Large liquid fuel boosters problem

[Peaceful Guy]

Hi everyone, I'm here because I have an issue

I'm used to my launchers using parallel symmetry liquid fuel boosters using power lines between the boosters so that those are going down gradually two by two, and I connect the last two boosters with the central fuel tank so that one empties last after having dropped all the boosters. I made a video to illustrate:

https://youtu.be/3V-ctPXO-Ck

I had a problem using larger tanks and thrusters, the first two pairs of boosters begin to empty properly but just in the end the second ones empty faster than the first ones so that they end up dry at the same time!

Here's the video:

https://youtu.be/IFgPQMaadMg

For information:

- the first video I used double tanks FL-T800 and a thruster "swivel" for each booster

- the second video where I have the problem I used double tanks FL-TX1800 and "skipper" thrusters

- I tried to put double power lines from the first pair of boosters to the second pair of boosters so that the first ones are empty faster: Same result

- I tried to add a line from the first pair of booster to the central fuel tank: Same result.

Can someone explain to me what's going on ?????

[MechBFP]

I think you accidentally messed with the fuel priority on a set of the fuel tanks. 

[Capt. Hunt]

more fuel lines don't add to the transfer rate.  It looks like they aren't draining in even pairs

Check that all of your fuel lines are going to the right place, and that fuel priority is set properly.

[Geonovast]

Do you have crossfeed enabled on the decouplers?

[Snark]

Moving to Gameplay Questions.

[Peaceful Guy]

After a bunch of tests and a couple of hours I finally found that this particular craft is glitched. Dont ask my how, I dont even know. But it seems that the second couple of boosters were acting as they were the first ones so they are empty first. The game noticing that at the very end of the first ones whitch were supposed to be empty, speeded up the display of lowering fuel so they appear empty at the same time.

The funny thing is that the engines were still burning even with empty fuel tanks, and when decoupled they were magically turned off. Look at the video here:

The solution was to decouple them as they turn empty and not to wait until the engines are off.

 

Thank you anyway guys

[Geonovast]

18 minutes ago, Peaceful Guy said:

The funny thing is that the engines were still burning even with empty fuel tanks

This would happen if you had crossfeed enabled on the couplers.  It would also explain your other issues.

[Peaceful Guy]

 

12 minutes ago, Geonovast said:

This would happen if you had crossfeed enabled on the couplers.  It would also explain your other issues.

 it was disabled

[Geonovast]

40 minutes ago, Peaceful Guy said:

 

 it was disabled

Do you still have the craft file?  If so, mind sharing it?

[Peaceful Guy]

17 hours ago, Geonovast said:

Do you still have the craft file?  If so, mind sharing it?

http://www.mediafire.com/file/6o1si9doiqki63l/Spaceinstitute_1.craft

I'm waiting for your analysis

[Geonovast]

@Peaceful Guy what mods do you have that are used on this?  It won't let me open it because of invalid parts.

[Peaceful Guy]

13 minutes ago, Geonovast said:

what mods do you have that are used on this?  It won't let me open it because of invalid parts.

- kerbal engineer

- x science

- mechjeb

- mission control on the go

- kerbal alarm clock

- transfer window planner

- docking port alignement indicator

- some parts are from the making history expansion pack

[Geonovast]

15 minutes ago, Peaceful Guy said:

- kerbal engineer

- x science

- mechjeb

- mission control on the go

- kerbal alarm clock

- transfer window planner

- docking port alignement indicator

- some parts are from the making history expansion pack

I have MH and KER, so no issue there.

If there's a MJ module on it, that's probably it.  I don't seen anything else on there that could be an issue.  I'll install MJ quick and try again.

[Geonovast]

Alright, so what I'm seeing, the fuel lines and decoupler are all configured correctly.  However, your staging was incorrect.  1 and 3 needed to be swapped.  Possible that was part of your issue?  If not, you might be looking at some kind of mod conflict causing your issues.

