[HN Gopher] Reverse-engineering a three-axis attitude indicator ...
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Reverse-engineering a three-axis attitude indicator from the F-4
fighter plane
Author : zdw
Score : 108 points
Date : 2024-09-28 17:05 UTC (5 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| kens wrote:
| Author here if there are any questions...
| farseer wrote:
| How accurate you think this instrument was compared to the ic
| based sensors found in your typical smartphone nowadays?
| dfox wrote:
| This instrument is only an display that shows data coming
| from another device that does the actual measurements. One of
| the reasons why the threewire synchro interface is used is
| that it is surprisingly accurate as long as you don't care
| about the fact that it is "slow" by modern standards. The
| same interface was used to direct artillery and similar
| things that require significant accuracy to be effective.
| echoangle wrote:
| Well this is just an indicator, the accuracy from the actual
| IMU would also need to be considered. The indicator itself
| probably isn't the main source of inaccuracy once the IMU has
| drifted a bit.
| kens wrote:
| According to a paper on navigation sensors, commercial grade
| sensors have gyroscope drift of 0.1o/s (which is consistent
| with iPhone data), while navigation grade sensors have a
| drift of <0.01o/hour. I couldn't find specific numbers for
| the F-4's inertial navigation system, but I assume it is
| navigation grade. So the aircraft gyroscopes would be orders
| of magnitude better than a smartphone. For the azimuth, the
| F-4 used a flux valve compass, which must be much better than
| the relatively poor compass on a smartphone. Of course, the
| smartphone sensors are orders of magnitude cheaper and
| smaller.
|
| [1] https://doi.org/10.1186/s43020-019-0001-5
| AIorNot wrote:
| pretty awesome to see the engineering details involved! -thanks.
| as a software person I always wonder how they handle bugs and QA
| when building complex pieces of hardware like this
| dev_tty01 wrote:
| The strangest concept for modern software engineers is that it
| had to ship bug free and it could never be updated with
| firmware patches. Shipping under those constraints brings a
| certain level of focus not experienced in modern design.
| consp wrote:
| So basically like designing and building a bridge?
| drtgh wrote:
| I think the key is that in those days you didn't launch a
| product until you were absolutely sure it was going to work
| well, it was prototyped and debugged before it was launched.
| At least that is the impression one get with classical tech,
| solid reliability.
| mpenet wrote:
| My dad used to work on certifying, servicing and making
| custom instruments for planes, subs, prototypes of all kinds
| of that era (60s to mid-90s).
|
| His "lab" was basically all about testing and simulating
| environments for the instruments. He had tons of sayings
| about not having room for error in his line of work. This is
| as close as you can get from "building bridges" and to this
| day I don't think I have seen this level of attention to
| detail/perfection in any other profession.
|
| His job involved electronical engineering , mechanical
| engineering and programming amongst other things, not to
| mention a deep knowledge of the physics of these
| environments.
|
| Back then also the tools or source of information that were
| available to them were quite crude compared to what we have
| now.
|
| His spare time was all about flying, pimping his ham radio
| gear with all kind of "home made" electronics, build antennas
| and messing with computers. I guess he'd qualify as a
| "Hacker" nowadays.
| eschneider wrote:
| Umm...If you ship firmware today, sure it _can_ be updated,
| but almost nobody does update firmware, so yeah, that shit
| has to work when it ships.
|
| Also, I've never been at a place that tested FW patches as
| well as full releases, so...do you _really_ want to install
| somebody else's random FW patch? I don't unless I have some
| known problem with a fix in the release notes...
| syndicatedjelly wrote:
| Physical products require "test engineers" to design and run
| appropriate physical tests of products. It's an entire
| discipline worthy of study. Design for Six Sigma is a great
| place to start if you're ever interested in understanding
| ultra-high reliability applications.
|
| https://www.youtube.com/watch?v=_g6UswiRCF0
| genter wrote:
| Thanks for including ridiculously high res images.
