Digital Fly-By-Wire: The Apollo Guidance Computer's final gift to the world

[@Alexander-the-ok]

Some corrections: Around 56:30 I briefly mention the 737 max incidents. What I didn’t make clear is these occurred because the aircraft DOESN’T have fly-by-wire. If they had been equipped with it there would be no need for MCAS in the first place (thanks @tonymcflattie2450) Thanks to @Ticklestein for pointing out that I mistakenly state at 21:35 that the photo of Margaret Hamilton includes the '36Kb of Apollo Source Code'. That photo is actually a collection of various revisions of the code they had around the office. The source code fits into a single (very large) binder and a copy recently sold at auction. We will be revisiting this point in a future video. Supercritical airfoils aren't for supersonic aircraft: they are designed for flow in the transonic region (ie large airliners). Thanks @LegateMalpais

[@horizob]

Thank you very much! I was about to type this. The only bit of fly-by-wire on the Max are the wing spoilers. I loved this video and found out many details I was unaware about. I am an aerospace engineer, so that is setting the bar high. Awesome work and keep it up! Cheers!

[@BarrettCharlebois]

Wait hold up…..I’m just hearing this for the first time. The 737max is not fly by wire? I’m not familiar with MCAS and how that differs from FBW

[@markellsworth980]

MCAS was the hidden avionic added to the 737-Max compared to the 737 NextGen whose sole purpose was to counter the nose-up tendency induced by high-engine-power take-off settings, not entirely unique to the Max but different from the NG whose behavior it was supposedly designed to emulate, so as to avoid the need for supplemental, in-simulator pilot training. The initial version was defective, unvetted, and not disclosed or certified. From my point of view, it wasn't even a good beta, but an unconscionably flawed hack.

[@tiggy2756]

@@markellsworth980 The Boeing CEO walked away with $62.2 million !

[@vasilis23456]

​@@BarrettCharleboisThe MCAS is a system which adjusts the pitch controls by wire to make the MAX aircraft behave like normal 737s, preventing recertification. I believe the main controls still have direct hydraulic inputs that override any autopilot by-wire instructions, making them not fly-by-wire. That being said making 737-MAXs entirely fly-by-wire would not fix the issue. The MCAS (an extension of the autopilot that is always on) was programmed incorrectly causing it to nosedive the aircraft when one of the pitch sensors failed. Making an aircraft entirely fly-by-wire doesn't fix programming mistakes, in fact the ability to override the MCAS system prevented more plane crashes and deaths.

[@connarcomstock161]

"Then crammed it into an obsolete fighter jet..." *F8 Crusader* "I took that personally."

[@Cythil]

And the plane was still in service at the time, even if it was a bit of an older airframe. ;) But hay. A proven airframe is great for an experiment like this. You know after all what to expect if the plane is operating as normal.

[@clasdauskas]

and that comment to the effect of the f4 being even more ugly! ;)

[@fafiteee]

the F-8 slander is real, man. i love that plane

[@LupusAries]

​@@clasdauskasWell, compared to the Crusader or the Tomcat, or the Sabre, or the F11F Tiger, or the F-16 Viper it is.....😉😋

[@clasdauskas]

@@LupusAries :) Effectiveness has a beauty of its own!

[@knpark2025]

"NASA sent people to the Moon with less computing power than a modern smartphone" gives the same vibe to me as "Tony Stark was able to build this in a cave, with a bunch of scraps". It's not about their hardware being obsolete, but rather about NASA working with so many talent who were way, way smarter than me.

[@RaquelFoster]

The military is sooooo about fault tolerance. I remember Air Force guys telling me "You need to be able to launch a missile off the left wing even if the right wing is blown off and your plane's on fire." The 1553 spec is very clear that any device on the bus needs to be able to handle every kind of failure including bad data coming from every other device. I've read about all these planes and seen most of them because I used to live next to the USAF museum at Wright-Patterson AFB. I would always go to the museum annex which had disassembled SR-71 engines and research planes hanging from the ceiling. That's also Hangar 18 ... so, there's a YF-16 in there, but they also have some plush aliens in the old Norden bombsight vault because they have a sense of humor about it. I've never seen many details about how we actually got from the fly-by-wire F-8 to the F-16. That is, how we got from using an Apollo computer to creating the MIL-STD-1553 bus in 1973, which was put on the F-16 and then on the AH-64 in 1975. The AH-64 actually made good use of 1553. It had a really cool helmet-based targeting system for the gunner. The helmet also weighed 4 lbs. Today everything still basically uses 1553. Even the JWST uses 1553. My first software job was an internship at a military avionics contractor in 2007. Basic 1553 is a 1 mbit bus. That's pretty fast compared to MIDI which is a 31.25 kbit bus! But the F-35 needs a lot more bandwidth to send video to the fancy helmet that lets you see through the floor of the plane. The F-35 helmet actually weighs 5 lbs - and a lot of that's carbon fiber. It's ridiculous. I think NASA first adapted 1553 to optical fibre with MIL-STD-1773 in the early '90s. But it wasn't for speed reasons. It was optical because that keeps you from having interference problems. So we had to adapt 1553 to an actually fast bus for the F-35, and that eventually became FC-AE-1553 == 1 gbit 1553 over fibre. I wrote several avionics databus test suites for a cart that plugs into the F-35. And if I had a question about any specific details, I literally needed to look in manuals from 1973-1978. You know what's a pretty tricky job for an intern? Dealing with 8b10b encoded data that's too fast for regular software, so you need to write code for the PowerPCs embedded in the FPGAs on the analyzer, and you need to manually convert from big-endian to little-endian and between 8-bit, 16-bit, 32-bit, and 64-bit word sizes because you're on an Intel machine with a 64-bit PCI-X card but the Xilinx chip has PowerPCs (big-endian) on it, but it also has an Intel ethernet controller going back the other way. Plus the packets/frames of everything is scrambled. If you're looking at an ethernet frame that came across the 64-bit bus you'll see a few bytes of the payload before you even see the header, because you're flipping the endian-ness while also rearranging the words in terms of least-significant vs. most-significant word being on different sides. We used those analyzers for a lot of things. I remember my boss demo-ing 8 gbit communications over a single wire while the wire was also powering a 100W light bulb. Because NASA wanted fewer wires on something. Sorta like POE but it was Power Over Fibre Channel On Copper. 🤣 It seems like everything uses 1553, but a lot of civilian stuff is ARINC 429. Anyway this is actually a nice overview of the evolution of embedded systems - which is funny since it never mentions the term. Today every car has computers that can reboot a few hundred times per second. And that's all goes back to the Apollo computer which managed to keep Buzz Aldrin from killing everybody when he overloaded the computer by not turning off the CSM rendezvous radar when he turned on the landing radar. You're more likely to have a hydraulic failure than a fly-by-wire communications failure. I remember hearing about a plane (I think it was a 767 evacuating people from Baghdad?) losing hydraulics because it was hit with a shoulder-fired rocket. I think those guys had enough adrenaline to move the control surfaces a little, but they mostly managed to land the plane by modulating the throttles.

