I don't understand "asparagus" staging.

[strider3]

I think everyone is missing the point? The Jumbo-64's are not transferring fuel, top to bottom? Until that happens, no amount of "tweaking" will change the issue. As I said...I have had this problem many times before when attempting to use these, or any other F/O tanks as a booster section...they don't play well when stacked. I do appreciate the input but, until the stacked tanks are transferring fuel correctly...everything else is moot? My fuel ducts are at the top of each stack. They transfer TO the adjacent tank (yes, I have verified this). The adjacent tanks transfer to the central stack (verified).

Gentlemen and Ladies...none of this will work if the Jumbo-64 fuel transfer problem, which I have experienced whenever stacking these tanks in a booster section, continues. I'm not an expert, but I have raised this problem before:

I have no idea if this is related, but any discussion seems useless until the issue of the Jumbo-64's not transferring fuel, top to bottom, is resolved? How can ANY fuel transfer scenario work if the very basic scenario of "top-to-bottom" is NOT working? As I have stated...I have had this problem when stacking LF/O fuel tanks in KSP...everytime.

I am NOT trying to be a biotch...I'm just saying that most of you are not GETTING the problem. The problem is my stacks are not transferring fuel correctly. Solve that and my triple asparagus experiment can move forward. It's NOT the experiment...it's the booster stacks not transferring fuel top to bottom! I will say it one more time...I have NEVER had any luck when stacking LO/F tanks!!!!!! They just NEVER transfer fuel correctly. AAAAaarghhhhh!

And now I'm done. I've vented and had my say. I just wish I could make you understand what I'm seeing here...because you are obviously not getting it.

Edited October 16, 2016 by strider3

[Plusck]

It does look a bit like you've surface-attached all those tanks, and so the mainsail is indeed drawing only from the tank it is attached to, the middle tank feeds nowhere, and the top tank is somehow feeding elsewhere...

[[ edit: bzzzt. wrong. HebaruSan has it right. You probably aren't doing anything wrong (although the stacks look far too close to the core). ]]

I would just rebuild it, methodically.

[[ edit: it probably doesn't need rebuilding. However if you want to line up all the tanks and be sure that it is properly built and will separate properly, the following method is a good way to do it. First of all, make sure you're looking at the "pitch right" or "pitch left" side of the rocket: that means directly facing or with the back to the VAB door. ]]

Place a single decoupler high up, near the middle of where the top orange tank is. Place an orange tank on it. Then alt-click the orange tank and (holding down alt to force it to node attach) attach that copy underneath, then do it again for the third one. Add a Mainsail. Add the nosecone. Then strut the bottom orange tank to the bottom of the centre stack.

Then, grab the decoupler, select your desired symmetry (I'd do 2x, but that's up to you) and re-place the decoupler in the same place. Then alt-click the same decoupler and place the next set of tanks. Then do that again if you're doing 2x symmetry.

If you need to slide the stacks up or down, turn snap off and use only the vertical slider on the first orange tank (you need to be careful about having enough clearance from the core stack, so leaving snap off stops it snapping inwards when you move it. Don't try to move it inwards unless you're sure it'll separate cleanly when you stage it).

Then add fuel ducts with symmetry again - from top tank 1 to top tank 2 (then again to 3 if 2x symmetry) then from the last stage to the core.

The aim with doing it this way is to be sure that your stacks are true stacks, and to save time and effort.

 

10 hours ago, Victor3 said:

I think everyone is missing the point? ...

I have no idea if this is related, but any discussion seems useless until the issue of the Jumbo-64's not transferring fuel, top to bottom, is resolved? How can ANY fuel transfer scenario work if the very basic scenario of "top-to-bottom" is NOT working? As I have stated...I have had this problem when stacking LF/O fuel tanks in KSP...everytime.

No, no, I get your point.

And I do think it is because you are surface-attaching each part of the booster stack. [[ edit: again, probably wrong. Keep going until you've emptied the stage to be sure. The rest of this post is, thankfully, right in principle... ]]  The booster stack must be surface-attached only once, to the decoupler. You start with one tank attached to a decoupler and then each additional tank has to be node-attached, above and/or below. 

