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Testing the F-35C Tailhook
- BruceEel 3y ago[flagged]
- dumpsterlid 3y ago[dead]
- fusslo 3y agoI think every engineer has been burned by faulty test equipment. and I think every senior engineer has been burned by not trusting test equipment that IS working properly! that was a pleasant read
- euler_angles 3y agoAuthor here. Did not expect to see this on HN at all. Just an engineering war story I shared.
- tra3 3y agoThis is really cool, thanks for sharing. What's wild to me is that the program started in the late 90s and only now is the F35 fleet up to originally specified? operational capacity. Since then I graduated high school, got a degree, got married etc etc. The time span is mind boggling. Would be interesting to see how continuity is maintained for so long. In software it feels like if a project is more than 6 months old, we throw it out and rewrite it.
- tekla 3y agoYou write shit down and you have career engineers that enforce continuity It's trendy in software to complain about doing annoying work like writing reports and documenting things. But most hard tasks require writing reports and documenting things.
- eitally 3y agoAnd this isn't limited to aerospace. My wife has spent a career in pharma (drug save & pharmacovigilance specifically) and it's the same way there. People complain about rigidity and sluggishness in these industries but there absolutely is an ingrained attitude of documentation and process compliance that pervades. At one point -- and this was just last year -- my wife took over running a monthly safety report that involves manipulating a bunch of data in Excel. Even that has a 9 page instruction guide, and since she now owns the output she also owns maintaining the manual. Too often in the land of software we underestimate the potential negative impact the traditional "move fast and break things" approach to product development can have when it comes to real world use in mission critical systems.
- trhway 3y agoOn the other side this unwillingness and mental non-acceptance of those reports/manuals/etc. as a wasteful activity frequently comes from the understanding that there are more efficient ways of doing things, and that drives the "software eating the world" effect. While I naturally don't know the details of the case you mention and pharma is far from the domains I've been in, yet in many business/enterprise situations the software approach is to code the many-page guide into business logic, including ETL-ing the data instead of manual import, etc. Move fast and break things brings you to the Moon in a decade using primitive tech, where is total process compliance can't do that even in 50 years using much more advanced tech.
- red-iron-pine 3y agoa lot of people died in germany, the ussr, and the us making those rockets work. and in exchange for that we planted a flag there and have a handful of rocks in a glass viewing box. move fast and break things worked real well for the folks who got literally creamed while they were viewing the titanic.
- wazokazi 3y agoWas there ever any consideration given to building a "testing harness" to physically simulate the F35 landing? Something like the "dead load" testing that the EMALS undergoes. Just in reverse. Anyway, that was great read.
- euler_angles 3y agoThere was a lot of static load testing done, and things like a drop test [0] of a full scale article. But to my knowledge, the only way to test the dynamics of a carrier arrestment is to actually do an arrestment. We do them on land; NAS Patuxent River and NAS Lakehurst (among others) have a full set of Mark 7 arresting gear like you would find on a Nimitz class. Lakehurst also has the advanced arresting gear present on the Ford class. [0] https://www.youtube.com/watch?v=lGPseVNfZO0 https://www.youtube.com/watch?v=lGPseVNfZO0
- fatbird 3y agoHow much of a difference is there between dry land arresting and carrier arresting? I would guess some since the carrier represents a somewhat dynamic surface, and flight conditions might likewise vary. Is there enough that a second round of carrier based testing is required that might trigger significant changes?
- euler_angles 3y agoAll of this was done as a work up to a carrier deployment. In software terms, trying the arrestments on land is deploying to test, doing them on a carrier is production. There were three separate developmental test deployments to carriers for the F-35C. Each deployment sought to expand the understood envelope and and handling procedures. The hook redesign happened before the first deployment. The hard landing story in the post happened during the work up to the third and final deployment.
- dotancohen 3y agoHad the hard landing occurred on a carrier, how would the gentle, flared landing be accomplished? Try to reach an airport on land, ditch the plane in the water, maybe catch the plane with the net on the deck? Our just do a normal carrier landing and hope for the best?
