[HN Gopher] Airfoil
___________________________________________________________________
Airfoil
Author : todsacerdoti
Score : 2431 points
Date : 2024-02-27 16:32 UTC (1 days ago)
(HTM) web link (ciechanow.ski)
(TXT) w3m dump (ciechanow.ski)
| Ancapistani wrote:
| I thought this was going to be about pipeline workflows... but
| then I saw it was Bartosz!
|
| I know what I'll be spending a stupid amount of time reading
| today :)
| Krastan wrote:
| Wake up babe, new Bartosz Ciechanowski just dropped
| Brajeshwar wrote:
| LOL! Yeah, so the next should be at least in 2025-Q1.
| ipqk wrote:
| If you like his work, here's his patreon:
| https://www.patreon.com/ciechanowski/
| diggan wrote:
| If you'd like to see more of their work, ranked by what HN
| thought was most interesting:
| https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
| frfl wrote:
| You can also see all-time top posts: https://hn.algolia.com/?
| dateRange=all&page=0&prefix=true&que...
|
| The mechanical watch post is 6th on the list
| flightster wrote:
| Dare I ask for the code?
| yeknoda wrote:
| It's right there. unminified and unobfuscated. just click save
| maxmcd wrote:
| Wow, I never realized this detail. What a wonderful thing.
| gembeMx wrote:
| You've been moving through life like an idiot
| Tmpod wrote:
| It's a bit sad this isn't the norn for education articles
| (and mostly everything else too).
|
| Bartosz's dedication and craftsmanship is really inspiring.
| pitzips wrote:
| IIRC you can view the source and it's all custom WebGL
| available for viewing.
| nuz wrote:
| Absolutely beautiful article and presentation
| mint2 wrote:
| Why does the first slider with the cube not say what the "one
| property" the slider controls is? Viscosity? Airspeed?
| H8crilA wrote:
| From the HTML: <div class="slider_viscosity"
| id="fdm_hero_sl0">(...)
| philote wrote:
| Also, it says "this substance", which I initially thought
| referred to the cube as it was just mentioned in the previous
| sentence. But I guess it's the "fluid".
| cryptopian wrote:
| You're kind of correct on both guesses. You can get that change
| by changing the viscosity OR the airspeed.
|
| He elaborates later on, but you're changing the Reynolds Number
| - a calculated value from the velocity, fluid density,
| viscosity and length. The cool thing about a Reynolds Number is
| that you get identical (in theory) airflow characteristics for
| two setups with the same Reynold's Number, even if e.g. the
| airspeed is different.
| Etheryte wrote:
| I think this is entirely intentional. All articles by Bartosz
| build up from simple basic principles and avoiding specific
| technical terms is a good way to onboard viewers of mixed
| backgrounds without scaring anyone off. Viscosity is actually
| mentioned for the first time only roughly three quarters into
| the whole thing.
| mint2 wrote:
| I think it would benefit by being broken up into modules and
| a little less simplified, at least naming the things.
| lobsterthief wrote:
| Maybe you learn best that way, but that doesn't mean
| everybody does
| bhasi wrote:
| His mechanical watch internals page is also equally amazing.
| RaoulP wrote:
| It is currently the 6th most popular post on HN:
|
| https://news.ycombinator.com/item?id=31261533
| globular-toast wrote:
| This looks incredible as usual. What puzzles me, though, is why
| some people find flying puzzling. At least the kind that we do,
| ie. helicopters and fixed-wing aircraft. It's easy to accept a
| fan works: just put your hand there and feel the draft. A wing is
| just like a linear fan pushing air down. It's completely
| intuitive to understand for me. The difficulties are just in
| making it practical and controllable. Conversely, many people
| don't seem concerned at all with bird or insect flight, which I
| find a lot harder to understand.
| pants2 wrote:
| Because an airplane doesn't move its wings like a bug or
| helicopter, and it's wings aren't shaped like fan blades. One
| might look at a plane and conclude that since the wings and
| engines are parallel to the ground, it must only move
| laterally.
| globular-toast wrote:
| Of course it moves its wings. That's what the runway is for.
| jahewson wrote:
| Rectilinear fan blades are shaped very similarly to aircraft
| wings. And it does only move laterally until the ailerons are
| moved away from being parallel with the ground.
| d--b wrote:
| I guess this is somewhat counter intuitive:
|
| https://www.youtube.com/watch?v=NBsvzMi9-f8
|
| So yeah, fans are puzzling too.
| convivialdingo wrote:
| If you watch it very slowly, the paper initially folds under
| the mouth and then it blows out straight.
|
| I'm guessing the initial puff creates a high pressure area on
| top of the paper, rolling it downward and back. Them after
| the puff has pushed the air away, there is now a low pressure
| zone on top of the paper which lifts it up as the air below
| is rushing upwards around the sides of the paper.
| stavros wrote:
| That seems like the Coanda effect more than anything.
| andrewla wrote:
| I think many of us were taught in school that airfoil shape was
| somehow magical -- that the fact that it was bowed more on the
| top was responsible for the fact that it worked.
|
| This is only partially true, though; a totally flat wing can
| also support flight. The shaped nature of the wing contributes
| to its efficiency (and other factors) but do not make other
| wing shapes incapable of supporting flight.
|
| The reality is that the Wright brothers' innovation was not the
| airfoil shape or even the lightweight motor. It was the control
| surfaces, to allow the operator to adjust the plane's attitude
| on the three axes of rotation, allowing actively stabilized
| flight.
|
| Paper airplanes and kites demonstrate all the same principles
| of heavier-than-air flight (the Wright brothers even had a kite
| version of their airframe they used for testing), despite the
| fact that they generally do not exhibit shaped airfoils.
| amenhotep wrote:
| The Wrights did use a rudder and "horizontal rudder" on the
| 1903 Flyer, but they were for some time determined to achieve
| roll control by warping the wings rather than using control
| surfaces, and were only forced to adopt ailerons as other
| pioneers began demonstrating how superior a paradigm that
| was. So they don't deserve _too_ much credit on that score!
| andrewla wrote:
| "Control surfaces" was more specific than I intended; what
| I meant was that their plane allowed them to control all
| three axes of rotation, and that was the innovation - that
| they could control pitch, yaw, and roll independently and
| that allowed them to have active stable flight.
|
| Without those controls, flight is basically impossible, and
| with them, you could use nearly any airfoil shape (modulo
| engine power, drag, and stall speed considerations) and
| achieve heavier-than-air flight.
| BWStearns wrote:
| Ailerons were really only invented when they were (and
| named in French) because the Wrights were extremely
| litigious, they sued Curtiss for using ailerons and
| basically destroyed American aviation for a decade allowing
| the French a temporary lead. This had an interesting
| cultural effect of lots of things becoming named in French
| across aviation (including things like the weather code for
| mist being "br" for brume to this day).
| p_l wrote:
| Because the explanation in school misses something like 90%
| of the detail replacing it with zero-explanation magical
| thinking.
|
| For example, yes, the air above the wing moves _faster_ than
| the air below the wing, and it 's related to shape of the
| airfoil.
|
| However, it has nothing to do with magical "air has longer to
| travel".
|
| It starts with how combining flows at the trailing edge of
| the airflow create a vortex which induces an opposite vortex
| around the wing, which is a bit counter-intuitive (but it has
| nothing on why swept wings work, which can be summarised for
| practical aircraft design purposes of "because if we
| calculate at an angle we get better values and reality is
| crying in the corner")
| djsavvy wrote:
| Growing up I got the "air has longer to travel on the top
| of the wing than the bottom" explanation, and it always
| smelled like BS. This is the first explanation of flight
| aerodynamics that really made sense to me -- incredible
| article as always from this author.
| plopz wrote:
| The whole air has longer to travel thing is obviously hand
| waving a lot of different properties that are all combining
| to get better efficiencies. For example, don't forget the
| coanda effect and its contributions to the shape of a wing.
| Luckily we can always just return to the navier-stokes
| equations to help us out.
| kqr wrote:
| > It starts with how combining flows at the trailing edge
| of the airflow create a vortex which induces an opposite
| vortex around the wing,
|
| Wait, I was under the impression this Cutta circulation was
| a computational simplification and the "real" reason were
| the pressure differences as explained in this submission.
| What am I missing?
| p_l wrote:
| Essentially the work in the article shows the harder to
| grok, but still half of the whole equation, with only one
| small mention of an effect that points to the wider
| environment. Essentially, this is a more close-in view of
| the airfoil without consideration of the wider flow
| around.
|
| One comment already mentioned how position of flaps could
| have visible effect on pressure sensors _in front of the
| plane_ , and this is slightly mentioned in how the
| pressure created by front of the air foil has an impact
| on air "at a distance" from the airfoil.
|
| The vortices created around the airfoil result in
| significant change of flows, which especially at low
| speeds provides big chunk of the pressure changes
| necessary for the creation of lift, with the effect IIRC
| getting lower as you go faster, with transsonic regime
| breaking it - because that's when the resulting speeds go
| beyond speed of sound at given pressure in the air, which
| in very simplified way means that air can't move towards
| front of aircraft anymore in those areas, breaking all
| sorts of flows you depend on at lower speeds.
| carabiner wrote:
| Without their wind tunnel optimized airfoils, the wright
| flyer wouldn't have flown. Without the controls, it wouldn't
| have flown. Without the high power to weight ratio motor, it
| wouldn't have flown. Which was the most critical?
| tekla wrote:
| This is an incredible (over)simplification of flying.
|
| We still don't have a very good understanding of turbulence.
|
| Navier Stokes equations still make Aerospace engineers drink.
|
| Yes its stupid simple if you care about the simplest of
| analogies, but if you try to understand it, there are reasons
| why 80% of people drop out.
| jebarker wrote:
| I think you mean incredible oversimplification
| NovemberWhiskey wrote:
| Surely it's a less impressive result that something powered by
| mains electricity can move the air in a draft than that a
| multi-hundred-ton aircraft can fly over the highest mountains.
|
| It's the size of the aerodynamic forces and the complexity of
| the physical mechanisms that create them that many people have
| trouble with. In particular: intuitions can be pretty wrong,
| most simplified explanations are wrong under simple
| experiments, and the problems exhibit scale variance that is
| unfamiliar (e.g. Reynolds number).
