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Helium Raft/Cell Phones on Planes Episode # 49 Original Air Date: March 15, 2006
Episode 49: Helium Raft/ Cell phones & Planes
Helium Raft
The Myth: Can you put enough helium into an ordinary life raft and use that to float through the air like a magic carpet?
Memorable/Quotable Moments:
Adam: This wins, as the strangest position I've ever been in...on this show...
Kari: Don't you love how he qualifies it with 'on this show'?
Jamie: That's huge!
Adam (after breathing helium): In every generation, a myth comes along...that does not thrill us.
Is it possible to fly in a raft filled with helium? Several fans seem to think so, and put it to the Mythbusters to try it out.
Jamie initially expresses disbelief, but concedes there's only one way to test this myth, and that is to actually fill a raft with helium and try it out.
So, the guys haul out one of their inflatable Zodiacs (the 'dinghy', as Jamie and Rob call it), deflate it, weigh it (they get a weight of 72 pounds), reinflate it, figure out the volume of the dinghy (around 20 1/2 cubic feet of air), deflate it again, and reinflate it with helium.
Adam expresses a desire to sit in the raft as they're filling it with helium, just in case it becomes airborne. Jamie seems to be more practical and realistic, thinking the raft isn't going to float away.
The raft is inflated...Jamie holds onto the rope (rather unconvincingly) as Adam jumps out...
And the flying raft...doesn't.
All the helium did was reduce the dinghy's weight by four pounds.
They then try the same thing with an airline life raft...with the same predictable result.
And, of course, the escape slide figures into the mix (with Adam's prerequisite clowning around), as well.
While helium is lighter than air (as diagrammed on a periodic table explained by Rob), it take much more of it to lift a raft. Even a blimp, such as a cutaway clip of the Hindenburg shows, needs a lot of buoyant gas to remain aloft. Compared to the ill-fated zeppelin, which used over seven million cubic feet of explosive hydrogen, the rafts and escape slide are simply too small to hold enough helium to become airborne.
It's numbers-crunching time, and Adam figures that they'd have to use around five thousand cubic feet of helium to lift just one of the Mythbusters (either himself or Jamie), and the raft.
A daunting task, to be certain. Helium they can get...but what about the raft? They figure they'll have to build their own, so...
Enter hundreds and hundreds of feet of lightweight plastic tubing used on movie sets for air conditioning. The guys basically want to turn these tubes into extremely long helium balloons...50 foot long helium balloons, to be exact.
Adam performs a test on one of their custom-made helium 'tubes', and determine that it has a lifting force of about 5 pounds. To build a raft capable of flying with 5000 cubic feet of helium in it, they'll need between 40 and 50 2 foot diameter, 50 foot long tubes, each holding about 153 cubic feet of helium, totaling about half a mile of tubing.
Adam suddenly realizes the scope of testing this so-called myth. He concedes that it may not be possible to build such a raft.
But, there is a solution on the horizon. An abandoned aircraft hangar is just the right size to contain the behemoth.
Adam explains the process they need to go through to accomplish this build. The look on Kari's face is a mix of 'you've got to be joking' and 'Oh God'.
First things first, though...sweeping the floor. This task alone takes quite awhile to do, and then, the rolling out of each tube. That in itself takes up the better part of a day, including taping each tube together.
The very next day, they decide that an extra, smaller raft atop the behemoth is needed to help distribute Adam's weight. Kari expresses some trepidation about the enormous task ahead of them, as a semi truck loaded with 36 helium canisters pulls up.
Per the 'clowning around' clause in his contract, Adam inhales a bit of helium and explains that this myth 'does not thrill us', as the filling of the raft commences.
Hours later, the raft begins to take shape. Adam dons a wetsuit for the extra 'cool factor' before he's lowered onto the raft.
But, as the ballast is cut away, disaster strikes. One side of the raft rises too quickly, causing Adam to slide off the mattress...and into the net. Within seconds, he's dangling from the underside of the raft (securely fastened to the overhead crane via his 'SWAT Team' harness), and, in typical Mythbuster fashion, states that the experiment has 'failed utterly'.
Well, with nothing left to lose, the Mythbusters slash the tubes to release the helium and bring this great experiment crashing to earth...a 'cathedral of failure', as Adam observed.
The verdict?
BUSTED.
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The Myth: Can using a cell phone on a commercial airliner really mess with the avionics?
Experts - Jeff Gutow, aerospace engineer
Tom Benvenuto, VP, Sunset Aviation
Ken Faeth, Faeth Aviation, Sacramento, CA
Memorable/Quotable Moments:
Tory: Sounds like we get to crash a plane!
Tory: Tower to Kenny...how much is this gonna run us? Over.
Kenny Faeth: Too much!
Grant: Houston, we have a problem. Abort mission
The Myth: Why aren't you allowed to use your cell phone on major airlines?
As we all know, cell phones use RF (radio frequencies). So do nearly every aircraft flying in the world today. It's these frequencies that could interfere with the aircraft's navigation and communications frequencies, though Grant dismisses this as the real reason why you're not allowed to use your cell phone on an aircraft. As he explains it, the myth was born out of a 'conspiracy theory' that the real reason the airlines want you to turn off your cell phones is to force you to use the more expensive in-flight phones.
