need help when using liquid fuel rockets as boosters

[Chris Solomon]

former topic name: bug found when using liquid fuel rockets as boosters

I just noticed on the ship that i built, the rockets i was using as boosters, the twin boar engines and the atached fuel tanks were using the fuel from other copies of the same setup (i had it setup as a quad booster setup. additionally the extra fuel that ibieng used, is not counting as additional fuel, but the fuels is being reduced from the tanks all at the same time. the central fuel tank is also being used, even when it's rockct has not been activated yet. Crossfeed has definitly been turned off on the couplers. I do not use mods on my copy of KSP. I have captured a screenshot of what im talking about (posted below) I will also upload a copy of the ship build to the workshop and post a link to it, for testing purposes.

ship download link: https://steamcommunity.com/sharedfiles/filedetails/?id=1547394798

https://steamcommunity.com/sharedfiles/filedetails/?id=1547391762

unless i am completely wrong, and i don't think i am in this case, each of the twin boars should be using their own attached fuel tank, and not depleteing other tanks also the fuel bieng depleted is no being counted right when it is being used (another aspect of the bug perhaps?) furthermore, there should be NO crossfeeding of fuel present.

[Chris Solomon]

to test to see what i am talking about, do the following:

WITH NO MODS launch the rocket i have posted above

manualy activate one of the twin boar rockets, but keep the throttle super low, like maybe 10%.

Observe the fuels usage of the attached fuel tanks as well as the fuel tanks attached to the OTHER twin boar rockets.

once those tanks get depleted, observe the fuel levels of the other inactive twinboars get depleted.

after you have run done this, feel free to tweak the design all you want, or build your own design too see if the bug is present in those as well.

the design as it is now, is 100% flyable, W/O any cheats active. flight is also 100% stable

[Mor'finn]

Your side tanks are attached directly to the middle tank, not decouplers.

[Chris Solomon]

ah ok. they should be attached to the decouplers i will try switching to the taller decouplers which are easier to attach to

[Chris Solomon]

OKay, changed out the decouplers, and problem went away

Originally posted by RoofCat:

Originally posted by DentedMarroW4:

Your side tanks are attached directly to the middle tank, not decouplers.

this. No decouplers mean fuel flows freely everywhere inbetween parts. Just set your tank priorities!

Also don't use Twin boars at upper stage. They are one of the best launch engines due to low own weight and rather cheap for that (stronger and cheaper than Mainsail with the same fuel amount). But their Isp in vacuum is some of the worst. Twinboar is thirsty so even as a booster it should have at least 1.5 jumbo tank (54+t) fuel for each (including internal one). Or you are just wasting money and mass what could be done with much cheaper SRB.
As a single launch engine it goes best with up to 2.5 Jumbo tanks (including internal one, so +1.5). Depends on your upper stage power and mass - how soon can you switch to more efficient vacuum stage without wasting too much on their price and mass. Often Twin boar goes to ~1800m/s+ or even to full LKO just because that's the cheapest way. You can even make it recoverable launcher stage. Basically you would have 90..100t lower stage with Twin boar plus tanks for it and then ~30t payload/upper stage for a single one and optimal launch TWR.

i am using the twin boars where they are due to a contract. the contract is one of my favorites - making kerbals pass out. the only trick here is it has to be with in the suborbital altitude, and the 'tourist kerbals' don't pass out easily. i needed some oomph to get them too pass out once i got into space.

[Chris Solomon]

since this is not due to a bug, i will be updating the thread titile

[RoofCat]

sepatrons have highest TWR thus highest G and best pass out chance. Not sure if those ~8 (?) sec are enough though. Also using many (to have power enough for larger cabin) isn't that cheap anymore.
Simple and cheap SRB solutions might be best for that as they are cheap and have very high power closer to end. Hammers have rather extreme powers and last for reasonable 24sec iirc. Much cheaper. SRB lose TWR the bigger they get, but if you keep payload low, kickbacks might still do the trick closer to the end of burn too.

[Chris Solomon]

the tourist's i was carrying didn't pass out until the G meter was almost maxed out, so they had a pretty high tolerance for G's.

[Mor'finn]

Cheaper way to get kerbals to pass out is to do a steep reentry. If you burn straight up until apoapsis is 500 km and let the ship drop to Kerbin, it will pull about 20 G's on reentry. No need to use expensive engines.

[RoofCat]

I just did a test and using 3 Hammers at once with MK1 pod made my 5* Jeb pass out. So tourists should be dead by that point I guess? :D

add some cheap probe, chute, sharp nose cones on 2 radial hammers, decoupler below pod, price <4000.

[Chris Solomon]

well i was also limited to maiking them pass out at a sub orbital altitude, but i noticed i had to hold the G meter a t max for a fixed period of time before they would finally pass out.... my build works fine. I usually do speciallized builds for my contracts. eventually i will get to the point where i can do a one build fits most design

[RoofCat]

put one kickback in the middle below those 3 hammers? Kickback is great for lifting 1/2 of it's own mass as payload. Which is really close to the mass of 3 Hammers and pod.
Suborbital only means your Ap is above 70km during that blackout. Going straight up or with minimal angle that is not too hard to achieve due to high velocity. Drag isn't calculated ahead while projecting your Ap. So having high speed medium low you might already have predicted suborbital Ap even though in reality you would never be able to reach it due to all the future drag.

As for really large amounts of those freaks, just launch MK3 cabin with 16 junkies high enough by any cheap means, let them fall back and add inflatable heatshield to the design. Deploy at 20km or so. Their brains will be all over the cabin after landing ;/

[Chris Solomon]

i tried a more simpler more rockets using only srb's like the kickback, but it got to only to the "reaching pass out limit' portion. I do appreciate the feedback though. I spent quite a while tinkering with more basic designs following the "keep it simple stupid" line of thought, but that just wasn't enough.

[RoofCat]

because Kickbacks are heavy lifters not sprinters. That's why you need hammers for that part.
It's all in engine own TWR.

[Chris Solomon]

thanks ill keep that in mind