Runway overrun areas marked with diagonal stripes have an Engineered Materials Arresting System. There are several different materials used. One is pumice embedded in styrofoam, with a thin concrete layer on top. Large aircraft weigh enough to break through, and the pumice is crushed to powder, absorbing energy. This yields a surprisingly short stopping distance. The aircraft landing gear will be damaged, but the rest of the aircraft is usually intact. The overrun material comes in prebuilt blocks, and after an overrun, only the ones damaged need to be replaced.
It gets a lot of use. The FAA has logged 25 overruns stopped by EMAS, out of 161 runway ends so equipped. That's surprisingly high.
Honestly - the video barely touches on this at all, despite making it the "hook".
I was pretty disappointed that he doesn't discuss the EMAS mechanics, structure, actual stopping distance, or impact to the plane in nearly any real way.
He does show a LOT of animation of layered runways, which are mostly not that informative.
There is some decent discussion around maintenance and material choice, and some very basic discussion of infrastructure requirements outside of the runways themselves that's... ok.
Overall... I thought this was a solid C+ video. It shows planes plowing into an EMAS, then does jack all to discuss that, while bringing up a lot of less interesting discussion of runway building (which despite the claims in the video, do actually correspond very highly to how we build highways, just with different weight/maintenance requirements.)
That’s pretty cool. I’d assumed there would be something similar to the run-away truck ramps you see on steep grades — basically a deep gravel pit. However, actually thinking about it, something along the lines of a gravel pit would likely cause significant damage to engines (not to mention risks created by engine damage) but also seriously impede emergency services.
These overrun areas aren't that long. This trick is used where there's not enough room for a long overrun area.
The high drag has to start fast.
With the styrofoam/pumice material, the wheels quickly drop all the way to the hard bottom of the arresting material, and then plow forward, dissipating energy by crushing pumice. With something more solid, the wheels may skim the surface for a while before digging in.
Hah, I guess this is the same then as in formula 1 (and possibly other motorsports). After the end of a straight (speeding) section, just before the curve they have 150/100/50 (m?) distance indicators. Sans the concrete block at the top. That would obviously shave the driver's head off.
It's not quite the same thing - the EMAS is the overrun surface itself, rather than the signs warning of it. However you are quite close to the money on another aspect of airfield design.
Lots of obstructions near the runway - signs, lights, aerial masts, meteorological equipment, fences - are supposed to be "frangible" [1]. They must break into pieces less likely to cause damage to an aircraft in a high-energy collision. There's a heck of a lot of GFRP used in lieu of metal around an airfield.
I saw a talk a long time ago about the structural aspects of runway design. The most interested fact I remember was that the stresses on the runway generated by departures was higher than those of arrivals, as departures repeatedly stress the same part of the runway, while jets land on a much more distributed area of the runway.
Plus jets weigh a lot less at arrival than at departure.
When I worked at Boeing, I talked about autoland systems with my lead engineer. He said the autoland was too perfect, as the airplanes would touch down at the same place every time.
This caused that place in the runway to suffer severe fatigue damage.
IIRC, there was a similar problem on aircraft carrier flight decks, where they had to induce some randomized amount of dispersion to keep the tailhook from hitting the same spot over and over again.
Do you know how they keep the concrete from cracking? All the pads in general are in way better shape than my driveway, and the driveway has decent support underneath and is subjected much, much less load.
Maybe they use plentiful jagged interlocking sharp granite as the base l? (like railroad track foundation)
Next time you're at SFO, SJC, or any other major hub sitting in the plane before it backs out of the gate take a second to gaze upon and admire how pristine all the concrete pads are, it's really impressive.
Mostly the extensive subgrade work, as I understand. Similar to a road, there’s a bed of sand and aggregate under the concrete surface.
The concrete they use is very precisely mixed to a specification and then it’s tested for adherence to the spec.
A runway is also going to be 3-4x thicker than a 4-6” thick driveway slab. Probably they also use fiberglass or PVC coated rebar instead of plain steel rebar.
Definitely not an expert here but I can read a civil site plan and hire civil site work subcontractors frequently.
Also, Grady is one of the best creators on YouTube, I can’t help but watch his full videos whenever they pop up. I always learn something, even if I’m familiar with the subject.
Most concrete cracking you will see in residential construction and private driveways are either because the ground wasn't compacted well enough before the pour, or more often they didn't put a thick enough layer of stone to prevent the ground from moving. Cutting out depth from the base of crushed stone is often the easiest way to cut costs because it means less material brought in and less material to dig out.
