Topic: Flying Kids
started by: Leisher
Posted by Leisher on May 15 2014,06:02
< Wind takes bounce house and kids for a ride. >
Posted by TPRJones on May 15 2014,06:13
What the ... okay, blown rolling along the ground makes sense. But how in the world did it get any altitude? There's no surfaces on that sort of thing to generate the lift needed to get itself that high off the ground, much less filled with kids. The wind would have to be gusting around 100mph directly upwards....
Is it possible he inflated it with helium?
Posted by Leisher on May 15 2014,06:22
QUOTE
Is it possible he inflated it with helium?
A legit question.
Based on the report, it sounded to me like it got hit with a microburst.
Posted by TPRJones on May 15 2014,06:30
That's still a lot of up going on, though. And it sounded like it was up there for awhile if kids are falling out over multiple locations.Just seems fishy is all.
Posted by TheCatt on May 15 2014,06:31
(TPRJones @ May 15 2014,09:13)
QUOTE
What the ... okay, blown rolling along the ground makes sense. But how in the world did it get any altitude? There's no surfaces on that sort of thing to generate the lift needed to get itself that high off the ground, much less filled with kids. The wind would have to be gusting around 100mph directly upwards.
...
Is it possible he inflated it with helium?
...
Is it possible he inflated it with helium?
Well, you're wrong.
It's happened before a few times, which is why these things are always supposed to be tied down. They are not super heavy, nor dense, and with their large volume/surface area they can be picked up by wind gusts, microbursts, etc just like anything else in the world.
Updrafts happen.
Helium is possible but way too expensive to fill that, I would think.
Posted by TheCatt on May 15 2014,06:31
Mythbuster should check this out..
Posted by TPRJones on May 15 2014,06:47
(TheCatt @ May 15 2014,08:31)
QUOTE
It's happened before a few times, which is why these things are always supposed to be tied down. They are not super heavy, nor dense, and with their large volume/surface area they can be picked up by wind gusts, microbursts, etc just like anything else in the world.
Oh, absolutely! The wind-facing surface area and low density would make one of these things ripe for being blown across the ground like a tumble-weed, there's no doubt about that.
QUOTE
Updrafts happen.
Yes, updrafts happen, but I don't usually hear about them picking up kids and tossing them around. Putting them in this not-all-that-large bouncy thing does increase the surface area to catch the wind, but there's also several of them in there. I'm not claiming it's impossible, just that it seems rather unlikely as presented so far. Like 2009 Balloon Boy levels of unlikely.
QUOTE
Mythbuster should check this out..
Now there's an idea!
Posted by TheCatt on May 15 2014,07:02
Ever seen a plastic bag get picked up by the wind and shoot into the air? Or a non-helium balloon? This is just a less-likely to happen version of those, imho.
Posted by TPRJones on May 15 2014,07:12
(TheCatt @ May 15 2014,09:02)
QUOTE
Ever seen a plastic bag get picked up by the wind and shoot into the air? Or a non-helium balloon? This is just a less-likely to happen version of those, imho.
Sure, but you need to tie a fair amount of weight to those to make it at all a fair comparison. Kids aren't weightless. Three or more of them are even less so.
Ever seen a plastic bag with a full can of soda in it get picked up by the wind and shoot into the air? Or a non-helium balloon on a string tied to a cat? That's more what we're talking about here.
Posted by GORDON on May 15 2014,07:14
(TPRJones @ May 15 2014,09:13)
QUOTE
What the ... okay, blown rolling along the ground makes sense. But how in the world did it get any altitude? There's no surfaces on that sort of thing to generate the lift needed to get itself that high off the ground, much less filled with kids. The wind would have to be gusting around 100mph directly upwards.
...
Is it possible he inflated it with helium?
...
Is it possible he inflated it with helium?
I believe it.
When my kid was younger we would get these inflatable pools every summer.
Not huge, not small.
One day I filled it up with air, and was about to start putting water in it.... but an errant BREEZE lifted the thing and sent it up and over my garage, over the fence, into the neighbor's yard. Not at all what one would consider a strong wind, just a good breeze. Those things act like sails and take off.
Posted by TPRJones on May 15 2014,07:16
Sure, empty I completely believe you. Do you think it would have gotten that sort of lift if you'd already put three kids - or at least that weight of water - into it?
Posted by GORDON on May 15 2014,07:22
I think a bouncy castle has more surface area with which to catch wind than this does:
That dude weighs as much as 2 kids.
edit - found a smaller picture. Also, 2 adult peeps can fly a hang glider at one time, too.
Posted by TPRJones on May 15 2014,07:33
Yes, but wing shape is very important to make a hang glider fly. The same surface area in a big non-wing shape doesn't provide lift, it provides drag which is the opposite of lift. And bouncy castles don't have wings.If only surface area mattered, kids running along trailing a sheet behind them would suddenly take off.
