FAR pre-launch wobble destroying rocket?

[ROXunreal]

Just installed FAR, as well as DRE, KAS, procedural fairings and RealChutes, and I feel like I bought a 50% expansion to the game which is great.

I have an observation and an issue with FAR:

First the observation - holy impolite word is it easy to get above 70km, thrust-wise. I used my first low-tech Minmus craft to test FAR, expecting epic fail.

I accelerated to the atmosphere friction burn threshold and the rocket started rotating along its length, but I made it, with an apoapsis of almost 200km just by using SRB's, whereas before I would barely bring my Ap up to 40km before SRB's ran out. Also, nothing fell off my completely exposed lander with all the little things sticking out. Some things started overheating due to DRE but never went critical. I can say I was somewhat surprised, mostly at the ease of reaching such high altitude. Again, this isn't a complaint, merely an observation as I found it curious, I can imagine the atmosphere in FAR is as more difficult to fly in as it is easy to transverse on a given powerplant.

Now the issue - this is my revised Mun craft. It was identical to the Minmus craft apart from the wider lander with more fuel, but as a FAR makeover, I removed the out of place centerline SRB's and replaced them with two BACC units on the sides (the centerline arrangement was a remnant from when my launch pad limited me in weight and I had no weight room to put two more BACC on). I also downloaded procedural fairings to streamline the ship and ended up with this. I strutted each SRB once near the top as I always do, using symmetry of course.

Thinking this would be awesome I went to launch. My rocket violently wobbled itself to death before I even launched, in less than 10 seconds. As soon as it settles on its rocket holders it starts wobbling and this only increases until it falls apart. I'm baffled. Do I need more struts, or the hardened joints mod or what? I really hope this isn't a glitch because I really want to play these mods.

SAS on or off makes no difference.

- - - Updated - - -

Turns out A LOT more struts fixes the problem. Though the rocket tends to look silly-ish with every booster connected with 4-5 struts.

Turns out I answered my own question, well wasn't that a bit pointless. Shouldn't get a head of myself when posting new questions on the forum I guess...

Still, is it normal to get so much more out of the same thrust with FAR? I mean I intersected Mun orbit just by strapping the big SRB to a pod and hitting space.

[DeMatt]

Thinking this would be awesome I went to launch. My rocket violently wobbled itself to death before I even launched, in less than 10 seconds. As soon as it settles on its rocket holders it starts wobbling and this only increases until it falls apart. I'm baffled. Do I need more struts, or the hardened joints mod or what? I really hope this isn't a glitch because I really want to play these mods.

Each of those S1 SRBs you've got on the sides, totally unsupported, masses almost 22 tonnes. Your first rocket has them supported by Launch Stability Enhancers; your second one doesn't. Add LSEs to them, or better yet, redesign your rocket to remove them. Think "long and pointy", not "moar boosters".

Still, is it normal to get so much more out of the same thrust with FAR? I mean I intersected Mun orbit just by strapping the big SRB to a pod and hitting space.

Pretty much, yeah. On a reasonably designed rocket, NEAR/FAR reduces drag by a lot - enough that surface->LKO takes something like 25% less delta-V. It does help that Kerbin and its atmosphere are SO much smaller than Earth's.

[Van Disaster]

IIRC something fat like an Ariane 5 loses about 200m/s to atmospheric drag on Earth, so you'd expect hardly anything for Kerbin. I would also suspect you have a structural issue - you might want to try Ferram's KJR joint reinforcement mod also.

[Sovek]

you need a completely redesigned rocket. That is way too much weight just to get to minmus. dV requirements for Kerbin to Minmus, land and return is somewhere around 6.5K with FAR, maybe less. Give me a few minutes to load KSP and I'll give you an example craft.

The above rocket will get to the Mun and back, its comprised of one orange tank to push it to almost LKO, powered by 4 LVT-45s, Second stage should get you into LKO, TMI, Munar Insertion and de-orbit, the lander. Second stage is a FL200 and 400 tank, powered by 909, Third stage is one FL200 tank with another 909.

Use the second stage to kill as much as your velocity when landing as possible, I was able only touch about 200 m/s of dV on the lander stage to land, leaving 1250 to get back into orbit and return to kerbin, more than enough.

Also note with FAR, right click on your stab fins and reduce the Ctrl Deflec amount to somewhere around 6.5-7.5, anything more and risk heavy rotation on your roll axis (at least without torque wheels), it also prevents you from trying to turn your rocket too aggresivly and causing it to flip out of control.

Edited January 13, 2015 by Sovek

[WuphonsReach]

http://i.imgur.com/ZksBZEq.jpg

At a minimum, you should add (4) EAS medium struts connecting the bottom of each booster to the neighbor. That keeps the wobble to a minimum.

Secondly, strutting across multiple "stages" is a recipe for disaster. Those radial SRBs should only connect to the next stage's parts (such as the 2.5m fuel tank in the center). In this particular case, I would go down about 1/3 of the way on the SRB and add EAS struts to each side of each SRB, linked upwards towards the top of the 2.5m fuel tank.

Third - install Kerbal Joint Reinforcement - the primary advantage is that whenever a scene loads, it eases into the scene. That tends to avoid sudden decompression of physics parts.

Fourth - get rid of the RT-10 and BACC on the bottom...