Could a helium balloon that size even lift a 50lb child?

I was really surprised when the balloon landed, and I saw the size of the balloon. It seemed to be about 20 feet in diameter, by maybe 4 feet tall when it was flying. so the area (PiR squared) would be 310 cubic feet if it was a 20x20 sphere, which it was not.

According to Yahoo answers, a cubic foot of helium can lift, the weight of the air it displaces. http://answers.yahoo.com/question/index?qid=20070107183329AAWq8ul

"At sea level, air weighs about 0.078 pounds per cubic foot, so the upward buoyant force on a cubic foot of helium is about 0.078 pounds."

Now at sea level air weighs more than at Denver's elevation, so at 5,000 ft above sea level that balloon could carry less weight.

Even if it were double that size (600 cubic feet),At sea level that 600 cubic foot balloon could lift 600 (X)times .078 pounds, or 46.8 pounds (including the mylar skin)

My conclusion is that the balloon in question (in a balloon that was more like 300 cubic feet) would not get off the ground with a 50lb child on board.

So I have great hopes that the boy is OK.

But that's from seeing adults carrying roughly the same volume of helium balloons.

Um.

I've no idea. My instincts are telling me: "ArrOOOOOOGA. BALONEY ALERT." But my instincts been wrong before.

:thumbsup:

They can carry several hundred pounds. But in this case IDK. I hope you are right.

So with a diameter of 20':

4/3 * 3.1416 * (10^3) = 4/3 * 3,142 = 4,084 cu ft

..balloon would be?

I'd like some help on the math. I was just guess-t-mating.

Thanks!

And it wasn't that big because it was thin around the edges.

A cylinder 20 feet in diameter and 4 feet high would be around 1,256 CF. Pi*(10)^2*4 = 3.14*100*4 = 1,256. 1600 CF would be correct if the object were a rectangular prism.

My Math-Fu is weak today.

I just started tutoring recently, so a lot of this stuff is fresh in my mind. It's good to know that my fears of my brain turning into mush after college are unfounded.

I don't exercise the math much in what I do, other than for bandwidth and storage space calculations.

But I try to find practical applications all the time. As of late, that's been finding the relative values of various pizza sizes :)

:crazy:

So around 1,000 CF. You'd need a lot more information than what's available to get a more exact number because it's not a typical geometric shape, but that's probably pretty close. A 20x20x4ft object would have 1600CF volume, I'd imagine this balloon is about 2/3rds that.

so can we divide by 5? 4,084/5 = 816

816 X .078 = 63 lbs at sea level. Less at 5,000 above sea level. Maybe 50lbs at Denver's altitude. The mylar, maybe 20lbs, so it could carry a 30Lbs. payload. Is that correct?

But we're stabbing about wildly here, we're not really sure how big the things meant to get. I think we might give pause, it's actually a closer thing than I thought, I was expecting it to be out by maybe an order of magnitude.

Are there any pics of it fully inflated? with anything for size comparison.

It occurs to me also that Dad would probably have an idea of what if could lift and if it was a ludicrous idea that Falcon ended up in the balloon probably this story would never have made it out....

Hm.

So that means 98 lbs at sea level. I don't know the relative density of the air at 5,000' (even though I lived in Denver for 10 years). But whatever it is, apply that ratio and viola.

The 1,256 figure would be for a cylinder 4 feet tall and 20 feet in diameter. This object is a saucer, not a cylinder. I'm guessing it's closer to 1,000 CF.

So if we take 4084 cubic feet as the volume of a "normal" 20' diameter
sphere, and we assume that the balloon was (say) 6' thick at the center,
we can then assume that the volume of the balloon is 4084 * 6/20 =
1225 cubic feet.

Tesha

that the boy unleashed the contraption to see what it would do, then headed for the hills. I agree that it probably wouldn't have gotten off the ground with the boy in it.

And then was afraid and is trying to blame the loss of the balloon on his (presumably) younger brother.

Either way, I hope the 6 year old is located, safe and sound. But I admit to feeling that there's something just not quite right with the way this story has been reported.

The kid got scared about getting in trouble and went somewhere to hide.