|
| One time I was working on air data computer for a transonic
| aircraft that could fly up to about M0.95 - during flight test,
| an air data probe mounted on a nose boom was used to supply
| impact and static pressures, angle of attack and sideslip etc.
| for various air data calculations like airspeed and altitude.
|
| I was fascinated that there was a term in the calculation that
| related to the aircraft flap position - what's happening way
| out on the trailing edge of the wing actually has a meaningful
| effect of pressures measured on a boom out the front of the
| nose during certain regimes of flight.
| globular-toast wrote:
| It's just a matter of scale. What's impressive to me with the
| big aircraft is that we can organise thousands(?) of people
| to build something that big. But when it comes to the
| _principle_ of flying it 's just a bigger version of the fan.
| If you were to say they used the same amount of energy as a
| fan then _that_ would be impressive. But they don 't, they
| burn tons of fossil fuels. Geese can fly over the highest
| mountains too and all they eat is grass.
| NovemberWhiskey wrote:
| > _it 's just a bigger version of the fan_
|
| I mean, actually, it isn't - that's the whole point about
| scale variance and Reynolds number and why wings that work
| for insects are not the wings that work for jumbo jets.
| risenshinetech wrote:
| Who are these mysterious people you're interacting with who are
| concerned with (but don't understand) the physics of flight,
| but who are also not concerned with bird or insect flight?
| nuz wrote:
| Blows my mind that my computer isn't even turning on its fans
| considering how many shaders are running in this thing.
| naikrovek wrote:
| They're simple shaders and it's amazing what a computer can do
| billions of times per second.
| baobabKoodaa wrote:
| Yeah, I mean come on, we're not rendering something hard and
| expensive to compute, like a React website that has to list
| items in a shopping cart.
| nuz wrote:
| Personally all the fluid simulation shaders I've written
| usually makes my fan go off, and I'm counting a few of
| those here so that's impressive in my eyes.
| baobabKoodaa wrote:
| Yeah. It's impressive to my eyes as well. I was just
| trying to make a joke about how normal websites need 100%
| of your CPU to render some text and images, and here's
| this guy doing multiple fluid simulations on a web page
| written in custom WebGL and it runs on a potato.
| efnx wrote:
| I think they pause when they scroll out of view?
| jakebasile wrote:
| I'm on Ubuntu and Edge (v122.0.2365.59) could barely render the
| page. Chrome (v122.0.6261.94) worked just fine, though. I don't
| know enough about browsers and GPUs to debug why that is, but I
| checked (edge|chrome)://gpu and nothing stood out as
| appreciably different.
|
| Edit: interestingly, it seems to only be the first animation.
| If I scroll it out of view the others all seem to render fine.
| fisherjeff wrote:
| What? A ciechanow.ski airfoil explainer? But I have things to do
| today!
| tandr wrote:
| It is too late for us to be saved, my friend, way too late...
| pcurve wrote:
| This man to me is a modern day Da Vinci of the Web
| anibalin wrote:
| It's truly impressive. the amount of time and dedication its
| uncanny.
| flokie wrote:
| His work is always a good reminder the open web is still an
| amazing place!
| 1970-01-01 wrote:
| Something that was never clear to me at this level of detail is
| how a tailwind enables an airplane to move faster. In other
| words, if the airflow is coming from behind, the lift equation
| should fall apart and the airplane should fall out of the sky.
|
| https://www.skytough.com/post/tailwinds-make-plane-faster
| CrazyStat wrote:
| The plane is just up in the air moving relative to the air
| around it, it doesn't care how the air it's in is moving
| relative to the ground.
|
| A tail wind is just saying that the air is moving in a certain
| direction with respect to the ground (the same direction the
| plane is flying). The plane doesn't give a shit about that.
| 1970-01-01 wrote:
| Yes that makes sense at a high level, but there must be a
| point of transition between calm air and a jet stream that
| makes the wings useless to the airplane for at least a few
| seconds.
| bityard wrote:
| Indeed it does, that's effectively what turbulence is.
| CrazyStat wrote:
| If you took a plane flying in still air and magically,
| instantaneously replaced all the air around it with a tail
| wind equal to its velocity then yes the plane would stall
| and fall out of the sky.
|
| Fortunately that kind of instantaneous change doesn't
| happen in real life.
| DrSAR wrote:
| GO AROUND, WINDSHEAR AHEAD!
| fh973 wrote:
| It's relevant in practice when landing against head wind.
| You need to have extra speed to not stall when you enter
| the slower air near ground.
| rockostrich wrote:
| Do you mean landing with a tailwind? A headwind should
| allow the plane to create the same amount of lift it
| needs to avoid stalling at lower ground speeds.
| Toutouxc wrote:
| Yes, that's correct, but the headwind stops being so
| headwind-y near the ground, so your plane needs to go a
| bit faster to compensate for the loss of headwind-ness in
| the seconds before touchdown.
| The5thElephant wrote:
| On the flip side you also get ground-effect when you are
| low to the ground where the high-pressure underneath the
| wing gets trapped against the ground creating a cushion
| of pressure increasing lift.
| bouchard wrote:
| Which can be a bit of a challenge when trying to land,
| especially for aerodynamically efficient aircraft.
| lanternfish wrote:
| Presumably the plane would accelerate as it climbed through
| the velocity gradient, never falling to a point of negative
| air-relative airspeed.
| rockostrich wrote:
| Yes, the wings are useless once the air is moving close to
| the speed of the plane. Thankfully, we have jet engines
| that help planes move a lot faster than the 100-200 knots
| that jet streams can reach. They'll still affect the flight
| but only temporarily.
| lovecg wrote:
| These sudden changes do indeed happen in stormy weather, as
| adjacent layers of air can move with different velocities
| relative to the ground (the technical term is "wind
| shear"). If an airplane climbs or descends through those it
| will look like your speed (relative to air) is suddenly
| increased or decreased by some amount and you would have to
| compensate. It's also a bigger problem for large, heavy
| airplanes as you have more work to do to accelerate for a
| given amount of speed loss.
|
| Jet stream boundary is usually not this sharp, and the
| airplane would fly much faster than the difference anyway.
| mechhacker wrote:
| It also changes a lot for sailboats, and even more for faster
| sailing craft (windsurfers, etc.).
|
| You can feel a much stronger pressure in the sail when moving
| towards the wind on a fast windsurfer/windfoil as you can do
| 15-20kts 45deg towards the wind, giving you an apparent wind
| that is 10-14kts stronger than the true wind.
|
| On the same craft, going away/downwind, you will feel the
| apparent wind at a similar angle 10-14kts less. In fact,
| because of the change in drag and forces, you'll probably be
| going faster and feel even less wind on the downwind leg.
|
| When you turn, this can be a big benefit for going downwind
| (jibing) as at some point the sail feels zero apparent wind
| (your motion cancelling out the true wind), feels very light
| in your hand, and easy to rotate to face the other way. Even
| knowing the physics of it, the timing and execution is still
| something that takes a lot of practice...especially on big
| race gear with a 9.0m2 sail.
| barbegal wrote:
| Yes airplanes have to travel faster (in terms of ground speed)
| to not stall. This is why head winds are preferred for landings
| and take offs as it allows ground speed to be lower. But during
| cruise you want a tailwind to reduce the amount of drag for a
| given ground speed.
| fouronnes3 wrote:
| Planes move through the air, and _relative_ to the air mass.
| ryandrake wrote:
| Airplanes are always traveling forward relative to the wind, at
| some angle of attack. Tailwinds don't work by blowing against
| the airplane's surface and pushing it forward. Since the
| airplanes are themselves traveling at, say, N kt forward
| relative to the wind, then if they are inside a 10 kt tailwind,
| they'll be doing N+10 kt over the ground, if they are inside a
| 50 kt tailwind, they'll be doing N+50 kt over the ground. If
| they are inside a 25 kt _head_ wind, the'll be doing N-25 kt
| over the ground.
| rockostrich wrote:
| The bottleneck when it comes to a plane going faster is drag
| which increases with the square of velocity relative to the
| air. More drag means the plane has to consume more fuel to stay
| at its current velocity. So if a plane normally goes 600 mph
| with no wind then a 100 mph tailwind will allow that plane to
| go 700 mph relative to the ground to experience the same amount
| of drag as if it were flying at 600 mph on a day with no wind.
| jahewson wrote:
| It works by reducing the amount of CSS the plane needs to
| carry.
| lovecg wrote:
| Our intuitive experience with wind on the ground is wrong. Next
| time it's windy outside imagine the entire volume of air
| stretching out for miles and miles moving across with the wind
| speed, we're just standing at the bottom of this vast air
| ocean. It will blow your mind and you'll think about wind
| differently from then on. So with that in mind, once the
| airplane is in the air, it doesn't "know" if there's a headwind
| or a tailwind at all, unless you have a way to reference the
| ground somehow (for example, with a GPS) - just like a boat
| doesn't "know" it's carried by a current downstream. If you are
| still on the ground, it is very possible that the tailwind is
| strong enough for you to not be able to takeoff in the
| available runway - but then you would go in the opposite
| direction or more likely sit the storm out :)
| klabb3 wrote:
| I've noticed this effect while diving. When you're in a
| current, you're basically the same density so you're moving
| with the water. In mid-water with poor visibility, this is
| really freaky, because you have no way of telling in what
| direction you're moving, and how fast. If you "forget" your
| orientation, you can't really recover it. Thankfully, you
| always have highly accurate depth gauge, but as for lateral
| movement, it's an eerie feeling. You could just pop up
| anywhere.
| dclowd9901 wrote:
| Yeah, I wish meteorologists explained this concept better to
| the general public, since they're basically poised for it.
| One day I was just wondering where wind _started_ from, and
| started digging deep into the topic, but essentially we're
| all just standing on the bottom of a roiling ocean floor that
| is very sensitive to heat changes from the sun.
| colechristensen wrote:
| This is a kind of relativity thing.
|
| The only connection a plane has to the universe is the air
| around it. It simply does not know or care what the ground is
| doing until the ground is quite close.
|
| A small plane in a very high wind is perfectly happy having a
| "backward" ground track.
|
| Same thing as if you were trying to swim upstream in a fast
| river. How fast you move through the water doesn't have
| anything to do with how fast the water is moving across the
| land.
