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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 landings. Or do hard landings and other forceful flight regimes typically not pose any significant structural concerns?

Update. Related on determining hard landing inspections:

From Aero Magazine on Boeing conditional inspections

Section on AMM changes:

Boeing is modifying the 737 AMM, section 05-51, and will revise the AMMs for other Boeing-designed airplane models, to include these vertical acceleration values (table 1). For Douglas-designed airplanes, similar values are being generated and will be available in the AMMs in early 2001. The values are intended as thresholds that can be used to help determine whether a hard landing inspection is necessary. If the flight crew concludes that it has experienced a hard landing, the AMM conditional inspections should be performed even if the acceleration readings do not exceed the values added to the AMM. The vertical acceleration values are to be used by operators, in addition to or in lieu of flight crew judgment, to initiate conditional maintenance inspections.

enter image description here

Source: Aero Magazine

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    $\begingroup$ Given many FBW laws are based on G forces, it would be astonishing if the F16, the A320, ... were not fitted with accelerometer. $\endgroup$ – Manu H Feb 19 at 7:24
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    $\begingroup$ Accelerometers are the basis of modern rate gyros which are widely used. $\endgroup$ – Peter Smith Feb 19 at 12:35
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    $\begingroup$ @PeterSmith Don't you mean accelerometers are the half the basis of intertial measurement units? The other half being rate gyros. Unless you consider rate gyros using the of coriolis acceleration to be a form of acceleroemter. $\endgroup$ – DKNguyen Feb 20 at 19:44
  • $\begingroup$ OP, the simple answer to your question is "Yes, of course, ubiquitously". OP, you seem to focus particularly on hard-landing-stuff. Even completely setting aside that issue, the answer is simply "yes, sure". $\endgroup$ – Fattie Feb 21 at 17:21
  • $\begingroup$ A smarty pants answer here would be "assuming humans are on board, yes". (Every human has at least one phone; every phone has many accelerometers.) $\endgroup$ – Fattie Feb 21 at 17:22
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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 three axis, as part of the inertial reference system.

They are important instruments for the autopilot, as they provide faster feedback on the effect of control deflections than the air-data references, and essential for navigation as cross-reference for detecting GPS errors and the inertial navigation serves as a backup for GPS (and served as primary navigation over the oceans before wide GPS availability). Airbus (since A320) even defines the pitch command by vertical acceleration in the normal law. And yes, they are also used for detecting hard landings and their severity.

The pilot never sees the direct accelerometer output except in fighter and aerobatic aircraft though (well, almost never; there are a couple of other cases).

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    $\begingroup$ +1 I like this answer because it specifies that, in most cases, the pilot doesn't actually see the value $\endgroup$ – Digital Dracula Feb 19 at 7:25
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    $\begingroup$ By the way, inertial systems also require gyroscopes or angular rate sensors besides accelerometers, and their data needs to be integrated and fused with an external reference for long-term accuracy, hence they usually serve integrated with GPS, and for a while the inertial system allows navigating during GPS outages. $\endgroup$ – Mefitico Feb 19 at 17:02
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    $\begingroup$ @copper.hat, on a side note, the linear acceleration can, and used to be, measured using gyroscopes. If you mount a gyroscope so it can only rotate around one axis, it will precess due to linear acceleration and it's orientation will correspond to the integrated linear velocity. The early inertial navigation systems did it that way. $\endgroup$ – Jan Hudec Feb 19 at 20:17
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    $\begingroup$ @JanHudec: I suspect you already know this, but in a vaguely similar manner the mems gyros. have two 'counter' oscillating masses that respond to rotation, the Coriolis force changes the capacitance between them which can be measured. $\endgroup$ – copper.hat Feb 19 at 20:33
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    $\begingroup$ Well I dunno, some aircraft are intended to be capable of doing the occasional aerobatic maneuver on the side, and thus have g-meters, even though aerobatic flight is not their primary mission. E.g. most Schweizer 2-32 sailplanes. Is this an "aerobatic aircraft"? Maybe... $\endgroup$ – quiet flyer Feb 19 at 23:45
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I think you need to define "modern" aircraft, the question is pretty broad as-is. And even interpretation of what you mean could vary. i.e. are you referring to a real time dial showing actual Gs in the cockpit?

As quiet flyer noted, as a reference instrument an accelerometer is very important for aerobatic flight.

However, while a real time instrument is not needed for a larger air carrier, accelerometers feeding data to a flight data recorder for mishap investigation and recording of life cycle data for airframe fatigue calculations is important.