But, how to test this myth?
Adam expresses some doubt as to the myth itself, noting that it's not so much the myth as the legality of the myth.
Grant says that while Federal law forbids using a cell phone in flight, Tory counters with the claim that it isn't illegal to do so while the plane is on the ground. With the airport instantly ruled out, Grant and Tory decide to build their own airplane by paying a visit to Faeth Aeronautics in Sacramento. They scout out several suitable cockpits, going so far as to purchase an entire functional 'radio stack', complete with NAV/COM, course deviation indicator, VOR (VHF omni-range) indicator, among other things.
As the guys head back to Mythbusters, it's learned that there was a flight that crashed in 2000 near Zurich, killing everyone onboard. The cause was traced to a couple of passengers who had received cell phone calls just before the plane crashed.
So, it would appear that there may be some truth to the myth of cell phones interfering with the navigation system on an aircraft.
Grant sets about assembling a working radio stack, but the task seems daunting at the outset, even for an electronics whiz such as himself.
Cue Jeff Gutow, an aerospace engineer and an expert in avionics. He volunteers to come in and help Grant get his radio stack working. As Jeff assembles the radio stack, Grant and Tory discuss the possibilities of how cell phones might interfere with an aircraft's electronics, such as masking or jamming the signals from the ground, the navigation beacons, the airport, etc.
Soon, Jeff announces that he's got the stack wired up and ready to go. He and Grant take the assembly outside, and power it all up.
Nothing.
So, they decide to raise the antenna to about 35 feet. The VOR Indicator's needle swings to the right, showing that they are indeed, receiving the signal from San Francisco International (SFO) Airport's VOR.
Now, for Grant's specialty...RF emissions. Using a spectrum analyzer, he demonstrates that most electronic devices emit RF (radio frequency) to some extent...some (like cell phones) more than others. To ensure a 'clean RF free' environment, it's off to the Mythbusters bunker, where a Faraday Cage is constructed.
First, Grant tests some common electronic devices with the spectrum analyzer. They barely register on the device. He then makes a call on his cell phone...and the analyzer registers a spike.
It’s time to put the radio stack and a 'ramp tester' inside. With all that RF bound to be bouncing around inside the Faraday Cage, one has to wonder if Grant could be microwaving himself. Tory makes the offhand remark of 'brain tumors' before Grant puts the whole contraption inside the bunker.
Grant brings a signal generator into the cage and runs a veritable gauntlet of common (and no-so-common) cell phone frequencies through the avionics, trying to disrupt the signal between the radio stack and the ramp tester. Some of the higher cell phone frequencies don't even register, despite Grant bringing the power way up beyond what a cell phone's PEP (peak envelope power) normally is. Part of the problem with the first test is that he's testing digital frequencies against an analog receiver; secondly (and more importantly), his radio stack isn't properly shielded, as would be with professionally-installed electronics.
Grant soldiers on, trying to find a frequency spread that will make the VOR needle swing wildly. He finds it in the 800 - 900 MHz range...a more common cell phone frequency spread. The VOR's needle deflects quite rapidly, showing that the instrument is being affected. However, Grant feels that, while significant, the myth is busted.
"Not so fast," says Rob. They still have to test this 'out of the lab', so to speak. So, they load up their gizmo into the surplus cockpit (at Kari's insistence, since she feels a lot of fans will gripe), and head out close to SFO to simulate a real-world aircraft on approach. They're far enough away from the airport that their test won't affect air traffic, but will still provide some conclusive data.
But, there's a problem. As Tory and Kari drive around the parking lot, with Grant in the cockpit, the VOR needle keeps bouncing all over the place, with the TO/FROM flag popping up and down. It's either some stray interference they hadn't counted on, or they're under the VOR signal, or a loose connection somewhere. Turns out, they can't figure out what the problem is.
So, Plan C...head to SFO itself and test the myth.
There is a problem though...that pesky Federal Law. Grant and Tory lament to the fans that they did indeed try, but because it's illegal to take an active cellphone up in any kind of plane, they just couldn't do it. So, they 'borrow' a Hawker 800P corporate jet, courtesy of Tom Benvenuto of Sunset Aviation, and a classy jet it is.
Tom volunteers to let Grant and Tory set up their test apparatus in the jet, and run a gamut of tests on the ramp. With all the avionics in the Hawker active, Grant tries valiantly to cause interference with the jet's electronics using a variety of cell phones. But, since this jet's state-of-the-art (with an all-glass cockpit and properly-shielded electronics), there's just no way that any of the devices can interfere with the instruments.
The discussion back at Mythbusters about in-flight phones proves that, while expensive to use, it's more practical, since the phones' signals are isolated from the aircraft's electronics, depending if you're over land or water.
The verdict?
BUSTED.
However, Grant, Kari, and Tory qualify that verdict as more of a 'better safe than sorry' conclusion, due to the complexity of aircraft avionics and cell phone technology.
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Episode Descriptions 
