[HN Gopher] Testing the F-35C Tailhook
___________________________________________________________________
Testing the F-35C Tailhook
Author : sklargh
Score : 279 points
Date : 2024-02-27 15:32 UTC (7 hours ago)
(HTM) web link (the-engi-nerd.github.io)
(TXT) w3m dump (the-engi-nerd.github.io)
| fusslo wrote:
| I 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 wrote:
| Author here. Did not expect to see this on HN at all. Just an
| engineering war story I shared.
| tra3 wrote:
| This 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 wrote:
| You 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 wrote:
| And 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 wrote:
| On 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.
| falcolas wrote:
| So, an amusing anecdote related to your second paragraph
| - one reason it's taking so long the second time around
| is everything has to be repeated. They lost the knowledge
| of how to make rocket stages and engines of that size,
| and had to re-learn those lessons.
|
| It's also quite important to remember how many lives were
| lost (or nearly lost) because of "breaking things" in the
| Apollo program. Something that's not nearly as acceptable
| today than it was at the height of the cold war.
| Something that directly implies moving more slowly and
| being more sure that everything works the first time,
| every time.
| roughly wrote:
| > In software it feels like if a project is more than 6
| months old, we throw it out and rewrite it.
|
| I think that would be a bad way to operate, but what's worse
| is what we _actually_ do, which is write the project like
| it's gonna be replaced in 6 months and instead keep that
| poorly-documented untested duct-tape contraption around for a
| decade as the central load-bearing component of critical
| infrastructure.
| wazokazi wrote:
| Was 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 wrote:
| There 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
| fatbird wrote:
| How 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 wrote:
| All 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.
| psunavy03 wrote:
| The Navy developmental test community does carrier
| suitability testing of every new airframe, and there's a
| whole program of nominal and off-nominal arrestments they
| have to test in order to prove the jet can recover in all
| expected scenarios.
| whartung wrote:
| I don't know if it's significant but on the carrier the
| arresting system is going 25-30 mph. The ship is moving.
|
| Again, maybe not enough to really matter, but enough to
| at least take into consideration.
| superjan wrote:
| Isn't there a normally a mechanism that lifts the wire after
| the landing gear has crossed it?
| euler_angles wrote:
| Yes, 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 wrote:
| Hey, would you mind adding an RSS feed to your blog?
| euler_angles wrote:
| I 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 wrote:
| Done!
| LorenDB wrote:
| Thank you!
| euler_angles wrote:
| Quarto made that really easy. Very cool.
| idontwantthis wrote:
| Sorry, it's been so long that I'm afraid to ask. What will
| you do now that it has an RSS feed?
| LorenDB wrote:
| Uh, put it in my feed reader? What else is there to do with
| RSS feeds?
| dylan604 wrote:
| If you're Googs, you deprecate them
| iab wrote:
| Are you actually euler_angles, or are you really
| tait_bryan_angles
| tiahura wrote:
| Instead of a lot of modeling and testing, wasn't Northrop just
| allowed to inspect an F18 and measure?
| euler_angles wrote:
| The 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 wrote:
| Why 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_?
| wbeckler wrote:
| It could be related to the fact that they didn't have much
| space for a normal size tailhook, as stated in the article.
| jtriangle wrote:
| I mean more the design of the hook itself, though, I don't
| know if that design is even atypical to be honest.
| mech987987 wrote:
| Even 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.
| wolverine876 wrote:
| Due to the planes and to the rest of the tailhook (the
| shank, etc.), they could hit at different angles, speeds,
| etc. That's just a guess, however.
|
| Each plane costs ~$100 million and the entire program
| will cost over $1 trillion when it's done. Performance
| needs are extreme: They need to land in all sorts of
| adverse, imperfect conditions - damage to the plane, the
| carrier, the wire, the personnel; bad weather; bullets
| and missiles flying around. It seems worthwhile to design
| the highest-performing tailhook for this plane, rather
| than to save a few bucks.
|
| Also, IME people doing something this sophisticated don't
| miss those really simple, obvious issues that we happen
| to be able to observe and grasp from the outside.
| imglorp wrote:
| They designed for the F-35B as the "baseline" with carrier
| requirements secondary. Also, the engineers knew but, "their
| concerns would have just as likely been ignored." This
| reference was 2012, when they knew it was a problem but
| before OP was fixing it.
|
| https://www.f-16.net/f-35-news-article4494.html
| mlekoszek wrote:
| Glad you did.
| aidenn0 wrote:
| > "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 wrote:
| > 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 wrote:
| Random 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.
| aidenn0 wrote:
| My point is that when models predict counterintuitive
| results (which they often correctly do; See e.g. Eurisco in
| the Traveller TCS championship, or the shape of the F-117
| compared to contemporary stealth aircraft), it's worth
| double-checking.
| MadnessASAP wrote:
| Unfortunately, my decade plus as a military aircraft tech has
| taught me that no, practical knowledge does not make it
| through the system nearly as fast as engineering "expertise".
| extraduder_ire wrote:
| I thought tailhooks predated the f35. Did they need a different
| design on this aircraft for some reason?
| jeffrallen wrote:
| The author says the design was constrained by the space
| available for it when stowed in the airframe.
| DiggyJohnson wrote:
| Yes, 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 wrote:
| Tailhooks 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 wrote:
| Most 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.
| avalys wrote:
| "Our existing service already has 'export to PDF'
| functionality. Why do we need to spend money building and
| testing 'export to PDF' functionality in our new service? Can't
| we just reuse the same code?"
| Scubabear68 wrote:
| One 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 wrote:
| That'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 wrote:
| This 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 wrote:
| Great 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 wrote:
| I have other threads on Twitter discussing the F-35
|
| > https://twitter.com/the_engi_nerd/status/1758633498464952414
| Labeling everything I could see in the cockpit >
| 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
| 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 wrote:
| I 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 wrote:
| _But 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/clipboa...
|
| You can see the original (blue) vs revised (red):
|
| https://the-engi-nerd.github.io/posts/welcome/images/clipboa...
| hef19898 wrote:
| Looking 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 wrote:
| My 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.
| euler_angles wrote:
| There isn't a similar carrier aircraft in the inventory
| that could have been used, as far as I know.
| wolverine876 wrote:
| > The guys field testing took one look and knew it wouldn't
| work.
|
| You have a hearsay, hindsight story (no offense to the
| author) that one person thought it wouldn't work.
|
| And now we have a hindsight HN comment that they would have
| known it all along. I'm guessing the people who worked on it
| weren't idiots, though people seem to delight in supposing
| they are smarter than all the dumb people whose plans don't
| work out perfectly.
| euler_angles wrote:
| No offense taken. The observation of an instrumentation
| technician and an engineer (me) definitely counted for not
| much at all in the grand scheme of things. And we could
| have just as easily been proven wrong.
| the_af wrote:
| Yes, that's what I'm thinking.
|
| Since you're the author: can you remember any cases where
| the person with "common sense" thought "this crap ain't
| gonna work" but it worked anyway? Surely people only
| remember those cases when common sense won, and
| selectively forget those where it didn't?
| krisoft wrote:
| > can you remember any cases where the person with
| "common sense" thought "this crap ain't gonna work" but
| it worked anyway
|
| I have one! Totally different field though. Cruise ships
| (and roro ferries) look sooo ungainly in water that
| regular people frequently ask how do they not just roll
| over. The Icon of the Seas goes 9 meter underwater and 20
| stories over the water. It does not feel or look right.
| Yet it is right, and keeps upright :), because it does
| not have uniform density. The engines and machinery, and
| tanks at the bottom of it keeps the center of gravity low
| enough to make it stable.