[@billyclone4289]

Did you work on the AH64 program ? I did from pre production through 1993. Im just curious you seem to really know your stuff !

[@darkside3ng]

Amazing explanation 👏👏👏👏

[@RaquelFoster]

@@billyclone4289 No I started there in 2007. But the EE nerds who owned the place had worked on the AH-64 helmet ... I think it was some kind of laser gyro thing that tracked your head movements? It's funny because these guys had done so much cool stuff, but the thing that everybody got excited about was the Blue Thunder helmet! I remember being in a meeting and these Air Force guys were getting excited talking to the engineers about what kind of energy weapons they could maybe put in the Air Force version of the F-35, because it doesn't have the cold air fan in the front like the STOVL version has, so you've just got this bay with basically a 20,000 horsepower (or whatever! that's a random guess LOL) PTO shaft from the jet engine that you could power whatever you want with. And then somehow someone mentioned the AH-64 helmet and everybody got excited and talked about Blue Thunder for the next half hour.

[@Schadowofmorning]

Virtual machines in the 1960's, programmers back then were of a different kind.

[@uis246]

No, this is just preemptive RTOS with syscalls

[@SoggaSogga]

@@uis246 🤓

[@jim2lane]

Yes, back then they were truly computer scientists

[@Roach_Dogg_JR]

A VM before there were even real operating systems

[@TheLukasDirector]

​@@manitoba-op4jxWhat are you on about? You can arguably even run a modern x86 without an OS. Not to say those aren't (over)complicated, but that has nothing to do with the need for an OS.

[@Sgt_Bill_T_Co]

I have to say as a retired engineer this is the most fascinating and informative youtube video I have ever watched. A huge thanks for making this.

[@jimlthor]

If you haven't seen it, watch "Light Years Ahead - The 1969 Apollo Guidance Computer" which is also on KZbin.

[@ctmme]

A detail: The reason the Sidewinder missile (excluding X model) has those gyro fins is because the way the guidance worked, it required there to be no roll at all to work. It's not really for compensating for adverse effects of controls in of itself. After all, other contemporary missiles didn't have those because their guidance was different and could handle (or even require) roll.

[@chaimshen-orr2993]

The Rollerons (that's what they're called, rather than "Gyro fins") do NOT keep the Sidewinder (or Atoll, or Shafrir . . .) with no roll at all - they are designed to keep the roll RATE of the missile within limits acceptable to the guidance system, in spite of roll disturbances induced by control canard's actions.on the roll axis, , as well as possible structural imperfections. Their original name - "Roll Dumpers"- indicates this function.

[@leoarc1061]

@@chaimshen-orr2993 So, the missile could roll 360 degrees, during the guidance stage, as long as it did not exceed a defined roll rate?

[@chaimshen-orr2993]

Correct - and recall that "guidance stage" starts at a safety distance (time) from launch, up to warhead activation.

[@VyarkX]

@@leoarc1061 for the vast majority of a missile's flight regime its position relative to anything other than the target is not important. As long as rates along each axis are kept low enough for the guidance and tracking system to work properly it will hit the target (other conditions permitting).

[@EricChristiansen-z6l]

Great video! I worked on the follow-on F-16 production system as a junior software engineer late 70's to early 80's at Lear Siegler Astronics. I used to estimate and time subroutine performance. I helped a little with the voter routines. I also burned our program versions onto very expensive nuclear blast resistant ROM chips. Best engineering team I ever worked with. Our system was a big success. Your kind comments about the significance of digital fly-by-wire made me feel good about my years on the project. Thanks for your efforts!

[@AckzaTV]

i wonder if they have nuclear blast resistant sd cards today

[@Alexander-the-ok]

Thanks so much for sharing your experience! It's almost surreal to spend the time researching for these videos and then hear from someone who was actually involved in the process!

[@EricChristiansen-z6l]

@@AckzaTV Standard SD card packaging probably would not suffice. Wikipedia has a good article on electronic "hardening" at en.m.wikipedia.org/wiki/Radiation_hardening

[@the20thDoctor]

That's awesome, thanks for sharing. Got any cool stories?

[@johnjimmies8256]

Are you bound by any NDAs from you time on the project?

[@mikerodent3164]

I can't wait to see where you're going next with this channel. These lengthily researched perspectives from an engineer who has so obviously been steeped in the culture of rigorous analysis for so long, but lost none of their excitement for the variety of amazing technological accomplishments of human beings over the past lifetime or so, make for some of the most compelling viewing on YT. Don't stop! 😊

[@jozsefizsak]

You expressed my thoughts better than I could! Thank you. 😊

[@Alexander-the-ok]

Thanks! It's really exciting to have an audience (beside my long suffering wife) that wants to listen!

