The art of strutting.

[Pbhead]

ok. so everyone knows, more boosters, more struts.

but really, this ends up with ships with really high part counts.

I am curious on what you all have found to be the optimal methods of placing your struts such that:

1. your ship doesnt blow up

2. your part count is not double or trippled from what it was pre-struts.

Does strut placement direction matter? is it better to place the base of the struts from the engine to the payload, or from the payload to the engine?

Is it better for lag purposes to strut from the initial stages to the final stages? does the game stop keeping track of a strut if the base of the strut is now off the rocket?

Is more struts always better? I have found that sometimes, placing more struts actually causes the rocket to blow up more frequently, perhaps because by making one area of the rocket stiffer, force was redirected to a less stiff location?

Something I have found useful, is placing struts between my tanks. literally. move the camera so that the camera is in one tank, place the strut on the top of the other tank, zoom out, and place the strut on the "top" of the second tank, which, cant reach the top of the second tank, and we end up with a super small strut connecting the very middle of the two tanks.

Anyway. How do you all strut?

we really should assemble some sort of guide.

[Stochasty]

we really should assemble some sort of guide.

Where's that booster/strut flowchart when you need it?

All joking aside, that's essentially what I do: if something wiggles and it shouldn't, I find something that doesn't wiggle and add a strut between them. I find that with judicious placement and lots of testing, I can usually get things stable without part counts going too high (although, I have been known to occasionally launch Jebediah into the sun using a rocket made out of nothing but boosters and struts - 579 of them, at final count).

Edited May 27, 2013 by Stochasty

[DMagic]

I believe that only the originating point of the strut is counted as a part. After you stage a little nub remains where the strut attached, but I don't think that is counted as a part. So I think it's better to put the initial point on the lower stage and connect it to the upper part. Though I'm not sure how much of a difference this actually makes for performance.

And no, more struts does not always make your craft more stable. I try to use as few struts as possible. If you find that you have almost as many struts as other parts then you probably need to redesign the ship.

The strutting tanks together thing is definitely a good idea. I do it all the time when putting a small grey tank below an orange tank to prevent overheating. Without struts that grey tank wobbles all over the place, but 3 or 4 short struts keeps it stable.

[1trocksmysocks]

Here's how I strut.

[georgTF]

I use sets of cubic struts and link them together. Typically 4 or 6 cubes on a large tank. It's important to link fuel tanks if Mainsails are going to be pushing because their thrust is intense. Wobbly rockets also waste fuel correcting so it's allways a good idea to secure things. In the screenshot below, the sets of two orange tanks are well connected as is the large RCS tank because it would be the weak link. The outer droptanks are also secured with several connections as radial decouplers are fairly weak.

If you're not sure what or where to strut, launch and examine the rocket. Once you see what lacks stability end flight and go back to VAB. If you add rigidity by strutting things near the bottom section of a rocket, usually the parts higher up will begin to wobble. Ideally you strut the whole thing together nicely bottom to top. Part count is fairly meaningless if you'll be dropping tanks as you ascend.

The payloads come in all shapes and sizes and since undocking or otherwise separating breaks links, you can go nuts. You want minimum flex and no breakage. If you achieve that further strutting is pointless. So it's less of an art of strutting, and more of an art of studying and testing the rocket as it ascends. That is not to say that moar struts is a fallacy... oh no.

Segue into a fairly ridiculous screenshot of a messy payload being launched:

Because i need that many satellites. Yes, need... Actually i can't remeber what it was for, it's just a weird looking payload i apparently launched.

[Atanar]

If you have simple 6-symetry of (not too big) rockomax asperagus, 12 struts can be enough. The radial decouplers at the center of the boosters, 6 sruts from the middle of the top of the boosters to the central rocket and 6 at the bottom of the boosters towards each other.

I also avoid diagonal struts. This is not based on any evidence, it just fells like they don't help as much. Someone should research that.

I also don't use the orange tanks, cause they wobble a lot more than 2 of half the size. That actually saves me on the part count at the end.

Edited May 27, 2013 by Atanar

[superm18]

strategically placing struts i most importent imo! in an asparagus stage setup you wanna place the strut FROM the core TO the droptank in a downward angel, so that the thrust is pushing on the strut (the strut is a singel part and its base is where you clicked the firt time).

[Atanar]

strategically placing struts i most importent imo! in an asparagus stage setup you wanna place the strut FROM the core TO the droptank in a downward angel, so that the thrust is pushing on the strut

Why that? I assumed it to be a solid link between 2 parts, not a rope-like mechanism.

[rakutenshi]

In my experience, when you strut something that's attached via a radial decoupler, the struts, even though they break when the decoupler is fired, still completely negate all of the ejection force of the decoupler regardless of which end of the link is the source and which is the terminus.

I have found that using an engine with less thrust than the central engine on the radial LFTs signifigantly reduces the shear force on the decouplers, reducing the need for struts as well. You want your biggest engine on the central stack, usually providing about 30-50% of the total thrust of the lifter's initial launch stage, with the radially mounted tanks having just enough thrust under them to bring up the total TWR to about 1.7ish. You can launch with as little as 1.3 safely, and it is kinda cool watching the rocket slowly pull away but it does cost a little more dV. I've launched 25 ton payloads with only 3 struts on the whole rocket using this technique- those three struts were because of the inherent wobble when using stack decouplers on the upper stages of taller rockets.

[Specialist290]

we really should assemble some sort of guide.

You're in luck; someone already has.

Six places you should be using more struts!

[Nao]

Where's that booster/strut flowchart when you need it?

My ships usually are really low on struts. I think it's more important, where you place them, to what you connect them and what the "load tree" looks like.

I use struts in two ways: for load transfer and as a rigidity enchantment. (sometimes one strut fulfills both roles)

If something moves one (or two in symmetry) struts connected to a part close to CoM solves it. No need to make a web of struts.

It's important to take staging into consideration, especially in asparagus staging, i tend to strut to the center tank so that it doesn't matter which tanks are staged and the ship keeps its rigidity up to last stage.

To negate rotational forces when using asparagus staging due to twisting of its stages, its nice to connect like this.

  O
 | |                | - strut
  O                 O- fuel tank

Also placing connections at a distance from each other (one on top one on bottom) can be enough for even large, complicated stages if the middle section is stiff. For example.

     /[]            / - load transfer strut (two in symmetry like above make also fix it from moving
   [] []            [] - fuel tank
   []:[]            :- radial decoupler
   [] []
   []_[]            _ - fixing strut near the engine.
   A   A            A-engine 

The radial decoupler also makes sure the middle section is stiff so the load transfers nicely from engine to top strut. Making sure there is as little vibrations wobble, and bending induced from long stack of tanks. Its good to have almost all parts connected to something else (1-3 connections are well enough usually)

Load transfers are harder since the more struts are in the system the bigger tensions there will be. Picking the right part to connect outer stages to is important. There also is a trick of mounting a docking port (or something similar) on either side of the strut connection. This is is making connection less rigid and allows wider distribution of load throughout the other strut-docking port pairs.

Also when there are many struts involved my first reaction to something exploding during launch is, removing struts, searching for the one that over-stiffens the construction.

If the exploding part doesn't have struts connected to it. It can mean either there is a natural load convergence in it, so more struts in parts around are needed to make more ways for the loads to go through. Or if there are enough load transferring struts its because rest of the construction around it is over-stiffened (it's hard to explain). The point is that not always more struts is better.

Also when removing struts there is a point where not enough stiffness creates a resonance or wobble that amplifies forces. Thats why i always make sure things doesn't move before trying to create paths for load to move.

Welp it really is an art, and being engineering student helps a lot haha