| BWStearns wrote:
| It's like swimming in a stream. Even if you did nothing you
| would move basically at the rate that the water is moving.
|
| Lift only comes from the interaction of the air and the wing,
| so if there's zero relative motion then you will fall out of
| the sky, regardless of if you have a 200 knot groundspeed.
|
| This also means that, if the wind at altitude is above your
| plane's stall speed, you can hover in place by flying straight
| into the wind! (example here:
| https://www.youtube.com/watch?v=n_e6ijREScE)
|
| Similarly, if you are in a packet of air that is moving at 200
| knots, the fact that you are moving at 500 knots indicated
| airspeed does not mean you are flying supersonic from an
| aerodynamic perspective, despite having a groundspeed of 700
| knots.
| danmaz74 wrote:
| Both drag and lift depend on the speed of the airplane relative
| to the wind, not relative to the ground. So, if the maximum
| efficiency dictates that the airplane should travel at speed X
| _relative to the wind_ , and the wind is flowing at speed Y in
| the same direction as the airplane needs to travel, then the
| airplane, flying at maximum efficiency, will be travelling at
| speed X+Y relative to the ground.
| porphyra wrote:
| It's pretty interesting that many airfoils used in aircraft
| design were derived by NACA in the 1920s and 1930s [1]. You'd
| think that with modern computer software it would be possible to
| design better airfoils, but apparently, those shapes have already
| been mathematically perfected by hand and by experiment. So
| nowadays if you want to design a plane you can just look up the
| desired NACA airfoil from a table based on the speed, air
| pressure, etc that you require.
|
| [1] https://en.wikipedia.org/wiki/NACA_airfoil
| colechristensen wrote:
| Eh, it's more like you can get to 90% of where you want to be
| with the 100 year old airfoils (though several of the other
| series are quite a bit newer).
|
| https://aviation.stackexchange.com/questions/20798/are-naca-...
|
| >You'd think that with modern computer software it would be
| possible to design better airfoils, but apparently, those
| shapes have already been mathematically perfected by hand and
| by experiment.
|
| No, modern computer software indeed does better, but there's
| not a whole lot of room to do better, small changes to bump
| performance a percentage point or two. These are optimizations
| which can be (and are sometimes) skipped for many commercial
| projects.
| g129774 wrote:
| "better" airfoils are used in experimental craft design. for
| example mark drela wrote and used xfoil to design wings for
| mit's project daedalus, a human powered long distance flight
| aircraft. this is the case where, like sibling commenter
| stated, you need that extra % to get better performance
| characteristics. you can still run xfoil, it's a delightfully
| oldschol fortran program.
| petsfed wrote:
| I have a friend whose PhD is in computational flow dynamics,
| as applied to airfoil design. He works almost exclusively in
| fortran (which is wild to me, for someone under 35, but I
| guess its the "industry" standard). I just asked him about
| xfoil and he observed that there are more modern programs for
| (as he put it) more "realistic/complex" designs, but said it
| was a good starting place.
| g129774 wrote:
| oh i'm sure state of the art has advanced since then. i
| have the necessary physics background, but it's not
| otherwise my domain: i once used xfoil to design an airfoil
| for an autonomous model glider as a hackerspace project
| back when i had free time for things like that many years
| ago. the glider was also loaded into x-plane to develop and
| test the autonomous part. so whenever various experimental
| aircraft projects popup, i'm likely to look into them, and
| then also notice the peculiar foils they use.
| aredox wrote:
| Because Fortran was the industry standard for any heavy
| scientific calculation (like aerodynamics or nuclear
| bombs), the Fortran compiler has been optimised to death...
| And thus Fortran is still the industry standard.
| KWxIUElW8Xt0tD9 wrote:
| FORTRAN is easier to optimize than something like C so is
| much used for numerical computation
| namirez wrote:
| It really depends. Up until the 90s Fortran was completely
| dominant. These days a lot of people have moved to C++.
| Important open source codes such as OpenFOAM and SU2 are in
| c++.
| bouchard wrote:
| Not really, they're a nice first step though, or if you require
| something "good enough".
| jayyhu wrote:
| NACA and the other published airfoils[1] are generally a good
| starting point for hobbyist/RC folks. However if you want to
| eke out that last 5% bit of performance (ie. you are a
| company/institution), you would start with one of the above
| airfoils and optimize them to fit your flight envelope &
| mission profile. Here's a neat video of optimizing a round
| profile into an airfoil optimized for supersonic speeds [2].
|
| [1] http://airfoiltools.com [2]
| https://www.youtube.com/watch?v=FHYTBguMfWc
| namirez wrote:
| Not quite true! Modern airplanes are way more complex. First of
| all, all modern airplanes have supercritical airfoils which go
| back to the 60s and 70s. Secondly, the airfoil of the wing root
| is typically different than the wing tip. Finally, new
| composite wings are adaptive during flight. They change their
| shape slightly to maximize efficiency.
| H8crilA wrote:
| Case in point would be modern gliders (sailplanes). One
| simple parameter that describes their aerodynamic performance
| is the maximum achievable Lift/Drag ratio, and that
| dimension-less ratio has climbed from ~30 in the 1960s to as
| high as 75 today. That means modern gliders can, using the
| same altitude/energy, go over 2 times further horizontally.
| The L/D is not the ultimate decider of performance but it is
| quite representative of the aerodynamic performance
| improvements.
|
| BTW, all lift based flying objects have an L/D ratio (which
| depends mainly on the airspeed), this includes birds, fighter
| jets, commercial airliners; and the discrepancies can be
| pretty interesting. For example if one looks at the L/D of
| the Concorde vs a subsonic jet it becomes clear why it was so
| damn expensive to operate. Or why the U-2 looks like a glider
| :). I cannot find any aerodynamic performance data on any
| famous long endurance (>24h) unmanned drone, but I bet it's
| rather high as well.
| dmoy wrote:
| > Concorde
|
| Another good example is the space shuttle. It does actually
| glide back down. But it glides like a brick at first (1:1
| during its initial braking into the atmosphere), and then
| like a less dense brick (2:1 while it's still supersonic),
| and then like a brick with shitty wings (a whopping 4:1 or
| whatever on final approach). Which is about what the
| Concorde is during landing, 4:1, yea.
|
| Pretty crazy stuff
|
| (Obviously the space shuttle was a tradeoff for, you know,
| getting it into orbit via rocket)
| travisjungroth wrote:
| Your numbers are right but your analogies are misleading.
| I get "glides like a brick" is hyperbole, but you've
| added enough detail I can see people taking it seriously.
|
| A brick's L/D is much worse than 1:1. I'm seeing people
| say 1:10 online, but I can't find a source and I think
| that's incredibly high. A real brick is going to tumble
| and essentially not make any lift.
|
| A less dense brick will have the same L/D. L/D is about
| the shape, not the mass.
| taneq wrote:
| I'm trying to get my head around the L/D being
| independent of mass. Does lift scale with airspeed at the
| same rate as drag? Or is L/D only considering lift-
| induced drag (whatever the term is) and not total drag
| including parasitic drag?
| teraflop wrote:
| Roughly speaking, both lift and drag are proportional to
| v^2 for a given geometry.
|
| _Neither_ lift nor drag has anything to do with mass.
| They are entirely determined by the _surface_ of the
| object, and are not affected at all by the interior
| properties, including density.
| travisjungroth wrote:
| L/D changes with angle of attack. You can have a
| different airspeed at the same angle of attack and the
| ratio does stay the same. I think the Wikipedia page
| gives good descriptions.
|
| Something a bit misleading done generally is aircraft
| don't have one L/D, they have many, depending on angle of
| attack. When you see one number, it's usually the best
| one.
| harshreality wrote:
| Aren't they comparing high-supersonic to supersonic to
| subsonic?
|
| I thought the point was that aerodynamics change from one
| domain to the next as shockwaves cause flow separation or
| eddies on or behind surfaces.
| kqr wrote:
| The way I've had it described is that when two objects of
| the same shape pitch for optimal glide (i.e. highest L/D)
| then the heavier one will reach the ground sooner (go
| faster), but both will take the exact same path and land
| the same distance away. In other words, same L/D.
|
| This is not the explanation you are looking for, but "aha
| the heavier object takes the same path but drops faster"
| was what made me okay with L/D not depending on weight.
| spenczar5 wrote:
| Space Shuttle pilots themselves referred to it as "The
| Flying Brick," I think that is mostly what they were
| referencing. It was a term of endearment :)
| dmoy wrote:
| Yea sorry, this was it. I didn't mean it literally has
| the glide ratio of a brick
|
| I mean it looks like a brick and it flies
| techdragon wrote:
| Despite knowing about its nickname... I found myself
| picturing a paraphrasing of the classic physicist's
| "spherical cow in a vacuum"...
|
| "Steerable brick in an atmosphere"... or the slightly
| more accurate "orientable brick in an atmospheric reentry
| regime"...
| dmoy wrote:
| If you want a _real_ "orientable brick in atmospheric
| reentry regime", check out how they steered the Apollo
| capsules back down. Kinda bonkers, but worked - they made
| it asymmetric and then rotated it depending on if they
| wanted to go down faster, slower, left, or right.
| Obviously it can't fly, and its glide ratio is actually
| brick-like unlike my facetious description of the
| shuttle. But it worked enough.
|
| Kinda like a single control plane missile that spins
| (rolling airframe?), except... without the control plane
| lol.
| kqr wrote:
| I guess you get maximum L/D out of a brick by giving it
| some serious backspin (which is a stable configuration so
| it might be able to maintain it on the way down) to set
| up the lifting circulation around it. But would this
| count?
| sandworm101 wrote:
| >> tumble and essentially not make any lift
|
| Tumbling itself can produce lift. The difference in drag
| between one side and the other can result in net pressure
| differences for a moving object. This is the basis of
| many baseball pitches. Spin a brick fast enough and it
| might just be able to climb if thrown horizontally.
|
| If static airfoils are complicated, try looking into
| airfoils that rotate or otherwise move in relation to
| airflows. A Russian engineer once said that all problems
| in aerospace are placed on the tip of every helicopter
| blade.
| petsfed wrote:
| The Magnus effect is super confusing to think about.