I also have a handful of concerns about the rocket design if you're interested.

[Peaceful Guy]

19 hours ago, Geonovast said:

However, your staging was incorrect.  1 and 3 needed to be swapped.  Possible that was part of your issue?

Maybe I tweaked a little bit the craft while searching the issue but its definetivly not that. Try if you want to remove all the boosters and reset a proper x6 configuration, you'll see that the issue will still be there.

19 hours ago, Geonovast said:

I also have a handful of concerns about the rocket design if you're interested.

For sure

[Geonovast]

3 hours ago, Peaceful Guy said:

For sure

Ok, my main concern is the drastic diameter changes you have.  The game hates these, and it creates a ton of drag.  I had issues with it flipping once it got too high, most likely because of the gap between the cupola module and that large decoupler.  These are really killing you.  You want to use the parts the transition from one diameter to another.  For the 1.875m stuff, I think all of those pieces are fuel tanks.

Another minor issue is the parachutes.  Unless you're using some kind of mod to recover them, like FMRS, they're completely useless and are just dead weight.  The game will not calculate their landing if they're out of physics range (which they will be well out of by the time they get to the ground), and the game is just going to delete them when they "hit" the ground.  

This one (other than the diameter change) is that your boosters are twisted a bit.  with the offset nosecone the way it is, it could push your rocket to roll.

 

I also recommend putting everything above the service bay in a fairing.  You've got a significant amount of radially mounted parts that are just adding to your drag.  And, toss the RCS stuff.  If you re-design to eliminate all that drag, you won't need the RCS to keep the rocket straight during launch.  It also appears this is meant to be a space station, and RCS on space stations is usually overkill.  The reaction wheel is plenty, put the RCS on the stuff that will be docking with the station.  You've got a lot of ports on there (drag), and you're hauling up 3.4Tons of stuff you don't need (MP tank)

I re-designed with the above in mind, and got to a 100k x 100k orbit with more than 2300 m/s left.  Be more than happy to share pics and the craft file, but I recommend taking a crack at it yourself first.

[Peaceful Guy]

Thank you for these kind and valuable advices, really appreciate

You right, I made this craft for being my first space station in career mode and also for a contract that requested me to get a station around the mun with 7 kerbals.

22 hours ago, Geonovast said:

you're hauling up 3.4Tons of stuff you don't need (MP tank)

The contract requested me to have 1000 MP units in the station (and also 4000 of liquid fuel!), so I planned to dock at least more 250 MP units, and some liquid fuel in a future launch.

22 hours ago, Geonovast said:

I had issues with it flipping once it got too high

Yes, I've noticed that but I think that's not about drag since the station was difficult to handle even in vaccum (without RCS) so my easiest solution was to add another reaction wheel which fixed that issue.

22 hours ago, Geonovast said:

Another minor issue is the parachutes.  Unless you're using some kind of mod to recover them, like FMRS, they're completely useless and are just dead weight.  The game will not calculate their landing if they're out of physics range (which they will be well out of by the time they get to the ground), and the game is just going to delete them when they "hit" the ground. 

Well, that made me laught because I realized that all the hard work and testing I made trying to put parachutes around the center of mass of each booster thinking gaining money was a waste of time, efficiency... and money. I'll give FRMS a try thanks for the tip

For information I reached with this craft LKO (80k x 80k) with 2260 m/s of dV left, notice that I didn't use RCS during the launch. But I'm defenitivly interested in your upgraded version if possible.

Thanks again dude

 

[Geonovast]

1 minute ago, Peaceful Guy said:

But I'm defenitivly interested in your upgraded version if possi

Certainly.  Although keep in mind that I did this in Sandbox, so you may not be able to load it in your career save.  Also I removed the MJ module, so if you want MJ to fly it, you'll need to stick that back on.  I didn't realize it was for a contract

https://kerbalx.com/Geonovast/Spaceinstitute-2