engine plates

[Hatsune]

I always get attachment wrong when I use it, how do I install it correctly?

[Laie]

1. Place tank.
2. Place engine plate below tank.
3. tweak engine plate to the desired number of engines.
4. add engines to the engine plate.
5. (optional)
   • add next stage to the large attachment note dangling far below the engine plate
   • tweak engine plate to a length that fits your engines.

Please note that the plate doubles as decoupler: when you stage it, the shroud and anything attached to the bottom node goes away, while the plate itself, and the engines, remain attached.

Also note that the shroud is mere optics, it doesn't work for aerodynamic purposes. This can create ridiculous amounts of drag and make rockets unstable if the assembly is near the top. In that case, it helps to place an actual, honest-to-god fairing base on the bottom node and build a real fairing, closing it at he engine plate.

[thelostburrito]

3 hours ago, Laie said:

it doesn't work for aerodynamic purposes

lol why. I feel like you can just make those shrouds act like shrouds from a decoupler. But hey, I'm not a dev 

[Tonka Crash]

I don't remember where I got this, but it's supposed to be a patch to fix the aerodynamics.

// Make the engine-plate shrouds shield the parts inside them from drag
@PART[EnginePlate*] {
    %MODULE[ModuleCargoBay] {
        DeployModuleIndex = 3  // Index of the jettison module for all plates as of Aug2018
        lookupCenter = 0,-0.5,0 // Shrouds extend from 0 to some negative Y
        lookupRadius = #$/MODEL:HAS[#scale[*]]/scale[0]$
        nodeOuterForeID = top
        nodeOuterAftID = bottom
        nodeInnerForeID = top
        nodeInnerAftID = bottom
    }
}

 

[Gargamel]

Moved to GamePlay Q's. 

[bewing]

5 hours ago, thelostburrito said:

lol why. I feel like you can just make those shrouds act like shrouds from a decoupler. But hey, I'm not a dev 

They do. The shrouds on a decoupler are only aesthetic too. They have no aerodynamic purpose.

[OHara]

There is context for the Module-Manager patch, that makes engine plates protect their contents from airflow, in this thread.
The shrouds we get on single engines, when we attach something like a decoupler to their trailing end, replace the engine for aerodynamics purposes, so the problem with drag that Laie mentioned is avoided with single engines and their shrouds.

@Hatsune, if you assemble the craft using the engine plate correctly, for example the way Laie describes, it will work as intended,
but the "Engineer's Report" in the VAB will tell you that "this decoupler is attached the wrong way." 
That is a bug in KSPs "Engineer's Report".

[Jestersage]

On 4/8/2019 at 5:29 PM, bewing said:

They do. The shrouds on a decoupler are only aesthetic too. They have no aerodynamic purpose.

So the stock game have shroud just for looks, but when ModuleManager is installed, it create an aerodynamic shroud?

If so, what other tidbits does ModuleManager do to "imrpove" physics?

[OHara]

5 hours ago, Jestersage said:

So the stock game have shroud just for looks, but when ModuleManager is installed, it create an aerodynamic shroud?

No.

For several engines that have optional shrouds, stock KSP keeps separate entries in PartDatabase.cfg labeled "Fairing, ..." and '"Clean, ..." to store the different areas and drag coefficients.  KSP's current model for drag, however, is too simplified to notice that the fairing smooths the area ruling and should lower drag; it just notices that the shroud adds surface-area and raises the drag for that case (by a small fraction of the drag of the whole rocket).  So KSP tries to make engine-shrouds have an effect, but in practice it is tiny, and the wrong direction, so the shrouds could as well be "just for looks".

The new Engine Plates in the Making History DLC are separate parts, and KSP adds their drag to that of the engines inside.  There is a bug report that argues that the shroud on the Engine Plate should protect the contents from airflow, just like a Cargo Bay does.

The mod ModuleManager lets us change the configurations of parts, without editing Squad's definitions directly.  ModuleManager makes no changes on its own, but will apply a patch like the one that Tonka Crash quoted above, to tell KSP "please make Engine Plates shield their contents, just like Cargo Bays do."

[Jestersage]

Also, even though the shroud does not shield drag in stock, does the size of the stage below matter? I recall that if there is a node mismatch, it added drag.

 

[bewing]

Yes, parts occlude airflow according to the frontal area of their "visible mesh". So if they look like they are different sizes, then there will be additional drag.

[Jestersage]

2 minutes ago, bewing said:

Yes, parts occlude airflow according to the frontal area of their "visible mesh". So if they look like they are different sizes, then there will be additional drag.

I see. And the node size are pretty much visible, right? I am debating for the stage below a 3.75m engine plat, if I actually need another 3.75m part, or if I can just go with a 1.25m part.

[bewing]

In general, aerodynamic drag makes up a very small portion of a rocket's total deltaV budget. If you can perform a reasonable gravity turn, then aerodynamics really isn't worth a lot of worry.

[Aeroboi]

You can also enable "part clipping in editor" in the cheat menu.
Then you can add let's say 8 engines to a engine plate, then move them in or to the side so the attachment is clear and then attach another set of 8, 6 or less so you can clip the whole engine plate if you desire for a almost similar drag penalty and fuel flow still works

[Laie]

22 hours ago, bewing said:

In general, aerodynamic drag makes up a very small portion of a rocket's total deltaV budget. If you can perform a reasonable gravity turn, then aerodynamics really isn't worth a lot of worry.

I almost agree, but...

I'm aware that we have inflational drag talk on this form, with people making a lot of noise about he proper choice of nose cone and stuff. Compared to that, the effect of the unshielded thrust plates is totally off the charts -- it can easily triple the drag of your vessel, and add the drag at a point where you don't expect it.

For all that, it's still barely noticable in ordinary rocketry off Kerbin. You really have to go to Eve to feel it. Down there, it's not merely noticeable but impossible to ignore. Like, "I've got TWR=2 and can't go supersonic, what's going on here".

I'm one of those who do a lot of Eve stuff, and that's why I keep bringing it up.

 

 

[Snark]

A gentle reminder to keep it on-topic, folks.

This is a simple gameplay question from a user who wants to know how to construct ships with them, how to attach, etc.  If you've got a response that answers that question, great, that's on-topic here.

But getting into a discussion of drag issues, and "why is it that way", and "how should it work instead", and so forth... well, there's nothing wrong with discussing that kind of stuff, but it's off topic for this thread, so if you'd like to chat about that, please take it elsewhere.  (Perhaps a topic in the Suggestions forum?)