[@zvisger]

I agree, and your comment was very well written 👏

[@WolfandCatUnite]

yes

[@jubuttib]

@@Alexander-the-okJust wanted to say that I'm happy you took the plunge to start making this stuff, many people wouldn't have bothered. The kind of stuff you and others do really is the beauty of internet, and IMO makes it worth it even with all the issues it has caused. Much love and respect.

[@igotes]

Don't use a Raspberry Pi as a flight computer, use three!

[@weaved-matters]

Noted

[@Starfireaw11]

Weren't you paying attention? 4 is the correct number.

[@IanMcCloghrie]

@@Starfireaw11 The 4th one was an Arduino :)

[@Guysm1l3y]

Be careful mixing up "analog electronic" with "analog mechanical". The early F-16 for instance had a fly by wire system, but it wasn't digital (ones and zeroes), instead it was analog electronics (continually varying electrical signals to electronic components). Later versions replaced the analog electronic flight control computer with a digital one because it was more compact, lighter and more reliable.

[@scottb721]

I used to fix the analogue F-111 navigation computer in the Australian air force. Half the work was servicing miniature gearboxes and was really interesting work.

[@wonjez3982]

45:28 its no digression it fits right in with the meaning of analog digital interfaces, love it

[@filmpjesman1]

The shot starting at 35:29 is amazing! To me it's the first time that a full-CGI shot feels real, and passes the uncanny valley. The other day I saw a video of a Norwegian church rendered in Unreal 5 where they boasted about the realism of the scene but it just felt too perfect; for some reason this shot hits the spot and looks "real"

[@Alexander-the-ok]

Credit goes to Artem Tatarchenko for that shot.

[@oleran4569]

Wow! I thought that was "real world". Cool!

[@x--.]

Oh, I thought that was real test footage -- In hindsight it seems obvious that such footage would be very unlikely but it was good enough that, honestly, I would have preferred a disclaimer somewhere in the video "uses computer-generated video" -- not because I feel tricked but because I hope we normalize the idea that we want be really clear about what's "original historical footage" and what's been newly generated. Just a personal preference. But also, don't get rid of it, absolutely beautiful.

[@aerox4979]

Definitely your best video so far! Man, this channel is awesome. Would love to see more aviation related content from you

[@Alexander-the-ok]

Thanks! There will certainly be more.

[@AsbestosMuffins]

the rope memory of the AGC is really such an archaic creation. You program your code, debug it, test it, then hand it off to another guy who converts it into a schematic matrix of iron cores who then hands that off to an army of old women who weave the physical code out of cores and wire

[@iitzfizz]

Fascinating huh?

[@MikeF1189]

I have been watching YT videos for over a decade, and this is literally THE FIRST video that made me, Like, Subscribe, comment, AND SHARE. Congratulations! I'm impressed.

[@Alexander-the-ok]

Thanks! That’s such a compliment!

[@hardyr]

I'm looking forward to more in-depth essays like this. This is a story of how rigorous engineering practices led to a quiet, but unqualified success that shaped our era. Engineering stories tend to follow a pattern where we often only learn the details of how systems work after they fail catastrophically, while engineering success stories are often sparse in technical detail. This video fills that gap well.

[@Alexander-the-ok]

Thanks very much. Yes there is a selection bias. There is no getting away from the fact that most engineering is pretty boring to the casual observer. We never hear about the accidents that don’t happen!

[@bobowzki]

How the hell do you produce something great like this? It's like an hour long very high quality documentary.

[@AccAkut1987]

Random dudes on KZbin doing what the History Channel etc did for TV up to around the end of the 90s.

[@c1ph3rpunk]

The book “The Apollo Guidance Computer, Architecture and Operation” is truly an excellent read. I was able to build most of an emulator with the info in it, it’s quite thorough.

[@Alexander-the-ok]

Yep, it was one of the main sources for this video - an excellent book.

[@flare2000x]

Haven't read that one but I highly recommend Digital Apollo on the same topic. One of my favourite books.

[@sciptick]

Don't miss "Sunburst and Luminary", by Don Eyles, the story of programming the AGC to land on the moon.

[@stephenhicks826]

What a fantastic piece of historical research. I was a teenager during the Apollo landings and I'm an aviation enthusiast, I knew the AGS computer was an impressive machine; but I had never heard about all this before. Wonderful and thank you.

[@thanksfernuthin]

That sidewinder fin is truly amazing. I am in awe of the people in our past and the solutions they invented. Your opinion on what makes a good looking super sonic plane is... let's say... unique. I think a lot of people find the Concorde pretty derpy looking... while the SR-71 is considered to be one of the most beautiful and coolest looking objects ever made by man. But... you be you!

[@Alexander-the-ok]

I need to get that fin restored and on ebay tbh. Ha I’ll do a bit of a ‘follow up’ on my stupid taste in my upcoming f-14 video.

[@ssssssssssss885]

If you ever flew through severe turbulence in an airliner like I did, you experienced the wonders of Fly-by-Wire. Awesome technical video. Learned something new I didn't know about NASA's AGC.

[@markellsworth980]

As I am a college-graduated software engineer and longtime aviation enthusiast, I wrote several Quora entries on the non-FBW digital foul-up in the 737-Max MCAS system. I did not know, however, the story of AGC adaptation onto the F8 airframe, though I felt some nerdy embarrassment to consider the author's comment late in the video anticipating that he had lost everyone already. I was still there following along just fine. It was like sitting alone in a movie theater. Did I miss a social cue? Had to answer quick. No, I was only one who was in on the lingo. Ah, well then. Thanks for informative and relatively thorough coverage up to and including mentions of the F-16 and Space Shuttle systems.

[@wirdy1]

You weren't alone. It's rare for a YT video to hold my attention for it's whole; but perhaps it's because I have I worked aviation flight control systems & then a 2nd career in safety-critical software engineering, so the mixtures of terminology & concepts all made sense.

