New answers tagged electrical-system
2
Every now and then I get to fly two DH82a Tiger Moth that are retro fitted with batteries and alternators to provide power for the radio and transponder as this type originally was not fitted with any electronic systems -- along a few other things e.g. brakes, tailwheel, flaps, a reasonably-sized windscreen, adjustable seats, some useful avionics and of ...
2
The better way to think of it is this: the electrical system of an aircraft is not battery powered at all. It is powered by engine driven generators or alternators. These devices provide all the electrical power used while the aircraft is operating in the air or on the ground. However, when the engine(s) isn't/aren't running, electrical power is needed to ...
3
You are getting the APU mixed up with the RAT:
The Auxiliary Power Unit (APU) is an engine powered generator, either a gas turbine or a piston engine. APUs deliver enough power to start engines, power cabin lights, cockpit instruments and radios, and in some cases power hydraulics. Often the APU can only be run at lower altitudes where the air is thicker
A ...
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 ...
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 ...
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 ...
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.
1
Regarding power cycling specifically (as opposed to software-based failures in general which other answers have detailed very well), it's not a problem at all. Unlike a typical PC or smartphone which takes time to turn back on and can lose data when power is lost, the control systems on an airplane are typically designed such that they will resume complete ...
0
Reboots can also sometimes be acceptable if you can reboot quickly without losing critical information. This occurred as part of the Apollo 11 landing when they had the 1202 alarm:
He realized that the 1202 was a code meaning that the guidance
computer on-board the landing craft was getting overloaded with tasks.
The programmers had anticipated this ...
4
as somebody who did software tests on an unimportant (class D, will explain soon) system for an airplane to be approved to be landed on civilian airports: In airplane there is a strict hierarchy on what kind of software functions mean; they are listed in DO-178B.
Class A systems are assumed to be "failure free"; they are extremely well tested. These ...
4
Occasionally a computer or smartphone will crash and reboot itself
This can happen for two reasons: a software error or a hardware error. Both can cause the CPU to stop processing new instructions (i.e. a "hang") or to cause the machine to reboot itself. The latter is close to a hang, because the Operating System detects it cannot continue operating ...
24
Before we start, it's important to say that your concern is not irrational. If this were to happen, or if your plane's control systems were to otherwise malfunction in a dangerous manner, your life would genuinely be in danger.
You aren't the first person to have thought of this, though. For this reason, we have a category of control systems we describe ...
66
I'm a programmer and private pilot, so maybe I can help dispel some of those fears.
The computers that run a commercial airplane are conceptually much simpler than the one that runs your phone. This means far less chance of a bug in the software, just because there's less for the programmer to keep track of.
If your phone restarts, it doesn't imperil ...
10
Your concerns are reasonable and justified. A mid-air shutdown or reboot would be catastrophic to an airliner. Which is why, engineers designed the systems such that this scenario is practically impossible to happen.
Electrical power
An airliner has multiple electrical power source. Each jet engine has a built-in generator. When the turbine spins, ...
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