Dragless parts and Drag overall

[Jestersage]

While I am trying to make the Mercury clone (Godspeed John Glenn), I couldn't help but to wonder: if it's possible to replace the small nose clone for the LES with Cubic Octagonal Strut, and how it would affect the drag of the overall ship. Would someone please explain whether I should do so?

[Snark]

Basically, no.

Bear in mind that the cubic octagonal strut (and other parts of its ilk) aren't "dragless".  They're physicsless.  There's a difference.

Once upon a time, in the early days of KSP, the so-called physicsless parts really did have zero mass and zero drag.  You could spam them and it would make not one whit of difference to the vessel's performance.

Those days, however, are long gone.  Now, they do have mass and drag.  However, it works differently from "regular" parts.  The way it works is, all the mass and drag for the "physicsless" part get added to the part's parent-- or, if the parent is itself physicsless, to the closest "ancestor" part that's not physicsless.

So, imagine that you have a part with a flat upper surface that's, say, 0.625m across, and you're thinking about putting the small nosecone on it, or alternatively, some physicsless part such as the cubic octagonal strut.

Here's how the game would see those two options:

• The nose-cone option:  Nice and low-drag.  The flat upper surface of the parent part won't hurt you, because it's not exposed (the nosecone sits on top of it).  The nosecone is nice and pointy.  Everybody wins.
• The physicsless-part option:  Draggy.  The game sees the physicsless part, so adds its mass and drag to the part you've attached it to.  The part you've attached it to therefore still has that flat forward-facing surface (because the physicsless part doesn't count for occlusion purposes), and then you add some extra mass and drag because of the presence of the physicsless part.

In other words:  Physicsless parts can never help you, in terms of drag.  All they ever do is add drag.  So no, your suggestion's not going to gain you anything in terms of drag-- quite the opposite.

[Foxster]

Good answer...but does it matter? If the octo is part of an authentic look and your craft has some dV to spare then the difference is probably going to be small. 

[Rhomphaia]

It will work fine, I use cubic octos for the LES on my own mercury clone.

You can combine them just fine too.

[fourfa]

8 hours ago, Foxster said:

Good answer...but does it matter?

Great point - KSP's toy-sized solar system means that realistic-looking models of IRL craft usually have WAY too much delta-V.  I strap all kinds of dead weights on my Apollo model just to slow down the ascent and avoid having to launch with quarter-full fuel tanks.

Edited December 11, 2016 by fourfa