[@DisfiguredGaming]

0 clue about aviation or engineering and I followed along fine

[@donerskine7935]

Fact: NASA Invented the non-stick Velcro frying pan.

[@non-human3072]

Hahaha, you gotta love them... "Never A Straight Answer"

[@Freddylot]

I think this is the first time anyone's really explained the AGC to me in a way that really got me to go.. oh.. wow. Keep up the good work ❤

[@Alexander-the-ok]

Thanks. The first of my linked videos is a really nice presentation on it. Never fails to amaze me.

[@Freddylot]

​@@Alexander-the-ok thanks. Familiar with curious Marc but your explanation hit on my (basic) level which is really a sign of good explanation!

[@rickpalmer9518]

The L-1011-500 was the FIRST wide-body commercial aircraft to have a digital autopilot (Collins FCS-240) instead of an analog system. It was produced in 1978 and was the first to use a supercritical wing and flew at M.90 but usually flew m.84 for lower fuel burn

[@Xboxgames2]

Supercritical wing was also developed at Dryden!

[@zounds010]

Airliners used supercritical wings before that. The Airbus A300 had one (first flight 1972), as did the Vickers VC-10 (first flight 1962).

[@Technoid_Mutant]

Doood. The F8 was a MONSTER. It was primarily limited as to speed by the composition of the wind-screen. That happened around mach 2.5. The latter iteration was ridiculous. With the afterburner lit, it could climb to orbit-(ish).

[@shaveandahaircut3bits]

Westminster isn't actually machine readable, it was only inspired by the machine-readable numbers on checks, a MICR font called E-13B which only has numbers and banking symbols, no letters at all. It's kind of wild that anyone thought to make fake-machine-readable alphabet characters at the time, but sci-fi authors etc went wild for it!

[@Alexander-the-ok]

Oh yeah, its right there at the top of the wikipedia page. Thanks for the clarification

[@ManuelSLaraBisch]

Incidentally, that E-13B font is still used on paper slips for bank transfers in Germany. Or at least it was as of 2017, before I completely switched to online banking.

[@LOLHAMMER45678]

It was a good visual shorthand for the computerized future at the time. Advertisers went wild for it for the connotations

[@IDWpresents]

I'm a computer engineer, and while you're correct to say that your phone is not comparable to the Apollo Guidance computer, you do quite a poor job of describing the technical reasons for this. This is a great video, and I don't think many people will be misinformed by this, but there were many critical errors so I'm going to be that guy and nitpick you. It's mostly false to imply, as you do at 13:51, that it would be easier to build a chip from scratch specialized to go to the moon than copying an existing design. Nowadays, Designing a custom CPU from scratch is absurdly expensive, and there's rarely a good reason to do so. Such reasons are relevant to the case of sending a chip to the moon, but almost none of them are mentioned in this section. Some of the reasons you mention, such as writing an operating system dealing with interrupts and subroutines, are technical challenges that must be dealt with regardless of whether you use an off-the-shelf phone chip or a custom CPU. Others such as needing to rewire the CPU to spaceship peripherals instead of phone peripherals are only relevant if you are using an off-the-shelf smartphone rather than the CPU of such a phone. Since you explicitly say "engine of a car" rather than "car" itself I find this a bit disingenuous. Writing a custom interpreter for an assembly language is a foolish & unnecessary thing to do. A human-rated spacecraft should NOT be programmed in assembly today. Realistically a custom JIT interpreter will add a layer of abstraction between the software and the hardware--a completely unnecessary point of failure. Sorry if I've been critical. Your point is absolutely correct and this is a great video but I felt I had to address these technical inaccuracies. I thought I would also include some legitimate reasons why you would not want to use an off-the-shelf CPU design - Spare Hardening: This is the most important problem. You'll want to use more robust materials to make the chip than what a cell phone is made of, for sure. Insulating substrates probably don't want any of the cutting-edge

[@Alexander-the-ok]

Yeah I let that metaphor run a bit too far. ‘You could fly to the moon with your phone but you probably shouldn’t’ would have sufficed.

[@pepn]

wow that gyroscopic stabilization system is indeed really elegant ! Also how cool is it to own a sidewinder fin ???

[@Alexander-the-ok]

Tbh I just went and bought it on ebay. It’ll be back up for sale in a few weeks.

[@skasow17]

It’s called a rolleron. The math works beautifully and so does it. :)

[@BarrettCharlebois]

The channel “smarter every day” has a really good video on the sidewinder fins! I think they are called “rollerons” iirc

[@SVSky]

@@Alexander-the-ok Should do an video on how the non-imaging seeker Sidewinders worked. It's a really cool system. Also explains why the missile couldn't be allowed to roll in flight.

[@Panzermeister36]

Now I'm going to have to order one myself...

[@EstorilEm]

Most supersonic planes are ugly?! F-104? SR-71? F-14? I think the F-22 is up near the top as well, but many seem to disagree.

[@cabanford]

What an epic production! A rare gem in the steaming pile that is normal KZbin content. Chalk up a new subscriber ❤

[@ChS9712]