P.S. @Signo did suggest, in that thread you linked, that you press alt when attaching the orange tanks. That forces the editor to node-attach only, which is what I think you need to do.

Looking at both of these rockets, the side stacks are far too close to the centre stack. They will certainly be physically attached to it when you try to stage, even if they are properly built as side stacks...

Edited October 16, 2016 by Plusck
Flawed premise.

[DD_bwest]

ya i agree with plusck. it looks like they are surface attached to the center core.  alt-click when placing helps fix this.  i ran into this problem alot early on.

if you have advanced tweakables on itll show a priority number on tanks, this can sometimes help show you if they are placed right

[HebaruSan]

7 hours ago, Victor3 said:

That fuel consumption pattern looks familiar (and desirable) to me.

Prior to 1.2, the rule for LF+Ox fuel flow was that each engine drew from the "furthest" non-empty tank, with distance reckoned in terms of the number of hops from part to part to get there. For a simple single-engine stack, the farthest tank is the top one, so tanks drained from top to bottom, often causing flips as the center of mass moves backwards. That accounts for the fuel missing from your top tank.

The twist is that you're also crossfeeding "nose to nose" as I like to call it. Inner stages draw from this stack as well, but since the fuel lines are at the top, the farthest tank for those engines is the one at the bottom! So you also get fuel flowing out of that tank, usually just over twice as much since it's feeding the next stage plus the final, central stage. And indeed, that's what your screenshot shows.

Why do I say it's desirable? Because of that earlier note about flips and center of mass. Since your bottom tank is draining faster than the top, your center of mass is moving UPWARDS instead of down, effectively improving your stability. In fact, this is a trick I like to use on purpose to make shuttles a bit easier to fly.

In short, I think your craft is working fine, and I hope that explanation helps you to see why.

[Capt. Hunt]

It looks to me like your boosters are surface attached to the core instead of the tanks to each other too.  try building the booster by itself and save it as a sub assembly, then import it and attach it to the decoupler.

Edited October 16, 2016 by Capt. Hunt

[Plusck]

6 hours ago, HebaruSan said:

That fuel consumption pattern looks familiar (and desirable) to me.

Prior to 1.2, the rule for LF+Ox fuel flow was that each engine drew from the "furthest" non-empty tank, with distance reckoned in terms of the number of hops from part to part to get there. For a simple single-engine stack, the farthest tank is the top one, so tanks drained from top to bottom, often causing flips as the center of mass moves backwards. That accounts for the fuel missing from your top tank.

The twist is that you're also crossfeeding "nose to nose" as I like to call it. Inner stages draw from this stack as well, but since the fuel lines are at the top, the farthest tank for those engines is the one at the bottom! So you also get fuel flowing out of that tank, usually just over twice as much since it's feeding the next stage plus the final, central stage. And indeed, that's what your screenshot shows.

Lol. OK now I want to change my previous answer because this is certainly right.

To @Victor3: This is not the same situation as your previous thread. HebaruSan is correct about the fuel flow.
As for the misaligned tanks, that is normal too because you're attaching the centre tank to the decoupler with symmetry (so each tank is rotated to be face the centre stack the same way) and the other tanks are simply node-mounted (therefore without any rotation off the default angle which is E-W, corresponding to the horizontal plane in the SPH). The other tanks which appear with symmetry are rotated with respect to the node you are actually placing your tank on, so the only stack you can build with perfectly aligned parts is one which is centred on the E-W axis.
If you built the stacks starting with a decoupler placed on the "left" or "right" sides of the rocket (facing E/W, basically looking out of the door of the VAB or with your back to it), the tanks would line up.

Edited October 16, 2016 by Plusck

[ForScience6686]

Did sound like an issue.  I figured you were on the middle tank causing the other two to drain first.  Beyond that, I'm not sure what would cause that.

[strider3]

OK...off to rebuild this using your suggestions. I'll be back.

[strider3]

23 hours ago, Plusck said:

It does look a bit like you've surface-attached all those tanks, and so the mainsail is indeed drawing only from the tank it is attached to, the middle tank feeds nowhere, and the top tank is somehow feeding elsewhere...