Posted by GORDON on May 15 2014,07:34
(TPRJones @ May 15 2014,10:33)
QUOTE
Yes, but wing shape is very important to make a hang glider fly. The same surface area in a big non-wing shape doesn't provide lift, it provides drag which is the opposite of lift. That's why kids running along trailing a sheet behind them don't suddenly take off.
And a sailboat sail is only going to flap in the wind unless it is anchored at 3 points so it can catch the wind. The bouncy castle is catching wind because of its shape.
Posted by TPRJones on May 15 2014,07:37
Sure, which would push it horizontally very easily. But based on what I know of aerodynamics the bouncy castle pictured in that news report with three kids in it wouldn't have anywhere near the proper lift to get as high as shown for as long as claimed unless there were a 220mph burst of wind.I'm not saying this is impossible. I'm just saying it would be unusual enough that someone who designs flying craft would be interested in how it was possible as presented, as it implies some things we know about the physics of flight is a bit off.
EDIT: Unless it was full of helium. Then it all makes sense. Or unless the news was using stock photos of the bouncy castle and it's flight and claiming those were real. If the real bouncy castle was much much larger than the one shown or had a particularly aerodynamic shape, that changes things a bit and lowers the required wind speed.
Posted by TPRJones on May 15 2014,07:49
Interestingly if I hadn't spent the last two months playing Kerbal Space Program - and a disturbing part of that time learning the mathematics of aerodynamics and calculating out how to build planes that actually fly because for some reason I was really really bad at building reliable spaceplanes without first doing a lot of homework - I wouldn't be quite so insistent. I have learned well that things with almost no mass will fly surprisingly well, but put a few dozen kilograms in there and you have to do a lot of design work to get something to go vertical. Horizontal is easy, but vertical is very very hard.
Posted by GORDON on May 15 2014,07:53
Well, like I said, I watched my swimming pool, weighed 25 pounds, or so, gently waft 20 feet in the air with a light breeze. No He involved. I have no trouble believing the bouncy castle caught major air.
Posted by Cakedaddy on May 15 2014,08:36
We do a fair amount of tubing with our boat. Being pulled by the boat on an inner tube for those who might not know. My favorite one is a flat round 'tube'. It's more of a round raft than a tube because there is no center hole. Just a round flat inflatable surface. It's about 5' in diameter. This one is my favorite because I get the best lift with it. When the boat it going about 25 mph, and you are going against the wind (just normal wind. Like 20 mph.) and you hit a good wake, you fly for about 10 feet. We have learned the best angle of attack, etc. You don't just jump. You glide. Also, in turns when you are being whipped on the outside of the turn, you are going FAST. Feels like 100mph, but it's probably closer to low 30's. If your leading edge catches that wind, you flip over. You have to push down on the leading edge of the tube to prevent this. Lastly, in high speed trials (boat going about 40MPH) you can lift the front edge of the tube and feel the wind trying to lift the tube. It doesn't though because the tow rope pulling forward on the leading edge of the tube counters any lift occurring. So, in summary, we fly, for very short distances, our 5' 'raft' behind out boat. I weight about 220.Point is, I have no doubt that there is enough surface area on that bouncy thing for a 40mph wind to EASILY lift a 150lb payload.
Here's the tube I use:
< http://www.sportsstuff.com/watersports/towables/1-rider/air-force.html >
At 10 seconds, you can see the person lift the leading edge of the tube and the tube and rider skip. Meaning, the tube completely leaves the water, on flat surface (no wave to jump).
Increase the surface area, and flight, at low speeds, is VERY possible.
< https://www.youtube.com/watch?v=Zokz1CyxzyE >
55mph, adult passenger. Hit some other videos and watch some at slower speeds shoot way up in the air (and almost kill the passenger).
Here is one that is not 'wing' shaped.
< https://www.youtube.com/watch?v=wYyu7n1rlKY >
FYI, the bernoulli effect is important when trying to achieve lift, but velocity and angle of attack contribute to flight as well.
Posted by TheCatt on May 15 2014,08:42
(TPRJones @ May 15 2014,10:12)
QUOTE
(TheCatt @ May 15 2014,09:02)
QUOTE
Ever seen a plastic bag get picked up by the wind and shoot into the air? Or a non-helium balloon? This is just a less-likely to happen version of those, imho.
Sure, but you need to tie a fair amount of weight to those to make it at all a fair comparison. Kids aren't weightless. Three or more of them are even less so.
Ever seen a plastic bag with a full can of soda in it get picked up by the wind and shoot into the air? Or a non-helium balloon on a string tied to a cat? That's more what we're talking about here.
Dude, a bounce house weighs MORE than 3 kids.
We're talking about a plastic bag "filled" with half a plastic bag.
Posted by TPRJones on May 15 2014,08:52
At 10 seconds if it weren't for the rope it would have flipped, not flown. Certainly not flown up over a two-story apartment complex.The second one is irrelevant because if you pause it and study the design (hard to do with the shaking, but I got lucky) it actually has lifting surfaces built into it to act as wings. The Little Tikes bouncy castle doesn't even have a roof to act as a wing, so it's much more like your regular inner tube than the manta ray glider.