Just for the record, and not to be that guy, but the choice of TLI as an example of the AGC handling guidance on the Apollo missions is technically one of the few times the AGC was absolutely *not* providing guidance. The Saturn V guidance was handled by the IBM-designed LVDC (Launch Vehicle Digital Computer) which was located in the Instrument Unit in the 3rd stage. The LVDC handled all primary guidance for the rocket, including the TLI burn which was executed by the S-IVB stage. The AGC had monitoring capability using its own gyros and IMUs during launch and TLI, but was not actively calculating control signals nor was it in the loop under normal circumstances. There was a basic capability of the AGC to takeover control of the LV in an emergency, but the guidance provided by the AGC was far inferior to that of the LVDC, consisting of basic polynomial steering calculations during the S-IC first stage burn, and only attitude hold capability for the S-II and S-IVB stages. Incidentally, there was also a capability to interpret pilot commands via the RHC (essentially a sidestick) as well, and in the event of an LVDC failure during TLI, this would have been the primary source of backup steering input, as the AGC was not capable of generating detailed steering information for TLI, only monitoring of dV and orbital parameters. For me, the most truly impressive display of the AGC capabilities during Apollo was the terminal phase of the lunar landing. The AGC actively handed not only steering of the LEM, but also throttling of the DPS engine as well as actively calculating a predicted landing location on the surface. This was displayed to the pilots in the form of an angle, which they could use in conjunction with marks scribed on the window to see the point where the AGC predicted landing would take place. Using the RHC the pilot could re-designate this point left and right, or closer and farther and the AGC would adjust accordingly. Additionally the rate of decent was managed by the computer, with the pilot having the option to increase or decrease the ROD as desired. None of the lunar landings actually occured under AGC control, with all commanders opting to switch to manual control a few hundred feet before touchdown (pilots being pilots and all), but by all rights the AGC was absolutely capable of controlling the LEM right up until the point of lunar contact.

[@Alexander-the-ok]

Classic ‘Alexander the ok’ moment right there. I just thought up a manoeuvre at random and completely forgot the S-IVb was still attached at that point!

[@wirdy1]

There are some awesome comments on this video & yours is one of the most detailed. I learned some more stuff from you, thanks.

[@AsbestosMuffins]

I remember listening to an interview with one of the engineers on the AGC who talked about how he was using many layer pcbs, something not common until the 1990s

[@Alexander-the-ok]

I seriously struggle to design multi layer pcbs with modern design software. Achieving that in the 1960's is beyond impressive to me!

[@tookitogo]

@@Alexander-the-okReally?!? Multilayer PCBs are, in many ways, easier to design than single-layer ones.

[@jonnyj.]

@@tookitogo What on earth are you on about???? You have literally no idea what youre talking about. Do you have any idea why modern motherboard manufacturers complain every day about the increasing pcb layers required?? Do you know why they keep costing more? Do you have any idea why multi layer pcbs only became common in the late 1990s? It wasnt because it was easier to make than single layer pcbs, thats for sure.

[@tookitogo]

@@jonnyj. I know exactly what I’m talking about, having designed single-, double-, and four-later boards of various ilks, from audio to microcontroller to power to multi-kilovolt analog to multi-GHz analog. I do it as part of my job. Multilayer boards make power routing much easier, and give you loads more room to route traces. And for sensitive circuits, they let you have dedicated ground planes. Don’t confuse a complex circuit with a multilayer board: if you’re having to lay out a 26-layer board (like some server mobos), it’s because the circuit is complex. The fewer layers you have to work with, the harder it gets to lay out a given circuit - and at some point may become impossible. I use professional layout software (Altium) and working with multiple layers is easy. (If anything, I wish Altium had more tools to support single-layer layouts! For example, I wish you could insert jumper wires without having to add them as full-fledged components.)

[@strung_music]

​​@@tookitogoone of you is talking about ease of design and the other is talking about ease of manufacture. I guess neither goes hand in hand

[@n7275]

15:30 There are direct coils to fire RCS jets, and the SPS engine. This is what the "RHC Direct", "Direct SPS", and "Direct Ullage" switches do. But they are separate redundant contacts.

[@judet2992]

I had zero clue fly-by-wire came from the Saturn V despite knowing it came from NASA. Thanks man!

[@AnthonyFrancisJones]

Truely outstanding! The work that must have gone into this! Yet another reason why I have not bothered with a TV for years if such quality 'programming' such as this can be found here!

[@MBkufel]

You deserve like 20x the subscriber count. Love your vids.Keep it up please.

[@bountyhunter_5150]

Actually the A5 vigilante had one of the first fly by wire systems. The electronics of the Vigilante were relatively advanced and complex at the time of its entry to service. It incorporated one of the first "fly-by-wire" systems on an operational aircraft, along with mechanical/hydraulic backup

[@solarfinder]

I have to say that I literally stumbled across your channel. I appreciate your writing, opinions with fact based details in an organized manner. Your channel seems more baked in than I would have thought. Definitely shared. Good job and Thank You

[@AdamCalloway-j4j]

Thank you so much. I never realised the direct lineage of the AGC to modern fly by wire aircraft. I’m sure you might be aware but this was a revolution not just for aviation but for everything in the modern world.

[@wirdy1]

Terrific video. Right up my street as an avid curiousmarc watcher & as a 30-yr fly-by-wire maintainer. Excellently written, narrated & choice of video (some clips I've never seen before). Superb effort & very watchable.

[@kevinalmgren8332]

I recently read about a particular B-17 bomber that suffered battle damage that separated the hydraulic system to the tail of the aircraft. However, the aircraft had an autopilot that was linked electronically to the Norden bomb sight. When the bombardier entered commands into the bomb sight, the bomb sight would relay that to the auto pilot, and the autopilot would orient the plane to the appropriate position to drop the bombs. With the hydraulics gone, they used the bomb sight to pilot the aircraft back to England.

[@mattmurphy7030]

Control Allocation is one of the most sophisticated and cool things I've come across yet in aerospace engineering

[@jmdibonaventuro]

Great video! I had an uncle who helped build the avionics in the Saturn V (Specifically the “Black Ring” Instrument Unit). I still have an old module of the erasable memory he gave me as a gift from his time at the program, along with original Mission Patches for Apollo 8-17. Learning more about the work him and so many others put in really shows just how impressive their designs were. The things that could be done with a drafting table and a slide rule are insane! Thanks for such an interesting look into a part of my family’s history, -J

[@MrParamedics]

A tough reality to accept is that the vast majority of aircraft accidents are caused by pilot error. We hold ourselves to an incredibly high standard -which is part of why accidents are so rare- but they still happen. Fly-By-Wire systems allow aerospace engineers to design planes that, on rare occasions, ignore pilot input and save the plane. Alpha floor protections on Airbus aircraft, Auto-GCAS on the F-16, are examples of the safety fly-by-wire can bring to aviation. Thank you for such an intelligent video on it!

