My rocket likes to do flips: Guidelines please

[officernickwilde]

Im playing in science mode and used too small decouplers in the bottom thinking it would provide resistance to keep the rocket straight anyway, but during flight, it bends and eventually flip over :l

Thanks

https://imgur.com/a/Cyo2ZWk

[Rocket In My Pocket]

Struts.

Or autostruts if you have advanced tweakables enabled.

Also, many short sections are weaker than one long section. Larger diameter connections are stronger than smaller, and node connections are stronger than surface attachment.

[pincushionman]

It looks like you have…lots of booster for that payload. Are you firing all the strap-on boosters and those three big cores at liftoff? If you are, you may well be hitting max-Q somewhere below 10 km or so, which is bad news. If your pad TWR is more than about 1.5, you may need to dial it back some.

Also, you said you put decouplers on for drag? Are those the devices on top of the side cores (I can’t see very well in the picture)? If they are, they may still be ahead of the center of mass, given how bottom-heavy that vessel is. The best drag-producing devices are always fins, and always waaaay at the back.

One other thing I notice is your top stage looks like four short tanks in a row. More joints = more flexibility, which will tend to exacerbate any bending going on in that portion of the stack, especially since your control point is at the tip of that spring, with the lower stages being much stiffer. You may want to replace that with a single long tank, or autostrut through it.

[Rocket In My Pocket]

10 minutes ago, pincushionman said:

Also, you said you put decouplers on for drag? Are those the devices on top of the side cores (I can’t see very well in the picture)? If they are, they may still be ahead of the center of mass, given how bottom-heavy that vessel is. The best drag-producing devices are always fins, and always waaaay at the back.

Yes, this.^

A proper rocket looks like an arrow.

Mass at the tip, sturdy shaft, fins at the rear for drag.

[officernickwilde]

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Also, you said you put decouplers on for drag? Are those the devices on top of the side cores (I can’t see very well in the picture)?

No, when I designed the bottom part of the rocket I had not yet researched larger joint decouplers, so I went with like mk1 decouplers

Anyway Thanks for your feedback, I already use struts (lots of struts), however I don't have autostruts and I have no idea how to check my TWR, and yes, a part of my upper stage is 4 mk1 tanks in a row

So meanwhile I gathered answers I had a second look on available engines suitable for my rocket and replaced all my engines with vector engines and replaced the entire lower area with just vector engines and some larger fuel tanks

https://imgur.com/a/Cyo2ZWk (second image)

I also added a shield at the top to move all the drag towards the back of the vessel <3

Flies ok now (a little heavy during launch, starting at like 5 m/s, but at least it files)

Also all my answers have to be moderated so it takes a while for my messages to reach the forum page

 

[officernickwilde]

as I have you people on the line

Ive mounted the "Drill-O-Matic" and the "Convert-O-Tron" on my vessel, do they require any storage tanks for the raw materials before they get converted into fuel??

[swjr-swis]

3 hours ago, officernickwilde said:

https://imgur.com/a/Cyo2ZWk

Are you sure those two pictures are of the same rocket? Because picture nr 2 does not look like it's the same craft as picture nr 1, not even after dumping all those SRBs and the side boosters. There's also suddenly a large fairing that isn't anywhere in the first picture, and the diameter of the center bottom is a size (or two?) bigger. They don't look like the same thing.

Either way, there's a whole lot going on with both of those craft. Sharing a craft file would allow more help, or a few more screenshots from better angles.

About the first one: you are attaching a lot of things on the outside surface, even though you have service bays - that's a lot of drag at the forward end of the rocket that doesn't need to be there. Additionally, the payload does not look heavy enough to need all those boosters to get to orbit.

On the second rocket: I would say the main problem is that your payload is bending out of the fairing - you need to use a few struts you ensure the top end stays firmly locked in place. I would say once you get that resolved, it should prove a lot easier to coax into a gentle gravity turn.

[officernickwilde]

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On the second rocket: I would say the main problem is that your payload is bending out of the fairing - you need to use a few struts you ensure the top end stays firmly locked in place.

Thanks! Didn't realize I could do that.
 

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Additionally, the payload does not look heavy enough to need all those boosters to get to orbit.

