Weak engine fairings and strange struts.

[Galane]

Yesterday I tried a design with a Rockomax tank with a 4x adapter, four tanks and engines stuck under that, then a second 4x adapter flipped upside down with 4 decouplers to connect to an adapter to the huge tank size from the ReStock parts addon, which had the really large adapter for 9 engines (4 of the Mainsail/Skipper/Poodle and 5 small) under it.

I kicked it off with a bunch of SRBs which staged off around 2000 meters then the main engines kicked in (IIRC just four Skippers and 4 of the small vevtoring ones) and it collapsed at the stage fairings.

Such interstage fairings on real rockets don't need to be stapled together with a ton of struts and they certainly don't hula dance around until the rocket falls apart. The automatic fairings in KSP need to be a lot stronger and more rigid - especially since putting a ton of struts, both straight and angled, across the gap doesn't do much for stiffness. The struts work better when there's a size difference between stages so they can angle outwards. Going straight across an engine between equal size stages all the struts seem to do is make the parts hold together a little better while still allowing things to flap back and forth.

Struts seem to be quite elastic, but somewhat variable in that property. I've had them break in cases where there ought not to be any reason for it and I have a rocket that might be manually flyable but MechJeb just slams the throttle up and down while the rocket does an impression of a slinky on fire - without one strut breaking.

What is there besides the too flexible struts for holding two stages *rigidly* together, which will also pop off like struts when staging?

I just made a rocket yesterday using procedural fairings, which help to some extent but the top end doesn't seem to actually be "bolted" to the stage above. I had to add angled struts from the tank above down to the fairing base, which quite unrealistically penetrate the fairing panels. It all holds together but still wobbles about a bit under thrust.

[Cuel]

A good counter is to sew the core stage together w/ 4 struts. It's easy with editor extionsions and 90 degree snap.

Does someone know if inner struts sewing make a difference? When you zoom in and drop the strut on the top of something and then towards what ever is above.

[Genius Evil]

Your rocket crumpled because only one of the decouplers connected to the adapter. Basically, because of how the game works, each part can only be attached to one part "closer" to the first part placed. There's a workaround using docking ports, but using struts is usually more solid.

[DisarmingBaton5]

Remember that the fairings are purely cosmetic; they have no strength. Try imagining your rocket without the fairings, like it would have been pre-0.18.

[Tiron]

Your rocket crumpled because only one of the decouplers connected to the adapter. Basically, because of how the game works, each part can only be attached to one part "closer" to the first part placed. There's a workaround using docking ports, but using struts is usually more solid.

Specifically, it uses a Tree structure to represent the craft. There's a single 'root part' (the first one placed), and every part branches off that. Each non-root part has exactly one parent and a theoretically unlimited number of child parts: anywhere from 0 to the maximum number you can trick the editor into fitting as radial attachments.

The requirement that each part has one, and only one, parent node makes it impossible to form a 'loop' structure with the normal parent->child connections. You can get around it via a PHYSICAL connection that isn't a link in the tree. There are two ways to get a physical connection at present: struts, and multidocking. Multidocking has the same limitations: only one port can be the 'parent' port of a substructure, the others can only make physical connections (this is why the magnetic attraction shuts off when the first pair mates, and the subsequent pairs are able to connect while not perfectly aligned: they're making physical connections instead of actual links.)

Struts can be connected in the VAB. You can also set up unconnected docking port pairs facing each other in the VAB: They'll automatically form a physical connection when the craft loads in on the pad.

[Giggleplex777]

Remember that the fairings are purely cosmetic; they have no strength. Try imagining your rocket without the fairings, like it would have been pre-0.18.

Oh man, were they ugly.

[Galane]

In other words it's not really possible to build a proper inline staged rocket with clustered engines like a Saturn V, not without some workarounds, trickery etc, or having to settle for one large core and fake it with strap on boosters on upper stages.

It would be so useful to flip those 1 to n adapters upside down.

How about some procedural girder struts that work just like the existing struts but are not at all elastic? Slap them upside the gaps across stages and eliminate the wobbly hula dancing that the struts we have can't eliminate.

[sojourner]

What wobble? Struts stop wobble just fine for me. It's all about placement.