Granted private driveways don't need to be absolutely perfect, but if you want it to last for a really long time you need deeper base layers.
Not sure if that's a serious question, but your driveway might lack a proper foundation, so the surface is moving and cracks. Also, it's likely not concrete, but tarmac (which is much softer).
"stress" (in engineering terms) has a particular meaning and is not a generic term. It is not really a synonym for "forces" or "what makes other stuff break"!
Let's look at just the downward forces:
I need some quick figures 1 - an early Boeing 747: 330 tonnes (metric) fully loaded and 160 tonnes empty. A tonne is 1000 Kg.
According to 2: 240 feet per minute vertical is a hard landing which about 1.2m/s. 60 - 180 is considered ideal, so let's go for about 150fpm which is about 0.7m/s.
We have to estimate the maximum downward force on take off. At the point of just before lift off, the plane has rotated to say, let's say 45 degrees, and its engines are delivering enough force and its wings are delivering enough force to push it into the air. Surely at take off, that vertical force is simply the weight of the aircraft, which has remained the same all the time. It doesn't suddenly push down harder than its weight, that's just what it feels like for a passenger.
So let's allow our jet to be empty on landing and also let the acceleration due to gravity be 10m/s/s
So what is the instantaneous downward force of a mass of 160 tonnes dropping at 0.7 m/s compared to a dead weight load of 330 tonnes. Both are in a gravitational field of 10 m/s/s (or m^s-2).
Now this is where I get a bit lost because force = mass x acceleration and the landing plane is descending at a constant velocity of 0.7 m/s. Mind you, the ascending plane is also ... ascending, or will do but it does not have an instantaneous upward velocity so at wheels off it has a vertical acceleration of zero.
1) when an airliner lands, the undercarriage legs, which are telescopic sprung and damped struts, spread the vertical deceleration over a finite period (I cannot say how long it lasts, but I would say of the order of a second or so.)
2) At the point of touchdown, the wings are generating lift about equal to the aircraft’s weight. This decreases quite rapidly, largely on account of the decease in angle of attack as the nosewheel comes down and from the deployment of spoilers, but it would be mistaken to think that the runway is immediately supporting the full weight of the airliner after touchdown.
3) On takeoff, until the nosewheel is lifted to initiate rotation, a significant fraction of an airliner’s weight is being supported by the runway. During rotation, as the angle of attack increases, the lift increases [1] until it exceeds the weight, at which point the airliner lifts off.
4) If we ignore the fact that the undercarriage is sprung, then the airliner has no vertical velocity until it lifts off. Right at that point, however, when the lift exceeds the weight, it gains a vertical acceleration.
I hope this helps!
[1] Plus a vertical component of the engine thrust, but no airliner rotates to anything like 45 degrees - in fact, if it has not left the ground at a rotation angle equal to the angle of maximum lift coefficient (~10 - 15 degrees), it is not going to do so without going faster.
Yeah, the higher departure stress due to greater fuel weight at takeoff was mentioned in this video.
I'm now curious about the engineering of the displaced threshold. This is a portion of the runway that aircraft can taxi onto and use for takeoff but not for landing. I thought (assumed) that the landing was harder on the runway surface than takeoffs, hence the displaced threshold wasn't designed for that force.
The displaced threshold could also be used to ensure obstacle and terrain clearance on landing - simply disallow that portion from being used in order to create an offset from the obstacle. But I don't know whether this is a very common reason for displaced threshold usage.
--
Video also mentions https://skybrary.aero/ which I'd not heard of previously. Looks neat. I'll have to check it out.
> And as the departing plane goes faster, doesn't the lift take stress off the runway?
Only for a short period between rotation and liftoff. Most of the takeoff roll is spent building up horizontal speed; the pilot doesn't command the aircraft to pitch up before it's ready to lift off.
It's the same principle as walking on snow in normal shoes vs. snow shoes. Taking off is normal shoes, a lot of pressure concentrated at the very first part of the runway. Landing is snow shoes because it's distributed across more of the physical surface, and the plane weighs a lot less when it lands anyway.
Planes all start their take off from basically the same position and stress the whole runway, slowly lowering as lift increases, but at their highest weight.
I guess his area is really close to my field (Mechanical Engineering + Robotics) so what I learn from his videos is less the concepts themselves and more the interesting examples of them in the real world.
