Episode 35: Border Slingshot
- Illegal immigrants entering the US by means of a giant slingshot that launches them 200 yards and is accurate enough to hit a mattress on the other side: mythbusted
This was one of the MythBuster team's more mishap-filled mythbustings, entertaining for the fact that they kept messing up with dangerous, spectacular results. It's hard to convey a giant slingshot flinging it's contents backwards without actual video.
Myth: Illegal immigrants entering the US by means of a giant slingshot that launches them 200 yards and is accurate enough to hit a mattress on the other side. A family package allows you to launch up to four people at the same time.
- Human Cannonballs: since the 1870s people have been launching themselves with cannons. They showed video of David Smith Jr. launching himself 170ft into a net. The World record is 201ft set by his father David Smith Sr, who recently made headlines by launching himself across the US/Mexico border.
- Trebuchet: In 2000 the Dangerous Sports Club launched Stella Young by trebuchet. She hit the net, then bounced onto the ground, breaking her pelvis. In 2002 a 19 year-old died in his attempt to repeat the stunt, missing the net entirely.
Jamie and Adam tested store-bought slingshots for velocity and for fun. For once, Adam was better than Jamie and was able to hit the target more accurately. They used markings behind them to measure the speed of the pellets at 85 mph, which is about half the speed of competition slingshots.
Scissor-Lift slingshot (materials test)
A scissor lift was used to create a slingshot to test the strength of various materials using a 1kg test shot. The arms for the slingshot were mounted to the top of the scissor lift and were raised for a 45 degree angle firing.
- military bungee: 67ft. 21m/s velocity.
- stranded shock cord: 43 ft. 15.5m/s velocity.
- solid shock cord: 38.5 ft distance. 14m/s velocity.
- surgical rubber: ~135ft. 30.5m/s velocity. Twice the pullback (14ft), 27lbs of tension.
The surgical rubber clearly outperformed the other materials so it became their choice for the rest of the tests. In order to figure out some of the final parameters for their test, they measured the point at which the surgical rubber would break by pulling back on the rubber with a forklift and attaching the other end to a scale. They decided that a 5:1 ratio was the maximum safe ratio for stretching the rubber.
Goal-post slingshot (1:10 scale)
In their continued scaling up of the myth, their next target was to go 1/10th scale and build a slingshot out of a football goalpost. Their test shot was a converted 8kg bowling ball. Encinal High unwisely allowed the MythBusters to use their goalpost for the experiment. They reinforced the goalposts with some guy ropes, but even then they were a bit flexible.
They tried a test shot with a smaller weight. Jamie had attached some chains to the ball basket to keep the ball from falling out too soon, which it did. The slingshot boomeranged back with the test shot and sent Adam and Jamie cringing:
Adam: "That was the scariest thing I have ever done on this show"
They added an automatical release system for safety and launched the test shot 205 ft.
Next up was the 8kg bowling ball, which came flinging back. It took out the goalpost camera on its way back, but the cameraman held his ground as Adam and Jamie went running.
They finally got a good launch out of the goalpost slingshot, which was showing a lot of strain from the previous, mostly failed attempts. The final shot launched the 8kg bowling ball 77 ft.
The full-sized slingshot
- 40, 10ft lengths of surgical tubing
- 2 radio masts (45ft. long)
- 3 guy wires on each radio mast
- 2 gradalls to tension the slingshot to 4000lbs (50ft pullback)
- mark at 201 ft for the human cannonball world record mark
Kari: "200 yards to get over the border? I think this myth might be slightly absurd. But you those Canadians... they're kinda crafty."
Child dummy launch
The first launch was with the 55lb simuloid child dummy. At launch it will be experience 6-9gs. A guy wire slipped as they were tensioning up, but they fired anyway. The dummy pinwheeled to a distance of 132 ft.
They switched to the heavier Susie dummy (130lbs) and prepared her for launch by duct-taping her into a ball. In a repeat of the goalpost slingshot, the sling rotated around during launch and flung her backwards.
Adam: "Well, that was a familiar result"
They made another attempt with Susie the dummy, this time taking up some of the slack in the harness and seating her sideways. The rope that was attached to Tory's gradall broke as the sling was being tensioned up, snapping the left side of the downwards:
They launched again after repairing the rope, but the results were pretty inspectacular as Susie fell out of her sling too early. She only went 128 ft.
After all the screwups (guy wire loosening, broken rope, boomeranging), they only had time for one more launch (it seems that they may have had some launches in between that they decided to not show). They used Rescue Randy for the final launch. His weight is similar to Buster (~185 lbs). They made some final modifications to the launch seat to hopefully keep Randy from repeating Susie's weak launch:
Rescue Randy went 211 ft, still short of their border but better than all the other launches. He still slipped out of the sling, though later than Susie, so he probably would have gone farther had they spent more time adjusting the sling.
The myth, as constructed, was easily busted. The idea that you could accurately hit a mattress at a distance farther than the human cannonball world record is absurd. However, at no point during the testing did they try to come up with a more plausible-sounding myth. David Smith Sr's recent human cannonball stunt across the US/Mexico border demonstrates that it is possible to be flung across the US border, so if they actually wanted to 'bust' this myth it would seem that they would have to spend more time figuring out what more realistic parameters would be: a distance much less than 200 yards and with something other than a mattress as a target. It would still be a dubious means of transport, but at least they would be trying to bust the myth rather than trying to build the largest possible slingshot.