SSTO Spaceplane - Why is this design worse?

[11matt556]

So I managed to get my first 1.0 spaceplane into orbit within an hour or so, but after that I've hit a brick wall as far as making them any better. My goal right now is to make an SSTO that can travel to anything within Kerbin's SOI, and can travel anywhere else after (such as Jol) after refueling.

The plane below is my best design so far and can make it into orbit around the mun and come back. The only major problem was that the nuclear engines tended to overheat everything around them.

Overheating

http://imgur.com/yShR5Tw

So, I made a slight modification to fix that problem. All I did was move the engines further apart so they wouldn't get as much radiated heat.

http://imgur.com/w3rTEnv

With the new design, I can't return from the Mun's orbit. There just isn't enough dV. Kerbal Engineer claims that the original (top image) had about 2,000 m/s dV after reaching orbit. The new design has only 1000 m/s dV, sometimes less. Even if I remove excess oxidizer and intakes, it doesn't seem to make any difference.

I've tried tweaking the fuel, adding wings, removing wings, but nothing seems to matter.

Anyone have any ideas about why this might be happening or a link to an advanced 1.0 spaceplane tutorial that could help? All I could find were basic tutorials for 1.0 so far. I always run into this problem with spaceplanes. I find a design that seems to almost work great, but anything I change only seems to make it worse.

This is my first time posting so please go easy if I messed something up.

Edited May 1, 2015 by 11matt556

[TrevTrevarian]

The only thing I can think of is that sometimes when I move fuel tanks, the fuel lines that feed them disconnect. That might explain the big dv loss. Other than that I'm as stumped as you. Exactly what changes were made from the 4B to the 4C?

Edit: one thought I had is that it might have something to do with lift. The central fuselage might produce more body lift in the first design, although I admit I don't know too much about that and I'm still adjusting to the new aero myself

Edited April 30, 2015 by TrevTrevarian

[11matt556]

The only thing I can think of is that sometimes when I move fuel tanks, the fuel lines that feed them disconnect. That might explain the big dv loss. Other than that I'm as stumped as you. Exactly what changes were made from the 4B to the 4C?

Edit: one thought I had is that it might have something to do with lift. The central fuselage might produce more body lift in the first design, although I admit I don't know too much about that and I'm still adjusting to the new aero myself

I thought about the fuel line as well, but I made sure to reattach it exactly as it was in the 4B. The body lift is a good idea, but they both seem to fly exactly the same, so any loss should be negligible.

AS for the changes between the 4B and 4C

*Moved landing gear forwards in 4C to make takeoff easier

*Moved engines further apart (main change)

*Slightly adjusted wings to keep COM and COL the same as the 4B design.

*Used the structural pylon (white thing) instead of the gray connector to connect engines to the main body.

[TrevTrevarian]

The only thing I can think of is some aerodynamic difference, but if they perform relatively the same then that's unlikely, in the 4B I don't see fuel lines running from the outer nacelles to those at the fuselage, I don't see how that would make a difference in the way you're describing, but it's worth investigation. I'm about to check and see if the the structural pylon switch might have been the issue.

I couldnt find any reason that that would have been the issue, even the structural pylon's advertised lack of crossfeed turned out to be only advertising. Such to say it still has crossfeed. I don't suppose there was any change to your ascent profile? I figure not but its worth asking. Flying the rapiers on rocket mode when they were previously on air breathing or vice versa? Etc. beyond that I'm stumped.

Edited May 1, 2015 by TrevTrevarian
typos on phone

[cybersol]

The grey attachments are decouplers, so 4B is two-stage and 4C is 1-stage. That could easily explain the dV difference if you were dropping the outer stage.

[11matt556]

The only thing I can think of is some aerodynamic difference, but if they perform relatively the same then that's unlikely, in the 4B I don't see fuel lines running from the outer nacelles to those at the fuselage, I don't see how that would make a difference in the way you're describing, but it's worth investigation. I'm about to check and see if the the structural pylon switch might have been the issue.

I couldnt find any reason that that would have been the issue, even the structural pylon's advertised lack of crossfeed turned out to be only advertising. Such to say it still has crossfeed. I don't suppose there was any change to your ascent profile? I figure not but its worth asking. Flying the rapiers on rocket mode when they were previously on air breathing or vice versa? Etc. beyond that I'm stumped.

I did the exact same thing with each plane, and flew them each probably 15 or 20 times now, so I doubt its my ascent. And the fuel line is connected in 4B, but from the angle its covered up.

The grey attachments are decouplers, so 4B is two-stage and 4C is 1-stage. That could easily explain the dV difference if you were dropping the outer stage.

I never dropped the stage though. I only used it as a connection. Kerbal Engineer considered both of them 2 stages anyway since I put the Atomic rockets on the second stage and had the decouplers as the last stage.

I'll try switching out the connectors though to see if it makes any difference. Maybe the dV is being calculated wrong somehow.

EDIT: So it looks like it was a dV miscalculation. I don't know how I managed to make it to the Mun and back before, but apparently both designs ACTUALLY have about the same dV. I guess I got lucky that time, or flew it very well, because I can't seem to make it back again.

Thanks for your help with my (very stupid) mistake. Any general suggestions or tips that might help with this or future designs?

Edited May 1, 2015 by 11matt556

[TrevTrevarian]

I'm honestly really happy it was human error, I've been trying to figure out how that significant of a difference could be made by such a small change all day and it's been killing me. As far as tips

for the future, I don't really have anything of particular value as I've never really cared to make a single stage go farther than orbit without refueling. There are a ton of posts all around the forum that have some pretty good tips in them, but with 1.0 I'm not sure how much of it still applies.