[[ edit: bzzzt. wrong. HebaruSan has it right. You probably aren't doing anything wrong (although the stacks look far too close to the core). ]]

I would just rebuild it, methodically.

[[ edit: it probably doesn't need rebuilding. However if you want to line up all the tanks and be sure that it is properly built and will separate properly, the following method is a good way to do it. First of all, make sure you're looking at the "pitch right" or "pitch left" side of the rocket: that means directly facing or with the back to the VAB door. ]]

Place a single decoupler high up, near the middle of where the top orange tank is. Place an orange tank on it. Then alt-click the orange tank and (holding down alt to force it to node attach) attach that copy underneath, then do it again for the third one. Add a Mainsail. Add the nosecone. Then strut the bottom orange tank to the bottom of the centre stack.

Then, grab the decoupler, select your desired symmetry (I'd do 2x, but that's up to you) and re-place the decoupler in the same place. Then alt-click the same decoupler and place the next set of tanks. Then do that again if you're doing 2x symmetry.

If you need to slide the stacks up or down, turn snap off and use only the vertical slider on the first orange tank (you need to be careful about having enough clearance from the core stack, so leaving snap off stops it snapping inwards when you move it. Don't try to move it inwards unless you're sure it'll separate cleanly when you stage it).

Then add fuel ducts with symmetry again - from top tank 1 to top tank 2 (then again to 3 if 2x symmetry) then from the last stage to the core.

The aim with doing it this way is to be sure that your stacks are true stacks, and to save time and effort.

 

No, no, I get your point.

And I do think it is because you are surface-attaching each part of the booster stack. [[ edit: again, probably wrong. Keep going until you've emptied the stage to be sure. The rest of this post is, thankfully, right in principle... ]]  The booster stack must be surface-attached only once, to the decoupler. You start with one tank attached to a decoupler and then each additional tank has to be node-attached, above and/or below. 

P.S. @Signo did suggest, in that thread you linked, that you press alt when attaching the orange tanks. That forces the editor to node-attach only, which is what I think you need to do.

Looking at both of these rockets, the side stacks are far too close to the centre stack. They will certainly be physically attached to it when you try to stage, even if they are properly built as side stacks...

OK then, using the step by step instructions Plusck provided (thanks buddy!), I rebuilt my original. Stuff still "looks weird"...but appears to be working? On the right are the fuel levels for one of the first 3 boosters to be jettisoned when empty, I'm surprised that the lower tank shows empty...but the darn Mainsail appears to be firing away...so I'm overlooking that bit of weirdness. On the left is the center stack and 2nd set of boosters...all looks good, no fuel being used and they should be fine when staging to them. On the lower far left, in the "staging" area...another weirdness...the fuel levels are not reflecting what I would have thought...but, perhaps, another anomaly due to the asparagus staging?

Anywho, at this point I am going to resume the flight, see how the 3 stack decoupling goes, and continue to verify the staging. If all goes well, I will call my "triplet" asparagus staging experiment a success...and then go to a "pairs" set-up as this is obviously more efficient, as you have stated...just hope my piloting skills are up to par for that!

Have I told you how awesome you guys are...lately?

Vic

Edited October 17, 2016 by strider3

[strider3]

Yep...can't get past decoupling the 3 boosters without blowing up my stuff. I'm wondering if shutting down all engines, just long enough to decouple, would help? I haven't really had this problem with SRB's and I'm not able to tell, so far, where the collisions are happening (radially with an adjacent booster stack, tail end of ejected stacks running into the Mammoth, etc.).

Going to restart flight and decouple with all engines off.

Oh...my apologies, also, for being...less than patient, earlier. My bad.

[Plusck]

7 minutes ago, Victor3 said:

Stuff still "looks weird"...but appears to be working? On the right are the fuel levels for one of the first 3 boosters to be jettisoned when empty, I'm surprised that the lower tank shows empty...but the darn Mainsail appears to be firing away...so I'm overlooking that bit of weirdness. On the left is the center stack and 2nd set of boosters...all looks good, no fuel being used and they should be fine when staging to them. On the lower far left, in the "staging" area...another weirdness...the fuel levels are not reflecting what I would have thought...but, perhaps, another anomaly due to the asparagus staging?

