Car vs. Rain

Episode #125

Myth: DRYving In The Rain In A Convertible

If you’re in a convertible with the top down and it starts to rain, will you stay dryer if you floor the accelerator instead of stopping to put the roof up?

The Experts:

Brian Frazier teaches the guys how to deal with hydroplaning.

Memorable/Quotable Moments:

Adam: Today’s Forecast: 70% chance of Science!

The Action/Results:

An unidentified (but clearly optimistic) fan agrees to let Jamie and Adam use his high-end convertible for this test.  The first step needs to be learning how to handle it in wet conditions.  Deputy Brian Frazier from the Alameda County Sheriff’s Department trains emergency vehicle operators in bad-weather driving, and is willing to do the same for the guys.  Once each of them gets a feel for how the car handles on dry pavement, they hook up a fire hose and soak down the concrete (and Adam’s wireless microphone).  Then Brian takes them through recovering from skidding or hydroplaning.  By the end of the session, they’re cleared to drive in the full-scale test.

Before going full scale, they run a smaller test back at M5.  Adam sets up a toy convertible in front of the high-speed grid.  Jamie is on the scissor lift over the toy car, with a pressurized water canister to provide rain.  On the control test, water falls into the driver’s compartment as expected.  Then Adam turns on a leaf blower to simulate driving through the rain.  At 15 MPH (24 KPH), there is a small amount of rain deflection.  At 30 MPH (48 KPH), the deflection is clearer.  There may be something to this myth, though Jamie isn’t sure how accurately rain scales down.

Another problem that has to be solved before full-scale testing can start is how to measure the amount of water that gets into the car.  A funnel-type collector won’t work with the small quantities they’ll get on each test run.  Instead, Jamie builds some plywood boards covered in blue acrylic and white tissue paper.  The paper is mostly opaque when dry, but translucent when wet, so there will be an obvious spot wherever rain lands.

Out at the Alameda runway, Jamie and Adam set up a special effects “rain bar”.  This rig will give them a 200-foot (61 meter) line of rain over their course, falling at a constant 2 inches (5 cm) per hour.  The car interior is covered to protect the upholstery, and a set of Jamie’s rain detector boards anchored.  A test run is made with the top up and Brian in the driver’s seat, going 120 MPH (193 KPH).  He hydroplanes and does a 450 degree spin, but recovers control of the car safely.

Jamie takes over driving duties for the actual tests.  The first run is the control – Jamie drives under the rain bar, stops, and puts the car roof up.  Both he and the detector boards are soaked.  Before they can start the speed-up tests, a real rainstorm breaks out.  The tissue paper detectors won’t work if they’re soaked before Jamie gets to speed.  While the guys wait for a break in the weather, they do some runs for the high-speed camera.  At 25 MPH (40 KPH), there’s a slight plume formed by rain deflected off the windshield.  At 55 MPH (88.5 KPH), there’s a definite plume.

Once the rain stops, testing can continue.  The detector boards go back in, and Jamie drives the course at 70 MPH (112.6 KPH).  The results are dramatically better than the control test.  The top edge of the front passenger board and one corner of the back seat board are the only wet areas.  Adam wants to try 100 MPH (161 KPH) and see if they can get totally dry boards, but Brian is worried about the extra soaking the pavement got from the rain.  He does approve a 90 MPH (145 KPH) run, provided Jamie leaves the traction control on.  This time, there is barely any dampness showing on the boards.

Adam calls for clips from “Tailgate Up Or Down”, from episode #43.  The “bubble” formed by the oats in the water tank, and the other oats flowing over the model pickup, matches the plume caused by the convertible’s windshield.  He argues that the same aerodynamic effect is taking place in both tests, and that effect is what keeps the convertible dry.

Driving at high speed on wet pavement can be very dangerous.  Neither of the guys is comfortable with calling this confirmed due to this danger.  They compromise on a verdict of Plausible (But Not Recommended!).