Its an outer space explorer, it will go as far as the fuel takes it

Also under the shield I added is the upper part of the original rocket, so nothing is yet changed there (from the science lab and above)

Now the largest problem with the vessel is its extra weight, it can just barely lift itself when it first launches, but at least it do lift itself  

[officernickwilde]

How do I connect struts to the airstream protective shield? The game is automatically moving them away when I hower my mouse over them (to let me see whats beneath it)

Help? <3

[officernickwilde]

Also here is a cool picture of my vessel in all its glory:

https://imgur.com/a/Cyo2ZWk

[swjr-swis]

3 hours ago, officernickwilde said:

How do I connect struts to the airstream protective shield? The game is automatically moving them away when I hower my mouse over them (to let me see whats beneath it)

There's a few ways to do this:

• The simplest would probably be to attach a strut to the fairing base in 3 or 4 way symmetry, and attach it to the payload as high up as they will reach.
• Attach a cubic octagonal strut in 2 to 4-way symmetry on the outside of the fairing base. With the offset tool, slide them up and inwards, to where they are near the top but still covered inside the fairing. Then attach a strut from those to the center payload. The cubic struts will work as if they are rigidly attached to the fairing, and wtih the struts will hold your payload in place.
• If you prefer attaching to the fairing shell, you need a workaround: you can temporarily attach some long parts outside the craft, extending far outside the fairing. Then attach a strut on the payload and extend to the temporary parts. If they're far enough away, your cursor won't make the fairing 'expand' anymore, it will stay closed, and when you try to attach the struts they will actually attach to the inside of the (now closed) fairing shell.
• You could close the fairing to surround the pod as well. That would allow you to put a Jr docking port on the nose. If you attach another Jr docking port on one of the fairing's interstage nodes, you can offset that one up so it's close enough above the pod's docking port that when the craft loads on the pad, they will dock together. This will hold the payload pretty well too.

[Vanamonde]

These questions about how to play the game have been moved to Gameplay Questions. 

[Sharpy]

5 hours ago, officernickwilde said:

as I have you people on the line

Ive mounted the "Drill-O-Matic" and the "Convert-O-Tron" on my vessel, do they require any storage tanks for the raw materials before they get converted into fuel??

Ore tank (may be very small) and of course fuel tanks for the produced fuel.

 

3 hours ago, officernickwilde said:

How do I connect struts to the airstream protective shield? The game is automatically moving them away when I hower my mouse over them (to let me see whats beneath it)

Help? <3

This is triiiicky. You can't attach struts directly to the fairing - but if you want to attach them to something else and the fairing is in the way, they will attach to the fairing.

I usually attach the Kickback SRBs (because they are looong) pointing around the rocket, then draw the strut from the part to the Kickback, make sure to keep the cursor away from the fairing (so that it 'settles'), then 'attach' the other end to the Kickback - and instead, it attaches to the fairing. Then I can just delete the Kickbacks.

[officernickwilde]

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• If you prefer attaching to the fairing shell, you need a workaround: you can temporarily attach some long parts outside the craft, extending far outside the fairing. Then attach a strut on the payload and extend to the temporary parts. If they're far enough away, your cursor won't make the fairing 'expand' anymore, it will stay closed, and when you try to attach the struts they will actually attach to the inside of the (now closed) fairing shell.

Worked, its not completely anchored in the shell tho, it still bends a bit, but not close to as much as before <3

It still bends where I have my second row of engines tho, ideas? 

https://imgur.com/a/yYkIiZ1

Thanks for all the responds so far, I got the Drill-O-Matic and the Convert-O-Tron working <3

[Superfluous J]

49 minutes ago, Sharpy said:

Ore tank (may be very small) and of course fuel tanks for the produced fuel.

While technically true I have found that having enough ore tanks to store 6 hours of drilling is a very good thing, as the simulation of drilling when you're not focused on the craft goes in 6-hour increments. If you've not got the space, you don't do the drilling and your ship will therefore drill a LOT less when not in focus than when it is in focus.

[swjr-swis]

54 minutes ago, officernickwilde said:

It still bends where I have my second row of engines tho, ideas? 

Using a decoupler of the same size as the tanks would be the best option. If you don't have one unlocked yet, struts to the rescue once again: attach them in symmetry from the part below to the part above the decoupler.

[Plusck]

56 minutes ago, officernickwilde said:

Worked, its not completely anchored in the shell tho, it still bends a bit, but not close to as much as before <3

It still bends where I have my second row of engines tho, ideas? 

https://imgur.com/a/yYkIiZ1

Thanks for all the responds so far, I got the Drill-O-Matic and the Convert-O-Tron working <3

That is a massive amount of bend there.

First off, I do get the impression you're trying to do too much, too soon here (/me plays The Specials "Done Too Much..." in the background). I feel you're trying to put too much rocket into space, all at the same time, which tends to produce disaster.

The next thing is that your SAS is trying to stick to "radial out" while you're still in surface mode on the NavBall. In itself that's not a problem as such... but the SAS takes its current heading from the "control from here" part, which is certainly at the top of the rocket. With all of the bend down lower in the rocket, the bottom is going to be significantly behind the times; therefore the top says it's going one direction, the bottom tries to correct, overcompensates, and then when the top realises it's going in a different direction the bottom is still in mid-swing; the top tells the bottom to reverse direction and it takes a second or so to do so. The end result is mad swings at the bottom until it ruptures.
The only solution is to create an aerodynamic rocket and leave SAS off: aerodynamic forces keep the rocket facing the right way until you get rid of the bottom stage and have proper control.

