Hot answers tagged

51

First off, you absolutely made the correct decision. As PIC/pilot you have not only the ability, but the duty to call off any flight you don't feel comfortable regardless of the reason. Your go/no go decision can be based off of anything and you should always be comfortable making that decision. Now as far as the battery goes I can tell you I was in exactly ...


33

It's the second option. In any other context, a small aircraft's electrical system would be called "24V". But the alternator regularly puts out 28V, so that's what's typically expected if you hook up your multimeter while the engine's running. Of course, the on-board equipment can operate over a wide range of voltages, often down to as little as 20V.


25

Multiple sources indicate that the 28 VDC bus on aircraft powered by 24 VDC batteries, and the 24 VDC systems on truck powered by 28 VDC alternators, are basically the same thing, and that is is just a naming convention. The number of cells is a function of the nominal voltage and the cell type. From this site: Lead Acid: 2 volts/cell Nickel based for ...


23

Before I answer its pertinent to clarify something as your wording it a bit tricky, I know that the plane is powered by the magnetos once started The spark plugs are driven by the magnetos, the airplane (electronics etc) is powered by the alternator/battery once started. This is important as you can have a running engine with both a faulty battery and a ...


18

is my decision to not fly unfounded or would there be good reason not to fly knowing that the battery was weak and unreliable? A weak battery does not generally pose a problem to an electrical system - even if it presents a constant load, the alternator should be more than powerful enough to maintain that load as well as all other electrical loads. The ...


18

I will expand a bit on @Noah Krasser's answer with some situations where you would want one or the other. FWIW under-volt scenarios are typically far less of a problem than over-voltage scenarios. Bad Voltage Regulator: Alternators vary their voltage output with RPM. To keep your system operating properly a voltage regulator is installed on the alternators ...


16

Let me start of with two facts that pretty much answer your question: A 24V battery is a battery that can output at least 24V over the majority of its capacity. To charge a rechargeable battery you need to push charge into it by providing it with a higher voltage than what the battery is currently at. To put a bit more meat on, here is a typical discharge ...


15

You'll see all kinds of power on large aircraft - 28 VDC, 115 VAC 60 Hz (and likely 230 VAC 50 Hz), 115 VAC 400 Hz, 5 VDC (USB power in cockpic/pax seats), 230 VAC, and 270 VDC. Here's a general idea of what the Boeing 787 Power Distribution System consists of: (Source)


15

Short and concise answer: Imagine there is a problem with the alternator. You have to shut it down. Now there is only one button to turn off both the alternator and the battery. You just want to turn off the alternator, but you would also lose your radios, the GPS, everything. Is that what you want?


9

There are a few electric aircraft now, and because batteries hold far less energy than fuel, they're low-performance and short-range compared to normal aircraft. If we imagine that at some point in the future we'll have batteries that can match fuel, the answer would be: Only slightly. Back in the 60's and 70's, airliners regularly carried a flight ...


7

If you're unsure of safety for any reason, "no-go" is generally the right choice. If it turns out later you didn't need to be so conservative, that's fine and you can always do it differently next time - what matters is your assessment of the situation at the time. Of course, you are correct that the magnetos will keep the engine running no matter what ...


7

Dead battery = no go for me. Even if the battery is good, if the engine is hard to crank and not just cold, what if the engine stops in flight and is hard to restart? I aborted a cross-country vacation in a rented 152 once because of a dead battery one leg into the vacation, went back, and spent a bummer Christmas at home, a decision I don't regret. (What ...


6

In addition to the other answers, most modern alternators have stator and rotor coils. One generates the electricity, the other consumes current to generate a magnetic field. When driven by the engine, the current consumed is a small fraction of the current generated. However, when you first power up your machine you really do not want the batteries ...


5

First, don't go if you aren't prepared and comfortable with all aspects of the flight, so from that aspect you made a great decision. As you seem to already understand, the financial aspect shouldn't make even a small difference when it comes to making these decisions. That being said, the main thing to consider is what happens if the alternator fails and ...