[AlamoVampire]

yup placement is key. I had a rocket go all 10 on the richter scale on me and shatter. reverted to VAB and hit 8x symmetry and placed 4 sets of struts. it looked as if dr frankenstein got a hold of my rocket, but it was very solid and launched just fine. hell, check this out:

middle of that ugly mess is a capsule, and 'ontop' is part of my station, but notice all the struts. wobble like a sausage it did, but never broke.

btw, it flexed everywhere BUT at the capsule

[CleverClothe]

In other words it's not really possible to build a proper inline staged rocket with clustered engines like a Saturn V, not without some workarounds, trickery etc, or having to settle for one large core and fake it with strap on boosters on upper stages.

It would be so useful to flip those 1 to n adapters upside down.

How about some procedural girder struts that work just like the existing struts but are not at all elastic? Slap them upside the gaps across stages and eliminate the wobbly hula dancing that the struts we have can't eliminate.

Use surface mounting for your engines rather than an adapter.

[Galane]

If you have an engine between stages of the same diameter and don't have something out to the sides to put in a bunch of angled struts to brace above the engine, it'll wobble like a Weeble, and break apart if you have too much thrust, no matter how many struts you put straight across the engine.

Put a Rockomax 64 on top of a Mainsail, a decoupler, a second Rockomax 64 and Mainsail, under that, then a whole bunch of struts across the gap between the tanks. Still too weak. Have to have other tanks and engines out to the sides or spanning the core stage gaps to strut to for stability.

The only mods I have installed are the root selector plugin, MechJeb, Stretchy Tanks, Procedural Fairings and ReStock. (That's the order I installed them.) I installed the fairings because I didn't like my satellite sitting out in the wind on its Snafu series launcher.

http://partsbyemc.com/pub/AARP-Kerbal-Space-rockets.zip

BLB-3 in there is my first success at getting the thing to not break apart between the big orange tanks. (It really should have been revision 5 or 6 but AARP's chief engineer decreed that it was going to be 3 no matter how many redesigns it took to come up with one that wouldn't break.) I first tried 8 struts across, didn't work. The small tanks stage off the towers as they empty but I had to leave the 2nd from bottom riding along as dead weight so it wouldn't come apart going through the gravity turn. Since that worked I took off the struts straight between the big tanks since they weren't adding anything but weight. BLB-3 is the first appearance of the AARP stock lander, which I've been trying to put a rocket under that can get it to Mun without using any of the lander's fuel until after it de-orbits the Mun. *Then* I'm hoping it'll have enough fuel left to leave Mun SOI and fall back to Kerbin and land.

There's two big failures in there, RD-BLB and RD-BLB-FAIL.

RD-BLB was supposed to be a "Reduced Diameter" rocket - reduced by using a slim core flanked by boosters. Well it doesn't work too well. It likes to lose fuel pipes during staging. It would often pop some just sitting on the pad so I put in some extras for backup. When it manages to get through the lower half without incident, the upper half doesn't have enough TWR so it slowly loses altitude. I gave up on it but saved it then wasted a bunch of time trying to build a lower half that could get the upper high enough it could keep going.

RD-BLB-DR sort of succeeds at it but gave up all pretense of being reduced anything. Gave up on the slim core design completely. I have a nuclear engine in the middle and nowhere to put angled struts to brace above it so I just put several straight across and it wobbles around. Fortunately RCS keeps it under control. It also has 16 large SRBs to get it off the pad before the big engines kick in, otherwise it'll break in half.

RD-BLB-FAIL is FAIL. MechJeb seems to fly it different every time. I just did and the throttle bouncing up and down wasn't as violent as the last time I tried (after which it became FAIL). It's probably workable manually flown but is also saddled with the slim core upper half that doesn't work. I kept it because during it's first test in its current form it made me laugh at how MechJeb was whanging the throttle up and down - I was waiting for it to fall apart but it didn't - at least not before I aborted the flight and started the DR design. The 70K variant just sets the AARP lander on top of the DR lower half - the sole object is to kick it up to a 70K orbit for eventual use for crew exchange of stations in LKO. Should work as long as there's fuel up there to top off the lander tanks if it has to climb higher than 70K.