|
| And it amazes me how many analog tricks they used. Modern day
| would be a couple lines of code.
| syndicatedjelly wrote:
| The 1950s were a time in computing where it wasn't a given that
| digital computing was clearly "better". We still hadn't
| developed methods of mass-producing reliable, fast, and cheap
| microelectronics and controllers. So for high-reliability
| applications, analog computing was THE solution.
|
| In 1954, Rex Rice wrote this piece about preferring a simple
| plugboard as the means of programming a computer, versus any
| sort of abstraction with a programming language
| (https://dl.acm.org/doi/10.1145/1455270.1455272). So it was
| still very much up for debate, whether high-level programming
| languages were even the right solution for the problems being
| faced.
|
| But I agree with you, our forefathers were simply geniuses to
| have figured out how to manipulate the physical world to
| produce mathematical computations. Early in his career, my dad
| had to disassemble and reverse-engineer some Soviet-made
| aerospace devices, and he still fondly recalls how superbly
| engineered and precise the Soviet devices were. I wish there
| was more information out there about Soviet computing, but the
| winners do write history after all.
| spitfire wrote:
| It's interesting that you note the unreliability. I always
| assumed tubes were unreliable, but thought anything solid
| state (even those card based systems) would be "reliable
| enough" to start taking for granted.
|
| But then you look at it and think Yeah, obviously they're not
| going to have MTBF times in the millions. It's going to be
| hundreds of hours - once a week, or maybe every few weeks
| between real hard crashes.
|
| How would that change your behaviour.
| Amir6 wrote:
| Fun fact is these airplanes are still being used as the backbone
| of Iranian Airforce and the very same unit was being used before
| they upgraded the avionics a couple of years ago on some
| variants.
| Scene_Cast2 wrote:
| I've wanted to add such an indicator to my car's dash (I already
| added a boat compass, which I find quite useful and aesthetic).
| Unfortunately, electronic indicators of any kind are much more
| rare than vacuum powered ones or all-glass cockpits.
| Onavo wrote:
| What you need my friend is a ring-laser gyro.
| dumbo-octopus wrote:
| Boat compass on the dash is awesome, I might have to borrow
| that. Any issue with interference from the vehicle itself?
| Scene_Cast2 wrote:
| Yeah. My compass (a Ritchie) has two axis calibration at the
| bottom; I ended up maxing out one of the axes (so it's still
| a bit off). Also, it tends to shift by a decent amount when
| the car is pointing up or down steep hills.
| bargle0 wrote:
| I bet the engineers responsible for this would be so stoked that
| someone figured out how they solved all these problems.
| dmitrygr wrote:
| kens@ is a treasure we do not deserve.
| kens wrote:
| Thanks!
|
| Wait, you're the Linux/4004 guy, aren't you? That project was
| truly amazing.
| liendolucas wrote:
| Asking just out of curiosity/ignorance. The author mentions that
| the F35 has a completely digital touchscreen to basically do
| anything on the aircraft (I assume). I can also image a powerful
| gun damaging it, then how does pilot manage if that screen stops
| working at all? Compare the same situation in the F4. The hit
| would only break/damage the instruments on that line of fire,
| correct? So in one case you would be totally screwed while in the
| other one you would partially lose some instruments, right? I
| must obviously not be taking into account something (or many
| things) for the F35, but in my mind having a 100% digital
| aircraft seems pretty scary.
| akgoel wrote:
| The F35 is not meant to be a dogfighter. If it has gotten shot
| such that the control screen in unusable, something else has
| gone wrong.
| the__alchemist wrote:
| It's a high performance fighter with a gun and SRMs, so...
| heavenlyblue wrote:
| If you project a line that crosses an aircraft instrument panel
| it's hard to imagine a line that didn't also go through pilot's
| body.
| StableAlkyne wrote:
| Generally, if the cockpit is getting hit with damage to the
| instruments, there is a _very_ good chance the pilot has also
| been injured or killed, and doesn 't care about the instruments
| anymore.