- superjan 3y agoIsn’t there a normally a mechanism that lifts the wire after the landing gear has crossed it?
- euler_angles 3y agoYes, there are pendants that are supposed to keep the wire above the deck, but the short space between the F-35C main landing gear and the tail hook point means that there's not enough time for the pendants to raise the wire above the deck in the manner that the original (erroneous) wire dynamics model would have suggested.
- LorenDB 3y agoHey, would you mind adding an RSS feed to your blog?
- euler_angles 3y agoI am but a grunt who mostly programs radar models, I didn't know Quarto blogs could do that until just now. Yeah, sure, I'll add it.
- euler_angles 3y agoDone!
- LorenDB 3y agoThank you!
- euler_angles 3y agoQuarto made that really easy. Very cool.
- idontwantthis 3y agoSorry, it’s been so long that I’m afraid to ask. What will you do now that it has an RSS feed?
- iab 3y agoAre you actually euler_angles, or are you really tait_bryan_angles
- euler_angles 3y agoDeep down I am indeed tait_bryan_angles
- iab 3y agoI appreciate your candor (and your article)
- tiahura 3y agoInstead of a lot of modeling and testing, wasn't Northrop just allowed to inspect an F18 and measure?
- euler_angles 3y agoThe F-18 tailhook geometry is far different than the F-35 tailhook geometry. F-18 hooks are much farther back from the main landing gear, and are also much longer.
- jtriangle 3y agoWhy exactly did they redesign the tail hook? Surely they could have just used one off any number of other aircraft with some modification? Or are all of those tail hooks bespoke designs because reasons?
- deleted 3y ago[deleted]
- wbeckler 3y agoIt could be related to the fact that they didn't have much space for a normal size tailhook, as stated in the article.
- jtriangle 3y agoI mean more the design of the hook itself, though, I don't know if that design is even atypical to be honest.
- mech987987 3y agoEven if two different aircraft have the same space constraints for the hook (which is a pretty big if), they have different mass and deceleration characteristics (i.e. minimum and maximum approach velocity) during landing- changing the force exerted on the hook. Designing a lighter hook for the lower loaded aircraft is VERY desirable for high tech fighter jets- every ounce saved is better range, better agility, etc. As far as the little lip at the very tip of the hook- it looks to me like the initial design was trying to minimize any risk of digging into the flight deck and causing damage- this is just a guess though.
- cwillu 3y ago“After the LSO finished what he had to say and left the ready room my B/N allowed that he might fly with me again. Me, I was still shaking inside. The next morning I went up on the flight deck before flight ops started and walked to the aft edge of the deck. I was looking for something and found it. About one foot from the end, there was a single, shiny, brand new, solitary hook imprint in the deck.” https://thelexicans.wordpress.com/2013/09/10/one-foot/ https://thelexicans.wordpress.com/2013/09/10/one-foot/
- mlekoszek 3y agoGlad you did.
- aidenn0 3y ago> “Boss,” he says to me, “This fucker ain’t gonna work. Look at this thing. It’s short, it’s too close to the wheels, and look at this dumbass hook shoe they got on it. If the wire don’t hit it exactly right, it’s just gonna go under the hook and you’ll bolter.” Did nobody with practical experience with arrested landings look at the arresting hook design prior to this? Obviously computer models can and do predict extremely novel solutions to existing problems, but it's worth double-checking the model when someone with practical experience says "it will never work" In this case, it seems like a simple slow-motion video of an arresting wire going under the wheels of an F-18 would have been enough to debunk the model.
