Questions tagged [sensors]

Questions about various sensors used in aviation, both on aircraft and ground equipment.

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How does an alpha (AoA) vane work?

The alpha vane (also called AoA vane) is an external probe used to measure the angle of attack. I have been trying to understand how exactly it works, but I can't find any clear explanation or ...
asheeshr's user avatar
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36 votes
2 answers
8k views

What are these boxes built into the tails of some fighters?

In looking at European-designed fighters of the 4th and 4.5th generation, I keep seeing a common design feature; a box-like structure built into the tail, often in the top half or third. Some examples:...
KeithS's user avatar
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33 votes
2 answers
10k views

What is the smiley face sensor at the stern of the F-4 Phantom?

The F-4 Phantom has an interesting collection of sensors at the extreme rear of the empennage. What are these sensors for? My daughter calls them them smiley sensors but I suspect that is not the ...
Happy Phantom's user avatar
22 votes
2 answers
8k views

What is this 'ball' in front of the cockpit of some fighters, e.g., an Su-57?

What is the lump/ball thing visible below and to the left of the canopy in this image of a PAK FA (which became the Sukhoi Su-57), and what is it for? It's also seen on other fighters. Image source
anonymous's user avatar
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18 votes
4 answers
4k views

Why is not every airplane equipped with 3 angle-of-attack sensors?

For critical systems, redundancy is built into the system. It is common knowledge among designers/architects to have three different inputs so in case one is faulty, input from the remaining two can ...
Regmi's user avatar
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18 votes
1 answer
4k views

What is this device protruding from the rear of this 787?

While looking at the photos from this question I noticed a small protrusion from the side of the plane. You can see it in the photo: and in the diagram from l@aeroalias answer: In the diagram it ...
TomMcW's user avatar
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17 votes
6 answers
8k views

Do aircraft have accelerometers?

Do modern aircraft employ accelerometers or other similar equipment to measure g-forces on the aircraft? I could imagine this being used as an inspection/service indicator, particularly after hard ...
Erik's user avatar
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17 votes
4 answers
3k views

How does the Guardian counter-MANPADS system work?

I came across this picture of a FedEx McDonnell Douglas DC-10 equipped with an anti-missile defense system. (wikimedia.org) According to the picture description: FedEx became the first U.S. ...
shortstheory's user avatar
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17 votes
2 answers
7k views

What are these bars on an F-16's nose?

I've always wondered what the purpose of these "bars" on the nose of the F-16 (and some other military aircraft) are. Are they sensors (if so, what kind)? Are they lightning strips? I can't ...
F16Falcon's user avatar
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16 votes
2 answers
4k views

How is fuel mass measured in airliners?

Large airliners display the amount of fuel in each tank as a mass (usually in kg or lbs) and not as a volume. This makes sense since mass is important for weight&balance considerations and the ...
Bianfable's user avatar
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16 votes
3 answers
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Do modern airliners have oxygen sensors in the cabin?

I know that airliners have pressure sensors to check the cabin pressure, and thus check if we can breathe (and get enough O2) inside it so we don't get hypoxia. But that got me thinking: Is there any ...
Gabriel Brito's user avatar
15 votes
1 answer
2k views

What were the advantages of the L-1011 AoA sensor design?

The Lockheed L-1011 had an unusual type of AoA sensor. Instead of the usual vanes it used a tube with two rows of holes in it about 90° apart. A diaphragm sensed the pressure differential between the ...
TomMcW's user avatar
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14 votes
1 answer
3k views

What are these sensors on the Night Stalkers' Chinook MH-47G?

What are these sensors (or lights) on this heavy assault Chinook MH-47G of the US 160th Special Operations Aviation Regiment, "Night Stalkers"? Source, picture by Russell Hill This regiment was the ...
mins's user avatar
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14 votes
2 answers
2k views

What is this tube in a jet engine's air intake?

I have long been wondering what is the official name of this little air intake tube located in front of the fan blades and its intended functions. I did search it on google but it was in vain. I guess ...
N.L.'s user avatar
  • 143
13 votes
2 answers
4k views

Why are the angle-of-attack sensors on most airplanes mounted on the forward fuselage rather than at the wing roots?

A source of reliable angle-of-attack information is important for airplanes, as flight at an excessively-high angle of attack can cause the airplane to stall, which is generally considered to be an ...
Vikki's user avatar
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11 votes
2 answers
2k views

At what point is the input data to glass cockpit PFDs converted to digital?

At a very basic level, primary flight displays take data from sensors, do calculations, and display the results on a screen. Of course, because they are digital computers, the input must be digital, ...
Someone's user avatar
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11 votes
4 answers
6k views

What is the ultraviolet signature, if any, of aircraft and jet engines?

The Wikipedia article on the FIM-92 B variant of the Stinger Missile says: In this version, the infrared seeker head was replaced by a combined IR/UV seeker that utilized rosette scanning. This ...
DrZ214's user avatar
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11 votes
1 answer
1k views

What is this thing on a FDX MD11 (MD10?)?

I assume something forward looking; not sure why there and how they got this to play nicely with radar
Greige of Thunder's user avatar
10 votes
3 answers
628 views

Is it common for automated control systems to use non-redundant sensors?

While reading an article about the Lion Air Crash with a Boing 737 Max 8, I was very surprised by the following paragraph: In designing the 737 Max, Boeing decided to feed M.C.A.S. with data from ...
user avatar
10 votes
2 answers
547 views

Why is this angle of attack sensor tab not symmetrical between the leading and trailing edges?

Here is an Angle of Attack (AoA) sensor I took from here. If you are interested to know the AoA detail, just click the link. You may see what is inside it. But not sure what airplane's AoA sensor it ...
AirCraft Lover's user avatar
9 votes
2 answers
4k views

Why is the pitot tube located near the nose?

The pitot tube located near the nose could be affected by the boundary layer and could increase the error. Then why is the pitot tube located near the nose?
Roh's user avatar
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9 votes
1 answer
10k views

How many AOA sensors does the 737 MAX have?

How many AOA sensors does the 737 MAX have? Given that it's reported in the media, that one faulty AOA probe activated the MCAS on the Lion Air flight, I was wondering if anybody also knows how an ...
user33651's user avatar
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9 votes
2 answers
4k views

How do tyre pressure sensors in aircraft work?

I am specifically interested in the sensors used on the B777 and B787.
Pritam's user avatar
  • 548
8 votes
3 answers
2k views

Why do aircraft stall warning systems use angle-of-attack vanes rather than detecting airflow separation directly?

Stall warning and protection systems on essentially all aircraft work by using several hinged vanes on the side of the fuselage (usually at least three, and preferably more), which align themselves ...
Vikki's user avatar
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8 votes
2 answers
1k views

What are those sensors on the forward A321neo fuselage?

What are those sensors on the forward (Airbus) A321neo fuselage? If it helps, this is WOW air's TF-DTR.
Florian's user avatar
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8 votes
4 answers
2k views

Are there wool threads for displaying angle of attack?

Like there is a wool thread on a glider's canopy for showing relative wind on yaw axis. Are there or have there been a wool thread as a long term mean of showing angle of attack? For instance placed ...
user721108's user avatar
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8 votes
4 answers
1k views

Why aren't angle-of-attack data sanity-checked before being fed to other aircraft systems?

For most fixed-wing aircraft, accurate angle-of-attack information is utterly essential for safe flight, due primarily to the risk of stalling the aircraft if the AoA of one or both of its wings ...
Vikki's user avatar
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8 votes
1 answer
2k views

What additional functionality is provided by the F-14 nose pitot, absent in early models?

Early model F-14A had no nose pitot: ... but they seem to have quickly acquired them sometime in the late 1970s. The Iranian F-14s have them, and it's quite hard to find a picture of an F-14 without ...
Party Ark's user avatar
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8 votes
1 answer
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What is the purpose of proximity sensors on hydraulic systems?

One of the planes I worked on had ground spoiler response checked with proximity sensors. The reason mentioned for that was - "The ground spoiler is hydraulic only - hence its response will be checked ...
user2927392's user avatar
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7 votes
3 answers
3k views

What types of fuel quantity sensors are used in an aircraft? How do they work?

Can you explain the different types of fuel quantity sensors used in most recent aircraft? Are ultrasonic tank sensors used these days? How does an ultrasonic sensor work?
Pritam's user avatar
  • 548
7 votes
3 answers
504 views

Could airliners fetch data like AoA and speed from an INS?

If I understood what an inertial navigation system (INS) is, it should be able to calculate speed and orientation of the aircraft. If this is possible, why do airliners solely rely on sensors to ...
user2591935's user avatar
7 votes
1 answer
895 views

Why would there be airflow from the back of a TAT probe?

During walk-around checks, I occasionally find airflow coming out from the back of the TAT probes on the Airbus A320. I wonder if it's air to cool down the TATs as they are heated during flight for ...
dingdingdong's user avatar
7 votes
1 answer
728 views

Why are the positions of an aircraft's angle-of-attack vanes dependent on airspeed?

According to this answer to an earlier question of mine, the positions of the angle-of-attack sensor vanes on the A330/A340 are dependent not only on AoA, but also on airspeed (and, according to @ymb1'...
Vikki's user avatar
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6 votes
5 answers
695 views

How do aircraft instruments determine the aircraft's orientation relative to the ground?

Autopilots exist for airplanes and drones, how is orientation measured with respect to ground? In particular how is the direction of gravity detected and how is it differentiated from acceleration due ...
FourierFlux's user avatar
6 votes
2 answers
3k views

How does a fuel density sensor work? (densitometer, cadensicon)

While some fuel volume sensors use ultrasonic measurements this answer to How is fuel mass measured in airliners? says: The FCOM lists the sensors involved in this measurement: The FQI system ...
uhoh's user avatar
  • 5,808
6 votes
2 answers
4k views

what type of sensors does the Boeing 737 MAX use for MCAS?

I can imagine there are several different ways to measure angle of attack (accelerometers, relative pressure measurements between pitot tubes, etc), but I'm curious which sensors the 737 MAX uses for ...
Nicolas Holthaus's user avatar
6 votes
2 answers
829 views

What sort of sensors are used for sensing the positions of the control surfaces for the ECAM F/CTL page on Airbus aircraft?

During the pre-flight flight-controls-check how does the ECAM F/CTL page report on the actual positions of the control surfaces? What sort of sensors are these? Is it a proximity sensor? This is ...
curious_cat's user avatar
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6 votes
1 answer
1k views

What sensors are required to fly RNAV 5 airways?

In the example shown above: Is an aircraft required to have all 3 sensors listed or just one of them to fly the L512 airway? What ICAO reference confirms the answer? Does 'critical DME' (bottom row) ...
longhaircat's user avatar
5 votes
4 answers
909 views

Why are the AOA sensors placed outside the aircraft?

Why should the AOA sensors be placed outside the aircraft? Is it not the angle between the chord line of a wing and a vector representing the relative motion between the aircraft and the surrounding ...
confused layman's user avatar
5 votes
4 answers
8k views

How are pitch angle and pitch rate measured in an airplane?

What equipment or method is used to obtain measurements of the pitch angle (θ) and pitch rate (q) during flight? Edit: I am asking about how the aircraft systems sense these quantities
Mateus de Freitas's user avatar
5 votes
1 answer
2k views

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?

For example, has an Airbus gone from cruise flight into an automated unrecoverable nose dive until it hit the ground because an AOA sensor failed in flight? Moreso, are there any cases of an AOA ...
Willy A's user avatar
5 votes
2 answers
5k views

What is the difference between IMU (Inertial Measurement Unit) and AHRS (Attitude and Heading Reference System)?

According to online sources like wikipedia the difference belies on the addition of an on-board processing system (I assume it means a microcontroller) which outputs already processed data and not ...
A. Fenzry's user avatar
  • 403
5 votes
1 answer
2k views

What is GPS HIL in layman's terms?

GNSS Horizontal Integrity Limit/ Horizontal Protection Level is a measure of GNSS position error/integrity that's very important in RNP operations and RAIM, but it has an obtuse definition in aviation ...
Cody P's user avatar
  • 6,775
4 votes
2 answers
6k views

How would the Airbus A320 PFD respond to failure of all pitot and AOA sensors?

In theory, if all 3 pitot tubes and all 3 AOA-sensors would fail simultaneously for a period of time, could the PFD still deliver correct roll angle and horizontal displays? How would the plane ...
Horizontal Vertikal's user avatar
4 votes
2 answers
7k views

How does a pilot know if he has headwind, tailwind or crosswind?

While in cruise, without GPS how does a pilot know the wind direction? The airspeed sensors only register forward speed. Is it a matter of reaching waypoints sooner or later? And if flying on a ...
TomMcW's user avatar
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4 votes
2 answers
1k views

What is this pod at the wing-tip of a U2?

In this image of a U2S, what it the very unaerodynamic looking pod at the wing-tip? It looks like it holds some sort of sensor package. However, it doesn't seem to appear on all U2s (at least not ...
FreeMan's user avatar
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4 votes
1 answer
143 views

Is there a system of automated sharing of current (experienced) weather between aircraft in flight?

For example, if say - Aircraft 1 is flying a certain route, being followed by Aircraft 2 at an interval of say, 5 minutes (over the same position). Is there a system by which Aircraft 1 can transmit ...
Jonathan MilTech Benjamin's user avatar
4 votes
1 answer
302 views

What does "half of the horizon circle" means?

The definition of Prevailing Visibility is: "Prevailing visibility is the horizontal distance over which objects or bright lights can be seen and identified over at least half of the horizon ...
mka's user avatar
  • 45
4 votes
1 answer
157 views

How are sensors in the wheels connected to power and data buses?

In this question the sensors to measure the tyre pressure are described. But how do such sensors receive the electrical power they need, and how are the signal values transmitted back to the relevant ...
Monolo's user avatar
  • 1,687
3 votes
1 answer
394 views

Can a laser Doppler anemometer be used to measure airspeed?

Could this be used in place of or in addition to a pitot-static system?
TomMcW's user avatar
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