The way fuel flow works in KSP is each engine "looks for" fuel.
Essentially, it follows each path and sets a priority for use of fuel along that path. Fuel lines give absolute priority to a path. Without using the new advanced tweakables, the engine will then draw from the furthest tank along the highest priority path.

So the centre stack sees all of the fuel underneath the upper stage. Its priority is to take fuel from your "1st triplet" (because of fuel ducts), so it draws from the most distant tank: the bottom one. As that triplet empties, it'll see its total available fuel (the gauge next to the staging icon) reducing slightly. Thats why it looks to be at about the 80% mark in your pic.

The 2nd triplet sees all the fuel in its stack plus the fuel in the 1st triplet. Its priority is also the 1st triplet, so it too will draw from the bottom of the 1st triplet. It sees all of its own stack as being "full" and (in the pic) about 1/3 of the 1st triplet as being full, so its staging icon has a gauge which is about at the 65% (50% full and 1/3*50% full) mark.

The 3rd triplet can only see the fuel in its own stack. No fuel ducts supply its stack, so it just draws from the furthest tank which is at the top. Since that stack is about 1/3 full, the gauge is at about the 1/3 mark.

 

So in a sense it is anomalous, because the fuel gauges for different engines will count the same tanks as "their fuel" even if they are actually going to be sharing it.

 

And as @HebaruSan pointed out earlier, the fuel use in the 1st triplet is perfectly normal following the same analysis. Most fuel is drawn from the bottom of that stack (via the ducts). Meanwhile, the engine at the bottom of the stack will draw (more slowly) from the top.

[DD_bwest]

15 hours ago, Victor3 said:

Yep...can't get past decoupling the 3 boosters without blowing up my stuff. I'm wondering if shutting down all engines, just long enough to decouple, would help? I haven't really had this problem with SRB's and I'm not able to tell, so far, where the collisions are happening (radially with an adjacent booster stack, tail end of ejected stacks running into the Mammoth, etc.).

Going to restart flight and decouple with all engines off.

Oh...my apologies, also, for being...less than patient, earlier. My bad.

have you tried using sepratrons? I dont see any in the picture.    where is your decoupler on the stack?  i cant really tell that one either.

if your decoupler is to high to the top(especially on xtra long boosters),  it can sometimes push the top hard enough that it causes the bottoms to move inward and collide with the center core /engines.    if its to low to the bottom, the opposite will happen happen making it collide at the top.  I almost always use sepratrons just incase.   i would use 6 per booster, but that might be over kill. (a pair at the top, middle and bottom)

 

[strider3]

On ‎10‎/‎17‎/‎2016 at 10:42 AM, DD_bwest said:

have you tried using sepratrons? I dont see any in the picture.    where is your decoupler on the stack?  i cant really tell that one either.

if your decoupler is to high to the top(especially on xtra long boosters),  it can sometimes push the top hard enough that it causes the bottoms to move inward and collide with the center core /engines.    if its to low to the bottom, the opposite will happen happen making it collide at the top.  I almost always use sepratrons just incase.   i would use 6 per booster, but that might be over kill. (a pair at the top, middle and bottom)

 

I have not tried sepratrons. My decouplers are at the top of the stacks and, yes, that is causing the bottoms to hit the center core. I have tried to center the decouplers in the middle of the stack but that was before learning about the "alt+click" trick to force a node attach, so I had other issues at the time.

I haven't had a chance to try anything to improve decoupling of the current craft, until this reply. I'm off to make some more modifications and test them out, now.

Thanks!

[Plusck]

2 hours ago, Victor3 said:

I have not tried sepratrons. My decouplers are at the top of the stacks and, yes, that is causing the bottoms to hit the center core. I have tried to center the decouplers in the middle of the stack but that was before learning about the "alt+click" trick to force a node attach, so I had other issues at the time.

I haven't had a chance to try anything to improve decoupling of the current craft, until this reply. I'm off to make some more modifications and test them out, now.

Thanks!

I think there are a few things to separate out here:

- if you are going perfectly straight through the airflow, then blowing out the top end will make the booster catch air and lift sideways off the craft;
- the heaviest part of the booster is the engine, so the CoM is low. Blowing out the top end should cause very little inward movement at the bottom;
however
- the bottom of the Mammoth sticks out from the stack.

