PSA: Engine Plates don't allow cross-feed

[micha]

So I love Engine Plates.  Not so much for the additional engines that can be mounted, but rather the very neat interstage fairings they provide.  Quite apart from actually mounting engines, they've proved quite useful in creating a small cargo bay for mounting probe cores and stuff between stages, for example, to create a "smart" booster which can be deorbited (and possibly recovered).

Just can't do that with standard Decouplers, and even for normal stage separation they don't have the same neat fairings when engine sizes don't match the tank sizes - I've never understood why those fairings match the engine size and not the tanks!

So having just brought my reusable Mun Lander to the orbiting Mun Station, I rudely discovered that there's no way to refuel the Lander! I had "cleverly" used an Engine Plate to mount a probe core and use the EP's shroud to hide it and all its paraphernalia (batteries etc). But with no cross-feed, once the Lander is empty, that's it(*).

Well, doh!


(*) I guess I could try to bring up a fuel line and mount it with KIS...

[AHHans]

7 hours ago, micha said:

I've never understood why those fairings match the engine size and not the tanks!

Because they are not fairings, but engine shrouds. They are part of the engine and not of the object that the engine is attached to. Think of them more as the structure needed to attach something to the bottom node of the engine, with the ability to occasionally  work as an interstage fairing a happy coincidence.

[klesh]

Not looking at my game, but if I recall doesn’t one have to specifically click to allow crossfeed on engine plates within the VAB prior to launch?  I could be mistaken and that option is not available.  

[Foxster]

On 11/23/2019 at 1:54 AM, micha said:

useful in creating a small cargo bay for mounting probe cores and stuff between stages

Except they don't reduce drag for those parts, so what you are doing is only cosmetic. 

[Streetwind]

On 11/23/2019 at 2:54 AM, micha said:

creating a small cargo bay for mounting probe cores and stuff between stages

Have you considered using a fairing base for the purpose?

The only reason that engine plates exist is that they allow you to mount a downsized engine in a stack without turning your rocket into a drag-happy wet noodle. For example, mounting a Spark or an Ant in the middle of a 1.25m stack. Also, clustering of non-surface-attachable engines.

But the interstage fairing/cargo bay, that was possible long before engine plates became a thing. You just use a fairing base. Just stick it onto the craft somewhere, rightclick it, and make sure that the options for truss structure and interstage nodes are both enabled. Now grab and attach the fairing base to the bottom of your previous stage (which should be a decoupler, since fairing bases don't decouple themselves), and voila - you not only have an interstage cargo bay, but one with a physical structure holding the rocket together to boot, rather than just an empty space between two sections of tanks.

Additionally, the fairing base will actually shield all the parts inside the interstage area. The engine plate on the other hand will only obfuscate the drag cube of what's directly attached to the engine plate.

Finally, the fairing can be ejected from the base once you are out of the atmosphere, allowing access to the contents of the interstage cargo bay even before stages separate. Or, you know, you can use this to build a shielded cargo bay inside stages, where no separation is meant to occur at all.

Oh, yeah, and incidentally it also allows crossfeed.  

 

Edited November 26, 2019 by Streetwind

[micha]

Great info, thanks, haven't tried using fairings for interstages before. Now that you mention it, I do dimly recall a changelog mentioning this.

Shame the fairings aren't decouplers though. IIRC, they also become available quite a bit after the engine plates.  The engine plates are great because they are really really cheap, are a decoupler AND a "fairing" all in one. I guess almost cheaty-good except for the downsides which I wasn't aware of (ie, not really shielding their contents and not allowing crossfeed).

Quick question : if you "deploy" the interstage fairing, don't you just end up with magical nothing holding the rocket together? ie, there's no actual truss graphics, right? And all the bits you mounted on the interstage nodes are just floating in space.

[Streetwind]

No, there is in fact a truss graphic. You enable it in the fairing base's right-click menu, as I mentioned above. When the option is active, then a truss will form automatically once one of the interstage nodes is used to attach something. It's not the most sturdy-looking of things, but it's better than nothing... and, well, the Soyuz rockets are held together with an arrangement of thin steel rods in between stages, so it's not strictly speaking unrealistic 

[RizzoTheRat]

I tend to use the 2.5m cargo bays quite a lot, can fit a remote guidance unit, KOS module, batteries and a few other bits in there easily enough.  Possibly slightly heavier than Streetwinds suggestion (not sure how heavy the faring panels are), and of course you can tailor the faring to be as big as you want if there's a lot to fit in, but it looks a lot more robust.  

[micha]

So I made a craft and yeah, it works. I forgot about those little side-trusses, they don't show up in normal (top-of-rocket) fairings.
But it's much larger than the engine-plate style interstage and there's still the lack of continuity I hate if the next engine up the stack is a smaller size.

I'd actually love to see more of the Soyuz-style interstages, especially if there was provision to mount stuff inside the structure.
 

[Gordon Dry]

On 11/26/2019 at 1:10 PM, Streetwind said:

No, there is in fact a truss graphic. You enable it in the fairing base's right-click menu, as I mentioned above. When the option is active, then a truss will form automatically once one of the interstage nodes is used to attach something.

This is true for the "Airstream Protective Shell" parts, but not for the "Engine Plate" parts this thread is about.

 

I'm necroing this as I don't get it why the "Engine Plate" parts have no "crossfeed" in my setup - literally the attached engines get no fuel. Really? Do I have to fiddle with fuel lines? As I never play stock I also never fiddled with those fuel lines since my first 2 weeks after I purchased KSP back in the days...

So, another patch has to be written to add

fuelCrossFeed  = True

to all "Engine Plate" parts?

Or is it even worse and initially those "Engine Plate" parts had fuelCrossFeed = True by default and that triggered other issues because that crossfeed did not only apply to the attached engines but also to the stage below it?
And then a KSP patch came and just removed fuelCrossFeed = True and that's it?

This would mean the whole concept of those parts is borked and they're useless without fuel lines ...

Edit:

I'm testing this patch:
GameData\zFinal\zzz_EnginePlates_get_fuelCrossFeed.cfg

@PART[EnginePlate*]:NEEDS[SquadExpansion/MakingHistory]:FINAL
{
	%fuelCrossFeed = True
	
	%MODULE[ModuleToggleCrossfeed]
	{
		%crossfeedStatus = true
		%toggleEditor = true
		%toggleFlight = false
	}
}

 

Edit:

^above patch works

Edited December 14, 2021 by Gordon Dry
patch works