50
votes
Accepted
Do aircraft have accelerometers?
Most modern aircraft, which includes long range airliners since around 1970, all airliners since not much later, and basically anything with glass cockpit, do have very accurate accelerometers for all ...
- 56.2k
32
votes
Why do aircraft stall warning systems use angle-of-attack vanes rather than detecting airflow separation directly?
The short answer is that we want to warn the pilots about an impending stall well prior to an actual stall condition. From a safety perspective, waiting until the airflow starts to separate, or at ...
- 581
28
votes
Accepted
What is this 'ball' in front of the cockpit of some fighters, e.g., an Su-57?
That is the infrared search and track (IRST). This particular model of an IRST is known as the OLS-50M in Russia and uses quantum well photodetectors.
Radar has two serious limitations, one is that ...
- 13.3k
24
votes
Accepted
What are these bars on an F-16's nose?
These are antennae for the IFF (Identification Friend or Foe) system. IFF is a system to help distinguish friendly aircraft from unfriendly ones.
This particular antenna arrangement is used on only ...
- 2,347
23
votes
Accepted
Why is the pitot tube located near the nose?
There are several reasons to have the pressure sensors in the front section of the fuselage.
The further aft the more turbulent the airflow is and the thicker the boundary layer caused by the ...
- 2,366
20
votes
Why are the angle-of-attack sensors on most airplanes mounted on the forward fuselage rather than at the wing roots?
Would installing the AOA vane (or, in general, sensor) at the wing root be more accurate than installing it near the nose? No, it wouldn't. In fact, it may be slightly worse due to the larger upwash ...
- 11k
19
votes
How is fuel mass measured in airliners?
On the Airbus A320 family, the fuel volume is measured via capacitance probes and then converted to mass by also measuring the fuel density:
The FQI [Fuel Quantity Indication] system calculates the ...
- 54.3k
18
votes
Accepted
At what point is the input data to glass cockpit PFDs converted to digital?
Glass cockpits are modular systems, and not all of them are exactly the same. But many/most include a module called an Air Data Computer (ADC) which performs the digitalization function for the ...
- 14.2k
17
votes
Accepted
What are these sensors on the Night Stalkers' Chinook MH-47G?
Those sensors are part of the AN/AVR-2A Laser Warning System. Here is a closeup of the system components.
The AN/AVR-2A is a passive laser warning system which receives, processes and displays threat ...
- 100k
17
votes
What is this thing on a FDX MD11 (MD10?)?
It's the infrared sensor for the Enhanced Flight Vision System (EFVS).
From FedEx Newsroom June 23, 2008:
FedEx Express is the first major commercial carrier in the airline
industry to receive a ...
- 19.4k
16
votes
At what point is the input data to glass cockpit PFDs converted to digital?
On smaller aircraft, the conversion is done within the Air Data Computer (see TypeIA's answer). This makes replacing older steam gauges with a glass cockpit relatively simple because you just send the ...
- 54.3k
15
votes
Accepted
What is this tube in a jet engine's air intake?
That's the EPR inlet pressure sensor (there's another one located aft of the engine in the exhaust).
EPR = Engine Pressure Ratio, one way to measure thrust.
(source)
See also:
What is the ...
- 849
15
votes
Why is not every airplane equipped with 3 angle-of-attack sensors?
Triple redundancy is necessary to detect a fault and exclude it. The system then continues to operate through the fault. Double redundancy is used to detect a fault but cannot exclude it, so the ...
- 6,487
14
votes
What is this 'ball' in front of the cockpit of some fighters, e.g., an Su-57?
That is an passive Infra Red Search and Track (IRST) sensor. Used to passively identify and track aircraft using their emitted infrared energy. The system pictured above is used solely for an air-to-...
- 72.8k
14
votes
Accepted
What is the ultraviolet signature, if any, of aircraft and jet engines?
Your assumption is correct - it is indeed about infrared (wavelength between 750 nm and 10,000 nm) and ultraviolet (wavelength between 100 nm and 400 nm) radiation. The sensor detected two specific ...
- 229k
14
votes
Why are the AOA sensors placed outside the aircraft?
No, it is not possible to place the sensors inside the aircraft, because the angle-of attack sensors need exposure to the surrounding air, in order to measure, as you mention yourself, "relative ...
- 12.8k
13
votes
Do modern airliners have oxygen sensors in the cabin?
While it would not significantly affect the O₂ percentage one thing that must be tabulated on a cargo aircraft is the amount of dry ice loaded. Dry ice is very common in packaging to keep perishable ...
- 28.4k
13
votes
Accepted
How many AOA sensors does the 737 MAX have?
The Boeing 737 MAX has 2 AoA sensors.
However, MCAS only takes input from 1 AoA sensor at a time.
Sources:
The black box flight recorder data for Lion Air JT610 shows the data from 2 AoA sensors, ...
- 366
12
votes
Accepted
Will an Airbus A320 plane go into an unrecoverable nosedive and crash if a single angle of attack sensor fails, like on Lion Air JT610?
if a single angle of attack sensor fails
No.
An A320 has three AoA sensors. If one reports a different value to the other two, the avionics will ignore values from that AoA sensor and use the values ...
- 26.3k
11
votes
Accepted
What is this device protruding from the rear of this 787?
As you have already imagined, it's the APU fuel line shroud drain, as visible here:
(Source)
Detail:
The fin gives an aerodynamic profile to the drain. The reason this drain exists seems to be:
...
- 70.9k
11
votes
Is it common for automated control systems to use non-redundant sensors?
In general, yes. Except in certain configurations, namely autoland, autoflight functions are usually fed with one set of sensors.
This matches the fact that pilots flight instruments are fed from a ...
- 6,487
11
votes
Accepted
Could airliners fetch data like AoA and speed from an INS?
An INS gives your speed & orientation in space, but without reference to what the airmass that you're flying in is doing.
The Pitot tube and AOA sensors give speed and pitch orientation in ...
- 49.8k
9
votes
What is the smiley face sensor at the stern of the F-4 Phantom?
Farhan is correct that these "bug eyes" are part of the radar warning system, but unfortunately is incorrect as to what that system actually does.
Radar warning systems are commonly installed on ...
- 3,775
9
votes
Accepted
Do modern airliners have oxygen sensors in the cabin?
The air conditioning system on board airliners is an open system: it scoops up air from the atmosphere, compresses it, expels it through the cabin vents, and then outflows it through discharge valves. ...
- 61.3k
9
votes
How does a fuel density sensor work? (densitometer, cadensicon)
I don't know what exact kind they are using in the A320 (from which the quote in the question is). @mins found a forum post about an Airbus A300-600 cadensicon:
The cadensicon measures fuel ...
- 54.3k
8
votes
Accepted
What types of fuel quantity sensors are used in an aircraft? How do they work?
From this PPRune forum thread, the Boeing 777 does use ultrasonic sensors (some 20 per tank)
This airplane has some 20 sensors per tank. Each of these is effectively a "radio doppler" and works on ...
- 2,543
8
votes
Why is not every airplane equipped with 3 angle-of-attack sensors?
Two AoA sensors are more reliable than three!
Let's have a look at probability calculation, and assume the fault probability of one sensor to be p = 0.1 % (per flight, or whatever you like to choose)....
- 10.7k
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