So really, I think that the main concern is clearance between the boosters and the Mammoth. You appear to be using the standard small radial decouplers, which means you've got to be very careful about clearance. Since you're using 3x symmetry, you can't avoid getting close to the jutting-out parts of the Mammoth, but the Mammoth isn't radially symmetrical: you'll get more clearance if you have the boosters centred on the "short" sides of the Mammoth (so one set of each triplet is centred where the Mammoth's engines are closer together). You could also try offsetting the boosters out a touch (but only a very small amount, with "snap" off, otherwise you'll weaken the link, possibly catastrophically).

 

The first thing to do is call up the F3 report as soon as it blows. It should list things like "X collided with Y". As far as I'm aware, the part X in that syntax is always the part that is destroyed.  So that should tell you where the problem is. Take a screenshot while you're at it ;--)

 

In my opinion, using the decouplers that give better clearance should solve the problem, and should avoid the need for separatrons, fins (this is another option, placing fins on the side with a slight outwards rotation to help the boosters peel off better), hydraulic detachment manifolds (very heavy, generally unnecessary except for truly massive rockets) or any other solution.

Edited October 21, 2016 by Plusck

[Jestersage]

Also, I notice that you do not have the priority numbers, so I guess you need to enable those. I think the advance tweakable is in settings?

Note that the use of fuel lines is still recommended.

Edited October 22, 2016 by Jestersage

[strider3]

An update (been busy at work and home). I tried the Sepratrons...they work well if I am heading 0 x 0 degrees (straight up from Kerbin) but collide if used after my gravity turn. Note that this is well after the 10 degree gravity turn and ship is completely stable on heading. This seems weird...why would being in straight flight after the turn cause this...but not before? I can wait on the gravity turn until after the first decoupling (and have done so, successfully)...but I'm not sure how badly waiting affects the efficiency of my orbit entry.

I think I will try the higher clearance decouplers next, without the Sepratrons.

2 learning opportunities..."F3 report", "priority numbers"...what are these things you speak of??

Vic the (eternal) Newbal

Edited October 27, 2016 by strider3

[DD_bwest]

priority numbers are when you are using advanced tweakables it lets yiu pick the order the tanks drain in

f3 will bring yp the flight report and will tell you what part collided with what. 

 

[strider3]

What I have is "StockBugFixControllerPlus.v1.1.3b.1.zip", don't know if that lets me pick the order my tanks drain in. I think I've resolved that issue, however. The numbers just look weird but everything works fine with the triplets, they empty completely and I dump them.

I was not aware of the F3 key. Thanks!

[DD_bwest]

advanced tweakables are new to 1.2,  you have to go into settings in the main menu.  this option also gives you auto strut, and rigid attachment.

the aim camera(on a specific part during flight) might be under that as well, but not sure. 

[ForScience6686]

12 hours ago, Victor3 said:

An update (been busy at work and home). I tried the Sepratrons...they work well if I am heading 0 x 0 degrees (straight up from Kerbin) but collide if used after my gravity turn. Note that this is well after the 10 degree gravity turn and ship is completely stable on heading. This seems weird...why would being in straight flight after the turn cause this...but not before? I can wait on the gravity turn until after the first decoupling (and have done so, successfully)...but I'm not sure how badly waiting affects the efficiency of my orbit entry.

I think I will try the higher clearance decouplers next, without the Sepratrons.

2 learning opportunities..."F3 report", "priority numbers"...what are these things you speak of??

Vic the (eternal) Newbal

Gravity is still a player here, and is why you might still be having collisions.  Sepratrons could help with this, but they can also cause damage to the craft if not placed properly.  Another method you could use, if not traveling too fast, activate chutes on the dropped boosters.

[Sharpy]

On 13.10.2016 at 2:32 AM, 5thHorseman said:

That said, SRBs are very nice to give you a boost off the pad, even in non-career modes it's frequently easier to "just toss some SRBs on it" than try to figure out how to get a little more TWR and/or dV out of LFO stages.

