Part Request: 3-noded structural part for engine mounts, shrouds, etc.

[bigyihsuan]

After playing for several years with this mod, I think Procedural Parts needs a 3-node part to help make more complex rockets, mainly for interstages and engine mounts. For example, many of the engines in BDB come with an engine mount part that attaches to the bottom of the tank. The mount has an outside node(s) for attaching engines to, and a hidden node inside of the part for hanging an interstage from. This helps make rockets look much nicer, and allows using engines that don't have a bottom node, a decoupler shroud, or the ability to surface attach onto tanks.

You can simulate such an engine mount by using a thrust plate from Procedural Fairings. However, for making an engine mount for a single engine, you need to attach the thrust plate, set the side node count to 1, attach the engine, and translate it into the center. However, this is fiddly, requires manual adjustment, and requires another mod.

So, I propose the following:

• The part should behave similar to the procedural structural part (i.e. no tanks).
• The part should have at 3 nodes: 1 on each end, and 1 "hidden" node inside the part.
  • The top node is for attaching to the tank.
  • The bottom node is for attaching to engines.
  • The hidden node is for attaching to decouplers and interstages.
• (?) The height of the hidden node should be adjustible.

To make a tank-engine mount-interstage kind of assembly, you can

1. Place the tank.
2. Place the engine mount.
3. Place the engine on the mount's bottom node.
4. Place a hollow decoupler on the mount's hidden node. Adjust the mount if it collides with the decoupler.
5. Place a hollow structural part on the decoupler. This is the interstage.
6. Attach more stages below.

You can make a semi-shrouded engine mount (like the engine mount for the RS-27) in this way, by not placing a decoupler onto the engine mount.

[bigyihsuan]

Implementation difficulty thoughts:

• The "base" form of this suggestion (a 3-noded part) was very easy (a single MM patch).
• (harder) Allowing the hidden node to be moved may require a plugin-side change, to add the hidden node height (relative to the top of the part) as a PAW field. Maybe as a subclass off of ProceduralPart?
• (scope creep likely) The ability to have multiple engine nodes, adjustable by the PAW. If this is done, can take code from/share code with ProceduralFairings KzNodeNumberTweaker modue

[bigyihsuan]

As an example for usage:

The following shows a hollow decoupler mounted on the hidden node, to allow for an interstage to be attached:

This can be used to build a Saturn SII-like interstage with sepratrons pushing the upper stage away from the lower one, then decoupling the interstage itself after the sepratrons burn out: