What's a tankbutt?

[CaptainKipard]

I see people sometimes complaining about it when engine mods are discussed.

What is it exactly, and what's wrong with it?

[Greys]

according to google a tankbutt is a protective covering put over the end of a capsuloid pressure vessel; that doesn't make much sense in this context.

Perhaps it's related to how a lot of mod engines have base disks that appear as if the fuel tanks should extend into them; but then many mod tanks clearly show the tank inside a cylinder of sheathing (KW in particular)

I've discussed before how this doesn't make sense and really the engine should contribute more fuel to the equation; but there's no easy catchall solution.

Or I could be totally wrong.

[biohazard15]

Tankbutt - a meme in realism-oriented players' circles that refers to disc-like structure on the engine's top that serves as attachment point. Usually, diameter of tankbutt = diameter of a corresponding tank (1.25, 2,5 and so on). In reality, tankbutts are part of a fuel tank, not part of the engine - hence the hatred. There even was a special patch in Realism Overhaul that moved top attachment nodes on engines, so tankbutts were inside the fuel tank.

To illustrate:

To the left, the M50 Main Rocket Engine (NovaPunch) has no tankbutt.

To the right, the SLS-250 engine (also NovaPunch) has tankbutt.

Compare to 2.5m fuel tank in the center.

With 0.90 and its offset gizmo, the meme is sort of dead.

[passinglurker]

really that's what it was about? I thought it was because the discs were often wider than the engine bells and prevented people from clustering engines in aesthetically pleasing ways?

[biohazard15]

really that's what it was about? I thought it was because the discs were often wider than the engine bells and prevented people from clustering engines in aesthetically pleasing ways?

Yeah, and that too. But this was also mostly RO and RSS users' problem, as they tend to use procedural fuel tanks.

[NathanKell]

Yep. Propellant tanks are pressure vessels, so their bottoms are domed. Somebody making assets for KSP a long time ago had the bright idea that that bottom dome should be part of the *engine* part, not the tank. Which means that clustering looks awful or extends past the edge of the tank, tanks aren't properly domed, etc.

It's bad enough when it's just a dome the diameter of the nozzle--that just looks weird and bad, but doesn't interfere with clustering. It's really bad when the dome is much wider than the nozzle (consider the Poodle)...

[CaptainKipard]

Ok this makes perfect sense.

How then would people deal with tanks that have the curved insides exposed, like KW or even Vens overhaul?

[ferram4]

The logical method is to have the engine thrust structure continue upwards a bit more than the attachment point, similar to the RL-10 in FASA. That would allow the engine to appear connected to the tank regardless of how far it is from the tank bulkhead.

[Voidryder]

My last girlfriend's nickname.

I'll let myself out now.

[CaptainKipard]

So is no one bothered by the cyllinder walls around an exposed butt then?

[Buzzou]

Ok this makes perfect sense.

How then would people deal with tanks that have the curved insides exposed, like KW or even Vens overhaul?

With KW, it seems silly to me that they did the tanks correctly, but the engines still have tankbutts

personally i think all tanks should have curved insides exposed at the ends. Even if you don't see them on an intact rocket or jettisoned stage, you will see them if the rocket explodes and they become debris. It's far better than seeing an ugly flat cylinder end...

[Whirligig Girl]

With KW, it seems silly to me that they did the tanks correctly, but the engines still have tankbutts

personally i think all tanks should have curved insides exposed at the ends. Even if you don't see them on an intact rocket or jettisoned stage, you will see them if the rocket explodes and they become debris. It's far better than seeing an ugly flat cylinder end...

The 2.5m rocket parts actually do have a curved bulkhead at the top and bottom. Look closely and you can see.

But proper bulkheads with orange spray-on insulation would be nice.

[Guest]

With KW, it seems silly to me that they did the tanks correctly, but the engines still have tankbutts

You could always ballpark a fuel quantity for the more curvaceous tankbutts and add that to their config files. Just a thought.