I often add a lot of old Hammers to the lowest stage. Easy, cheap, quick extra TWR in the first seconds of flight.

The keyword is gravitatiional drag. Every second you spend at speed considerably lower than orbital is wasting a whole lot of fuel just to keep you from falling. You can't reach speeds considerably close to orbital at altitudes lower than some 25-30km. So, the key is to reach these altitudes and speeds quickly. If you take two minutes to reach 400m/s and 10km, that's a horrible waste of fuel. Four clusters of 6 hammers each can reduce that time to half a minute.

On 27.10.2016 at 4:18 AM, Victor3 said:

An update (been busy at work and home). I tried the Sepratrons...they work well if I am heading 0 x 0 degrees (straight up from Kerbin) but collide if used after my gravity turn. Note that this is well after the 10 degree gravity turn and ship is completely stable on heading. This seems weird...why would being in straight flight after the turn cause this...but not before? I can wait on the gravity turn until after the first decoupling (and have done so, successfully)...but I'm not sure how badly waiting affects the efficiency of my orbit entry.

 

Oh, the reason is very simple.

Switch the engine off during ascent - your rocket starts falling, right?

The engines on boosters are off - the moment you decouple boosters, they are falling.

The one below, falls clearly down. The one above - tossed up a bit by the decoupler, starts falling down too. But there's your core rocket in the way.

Make sure the separatrons are angled to propel the boosters away from your rocket. Alternatively, if you don't have long fins that could collide - send your rocket into a spin before separation (hold Q). Centrifugal force gives a pretty neat separation.

[Kryxal]

For that matter, just having the decoupling parts on the same level tends to work fairly well.  The biggest problem is, the detached parts ARE going to want to fly engine-forward (empty tanks are much lighter), so you really do need to get them clear in a bit of a hurry.  Paired seperatrons angled to the sides and a bit up or down (so you don't fry the ones on the next stack over) work pretty well.

[strider3]

Thanks for that, guys...I neglected to think about gravity still being a factor.

[DD_bwest]

On 2016-10-15 at 2:27 PM, Victor3 said:

As I suspected...the Jumbo 64's are not transferring fuel correctly. Notice the middle tank is remaining full? It appears the lower tank is feeding the Mainsail rather than all 3 tanks feeding top to bottom. Some kind of "disconnect" between the middle and bottom tanks:

This is one of the first "triplet" stacks, and should be feeding fuel to all stacks. I would need another launch, this time viewing this stack and it's adjacent one, to see what is really going on. Obviously, however, there is the recurring problem I've had stacking Jumbo-64's. It appears to me the middle tank is doing nothing? Obviously a "build" issue when I stack these tanks as booster stages...never really had any luck with them working in unison. Maybe that's why I usually go with SRB's?

Not that SRB's are the answer...I need to figure out why this is happening.

in relation with your other thread about funds in career mode, ill make the tip that this launch vehicle is way more then what is needed to get that load into orbit. lol  Im not sure if that is a dummy load for testing, but that rocket could lift a heck of alot.   Its okay tho, as its something i used to do, and probably everyone.  Over engineer to get the job done, then as experience grows, wean back slowly.

[Gordon Fecyk]

On ‎10‎/‎15‎/‎2016 at 4:08 PM, Victor3 said:

Here's a picture of the craft I'm trying this with:

[snip]

I've strapped Kickbacks to the stock Kerbal X, and I've built something with a single S3-14400 and six orange tanks that I called the "Kerbal O" (for "Overkill"). That craft? That's the "Kerbal OMG!"

That being said, one of my Kerbal X clones used six stacked FL-T800 pairs and the 'traditional' stack of three X-200 32s, and don't seem to have a problem with fuel flow. Here: The Iktomi build has a couple of launcher subassemblies you can inspect to see how the fuel flows; see if this helps any. It's the same idea as your rocket with stacked tanks, just using smaller parts. One thing I did though is made sure my fuel lines were attached to the bottom tanks only. It was originally designed for KSP 1.1.3, but still applies to KSP 1.2.1 because the decouplers have crossfeed disabled.

Being an ex-n00b I didn't understand the Wiki article either, so I tried building my own tutorial.

--