- icegreentea2 3y ago> Did nobody with practical experience with arrested landings look at the arresting hook design prior to this? I mean... it's very likely that the answer is no. The last new carrier aircraft made was the Super Hornet - and that design was basically done by 1995 (the F-35 tests in question were in 2011/2012). That expertise would also be at McDonald Douglas/Boeing. Northrop Grumman has a long history of carrier aircraft development, but it would have been long dormant by that point. I'm sure there's all sorts of reasons the model's inaccuracy wasn't caught before hand, but sometimes... if you're given a model that's someone says that's been V&V'd, and it produces a result that's only a little weird, you just go with it. There are only so many things you can add extra testing onto in a project. Sometimes you choose wrong. Anyhow, consider that the model results were probably exactly what they were expecting. Remember that the designers would be honing in on the shorter tailhook. You can imagine their mental model going - "ok on legacy aircraft, we have flatter tailhooks because there's enough time for the cable to settle". And then going "ok, with a shorter tailhook, there won't be enough time to settle". And then their model comes out and say "ya, with the shorter tailhook, it won't have enough time to settle - it'll be UP IN THE AIR". Whereas reality is "ya, with the shorter tailhook, it won't have enough time to settle - it'll still be displaced DOWN".
- the_af 3y agoRandom thought: this is a case where someone's intuition matched what actually happened, making us think "why don't they listen to people with common sense?". But what about the many other cases where someone with "common sense" said "this fucker ain't gonna work" but the thing worked as predicted by simulations? Surely they must have happened too.
- throwanem 3y agoThe name "ham-peas" might be familiar. If so, how've you been keeping lately? Been a minute!
- euler_angles 3y agoI have not forgotten your user name here, ha. Yep, been a minute. I should hit you up via email.
- throwanem 3y agoI wouldn't mind that at all. If you don't still happen to have the address, the one in my profile here's good too.
- euler_angles 3y agoI actually still have your personal email address. Expect something from me soon. It took a few years but I work as a developer now (C++, electronic warfare simulator)
- throwanem 3y agoThat's great to hear! I'll keep an eye out, and hoping all's well in the meantime.
- kevin_thibedeau 3y agoHope you have proof that the diagrams aren't export controlled. Otherwise you're going to receive some unexpected visitors soon.
- euler_angles 3y agoThey all came out of a book that anyone can buy called "F-35: From Concept to Cockpit". That book is a compilation of papers presented at an AIAA conference in 2018.
- egorfine 3y agoFirst of all, thank you for the super interesting read! Now, as a Ukrainian I do have a philosophical question of sorts. What we have seen here in a real full-scale combat is that some of the modern machines are way too delicate for actual operations on the ground. For example, I have heard some feedback about the Abrams tank: way too finicky for real use, not durable, not reliable. The same goes about many other western items. (Some hardware demonstrated exceptional reliability, like Bradleys and HIMARS) My question is about modern fighter jets like F-35. Does that level of engineering and the amount of delicate electronics somewhat limit the durability and reliability of the airplane compared to much simpler designs?
- nradov 3y agoThe F-35 was never really intended to be durable or reliable for ongoing use in long wars of attrition. It was designed to be survivable on penetrating strike missions against near-peer adversaries. Essentially to "kick the door in" and destroy high value targets such as air-defense systems during the first few days of a conflict. War games and simulations have shown that simpler designs can't accomplish that mission anymore so concerns over F-35 durability and reliability are somewhat misplaced (although there is certainly room to improve mission readiness rates). No one is even remotely contemplating sending F-35s to Ukraine. Besides and costs and security risks, the Ukrainians unfortunately have nowhere near the infrastructure and logistics to sustain such a complex platform.
- egorfine 3y agoAh, so in that case it looks like reliability and durability are not exactly important or desired features for that kind of missions. Did I get it right?
- extraduder_ire 3y agoI thought tailhooks predated the f35. Did they need a different design on this aircraft for some reason?
- jeffrallen 3y agoThe author says the design was constrained by the space available for it when stowed in the airframe.
- euler_angles 3y agoYes, the tailhook bay is very, very small. We had a primary disconnect in the bay for the instrumentation wiring for our tailhook sensors. Any time we had to get at that disconnect without having the tailhook trestle removed, we would call it "proctology".
- DiggyJohnson 3y agoYes, the packaging geometry is pretty different on the F35C compared to other carrier-operated platforms like the F14, F/A-18, or E2C. Notably the platforms I just listed were designed from the ground up for CATOBAR operation. The F35C is just one variant of the platform, and must share certain geometries and constraints with its conventional and hovering sisters.