|
| In old gun fights (which just don't happen anymore), shots were
| likely to come from behind (so, they intersect the pilot) or
| the top (so, through the canopy if they're hitting the
| instruments). This has to do with the orientation both planes
| are probably in if one is shooting at the other. Go back
| farther and you get shots from the front, not from fighters
| (head-ons are very difficult to pull off outside of videogames)
| but from bomber tail gunners - very old planes from WWII even
| had bulletproof glass in front of the pilot for this reason. If
| the F35 has gotten into a gunfight, the pilot has fucked up,
| it's not a dogfighter and wasn't designed to be one.
|
| Even nowadays, if the missile or flak pops next to the cockpit
| and has managed to damage the instruments, there is a very
| strong chance the shrapnel has also hurt the pilot to the point
| that they're not flying home that day. This is the most likely
| way for the F-35 to be damaged in the modern era.
|
| There are obviously scenarios where the instrument panel gets
| damaged but the pilot is okay, but it's such a low probability
| scenario that they likely deemed it to be less harmful than the
| benefit they foresee in a glass cockpit.
| liendolucas wrote:
| Thanks for replying! As other mentioned I was missing/not
| considering the most important case that the pilot is assumed
| to be dead and that the plane is not supposed to receive such
| fire.
| hydrolox wrote:
| to be fair isn't the purpose of the F35 fairly different since
| it's extremely reliant on stealth and beyond visual range
| engagements?;Instead of getting close enough to be gunned down,
| it is supposed to strike from so far away that the enemy
| wouldn't know it's there.
| zppln wrote:
| Can't speak for the F35, but for the fighter I work on we
| basically consider the pilot dead if you have shrapnel damage
| in the cockpit. For instance, the FCS is located behind the
| pilot. That being said, I would assume the F35 display being at
| least dual redundant (think two displays merged together, which
| can be done seamlessly) for flight safety reasons.
| toast0 wrote:
| I'd imagine the ejection system is going to be activated by
| traditional handles, and not a screen. Same with the basic
| flight controls; there's no reason to move to a touch screen
| throttle or flight stick.
| iancmceachern wrote:
| They're not just regular screens. They're highly hardened,
| redundant, specialized displays, it's a whole industry.
|
| There are companies that make displays that have clear
| conductors over the screen so they can heat them so they can be
| used and maintain function even when on the deck of an aircraft
| carrier in the arctic.
|
| There are companies that still make CRTs for specific military
| purposes.
|
| These screens are safer, more reliable, and durable than the
| mechanical systems they replace.
| dfox wrote:
| The displays aren't that much special. Probably the main two
| things that are special about them are color rendition and
| contrast and the rest is just about the certification
| process. And extrapolating from automotive experience, the
| color rendition and contrast is about some team of engineers
| being solely dedicated to simulating various lightning
| conditions and verifying that the screen remains legible,
| does not interfere with night vision and does not cause
| reflections on other instruments that would make them hard to
| read. In automotive this kind of simulations use multiple
| terabytes of reflectivity data for various mostly "dull"
| materials (gigabytes upon gigabytes of data on what the
| driver might wear...), so extrapolate from that to "most
| advanced fighter aircraft".
| jeff_vader wrote:
| Basic flight instruments almost always have a backup. In case
| of F-35 there's a small square screen in centre console which
| shows attitude indicator and flight parameters. Needless to
| say, if main screens are out you are turning around and looking
| for the nearest airport.
| the__alchemist wrote:
| Depending on the fighter: redundant systems. Ie multiple
| independent Ring Laser Gyros, (viewable on multiple independent
| displays), backed up by analog "round dials" instruments.
| kens wrote:
| The backup for the display is an integrated standby instrument
| system (ISIS), which combines several essential instruments
| into one small digital display. An ISIS typically has its own
| sensors and a battery backup, so it should stay operational
| even if the main display fails.
| https://en.wikipedia.org/wiki/Integrated_standby_instrument_...
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(page generated 2024-09-28 23:00 UTC)