5

As far as I can tell, current aviation lithium batteries do not use active cooling. I know the True Blue Power TB17 (Robinson R44 & R66, Bell 505 Jet Ranger X) and TB44 (Cessna Caravan, DHC-6, DHC-8) do not require active cooling. I haven't seen any easily accessible info on the Saft batteries for the A350.


5

No, it is not safe to fly on an aircraft that has lithium-ion batteries in the hold. There is a commentary on FAA Safety Alert for Operators (SAFO) 10017 here, which was issued after the crash of UPS Flight 6. Admittedly, this was a bulk load of 81,000 batteries on a cargo flight. However a search for 'battery' on AV Herald shows between one and two ...


4

Lithium batteries do NOT produce oxygen. The problem with extinguishing them is that they do not NEED oxygen to produce heat. They produce heat through electrical discharge rather than combustion. The reason they are allowed in the cargo hold only when installed in devices is that they are less likely to get damaged or shorted out while in the device. ...


4

Airbus use 28V DC, largely for things like sensors etc., so the overall power usage on the DC system is quite low: As an example, the A350 has 4 Transformer Rectifier Units (TRUs) which convert AC to DC. 2 of them are designated as 'normal' and 2 as 'emergency'. Each one has a nominal power of about 300W. Total DC system usage is about 500W. . Unfortunately ...


4

But in reality, the fully charged/charging/float voltage of the system with alternator running is higher Yes. If a car battery states 12V that's kind-of the lower limit. As in, it really shouldn't drop below 11.8 when fully discharged, although depending on the type of battery and vehicle it may still function (for some values of function). A fully charged ...


4

What are the disadvantages of such a system being used as an auxiliary power source if not the main one? Is it not worth the money? It's not worth the weight. The power that can be extracted from piezoelectronics is on the order of microwatts (100 uW in the above article). In contrast, light aircraft have their power measured in kilowatts and commercial ...


4

This aircraft museum says that the "Trolley Acc" (Trolley Accumulator) used for Spitfires and other aircraft supplied 12 volts. Lots of sources state that Spitfires had 12 volt electrical systems, including the Pilot's Manual.


3

Robin makes a lot of great points, but since we are talking on a purely hypothetical case lets have fun and take it to supersonic speeds. Let's assume that somehow batteries have the required energy density to be used to run some sort of low-bypass electric turbofan to propel our aircraft to high speeds where the neutral point of the aircraft starts ...


3

An EDF is an electric ducted fan, so I assume you're not interested in the fans powered by internal combustion engines (or actual turbines). You'll need: an ESC (electronic speed controller) that is rated for at least the maximum current and voltage of the motor in the EDF. a battery that can provide that current and voltage. something to provide a ...


2

From this presentation for the A320 family: Battery ventilation Achieved by ambient air being drawn around the batteries and then vented directly outboard via a venturi. So the ventilation air provides cooling as well, especially when at cruise altitude. Batteries in the avionics bay are further cooled by a separate aircon system. From the same ...


2

Constant-voltage, but there's more going on. Batteries prefer a mildly complex charging curve, because both lead-acid and NiCd charge efficiently in their mid-cycle (20-80%) -- but inefficiently at the top of their range (80-100%). In a perfect world, a charger pushes them heavily (constant-current) in their midrange, but tapers off for the top-up charge. ...


2

Airliners like the Airbus A320 use Nickel Cadmium batteries; in case of A320, a pair of main batteries with 23 Ah capacity is used. While on the aircraft, the batteries are charged using a constant voltage method. As this article notes: ... are "constant-voltage chargers" that apply a fixed voltage to the battery as it charges, similar to what the ...


1

Is it possible to power a very small jet using batteries? Yes, with some major provisos. Jet It is misleading to use the word "jet" because a jet engine requires combustion of hydrocarbon fuel to create heat to expand exhaust gasses to drive a compressor and produce direct thrust and/or to power a bypass fan. An electric powered aircraft engine would most ...


1

On some scale, of course this works -- look up "EDF", Electric Ducted Fan R/C models of jet planes. For something the size of a Honda Jet, you still likely wouldn't get the performance (and certainly not the range) that you might desire. Go smaller, and something in the size range of a BD-5J/Acrojet, which originally flew on a very small engine, might ...


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