Launch Clamp Issue

[Streetwind]

I'm currently in the process of designing various rockets. Since I'm still new, I don't really push for any particular goal (despite playing career mode), I just stick stuff together and launch it to see how it behaves, what leaves me with the most fuel in orbit, what makes rockets easy or hard to control and such. It also helps me practice controls... At this point I can launch directly into a perfectly equatorial 70km orbit with periapsis and apoapsis within 250 meters fo each other... and reproduce the feat at will. I have never installed any autopilot mods.

However, there's something that's seriously cramping my style, and that's the way launch clamps work. Rockets are naturally slimmer up top, because later stages are smaller and lighter... and as a result, the wide lower stages (especially with boosters) keep me from attaching launch clamps to the upper stages. This, in turn, results in the upper part of any rocket higher than 2-3 fuel tanks wobbling about erratically on the launch pad, and eventually settling into a minimal lean off to one side. The result is that even with perfectly symmetrical rockets fitted with gimbaling engines, extra SAS modules and control winglets, the craft just won't fly straight.

At this point I am still using less than a quarter of the VAB's vertical space, and I honestly have no idea how I could utilize more of it. I've tried slimming down the lower stages or fattening the upper ones, but I always end up in a situation where I can't fit enough engines on the first stage to launch to any meaningful speed. I need the wide base for engine space, and the slim top to save weight. So how can I properly stabilize the top of a tall rocket?

Edited January 4, 2014 by Streetwind

[KvickFlygarn87]

Try getting Kerbal Joint Reinforcement addon helps stability a lot. Alternatively, slap some struts to all your everythings.

[Rhomphaia]

You can attach things to the launch clamps, like extra long girder segments, then struts from them to the upper stages

[Streetwind]

Won't that make the lower stages collide with the girders and/or struts as they fly up, though?

Edited January 4, 2014 by Streetwind

[KvickFlygarn87]

Could we see some pics? If you don't know, hit F1 and check the screenshots folder in KSP.

[Rhomphaia]

Won't that make the lower stages collide with the girders and/or struts as they fly up, though?

the struts dissapear when the launch clamp releases. the girders go straight up

[Streetwind]

Right, I tried some of these suggestions.

For starters, I was able to firm up my rocket by using struts on the rocket itself, so that it wasn't quite as "bendy" anymore. I noticed that it especially helped to support the decouplers that held the boosters... because the boosters were held by launch clamps, and therefore the entire rocket was effectively suspended by the set of decouplers.

Then I went and built girders up on the launch clamps, and conencted struts to the top stage. This actually made things massively worse, because the tall towers of girders wobbled about in an extreme fashion. I tried to solve this by attaching extra launch clamps to the top of the girders, and strutting them among each other.

Ultimately I ended up with this. Which sadly still jittering about (you can see the 0.1 m/s velocity display even though the rocket is just sitting on the launchpad).

[Kasuha]

You can always support your inner stages from below. You cannot stick the clamp to an engine, but you can use a decoupler. That grey thing is a shroud around the engine added together with the decoupler.

[Seret]

Moar struts required. You can strut tanks stacked on top of one another, just use the tiny truss segment on either side of the join and strut the two trusses. Apart from that, engage your reaction wheels first thing when you're on the pad and it should help to damp any wobbles.

As for your rocket in the pic, it's not really that big, you should be able to get it working reliably. If you could lose a couple of your boosters you should have room to get your launch clamps onto the main rocket body higher up. Do you really need that many engines at launch? Your boosters are short and fat, fewer long slim ones might do the job. If you're after mega thrust for a short period you could just use SRBs instead of clustered liquid engines.

[Streetwind]

Interestigng idea with the support from below.

@Seret: Yeah, I did that. Adding struts to the rocket itself helped. The reaction wheels are of course always on, and help stability in flight, but don't really do anything at all about wobbling onthe launchpad.

And no, that rocket cannot lose any boosters, and doesn't stand to gain anything from making them taller Mind you, I have other rockets too that suffer from the wobbling, but I randomly grabbed this one for the screenshot because it was the one I worked on last. It's a silly experimental design that I wanted to do just because I could. The boosters are neither solid nor liquid engines... they're jet engines, six times three of them. And because they start to flame-out north of 10 kilometers, they hardly need any fuel. Those already tiny tanks carry only 10% of their maximum filling amount. All in all that gives me a ridiculous thrust-to-weight ratio of over 100 kN per ton of booster. No liquid or solid fuel engine comes even close to that. Here's another screenshot of the boosters without all the hubbub around them.

They're kind of iffy to handle overall though and cut out just a bit too early for my tastes, so I probably won't be using that design for regular carrier duty. Maybe when I unlock some of the better jet engines and intakes, these are just basic ones.

Edited January 4, 2014 by Streetwind

[Seret]

The boosters are neither solid nor liquid engines... they're jet engines

Ah, actually I see your intakes on your original pic now that you've said that. That makes a bit more sense.

Could you squeeze a clamp in between them? Maybe shift the fins a bit? You could try shortening the whole rocket a bit, you could use clusters of smaller tanks attached radially on upper stages? Might look a bit odd, but it'd get that CofG lower. Can you launch something stably without all the mass of the upper stages?

Trusses attached radially half way up the rocket, to make attachment points for the clamps? Blow them when you ditch the boosters (or maybe before with sepratrons?)

I wonder if it's possible to rig up self-destructing launch clamps?

Edited January 4, 2014 by Seret

[Streetwind]

Yeah, making rockets shorter and wider seems to work, as long as you liberally apply struts. Kind of counterintuitive to RL, but I suppose that might have to do with KSP's simplified physics simulation.

Building handmade launch clamps with decouplers and girders was something I also thought about briefly. Might be a fun project to mess around with sometime

[DerekL1963]

Kerbal Joint Reinforcement is your friend for life.