| Basically, to provide lift, the brick or ball or whatever
| would need to be "rolling" backards, like a wheel. In
| baseball, e.g. fastballs are usually thrown in such a way
| as to "roll" backwards, which causes them to climb.
| Curveballs are accomplished via topspin. Sinkers roll
| forward. You can even tune this behavior by making the
| surface of inconsistently "sticky" to the air, so flow of
| air is more or less affected by the objects rotation.
| This is why licking the baseball is against the rules.
|
| Curiously, the rotation can also lend the ball's path
| greater stability against changing air currents/densities
| and crosswinds. Knuckleballs are famously hard to throw
| because they have very little spin, but they are also
| notoriously hard to hit because the trajectory is so
| subject to the vagaries of airflow between pitcher and
| batter.
|
| This is to say nothing about when the axis of rotation is
| predominantly parallel to the direction of travel (e.g.
| rifle bullets and American footballs), where the Magnus
| effect effects the rotating objects ability to continue
| to rotate parallel to the direction of travel. Get it
| right and the spin makes the path more stable, but get it
| wrong, it becomes _less_ stable. The hows and whys of
| that are beyond my understanding of fluid dynamics, but
| its fun to think about how complicated it can get.
|
| edit: got my spin directions confused
| Lance_ET_Compte wrote:
| I saw the space shuttle land once. From my perspective,
| it seemed to drop like a rock (fast!) and then as it got
| closer to the ground, it started "flying". I'd never seen
| anything like it.
| DiggyJohnson wrote:
| For whatever reason the way I think about this phenomenon
| is like autorotation in a rotary craft.
| hanche wrote:
| The flare-out is really difficult to get right, from what
| I've read. As soon as you start leveling off, air speed
| is going to drop really fast, and you have very little
| time to get that bugger on the ground before you get in a
| stall. They used to practice using a modified jet, flying
| from high altitude to a landing with thrust reversers
| engaged all the way!
| namirez wrote:
| The case with gliders and U2 and the max L/D is due to the
| wing aspect ratio (look up the formula for drag polar).
| Modern aircraft have much higher L/D because they have long
| skinny wings and these wings are possible because we moved
| from aluminum to carbon reinforced composites.
| CPLX wrote:
| The big variation now though is that the airfoil shape varies
| quite a bit from one end of the wing to the other.
| jabl wrote:
| Different airfoil shapes for the root and tip were common
| already in WWII era planes.
| jameshart wrote:
| NACA airfoils aren't so much a numbered set of standard, tested
| designs as a useful set of mathematical curve formulae for
| making airfoil-like shapes, and describing them using
| parameters.
|
| NACA published empirically determined wind tunnel performance
| numbers for selected parameters, which was useful research but
| not a declaration of 'these are the good values, you should
| only use these'.
|
| It's a bit like saying all satellites follow TLE orbits derived
| by NASA/NORAD in the 1950s - they do, but only because that's
| just a standard way of writing down the orbital elements that
| describe a particular ellipse, not a catalog of 'known good'
| orbits.
| KWxIUElW8Xt0tD9 wrote:
| my recollection was that the P51 wing used a NACA airfoil and
| it had low drag properties not commonplace at the time
| roeles wrote:
| For gliders the naca airfoils have been abandoned around 1970,
| when the first glasfiber composite gliders were made. We mostly
| use airfoils from German professor Wortmann (FX) , Quabeck (HQ)
| or Boermans (DU). The naca airfoils are still used in wind
| turbines though.
| atlas_hugged wrote:
| I swear Bartosz' posts deserve to be pinned to the top of hacker
| news on release day at this point.
| civil_engineer wrote:
| The wings of an airplane in level flight direct air downward with
| a force equal to the airplane's weight. If one were to build a
| large scale on the ground, as an airplane flies over it, the
| scale would register the weight of the airplane. The wings act
| like a scoop forcing air downward behind the wing. At least
| that's the way I think about it when I'm out flying around in my
| Cessna.
| WanderPanda wrote:
| That's my mental model as well. The incompressible fluid-based
| explanations never made much sense to me
| ivanjermakov wrote:
| Although it is a nice mental model, that's not quite true.
|
| > The wings act like a scoop forcing air downward behind the
| wing
|
| Only bottom side of the wing acts as a scoop, creating positive
| pressure. Upper side, in opposite, creates negative pressure
| which "sucks" the plane into it, creating additional lift.
|
| It surprised me how much lift is coming from the negative
| pressure - about a half:
| https://aviation.stackexchange.com/a/16202
| danmaz74 wrote:
| Actually, it _is_ quite true. Gravity is exercising on the
| airplane a force F equal to the weight of the plane, towards
| the ground. For the airplane to stay at the same height, air
| needs to exercise a force that is equal and opposite to that
| of gravity. For an airplane buoyancy is negligible, so the
| force comes from accelerating enough air towards the ground
| so that F = M*A when M is the mass of air being accelerated,
| and A the (average) acceleration.
|
| Notice that this isn't a separate effect from the effect of
| pressure - it's just a different way of seeing the same
| effect. The wing is accelerating the air both upwards and
| downwards, but because the pressure is higher below the wing
| than it is above it, more air is accelerated down than it is
| accelerated up - which lifts the airplane, but makes the air
| go down.
| topaz0 wrote:
| GP was not disputing the redirection of flow or the
| magnitude of force/air momentum change. They were just
| saying that not all of this is because of the "scoop"
| effect from the bottom of the wing: a significant part of
| the redirection also comes from the low pressure above the
| wing (at least in practical cases).
| jameshart wrote:
| Except that negative pressure is not a thing. Air molecules
| are not grabbing the wings and pulling them up - they are
| just not pushing down on the top as much as the ones
| underneath are pushing upwards.
| Tyrannosaur wrote:
| Negative pressure is not a thing, except you just described
| it.
|
| If you take the _difference_ between the pressures above
| the wing and below the wing, you get a negative number.
|
| A thing not existing absolutely can still exist relatively.
| jameshart wrote:
| That's just a pressure differential, and not what the OP
| meant by 'negative pressure'. _100%_ of the lift force on
| a wing is attributable to the pressure differential
| across it, after all.
|
| They (or their stackexchange source at least) are - like
| the referenced article and as is commonly done in aero
| engineering - subtracting out ambient pressure as a
| reference pressure, and then viewing pressure above the
| wing as 'negative' and pressure below as 'positive'. It's
| a convenient choice to make, for various reasons, but it
| is essentially an _arbitrary_ one.
|
| The problem comes when you then go on, like OP did, to
| come across statements like "how much lift is coming from
| the negative pressure - about a half"
|
| Now, since in analyzing the pressure we have subtracted
| the reference pressure and made a zero point in between
| the low pressure value above the wing and the high
| pressure value below it, it actually shouldn't surprise
| us at all that 'about half' of the lift seems to be
| attributed to the positive pressure below the wing, and
| half to the negative pressure above the wing.
|
| This is just saying that half the lift on the wing is
| attributable to the first half of the pressure
| differential across the wing, and about half the lift
| attributable to the other half.
|
| One of the problems of using a relative pressure and
| thinking about negative air pressure is that it gives the
| impression that negative air pressure, like positive air
| pressure, can grow arbitrarily large. It can't. You can't
| have a negative air pressure lower than negative ambient
| air pressure, because the absolute air pressure cannot go
| below zero.
|
| But what you're talking about is a relative pressure
| _differential_. We can have an arbitrarily large negative
| pressure differential because we can have an arbitrarily
| high pressure on one side of it.
| topaz0 wrote:
| It's not arbitrary: negative gauge pressure above the
| wing means that (by definition) there is a pressure
| gradient increasing away from the wing (because the
| absolute pressure far from the wing is ambient pressure),
| so the net force on the air there is downward.
|
| > made a zero point between ... shouldn't surprise us
|
| Whether or not you are surprised is immaterial, but it is
| not guaranteed a priori -- you could get a net upward
| force with ambient pressure above the wing and positive
| pressure below or with ambient pressure below the wing
| and negative pressure above (meaning gauge pressure,
| relative to the ambient pressure distant from the wing,
| to be clear). The person who started this thread seemed
| to be implying that the former was a good mental model,
| and the person you replied to was just saying that in
| fact for practical wing designs it is somewhere in
| between.
|
| FWIW it is very common to talk about positive and
| negative gauge pressure. Some people may say that without
| understanding what is going on, but it is a mistake to
| assume that they don't understand just because they use
| that language.
| bloppe wrote:
| Ya, I was hoping for more nuance related to this. I'm sure the
| air foils generate lift, but atmospheric pressure at cruising
| altitude is ~4psi, and the pressure differential across the
| foil must be only a tiny fraction of that. According to my
| understanding of Bernoulli's principle, you'd have to quadruple
| the speed to cut the pressure in half, and I can't imagine the
| top air traveling _that_ much faster than the bottom air.
|
| Yet a 747 can produce 850000 pounds of lift with only 729000
| square inches of wing? Feels like a very incomplete description
| at best
| p_l wrote:
| The airfoil shape causes formation of vortex around the wing,
| which ridiculously changes the relative speeds and pressures
| involved. At low pressure you compensate with speed, which is
| squared in lift equation.
| p_l wrote:
| ... I'm honestly surprised it's possible to get PPL(A) without
| learning about wing vortices responsible for lift generation.
|
| In order to use "scoop" approach for lift, you need to have
| either _very low_ wing loading (think paper airplanes) or very
| high speeds (above transsonic range).
| Rapzid wrote:
| > If one were to build a large scale on the ground, as an
| airplane flies over it, the scale would register the weight of
| the airplane
|
| No, it wouldn't.
|
| I think the article does a pretty good job building a more
| complete understanding than the simplistic "deflection" mental
| model.
| turtledragonfly wrote:
| I think what they were saying is that from a pure "Newton's
| 3rd law" standpoint, if the plane has an upwards force, then
| the air has a corresponding downward force, which must go
| somewhere. Yes, it is spread out and complicated and
| turbulent, etc, but ultimately must balance out.
|
| If we could somehow "draw a box around" the entire plane+air
| system, then the plane's upward lift will create a
| corresponding downward force on the box, one way or another.
|
| So, in the broad sense that you push the earth away from you
| when you jump, the plane also pushes the earth away from it
| when it flies (mediated by a bunch of fluid dynamics).