That's my best guess.

that there was a basket attached that wasn't meant to carry people but batteries for experiments. They did not say what size batteries.

Looks to me like about 15ft diameter.

Maybe it could drag a kid along the ground, but soar, I don't think so.

It might be a close thing...

No basket?

lets see now 20 ft circle 4 ft tall average, 10x10x3.14=314 sq ft x 1 ft gives 314 cubic ft, now times say 4 ft tall and you have 1256 cu ft.

I think the OP calculated the volume of a flat disk :)

Sid

too me it looks like, considering the oval shape from top to bottom, to be somewhere around 8 maybe 9 hundred cubic ft.

The balloon should be able to lift between 70 and 100 lbs, depending on it's volume.

Sid

1256 X .078 = 97 Lbs at sea level, minus weight of the balloon (20 lbs?) = 77lbs at sea level, less at 5,000 feet above sea level.
Maybe it could lift a child. I hope not.

Maybe it is only 15 ft in diameter. It just does not look like it could hold over 1,000 cubic feet of volume.

If it had flat walls, that would be correct. But the actual figure is less because it curves in around the sides. I'd say it's closer to 1,000 CF.

Not a good sign, and probably indicative of the fact that the balloon could not carry the weight and that the basket broke off somewhere after taking off.

:hi:

I can't remember the exact numbers, but it was something like 5,000 helium balloons to lift a kid and a warehouse sized balloon to lift an adult.

Myth statement Status Notes
A 4 year old child can be lifted by a bunch of party balloons. Busted It would require such a large number of balloons (3,500) to lift an average four-year-old girl of 44 pounds (20 kg) just a few feet off the ground that there is no way the myth could have happened unintentionally.
http://en.wikipedia.org/wiki/MythBusters_%282004_season%29

Keep in mind there's a big difference between 3,500 separate balloons (each adding both buoyancy AND weight) compared to a single, large, Helium-filled balloon.



See also:

Girl swept away by balloon

A British five-year-old girl has been killed after being swept away by a helium balloon in Germany.

Her body was found two hours later near the balloon, 40 miles (70km) away.

The freak accident happened when the girl became entangled in the mooring ropes of the balloon as it was taken by high winds.

It was about to be used for fun rides at a British military show at Rheindalen, near Moenchengladbach in western Germany.

British military spokeswoman Lt Col Helen Wildman said the plan was to lift people up and down with the balloon tethered to a rope on a hot, sunny day.

More:
http://news.bbc.co.uk/2/hi/europe/2973922.stm

One priest even died in the ocean that way.

<snip>

Helium Raft

Myth: If you fill a raft with helium, you can fly on that raft

"This wins as the strangest position I have ever been in on this show." - Adam

"Don't you love how he qualifies it with, 'on this show'?" - Kari

Previously: * Lawn Chair myth * Helium Football myth
Test 1: Inflated dingy

They inflated a small dingy (raft) with helium to see if it would fly. They first filled it with air and measured the volume, which was 20.5 cu ft. Then they refilled it with helium to see how much weight it would lose. The helium-filled raft gained 4 lbs of buoyancy -- nowhere near enough to fly even by itself.
Test 2: Airline life raft

They figured that filling up a larger raft may get them closer to liftoff, so they tried out a 25 ft. diameter life raft. The helium-filled raft lost 1/4 of it's weight -- about 60 lbs. It still wasn't enough for liftoff.
Test 3: Escape slide raft

They next tried the escape slide raft (last seen in the Escape Slide Parachute Myth, which can hold 325 cu ft of helium. The escape slide lost about 40 lbs but still weighed 121 lbs -- no liftoff.
The math

It takes 16 cu ft of helium to lift 1 pound. In order to lift 300 lbs (200 lb Jamie/Adam plus a 100 lb raft), it would 5000 cu ft of helium, which is approximately 1/3 the cabin size of a DC-9 airplane. For reference, the Hindenburg carried 7,000,000 cu ft of hydrogen.
Massive pontoon raft

Given the need to build a raft for 5000 cu ft of helium, they decided to make pontoons out of heat-sealed polytubing, which is a clear plastic tubing used to transport A/C around a movie set. Their 50 ft test pontoon had 5 lbs of buoyancy -- a little bit less when you consider the tape to hold together the tubes -- which means that it would take 40-50 tubes in order to lift Jamie or Adam.

