Batteries in Airplanes

Batteries seem to be a popular subject these days. Certainly the 787 has had it's share of trouble. Even a couple years ago, batteries in phones and laptops were catching fire, seemingly randomly. Mostly the fires have been harmless to people, but the equipment hasn't come out so well. During 2007 there were several laptops that spontaneously combusted Here is one (warning coarse language) http://www.youtube.com/watch?v=mlZggVrF9VI. Several manufacturers had recalls, and since then, there haven't been too many laptops that caught fire..

About the time everyone figures the trouble is over, people start getting burned with cell phones in their pocket. I have a couple batteries from my previous phone that are slightly bulged. The bulges signify something bad happening on the inside of the case. Bulging is a mechanical function, charging is normally a simple exchange of electrons.

I don't know the details of the 787 exactly, just what I have read, and the pictures I've seen. It seemed the original design had multiple cells packed together inside of the blue box. The new design has insulation between cells, and the cells are isolated. Lithium batteries are more likely to fail when heated. If one cell is misbehaving and getting warm, and touching another cell, the non-warm cell is more likely to do something bad, even though everything about it is normal. The misbehaving cell will inspire the adjacent cell to enjoy its company. Their friends may joint in, being neighborly, and things are getting quite hot now. The heat seems to multiply, especially being in a box, and suddenly there is smoke coming out.

There is a theory that all electronics run on smoke. When the smoke gets out, they quit working. Batteries tend to be the source of smoke for many electronics, so when the smoke gets out of them, things really don't work.

Why would anyone put something that dangerous in their airplane? As Collin Chapman used to say about building race cars, "Simplify, then add lightness", or Burt Rutan used to say, "Throw it up, if it comes down, it doesn't belong on your airplane". Basically what these people are saying, that making things light is the proper way to build airplanes, and cars. Why lithium? Look at this table:

    -----------------------------------------------

      Fuel        |             Watts / Kilogram

    -----------------------------------------------

    Lead Acid     |            0.05

    -----------------------------------------------

    Lithium       |            0.224

    -----------------------------------------------

    Gasoline      |           12.88

    -----------------------------------------------

Lithium batteries are much lighter per unit of work (watts).

Wow, that does seem dangerous, or does it. Well, it is significantly more dense than a lead acid (the traditional airplane battery, although some airplanes are now ni-cad powered), and quite a bit less dense than gasoline. No one carries gasoline in their pocket.

How much battery does an airplane need. I built and airplane once, and was told I only need enough battery to start the engine. Once the engine is started, then the Alternator should take over powering all the accessories. All the radios, gear retracting motors, and lights all run off the alternator. A bigger battery might be handy in case the alternator quits, but then you are hauling around a battery for every flight that you may never need. A second "back-up" battery is just extra weight that you haul around.

Airplanes should be designed so failures are an inconvenience, not a catastrophe.  If your alternator fails, you know the battery will be dead eventually. Once it fails, you can continue without radios and such, or you need to land before it gets dark. With a backup battery, you may continue farther, but you will still need to land soon.

In a modern jet airliner, there are alternators on each engine. Two seems like a good idea. There are actually 3, since the aircraft actually has a third turbine engine called the auxiliary power unit (APU). The APU is hidden in the tail of the aircraft, and connected to a generator capable of starting both engines, and running the majority of everything electric in the aircraft.

The 787 is unique, in that there is no hydraulic system to help the pilots fly the airplane. The items normally controlled by hydraulic fluid are run by servo motors, including control surfaces and brakes. The electrical system is quite important.

The batteries will help start the airplane. On the ground, there will usually be a device called a ground power unit (GPU) that will allow the aircraft to be started. The GPU can also be used to charge the batteries.  If the aircraft is operated away from the GPU, the battery will usually start the APU since that is a smaller turbine. Once the APU is started, it will be used to start the other engines.

