Bending mechanics in ksp

[Markus Kerman]

Hi, I just got really curious when I saw what I did (see the pic). When I was messing around with gravity and a super long plane ( that I crashed into the ocean ;D ) I got this weird bent fuselage thing somehow after a lot of messing around. So is there actually a mechanic like this?

https://imgur.com/a/pHycx7H

Edited October 24, 2018 by Val
Fixed imgur link

[pincushionman]

Is there structural deformation? Yes there is. The physics engine KSP is using  simulates structures as a number of rigid bodies connected together, but the joints between them are allowed to be flexible.

The vehicle you’re showing here is very long, but the parts making it up are individually quite short. Therefore, there are a lot of segments, and by extension, many joints, which makes the whole structure quite flexible. This has an effect on early-tech-tree gameplay - all you have at your disposal are short parts, so you’re forced into building small rockets until you can buy the ability to build something not so wobbly and noodle-y.

EDIT: Welcome to the forums!

Edited October 24, 2018 by pincushionman

[MR L A]

48 minutes ago, pincushionman said:

until you can buy the ability to build something not so wobbly and noodle-y.

This should be fixed, to a large degree, by using rigid attachment and autostrut in advanced tweakables, should it not? It's been an incredibly long time since I've had any noodle-like behaviour...

I understand it isn't perfect still, but "noodle" seems a bit of a stretch these days

[Markus Kerman]

53 minutes ago, pincushionman said:

Is there structural deformation? Yes there is. The physics engine KSP is using  simulates structures as a number of rigid bodies connected together, but the joints between them are allowed to be flexible.

The vehicle you’re showing here is very long, but the parts making it up are individually quite short. Therefore, there are a lot of segments, and by extension, many joints, which makes the whole structure quite flexible. This has an effect on early-tech-tree gameplay - all you have at your disposal are short parts, so you’re forced into building small rockets until you can buy the ability to build something not so wobbly and noodle-y.

EDIT: Welcome to the forums!

Thanks for the welcome man, but this bending got "fixed" when I switched to another nearby (broken off) part, why ? Why can't the bend be a permanent ?

6 minutes ago, MR L A said:

This should be fixed, to a large degree, by using rigid attachment and autostrut in advanced tweakables, should it not? It's been an incredibly long time since I've had any noodle-like behaviour...

I understand it isn't perfect still, but "noodle" seems a bit of a stretch these days

Also, auto strutted almost every part of the fuselage cause the plane was sagging so much under it's own weight XD. But the bend happened anyway

[natsirt721]

3 hours ago, Markus Kerman said:

Why can't the bend be a permanent ?

KSP Explanation: Vessel specifics (i.e. what parts are where) are stored in a file and bending is caused by the physics engine.  When you switch to a nearby part, your vessel can get 'packed', which is like being in warp but not exactly.  When you switch back, you get 'unpacked', where the game loads the vessel data from the file again.  On packing, things like joint bending data are not stored, probably because a) a pilot seeing bending will stop doing whatever he is doing, because bending leads to breaking or b) aforementioned bending is about to become breaking.  So, on unpack the vessel maintains its orientation but all the parts go back to their 'proper' places, i.e. how they are defined in the file.

Science Explanation: Bending of structural components is not inherently a bad thing - in fact is is an unavoidable consequence of loading (applying a force, not saving/loading) a structure.  At low stresses, the components bend 'elastically', that is, they will return to their original length if they are unloaded.  At high stresses, they bend 'plastically', and will not completely return to their original length.  What you are describing, plastic deformation - or saved part rotation - is VERY VERY BAD for structures, because every time it is stressed and unstressed the part gets a little bit longer (if loaded in tension) or shorter (if loaded in compression).  As parts/structures are usually composed of multiple beams, forces will cause some beams to elongate and some to shrink.  The beams that elongate still have the same amount of material, which means that their cross-section (and their ability to resist loadings) shrinks - this will cause even more elongation the next time the same force is applied.  Eventually, load/unload cycles will cause the beam to be loaded beyond its ultimate strength, at which point it fails.

Oh, and welcome to the forums 

[Markus Kerman]

Wow....Funny how I've started  the chapter about elasticity and all in my class and here it is

Edited October 24, 2018 by Markus Kerman

[Markus Kerman]

Well thanks a lot,... also what's this "your content will need to be approved by a moderator"

[dreadanaught]

Simple explanation: It turned into a sea serpent. (KSP has Krakens, so why not?)

 

In all reality though, it's just joints between parts bending.

[Markus Kerman]

XDXDXD Yeah sea serpent, why not

[Vanamonde]

3 hours ago, Markus Kerman said:

Well thanks a lot,... also what's this "your content will need to be approved by a moderator"

Your first few posts require approval until we are sure you are not a dirty spambot. 

[Markus Kerman]

ahh I see thanks a lot

Also how do I end this thread ?

Edited October 25, 2018 by Markus Kerman

[Aeroboi]

17 minutes ago, Markus Kerman said:

ahh I see thanks a lot

Also how do I end this thread ?

That doesn't happen. Posts will wander for ever to face the test of time so intriguing curious players can still read the questions and answers of others like in this case.

Bending or the loose joints can also be benefited from by making springs for suspension or stock made cords. I used the spring effect lately to create a stage activated engine pivot for thrust realignment. The only reason I begin about it is that these wonky physics are beneficial for creative out of the box ideas so I hope this will always remain.

[Vanamonde]

3 hours ago, Markus Kerman said:

Also how do I end this thread ?

You could ask us moderators to close it, but there's really no need. 

[Markus Kerman]

ok nvm then thanks all for your help

[Sharpy]

On topic: bending is often creatively used. Various parts have various breaking force and various flexible bending force. You can prevent bending using autostrut and strut connectors (very rigid), or you can embrace it - the classic part abused for that is the Spider engine (the surface-mounted Ant variant) which has quite high breaking force but relatively weak bending/flexing force - so you can use it as a hinge joint. 

This is a vehicle suspension made using the Spider engines as hinges. (doing this currently requires hacking KSP to disable autostrut on wheels, which automatically autostrut to heaviest part(s) - so without the hack this trick doesn't work.

 

But an alternative is trailer hitches from the Lynx rover. A set of parts that allows similar creative liberties without affecting core mechanics:

And this is another "creative" use of the mechanics, using I-beams and struts (which, as I said are very rigid and strong) plus excessive weight:

 

I even managed to simulate cloth physics using the stock bending mechanics: https://kerbalx.com/sharpy/Quilt