Episode 96: Lead Balloon, Surfing with Dynamite
- Lead Balloon: A lead balloon cannot fly busted
- Surfing with Dynamite: You can use dynamite to make surfable waves busted
Lead Balloon featured the MythBusters at their best: clever design, difficult construction, good results. It was an engineering challenge and Adam and Jamie succeeded with a delicate 10 ft lead cube balloon.
The Surfing with Dynamite continued the trend towards busting Internet videos that has been appearing in MythBusters. In this case, they busted an absurd video that features people throwing dynamite into a canal and catching waves from the resulting churn. It was mostly an excuse to explode 200lbs of TNT beneath the water.
Myth: It is impossible to make a balloon out of lead, as in the idiom, "Going down like a lead balloon."
Hot air ballons were invented in 1783 by the Montgolfier brothers in France. The envelope of a modern hot air balloon is quite heavy at 500 lbs, but it is made of light and strong material. Lead sheets, on the other hand, are very heavy and very weak.
Adam and Jamie each constructed a balloon out of tinfoil. Tinfoil is stronger and 6x lighter and than lead, but this would allow them to test different construction techniques. Adam built his design based on a platonic solid -- the icosahedron -- while Jamie draped triangular pieces over a hemisphere and taped the two halves together. Both designs at their small scale were successful, but that was using tinfoil. Unfortunately for Jamie and Adam, lead foil is "like wet toilet paper" (in Jamie's words).
Small-scale lead balloon test
Jamie and Adam taped together sheets of lead foil on a table, rubbing their facial hair on the tape to get the static out. The design was simple: two sheets of lead foil on top of one another to form a pocket in between. Although tears formed very easily, they were able to inflate their design. It wasn't able to fly as there was too much lead for the amount of helium at that size. By making the balloon larger, they could increase the ratio of helium to lead and make it fly. According to their calculations:
- 2'x2'x2' design: 225g Helium, 408g Lead, -183g Lift
- 5'x5'x5' design: 3500g Helium, 2550g Lead, 950g Lift
- 10'x10'x10' design: 28kg Helium, 10.2kg Lead, 17.8kg Lift
Based on these calculations, they went with the 10'x10'x10' design.
Full-scale lead balloon Test
Adam and Jamie setup shop in an Alameda Naval Base Hanger, where they carefully scrubbed the floor and laid down some paper on top to create their assembly area. Jamie also constructed a swinging boom arm on a forklift so that they could be suspended over the lead sheets as they assembled it.
Adam came up with an origami-like design that would allow them to construct the lead balloon flat and then have it unfurl into a cube as it was inflated, i.e. 'flower-style'. The design appeared to be a sandwich of two square sheets of lead with twelve triangular pieces in between. As the design unfurled, the top and bottom pieces twisted as the triangular pieces sprung up to form the sides. There was much care taken as they assembled the master piece: in addition to the paper and boom arm, they filled the balloon from both the top and the bottom to avoid any pinchpoints that could rip the sheets, and they laid a plastic drop cloth on top to keep the inflation even. They also mixed in air with the helium to prevent the balloon from having too much lift and ripping itself apart -- they knew that they had lift to spare.
True to Adam's design, the 11kg lead balloon twisted and unfurled into a cube. As the balloon gained lift, rips started to appear, but it contiued to fly upwards. Adam hung a little basket with a paper Adam and Jamie from below and they had to hold onto the balloon to keep it from flying upwards.
Adam: "Busted Idiom!"
Their glittery balloon was brought down as Adam and Jamie took turns puncturing it with a baseball. They proceeded to roll it up into a small, 11kg block of lead, illustrating how thin the material really waas.
Surfing with Dynamite
Myth: You can use dynamite to make surfable waves
In an Internet video, some surfers in a city find a canal and drop dynamite in to make some surfable waves:
Can you create a wave with explosives? Which depth is most effective
Proof of concept experiment + learning to surf
The build team built a water tank in the parking lot and used a dry ice soda bottle bomb as their explosive. This wasn't a small-scale experiment: they just wanted to see what sort of waves and explosion would make and how the varying depths affected it. The set the dry ice bomb off at the bottom, mid-depth, and surface of the tank. The mid-depth seemed to produce the best waves, though the waves didn't break like surf waves.
The build team also went down to Santa Cruz to learn how to surf, which was fun for them though they weren't going to actually surf the explosion themselves. As Dr. Van Romero, VP Research, New Mexico Tech explained, the shockwave from the explosion would be fatal to humans as your lungs would bleed.
Grant constructed a mechanical paddling robot, aka "Robo-Grant", to surf the waves. Steel arms spun by a motor were mounted on a 10 ft foam surf board. They added foam legs and torso molded off grant as well as a rudder for steering. The paddling mechanism swiveled somewhat like human shoulders and was capable of both freestyle (alternating) and butterfly (simultaneous) strokes.
Grant: "I'm hoping that RoboGrant has been embued with the natural surfing talent that real Grant has"
Kari: "does anybody find it creepy how many "Grant" robots have been on this show? Is it just me or is he trying to clone himself and make a little army?"
They performed their test at a quarry lake at Angels Camp, which was devoid of fish so that no fish would be harmed in the experiment. They found a good spot using a depth finder to set their explosions and did some tests with 50 lbs of TNT to find the right depth. The Internet video only showed about 2-3lbs of dynamite, but expert Frank Doyle figured that they would have to go much bigger. The 50 lbs of TNT at 30ft generated a big explosion, but the wave was only about 1" high. They set off another 50 lb charge at 12 ft and manged a 1 ft high wave, with some tiny breaks at the shore.
Based on these results, they decided to put all their remaining explosions on the line -- 200lbs of TNT. Robo-Grant paddled up to speed going away from the explosion as the TNT was set off 12 ft below the surface. A giant column of water shot up and a wave taller than Robo-Grant sped out, but by the time it reach the robot it seemed to disappear beneath the surface. Unlike the waves you surf on and portrayed in the Internet video, waves from explosions lose energy as they radiate outwards from the explosion. Definitely not surfable.