Episode 64: More Myths Revisited
- Salami Rocket: they admitted that the viewers may have been right about their original rocket failing, but this time around they were able to properly confirm that you can use a salami as rocket fuel.
- Rough Road Driving side myth: Holding your hand against a windshield will prevent rocks from shattering it: busted
- Tailgate Up or Down Revisited: in addition to tailgate up/down, also tested hardcover over pickup bed, tailgate removed, and tailgate mesh. Tailgate mesh was most efficient by 5%. busted
- Cutting a Sword Revisited: During WWII, Japanese soldiers were able to slice American machine gun barrels in half: busted
With the exception of the Salami Rocket revisit, these were all side myths rather than retests of the original MythBusting. They tested another myth related to rough road driving, swords cutting gun barrels instead of other swords, and other fuel efficiency measurements for pickup truck tailgates. The Salami Rocket retest was notable in that the viewers complaining may have been right: the original salami rocket probably did not fire, but flew anyway. With some tweaking, they were able to get the new salami rockets to fire and generate 800lbs+ of salami power.
The original salami rocket used liquid nitrous oxide (NOX) and a salami. Viewers claim that the salami did not ignite and that their original salami rocket launch was really just the NOX providing thurst. The viewers also complained about Adam's original graphite nozzles, so Adam redid them with a thicker lip.
- Shipping container bunker: instead of launching the rockets, they decided to measure the force of each rocket. This made testing for ignition much easier.
- Clamp to hold rockets in place
- Force meters to measure rocket ignition
Pure NOX rocket: 78lbs of thrust
Adam: "Okay, I will give it the viewers. They may actually be right. The evidence supports it here. That just the pure release of nitrous oxide from that top tank would be enough to get the rocket off the rocket stand."
NOX + Salami: 19.6lbs
The salami failed to ignite and the rocket was much less powerful than the NOX by itself. Jamie decided that they should use a smaller nozzle to increase the pressure for ignition.
- 5/16th" nozzle: 218lbs of thrust. The nozzle was blown out, but they were able to achieve ignition. The combined rocket was almost 3x as powerful as NOX alone
- 3/8" nozzle: 880 lbs of thrust. They maxed out their force gauge and ruined it
Jamie: "This thing would have taken off like nobody's business if we had had this launched. It would have exploded in mid-air at some point and stopped going, but with 500lbs of 'I'm going up,' something that weighs under 20 lbs is going up."
Rough Road Driving Revisited: Shattering Windshields
See: Rough Road Driving
New myth: Placing your hand on a windshield will prevent it from shattering if a rock hits it
- Slingshot rig: Tory built a rig for a slingshot to fire rocks
- Chronograph (ProChrono)
- Target speed was 70mph, which they were able to calibrate with the slingshot rig and chronograph
- Front windshield in car (Camry)
- Small rocks
- Blanket to catch stray shots
The first and second shots only dinged the windshield without shattering it. They then tried a 150g stone, which caused significant cracking, but no shattering.
Problem: Since the 1920s, American cars have commonly used laminated windshields, which don't shatter as easily. The MythBusters believe that this myth may have originated in another country where use of tempered glass windshields have been more common (up until 1994). Tempered glass windshields are much more shatterable.
Luckily for the MythBusters, the rear windshield of the Camry is tempered glass, so all they had to do was flip the car around. They also decided to swap the BB gun for a slingshot. The BB gun is easier to aim and the BBs are more uniform than the rocks. Their test shot shattered the rear windshield of the Camry, so they swapped in a new rear windshield and were ready to go.
Kari: "What's your prediction?"
Grant: "He's going to take a BB in the nuts"
- BB gun fired by Tory
- Rear windshield in car (Camry)
- Grant in the back seat, wearing a motorcycle helmet, while bracing his gloved hand against the rear windshield.
Tory: "I'll miss you buddy"
Grant: "I'm going to catch it in my teeth"
Even with Grant's hand propped against the windshield, the windshield crumbled to little pieces. However, they didn't do much calibration with the speed of the BB -- it may have been far too strong. They decided to do more testing to figure out at what point a BB would shatter a windshield so they could retest at that point and see if there was a difference. Tory was able to figure out that it took six pumps of his BB gun to shatter the windshield. So, they decided to do one more shot at the rear windshield with the BB gun pumped six times and Grant bracing the windshield with his hand.
Again, with Grant's hand against the windshield, the windshield shattered to little pieces.
Tory: "You're so over this one, huh?"
Grant: "You try and get BBs and rocks shot at you about a dozen times and see how you feel."
Tailgate Up or Down Revisited: Mesh tailgate, hardcover, tailgate removal
See: Tailgate Up or Down
For the original myth they did a driving test and a water vortex test, both of which showed that you save more gas with the tailgate up. Their viewers suggested that they test three new conditions:
- Hardroof cover over pickup bed
- Mesh tailgate
- Remove the entire tailgate
They had a much simpler test setup this time. They had an electronic flowmeter hooked into fuel line of Jamie's pickup. Adam: "For anyone out there that wants to e-mail telling me that we screwed up this test, we have already calibrated this thing, to this car. So it's going to be perfect!" They drove the pickup truck up and down the stretch of 101 around Candlestick and the Cow Palace.
- Tailgate down: 5.2 gallons/hr @ 55mph. 1.2 gallons/hr @ 25.
- Tailgate up: 5.0 gallons/hr @ 55mph. No reading for 25mph given, but tailgate up was once again confirmed as more efficient.
- Hardcover over pickup bed: 5.0 gallons/hr @ 55mph. 1.2 gallons/hr @25mph
- Tailgate mesh: 5% more efficient
- Tailgate removed: about the same as tailgate up and hardcover
Mesh was most efficient by 5%
Cutting a Sword Revisited: Cutting a Machine Gun Barrel
New myth: During WWII, Japanese soldiers were cutting through hot American machine gun barrels with their swords
- Grant upgraded the robotic cutting arm with a new pressure cylinder that made it twice as powerful.
- Browning .30 cal machine gun barrel
- BBQ: Tory BBQ'd the machine gun barrel to get it hot enough to replicate a crucial element of the myth: that the machine gun barrels were superhot from firing, thus making them easier to cut.
Test 1 (Heated Machine Gun Barrel)
- 600 degrees: the sword was able to gash the barrel, but the sword shattered
- 1500 degrees: the red hot machine gun barrel was gashed, but still intact, and again the sword shattered
Grant decided that it might make it easier to cut the barrel if they repeatedly heat the barrel and quench it. The metal would harden, but also become more brittle. Kari also brought out the strongest sword in their inventory to do the cutting.
Test 2 (Brittle Machine Gun Barrel)
Under the new conditions, the strong sword broke the gun barrel into four pieces. However, they gave three reasons why this didn't confirm the myth:
- The gun barrel did not get sliced, it shattered into four pieces
- They weren't using the outside guard for the gun barrel
- Grant's robotic arm was super-human strength -- not even an expert swordsman could deliver such a blow.
Test 3 (Tommy Gun)
For the last test, they went used a tommy gun heated to 2000 degrees, which has a much thinner barrel. The modern alloy sword bent the sword and sent up sparks, but did not slice it.
busted, though under certain conditions -- repeated heating and quenching of gun barrel -- you might be able to shatter a machine gun barrel.