Talk:3279: Main Span

Surely anchor lines from the balloon to the sea floor perpendicular to the bridge would sort the wind issue. Drummertv (talk) 16:27, 31 July 2026 (UTC)

I added a transcript, but I left the d=... formula vague. If someone can fill it in that would help. We don't use MathJax in transcriptions, do we? Barmar (talk) 16:30, 31 July 2026 (UTC)

I read this with my brother, and as soon as we saw the title text I cracked up (we live in Tacoma.) RadiantRainwing (talk) 18:40, 31 July 2026 (UTC)

Ah... So it resonated with you! 92.23.10.248 20:02, 31 July 2026 (UTC)

(Imaginary upvote) RadiantRainwing (talk) 23:03, 31 July 2026 (UTC)

I saw that video three times in three separate classes in uni. Fephisto (talk) 14:35, 3 August 2026 (UTC)

I didn't...but then literature and linguistics don't really provide much opportunity for that. I saw it at school though – I'm pretty certain it was in music when we were talking about resonant frequencies and how they interfere with each other, but the same teacher taught me geography, so there's a small chance it was to do with that instead. Weird crossover of relevance that I never considered before. Yorkshire Pudding (talk) 16:58, 3 August 2026 (UTC)

Strange that the title text is specifically "Wind stress," which is specific to the wind interacting with the surface of the water rather than the other stresses such as pulling on that balloon or of course Tacoma Narrows. 99.70.40.149 (talk) 20:45, 31 July 2026 (please sign your comments with ~~~~)

Bridges are extremely heavy. I'm actually curious just how absurdly huge a balloon would have to be to support that much weight. It'd almost certainly be bigger than in the comic. 206.193.5.5 21:35, 31 July 2026 (UTC)

I just logged in to ask the same question. How many Hindenburgs would this require? I'm assuming that upsidaisium and unobtanium remain synonyms, and hence unavailable for the project. 205.175.118.2 21:58, 31 July 2026 (UTC)

Let the total mass of the span to be supported be 100,000 tonnes - I read that the current maximum is around 90,000 tonnes. Let the mass to be supported by balloon be 10,000 tonnes, with the remaining 90,000 tonnes to be supported by cables. Let the balloon design to support the bridge be that of the dirigible Hindenburg, containing 200,000 cubic meters of hydrogen. 833 cubic meters of hydrogen is needed to lift 1 tonne; 1 Hindenburg can lift 240 tonnes. To lift the specified span, 42 Hindenburgs containing hydrogen are required; if the lifting gas is helium, 46 Hindenburgs will be required. 2605:59C8:160:DB08:B038:6886:5D34:C618 01:08, 1 August 2026 (UTC)

If the load on the balloon is 50,000 tonnes (more in keeping with the scenario as shown), you'd need 208 (hydrogen) - 229 (helium) Hindenburgs. 2605:59C8:160:DB08:B038:6886:5D34:C618 13:22, 1 August 2026 (UTC)

If the length of the bridge deck be set to 5 km, I make out the balloon's radius to be ca. 350 m. A sphere with that radius has a volume of 1.8 X 10^8 cubic meters - or about 900 Hindenburgs of lifting gas at 200,000 m^3 per dirigible. If this is correct, the scale of the balloon in the cartoon is accurate; if anything, it's overengineered. 2605:59C8:160:DB08:A820:FB4F:7559:1B42 09:56, 2 August 2026 (UTC)

Is there really is a theoretical limit? I could not find any source for that claim. 200.86.125.34 00:33, 1 August 2026 (UTC)

Hang a cable (rope, chain, etc) vertically. Hang more. At some length the cable will rip from its own weight. The maximum length before failure is hardly affected by diameter so the maximum length is fairly consistent for a specified material (steel, nylon, cotton). The current winners are expensive synthetic ropes (or spider webs?). IIRC this length, for typical rope-stuff, is something less than a mile or a KM. How to convert from hanging rope to bridge-rope is beyond me. --PRR (talk) 22:46, 1 August 2026 (UTC)

"The maximum length before failure is hardly affected by diameter" - to see that, consider that if you can hang one cable of diameter D, area A = πD^2/4, and make it length L before its own weight breaks it at the top, then you can hang *two* identical cables next to each other. Then just glue them together along their length (using a very light glue), and you have 1 cable of area 2*A. What you *can* do to optimize the cable length is vary the diameter along the length - the top of the cable is carrying the most weight, so it needs the largest cross section, and the bottom of the cable is carrying nothing, so it can have zero cross section. (If you do the math, you'll find that the cable diameter along its length is an exponential function, and it can be infinitely long, if you ignore a few minor details.) 163.116.145.66 17:12, 4 August 2026 (UTC)

This reminds me of some levels in the Polybridge games, in which anchor points are visually attached to the basket of unsuspecting hot air balloons 2600:1014:B090:633:0:15:E4DC:901 00:50, 1 August 2026 (UTC)

I was about to say. My first reaction to this comic (after the scoff) was “Someone’s been playing Poly Bridge again.” HaruruChanDesu (talk) 01:51, 1 August 2026 (UTC)

I ran in to the wiki JUST to mention this exact thing XD

Makes you wonder, are we gonna actually mention this being either intentionally or unintentionally a Poly Bridge reference in the main article? 71.236.133.105 18:34, 1 August 2026 (UTC)

This XKCD gets uploaded right as I begin playing Polybridge again? What are the odds! Tux1 (talk) 06:24, 2 August 2026 (UTC)

At this point, "bridge crime comics that could be read as Poly Bridge references" is big enough to be a category. There's the dangling bridge one, there's the jumps one... 2601:1C2:97C:F550:BC90:66AF:8E4D:9FAE 06:31, 3 August 2026 (UTC)

An alternative to a balloon would be a space elevator. That presumably results in a different set of problems. 87.75.45.201 14:11, 1 August 2026 (UTC)

I am glad someone finally mentioned a very carefully unbalanced space elevator. Maintaining exactly the right connection height and lift force with perturbations is left as an exercise to the reader. 208.198.19.195 14:35, 3 August 2026 (UTC)

That looks like a balloon shaped by some ropes plus its own envelope, and no such balloon I ever saw is as spherical as the depiction in the comic. And yes, I am aware of how pettily pedantic this sounds! It's just that xkcd accuracy standards are so high that I am spoiled. 69.191.176.41 14:52, 3 August 2026 (UTC)

It's a schematic (as evidenced by the annotations), so obviously it's an idealised depiction. 82.13.184.33 15:09, 3 August 2026 (UTC)

To stop leakage of helium, hydrogen, or hot air, an envelope material might be expensive, and a sphere minimizes area per volume. At km-scale area, this might be more cost effective and simpler to design than other shapes. --99.48.45.17 19:32, 6 August 2026 (UTC)

You could search for images of American Civil War balloons. Some of them were quite spherical. Also as noted below shockingly small if you are used to hot air balloons. IIRC there is a replica of the Intrepid flying somewhere. Although the reenactors use He instead of H2. Also they usually don't put shot in the muskets. 76.180.39.133 18:06, 7 August 2026 (UTC)

The balloon diameter would be much smaller if filled with hydrogen. What could go wrong? 192.5.18.7 (talk) 14:53, 4 August 2026 (UTC) (please sign your comments with ~~~~)