Tiny nose cone on rapiers?

[Der Anfang]

So, is this some kind of exploit? 

I've seen it many times, not just on this. People always seem to put the tiny nose cone on their Rapiers, and I don't get why. I thought that either: a) they'd blow up from heat exhaust or... b) they'd block the thrust of the craft. Is it just aesthetics, or is it an actual exploit or what?

 

Whatever it is, if it isn't aesthetics, then I have no idea what it is for.

 

Edited September 17, 2016 by Der Anfang

[Stoney3K]

The drag model in stock KSP assigns higher drag to 'open nodes', ie. engines that have nothing behind them. It assumes that if something is attached behind the engine, it's occluded and therefore shielded from drag.

If you stick a nose cone or other component on the back of a rocket engine it will become less draggy and therefore get you farther into space.

[Val]

2 hours ago, Stoney3K said:

The drag model in stock KSP assigns higher drag to 'open nodes'

No. It is not the open node that creates drag. If you edited the cfg file to remove the node the drag would not change.

An open node on an engine is an opportunity to reduce drag, by mounting a more aerodynamic tailcone.

[Stoney3K]

Just now, Val said:

No. It is not the open node that creates drag. If you edited the cfg file to remove the node the drag would not change.

An open node on an engine is an opportunity to reduce drag, by mounting a more aerodynamic tailcone.

Which is kind of ridiculous if you think of it, because such a tailcone would immediately be incinerated by the engine exhaust.

In real life, the reduced drag is caused by the laminar flow of exhaust coming from the engine which pushes back the vortex behind the aicraft. It's this vortex (column of turbulent air) which creates drag, and when the engine is off, the vortex is directly behind the engine, but when the engine is running, the vortex is way further back which means it's not slowing down the aircraft anymore. Real aircraft only have tail cones in specific engine configurations which requires them for more laminar exhaust flow.

In any case, it's something iffy involving the drag model used by stock KSP which makes the engine have less drag. I suspect the results would be different using FAR.

[Val]

2 minutes ago, Stoney3K said:

Which is kind of ridiculous if you think of it, because such a tailcone would immediately be incinerated by the engine exhaust.

If you're building a craft with separate airbreathing and rocket engines, then you could mount tail cones with decouplers on the rockets, but in all other uses I agree.

But the effect goes for all open nodes at the back off a stack, not just those on engines.

[Red Iron Crown]

28 minutes ago, Stoney3K said:

In any case, it's something iffy involving the drag model used by stock KSP which makes the engine have less drag. I suspect the results would be different using FAR.

It reduces drag under FAR, too.  

The technique shown is called a Rapierspike, discovered and popularized by Levelord here. Opinions vary on whether it's an exploit or not, I've used them in a few challenges that didn't forbid them because a) they shave a bit of drag and, more importantly, b) they look pretty cool. 

[katateochi]

2 hours ago, Red Iron Crown said:

discovered and popularized by Levelord here.

Thanks for sharing that link, I'd missed that post. 

2 hours ago, Red Iron Crown said:

more importantly, b) they look pretty cool.

All other reasons are secondary!

[fourfa]

8 hours ago, Stoney3K said:

Which is kind of ridiculous if you think of it, because such a tailcone would immediately be incinerated by the engine exhaust.

and @Der Anfang

KSP might be more advanced than you think.  First of all, this discussion is only about the Rapier, because none of the other jets have a rear attachment node at all.  The Rapier is actually four smaller jets inside the single piece (note that it can produce vectored roll all by itself).  Each of these has a defined point in space where the exhaust and thrust originates (I hear people call this the 'thrust transform').  If your rear nose cone surface obstructs the actual thrust transform, it will be incinerated and/or you won't produce thrust.  If you tuck the cone in just the right amount, it doesn't.  

Try it yourself - place a nose cone or shock cone intake on the back, watch it blow up.  Then use the offset tool with angle snap on - five snaps is the sweet spot for the shock cone intake.  

It's not obvious why, but the shock cone seems to have the best overall drag reduction despite its somewhat large mass and higher drag numbers listed in its cfg, so it's the usual tail accessory for rapiers. The tiny nose cone in the video is actually not as good as the clipped shock cone.  But without clipping, it sits just behind the thrust transform, so no incineration.

Edited September 17, 2016 by fourfa