|
| The funny twist is that vehicle carrier ships also look
| unstable the same way and there the intuition is more
| correct. There have been multiple accidents where such
| ships capsized. But the intuition there is still not
| correct about the reasons why they flip over. (It is not
| that they don't have enough draft, but due to free
| surface effects and the cargo destabilising).
| euler_angles wrote:
| For F-35 flight test specifically, nothing comes to mind.
| Perhaps I'm a victim of the forgetting you mention.
| ckozlowski wrote:
| It's true, and it often forgets that most other aircraft go
| through the same teething problems.
|
| As the article skillfully shows, there's a lot of work that
| goes into seemingly simple things like a hook. Other elements
| can be really complex to work out. The F-35's integrated power
| pack[1] was the source of quite a few issues if I recall
| correctly. But it was developments like that which allowed the
| plane to keep weight under control such that we now have a
| supersonic STOVL jet in the F-35B.
|
| It's a pet peeve of mine when commentators say "that's stupid,
| they should just do <this>!" . Well, if it were so easy...
|
| I get your sentiment regarding the need for new fighter jets.
| At the very least, some of these engineering developments end
| up helping commercial applications as well. A good example is
| the C-5 Galaxy, which went through torturous development. But
| lead to the development of the TF-39 engine, which was
| revolutionary in concept. It then became the CF6, which then
| went on to power a long line of successful airliners.
|
| [1] https://www.defenseadvancement.com/feature/3-aircraft-
| system...
| MadnessASAP wrote:
| > It's a pet peeve of mine when commentators say "that's
| stupid, they should just do <this>!" . Well, if it were so
| easy...
|
| Why don't they just put windows in the submarine...
|
| It's good to remind ourselves and occasionally others that if
| the answer to a problem in a domain we don't have much
| knowledge on seems simple. Chances are the people with the
| knowledge are well aware of your answer and know why it won't
| work.
| helpfulContrib wrote:
| The cost of a single F35 could fund so much peace in the world.
| The only reason this isn't happening is because the people
| making sure the American people keep endlessly funding these
| programs have no intention whatsoever to make peace. _They just
| don 't have the intention to do so._
|
| They intend for there to be endless war, which is what these
| machines produce. It is the only thing they can be used for..
| foxyv wrote:
| I would love to live in a world where I can know for a fact
| that war will never again happen. However, the path to that
| world is a very long one. In the meantime I want to know that
| the acquisitive psychopaths that run many of the countries in
| the world have a very good reason to not line me up in front
| of a wall and shoot me.
|
| Should we be taking steps to a more peaceful world that we
| aren't right now? Yes, very much so. However, unless you want
| to imitate the path of Tibet or Ukraine, then you better
| spend some money on guns and fighter jets.
| avalys wrote:
| This is such nonsense. Could the USA have won WWII by paying
| off Hitler?
| marcinzm wrote:
| Yes, America funded Russia's recent invasions. Yup. All
| America.
| euler_angles wrote:
| I abhor war. I believe the only way to secure peace is to be
| very good at war. That's why I participated in flight testing
| the F-35, and why I work on electronic warfare simulations
| now.
|
| I wish I lived in a world where there's no need for any of
| this, but as far as I know, war is as old as the species.
| mardifoufs wrote:
| Yeah it's amazing how it is currently the best jet in the world
| considering how reviled and criticized it was in the media. And
| said criticism had real consequences, here in Canada we
| basically got stuck buying 1970s trash just because the f-35
| became a taboo and a meme due to projected costs, even if it
| means that we will pay even more for the alternatives for much
| much less capabilities.
| foxyv wrote:
| To be honest, I think the F/A-18 is an excellent jet for
| Canada's needs. Also Canada currently has 88 F-35s on order
| and will get their first ones in 2026.
| dralley wrote:
| The ancient F/A-18s airframes Canada purchased however,
| were not.
