Rockets lacking stabilty?

[Philoman]

I've been playing KSP for a while and it has always annoyed me a little bit that the rockets never seemed to fly perfectly. While I was still playing with only the stock parts i managed to build relatively stable and reached Eve, Duna, Jool etc.

Then I recently decided to upgrade my KSP experience with some different Part Packs (primarily KW), which contains fairings and much bigger tanks and parts. It's all very nice until I launch one of these things and they disintegrate on its way out of the atmosphere. With some of the smaller engines there doesn't seem to be any problems, so the only obvious explanation to this is that there is a certain limit when it comes to how much thrust a rocket can tolerate. Now I am, of course, using a lot of the extra strong struts, which I btw hate because they are ugly and we don't see them in real life, but even with these struts it always breaks apart.

I know some if not most of you would just think "try building a proper rocket" but i am building it properly. I'm watching several videos on youtube and try to keep up as much as I can on this very busy forum, and I have, as I said, played it for a while.

It's just that when we often seek more and more realism and there is this constant discussion about realism vs. gameplay over numerous ideas, I believe that it would be both more fun and inviting to new players if parts weren't that wobbly and it would at the same time be more realistic since you don't really see it on rockets in real life. I hope somebody share this view with me

PS I know that struts were used on the space shuttle to connect the external fuel tank to the shuttle, but you don't see eight or sixteen struts between to segments on the Apollo rockets for instance.

[Psycix]

Huge things wobble and lack structural stiffness. This gets worse with larger objects, especially the big KW tanks.

Just recently, ferram released a mod that should mitigate this:

http://forum.kerbalspaceprogram.com/threads/55657-0-22-Kerbal-Joint-Reinforcement-v1-0-Properly-Rigid-Part-Connections

Perhaps you could post a couple of screenshots of your rocket designs, and explain how and when they fail?

[Ruinsage]

I recently suggested that the connection between parts should be more rigid if the parts fit together (like identical fuel tanks, and the connection between engines and fueltanks of the same diameter), making logical rockets use less parts due to struts, which you really have to use to make large rockets, improving quality.

However, this in on the "what not to suggest" list, as the devs want rockets to be wobly.

Edit:

If you don't want to use struts because they look bad, i have a technique you can use:

When you attach two fueltanks, put a fueltank with a smaller diameter between them. Then place struts on the top of the bottom fueltank, attach them to the bottom of the top tank. Then remove the bottom fueltank, without deleting it, delete the small middle fueltank, and reattach the bottom fueltank. The struts will attach in the space between the fueltanks, but you wont see them because they will be "inside" the fueltanks.

Edited October 29, 2013 by Ruinsage

[digitalsingularity]

Wow! Thanks for sharing. I built a 8000 ton monstrosity to get about 600 tons of fuel into orbit (I like having a fuel depots, got tired of launching refueling ships into orbit). The thing basically dances on the launch pad because the parts wobble so much. It's kind of amusing... I should probably make a gif of it.

[ANWRocketMan]

I once built a rocket of equal mass... Once... It was about 250m tall, with a base of around 18.75m diameter(5x 3.75m KW Rocketry fuel tanks).

...

It didn't work.

A rather effective(and ugly) strutting mechanism seems to be using small octagonal structural pieces on each tank, with a strut between them:

_

X| ~ Octagonal Truss

|

| ~ Strut

|

_

X ~ Octagonal Truss

Another method I found is adding a ring of struts sandwiched in-between fuel tanks, fairings, engines, decouplers, the lot. It works relatively well. It is also well hidden so it doesn't look ugly either.

For flight stability I usually add some linear RCS ports around the top of the rocket with extra RCS fuel. I also add fins(controllable) to the bottom near the lifting engines. This provides good control, even when using FAR.

I should note that I only build realistic looking rockets. Stacks on-top of each other, with possibly two side mounted boosters(usually liquid but depends on payload). No fuel crossfeeding. For roleplaying's sake.

[digitalsingularity]

Unfortunately, the game doesn't allow multiple attachment points. I'd imagine rocket structures would be a lot more stable if you could do things like attach parts via multiple trusses / beams, as opposed to having a single point, which is further supported by a bunch of struts. I don't care about truly realistic (I use asparagus staging)... the game's just fun to me and allows me to do the kind of stuff I wish NASA / JPL had the money to do.