So, about them orange tanks...

[capi3101]

I've built most of my heavy designs using Rockomax X200-32 Fuel Tanks because I've heard repeatedly that there are some significant disadvantages with the Rockomax Jumbo 64 in the current version. As I'm wanting to launch heavier payloads, though, and I'm noticing that my part counts are starting to make my CPU smoke a bit, I can't help but wonder if I should switch out. I've also seen you guys use the orange tanks a lot, so I have to ask: are they really all that bad?

[Canopus]

They aren't bad but they cause your Mainsail to overheat faster. Just put a small tank between them and your engines and the problem should be solved:)

[K^2]

They aren't bad but they cause your Mainsail to overheat faster. Just put a small tank between them and your engines and the problem should be solved:)

This solution still gives you two parts where there is one, and it seems that OP's problem is specifically with part count.

If you attach mainsails directly to jumbo tanks, you will have to cut throttle a bit. But that's not necessarily bad, depending on how good your TWR is.

[Canopus]

Well its just a small tank.

[capi3101]

Planned a TSTO using the orange tanks - looking at 1.75 on the first stage, 1.68 on the second, and 1.24 on the third. Payload's just under 120 tonnes; total mass at launch is looking at a little over 1500 tonnes with about 4601 delta-V and around 275 parts. That's assuming all the math's right. Haven't built it yet, obviously.

[Blackstar]

Stacking two on top of each other tends to result in structural failure, especially if there's any load above them. They're so heavy that they just can't handle the weight. If you need to do that, be prepared to add a dozen struts just to distribute the load and keep the two tanks from trying to occupy the same space.

I like to use them as drop tanks at the bottom of my heavy lifters -- off rockmax decouplers attached to support structures away from the main engines. I know, I'm doomed if we ever get accurate aerodynamics.

[capi3101]

Okay; I've actually got several stacks of two planned in my design...

When you say I should "be prepared to add a dozen struts", is that between the two tanks or between them and the tanks surrounding them? I.e. can you put struts between two tanks with one on top of the other? I've tried and haven't had much success in that regard.

[K^2]

Well its just a small tank.

It's not about the size of the part. Just number of parts.

[Noticeably FAT]

You can (and I generally do) place struts between tanks. I like to use at least 2x symmetry, and I'll place the struts at the very bottom of the upper tank and very top of the lower tank to 'stitch' the tanks together. You really can't even see the strut, just the two end brackets. It does increase part counts, but two orange tanks and a small tank (for overheating) strutted together seem to work pretty well as boosters. I haven't really tried to put anything on top of them, but I will strut the payload to them to help with wobbling during the ascent.

[Anglave]

Okay; I've actually got several stacks of two planned in my design...

When you say I should "be prepared to add a dozen struts", is that between the two tanks or between them and the tanks surrounding them? I.e. can you put struts between two tanks with one on top of the other? I've tried and haven't had much success in that regard.

Stacks of two should be fine. I even use stacks of 3 sometimes. I do recommend "stitching" them together (struts across the join, with symmetry around the stack). Unfortunately, this adds again to the part count.

Regarding the "use a small tank under the orange tank:

My recent Laythe mission's Kerbin ascent stages used that design.

And the main ascent used some stacks of three:

[ouion]

What are your specs ?

[Vanamonde]

This solution still gives you two parts where there is one

A small gray below an orange still has a larger capacity than any other pair-combination of tanks, so at worst you're trading 2 tanks of lesser capacity for 2 tanks with a larger capacity. Edited May 8, 2013 by Vanamonde

[capi3101]

What are your specs ?

Pretty much what I said earlier; payload's just under 120 tonnes. I've designed a TSTO booster for it using the orange tanks - looking at TWRs of 1.75 on the first stage, 1.68 on the second, and 1.24 on the third. total mass at launch is looking at a little over 1500 tonnes with about 4601 delta-V.

So...I've built this design at this point and I didn't know you could stitch the tanks together, so as y'all can imagine I've been treated to some fairly spectacular unplanned vehicular disassemblies this evening. I think my record for skipping a Standard Canard across the KSC is maybe half a dozen bounces so far. You know it's bad when the TT-18-As get knocked over; yet the Probodobodyne OKTO sitting at the top of the third stage survived. Even still had a PB-NUK attached.

Actually did get the design into the air once and it did pretty well up until first stage separation. That's when I realized I hadn't put any control surfaces on the second stage...

Good thing that A) the designers have yet to account for radioactivity from exploding PB-NUKs and LV-Ns and I was doing all this in the "Construction Basics" tutorial, so I didn't clutter up my persistent game with moar junk...

[capi3101]

So here's one I don't understand...I've got "ringed asparagus staging" going on between my stage rockets if I understand the term correctly; the third stage feeds off the second stage which feeds off the first. 8 mainsails in the first stage, 8 mainsails in the second stage and the third stage (the central stack) is one mainsail with 8 Mark 55s (without which the third stage TWR would only be 0.9 if I've done the math correctly). I've checked the fuel ducts and they're all running in the right direction. Launch at 80% thrust and the first stage runs out of gas just before 10k following a fuel-optimal ascent profile; I eject it and throttle up. Twice now, when I get to about 14,000, the center engine shuts off because it's out of gas. You know, my third stage - the one that's supposed to make the orbital insertion burn and should be drawing off the fuel supplies of 16 mainsails.

Any ideas on what might be happening?

I'll try to post the .craft file and some screenshots in the near future; still haven't found a repository I like yet.