold. Maybe we're getting too good at the suspension-of-disbelief aspect of entertainment, and rarely critically appraise stuff any more.
posted by samworm at 3:38 AM on October 18

Très cool.
posted by bru at 7:51 AM on October 18

If possible, you should include a third picture of the balloon in flight, so readers can compare it to the loaded teardrop balloons.
posted by zamboni at 12:38 PM on October 18

zamboni, I would have included a picture of the balloon in flight, but I was a little unsure about the copyright status of the TV images.
posted by alby at 1:13 PM on October 18

About 260-270 cubic feet of helium in an 8 foot sphere lifts about 7 pounds net, including the weight of the balloon, give or take a pound or two depending on altitude, air pressure and temperature and the dry or wet weight of the balloon.

Go!
posted by loquacious at 1:58 PM on October 18

I may be misquoting and seriously underestimating that lift amount via third party, but I'm still in the ball-park considering the weight of balloons, strings and other hardware:

From here:

Q. I want to build a lighter-than-air craft. How do I estimate how much weight a given volume of helium will lift?

According to The Noble Gases by Isaac Asimov, helium has a weight of 0.178 grams per liter at ordinary atmospheric pressure. Ordinary air is 7.25 times as dense, at 1.29 grams per liter. Each liter of helium will therefore lift 1.112 grams of dead weight.

For a real-world example, a six-foot (approximately 2-meter) weather balloon has a volume of 4.189 cubic meters, or 4189 liters. Filled with helium, the balloon would lift 4658 grams, or about 10.25 pounds. The 45 such balloons used by Larry Walters would have a combined lift capacity of over 450 pounds, which is why he zoomed to such an unexpectedly high altitude. Of course, the actual buoyancy would be slight less, since the balloon must be filled to a pressure slightly higher than ambient in order to maintain its shape.

And here:

Lift of Helium Balloons



Dia. Ft.  Vol. l     Lift gr.    Lift Lbs.



   1      14.83       15.2        0.03 

   2     118.62      121.7        0.27 

   3     400.34      410.9        0.91 

   4     948.96      973.9        2.15 

   5    1853.45     1902.2        4.19 

   6    3202.76     3287.0        7.25 

   7    5085.86     5219.7       11.51 

   8    7591.72     7791.5       17.18 

   9   10809.30    11093.7       24.46 

  10   14827.58    15217.7       33.55 

  11   19735.50    20254.8       44.65 

  12   25622.05    26296.2       57.97 

  13   32576.18    33433.3       73.71 

  14   40686.87    41757.4       92.06 

  15   50043.07    51359.8      113.23 

  16   60733.75    62331.8      137.42 

  17   72847.88    74764.7      164.83 

  18   86474.42    88749.8      195.66 

  19   101702.34   104378       230.12 

  20   118620.61   121741       268.40 

  21   137318.18   140931       310.70 

  22   157884.03   162038       357.24 

  23   180407.11   185154       408.20 

  24   204976.41   210369       463.79 



Dia. Ft.  Vol. l   Lift gr.     Lift Lbs.

For the record my theoretical "Larry Walters" attempt would have utilized a linear spring scale and the addition of an appropriate amount of water ballast to determine the actual lift weight. I can do the math with a calculator but the math will change a bit on the morning of any such theoretical launch, so you might as well measure it.
posted by loquacious at 5:56 PM on October 18

I'll never be able to watch "Up" the same way again.
posted by buriednexttoyou at 4:34 PM on October 19

I've heard lots of people mention the shape of the balloon to try to prove that it couldn't have been load bearing, but is there any reason to think it didn't have some structural support?

Look at the top of the balloon in this video you can see it's indented in the middle, indicating that there is some kind of internal structure. If there was a strong enough cable from the top of the balloon to the bottom, it would have kept it's shape.
posted by delmoi at 1:07 AM on October 22

The problem is the police should be worried when a parent makes a claim like that, whether or not the physics supports it...it was their intention to exploit the police and rescue's emotions/vulnerabilities. Sorry for derailing the convo a little...
posted by schindyguy at 11:05 AM on October 22

If there was a strong enough cable from the top of the balloon to the bottom, it would have kept it's shape.

This is true, but it would have put an enormous amount of stress on the fabric of the balloon, requiring a much, much stronger (and therefore heavier) material for the envelope. I guessed at Mylar for the balloon's skin (which seems to have been correct) and there's no way Mylar has the requisite tensile strength.
posted by alby at 6:46 AM on October 24

I'm pretty sure a screen cap of the balloon would be fair use in this instance.
posted by cjorgensen at 5:19 PM on October 25

This is true, but it would have put an enormous amount of stress on the fabric of the balloon, requiring a much, much stronger (and therefore heavier) material for the envelope.

Hmm, that's a good point.
posted by delmoi at 4:23 AM on October 26