Coalesced rockets giving reduced efficiency or not?

[THX1138]

The construction part of the game is still a bit rough and lets me put rockets partially inside one another. Does that affect the efficiency of those rockets or does it calculate out the same? Also, does the positioning affect the aerodynamics? Surely putting a rocket partially inside another would reduce it's drag!

On the topic of drag, SRB-KD25K is not specified to have drag but the "Aerodynamic Nose Cone" has 0.1 drag. Does that mean the drag is higher with the nose cone than without?

Edited July 1, 2014 by THX1138

[solohobo]

Thank you for asking this question, THX1138. It's a common one, and confuses many people.

KSP calculates the drag of a rocket (in simpler terms) by how much it weighs.

Thus, we can conclude the answers to both of your questions.

#1: Putting a rocket inside another rocket does not reduce drag, due to the fact it would weigh the same as a rocket attached to another rocket.

#2: Yes, as much sense as this doesn't make, having a nosecone creates more drag. Silly, right?

More in-depth article at these links:

wiki.kerbalspaceprogram.com/wiki/Atmosphere

forum.kerbalspaceprogram.com/threads/58049-How-does-KSP-calculate-drag

Anyone willing to add more onto this or to correct me (Yes, I'm kerbal, I make mistakes), feel free to.

[UmbralRaptor]

Stock KSP's aerodynamic model is a bit weird. All parts contribute to drag no matter the location. As best I'm aware, the force on a given part is .0049 * pressure(in atm) * Cd(as seen in the VAB) * mass(yes, really!) * v^2. The nosecone does add to the overall drag on your rocket, but in a non-obvious way. Most parts have a drag of 0.2, so the nosecone experiences less. This will slightly raise your terminal velocity (not enough to matter usually), and move your center of drag. If the nosecone is ahead of the center of mass, you'll get a slightly more stable rocket. If it's behind the CoM (say, on a booster), you're likely to see slightly reduced stability.

[Pecan]

Only thing to add is that some people use extensive 'part clipping', as putting one object inside another is known, for aesthetics or to make artificially small vehicles. Most consider going as far as putting an engine inside another to be 'cheating', but will use clipping 'allowed by the editor' and some don't use it at all. There is no right way to have fun.

Much as I tried to resist it I couldn't help myself when it came to the intakes on the spaceplane in chapter 7 of my tutorial. Other than that I use clipping for octagonal struts to attach parts where they otherwise wouldn't (eg; radially).

[LethalDose]

Personally, I try to avoid part clipping for two reasons. One, it feels "cheaty". I'm fine with the fact that other people are okay with it, it's just not my play style. And two, I've had some phantom explosions in my games on vessls where I've had some part clipping that was allowed by the editor. For example, last night I had an SSTO docked to my LKO station, and sometimes when I reloaded, a wing would just blow off from the vessel. That wing clipped slightly into a fuel tank. I've had similar things happen infrequently, but it's enough to keep me away.

[THX1138]

Personally, I try to avoid part clipping for two reasons. One, it feels "cheaty". I'm fine with the fact that other people are okay with it, it's just not my play style. And two, I've had some phantom explosions in my games on vessls where I've had some part clipping that was allowed by the editor. For example, last night I had an SSTO docked to my LKO station, and sometimes when I reloaded, a wing would just blow off from the vessel. That wing clipped slightly into a fuel tank. I've had similar things happen infrequently, but it's enough to keep me away.

It doesn't seem that cheaty since the game fails to take into account the aerodynamics but in a similar vein, I'll be leaving the nose cones in place because excluding them is definitely cheaty!

I dislike the clipping but it's hard to get the game to position rockets where you want. It's so frustrating sometimes. The KSP devs should look at how Google Sketchup handles putting together objects in 3D space.