For example that hydroplaning is a real consequence on runways; or that higher takeoff weight has an order of magnitude greater effect on runway wear than the shear force of braking during landing.
I also learn from Grady's phenomenal skill at communicating technical concepts from our field in layman accessible terms! Most times I prefer to watch his videos and appreciate what he does, but there are days that I'm in the mood to read rather than watch. I'm glad that he gives us that option.
If you already understand the concepts you're not gaining much by watching the video.
If you don't then I'm sure it's better than nothing but idk if stock footage is where you should be developing your mental model of how a tire hydroplanes or how a paved transfers load into what's below it.
Video is great, came up in my youtube recommendation cycle last week.
Honestly one of the better things youtube has pitched to me, the quality/relevance of the rest of its recommendations have been nose diving over the last year (or so it feels).
100% anecdata, but I think YouTube nudges your ad profile towards some averaged out cosign product of everyone’s ad profile at regular intervals.
I’ll discover something new, then get pushed a ton of things related to it, which is really good! After a very long break of ~4 years, I started playing oldschool RuneScape again, and that interest weaved its way into my recommended feed perfectly for a month. Felt like I was picking up where I left off, new folks making OSRS video essays, folks I remembered from a long time ago that I had unsubscribed from, exactly what I want out of an algorithmic feed when I’m freshly into something.
Then BAM, gaming content. Some sort of threshold gets hit and now I’m being pushed hyper popular gaming content regardless of RuneScape-y-ness. There’s still a nudge towards it, but I got placed in some “gaming” cohort and it totally crowds out my recommended feed. I don’t really do much gaming outside of this stupid old MMO!
All that’s to say: it might have been a year since you last had one of these inflection points where YouTube will let your ad profile exist as an outlier for a bit.
100%. I've always used youtube on desktop (connected to the TV usually), and it seems to me they're just making all versions of youtube into a mobile app optimized for shorts type content. Recommendations are hugely influenced by what you watched very recently. What used to be related videos in the side panel of the player is now just the home page again, but vertical. Even just generating a recommendation from "Whatever (part 2)" to "Whatever (part 3)" is hit or miss now. Some of the recommendations are actually quite good, but at least for the way I like to watch, it's only getting worse over time. The category labels on the home page are also pretty telling - horrible labels (e.g. I watch some cooking/recipe videos and the label will be "Baking sheets" or something like that), plus it emphasizes the recency bias when it shows 5 categories that are basically just the same content with different labels and forgets what I've always liked watching.
> Recommendations are hugely influenced by what you watched very recently.
Ah, well, I don't know that I fully agree.
I watch channels that are people building things, repairing tools, or goofing around in an easy-going way without a lot of product placement or sponsored content.
And yet, all of the recommendations I get are either sponsored unboxing videos with AI voiceovers or click-baity channels with ugly reaction faces in the video thumbnails. I guess those probably make more money for Google.
For me my home page is now 95% videos I've already watched. The side bar is the only reliable source of new content. Until recently I had no subscriptions but that never used to matter. I had to subscribe to Patrick Boyle in solidarity when they demonetized his Epstein video.
One of the issues of YouTube is there is "discovery" vs "what I want to watch". https://www.youtube.com is ok for discovery and pulls a lot of the "this is what I've subscribed to" in there too. Doing a subscribe to channels that give you consistent media that you want to watch and then going to https://www.youtube.com/feed/subscriptions as the "this is where I want to be when on YouTube" gives a completely different experience.
(I'm also quite free with the "don't recommend this channel to me" option if something disappoints me)
The way Youtube (and I've started to notice in other platforms) does recommendations, for every 5+ that are nonsense, I'll get one I like. Youtube will then start showing me more of that video's channel content and similar channels for a week or so, and then it'll just stop showing any of it to me quite randomly. Sometimes it's when I click on that random recommendation out of 5 from a different topic.
then the cycle starts again. sometimes youtube brings the content back and sometimes i really need to hunt for it.
it's almost like they base interests into like a top 3 or so list and if the third favorite one cycles out a lot (however they deem it is being cycled out) they'll stop recommending or otherwise showing it to me.
I absolutely love this channel. It provides a reasonably no nonsense view into parts of engineering I'm not super familiar with. It's made cooler by the fact that I occasionally interact with the systems being described. (Though hopefully not this one).
Does anyone have recommendations for similar high quality engineering adjacent content?