Will the new battery solution help prevent a catastrophic failure on the 787. Probably, since the misbehaving battery cell will be isolated from its neighbor. Will there be cell failures? Probably, but the new monitor system will alert the pilots, and isolate the bad cell when needed.

If someone wants to have a wanna be engineer to ride around on the 787 during test flights, I'll volunteer. Give me a call, we'll set something up.

 

Hijacking With Android

Nope! not gonna happen. Well, not without a lot of other technology.

CNN as they are wont to do, posted a sensational article about some dude using an Android phone app to take over an airplane. That is all it is, sensational. There are some bits that could be true, but lets look at things from a more technical point of view.

Hugo Teso used a simulator to 'demonstrate' this 'hack'. It wasn't on a real airplane. The hardware he chose was not flight certified, so most of his claims are completely dubious.


First, lets get some terminology right. Hackers are getting a bad rap by this Hugo. Malicious people are crackers or criminals. Hackers are are people who repurpose technology. Think of a car customizer, someone who takes perfectly good cars and makes them better or different, they might be considered a hacker. In the pre-computer days, hackers were the folks who could do amazing things with very little. They were the folks you went to, to get things done. Places like Hack A Day is an example of a group of these folks, or the Maker movement.

An Android cellphone only work in frequencies maybe at the low end 700MHz, and if you include Bluetooth and WiFi there are radios that talk in the 2.5GHz or 5GHz frequencies. There are actually several radios covering the various modes, including Voice and the various data modes, like 3 and 4G, HSPA+, LTE, etc. They are all between about 700MHz up to about 5GHz.

ACARS is a ground to air digital messaging system. Think of it like instant messaging ( IM) from the airline operations center to the airplane. ACARs allows the airtraffic Controller Pilot Data Link Commands (CPDLC). The ACARS radios are in the 110-130Mhz frequencies. The Cell phone can't talk on frequencies that low. He would need a radio that will talk on those frequencies to talk to the ACARs device to inject some CPDLC commands. The CPDLC commands are like "turn right heading 230", the pilot must acknowledge or reject that 'command' before the aircraft will react.


ADS-B is a technology that allows the airplanes to tell each other where they are using GPS location, and a transceiver that are in the participating aircraft. The ADS-B signals are either on Universal Access Transceiver (UAT) on 976MHZ or on 1090Mhz mode-s transponder frequencies. Since UATs are US only, the dude might have gotten his cellphone to talk on the 1090Mhz frequency (although that is highly unlikely, but I don't know what brand phone he had or what radios the european version of that phone contains, it may be possible). Most of the radios in the phones aren't that programmable, and the FCC pretty much gives the 1090MHz frequency and surrounding frequencies to aircraft and not cell phones.

The Flight Management System (FMS or FMC) are the 'brains' of the aircraft. It manages the auto pilot, connects to the ACARs radio, and the initertial reference system (IRS) some of the other navigation systems. The FMS talks to the airplane. The FMS doesn't talk WiFi, so you can't just use the WiFi on the airplane to talk to the FMS or any of the displays in the cockpit (unless they have an iPad or other tablet, but those aren't connected to the airplane anyway). The FMS usually talks something like ARINC-429 and has a giant plug on it with each device having a separate wire.

FMSs can be reprogrammed, but not over the air (at least that I know of, there may be some new brand or version that can be, but if that were allowed, I am pretty sure it wouldn't allow being reprogrammed while controlling the airplane). They are finicky, and the ones in version X of the 737 can't be programmed the same way as version Y of another 737. If you want to know if Airbus and Boeing share anything, it is unlikely any of those FMSs would even share one line of code.

There is no one technology that can get this guys app to hijack a plane. You aren't going to find terrorists lining up at the T-Mobile stores to buy Android phones and downloading the app so they can take over the airplanes. Actually some might, it might be good for the stores selling phones, but folks are gonna be disappointed, and return the phones, and go buy and iPhone to be like all the cool kids until Apple comes out with that app.

We can all relax, sit back and enjoy the ride. Airplanes won't be hijacked by cell phone.