|
| >Canada expects to receive its first four F-35As beginning
| in 2026, another six in 2027, and six more in 2028, with
| the full fleet to arrive in time to enable the phase out of
| the CF-18s by the end of 2032. But its CF-18 fleet, even
| bolstered by the purchase of 18 ex-Royal Australian Air
| Force F/A-18A-Bs, may not be able to effectively hang on
| until then.
|
| They wasted a lot of time and money setting up supply
| chains and training pipelines for a fleet of near-end-of-
| life airframes that required constant maintenance, provide
| only the bare minimum capabilities and won't end up in
| service for very long. And they're having so many retention
| issues with their pilots that even that is wasted.
| wolverine876 wrote:
| The world changed significantly since that initial order,
| with the threats greatly increasing (from China and
| Russia). F/A-18 jets might have made sense in a more
| peaceful world.
|
| Now Canada has bigger problems and needs to better
| interoperate with NATO allies. Many countries switched
| their plans to F-35's after Russia invaded Ukraine.
| mardifoufs wrote:
| The issue is really that they bought used, worn out
| airframes just because they weren't as old as ours. From
| another Airforce that basically deemed them to be too old
| and worthy of replacement by the f-35... the same f-35
| that we chose to not buy instead! It's such a Canadian
| thing but we just basically swept the problem away for
| the couple of years that we can get from the airframes,
| but we had to basically go through all of the procurement
| again not even half a decade after that decision.
|
| So there was no point at all, we could've just bought
| actual replacements (f-35 or not) that would last for an
| entire generation back in 2p15. But hey, problem solved
| for the current government so who cares about what
| happens in 10 years! But then the issue got too big and
| we ended up circling back to buying the exact same f-35
| that we wanted to have for the past 20 years. Just with a
| worse deal and even more clapped out f18 and pilot
| accidents.
| foxyv wrote:
| I don't mean that the airframes are any good, I just mean
| that Canada has a population similar to that of
| California and almost half the GDP. They neighbor their
| closest ally and are separated by ocean and arctic wastes
| from anyone who would want to invade them. They don't
| really have much expeditionary need and their defense
| would be backed by all of NATO.
|
| So a couple old multi-role fighters are sort of okay for
| what they are doing. Mostly air to ground missions and
| demonstration flights. They need to up their defense
| spending a bit to meet NATO obligations, but not that
| much honestly. No one is going to kick out Canada,
| especially after the USA dragged them into Iraq.
| euler_angles wrote:
| As a guy who knows the F-35 and the program pretty well, I
| think the best Canadian minds on the F-35 are Richard
| Shimooka with the Macdonald-Laurier Institute, and former
| CAF and F-35 test pilot Billie Flynn.
|
| Shimooka has a number of works chronicling the Canadian
| F-35 decision making process, e.g.
| https://macdonaldlaurier.ca/assessing-damage-canadas-
| fighter...
|
| Billie Flynn discussing the F-35 and the current state of
| the CAF on "The Merge" podcast:
| https://youtu.be/kibWNHr9hdg
| 2OEH8eoCRo0 wrote:
| > the f-35 became a taboo and a meme
|
| Who benefited? I assumed that while criticism is healthy,
| some calls for cancelling the aircraft were from adversaries.
| Easiest way to defeat the plane is to get Congress to kill
| it.
| jessriedel wrote:
| > 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 wrote:
| I thought there's also the net they can use if, say, an
| aircraft lost tailhook
| jessriedel wrote:
| Sure but that's emergency only.
| euler_angles wrote:
| The 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 wrote:
| > 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.
| hbrav wrote:
| I think "wire only" means the hook catches while the wheels
| are still off the deck.
|
| I suppose that hard landing might have, in some ways,
| replicated the hard slam-down this would produce. Author,
| is that the case? Was the hard landing judged to have been
| a decent proxy for the wire-only arrestment?
| bronson wrote:
| Seems unlikely. One is slamming due to a heavy
| glideslope. Two is slamming due to a serious yank on the
| rear section. The airframe stresses and flight dynamics
| will be different.