There's Farmcraft101 if you are interested in DIY builds and repairs. There was a series of videos repairing an excavator from scrap to finish, and he is currently doing a series of videos adding hydro generation to a pond. Interesting metal fabrication, hydraulics, power, etc content.
Farmcraft101 is my absolute favorite channel right now. I can’t wait for fridays when he puts out a new video. I found him a couple of months ago and binge watched all his playlists.
Every time I fly, I marvel at how much engineering and know-how went into making the airport that I'm using. From the oddly shaped trucks with various functions, to mundane elements (elevators, escalators, ...) to advanced technology (radio communication, radars...) to the sheer organizational feat (thousands of people coming in every day to execute their carefully planned tasks). This text will give me one more thing to think about :)
Same, and I also just marvel at the airplanes. This video made me think of the several grass runways that are in my area. They're literally just maintained by some guy mowing them, and yet people land on them in tiny planes as well as two-engine aircraft.
We had group coding projects at university, and the first one was always "sponsored" by the local airport. I think the ATC manager was friends with a lecturer. Every year the students built to the same spec in groups, being able to compare and contrast. It was great fun.
The year before me was all about runway markings: take a bunch of industry specified XML describing the runway and produce accurate diagrams in a GUI browser.
My year was runway "redeclaration", if a vehicle has broken down on the runway, you can still use the runway as a shorter strip, accounting for the onion layers of different zones radiating out from the tarmac itself, accounting for the height of the obstacle and angles of approach, accounting for all the necessary safety margins.
It was my first real exposure to working in a team and to solving a real world problem with a good spec. Of course it was an absolute shitshow, but I look back on it fondly.
> The FAA says that for each percent of downhill slope, landing distance is increased by 10%.
This is accurate as to their recommendation, but it was surprising. I know it’s inaccurate, because at a perpendicular angle there would be no way to land. I know they don’t allow an angle that steep, but that means this is “gut feel” inexact math that seems unsafe.
The force required to stop on an inclined plane is proportional to the sine of the angle. At angles less than 10 degrees (~17% slope, far steeper than the FAA would allow for an airport), the small angle approximation of sine is within 0.5% of linear.
I don't know if their math is incorrect, but your intuition of the limit case is - downhill slope is the ratio of height change per length. A perpendicular angle thus has "infinite percent" slope (since the denominator, length, is zero), which intuitively matches an infinite landing distance.
He does such great videos and content. Might have to watch this one with my dad; he used to joke that his Eagle Scout project was putting in the north-south runway at MCI.
Something which still confuses me is the nature of the illuminations in the roadway. Because we can see edge elements, we see things on stalks. I don't see how that can work, for things the tires run over. But, the illuminations are there. They must be super-designed cats-eyes.
Also, the approach lighting has very good engineering to keep you in the safe slot for approach angle. The lights must have fresnel lenses or shading or something to keep a very narrow angle of approach lit up "best"
On take off if I have a window, I now look for the banding which I mentally model as "not yet.. " "almost .." "if you are doing <x> kph then YES" .. and "nope. don't wanna see this one"
Gate approach, there are clues that pilots drive by following lines. So many lines! marked by aircraft type: if you are a <this> then follow <this track> type markers.
Here's the one-minute version from the FAA.[1]
Runway overrun areas marked with diagonal stripes have an Engineered Materials Arresting System. There are several different materials used. One is pumice embedded in styrofoam, with a thin concrete layer on top. Large aircraft weigh enough to break through, and the pumice is crushed to powder, absorbing energy. This yields a surprisingly short stopping distance. The aircraft landing gear will be damaged, but the rest of the aircraft is usually intact. The overrun material comes in prebuilt blocks, and after an overrun, only the ones damaged need to be replaced.
It gets a lot of use. The FAA has logged 25 overruns stopped by EMAS, out of 161 runway ends so equipped. That's surprisingly high.
It's a simple, clever system.
[1] https://www.youtube.com/watch?v=hVSvU06_NGE
That's only a small portion of what the video is about.
Honestly - the video barely touches on this at all, despite making it the "hook".
I was pretty disappointed that he doesn't discuss the EMAS mechanics, structure, actual stopping distance, or impact to the plane in nearly any real way.
He does show a LOT of animation of layered runways, which are mostly not that informative.
There is some decent discussion around maintenance and material choice, and some very basic discussion of infrastructure requirements outside of the runways themselves that's... ok.
Overall... I thought this was a solid C+ video. It shows planes plowing into an EMAS, then does jack all to discuss that, while bringing up a lot of less interesting discussion of runway building (which despite the claims in the video, do actually correspond very highly to how we build highways, just with different weight/maintenance requirements.)