|
| Or, classic example: if a (sealed) truck full of birds is
| jostled so that they start flying, does the truck weigh less?
| [1]
|
| [1] https://www.youtube.com/watch?v=lVeP6oqH-Qo&t=35s
| Rapzid wrote:
| It's wrong though. A large, hypothetical scale under the
| plane would not register the weight of the plane as it
| flies over. And not _just_ because diffusion but that being
| one of many reasons.
| somat wrote:
| The simple newtonian deflection model is correct however, As
| you engineer your deflector to have the least possible drag
| the airfoil shape naturally falls out.
|
| Actually that is a bit of a lie, the airfoil shape only falls
| out due to a third implied force that needs to be accounted
| for. the wing needs to be strong enough to hold itself up. if
| you had infinitely strong materials the deflector shape that
| would fall out would be like a slightly bent piece of paper.
|
| A clarification note on fluids: you are deflecting fluids,
| and everything this implies. just because I say newtonian
| deflection don't think I mean billiards balls, or if it has
| to be billiard balls think trillions of them simultaneously
| Rapzid wrote:
| https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/
| a...
| somat wrote:
| I did not say reflector as implied by that link but
| deflector, a thing put in the fluidstream to move it
| somewhere else. airplanes lift because you are moving air
| down. People get hung up about the convex side of the
| airfoil but what else is the fluid going to do, stay a
| vacuum? it is going to move in the way the deflector
| shaped, adding to(actually providing most of) the
| downward flow. There is a lot of engineering that goes
| into it but at the end of the day an airfoil is the shape
| that moves enough enough air downward with the least
| drag. The only reason it is a thick teardrop shape is it
| has to be strong enough to support itself and the
| airplane. otherwise the ideal shape would be super thin
| shaped like the upper surface of the wing bending
| slightly from the cord(aspect directly into the stream)
| to the trailing edge(a few degrees of slope).
| Rapzid wrote:
| IDK man, what I said was correct; it's wrong. GLHF.
| diimdeep wrote:
| This is the future of education. Very approachable and seems to
| target the most common denominator of knowledgeable people that
| out there.
|
| I wonder will there be articles in the future with more math and
| code snippets?
| elwell wrote:
| The future of education is as an entertainment. There will be
| no need to educate oneself in the AI future (except for merely
| egotistical reasons?).
| cloogshicer wrote:
| Imagine a world in which _all_ education was this level of
| quality.
|
| Imagine how much more you'd know, be able to do and understand.
|
| I really wish good education was valued more highly in society.
| pomian wrote:
| Yes, that. Call it enhanced learning? For instance, add Dan
| Carlin - Hardcore History podcasts for your history lectures.
| If everyone listened to those podcasts, then all you would need
| is a good teacher/professor to discuss what you learned - and
| there is 'so much' learned from any one of his episodes.
| password54321 wrote:
| While this is good quality, this is not replacement for real
| education. Real education involves sweat and hard work, not
| just consumption. This is somewhere between education and
| entertainment.
| cloogshicer wrote:
| What's missing for it to be real education? Genuine question
| :)
| password54321 wrote:
| >Real education involves sweat and hard work, not just
| consumption.
|
| Anything that fits the above as was stated :)
| justinzollars wrote:
| I'm taking a sailing class, and learned sails in addition to
| keels utilize this concept.
| colechristensen wrote:
| For anyone really interested, this is the authoritative reference
| for NACA, etc. airfoils.
|
| _Theory of Wing Sections_ by Abbott and von Doenhoff (1959)
|
| https://www.amazon.com/Theory-Wing-Sections-Aeronautical-Eng...
| simple10 wrote:
| The javascript code is not minified and is easy to follow.
| Beautifully done.
|
| https://ciechanow.ski/js/base.js
|
| https://ciechanow.ski/js/airfoil.js
| caditinpiscinam wrote:
| I've never used webgl -- what's its advantage over normal 2d
| canvas drawing for a project like this?
| modeless wrote:
| Speed. Drawing thousands of objects (such as the blades of
| grass or air molecules) with 2D canvas will be very slow.
| WebGL allows all drawing to be offloaded to the GPU, which
| can draw thousands of objects in parallel given a single CPU
| command. 2D canvas also doesn't provide any 3D primitives (as
| the name would suggest), while WebGL natively supports
| rasterizing 3D triangles with perspective correct texture
| mapping and z-buffering.
|
| The downside of WebGL is its complexity, but there are many
| libraries to help with that.
| 0xbadcafebee wrote:
| As part of building my own truck-top camper, I got into
| researching aerodynamics of vehicles in order to try to reduce
| loss of fuel efficiency. The most interesting ideas I found were
| that aerodynamics don't matter much on most vehicles until they
| pick up significant speed.
|
| Most automobiles are pretty heavy, so the engine has to do
| significant work just to get it to move. At a certain point, the
| vehicle can change gears to get the engine to do less work and
| use less fuel. But around the same time, the force of the air is
| increasing. By the time an automobile goes over about 50mph, the
| air forces are getting increasingly strong, and the engine has to
| work harder to keep the vehicle moving. At this point, beginning
| to lower the air's coefficient of drag on the vehicle will lessen
| the work the engine needs to do to keep the car moving at speed.
| So you can optimize the design of the vehicle's exterior to
| reduce the drag coefficient, which will reduce things like flow
| separation and turbulence, creating fewer rear pressure zones and
| causing less drag.
|
| So you might wonder, why aren't more cars teardrop-shaped like
| the airfoil? The answer is, it depends. Most people want
| something that looks good more than they want efficient operation
| at speed. But sometimes having more drag actually helps. For
| example, the Lotus Elise: while it is smaller and looks more
| sleek than a Tesla Model 3, it actually has a much worse drag
| coefficient than a Tesla Model 3. The Lotus has way more force
| acting against it at speed than the Tesla. But the Lotus is a
| sports car, and sports cars benefit greatly from increased
| traction, and you can get more of that traction by increasing the
| downforce on the car. So the Lotus's design sacrifices top-speed
| drag coefficiency in order to gain some downforce which helps
| traction when cornering at speed.
|
| What about pickup trucks? Even though modern pickups actually
| have lots of subtle design changes to improve drag coefficient,
| they all tend to have open beds, which is _terrible_ for drag. It
| creates this giant messy turbulent pressure area in the bed which
| drags on the tailgate and the rest of the car. By adding a truck
| topper, the drag is significantly reduced, but you don 't see
| most trucks driving around with a topper on. But trucks naturally
| have worse gas mileage, so nobody really thinks twice about the
| aerodynamics.
|
| (To be fair, the air's impact on gas mileage is minimal unless
| you're going quite fast. But for trucks with extremely bad gas
| mileage, like 18-wheelers, it makes much more difference. That's
| why they often have airfoils on the front of the truck, gaps
| between cab and container closed, and skirts to reduce drag from
| the undercarriage. Strangely though, the biggest improvement to
| reduce drag coefficient actually comes from modern European big-
| rigs whose containers are actually tapered like a teardrop. The
| rear of the vehicle's shape makes the most difference to how
| severe flow separation is, and thus how big of a pressure area
| develops, pulling on the rear of the vehicle. If we wanted to
| make trucking more fuel efficient globally we'd change the shape
| of the containers to be more like teardrops, but that would make
| handling and shipping them much more awkward)
|
| You'll usually only see these effects on automobiles at higher
| speeds, due to the vehicle needing to overcome gravity before the
| air forces build up. Lighter vehicles (say, bicycles) with less
| impact on them from gravity will be impacted earlier (at lower
| speeds) by the force of the air, so optimizing drag coefficient
| is much more important, which is why bicycle racers have to put
| so much into aerodynamics at significantly lower speeds than an
| automobile. Interestingly, the drag coefficient on a bicycle and
| rider is actually equivalent to that of a small car.
| onetimeuse92304 wrote:
| I wish every presentation on how planes fly started with an
| actual flat plane. A wing that has a flat crossection. I think
| the shape of the airfoil of the wing is absolutely distracting
| and prevents people from understanding what is really happening.
|
| Every person who ever stuck a flat object outside the window of a
| moving car knows that you do not need a fancy shape to have lift.
|
| And so many people are stuck thinking that the shape of the
| airfoil is responsible for the plane to be able to fly,
| supposedly because the air needs to run a longer way around the
| foil above the wing than below the wing. And this somehow causes
| pressure difference due to Bernoulli law and this is what keeps
| the plane up. Which is almost total BS because planes can
| obviously fly inverted.
|
| Now I admit I only skimmed the article, and although the
| animations are beautiful, I am missing what really is key to
| understanding of what is happening.
|
| I am looking for a bigger, far away view of the wing and showing
| what happens to the air BEHIND the wing.
|
| Because how the plane really works is as it flies forward, it
| diverts large masses of air downwards. It pushes off of air.
|
| Part of the air is diverted by the lower portion of the wing, but
| the much larger portion of lift is generated by larger masses of
| air above and behind the wing. Those can be thought as being
| sucked down behind the wing (if you look at it from the point of
| view of a stationary air mass, not from the point of view of the
| wing).
|
| And the main role of the airfoil is to keep that mass of air
| behind the wing stuck to the airfoil at wide range of angles and
| speeds as possible, because a flat sheet is very poor at doing
| this.
| p_l wrote:
| Unfortunately, your explanation is entirely wrong... and you're
| attacking a "lies to children" simplification with your mention
| of "needs to run longer way around" bit.
| avn2109 wrote:
| Well in defense of the GP, the "planes can observably fly
| upside down" point (and its close cousin the "flat wing cross
| sections can fly too" point) is a good one, this pokes holes
| in the usual two-dimensional "the air goes faster on top"
| themed explanation that omits any discussion of vortex
| shedding/third-dimensional effects.
| p_l wrote:
| Oh, to be quite honest, I loved trolling my high school
| teachers with "your explanation fails, here is a real world
| airfoil, please explain it" and I would draw a symmetrical
| airfoil or - for extra trolling - a trapezoid one. (At that
| point I had already flown solo)
|
| But the same I found myself unable to pass by someone
| pushing "flat plane at an angle".
| quickthrower2 wrote:
| Did you have to write the lie in an exam to pass too?