- shitlord 3y agoTailhooks do predate the F-35C, but this particular airframe needs to maintain certain properties (low observability, aerobatic performance, weight, etc.). You can't simply enlarge the tail hook compartment and use the other aircraft's hook without compromising some of these properties.
- jcgrillo 3y agoMost machines don't have modular, swappable systems. For example you can't generally take the wheels of one model of car and just bolt them onto another (even if the bolt holes and centering ring line up) expecting it to go well. A tailhook is undeniably more complex than a car wheel--it's not a reasonable expectation to be able to just bolt one on from a different aircraft.
- Scubabear68 3y agoOne thing that stood out to me - based on the narrative here the tail hook never could work in real world conditions. The blog mentions that the computer model used by the manufacturer was wrong. Does that mean that manufacturers don’t field test the hardware? If so, that is scary.
- euler_angles 3y agoThat's what the flight testing was for. I am not aware of a way to all-up test something as dynamic as an arrestment without actually building a jet and trying to catch a wire.
- toast0 3y agoThis is the field test of the hardware. When you've got a single customer anyway, it makes sense for the customer to participate in or fully drive the field test.
- vlachen 3y agoGreat read. Looking forward to more! I was once a Harrier mechanic, and I was told very often that I'd be learning to work on the F-35Bs during my 2002-2007 enlistment, which obviously didn't happen. So, as a former mech and current engineer, I am very interested in hearing more about it's development.
- euler_angles 3y agoI have other threads on Twitter discussing the F-35 > https://twitter.com/the_engi_nerd/status/1758633498464952414 https://twitter.com/the_engi_nerd/status/1758633498464952414 Labeling everything I could see in the cockpit > https://twitter.com/the_engi_nerd/status/1757243336941871159 https://twitter.com/the_engi_nerd/status/1757243336941871159 a discussion of my primary job in flight test, aircraft instrumentation. > https://twitter.com/the_engi_nerd/status/1747803565987381495 https://twitter.com/the_engi_nerd/status/1747803565987381495 riffing along with chapter one of "F35: From Concept to Cockpit", a compilation of papers written by Lockheed-Martin employees at the conclusion of F-35 system design/development.
- foxyv 3y agoI love hearing about these engineering challenges. Media loves to point to these design iterations as proof that the F-35 is over-hyped or inferior to existing jets. But what I see is innovation and trying new stuff. Sometimes failing, but in the end making an amazing jet. I just kind of wish we lived in a world where we didn't NEED a new fighter jet and could instead invest this time and effort into peaceful pursuits.
- rkagerer 3y agoBut what I see is innovation and trying new stuff. I like your positive attitude. Though I think there were some engineering shortfalls that should have been avoided with common sense. Eg. The original hook didn't work because the shoe was angled up too high to catch the wire. The engineers designed it based on a flawed simulation model. The guys field testing took one look and knew it wouldn't work. Heck, I showed this photo to my partner (non-engineer) and the first thing she said was "it's not pointing right". https://the-engi-nerd.github.io/posts/welcome/images/clipboard-4283089921.png https://the-engi-nerd.github.io/posts/welcome/images/clipboa... You can see the original (blue) vs revised (red): https://the-engi-nerd.github.io/posts/welcome/images/clipboard-1418549673.png https://the-engi-nerd.github.io/posts/welcome/images/clipboa...
- deleted 3y ago[deleted]
- hef19898 3y agoLooking at the image, and knowing designers assumed the cable would rebound before being cought by the hook, the original design of the hook itself makes sense: catch the cable in the air and make sure it doesn't slip down the hook. Obviously it doesn't work to catch cable lying flat on the ground. Which was, again, not the initial design requirement. In another thread about Boeing, the topic of good sources to learn about real engineering came up. Well, this is a great example. Just assume the engineers designing the initial hook were not complete clueless idiots.