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That’s pretty cool. I’d assumed there would be something similar to the run-away truck ramps you see on steep grades — basically a deep gravel pit. However, actually thinking about it, something along the lines of a gravel pit would likely cause significant damage to engines (not to mention risks created by engine damage) but also seriously impede emergency services.
These overrun areas aren't that long. This trick is used where there's not enough room for a long overrun area. The high drag has to start fast. With the styrofoam/pumice material, the wheels quickly drop all the way to the hard bottom of the arresting material, and then plow forward, dissipating energy by crushing pumice. With something more solid, the wheels may skim the surface for a while before digging in.
Gravel flies. You can't have it anywhere near an airport runway.
(Some planes have no problem with it, though. You can make even the entire runway of gravel if you only fly those.)
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Hah, I guess this is the same then as in formula 1 (and possibly other motorsports). After the end of a straight (speeding) section, just before the curve they have 150/100/50 (m?) distance indicators. Sans the concrete block at the top. That would obviously shave the driver's head off.
When a driver hits these, they evaporate as dust.
It's not quite the same thing - the EMAS is the overrun surface itself, rather than the signs warning of it. However you are quite close to the money on another aspect of airfield design.
Lots of obstructions near the runway - signs, lights, aerial masts, meteorological equipment, fences - are supposed to be "frangible" [1]. They must break into pieces less likely to cause damage to an aircraft in a high-energy collision. There's a heck of a lot of GFRP used in lieu of metal around an airfield.
1. ICAO Doc 9157, particularly part 6.
EMAS is going to save a LOT of lives in the long run. It's consistently effective at its job. I'm very excited to see it more widespread.
I saw a talk a long time ago about the structural aspects of runway design. The most interested fact I remember was that the stresses on the runway generated by departures was higher than those of arrivals, as departures repeatedly stress the same part of the runway, while jets land on a much more distributed area of the runway.
Plus jets weigh a lot less at arrival than at departure.
When I worked at Boeing, I talked about autoland systems with my lead engineer. He said the autoland was too perfect, as the airplanes would touch down at the same place every time.
This caused that place in the runway to suffer severe fatigue damage.
IIRC, there was a similar problem on aircraft carrier flight decks, where they had to induce some randomized amount of dispersion to keep the tailhook from hitting the same spot over and over again.
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Do you know how they keep the concrete from cracking? All the pads in general are in way better shape than my driveway, and the driveway has decent support underneath and is subjected much, much less load.
Maybe they use plentiful jagged interlocking sharp granite as the base l? (like railroad track foundation)
Next time you're at SFO, SJC, or any other major hub sitting in the plane before it backs out of the gate take a second to gaze upon and admire how pristine all the concrete pads are, it's really impressive.
Mostly the extensive subgrade work, as I understand. Similar to a road, there’s a bed of sand and aggregate under the concrete surface.
The concrete they use is very precisely mixed to a specification and then it’s tested for adherence to the spec.
A runway is also going to be 3-4x thicker than a 4-6” thick driveway slab. Probably they also use fiberglass or PVC coated rebar instead of plain steel rebar.
Definitely not an expert here but I can read a civil site plan and hire civil site work subcontractors frequently.
Here’s some information on concrete testing: https://www.concrete.org/frequentlyaskedquestions.aspx?faqid...
Also, Grady is one of the best creators on YouTube, I can’t help but watch his full videos whenever they pop up. I always learn something, even if I’m familiar with the subject.
Edit: Granite is not one of the listed materials in Part 4 - Base Courses of the FAA runway construction guide, here’s the entire thing for reference - https://www.faa.gov/airports/engineering/construction_standa...
Most concrete cracking you will see in residential construction and private driveways are either because the ground wasn't compacted well enough before the pour, or more often they didn't put a thick enough layer of stone to prevent the ground from moving. Cutting out depth from the base of crushed stone is often the easiest way to cut costs because it means less material brought in and less material to dig out.
Granted private driveways don't need to be absolutely perfect, but if you want it to last for a really long time you need deeper base layers.
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If I had to guess, all things equal, its probably much thicker than your average driveway.
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Not sure if that's a serious question, but your driveway might lack a proper foundation, so the surface is moving and cracks. Also, it's likely not concrete, but tarmac (which is much softer).
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"stress" (in engineering terms) has a particular meaning and is not a generic term. It is not really a synonym for "forces" or "what makes other stuff break"!