BLB originally stood for Big Light Booster as I figured it might be possible to stack up a few Rockomax 64 tanks and engines. Big and relatively lightweight for its size. AARP's chief janitor and test pilot says the Light in the name now stands for the blinding glare of the massive amounts of fire coming out the bottom end.

[Kerbart]

What is there besides the too flexible struts for holding two stages *rigidly* together, which will also pop off like struts when staging?

I-beams?

Besides that, I have the habit of mounting hardpoints on my tanks and attaching the struts to those. I'm not sure if that actually works but if the struts work like real mechanics (naively I'm inclined to suppose they do) they'll get more effective the further you put them away from the central axis.

[Galane]

Hadn't thought about a ring of small hardpoints. Hmmmm.

[Tiron]

I-beams?

Besides that, I have the habit of mounting hardpoints on my tanks and attaching the struts to those. I'm not sure if that actually works but if the struts work like real mechanics (naively I'm inclined to suppose they do) they'll get more effective the further you put them away from the central axis.

I-Beams have *quite* flexible joints though.

But yeah, if you stand the struts off they'll create a more rigid connection. You could also try a multi-docking connection, although they have their own rigidity issues:

Note the port at the BOTTOM is the fully-connected one.

[Johnno]

I thought I'd reply earlier but never got around to it, seeing as you're not happy with just written replies however I took the time to do a few flights and take a few screenshots, as I personally feel there's no issue with struts being 'flexible' nor any hulahooping of rockets if you design them correctly.

If you have an engine between stages of the same diameter and don't have something out to the sides to put in a bunch of angled struts to brace above the engine, it'll wobble like a Weeble, and break apart if you have too much thrust, no matter how many struts you put straight across the engine.

I'd say this is false straight off the bat. You can place struts straight across as you already mention, nor does it take angled struts to give their full effect. I understand if you're trying to exaggerate the problem to try and get your point across, but as such it falls flat on its face. I'll demonstrate shortly.

Put a Rockomax 64 on top of a Mainsail, a decoupler, a second Rockomax 64 and Mainsail, under that, then a whole bunch of struts across the gap between the tanks. Still too weak.

Allright here's where my demonstration starts. I'll have a full gallery at the bottom for 'proof' of no wobbliness, I'll just link the craft designs while writing.

Your exact design, mainsail, jumbo, decoupler, mainsail, jumbo (from the bottom), I threw on a 3man pod on top for 'realism'. I usually go with 4-symmetry, so I decided to just go with that. Worked fine, no wobble whatsoever. Demo picture of craft (click for hires).

I figured you'd retort with "not full thrust", well I couldn't since mainsails overheat while straight on a jumbo tank. So I figured I'd throw on some thin tanks instead. Also I figured you'd say the decoupler 'sticks out' allowing me to place struts, so I went with the separator. In this design there's actually more wobble between the tanks themselves, but I figured I'd strap it in properly... and before you say I use too many struts, may I remind you that you felt that 'no amount' was enough. I could've probably done it with less. Again, no wobble whatsoever, I tossed and turned the craft much as I could.

Now you'd likely retort with that the rocket is too slow and doesn't get enough g-forces onto it or somesuch. So I figured I'd put some smaller tanks, and several of them. But to top it off I thought why not put the larger one on top, as to help crush the smaller one. Strapped them in properly.. no wobble whatsoever.

Now if you're going to make a bold statement such as "no matter how many struts" you'll be told otherwise. Someone is going to bother proving you wrong. Struts work very well once you learn to use them, which I suspect you haven't. My first test shows a simple 4way symmetry is enough. So you must be doing something wrong somewhere.

You can claim that you shouldn't have to use struts all you want, you can compare to reallife rockets all you want, but the reality of the situation is that this is a computer game, it has limitations in design due to coding constraints, due to decisions made earlier in the process, or any other reason you could conceive. As much as you dislike it, it's what it is right now and the best thing you could do is actually learn to work with it. Learn to use the tools available.

Struts can do amazing things, but they do rely on you knowing how to use them.

Full gallery of flight tests, sorry bout the first flight taking place during nighttime.

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