More fun with Fuel Ducts, no doubt.

[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. Maybe some crappy ASCII art would be helpful?

â–‘     â–‘    â–‘
  ââ€Ëœ   ↓   ââ€â€
   â–“  â–“  â–“
     ââ€ËœÃ¢â€ â€œÃ¢â€â€
â–‘>>â–“>>â–ˆ<<â–“<<â–‘
     ââ€Â↑ââ€Å’
   â–“  â–“  â–“
  ââ€Â   ↑   ââ€Å’
â–‘     â–‘     â–‘

â–‘ STAGE 1
â–“ STAGE 2
â–ˆ STAGE 3

EVERYTHING ELSE IS A FUEL DUCT

[DMagic]

From your diagram that's not really asparagus staging, that's just one stage feeding directly into the each inner layer. The wiki has a diagram of what it should look like.

I assume that when you drop stage 1 all 8 outer engines fall off. In asparagus staging you should only be dropping 2 at a time (from opposite sides). So instead of 3 stages you should have 9, I think. It's a little bit trickier to set it up like that; things can be very unpredictable, but I have made a launcher with 4 layers of asparagus staging, you just have to be careful with ordering the stages.

To better track your fuel flow try right-clicking on the fuel tanks during ascent. The inner tank should not decrease at all until all of the outer tanks have been dropped (assuming that the inner engine has the same fuel flow as the outer ones, which yours does). If it starts going down before that then something is off.

[BigFatStupidHead]

The inner tank should not decrease at all until all of the outer tanks have been dropped (assuming that the inner engine has the same fuel flow as the outer ones, which yours does). If it starts going down before that then something is off.

Be careful, the inner tanks will APPEAR to decrease before this point, but should be full when clicked on and when the outer stages are ejected.

[shand]

my suggestion would be to delete the inner ducts and place them again. sometimes something odd happens. ensure they are going to the tank not the engine.

[Zephram Kerman]

Technically, what your describing as "ringed" asparagus is actually "onion" staging. I'm not kidding. Someone called it "onion" because the layers peel off. Onion staging is not quite as efficient as asparagus, but it's a lot simpler.

Anyway, Shand's suggestion is probably your best bet. If that doesn't work, try deleting the outer stage and fly it starting with stage 2. Then you can get a better look at what's going on. (Just don't save, so that you can avoid rebuilding it.)

[HoY]

Also for your inner stage, you could replace the mainsail and radial engines with a cluster of 8 LV30's and 4 LVT45's. this will give you a higher thrust and better fuel efficiency, as long as you can handle the extra 24 part count haha.

For an example of what I mean, look on the spacecraft exchange at a thread by Temstar called the Zenith family of rockets

Here's a link to the thread. The one you want to see is the Nova

http://forum.kerbalspaceprogram.com/showthread.php/24787-0-19-1-Zenith-rocket-family

Edited May 8, 2013 by HoY

[Noticeably FAT]

Are you sure you ran all the fuel lines TO the center stack and not FROM it?

[RawChicken]

Are you sure you are placing the fuelo ducts correctly?

You have to click first the tank of gas you want to transfer FROM and then click to where you want to transfer TO.

You also have smal ▶▶▶ at the middle of the duct that shows flow direction.

[Zephram Kerman]

Also for your inner stage, you could replace the mainsail and radial engines with a cluster of 8 LV30's and 4 LVT45's. this will give you a higher thrust and better fuel efficiency, as long as you can handle the extra 24 part count haha.

For an example of what I mean, look on the spacecraft exchange at a thread by Temstar called the Zenith family of rockets

Engine clusters are cool. But let's wait until the troubleshooting is done before making the thing even more complicated!

By the way, the inner stage TWR may be less than 1. So a cluster of 5 or 6 LV-T30, perhaps with one LV-T45 in the center would be plenty. Or, for simplicity, just the one mainsail by itself, without the mk 55s.

[capi3101]

Are you sure you ran all the fuel lines TO the center stack and not FROM it?

Are you sure you are placing the fuelo ducts correctly?

You have to click first the tank of gas you want to transfer FROM and then click to where you want to transfer TO.

You also have smal ▶▶▶ at the middle of the duct that shows flow direction.

I'm positive they're flowing the right direction; I include fuel ducts with almost all of my desigs, so I am pretty well versed in how they function.

By the way, the inner stage TWR may be less than 1. So a cluster of 5 or 6 LV-T30, perhaps with one LV-T45 in the center would be plenty. Or, for simplicity, just the one mainsail by itself, without the mk 55s.

I did the math on that one. TWR at Stage 2 seperation is 1.2 with the Mk-55s and 0.9 without; it's the whole reason why I included them in the first place.

Also for your inner stage, you could replace the mainsail and radial engines with a cluster of 8 LV30's and 4 LVT45's. this will give you a higher thrust and better fuel efficiency, as long as you can handle the extra 24 part count haha.

I actually had given that idea some thought; I've noticed a lot of wobble in the central engine during takeoff, no doubt due to the plethora of gimballing engines I've got on the design. I haven't crunched the numbers on putting in a cluster yet; might be worth investigating.

I am familar with Temstar's heavy booster designs; whole reason why I'm trying a 120 tonne payload. I finally know it's in the realm of possibilities...

"Onion"-staging, huh? I'll remember that. Meantime I'll do what y'all have suggested and report what happens.

[capi3101]

Alrighty: found the problem. I had put the interior fuel ducts in the open space in a set of Hydraulic Separation Manifolds. Game wasn't counting them as connected to the interior tank. Moved 'em up a bit and they worked fine. Next UVD from the wobble getting too severe and causing the center engine's lower fuel tank to break off. Struts solved that one; things worked a bit too well after that - the second stage tanks still had gas in them at SECO, so I kept 'em on for the orbital insertion burn, despite the fact I had made no provision for steering with those tanks still attached out outside the atmosphere. I had sufficient RCS thrust available to get turned for the burn. Tanks in the second stage ran dry during the OEB; the subsequent attempt at stage separation caused the next UVD.

I'm out of time to make another launch attempt tonight; next chance I get I'll shut off the second stage engines and separate them when I'm supposed to. If I get another UVD from that I may attempt the orbital insertion burn with them still attached; see what that does.

Anyway, thanks for your help, y'all.