Myth: Popcorn Pandemonium

Two myths about the popular snack food.

Sub-Myth 1: Can you pop popcorn with an explosion?

The Experts:

Sgt. JD Nelson supervises the tests.

Garry Smith explains what popcorn needs to pop.

Memorable/Quotable Moments:

Tory: That’s a recipe for disaster.

Kari: And hopefully kettle corn.

The Action/Results:

There are many versions of this myth, everything from a container ship loaded with popcorn being torpedoed to an accident at a prepopped-popcorn plant.  The team decides to test this with two of their favorite explosions, redone with popcorn added.

First up at the Alameda bomb range is the exploding propane tank from the James Bond special.  Kari pours popcorn onto a sheet of foil, wraps it up, and places it on top of a full propane tank.  JD Nelson adds C-4, and everyone retires to the bunker.  The propane makes a nice fireball, and popcorn goes all over the range, but none of it pops.

The second test uses the creamer cannon from the Viral Hour.  The creamer and popcorn are mixed together in the cannon.  Both Kari and Grant think this may work, since the popcorn will receive more heat from the sticky creamer.  And once set off, it looks like it did work.  Unfortunately, what they thought was burning popped popcorn was just burning bits of creamer.  Once again, none of the popcorn popped.

Kari talks to Garry Smith, president of the American Popcorn Company, to wrap this myth up.  It turns out that popcorn needs even and prolonged exposure to the right temperature to pop.  An explosion is too fast, too uneven, and probably the wrong temperature, and doesn’t give the kernels a chance to pop.  This myth is Busted.

Sub-Myth 2: Can you pop popcorn with a laser, as in the movie “Real Genius”?  And if so, would the popping force be enough to destroy a house?

The Experts:

Karel Urbanek from Ginzton Laboratory, Stanford provides laser information.

Memorable/Quotable Moments:

JD Nelson: I don’t think they taught me this in bomb school.

The Action/Results:

Tory and Kari start off with a trip to Stanford University to talk with Karel Urbanek.  The first problem with this myth is that in the film, they used a 5-megawatt laser.  High-end chemical lasers running on top power can only hit 100 kilowatts, 1/50th the movie power.  However, the proof of concept test with a 10-watt laser proves that you can pop a popcorn kernel (with a little foil wrapped around it) with a laser.

Meanwhile Grant has been running the math.  He learns that popcorn expands 30 times when popped, and that the force of the pop is 0.22 PSI.

At M7, the team puts together a test rig to see if popcorn pressure can break a window.  Instead of a laser, they build a large metal tray and use induction heating to pop the corn.  Kari builds a wall-section “lid” with a standard-sized glass window mounted in it.  Coconut oil and popcorn go in the pan, the lid is screwed into place, and they start popping.  According to Grant’s math, the ¾ inch (just under 2 cm) layer of popcorn they put in the pan should expand to over 20 inches (51 cm).  The pan is only 6 inches (15 cm) deep, so if popcorn can break glass this should do it.  It doesn’t.  It seems that confining popcorn keeps it from popping to full volume … or at all, which is why they don’t simply put more popcorn in the pan.

Plan B is to just test the pressure of popping corn and see if that can break the window.  They build a 6-foot (1.8 meter) by 6-foot by 6-foot house, with one door and one window, and borrow several large popcorn makers to pop enough corn to fill it.  Grant builds a hydraulic piston, which will push up on the floor of the house at 0.22 PSI.  Once the house is filled, they turn on the piston.  The popcorn compresses to some extent, but that’s all that happens.  The house is undamaged, popcorn pressure isn’t enough to break windows or doors.  Just for fun, Grant turns his piston up to full power, and 15 tons of pressure pops the roof off.

This myth is Busted, but they still have a mostly-intact house.  So they haul it out to the bomb range and get JD Nelson to bury a bucket of C4 in the middle of the popcorn.  This gives them an explosion to wrap the episode on.