# Tag Info

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 ...

57

If no, why not? While I can't say categorically that it's not happened, I'm pretty sure. Solar radiance is approx. 1kW/m^2. A 737 has approximately 100m^2 wing area. Solar cells are approximately 20% effective. If you covered the entire wings in solar panels, that would work out to 20kW of electrical power at best. At night, it would be close to zero ...

48

Congrats on earning your wings! Because ammeters measure the flow of current (positive or negative) they can immediately show when the alternator is no longer providing power and the battery is discharging instead. In a voltmeter, like most modern automobiles have, you would have to wait to see the charge level on the battery drop, and by that point, several ...

45

The reason for the failure is important actually. If all the electrical systems on an EC135 helicopter fail in your classic EMP scenario then the helicopter has to make an emergency landing as the jet engine is run by a computer system which requires electricity. A power failure of that system would most likely cause the engine to revert to manual backup, ...

37

Image source The generators are usually driven from the Accessory Gearbox. This CAD drawing is from the company that makes accessory gearboxes for the Rolls Royce Trent engines driving the A330 and A350, and it shows the connection of the accessory gearbox to the high pressure rotor. This picture from the book The Jet Engine by Rolls Royce shows the ...

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.

31

Short answer In flight, unless you use external energy sources like the Sun, each change in the use of electricity leads to a proportional change in the quantity of fuel burnt in the engines (or in the APU). On an aircraft, generators only convert fuel potential chemical energy into something else, usually electricity, hydraulic energy or pneumatic energy. ...

30

To fill the voids in aeroalias' answer: Hydrazine is a monopropellant, something which does not need to be mixed and burned to free up the energy contained in its chemical bonds. This energy is freed by letting the hydrazine stream over a catalyst, in case of the F-16 EPU that is iridium. This breaks the chemical bond, producing ammonia, nitrogen gas, ...

30

IDG Location: Dedicated pad on the accessory gearbox If it's gonna be coaxial, the only place is the rear (it will be burnt) or the front (it will get in the way of intake). That's a good question and remark. Actually the generator (integrated drive generator or IDG) is off engine axis and goes on the corresponding IDG drive pad of the accessory ...

30

Stays where it is. The mechanism is a leadscrew and like most leadscrews it's "self-locking", which means that it's held in position by frictional forces whenever the motor isn't turning and it can't be back-driven even by substantial loads. The 20 degree (etc) "stops" are just reference positions for which aircraft performance and load limit data have been ...

28

My one experience with this was in a 737-300 that had the battery charger die, and the battery depleted while in flight. The Battery Bus was still powered by TR3, but the Hot Battery Bus died (interestingly, not a scenario I'd ever seen in the simulator). We got to the gate & couldn't start the APU and couldn't connect ground power, so when we shut ...

27

Induction motors turn at a speed proportional to frequency, so a high frequency power supply allows more power to be obtained for the same motor volume and mass. Transformers and motors for 400 Hz are much smaller and lighter than at 50 or 60 Hz, which is an advantage in aircraft (and ships). Transformers can be made smaller because the magnetic core can be ...

25

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 ...

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

Other than the APU, there are multiple ways to provide electrical power to an aircraft: Battery: The battery is typically the first thing you would turn on and it usually provides DC power to emergency systems only (at least on an airliner, smaller aircraft are fully powered by the battery). Running only on battery power will however deplete the battery ...

22

Because it displays how much current, and thus how much power, your electrical system is consuming. This provides a quick reference for diagnosing problems. Negative values can indicate a malfunctioning alternator and large power draws can indicate a short circuit somewhere in the system.

21

Yes, because (like a car for example), the aircraft is a closed system, and all energy must be provided internally. So, in flight, that energy must come from the engines, and therefore, the engine must either slow down, or use more fuel.

20

For the complete electrical failure in the aircraft, the following systems have to fail: The onboard power generation system, usually a synchronous generator has to fail in all the engines. The APU (Auxiliary Power Unit) has to fail. The RAT (Ram Air Turbine) should fail to deploy. The batteries and static inverters should fail (this won't help in ...

19

Are there any still commercial airplanes in use that are still steerable with complete loss of all electric systems? Do some commercial airplanes still have mechanical backup steering mechanisms? Yes and Yes. On most(*) Airbus aircrafts, In case of a complete loss of electrical flight control signals, the aircraft can be temporarily controlled by ...

19

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 ...

19

This is one of the four Variable Frequency Generator (VFG) of the Airbus A380. It's apparent power is 150 kVA. Rotor, source: Safran The total power available from the engines is 600 kVA. Seen from the other side: Stator, source: Thales The A380 is a one of these "more electrical" planes, where hydraulics tends to be replaced by electric devices, and ...

19

The three most important factors in passenger air travel are safety, safety & safety. So that is where most of the questions will focus on, and where most of the engineering effort will be put into. Couple of questions: Artificial stability: what happens if the stability circuit breaks down? What happens if one of the motors fails, for instance one of ...

19

Cable is not just the metal wire. It's also insulation, installation, cable channels, extra space at tight bends where cable flexibility is insufficient, and maintenance of said cable. Aluminum corrodes in a lot of conditions and happens to be one of the most fatigue-susceptible metals. For these reasons, most aircraft wiring is copper and silver-plated or ...

19

The more unpleasant a failure of some system is, the more tools you get to prevent, diagnose and mitigate the failure. An ordinary passenger car can stop in a middle of nowhere because the alternator failed and the battery depleted. Quite unpleasant, but rarely fatal - and modern cars tend to be reliable enough anyway. An offroad rig with winches, extra ...

18

The biggest problem with an all-electric-powered aircraft is the same as those plaguing all-electric cars; our current battery technology has nothing on the energy density of fossil fuels: There's just no contest in being able to pack the energy needed to push a plane through the air into a volume and weight compatible with an airliner. Jet fuel is kerosene,...

18

The EPU of F-16 is fueled with a monopropellant hydrazine mixture, H-70, which contains 70% hydrazine ($N_{2}H_{4}$) and 30% water, by weight. The main requirements for the EPU are that it should be simple, maintenance free, supply power immediately and consistently for the required time. Use of Hydrazine assures this while requiring careful handling. ...

18

The cockpit is clean and uncluttered thanks to the absence of the large circuit breaker panels that we’re used to in traditional types. Almost all circuit breakers are ‘virtual’ and are accessed via the forward Multi-Functional Display (MFD). — flight.org The 787 and its contemporaries have moved away from physical CB's and use virtual CB's instead. One of ...

18

There are several max ratings of a particular generator, depending on the duty cycle: peak rating (5 sec); max. Continuous (no time limit); and often an intermediate value for 5 minutes is given. The generator produces internal heat together with the electricity, which is not easy to remove by forced cooling and must dissipate through convection. The ...

17

AC is easier to produce with the engines, that act as generators. The engines have a rotating shaft that it is easily equipped with magnetic dipoles all around. Then, depending on the instrument, the current is either used directly or, by the use of converters, in DC form as not only it is easier to produce, it is also easier to convert. So electronic ...

17

It's not even true that most airliners use fly-by-wire. Among Airbus and Boeing models, the A320 and beyond use FBW on the Airbus side (note that the A300 was produced until 2007), and the 777 and beyond use it on the Boeing side. This is probably a majority of major commercial aircraft, but it's by no means a vast majority. Among these aircraft, virtually ...

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