[@barracuda7018]

Todays modern avionics would not have been possible without Apollo project and the research carried out at MIT...

[@taproom113]

Outstanding presentation! Well done. One small point , if I may ... At 42:10, there's a very good shot of the wing in the raised (takeoff & landing) position. In this position, the leading edges droop and the trailing edge 'flap' and flaperon droop. You can see the small 'flap' next to the fuselage (not moving). Next to it moving outboard on the trailing edge is the flaperon. This device acts as the flap extension AND the entire aileron. Above the wing, and in front of the flaperon, are spoilers that you can see popping up when the flaperon moves to the 'up' deflection position. When the wing is in the down and locked position, the flaperon acts as the aileron for that wing. Respectfully, there are no flight control surfaces on the trailing edge, outboard of the wing fold hinges like on most other aircraft (as you show in the animated graphics). Those massive flaperons, so close to the longitudinal axis of the aircraft, were responsible for the exceptional roll rate of the Crusader,. A prized asset, essential in Air Combat Maneuvering. F-8's Forever! ^v^

[@ryanreedgibson]

I came here knowing very little about flight controls but your ability to explain in simple terms made this really enjoyable. Thank you for sharing!

[@n7275]

16:27 TLI burns were performed by the LVDC (made by IBM), in the third stage of the saturn 5. The AGC is only used to monitor the burn and update the state vector.

[@Alexander-the-ok]

You’re right! I picked a manoeuvre at random and completely forgot the stage IV-B was still attached for that one!

[@ApolloCDR]

LVDC? Translation please. I'm always looking for new Apollo terms and acronym descriptions. For instance I know TLI = Translunar Injection and what it is, LVDC will help me understand the burn and the hardware better. Thank you.

[@Lcfp]

@@ApolloCDR Launch Vehicle Digital Computer, it's the computer in the Instrument Unit of the S-IVB (third) stage of the Saturn V launch vehicle

[@BelgianSquirrel]

I watch all CuriousMarc videos for several years and I wish that I could first see your synthetic intro about the AGC. It provides an excellent overview !

[@i-am-ber]

KZbin has been recommending me your content for a while now and I feel ashamed for not having subscribed sooner. Really in depth and fascinating whilst being thoughfully presented videos about things I've always wanted to know more about - and delivered in a way that I can actually relax while watching. Really good, thanks so much.

[@Alexander-the-ok]

Thanks! This particular video was particularly fun to make - I'd always wanted to do one on the AGC but didn't really know what aspect of it. Then I made a mistake about FBW in the previous video which led me down a rabbit hole of research....which became this video.

[@x--.]

Two Lessons I take from this: 1. Never fly a new type (or pretend old-type) in the first year of operation -- that chart was striking. Not as striking as the 737MAX plowing into the ground but still clearly important. 2. Heroes of modernization and great advances rarely get acknowledged. The team that came together for this was clearly incredibly capable but you couldn't politically capitalize on the effort and advancement. In fact, without the military adopting it, it may have been another decade or two before the economics forced the issue. Truly astounding work that I would never have known about without this video and our host here. Thanks for a great video and well-constructed story. As good as the Apollo Guidance Computer? No... but I think the folks who created it would be proud of this.

[@squ1dd13]

these videos are so good. love your channel. your semi-informal presentation style works perfectly, and it’s obvious how interested you are in this; your enthusiasm about the topic is in itself very engaging. keep it up, and i really hope more people find your channel.

[@thespacemanfil]

Much like fly-by-wire, our own bodies have a built in system to keep us standing straight and level, making tiny muscle movements. If we had to fully control ourselves, we just wouldn't be able to walk in any useful way.

[@davidbaldwin1591]

Good point. Much knowledge about flight is still right there in birds. Look how the whole tail stabilizer pivots, like we pivot at the hip. Are there any planes that do that?

[@Kieselmeister]

​@@davidbaldwin1591 1. Go look at the horizontal stabilizers on the tail of pretty much every modern fighter jet since the Korean war... Instead of unmoving tail-planes with a moving elevator flaps, the horizontal stabilizer & elevator have been merged into one, which works exactly like a bird's tail. 2. Birds have tails, which bend to move their tail-feathers. Their hips are almost entirely immobile. In mammals the pelvis is joined to the 5 sacral vertebrae, while the ribcage is attached to the thoracic spine, and there is a length of lumbar vertebrae in between which lets the spine bend. Bird pelvises are fused to 14 vertebrae, including ALL of the lumbar vertebrae, and also the last of the thoracic vertebrae of the ribcage. Birds cannot "bend at the waist", because they do not have a "waist". Their hips overlap their ribs.

[@wirdy1]

​@@davidbaldwin1591the closest resemblance would be the gimballing of a rocket motor nozzle or the jet engine nozzle control for vectored thrust.

[@cabanford]

I'm now going to watch all of your other clips. You've been added to my "favorite channels" status 👍💪

[@Alexander-the-ok]

Thanks. Only the previous couple of videos are ‘high quality’ ones (albeit with bad audio). Everything before then, i had like 40 subscribers. More on the way though!

[@cabanford]

@@Alexander-the-ok something tells me that your early videos will still be great 👍

[@MarkBarrett]

This video made my mind think, and brought back memories.

[@ApolloTheDerg]

Dude, this is an absolutely fantastic video, I thoroughly enjoyed the history and thought put into it. From the titan tragedy to the inspiration to make amazing content, I sincerely hope it pays off multiple times over!

[@nabeel.shaikh]

This is the first time I have come across your channel, and it is the most fun I have had watching a KZbin video, EPIC stuff !

[@CollinKeegan]

Just wanted to say that that title is amazing. Your videos tend to have really good titles but that title is genuinely inspiring.

