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Chris Hopkins

Large Spaceplane Wings

Question

Hi,

I'm having trouble with my larger spaceplanes getting wings that are big enough using stock parts. Checking out the designs on KerbalX i see a lot of people crack this by variations on the theme of using two delta wings to form a square. Several of these form a large flat expanse, then it's more delta wings to make one huge wing. Alternatively the wing connectors can be used to similar effect. So far so good.

However the problem I hit with this technique is the classic "a part can only have two connections"*. Therefore my wings have near zero rigidity and I end up using struts to shore the whole thing up. It works, but it's messy. Is there a trick I'm missing? I look at other's designs and they don't have this mess of struts but when I try and copy their designs I get the parts phasing through each other (Yes I know collision detection doesn't function between parts on the same craft so there is no rigidity gained from overlapping the parts). Is there some cunning way to bond parts together other than using a strut?

*actually I hit several other issues including the part placer doing anything other that putting it where I want, and attaching in any rotation but the one that makes sense, but that's what the move/rotate tools are for :-) 

Thanks

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2 hours ago, Chris Hopkins said:

Yeah I keep hearing about them, but without context I've no idea what they are. I'd searched https://wiki.kerbalspaceprogram.com but nothing really enlightening on there.

Yeah, the wiki seems... curiously mum on the subject of autostruts.  Really oughta have an article there.

Here's the idea behind autostruts:

You're familiar with the EAS-4 Strut Connector, yes?  It's that part that you can place where you attach the two ends wherever you want, and it holds them rigid.  Useful for making a ship stronger / stiffer... but it comes at the cost of weight and drag (struts are heavy and draggy), and also the fact that it's a physical part and has to be a straight line places some constraints on where you can put them.

Well, an "autostrut" is functionally similar to a physical strut-- in that it connects two different parts, and holds them fairly rigidly in the same position with respect to each other.  However, it's not a physical part, and has no mass or drag.  It's just part of the hidden internal physics model that the game uses when putting stresses on a craft.

Autostruts are always available in sandbox games.  In career mode, they're only available after you've unlocked the necessary tech node, which (I think) is General Construction.

To be able to work with them, though, you need to have Advanced Tweakables turned on in the game settings, as bewing mentions above.

If they're available to you (because you're in a sandbox game, or a career game after getting General Construction), and if you have Advanced Tweakables turned on, then you can see them on a part's right-click menu, either in the vehicle editor or in flight.  For example:

DoVBbPU.png

Clicking the button allows toggling among the various autostrut modes.  The choices are:

  • Disabled.  (This is the default.)  No autostruts are applied to the part.
  • Heaviest part.  Generates an auto-strut to the heaviest part in the ship (or set of parts, if it's a symmetry group).  Note that this is dynamic:  if "which part is heaviest" changes (e.g. with docking/undocking, or a fuel tank emptying), then it'll switch to the new heaviest part.
  • Root part.  Generates an auto-strut to the root part of the ship.
  • Grandparent part.  Generates an auto-strut to the parent part of this part's parent.  This is chiefly useful for things like radial boosters:  i.e. you attach a decoupler to the central core, then you attach a fuel tank or whatever to the decoupler.  You can set that fuel tank to "autostrut grandparent part" and it'll be locked to the central component, which is typically what you want.

Advantages of autostruts:

  • No mass
  • No drag
  • They're free (no part cost)
  • They're not physical pieces, so there's no constraint about their maximum length, or whether there are any other pieces in between the two parts that are autostrutted together.
  • You can edit them while in flight, not just in the editor.

Disadvantages of autostruts:

  • Judicious use in just the right strategic spots is fine, but don't go nuts and spam them everywhere.  They complicate the physics model and (if abused) can slow down your frame rate and/or can attract the kraken.
  • Some might call them "cheaty", if you're the kind of person who cares about that (I'm not, myself) ;)
  • Since you can't see them, it's easy to forget that they're there, which means it can sometimes be non-obvious why a ship is behaving as it does.

Personally, I use them, but sparingly.  I will commonly use the "autostrut grandparent part" for radial boosters-- but usually it's only there.

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Sounds like you haven't heard about autostruts? You need to turn on Advanced Tweakables in the settings.

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21 minutes ago, bewing said:

Sounds like you haven't heard about autostruts? You need to turn on Advanced Tweakables in the settings.

Yeah I keep hearing about them, but without context I've no idea what they are. I'd searched https://wiki.kerbalspaceprogram.com but nothing really enlightening on there.

I'll see if I can find them next chance I get to play.

Thanks

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Posted (edited)

I would start to recommend autostrut use. If you have *one stack (*one serial stage without boosters that is) it is best to only use grandparent on that length between the parts and every exterior part to root including the rear end which are engines presumably. That stiffens the vessel over it's length.
When using a parallel stage on top of the serial (a pair of boosters) it is best to use grandparent to the tank directly attached to the tank, or decoupler (also set to grandparent)
The other tanks or parts should be welded to heaviest with the fwt and aft parts set to root. When adding a parallel booster make sure you place the first fuel tank in or close to the middle of the center stack so the grandparent connection of the pair is connected through the center.
Don't use rigid attachment when used under stress like flight and high twr rockets. Rigid attachment is best used for very loose constructional pieces that tend to flex like on a rover or base.

I consider myself a expert at wing design especially using larger space planes. I have a space plane that takes close to 1.5 Kiloton to orbit using massive wide Big-S wings.
https://kerbalx.com/Aeroboi/Hearts-Chevron-96-Cargo-Lifter-2375MC

Always strut wing pieces to the heaviest part. Make sure that the wing pieces are moved (move:tool) as much away from one another as possible without leaving a gap. If you attach a Big-S wing straight on you will always be able to move one away from the other before the gap occurs. There's also a slight uneven alignment so use rotate to mirror the other. If wings are close to each other during stress they tend to fall off. If the wing construction isn't wide then the stress is within limits, in that case seperating wing pieces away from each other shouldn't be necessary.

Beyond that there's a secret but annoying workaround to large wing design. That is placing each wing piece seperately from the other. Let's say the whole wing would want to be attached to a center fuel tank then the first piece is placed. Instead of placing the 2nd piece on the first piece you place it directly to the tank and then use move and rotate to place it as you want, expectedly as it would if you connected it directly. Continue until the wing is made. Remember you can hold Shift while dragging a part to offset it to unlimited range. If the wing is placed to much forward you need to move each wing piece one by one until the center of lift is in the proper direction. This may seem tedious but I've got a hand in it, as you will with practice.

Edited by Aeroboi

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Posted (edited)
9 hours ago, Snark said:

 

  • Heaviest part.  Generates an auto-strut to the heaviest part in the ship (or set of parts, if it's a symmetry group).  Note that this is dynamic:  if "which part is heaviest" changes (e.g. with docking/undocking, or a fuel tank emptying), then it'll switch to the new heaviest part.

If i may i add that you should be VERY carefull when to use it.When the heaviest part changes it might cause kraken to attack.So try to avoid it especially if you plan to dock with something that has a part that is heavier than any of the parts of your current vessel.

Edited by Boyster

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Thanks everyone for this amazing help. Lots for me to digest and experiment with here so I'll look forwards to having a play next chance I get.

Really blown away, thank you.

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Thanks everyone, I had a chance to experiment with this over the weekend. Success!

Except now the plane re-enters the atmosphere backwards because I got carried away with engine placement and my COM when the fuel tanks are almost empty is now behind the COL. It's okay I *think* I know how to fix this. :-)

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