Most small modern general aviation aircraft don't have them though.

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    $\begingroup$ Any plane with an AHRS system will most likely employ accelorometers in the attitude solution. $\endgroup$ – selectstriker2 Feb 18 at 23:07
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    $\begingroup$ Technically, "accelerometer" is the sensor itself, and this is how I would interpret the question. In this case, most but the simplest aircraft have them, primarily as a part of automatic/augmented control and/or navigation systems. $\endgroup$ – Zeus Feb 18 at 23:18
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    $\begingroup$ Why GA? The question is not limited to GA; if anything, a random person would more likely think of airliners by default. But even in GA, those airplanes that are equipped with AHRS (e.g. G1000 suite), can display a technical page with all accelerations. But it is true that pilots don't normally refer to acceleration/G force (except for aerobatics/fighters), so it is not common to have the indicator in the cockpit. $\endgroup$ – Zeus Feb 18 at 23:41
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    $\begingroup$ My Dynon Skyview EFIS uses the accelerometer data from its AHRS to pop up a G meter display when load exceeds a configurable level (1.6 g by default, IIRC) and gives an audible warning "geez!" if you exceed another configurable threshold. This data is also logged. $\endgroup$ – pericynthion Feb 19 at 0:03
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    $\begingroup$ @michaelhall I don't think the GTN-650 even has any connection to an AHRS $\endgroup$ – pericynthion Feb 19 at 1:10
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When I worked in the industry in the early 2000s, Eurofighters had g-sensors recording during flight, and put you into a different engine service regime above a certain limit. There was a matching detent on the stick (not sure if virtual or physical) that warned pilots if they were going to go over the limit.

Twenty years on, given the cheapness of modern mems sensors, I'd find it unlikely that any large aircraft engine lacked any accelerometers, though in most cases they are more likely to be used to monitor vibration or fatigue life than g load. A quick search finds many suppliers, e.g. Meggitt, who list the following uses, but not specific engines or airframes they are used on:

Our piezo-electric accelerometers are ideally suited to a wide range of jet engine (civil and military), helicopter and space applications:

  • gas turbine engine monitoring
  • airframe structure vibration analysis
  • gearbox analysis
  • bearing analysis [etc]
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  • $\begingroup$ Eurofighters are rather different than the Cessnas, Pipers, and such that I expect most of us fly, and both are different from commercial airliners. $\endgroup$ – jamesqf Feb 20 at 3:59
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Of course they do. You can find them in just about any cockpit from the modern aircraft of today down to about the 1930's. Here's an example.Accelerometer

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    $\begingroup$ Strange. I'll grant that my experience is fairly limited, but I've never seen one. And why is the one in your picture showing -5 (g, I suppose)? $\endgroup$ – jamesqf Feb 19 at 4:29
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    $\begingroup$ "Just about any"? Are you excluding GA? $\endgroup$ – Michael Hall Feb 19 at 4:48
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    $\begingroup$ He's also excluding airliners. They don't have them either. The "just about any" part of this answer is incorrect. $\endgroup$ – Ralph J Feb 19 at 4:55
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    $\begingroup$ Erik is asking for sensors, not gauges. $\endgroup$ – bogl Feb 19 at 7:55
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    $\begingroup$ @user46893, if you don't know that GA stands for General Aviation you are definitely not qualified to make such a broad sweeping, (and un-substantiated) statement as you did in your answer. When was the last time you were in a cockpit and saw such an instrument, and what type aircraft was it? $\endgroup$ – Michael Hall Feb 19 at 19:19
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Depends on the aircraft in question. Airplanes used for aerobatics or military fighters will commonly carry them as a reference for pilots on just how hard they’re loading the airplane at any one time, though many good aerobatic pilots have enough time that they can kinesthetically sense just how hard they’re loading the airplane.

Transport category aircraft don’t carry G meters as it’s not very useful to their flight profiles. Hard landings are gauged kinesthetically and by the vertical speed at touchdown. Exceed certain metrics and the airplane will be inspected by protocol.

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  • $\begingroup$ I suspect that Gz is part of the automatic hard-landing detection support on some airliners (I believe Airbii will spit out a report automatically if you land hard enough) $\endgroup$ – UnrecognizedFallingObject Feb 21 at 4:59
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It has been answered for big aircraft, so just as a sidenote: Multicopters ("drones") have accelerometers (and other sensors) as integral part of their flight computer. Without it they would drop from the sky pretty quickly.

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