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Virgin "It's literally cheaper to keep repairing it" vs. Chad "I don't care how 'overengineered' you say this is, the budget is coming from the Emperor himself"
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this post was submitted on 13 Sep 2025
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You're absolutely right, and I was more-or-less generalizing, given that modern structures tend to focus on maximizing the tensile strength, such as carbon fibre for fuselage sections. There's even the combination where tensile strength is used to augment compressive strength, like with tensioned concrete slabs. Honestly, the fact that some steel wires pulling within a piece of concrete makes it stronger is kinda nuts to me.
We're at a unique juncture where wood is being revisited as a sustainable material, but also because it's quite interesting if its natural drawbacks can be tamed. The fact that wood bends well before it snaps gives it some very forgiving characteristics, unlike steel which will hold until catastrophically failing.
I suppose if we look more closely at wood, it does in-fact have some tensile strength, as the bottom-side of a heavily-laden beam does stretch. But I'm not material engineer.
I have to mention that this is precisely why the phrase "you can't push a rope" exists, for folks not familiar with this expression for an impossible assignment.
TIL!
I once considered this as a thought experiment, just to see if it would work. And my conclusion is that it would be a phenomenal waste of a log to make a solid disc, when a spoked wheel made from conventional, longitudinal boards cut from the same log would yield a satisfactory wheel at greatly reduced material consumption. That said, it may very well be viable for smaller-diameter wheels, where rendering a slender log into boards would result in too much lost material as sawdust.
If I'm not mistaken, this is how steel tires for steel railway wheels are attached. Plus ça change!
TIL! I'm kind of surprised that significant compressive forces don't inevitably show up in something big and highly mobile like that.
In a way it's too good to be true; a fibre composite that literally grows on trees, and that produces several useful compounds and enormous amounts of energy when burned. The Inuit weren't wrong to scrounge for it.
It still exists because trees end up solving a lot of the same problems as human inventors.
The grain is strands of mostly cellulose, so it's almost rope-strong. Even across the grain, lignin is a decent glue (and with high strain at failure, resulting in the flexibility you mentioned), although the fact you can split wood obviously implies that that is a relatively weak pair of axes, under tension.
I actually have seen wooden wagons careening around pretty good. Modern wheels are going to be better, but most of the time when you read about a historical wheel failure it involves, like, a panicked animal and/or some truly rough off-road terrain. Which TBF definitely came up.
There's actually another factor here! The exact shrinkage of a green log as it seasons is something like 15% radially, 5% axially and not at all along the grain. If you think about the geometry of that, it's going to build up quite a lot of stress and spontaneously fail, unless it has been cut and can warp instead. And that's exactly what you see in old, unsplit logs; they get one big, longitudinal crack that spreads open almost to the center.
IIRC your wheel will have to be wrist size or smaller, by the conventional wisdom. Or, I guess, stay permanently soaked and soft, either by way of sealant or having a job underwater.
TIL! I had always assumed they were bolted.
In the case of aircraft fuselage -- using the Boeing 787 as the prime example -- the pressurized cabin means that the airplane is basically a balloon, as the pressure inside is typically something akin to being at 6000-8000 ft MSL (~2-3 km) but the outside air pressure is something like 32,000-38,000 ft MSL (~10-12 km).
Expressed another way, the delta between 6000 ft pressure and 38,000 ft pressure is about 600 hPa, or roughly 60% of sea level pressure. Since 1 Pascal is 1 Newton per square meter, and if we say an aircraft door is 2 sq meters, the force trying to push the door open at cruise is 120,000 Newtons, or the equivalent gravitational force expressed an object measuring 6 tonnes!
As a balloon-like tube, the 787 fuselage has a lot of similarities with how its fibres are arranged, not unlike the plies that stretch across the tread of a pneumatic bicycle tire.
Ok, I have to know: what sort of situation would this have been at? Medieval chariot racing?
I've never thought about the shrinkage rate before, but it makes perfect sense that wood would shrink at different rates in different dimensions. Would this also suggest that steam bending of wood is less effective in certain directions?
Hmm. Is that why passenger jets have stuck with aluminum for the wings, then? They do have to actually bend a visible amount, as opposed to just being an inflated balloon.
I can't remember now how much chariot racing I've seen. I don't think ever in person, although wooden carts have been around at re-enactor things.
I was thinking about this local specialty, which I'm pretty sure still uses traditional wooden wheels.
Maybe, but not directly for that reason. The relevant effect there is the lignin reaching a heat and moisture-induced glass transition and plasticly deforming. I'm not actually sure if the relatively large shrinkage along the growth rings is due to capillary and cell shape, arrangement of the polymers, or both.
I want to say the 787 also has composites in the wings, but I'm not certain. It does, however, bend quite a lot during takeoff. But I think most wings do too, but controlled so it doesn't cause fatigue cracking at the wing roots. A composite wing wouldn't have the same fatigue failure mechanism.