When you go tubing and it glides up to 50' high above the boat with you on it, then I'll believe it is possible.
Posted by Cakedaddy on May 15 2014,09:11
(TPRJones @ May 15 2014,11:52)
QUOTE
At 10 seconds if it weren't for the rope it would have flipped, not flown. Certainly not flown up over a two-story apartment complex.
The second one is irrelevant because if you pause it and study the design (hard to do with the shaking, but I got lucky) it actually has lifting surfaces built into it to act as wings. The Little Tikes bouncy castle doesn't even have a roof to act as a wing, so it's much more like your regular inner tube than the manta ray glider.
When you go tubing and it glides up to 50' high above the boat with you on it, then I'll believe it is possible.
The second one is irrelevant because if you pause it and study the design (hard to do with the shaking, but I got lucky) it actually has lifting surfaces built into it to act as wings. The Little Tikes bouncy castle doesn't even have a roof to act as a wing, so it's much more like your regular inner tube than the manta ray glider.
When you go tubing and it glides up to 50' high above the boat with you on it, then I'll believe it is possible.
You have to play with more tubes, outside, in the wind. I can't explain the physics. But I KNOW tubes fly with no passengers.
Posted by GORDON on May 15 2014,09:14
Well I certainly hope that people will stop talking about the fact I didn't believe some mythbusters results and use this thread, instead.
Posted by TPRJones on May 15 2014,09:16
Hey, if Mythbusters proves me wrong I'll believe them. Well, as long as it's part of the 70% of things they do reasonably well, and not the 30% where they make some glaringly obvious mistake and need to go back and try again. 
Posted by TheCatt on May 15 2014,09:40
(TPRJones @ May 15 2014,12:16)
QUOTE
Hey, if Mythbusters proves me wrong I'll believe them. Well, as long as it's part of the 70% of things they do reasonably well, and not the 30% where they make some glaringly obvious mistake and need to go back and try again.
We already know you're wrong.
People keep saying MB make mistakes, etc, but I've never seen much evidence of it.
Posted by Malcolm on May 15 2014,09:45
QUOTE
People keep saying MB make mistakes, etc, but I've never seen much evidence of it.
They totally fucked up the hangover experiment.
Posted by Cakedaddy on May 15 2014,09:46
< https://www.youtube.com/watch?v=2xm2HhYCYLI >At 45 seconds, is that tube flipping, or flying? The only reason those tubes don't continue to stay air born is the drivers are cutting the throttle. A flying tube crashing into the other rider hurts.
< https://www.youtube.com/watch?v=7_0UCh38oh4 >
At 3:10, the wipe out occurs and the tube is nosediving into the water. When the tube comes back into frame, it's on an upward trajectory until the tow rope pulls the front down and the tube dives again. These tubes want to fly.
< https://www.youtube.com/watch?v=BxxlennWaLM >
At 10 seconds, is that tube just flipping?
Posted by Cakedaddy on May 15 2014,09:48
Ya, at this point, multiple people on this board have witnessed first hand, inflatables flying. Not our fault you've never seen it.
Posted by TheCatt on May 15 2014,09:55
(Malcolm @ May 15 2014,12:45)
QUOTE
QUOTE
People keep saying MB make mistakes, etc, but I've never seen much evidence of it.
They totally fucked up the hangover experiment.
Good explanation there. I'm convinced.
Posted by TPRJones on May 15 2014,10:03
(Cakedaddy @ May 15 2014,11:46)
QUOTE
At 45 seconds, is that tube flipping, or flying?
...
Ya, at this point, multiple people on this board have witnessed first hand, inflatables flying. Not our fault you've never seen it.
...
Ya, at this point, multiple people on this board have witnessed first hand, inflatables flying. Not our fault you've never seen it.
It's flying, but it also has much more flat surface area than the bouncy house in the news story and isn't loaded down with kids.
Show me a video or tell me a truthful first hand account of one of these tubes of a similar size to the small bouncy castle loaded down with similar weight flying 50' into the air and staying up there for a couple of city blocks and then I'll believe, because that is what is being claimed as having happened in this news story. So far I've seen nothing even remotely close to that and no evidence that it should be possible given the circumstances reported. The manta ray one could do it, but it's different because it has built-in lifting surfaces as part of the design.
What I will do, however, is shut up about it for now. Fair enough?
Posted by Malcolm on May 15 2014,10:11
(TheCatt @ May 15 2014,11:55)
QUOTE
(Malcolm @ May 15 2014,12:45)
QUOTE
QUOTE
People keep saying MB make mistakes, etc, but I've never seen much evidence of it.
They totally fucked up the hangover experiment.
Good explanation there. I'm convinced.
They tried to measure hangover severity and recovery time without using:
- similar drunks
- similar alcoholic drinks