- foxyv 3y agoMy first class in Calculus based physics, my professor did an interesting thing. We would be asked to intuit the answer to problems before we did the math to know for certain. Physics is simply not intuitive. Now, with regards to the simulation, the thing I think they failed on wasn't a lack of common sense. I think what they should have done is reproduce the results in real life using a similar jet. They relied on the model a bit too much and "Tested in production." However, as far as mistakes go, this is a pretty small one.
- deleted 3y ago[deleted]
- jessriedel 3y ago> The program decides to officially stop trying to chase the off-center arrrestments and wire only arrestments. What does this mean? That the F-35C can only hook correctly when it lands very close to center? And what does "wire only" mean? Aren't all arrested landings on carriers "wire only"?
- moelf 3y agoI thought there's also the net they can use if, say, an aircraft lost tailhook
- jessriedel 3y agoSure but that's emergency only.
- euler_angles 3y agoThe whole purpose of this series of tests was to try to exercise the arresting gear in the most punishing ways. One way that's usually done is to try to arrest far off the centerline (where the arresting force will be applied far more intensely to one side) and also to try to have the arresting hook grab the wire while the jet is still wheels above deck (this slams the aircraft down, HARD) After this incident it was determined that we had fulfilled the intent of the test plan. Also, instrumented aircraft capable of doing arrestments were in short supply: the program only had two of them, and we pushed one to its very limit.
- jessriedel 3y ago> After this incident it was determined that we had fulfilled the intent of the test plan. Ok, so it was considered good enough? (This quote made it seem like the testing had failed and they were giving up: "The program decides to officially stop trying to chase the off-center arrrestments and wire only arrestments.) Also, I still don't understand what wire-only arrestments are. Aren't all arrestments wire only? Thanks.
- 3y ago
- torcete 3y agoSince the new aircraft carriers have this new fancy electromagnetic catapults. Why don't they just use regenerative braking like the hybrid cars? They could save a lot of energy recharging those catapult accumulators. I'm joking, of course.
- deleted 3y ago[deleted]
- scirner22 3y agoAwesome read! I worked on IFLOLS as a new grad software engineer during this time. Since leaving the government to work at various software startups, I miss real world engineering like this.
- wolverine876 3y agoWhat do you mean by "real world engineering"? That is, how does it differ in your perception?
- euler_angles 3y agoI went from doing things like I describe in the blog post, to verifying and validating the most complex electronic warfare simulation the DOD has ever done, to being a developer of one of the enabling technologies of that simulation. I believe what I do now is important, but getting an issue past test and into the release that's sent to customers isn't nearly as satisfying as "I fixed the tailhook last night, which let today's flight test happen". I miss having an aircraft that I can touch.
- scirner22 3y agoWriting software to control a dynamic light plane compared to writing springboot rest apis.
- lchengify 3y ago> Engineers, saving your program time and money out of the sheer laziness of not wanting to make a new XML format for an instrumentation project. This is how progress is made in the world, I guess. I've worked in healthcare, fintech, and ads and this is one thing I've done in all three fields. I swear i've written or debugged XML parsers in 20 different languages at this point just so I didn't have to get consensus on a new format.
- euler_angles 3y agoWe made our XMLs with, horror of horrors, a Visual Basic script that ran in Excel and digested several input documents to generate a map template that we could then tweak by hand and turn into an XML through another VB script.
- lchengify 3y agoHonestly, makes sense. This is how much of finance runs their models.
- euler_angles 3y agoWe weren’t allowed to have any other real programming tools, and the telemetry “maps” we were trying to make were/are major/minor frame oriented. This maps nicely to a grid of data: a spreadsheet. IRIG 106, Chapter 4 PCM telemetry covers what we were doing in this process, along with Chapter 9.
- ghc 3y agoWait, what? Why weren't you allowed to have real programming tools? I mean, I see a lot of FTEs using Excel, but I thought it was a matter of familiarity. I've also encountered some who are using Matlab, SAS, Python, R, etc.
