Physics behind cylindrical objects in free-fall

[DareDemon666]

Hi,

So I was playing KSP and I noticed that cylindrical objects - like jettisoned stages, fuel tanks, etc - seemed to fall with an attitude perpendicular to the flight path, Basically they fly/fall sideways. The weird bit is that this even happens with parts with nose cones so that it has the least drag with the nose into the wind as it were. I mean here even the centre of mass is shifted slightly forwards.

It got me thinking, though I understand a fair amount of physics I can't figure out why it doesn't fly aerodynamically? -And once sideways it's incredibly hard to orient any other way (as you'd expect).

So am I being an idiot here and missing something I really should've learnt by A-level physics, or is there some underlying phenomenon at work here?

Cheers,

Jack

[Cunjo Carl]

First off, welcome, @DareDemon666!

You're not crazy.

If you have a version prior to the latest release (1.2), individual components tend not to fall in sensible ways. My favorite was single airplane wings on the ground in v1.1- would flip themselves upright like bopbags rather than lay flat. This seems to have been fixed in v 1.2- Thanks Devs!

You mentioned this happening on jettisoned parts with multiple components, though. It's not uncommon for decoupled things to briefly turn sideways due to the torque of decoupling + aerodynamic forces if it's bottom heavy. This is normally followed by random tumbling though, and it sounds like your case isn't. Maybe, are you describing something like a 'flat spin'? I have to admit, I've only ever noticed my ejected junk peel away and slow-tumble erratically like you might expect (or for something particularly aerodynamically inclined, eventually flip around and nosedive like a dart). If you post a picture I'd be happy to hm and haw some more, but otherwise we can leave it as you're physics understanding sounds good!

 

If you're curious to see a real world example, check out these videos of the the space shuttles SRBs decoupling:

https://youtu.be/uuYoYl5kyVE?list=PLe8qRS4LwO8mYtQEFcjh8S0xT1nM3VaQ4&t=123

https://youtu.be/2aCOyOvOw5c?t=110

 

[DareDemon666]

Thanks for the answer!

In the case of jettisoned stages it might be the motor's mass throwing things off, but then I'd expect it to fly with the engine forwards.

I also mostly see things like boosters falling 'away' from the craft with a slight spin - shortly becoming random spinning.

It seems most likely that I've got an out of date version, I'll go take a look...

Once again, cheers!