67
votes
Accepted
What prevents a commercial jet from electronically "resetting" the way a computer sometimes does?
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 ...
- 12.8k
57
votes
Accepted
Has there ever been an airliner design involving reducing generator load by installing solar panels?
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%...
- 1,523
48
votes
Why do we still need ammeters?
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 ...
- 4,877
46
votes
Accepted
What happens when all electrical systems in a helicopter fail?
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 ...
- 54.4k
45
votes
Accepted
Why are Li-ion batteries not being used in aircraft but are widely used in electric vehicle industry?
Boeing put them in 787. They caused the type to be grounded for a bit over two months in 2013 due to battery fires.
Li-ion battery fires of consumer electronic devices are also semi-regular occurrence ...
- 56.5k
39
votes
Accepted
Where is the generator in a large turbofan of a commercial airliner?
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 ...
- 63k
37
votes
Accepted
How do jet engines generate electrical power?
All jets and turbofans run a gearbox driven off the outer spool shaft. The gearbox has drive pads for all of the powered accessories like hydraulic pumps, fuel pumps, and the generator, and an input ...
- 136k
33
votes
What does "28 volts DC" mean, really?
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 ...
- 12.8k
32
votes
Accepted
Why do aircraft use 400 Hz AC instead of the 50 or 60 Hz of wall outlets?
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 ...
- 53.7k
32
votes
Where is the generator in a large turbofan of a commercial airliner?
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 ...
- 81.2k
30
votes
Accepted
What happens to Cessna electric flaps that are moving when power is lost?
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 ...
- 4,640
30
votes
Accepted
Can a completely drained battery be recharged via ground power on an airliner like the B737?
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 (...
- 53.7k
27
votes
What prevents a commercial jet from electronically "resetting" the way a computer sometimes does?
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 ...
- 2,424
27
votes
Why are Li-ion batteries not being used in aircraft but are widely used in electric vehicle industry?
If we're talking about using the batteries for propulsion (and we're talking about aircraft that can carry at least one person) then it boils down to, in a word, weight, or in two words energy density....
- 1,056
27
votes
Accepted
Why use a RAT when engines can windmill?
There are a few things to consider:
In an Airbus (such was the case with Air Transat Flight 236) when both engines are lost the RAT will automatically deploy (see the answer to this question) so in ...
- 102k
27
votes
Accepted
Why doesn’t lightning punch a hole in the fuselage?
Potentially, yes, but this would be a very rare event. The principal reason that lightning does not create damage to an aircraft is that the airframe, particularly aluminum airframes, are electrically ...
- 75.1k
25
votes
What does "28 volts DC" mean, really?
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 ...
- 63k
23
votes
What powers an aircraft prior to the APU being switched on?
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 ...
- 58.3k
22
votes
Accepted
What is the process to disconnect ground electric power before pushback?
When is the GPU disconnected?
Airports have rules regarding APU use, to reduce noise and pollutants near airport gates.
Airline operating procedures usually specify when to start APU and engines. The ...
- 81.2k
22
votes
Why do we still need ammeters?
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 ...
- 75.1k
20
votes
Can electricity be harvested from magnets in jet engines?
The power generation method you propose is used on almost all motorcycle and small lawnmower engines: magnets pressed into the rim of the flywheel, with stationary coils nearby in which current is ...
- 22.2k
20
votes
Can jet engines stay running without electrical power?
Yes, a jet engine can operate without electrical power. Or at least they used to be able to...
A jet engine uses igniters (like electric spark plugs) to initiate combustion in the combustor. Once ...
- 17k
19
votes
What's the point of separating the Alternator and Battery switches?
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.
...
- 102k
19
votes
How much electrical power does one generator produce on a large turbofan?
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 ...
- 81.2k
19
votes
How much electrical power does one generator produce on a large turbofan?
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.
...
- 63k
19
votes
Can quadrotors be used for commercial passenger flights?
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 ...
- 63k
19
votes
Is aluminum electrical wire used on aircraft?
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 ...
- 30.2k
19
votes
Why do we still need ammeters?
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 ...
- 1,543
19
votes
Accepted
Why is the battery turned off for checking the voltage on the A320?
The voltage varies with what is connected to the bus.
Adding load will, for every electric source, reduce the voltage. And you wouldn't know how much is still OK without also knowing what is powered.
...
- 56.5k
Only top scored, non community-wiki answers of a minimum length are eligible