| p_l wrote:
| Fortunately the exam questions that involved lift in high
| school were simple enough they didn't trigger "you're
| wrong and the textbook is wrong" response XD
|
| Fortunately my exams were open ended not "fill in the
| circle in answer sheet" so worst case I'd have written a
| more complete answer and fought it out.
|
| Worrying about having to fight against "answer key" is
| part of why only one person (and only on a lark) took
| computer science on Matura exam in my class - which was
| CS-math-physics focused one
| dameyawn wrote:
| Yea, I agree and try to explain it this way to friends.
| Airfoils help, but it's ultimately just the wing pushing air
| down and why planes can fly upside down.
|
| FWIW, aerospace engineering degree, used xFoil, did tons of
| fluid sims, etc.
| p_l wrote:
| And it's an "even more wrong" explanation than the "lies for
| children" diagram used in school physics class.
|
| For reference, actual "proper" discussion of lift in
| textbooks on aerodynamics have tendency to start with a
| sphere/cylinder.
| Xirgil wrote:
| Do you have any recommended reading on this topic? I'd like
| to brush up.
| p_l wrote:
| There used to be a good one from NASA, written for K-12
| but 100% adhering to actual science not "lies for
| children".
|
| EDIT: This is a good starting point for the frankly
| awesome material from NASA Glenn Research Centre: https:/
| /www.grc.nasa.gov/WWW/K-12/VirtualAero/BottleRocket/a...
|
| Unfortunately it partly bitrotted due to using java
| applets for interactive demos, but I think most of it is
| still reachable - I'll try to find it later when I'm at
| the desk.
|
| Personally I learnt from a 1980 book that was still part
| of mandatory reading for glider pilot course in Poland in
| 2005.
| bouchard wrote:
| Understanding Aerodynamics: Arguing from the Real Physics
| by Doug McLean, a former aerodynamics Technical Fellow at
| Boeing Commercial Airplanes.
| po wrote:
| Bill Beaty's site was the one that opened my eyes to
| these misunderstandings:
| http://www.amasci.com/wing/airfoil.html
|
| If the diagram shows lift but doesn't show the air being
| directed downward after leaving the tailing edge of the
| wing, I basically stop reading. That's the whole thing.
| onetimeuse92304 wrote:
| Thank. You. That's exactly what is missing and that's
| exactly what I have mentioned in my... highly criticised
| comment. It just shows how pervasive the misconception
| is.
|
| If you take a step back there is a simple way to think
| about this. In order for the object to stay up there,
| there needs to be equal and opposite force from some
| other body. What is that other body? It is the mass of
| air that is being directed in the opposite direction of
| the lift force acting on the plane.
| Ono-Sendai wrote:
| Why is it wrong?
| dameyawn wrote:
| There is no lift on a sphere or cylinder without rotation
| dude. The whole point of parent post is that the "proper"
| discussion does not inlay a good intuitive understanding of
| lift, which in my opinion, should start with "push air down
| to go up".
| p_l wrote:
| Yes, there's no lift.
|
| But there's quite different flow _and drag_ around it,
| which was used as opening for for adding rotation (which
| would add viscosity effects including lift from rotation)
| and other changed shapes in better way than starting with
| flat plane.
| danmaz74 wrote:
| I once found an explanation that finally made it clear to me
| why the shape of the airfoil can create lift. Yes, the air
| above the wing needs to travel a longer distance with the
| typical section used in wings, which means that it goes faster
| than the air below the wing. It also leaves the wing moving
| downwards - and when this downward-moving, faster flux of air
| meets the slower one from below, the result is that a mass of
| air is pushed downwards - exactly as needed to lift the plane,
| as you correctly said.
|
| As the article says, you can have lift by just changing the
| inclination of a symmetrical airfoil, but an asymmetrical one
| can generate lift even without inclination (and with lower
| drag). The article also explains that acrobatic airplanes have
| symmetrical wing sections exactly because they need to be able
| to fly just as easily inverted.
| kqr wrote:
| > Yes, the air above the wing needs to travel a longer
| distance with the typical section used in wings, which means
| that it goes faster than the air below the wing.
|
| Both of these sub-clauses are true, but the "which means"
| connecting them aren't. There's no law of physics saying a
| fluid that has a longer path ahead of it speeds up in
| anticipation.
| danmaz74 wrote:
| My understanding is that "which means" only makes sense
| with the assumption that what is being studied is the
| laminar flow of an incompressible fluid (which was
| described as a fair assumption for air and a wing at
| subsonic speed). But thinking more about it, it's probably
| right that this isn't about the fact that the air above
| needs to travel a longer distance, which would also be true
| for a concave wing section, but the fact that the layers
| immediately above the wing need to travel the same X
| distance through a thinner Y section - as in a tube which
| becomes thinner. Which forces the fluid to go at a higher
| speed, and have a lower pressure.
| prmph wrote:
| Isn't there an even more basic explanation: If incoming air
| hits a flat surface at an angle, and is deflected
| downwards, then by the law of action and reaction, the
| surface itself moves upward.
|
| As a child, I quickly outgrew the airfoil explanation when
| I realized this.
| Gibbon1 wrote:
| My dad who worked on wind tunnels just flat said you can
| either integrate the pressure over the surface of the
| wing or the momentum change as the air passes over to
| derive the amount of lift.
|
| Both give exactly the same results and are convertible
| mathematically.
|
| For wind tunnel work it was easier to measure pressures.
|
| I'm with you I don't think the standard hand wavy
| explanation gives you the ability to attack the problem
| mathematically. So it's basically wrong.
| kqr wrote:
| Yes and no. The thing you describe happens, but it's not
| enough to explain the amount of lift generated by a wing,
| because a surprising amount of air hits also the top of
| the wing! The difference in pressure between top and
| bottom wing surface is just a few percent.
|
| The reason wings produce significant lift anyway is that
| they deflect air far beyond their surface. Air several
| metres away from the wing is also deflected downward,
| even though it doesn't actually hit the wing itself.
|
| So yes, Newton's third law is involved, but in a "spooky
| action at a distance" form, where the wing somehow
| manages to deflect a bunch of air it doesn't even touch!
| onetimeuse92304 wrote:
| That's exactly what is happening. But it is also not
| enough for the airplane to fly.
|
| In a normally flying airplane, the wing compresses and
| pushes an amount of air under its wing. But there is
| actually even greater amount of air sucked down by the
| region of underpressure created above the wing and by the
| laminar flow directing it downward. Here, the drawing at
| the top of the page makes it clear:
| http://www.amasci.com/wing/airfoil.html
|
| When you have a stall condition, what happens is that the
| air below the wing is still being compressed and directed
| downwards, but the air above the wing becomes turbulent
| and "unsticks" from the surface of the wing. Rather than
| being nicely directed downward, it just dissipates a lot
| of energy in turbulent motion that is not directed in any
| particular direction.
|
| This turbulent air not only ceases to provide lift, it
| also prevents the air from below the wing to be directed
| downwards efficiently.
|
| The main job of an airfoil isn't to create a pressure
| difference, it is to create conditions for the air to be
| laminar at as wide range of speeds and angles of attack
| as possible to make the plane nicely behaving and
| possible to takeoff and land. It is super critical for
| landing as you need to have higher the angle of attack
| the slower you fly and all planes essentially are driven
| as close to stall as possible during landing. Similar
| happens at high altitudes and high speeds, but for a bit
| different reason (read up on "coffin corner" if you are
| interested in that sort of thing).
| lovecg wrote:
| To me the most intuitive and practical mental image is
| imagining two large bubbles of lower pressure above the wing
| that hold the wing up by suction (you can see those literally
| as condensation under certain conditions). As you increase the
| angle of attack the bubbles get larger and stronger, until the
| angle is so large that they "break off" and the wing stalls.
| itishappy wrote:
| > planes can obviously fly inverted
|
| Many (most?) planes cannot sustain inverted flight.
| mechhacker wrote:
| IIRC that is due to other issues, not aerodynamics.
|
| For instance, the engine no longer receiving oil at negative
| 1 g, or fuel, as the system is designed for gravity flow.
|
| Stunt planes and airplanes capable of long inverted flight
| need special oiling and fuel systems to keep the engine from
| starving from either.
| itishappy wrote:
| Fascinating! Commercial airliners have also optimized their
| engines enough they don't have the power budget to make up
| for the difference in lift.
| quickthrower2 wrote:
| You mean it is more akin to those grills you position to
| control your AC pushing the air in a certain direction. But
| with just one surface you get the AoA too high problem. Hell I
| am gonna stick my hand out next time in a car (being safe about
| it!) and see the stall angle of my hand.
| ubj wrote:
| Obligatory XKCD comic (also with the name "Airfoil"):
|
| https://xkcd.com/803/
| CrimsonCape wrote:
| I grew up duck hunting and learned intimately how ducks use their
| wings and the variations of shapes at different velocities as
| they slow down to land on the water. I also grew up boating and
| swimming and have a likewise similar understanding of paddling,
| tracking a canoe straight, and using boat motor trim to "get on
| the plane".
|
| I guess I struggle with articles like this because it's already
| so intuitive as a mix of air and fluid dynamics. In fact, fixed
| airfoils are so boring when you see what a duck can do.
|
| https://www.youtube.com/watch?v=-3CVZYY8xS4
|
| So for all the fancy physics talk, this duck is literally just
| paddling air with his wings. The same physiology I use to stay
| afloat when treading water while swimming.
| mondrian wrote:
| Fixed airfoil physics become really important at very high
| speeds.
| jameshart wrote:
| Or if your Cessna isn't equipped with a flapping system.
| mometsi wrote:
| Amusingly, the flappy Cessnas were designed with the engine
| mounted right in front of the windshield.
|
| Where else could it possibly go?
|
| https://gallery.vtol.org/image/P2xYJ
| solardev wrote:
| But when that fancy duck wants to get to Paris in a hurry, it
| still has to hop on a fixed-wing Concorde like everyone else.
| kjkjadksj wrote:
| Give it a strong selective pressure towards speed and a few
| million years and you will have your supersonic duck.
| LargoLasskhyfv wrote:
| Reverse dragooning by expelling fiery farts made of
| hypergolics fueled by fantastic fermentation?
| bloopernova wrote:
| Something like that is featured in Terry Pratchett's
| _Discworld_ series of books. (Don 't spoil the book it's
| in!)