The final raft design: * 2500 ft of plastic tubing * 2 tiers of 25 pontoons each, set cross-wise to each other * packing tape at 10 ft intervals to stitch the pontoons together * silicon caulk and zip ties to seal each tube * water jugs to use as ballast * netting across the top of the pontoons

Prophetically, back at M5 Adam declared, "It's looking to be nigh impossible to pull this off"

They used what appears to be a hanger at Alameda to assemble their gigantic raft. It took took two days to construct and used up 36 cylinders of helium. Adam and Jamie weren't very thrilled with the difficult build:

"Once in every generation a myth comes along that does not thrill us" - Adam (in helium voice)

"This is strange, I have never seen anything like this before" - Jamie

"It has to be the single largest thing I have ever built, bar none, let alone in two days" - Adam

Adam was, however, happy with his outfit:

"This is my new toy, my new SWAT team tactical black climbing harness. My sister gave it to me. My whole family is like this." - Adam

"I'm wearing the wetsuit because it makes me look good, damn good." - Adam

Adam, in black SWAT team tactical climbing harness and wetsuit, was lowered onto a mini-raft on top of the massive raft. They started cutting the ballast on the raft, but one part of the raft started raising too quickly, sliding Adam off his mini raft, down between the pontoons, until he was hanging beneath the raft hanging inside of the netting they had spread across the raft.

Jamie: "Hey Adam"
Adam: "Yeah"
Jamie: "This isn't working"
Adam: "No, it seems to have failed utterly"
Jamie: "You've liked slipped right through to the bottom side"
Adam: "I feel like something that got cut out of The Matrix here."
Jamie: "Are you alright"?
Adam: "I'm fine. I'm upside down and I'm in a net and I'm below the biggest thing ever built out of helium and balloons, but I'm fine."

Adam was cut out of the net and then started taking a knife to the helium pontoons. A very high-pitched Kari declared, "Oh my god, we might need to open a door. It's getting kind of weird."

A very tired/frustrated Adam declared this one busted. A raft would have to be too big and unwieldily to lift a person.

More:
http://kwc.org/mythbusters/2006/04/episode_49_cellphones_on_plane.html

Seeing Adam dangling helplessly in the netting.

It's all Archimedes' Principle.

so that the helium CAN lift the weight and still be strong enough to hold. The foil they used was thinner than aluminum foil but 10 times more fragile.

but given that Helium has an molecular weight of 4 vs air being about 28.9 something about 6/7s of the gas's mass would be displaced.

It's the difference in weight between the two gases for a given volume that determines the bouyancy.

Actually if we approximate the volume of the balloon as a cylinder 10 ft in radius x 6 ft hight that gives:

Density of air at STP =

P/ro=RT

(101325 N/m^2)/ro=287*(273.15+15)

solve for ro (density) =1.225 kg/m^3

355/113*10*10*6=600*355/113=(180000+30000+3000)/113=213000/113=1884 cubic ft of gas = 53.4 cubic meters x 1.225 kg/m^3 = 65.43 kg of displaced air in the volume maximum =642.3 N = 144 lb of lifting force maximum or more realistically around 120 lb when the weight of the helium gas is accounted for so yes this balloon was capable of lifting a 60 lb child.

:D

eta: my guess is that dad had been givin 'em rides. The youngens tried it themself. Safety tether failed.

I'd imagine it would be at least half the weight of the kid.

Seems like it could still lift him, but it would be very close.

The mylar for a balloon that size is probably 2-3 lbs, and the thin plywood box is maybe 5-8 lbs

http://en.wikipedia.org/wiki/Ellipsoid

Volume = 4/3 x pi x 10 x 10 x 2.5

or about 1046 cu. ft...

Gives us about 65 pounds of lift.

Add the weight of the kid to the weight of the craft and you're right on the edge.

But you are right, it's close.

Capable of holding a 50lb child but only wanted it to hold something the size of batteries? Why would you build the box that big?

:shrug:

Per 7 news Denver.

"Good news is that he's fine"