Let's look at just the downward forces:
I need some quick figures 1 - an early Boeing 747: 330 tonnes (metric) fully loaded and 160 tonnes empty. A tonne is 1000 Kg.
According to 2: 240 feet per minute vertical is a hard landing which about 1.2m/s. 60 - 180 is considered ideal, so let's go for about 150fpm which is about 0.7m/s.
We have to estimate the maximum downward force on take off. At the point of just before lift off, the plane has rotated to say, let's say 45 degrees, and its engines are delivering enough force and its wings are delivering enough force to push it into the air. Surely at take off, that vertical force is simply the weight of the aircraft, which has remained the same all the time. It doesn't suddenly push down harder than its weight, that's just what it feels like for a passenger.
So let's allow our jet to be empty on landing and also let the acceleration due to gravity be 10m/s/s
So what is the instantaneous downward force of a mass of 160 tonnes dropping at 0.7 m/s compared to a dead weight load of 330 tonnes. Both are in a gravitational field of 10 m/s/s (or m^s-2).
Now this is where I get a bit lost because force = mass x acceleration and the landing plane is descending at a constant velocity of 0.7 m/s. Mind you, the ascending plane is also ... ascending, or will do but it does not have an instantaneous upward velocity so at wheels off it has a vertical acceleration of zero.
Help!
1 https://measuringly.com/how-much-does-boeing-747-weigh/ 2 https://aviation.stackexchange.com/questions/47422/what-is-t...
You might find these points helpful:
1) when an airliner lands, the undercarriage legs, which are telescopic sprung and damped struts, spread the vertical deceleration over a finite period (I cannot say how long it lasts, but I would say of the order of a second or so.)
2) At the point of touchdown, the wings are generating lift about equal to the aircraft’s weight. This decreases quite rapidly, largely on account of the decease in angle of attack as the nosewheel comes down and from the deployment of spoilers, but it would be mistaken to think that the runway is immediately supporting the full weight of the airliner after touchdown.
3) On takeoff, until the nosewheel is lifted to initiate rotation, a significant fraction of an airliner’s weight is being supported by the runway. During rotation, as the angle of attack increases, the lift increases [1] until it exceeds the weight, at which point the airliner lifts off.
4) If we ignore the fact that the undercarriage is sprung, then the airliner has no vertical velocity until it lifts off. Right at that point, however, when the lift exceeds the weight, it gains a vertical acceleration.
I hope this helps!
[1] Plus a vertical component of the engine thrust, but no airliner rotates to anything like 45 degrees - in fact, if it has not left the ground at a rotation angle equal to the angle of maximum lift coefficient (~10 - 15 degrees), it is not going to do so without going faster.
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Wouldn’t the force be the force required to decelerate the plane’s vertical velocity to 0 m/s over whatever small amount of time?
Isn’t the acceleration here just the difference in velocity between the plane and the runway so 0.7 m/s/s?
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Yeah, the higher departure stress due to greater fuel weight at takeoff was mentioned in this video.
I'm now curious about the engineering of the displaced threshold. This is a portion of the runway that aircraft can taxi onto and use for takeoff but not for landing. I thought (assumed) that the landing was harder on the runway surface than takeoffs, hence the displaced threshold wasn't designed for that force.
The displaced threshold could also be used to ensure obstacle and terrain clearance on landing - simply disallow that portion from being used in order to create an offset from the obstacle. But I don't know whether this is a very common reason for displaced threshold usage.
-- Video also mentions https://skybrary.aero/ which I'd not heard of previously. Looks neat. I'll have to check it out.
Isn't it the opposite? Landing stress a sub-section of the runway while departures stress a larger portion?
I'd be surprised that a heavier plane on takeoff exerts more force on the runway than a lighter plane landing.
And as the departing plane goes faster, doesn't the lift take stress off the runway?
> And as the departing plane goes faster, doesn't the lift take stress off the runway?
Only for a short period between rotation and liftoff. Most of the takeoff roll is spent building up horizontal speed; the pilot doesn't command the aircraft to pitch up before it's ready to lift off.
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It's the same principle as walking on snow in normal shoes vs. snow shoes. Taking off is normal shoes, a lot of pressure concentrated at the very first part of the runway. Landing is snow shoes because it's distributed across more of the physical surface, and the plane weighs a lot less when it lands anyway.
Planes all start their take off from basically the same position and stress the whole runway, slowly lowering as lift increases, but at their highest weight.