|
| GNU Terry Pratchett
| solardev wrote:
| There's also that Harry Potter spinoff movie in which he
| becomes a supersonic corpse with a farting jet-butt in
| order to visit some pretty redwood parks:
| https://www.inverse.com/article/17614-how-swiss-army-man-
| mad...
| LargoLasskhyfv wrote:
| Something similar already happened in reality in another
| evolutionary chain:
|
| https://en.wikipedia.org/wiki/Bombardier_beetle
|
| (on a much smaller scale)
| solardev wrote:
| Intercontinental ballistic mallards? Just another trillion-
| dollar boondoggle from the military-ornithological complex.
| CrimsonCape wrote:
| Hummingbirds go to mexico to vacation a lot more than I do.
| Imagine if humans had a manadatory 2000 mile trip and 6 month
| layover twice a year to survive.
|
| Once you have technology that enables flapping type motion,
| it's opening up the applicable physics to like 6 degrees of
| freedom versus zero in current wing technology (fixed = 0
| degree of freedom); much more complex and interesting to
| study.
|
| How else will we move toward ornithopter style wings, or
| vehicles that can hover via wing movement.
| KeplerBoy wrote:
| Rotating wing aircraft have no problem hovering mid-air.
| All we need are a handful of breakthroughs in battery tech.
| seer wrote:
| Rotating wing aircraft have problems with supersonic
| flight - and the wing (rotor) itself reaches supersonic
| much quicker than the aircraft itself, thats why helis
| are usually slow, compared to aircraft.
|
| I guess "supersonic wing flapping" would have similar
| problems, but maybe there are more clever solutions than
| can be modeled, with so much degree of freedom?
|
| And is "supersonic flapping" even possible?
| invalidlogin wrote:
| I once ate duck in Paris.
| solardev wrote:
| That is a remarkable story...
| megablast wrote:
| The arctic tern flies from the north pole to the south pole.
| turtledragonfly wrote:
| > this duck is literally just paddling air with his wings
|
| Grossly speaking, sure. But I feel like this simplifies away a
| lot of the interesting bits. It's not as simple as, say,
| someone on a canoe paddling. Why is the duck's wing shaped
| _just so_ , and not another way? Why does it move its wings
| _just so_ instead of another way?
|
| I'm reminded of an analysis of fruit fly wings, showing how
| they re-capture energy from the air when flapping[1]. Maybe the
| duck is doing similar; I don't know.
|
| Of course, these animals make it look easy, thanks to millions
| of years of evolution (:
|
| https://www.nature.com/articles/s41598-021-86359-z
| estiaan wrote:
| I think you might be experiencing a bit of a dunning-kruger
| effect
|
| Also, in my experience there's a huge difference between having
| an intuition for something and having an understanding of
| something to the point where you could model it.
| aredox wrote:
| For an example of a flat-ish airfoil that performs well enough
| for model airplanes (and is easier to build than a NACA & co
| airfoil), see the KFm airfoil family:
|
| https://en.wikipedia.org/wiki/Kline%E2%80%93Fogleman_airfoil
|
| Very useful when making model airplanes out of foamboard.
| kqr wrote:
| Huh, odd. I was under the impression that for swept/delta
| winged paper airplanes one wants a smooth top surface to
| encourage attachment and any steps on the bottom to provide
| decalage. (I.e. the area ahead of the step acts as a canard-
| like surface.)
|
| Is this an airfoil that works for tailed aircraft but not
| tailless ones, perhaps?
|
| Edit: I just skimmed the book on paper planes by KF and indeed
| they are using the variation with the step on the bottom for
| their paper planes.
|
| I'm actually even more surprised now. How on Earth did they
| manage to patent the idea of reflex on a delta wing to give a
| tailless plane stability? This seems like the thing that (a)
| was known since early human-carrying gliders, and (b)
| implicitly discovered by anyone that folds a lot of paper
| airplanes. I will definitely read their book in more detail.
| skykooler wrote:
| Attachment isn't as much of an issue with paper planes since
| the small size and low speed give much more favorable
| Reynolds numbers.
| kqr wrote:
| Could you elaborate on that, please? This is just at the
| edge of my understanding and I'd like to learn more.
| skykooler wrote:
| You can see the effect in the second animation of the
| linked page, but the basic idea is the lower the Reynolds
| number, the less likely for flows to separate and become
| turbulent. Shrinking the scale and slowing the airspeed
| both lower the Reynolds number, so paper planes have
| vastly different aerodynamics to full size aircraft.
| aredox wrote:
| And even further, insects have also vastly different
| aerodynamics, which explains why flapping flat wings
| works at insect-size and not at bird-size (nor plane-
| size).
| kqr wrote:
| I agree with the other commenter that the specific shape of the
| cross section of the wing is overemphasised in almost all
| material including this one. Any shape longer than it's thick
| will, at a reasonable angle of attack, provide lift.
|
| This article did provide a barn door model also, but it was quite
| far down.
|
| The shape is mainly about efficiency and increasing the range of
| reasonable angles of attack, and then further nuances.
| tjkrusinski wrote:
| It's amazing how the article did such an incredible job
| building a deep understanding of how the airfoil works, yet you
| managed to completely miss that and find something to so small
| to critique.
| MattRix wrote:
| I think many of these kinds of comments are driven by a form
| of insecurity. They subconsciously wish they had written the
| article and are envious of the attention the author is
| receiving... so they find whatever small nitpick they can in
| order to tear it down.
| mrks_hy wrote:
| Sorry for my low-value comment, but I think it is
| appropriate here. Doing a psychoanalysis of OP does not
| really add to the discussion meaningfully. Same applies to
| parent comment.
|
| https://news.ycombinator.com/newsguidelines.html
|
| > When disagreeing, please reply to the argument instead of
| calling names
| kqr wrote:
| To be clear, the article was amazing. That has already been
| said multiple times by others so if I left a comment saing
| just that I would contribute nothing. Besides, the size of
| the criticism (in this case small, as you point out) is an
| even better measure of quality than number of fawning
| comments.
|
| I also publish articles (though nowhere near as good or
| ambitious as this one) online and the comments I look forward
| to most are the constructively critical ones. They are the
| reason I publish in the first place.
|
| My only goal of giving and receiving constructive criticism
| is to improve our collective understanding of the world.
| There's nothing sinister or ill-natured about it as another
| commenter suggested.
|
| (This extends to comments as well. I really appreciate you
| prompting me to check my tone.)
| carabiner wrote:
| bro just stop
| spurgu wrote:
| This made me think of how I hate Youtube comments. All the
| high-fiving positive ones end up on the top and not the
| ones that provide an opportunity to learn or think
| critically.
| milliams wrote:
| I thought they made it very clear and talked at length that the
| shape isn't the key important factor. They do also then go on
| to talk about the benefits of different shapes and why they are
| chosen.
| carabiner wrote:
| You gotta wonder why the Wrights spent so much time optimizing
| an airfoil. You could have been there to tell them to use a
| barn door wing and flat plate prop to save them a lot of time.
|
| I have noticed this "it works or it doesn't work. Everything
| else is nuances." binary thinking among SWEs. It's odd.
| r3d0c wrote:
| effect is amplified on hn
| 8n4vidtmkvmk wrote:
| An odd thing to say for a SWE. There's huge differences in
| the quality of apps, both from a user perspective and an
| internal/dev perspective.
| kqr wrote:
| Don't get me wrong -- for practical flight it is really
| important to expand the reasonable range of angles of attack
| because angle of attack is one of very few ways one has of
| controlling the aircraft.
|
| But for explaining how lift appears, it is an irrelevant
| detail.
|
| The purpose of modeling is not to mimick reality at high
| fidelity but to focus attention on the o parameters that
| matter for a specific situation. When you change the
| situation (going from explaining how lift happens to trying
| to fly) it is not surprising to have to switch to a different
| model.
| ajkjk wrote:
| Pretty impressive. I was curious how they made the whole thing so
| I went to look at the source for the images. It's mostly in one
| 10000 line JS file which draws all the graphics onto <canvas> in
| JS, plus a bunch of WebGL that goes over my head. The code looks
| like function draw_car(ctx, rot) {
| ctx.save(); let sc = 0.04; ctx.scale(sc, -sc);
| ctx.lineWidth \*= 1 / sc; ctx.translate(-286, -51);
| ctx.beginPath(); ctx.moveTo(463.93652, 9.89137);
| ctx.bezierCurveTo(462.12793, 6.72347, 461.22363, 3.5344,
| 461.22363, 0.32417); ctx.bezierCurveTo(447.58911,
| -1.16177, 434.20691, 2.81333, 434.85754, 5.10777); ...
|
| I wonder what their workflow was. Surely all those curves weren't
| programmed by hand?
| plopz wrote:
| Just a small note, that code looks like Context2d rather than
| WebGL unless you were looking at something else in the code
| ajkjk wrote:
| Ah, I wasn't clear. There's a bunch of both in the same giant
| file.
| dubcanada wrote:
| Not sure what you are looking at but
| https://ciechanow.ski/js/airfoil.js is the JS that contains the
| code for the graphics/visuals. And it is completely readable.
|
| The 2d part though is probably generated.
| nequo wrote:
| Yeah, the "draw_car" snippet quoted by parent is from the JS
| file that you linked.
|
| It looks like maybe an SVG file converted into JS? Do you
| know if there is some standard tooling that generates this?
| bastawhiz wrote:
| SVG paths translate pretty directly to canvas commands. If
| you have an SVG path parser, it's pretty straightforward to
| walk it and output the equivalent js.
| ajkjk wrote:
| But for that many paths it seems... tedious. Wondering if
| they had a better way.
| ajkjk wrote:
| Yeah, that's the file I was looking at. I was wondering how
| that file got created. By hand, or generated somehow?
| grishka wrote:
| I asked him on Twitter about one of his previous articles,
| he said he writes all that JS by hand.
|
| https://twitter.com/BCiechanowski/status/152206790452242841
| 7
| syncsynchalt wrote:
| It doesn't look like it's publicly viewable but he has a
| writeup of his process for patrons at
| https://www.patreon.com/posts/on-airfoil-99289324
| komodus wrote:
| Things fly because of thrust, not wings. Rockets, missiles, don't
| have wings and yet they still fly even longer distances. Shut the
| engines of a 747 and it will fall like a rock, no matter how
| perfect the airfoils.