[@xijinvegg]

Once again an amazing video Alexander. Keep up the good work! I find it awesome that we have people like you on KZbin producing well thought out and informative content.

[@Alexander-the-ok]

Thanks. To be honest I find it awesome that there are so many people happy to listen to me just talk about stuff that fascinates me.

[@eddievhfan1984]

Liking the video! For added information/context, the Apollo Command Module also included an all-analog flight computing system, the SCS or Stabilization and Control System. It naturally wasn't as advanced as the AGC, but it could still provide orientation information from body-mounted gyros, attitude rate dampening, attitude hold, and semi-automatic control of engine burns. In combination with ground communications, it could be an effective backup for the AGC in a fair number of cases.

[@Statueshop297]

What an interesting topic. Thanks for ur hard work

[@rowanjones3476]

Nice work - lovingly researched and produced. Thanks for the list of sources - a bit of reading!

[@DanielFCutter]

Unbelievable. I found the entire back end of a sidewinder out in southern Arizona stuck in a hillside. I brought it home. I wondered what those spinning things were for. Now I know. Thanks! Unfortunately my ex-wife took it to the dump.

[@wirksworthsrailway]

An excellent description. Well researched, engagingly presented and generally spot-on.

[@nomar5spaulding]

Man alive, this video has a *lot* of shots fired moments directed at modern aircraft.

[@nazcaplain]

One of the best videos ever made on any topic, all hyperbole aside. And the disclaimer at the end about benefitting from military tech hits me in the feels - as I too am a pacifist who understands that sometimes you need to be well defended.

[@dongiovanni4331]

You take that back! The SR 71 is beautiful

[@Alexander-the-ok]

Yeah I was 100% wrong there

[@Aviate68]

As a pilot and aviation enthusiasts this was an amazing video and I learned and relearned things!

[@Kneedragon1962]

I learned a few things there. The use of virtual machines is one. I have heard (read / been told) that mainframes in the 1970s used them, but I had no idea they were used in the '60s by the space program, and the very early fly by wire systems. I am struck hard, by the confidence of the Air Force and General Dynamics, to design the F-16, not just to use FBW, but to be dynamically unstable and to depend on it, completely, at a time when it was still in testing and development and revision. I knew they built it with that concept as central, from the get-go, but I didn't know how new that technology was when they started using it. That's real bravery there. You've got to have some courage to bet the farm on something that's still in fairly preliminary testing ...

[@NanNaN-jw6hl]

@27:36 -- another important improvement illustrated in this graph, is that you get flight-data-telemetry recording for-free compared to prior control mechanisms. Imagine the complexity of recording all flight control inputs from push-rods and control tension-wires!

[@kennyxkazuki713]

I immediately recognized that font on the jet as the font on checks. I always wondered why it looked like that

[@Esteb86]

The PIO issues makes me think of the space shuttle landing tests. Haise got a lot of PIO right before touchdown. A huge deep-dive was done and found that the program acted differently at that altitude, air speed, on approach. A lot of people thought his landing issue are the reason why he didn't get an actual shuttle flight. But, that wasn't the reason at all. They knew what was wrong. Edit: Well, shit. I commented before the shuttle PIO was brought up in the video lol

[@laurencedawson7754]

One of the best KZbin videos I've ever watched

[@tonymcflattie2450]

Max is NOT fly by wire. It is a 3rd generation aircraft. A220 and a320, 787, 777 are 4th gen

[@Alexander-the-ok]

Actually yeah I think I’m gonna pin a correction on that. If it did have fbw the incidents would have never happened in the first place.

[@TomFynn]

Concorde may be the only good-looking supersonic aircraft ever made, but the SR-71 is the most badass looking supersonic plane ever made.

[@natespurgat6245]

"please don't use a raspberry Pi as a flight computer" just try and stop me

[@alexanderarnett4966]

Thank you for all of your time and effort that went into this video. It was brilliant. Kudos to you.

[@jean-baptiste6479]

Dear Sir, I work within Airbus and I would like to thank you very much for this video. I agree that we owe a lot to Apollo, I do not have many examples of nowaday's Aircraft technology that can not be traced to the 1960's and the space programme, (or to B747, B737 on some aspects) It does not reduce the merit of Airbus to say that. There is simply some notion of technology filiation that could be taught in engineering schools.

[@Alexander-the-ok]

I always get really nervous when someone that's actually involved in these stories watches one of my videos! Learning this story actually gave me a lot of respect for Airbus in identifying the safety benefits of FBW and adopting it before their competitors.

[@jean-baptiste6479]

The integration machine is very clever. Such machines were used to integrate the Fourier coefficients for tide record and prevision... making computerscience out of mechanics is 😮. There is also a mechanical device able to calculate the surface inside closed curve (based on Green's theorem). Thats another masterpiece. I miss those times to be honest

[@martinda7446]

This has been the best thing I've watched on any medium, (TV, cinema, streaming services..and so on). so far this year. Wonderful, entertaining, educational, and beautifully made. To be honest, I'm 33 minutes in. But I don't want it to end. You know that feeling? Its like I'm watching a 1970s BBC Horizon episode. One of the best ones, or CH4 Equinox. Check out James Burke, though I'm absolutely sure you know him already what with the Apollo and science documentary ''connections'' (pun was unintended) but it gives the same feel. That has to be a very special thing. PS. You may remember I was the twit who had a go at your diction... I still feel bad about it. I am not compensating for past indiscretions by writing the above. I'm sure there are many more comments praising your work in the comments.🤠

[@Alexander-the-ok]

You've got it spot on! James Burke was actually an inspiration for this channel. His connections series and Apollo coverage happened long before I was born, but I discovered them from a particularly unusual source: connections is featured in the computer game 'the Witness'. Interestingly, this particular video has 'connections' to all of my subsequent videos - the AGC and its descendants were absolutely pivotal in shaping the late 20th century and beyond.