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Watch the video. He says for long range flights, fuel is half of the total weight of the plane.
According to the video the much larger weight is the main or even only cause of takeoff exerting more load on the runway than landings.
I absolutely love that Grady includes full transcripts of his videos.
It's much faster to read the article than watch the video, even though that hurts him by 1 view.
I just watched parts of the video after reading because I wanted to see his explanations.
One of the few really good creators out there.
Reading the transcript doesn’t even give you 10% of the information actually conveyed in the video which is why it’s so much faster.
I guess his area is really close to my field (Mechanical Engineering + Robotics) so what I learn from his videos is less the concepts themselves and more the interesting examples of them in the real world.
For example that hydroplaning is a real consequence on runways; or that higher takeoff weight has an order of magnitude greater effect on runway wear than the shear force of braking during landing.
I also learn from Grady's phenomenal skill at communicating technical concepts from our field in layman accessible terms! Most times I prefer to watch his videos and appreciate what he does, but there are days that I'm in the mood to read rather than watch. I'm glad that he gives us that option.
If you already understand the concepts you're not gaining much by watching the video.
If you don't then I'm sure it's better than nothing but idk if stock footage is where you should be developing your mental model of how a tire hydroplanes or how a paved transfers load into what's below it.
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Video is great, came up in my youtube recommendation cycle last week.
Honestly one of the better things youtube has pitched to me, the quality/relevance of the rest of its recommendations have been nose diving over the last year (or so it feels).
100% anecdata, but I think YouTube nudges your ad profile towards some averaged out cosign product of everyone’s ad profile at regular intervals.
I’ll discover something new, then get pushed a ton of things related to it, which is really good! After a very long break of ~4 years, I started playing oldschool RuneScape again, and that interest weaved its way into my recommended feed perfectly for a month. Felt like I was picking up where I left off, new folks making OSRS video essays, folks I remembered from a long time ago that I had unsubscribed from, exactly what I want out of an algorithmic feed when I’m freshly into something.
Then BAM, gaming content. Some sort of threshold gets hit and now I’m being pushed hyper popular gaming content regardless of RuneScape-y-ness. There’s still a nudge towards it, but I got placed in some “gaming” cohort and it totally crowds out my recommended feed. I don’t really do much gaming outside of this stupid old MMO!
All that’s to say: it might have been a year since you last had one of these inflection points where YouTube will let your ad profile exist as an outlier for a bit.
100%. I've always used youtube on desktop (connected to the TV usually), and it seems to me they're just making all versions of youtube into a mobile app optimized for shorts type content. Recommendations are hugely influenced by what you watched very recently. What used to be related videos in the side panel of the player is now just the home page again, but vertical. Even just generating a recommendation from "Whatever (part 2)" to "Whatever (part 3)" is hit or miss now. Some of the recommendations are actually quite good, but at least for the way I like to watch, it's only getting worse over time. The category labels on the home page are also pretty telling - horrible labels (e.g. I watch some cooking/recipe videos and the label will be "Baking sheets" or something like that), plus it emphasizes the recency bias when it shows 5 categories that are basically just the same content with different labels and forgets what I've always liked watching.
> Recommendations are hugely influenced by what you watched very recently.
Ah, well, I don't know that I fully agree.
I watch channels that are people building things, repairing tools, or goofing around in an easy-going way without a lot of product placement or sponsored content.
And yet, all of the recommendations I get are either sponsored unboxing videos with AI voiceovers or click-baity channels with ugly reaction faces in the video thumbnails. I guess those probably make more money for Google.
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For me my home page is now 95% videos I've already watched. The side bar is the only reliable source of new content. Until recently I had no subscriptions but that never used to matter. I had to subscribe to Patrick Boyle in solidarity when they demonetized his Epstein video.
One of the issues of YouTube is there is "discovery" vs "what I want to watch". https://www.youtube.com is ok for discovery and pulls a lot of the "this is what I've subscribed to" in there too. Doing a subscribe to channels that give you consistent media that you want to watch and then going to https://www.youtube.com/feed/subscriptions as the "this is where I want to be when on YouTube" gives a completely different experience.