| euler_angles wrote:
| Yeah, dynamics will be different, though caveat I am not
| a structures/loads engineer.
|
| I just don't think anyone had the risk appetite to chance
| a test asset against a very difficult to achieve test
| point.
| hef19898 wrote:
| It is also fair to assume the decision to not do
| additional testing of wire-only arrests was well analyzed
| by the respective engineering teams.
|
| Program management _does not_ take decisions like this by
| themselves.
| euler_angles wrote:
| Absolutely. We had a whole carrier suitability team full
| of people who lived and breathed this stuff. It was just
| my responsibility to make sure the aircraft
| instrumentation system got them the data they needed, at
| a high enough quality, to empower their analyses and
| decision making process.
| werrett wrote:
| Based solely on the above description -- wire-only is when
| you don't have wheels on deck, also slowing the craft down.
| jessriedel wrote:
| Got it, thx!
| ferfumarma wrote:
| > 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.)
|
| Kind of both: it was too dangerous to test a wider range of
| parameters, and the testing was therefore "successful"
| because it was crystal clear that going beyond the point
| where they had the problem would not be safe. So in this
| case "giving up"/stopping and "determining the limits of
| the landing envelope, were reached at the same time.
| bombcar wrote:
| I assume wire-only means no reverse thrust and no brakes.
| jessriedel wrote:
| No, aircraft land on carriers while applying full
| _forward_ thrust and (I am 99% sure) no wheel brakes. The
| idea is that if the wire fails to catch they "bolter",
| i.e., do a touch-and-go, so they can come around for
| another landing attempt. (If they stopped or reversed
| thrust and the wire didn't catch, they'd end up in the
| drink.)
|
| Based on other comments (or re-reading the authors
| comment carefully), it turns out that "wire only" mean
| that the wire catches before the wheels touch the ground.
| (This puts additional strain on the wire and airframe.)
| wolverine876 wrote:
| > no wheel brakes
|
| There are brakes on the wheels (that can slow a plane
| moving at flying speed)? That's a lot of force. I assumed
| the wheels merely prevent friction between the plane body
| and the deck, and the engines and control surfaces, and
| the wire, did the braking.
| ambichook wrote:
| "no wheel brakes" here means that the brakes aren't
| engaged, as stated so that if the aircraft misses the
| wires it can touch and go without drowning the pilot and
| destroying an $80m aircraft
| jessriedel wrote:
| (BTW, the twitter link on your blog is mistakenly going to
| twitter.com. I think you meant to link to your account:
| https://twitter.com/the_engi_nerd Cheers!)
| euler_angles wrote:
| Oh, thanks for the spot. Not sure why it's doing that...
| euler_angles wrote:
| Fixed
| torcete wrote:
| Since 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.
| superjan wrote:
| Well the ship gets a little nudge in the right direction for
| free.
| dieortin wrote:
| Or in the wrong direction, depending on the wind
| jcgrillo wrote:
| If those hybrid cars just had nuclear reactors they wouldn't
| need all that complex regeneration stuff, or an IC engine even
| :)
| scirner22 wrote:
| Awesome 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 wrote:
| What do you mean by "real world engineering"? That is, how does
| it differ in your perception?
| lchengify wrote:
| > 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 wrote:
| We 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 wrote:
| Honestly, makes sense. This is how much of finance runs their
| models.
| euler_angles wrote:
| We 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.
| HumblyTossed wrote:
| Isn't this over engineered aircraft supposed to VTOL?
| ranger207 wrote:
| There'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
| dralley wrote:
| Only 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 wrote:
| An 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 wrote:
| Your 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...
|
| 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 I
| believe that the USN didn't want to depend on conventional
| helicopters because of their relatively short range.
| euler_angles wrote:
| The CH-46 has been out of US Navy service for 20 years and
| Marine Corps service for almost 10, just as a program note.
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