|
| Bernoulli and Coanda are important but without thrust/velocity
| there is no lift
| travisjungroth wrote:
| A 747 won't fall like a rock. It will glide.
| rjmunro wrote:
| You can't say that without mentioning
| https://en.wikipedia.org/wiki/British_Airways_Flight_009
|
| Where the pilot said what is probably the most British thing
| ever said in history:
|
| > Ladies and gentlemen, this is your captain speaking. We
| have a small problem.
|
| > All four engines have stopped. We are doing our damnedest
| to get them going
|
| > again. I trust you are not in too much distress.
| tstrimple wrote:
| Just in case folks don't click on the link, it was a safe
| landing and everyone survived. It turns out modern planes
| can glide quite well.
| kqr wrote:
| This is a very important point.
|
| The key difference is that a rock (like any ballistic
| projectile) accelerates until terminal velocity. In contrast,
| a 747 (like any airplane) descends with a constant vertical
| velocity when they lose power.
| hex4def6 wrote:
| The engineers at Boeing are going to be really embarrassed once
| someone tells them they don't actually need to put wings on
| their aircraft...
| signa11 wrote:
| not to mention authors of rfc-1925 as well :o)
| alanbernstein wrote:
| I expected to see a mention of the Joukowski airfoil
| (https://complex-analysis.com/content/joukowsky_airfoil.html). I
| guess there was plenty of other content to cover though.
| Tistron wrote:
| I really enjoyed reading this, and felt excited when the author
| promised to explain viscosity at a particle level. But there was
| just a short presentation about two colliding molecules and I
| didn't understand the connection to viscosity. It's like a
| section is missing or something..?
|
| How does viscosity work?
| turtledragonfly wrote:
| Not really a full answer for you, but one thing that this page
| clarified for me:
|
| I had generally previously thought of viscosity as "how slow" a
| fluid is. High viscosity means high "thickness," which means it
| flows slowly (like molasses vs. water).
|
| But as presented on this page, viscosity is actually a measure
| of "how fast" -- how fast the effects on one molecule can
| spread out from there to neighboring molecules. Perhaps you
| could think of sounds waves moving through a substance -- a
| "thick" substance like solid metal propagates those waves
| quickly (on a molecular level), while with a "thin" substance
| like air it's much slower. In the more precise language from
| the article: "viscosity controls the diffusion of momentum..."
|
| So, because this diffusion happens quickly in a high-viscosity
| situation, little whorls of turbulence are inhibited, because
| the forces governing those whorls get spread out/diffused
| quickly.
|
| Perhaps you missed the part of the article talking about
| diffusion, or did not see the connection? The link between that
| and viscosity was not immediately apparent to me, either.
| Tistron wrote:
| Thank you, this feels helpful.
|
| Though I don't think I missed a part of the article, I feel
| more like the author did ;)
|
| What I still don't get is what the difference between high
| and low viscosity looks like on a particle level. I don't
| understand why he introduced the collision between two
| molecules and then never explained that.. :)
| apognwsi wrote:
| viscosity has very interesting units - stress (force / area)
| divided by rate (1 / time). viscosity is measured (a field
| known as rheology) by, in some way, moving a thing through a
| fluid at increasingly fast accelerations, or equivalently, at
| increasingly high frequencies. that is, imagine moving your
| hand back and forth in a fluid - the faster you do so (the
| number of back and forth motions per second), the more
| resistance you will feel from the fluid. for newtonian fluids,
| the resistance you feel (measured in force / area, ie the area
| of your hand), is proportional to the frequency of your hand
| moving back and forth in the liquid, so, the graph is a line.
| non newtonion fluids do not have a linear relationship between
| shear stress and shear rate. air is also a fluid - all gasses
| are, and thus possess rheological properties. air, however, at
| stp, is essentially an ideal gas, that is, it is non-
| interactive, and thus, has 0 viscosity. the point here, is that
| viscosity is a consequence of the interactions of particles. as
| gases become denser, their viscosity increases. liquids, for
| comparison, is ~1000x as dense as air. the details of how
| molecular interactions lead to viscosity is actually quite
| complicated.
| Tistron wrote:
| Thank you. I seem to have trouble using rate as a concept,
| especially dividing by it :) But I think I get it when I add
| a virtual distance into what you are saying.
|
| You are saying (force / area) / (1 / time). I add two
| distances that cancel out: (distance * force / area) /
| (distance * 1 / time) and get (energy / area) / speed, which
| is energy used per area and speed. I can feel that, and it
| seems to be what you are saying, right?
| Eudaimion wrote:
| If you find this interesting, I would also recommend
| https://ciechanow.ski/bicycle/. It is by the same author.
| quickgist wrote:
| This is one of the best thought out UX I've ever seen. It's
| extremely well laid out and simple to navigate through, all the
| design choices are very meaningful, UI elements (like the unit
| conversion) are available inline when you need them...
|
| Not to mention the content itself is great.
|
| I'm taking notes.
| IncreasePosts wrote:
| You probably want to check out the rest of his site, which is
| pretty much on par with this:
| https://news.ycombinator.com/from?site=ciechanow.ski
| akouri wrote:
| I'd love to know how long it takes him to make each one of
| these "interactive essays"
| wraptile wrote:
| A long time would be my guess but writing interactive
| articles is much more engaging and addicting. We've started
| adding interactive stuff to our docs and it is really
| engaging so the spent hours just fly by!
| matheusmoreira wrote:
| I'd love to read about _how_ he does it. How talented do
| you have to be to not only learn all this stuff but also
| model them in 3D and simulate them in real time and
| interactively?
| Ringz wrote:
| I would also be interested in knowing which software is
| used?
| ImHereToVote wrote:
| Looks like pure JavaScript using the WebGL Canvas.
| 9dev wrote:
| Hah. That question comes up on every single one of his
| explainers. The answer is none; he hand-crafts the
| JavaScript and WebGL shaders. From the design language,
| I'd guess he has built up a library of templates and
| snippets to draw from by now, but all in all, each of
| these pages is a bespoke work of art.
| justinpombrio wrote:
| https://ciechanow.ski/js/airfoil.js
|
| :head-exploding-emoji:
| kqr wrote:
| Guessing from personal experience, I would not be
| surprised if 70 % of the domain knowledge is learned in
| the process of writing and modeling.
|
| Whenever I encounter a tricky subject I'm having a hard
| time learning, I start writing an article explaining it
| to someone else. It really forces me to confront the gaps
| of my knowledge because I can see so clearly that "Wait,
| I can't explain what happens between these two steps
| here. What am I missing?"
| hanche wrote:
| His mechanical watch piece is really something to behold.
| Antrikshy wrote:
| Also check out https://pudding.cool if you're unfamiliar and
| enjoy extremely high effort visualizations alongside editorial
| and educational text content.
| taco-hands wrote:
| Regardless of all the exacting comments, this is one of the most
| astonishing accounts and content on a topic I've seen for years;
| beautifully delivered and interactive to boot.
| gwbennett wrote:
| I agree! His articles always have fantastic content!
| hubraumhugo wrote:
| Ciechanowski is likely the best content producer we know,
| absolutely fascinating reads. Imagine having such a person as a
| teacher - he could probably excite students about any scientific
| topic.
|
| I'd love to spend my time working on such articles when I'm
| retired :)
| larodi wrote:
| Without doubt. Question is why so many people who try to teach
| approach it like it's 1878.
| tigerlily wrote:
| In what ways do so many people who try to teach approach it
| like it's 1878?
| garyiskidding wrote:
| As an aerospace major in college, this has content from several
| semesters combined into a really well structured, clear and
| visual explanation of various aspects of flight dynamics. Thank
| you.
| Limborg wrote:
| Oh, thanks todsacerdoti. I really need such thing. Actually, I
| love reading contents which related to Planes, Wings and the base
| reasons of their flying. It shows that you and your posts are
| going to be the best items for my hobbies in the future. Thank
| you.
| denton-scratch wrote:
| That page made my laptop fan start roaring.
| 4gotunameagain wrote:
| You're probably lacking webgl HW accleration.
|
| https://webglreport.com/ , or check about:support if you're on
| firefox.
| denton-scratch wrote:
| Thanks. Yes, it's Firefox, but apparently it supports WebGL 1
| & 2.
| 4gotunameagain wrote:
| yes but is the rendering performed in GPU, or in software
| is the question
| denton-scratch wrote:
| How do I tell? I tried about:support and webglreport.com.
| 4gotunameagain wrote:
| https://googlethatforyou.com?q=firefox%20check%20hardware
| %20...
| denton-scratch wrote:
| So I disabled "Use recommended performance settings" and
| "Use hardware acceleration" was enabled.
|
| The fan still roars.
| einpoklum wrote:
| What an astounding amount of work must have gone into that
| post...
| RobinL wrote:
| Amazing work as always.
|
| Is it just me who sees diagonal lines on the first interactive
| graphic? Are they a bug? They appear after a little while, fade
| out, then reappear
|
| https://gist.github.com/RobinL/aa4a5e14d35e61e46c1e99c8198d0...
| slumberlust wrote:
| The same author has a great similar piece on mechanical watches.
| Love the format!
|
| https://ciechanow.ski/mechanical-watch/
| tejohnso wrote:
| Not a single mention of Bernoulli. Bravo!
| yakito wrote:
| For anyone interested in bio-inspired aerodynamics, there's a
| fascinating study published in Scientific Reports exploring the
| aerodynamic efficiency of dragonfly and NACA4412 airfoils in
| ground effect. This research uses URANS simulations to offer
| insights into optimizing MAVs' (Micro Air Vehicles) performance
| close to the ground.
| https://www.nature.com/articles/s41598-022-23590-2
| billbrown wrote:
| This guy's whole corpus reminds me of Nevil Shute's _Trustee from
| the Toolroom_: quiet, fastidious, and expert work appreciated
| worldwide.
| Andrew_nenakhov wrote:
| Oh no. A while ago I stumbled on this guy's page about mechanical
| clocks - a subject I was never interested in - and was forced to
| spend the rest of the day studying clocks.
| anonporridge wrote:
| https://ciechanow.ski/mechanical-watch/
| wolverine876 wrote:
| An important question before I read something that long (or
| anything, really): Who is Bartosz Ciechanowski?
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