(I'm also quite free with the "don't recommend this channel to me" option if something disappoints me)
The way Youtube (and I've started to notice in other platforms) does recommendations, for every 5+ that are nonsense, I'll get one I like. Youtube will then start showing me more of that video's channel content and similar channels for a week or so, and then it'll just stop showing any of it to me quite randomly. Sometimes it's when I click on that random recommendation out of 5 from a different topic.
then the cycle starts again. sometimes youtube brings the content back and sometimes i really need to hunt for it.
it's almost like they base interests into like a top 3 or so list and if the third favorite one cycles out a lot (however they deem it is being cycled out) they'll stop recommending or otherwise showing it to me.
"Sign in to confirm your not a bot"...gone.
I absolutely love this channel. It provides a reasonably no nonsense view into parts of engineering I'm not super familiar with. It's made cooler by the fact that I occasionally interact with the systems being described. (Though hopefully not this one).
Does anyone have recommendations for similar high quality engineering adjacent content?
Veritasium (https://www.youtube.com/veritasium) has well researched content, but they are broad in terms of their topic selection.
Real Engineering (https://www.youtube.com/@RealEngineering/videos) is focused on engineering, but more on specific vehicles or products than individual concepts.
There's Farmcraft101 if you are interested in DIY builds and repairs. There was a series of videos repairing an excavator from scrap to finish, and he is currently doing a series of videos adding hydro generation to a pond. Interesting metal fabrication, hydraulics, power, etc content.
Farmcraft101 is my absolute favorite channel right now. I can’t wait for fridays when he puts out a new video. I found him a couple of months ago and binge watched all his playlists.
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Every time I fly, I marvel at how much engineering and know-how went into making the airport that I'm using. From the oddly shaped trucks with various functions, to mundane elements (elevators, escalators, ...) to advanced technology (radio communication, radars...) to the sheer organizational feat (thousands of people coming in every day to execute their carefully planned tasks). This text will give me one more thing to think about :)
Same, and I also just marvel at the airplanes. This video made me think of the several grass runways that are in my area. They're literally just maintained by some guy mowing them, and yet people land on them in tiny planes as well as two-engine aircraft.
Glad I'm not the only who is fascinated with airports and the technology/engineering that makes them function at scale.
We had group coding projects at university, and the first one was always "sponsored" by the local airport. I think the ATC manager was friends with a lecturer. Every year the students built to the same spec in groups, being able to compare and contrast. It was great fun.
The year before me was all about runway markings: take a bunch of industry specified XML describing the runway and produce accurate diagrams in a GUI browser.
My year was runway "redeclaration", if a vehicle has broken down on the runway, you can still use the runway as a shorter strip, accounting for the onion layers of different zones radiating out from the tarmac itself, accounting for the height of the obstacle and angles of approach, accounting for all the necessary safety margins.
It was my first real exposure to working in a team and to solving a real world problem with a good spec. Of course it was an absolute shitshow, but I look back on it fondly.
> The FAA says that for each percent of downhill slope, landing distance is increased by 10%.
This is accurate as to their recommendation, but it was surprising. I know it’s inaccurate, because at a perpendicular angle there would be no way to land. I know they don’t allow an angle that steep, but that means this is “gut feel” inexact math that seems unsafe.
The force required to stop on an inclined plane is proportional to the sine of the angle. At angles less than 10 degrees (~17% slope, far steeper than the FAA would allow for an airport), the small angle approximation of sine is within 0.5% of linear.
I don't know if their math is incorrect, but your intuition of the limit case is - downhill slope is the ratio of height change per length. A perpendicular angle thus has "infinite percent" slope (since the denominator, length, is zero), which intuitively matches an infinite landing distance.
I can never watch just a minute of these guy’s video — it’s always the whole thing, always so interesting.
He does such great videos and content. Might have to watch this one with my dad; he used to joke that his Eagle Scout project was putting in the north-south runway at MCI.
Something which still confuses me is the nature of the illuminations in the roadway. Because we can see edge elements, we see things on stalks. I don't see how that can work, for things the tires run over. But, the illuminations are there. They must be super-designed cats-eyes.
Also, the approach lighting has very good engineering to keep you in the safe slot for approach angle. The lights must have fresnel lenses or shading or something to keep a very narrow angle of approach lit up "best"
On take off if I have a window, I now look for the banding which I mentally model as "not yet.. " "almost .." "if you are doing <x> kph then YES" .. and "nope. don't wanna see this one"
Gate approach, there are clues that pilots drive by following lines. So many lines! marked by aircraft type: if you are a <this> then follow <this track> type markers.
You’re on the right track! Some of them are embedded, some of them are on stalks, and some of them are highly directional: https://flightlight.com/airfield-products/