[@martinda7446]

@@Alexander-the-ok Amazing. I was lucky enough to watch the later missions with James Burke, Patrick Moore etc. (I was a bit too young to remember much about the first, being six). You would make James Burke really proud, and that is a certainty.

[@plat216]

every once in a while, a hidden gem appears on my yt recommendations

[@mittman9977]

Thank you Alexander, this is a wonderful video! I learned a ton and was truly fascinated! Awesome job!

[@malcolmking752]

Can’t tell you how excited I am to see this uploaded.

[@federicoandreoletti4476]

Amazing video! As a utility pilot, I'm not a fan of Airbus school model, but you made me saw it from another very interesting prospective.

[@user-qf6yt3id3w]

Wozniak invented a VM called SWEET16 for Apple Integer Basic. Actually Microsoft C++ on PCs had a P code option back in the 16 bit days. Basically you trade a lot of speed for compactness. Also on an 8 bit CPU the VM code might be more high level. SWEET16 was better at dealing with 16 bit data than straight 6502. Of course in the modern world almost everything is written in .Net or Java, both of which are VMs. Theoretically JIT/AOT can make them fast but they always seem to run like molasses to me.

[@mrlazda]

SWEET16 never used VM it was just interpreter (big difference).

[@TheLoneWolfling]

The biggest issue with "redundancy" of flight control software - and software in general - is that N computers all running the same garbage algorithm on the same inputs will all agree on the same garbage output, and then all your fancy calculations about MTBF go out the window. This can happen even if you have multiple independently-developed sets of software (if e.g. a corner of the spec wasn't well-written, the implementers can come to the same erroneous conclusion). This is, of course, also possible with analog systems, however analog systems tend to have both far less state and far more variation between components. The former means that they tend to be far more exhaustively tested for logic errors, and the latter means that they tend to not all fail at once in quite the same manner. There are ways to alleviate this to an extent, but nothing great.

[@alexhajnal107]

This is why the backup Shuttle computer ran on a different hardware platform (from a different designer/manufacturer) running different software written by a different team (working for a different company) who had no contact with the primary flight computer team. The idea was to eliminate as many sources of systemic error as possible.

[@TheLoneWolfling]

@@alexhajnal107 The space shuttle actually had a near miss here, due to... guess what, 'redundant' computers carefully calculating the same garbage output. STS-41D luckily aborted on the pad, because if it hadn't, it would have had a ~1-in-6 chance of catastrophic failure due to a software issue. Look up DR56938. (As a few sidenotes: note that the space shuttle did _not_ switch automatically from PASS to BFS - that was done by the crew. Otherwise you're back in precisely the same 'who watches the watchman' scenario - but also as a result it means that the space shuttle was _not_ tolerant of PASS failures that would cause permanent damage before the crew could switch over. Also, PASS and BFS were running on multiple copies of the same hardware, not differently-designed hardware. Not sure how you got that impression.)

[@atypicalprogrammer5777]

These antiquated computers are so elegant and fascinating.

[@ApolloCDR]

I totally heard that in my head as Warner bros. Marvin the Martian's voice 😊👽😁

[@MostlyPennyCat]

50:56 Airbus's graceful failure laws are also a wonderful piece of design (although not as exciting as Azimov's), starting at and falling back to: 1) Normal Law (with Ground, Flight and Flare Modes, full envelope protection and secondary effect motivation) 2) Alternate Law 1 (You lose HOA and Stall protection) 3) Alternate Law 2 (Further lose Attitude, Angle and Energy protection, SEM loses roll and yaw mitigation) 4) Direct Law (Direct surface control, all protections lost, all mitigations lost) 5) Mechanical Law (You have mechanical control of pitch and lateral direction via the tail surfaces. Best of luck! 🤢)

[@paulcook8700]

fabulous insightful description of a massive subject well done

[@JPR3D]

I just stumbled across your channel and I love it, thank you for such cool videos!

[@Kaiser_Kenny]

I'm not subbed here but this vid was on my home page for like 3 days so here it goes.

[@das250250]

You want those bearings to be pretty good on that wheel

[@Alexander-the-ok]

I wore a face shield the first time I spun it up. I was paranoid it was going to fly off

[@nicktrabosh9277]

now this sounds like the missile knows where it is, but its just math u see

[@archdornan4389]

The missile knows where you are, because it knows where you aren't.

[@sixstringedthing]

Absolutely fascinating presentation mate, very well done. The challenge of cooling a mere 55 watts of heat load for an hour and twenty minutes were particularly interesting. I assume that the bulk of this challenge stemmed from the fact that even the most minor of modifications to the airframe internally or externally would have demanded recertification processes for which there was no budget.

[@Alexander-the-ok]

Thanks. Yep pretty much - it's difficult to dump heat into the rarefied upper atmosphere: even 55W is a fair amount over the course of a flight. So the easiest solution was a 'total loss' system using liquid Nitrogen to carry the heat away.

[@tiggy2756]

Got be best video on the AGC fly by wire tests and that info on the Digital text font was interesting , keep up the good work

[@manuelb636]

Another amazingly good video, thank you! As soon as I can, I will be supporting you channel for sure.

[@BillyBobCornontheCob]

Startling to see your own model (the AGC) appear in a random video! I think i share your same fascination with that piece of kit.

[@Alexander-the-ok]

No way! Can’t believe you found the video. My email address is on the channel homepage - fire an email across to me and i’ll send you some free goodies if you want!

[@BillyBobCornontheCob]

@@Alexander-the-ok Ah I was looking for that, aren't allowed to see it on the mobile app for whatever reason. Thanks!

[@Jon-mf2no]

Fantastic video! You clearly have a wealth of experience to draw on and have done extensive research. Everything is explained clearly and in an entertaining fashion. It's also worth pointing out that the original stealth aircraft, the Have Blue prototype and the F117A that followed on from it, would have been impossible to get into the air without fly-by-wire.