- tacticalDonut 3y agoUS DoD heavily controls what can and can't be installed on their stuff. To make matters worse each branch and organization has their own approach to how they control what gets installed. Sometimes it's just the path of least resistance to use what you already have. I remember putting in a request to install Python. It took me 6 months to get a response of no. I had the opportunity to appeal with more information on the use case, but I just did it in VB for Excel at that point.
- HumblyTossed 3y agoIsn't this over engineered aircraft supposed to VTOL?
- ranger207 3y agoThere's three versions. The F-35B is the one that can take off in a short distance and land vertically[0] and it has a big lift fan behind the cockpit. The F-35A and F-35C don't have the lift fan; the C has large wings and a reinforced tailhook[1] compared to the other versions. [0] The F-35B _can_ take off vertically, but it can't do so with any reasonable weapons or fuel load. [1] Many non-Navy planes have tailhooks to work with emergency arresting wire systems at Air Force bases, but those are for emergencies and are rarely used, whereas the Navy uses tailhooks all day every day
- deleted 3y ago[deleted]
- dralley 3y agoOnly the B, and the B is only intended to do short takeoffs not vertical ones (it is possible to take off vertically but pointless, you can't do it with a combat load). The C is meant to do carrier takeoffs and landings. Landing on a carrier the traditional way is more reliable than trying to land vertically every time.
- sillywalk 3y agoAn interesting side-note on the F-35C - when it was ordered/designed there was no aircraft that could deliver replacement engines (even when disassembled) to an aircraft carrier. They wouldn't fit into the C2 Greyhound. Kind of an odd oversight. They can fit into the CMV-22B variant of the Osprey, which is grounded for now, and I believe the CH-53K King Stallion. But they those aircraft didn't exist until recently. edit: I meant to say that the C-2 couldn't carry F-35 engines in particular because they don't fit, not that they couldn't carry replacement engines in general.
- nickff 3y agoYour statements are vague and incorrect. First off, there are CTOL airplanes which can deliver replacement engines to aircraft, just not F-35 replacement engines (because of their large blade diameter). USN had previously used C-2 Greyhounds for these sorts of duties, but they have too small a fuselage, and were being decommissioned. There was talk of converting some decommissioned S-3B for COD, exchanging their fuselage for a wider one to accommodate the F135, but this was not pursued. https://archive.ph/20150209193642/http://www.defensenews.com/article/20140409/DEFREG02/304090028/#selection-735.145-739.305 https://archive.ph/20150209193642/http://www.defensenews.com... Second, lots of helicopters can carry F-35 replacement engines, including the Boeing Sea Knight. https://en.wikipedia.org/wiki/Boeing_Vertol_CH-46_Sea_Knight https://en.wikipedia.org/wiki/Boeing_Vertol_CH-46_Sea_Knight I believe that the USN didn't want to depend on conventional helicopters because of their relatively short range.
- euler_angles 3y agoThe CH-46 has been out of US Navy service for 20 years and Marine Corps service for almost 10, just as a program note.
- sillywalk 3y agoI edited my comment to make it clear it was just F-35 engines that couldn't fit. But I think the rest stands true. There was no V-22 COD variant at the time and the main COD aircraft couldn't deliver replacement engines. Other helicopters could deliver replacements to the carriers, as you said, but the carrier would have to be relatively close to shore. Other side note: the V-22 isn't pressurized, so they have to stay at a relatively low altitude.
- someotherperson 3y agoJust of curiosity, I would have thought that things like this are considered classified? Did you need to seek clearance to publish this? Or is there certain things that the US military isn't as fussy about (like this)?
- speed_spread 3y agoI assume that since the plane is public and there are pictures of it landing, information regarding the tailhook doesn't have to be classified. People who want to know, will.
- euler_angles 3y agoMy own engineering war stories are just that, stories. Any technical information I gave was taken from released sources only. I am extremely conscious of this
- brokenmachine 3y agoTIL where "galling" comes from.
- ballooney 3y agoQuestion for anyone still browsing this far back in the timeline - any recommendations for other good engineering war-story blogs? Ideally aerospace, robotics etc.