The Accordion Problem

[Sabastian]

I'm attempting to put a tanker into LKO to service my interplanetary transport ship, but I keep running into the same issue. The goal is to get a full orange tank into orbit, but my mainsail engines keep plowing through my stack. My lifter is pretty standard: four well-strutted 2.5m boosters, each three Rockomax Jumbo tanks tall, around a core that is one orange tank on top of two Rockomax Jumbo Tanks. Each stack has a Mainsail under it. Has anyone else run into the issue of mainsails causing their stack to accordion? What causes this? Too high of a TWR? Too much thrust under a heavy payload? The ship has very little wobble as is, so I'm having a tough time trouble shooting. Thanks!

[sal_vager]

Those engines are powerful Sabastian, throttling back can help or more struts, especially struts from the parent part to the child part.

It's a combination of mass and thrust like you suspect

[Conarr]

Also, if you use MechJeb, it can limit the G's applied to your spacecraft. I use 25.25m/s2

[EndlessWaves]

What do you mean by 'accordian'? My first thought was that you meant the behaviour where parts passed through each other, but that's due to high acceleration and wouldn't generally happen when you're pushing >100 tons with a mainsail.

[capi3101]

"Telescoping" is the more common term for this, unless I'm mistaken. Like sal_vager said, it's a combination of mass and thrust. More struts help, particularly set vertically between the orange tanks (alternatively, you could replace them with pairs of X200-32s; those have been observed to be more structurally stable. You can try throttling back too - if you're going faster than 130 m/s at 3000m, you need to throttle back. Same goes for 160 at 5000m and 215 at 8000m.

[dr_jt]

Consider Kerbals

Edited June 6, 2013 by dr_jt

[Titler]

Orange Tanks to White Tanks will pancake if using mainsails; the game seems to have differing structural values for the two, and when under enormous thrust as when using a mainsail engine, it sees it as stronger tank pushing into weaker and collapses at the connecting points of the white tanks. So if possible mass struts around the white tanks, or use girders at 90 degrees from the white tanks and then struts to the girder each side, to make a kind of "kite" design around it, thus taking strain off the connection points. My own design now uses white only as the booster connection due to the difficulty of placing oranges radially at first; it currently looks like this, with a few struts placed flush between tanks for added security. This will arrive around Mun with a 17-30t lander stage and half an orange tank and nearly all the RCS intact...

The important thing though is because there's no white tanks on the centre of thrust, it avoids the Accordion Of Doom effect, at least in the last 10 launches or so!

Edited May 15, 2013 by Titler

[Sabastian]

Thanks all! Struts between the orange and white tanks really did the trick. My large exploration ship is now ready for its maiden voyage (destination TBD)!