With such a massive amount of bend, I also wonder what is actually connecting those tanks in the core section. I can't see much from the pic, but I suspect there may be something between the big tanks there.
One thing that people often try to do is to put a big torque wheel in between two large tanks. The reasoning is clearly that the torque should be centrally located to turn the craft. That is fallacious since it doesn't matter where the torque wheel is (if you have nothing solid to push against, torque wheels have exactly the same effect wherever they are located on the craft) and often disastrous because you're adding two separate connection nodes in the middle of what needs to be the strongest joint, thereby tripling the amount that the joint can bend.
So if that is actually the case, get rid of it. Keep the minimum number of joints in the core stack. Join one huge tank to another huge tank and do not ever put anything else in the middle.

And finally, to sort your problem, disactivate gimbal. In the VAB, go to the action menu, choose a number (I always use key 7 for this, on every craft, but you choose your own system) and then click on every single engine and choose the "toggle gimbal" option. As long as your craft is going in the right direction, gimbal is unnecessary and should be toggled off. When you need it, toggle it on. If the craft starts oscillating, toggle it off again. Gimbal is indeed a Good Thing on rigid craft, but it is a killer on any wobbly one.

[officernickwilde]

Thanks again, I already have a decoupler in the size of the fuel tanks, but Im unsure what size the joint I have connected it to is

In the middle stage I use a S4 sized adapter that adapts to 5 smaller joints (unsure of what sizes) (you can see the aerodynamic hull surrounding the joints on the picture)

Idk how to fit Vector engines at the second stage without changing from the S4 joint size without simply side attaching the vector engines

Maybe disactivating the gimbal for the first stage vector engines and attaching oxi+fuel powered RCS engines to the second stage body would fix the bending problem??

Closer image on the middle body:

https://imgur.com/a/QgMshG0 (second image)

Edited November 19, 2018 by officernickwilde

[officernickwilde]

I just tried another setup for the second stage using a engine plate replacing my adapter tank, but it appears weaker than the adapter tank and breaks in the first stage

https://imgur.com/a/QgMshG0 (first image showting the engine plate setup and the second showing the adapter tank setup)

I also tried putting a RoveMax on the hull of the second stage fuel tanks and using its SAS system in the first stage but it didn't keep the ship closely to as stable as using the cockpits SAS (The name might tell why) and if I disactivate gimbals the ship looses control

Edited November 19, 2018 by officernickwilde

[swjr-swis]

3 hours ago, officernickwilde said:

In the middle stage I use a S4 sized adapter that adapts to 5 smaller joints (unsure of what sizes)

Those nodes are only meant for engines, even the center one. It's not meant to be used as an interstage, the center node is not big enough for that, which is what causes the bending.

It's a bit of a puzzler to me, because as far as I can tell, the only configuration that even works ok is placing 5 Mastodons on those nodes, and then only in the bare variant. Might as well just've made it one part with the engine bells included, like a supersized Mammoth.

 

3 hours ago, officernickwilde said:

I just tried another setup for the second stage using a engine plate replacing my adapter tank, but it appears weaker than the adapter tank and breaks in the first stage

Not sure what to say about that one. The center nodes of the engine plate are definitely the right size, it should be stronger - assuming you used the largest size one.

 

Either way, looks like you'll still need to do some additional strutting to rigidize it.

[Plusck]

Yup, definitely as swjr-swis says, which also applies to any other multi-node engine plate or stack splitter: they really aren't a good idea if you plan to add anything below them, since each node is necessarily weaker and only one node will ever connect to any item placed below them.

Bearing in mind that craft have a tree (parent/child) structure. Therefore each node on that engine plate will connect to one engine. Only one engine can then connect to the decoupler below it, which then connects to the tank below that. So it's a 1.25m node connecting to the 3.75m node on the decoupler, far too weak to resist bending.

[officernickwilde]

Currently Im facing difficulty landing on another body (mun): Guidelines please

https://imgur.com/a/QgMshG0 (3rd image) (As you can tell by the picture did half of my landing struts break on impact and the entire rocket fell to the side, Im using Lt-2 landing struts)

[Kerbart]

Are those 5m tank sections? At least three of them? With on top an entire 2.5m stack with engines and the works? I’m not sure how many landing legs you are using (the picture doesn’t allow to see particular details) but unless it’s an insane amount it might simply not be sufficient to carry all that weight, especially when you’re impacting landing at higher speeds. The wiki mentions ~12m/s as the maximum they can absorb, but I’m sure that drops significantly when you’re putting a gigantic load on them; “gigantic” being anything taller than a fully loaded jumbo 64 tank.

[swjr-swis]

20 minutes ago, officernickwilde said:

As you can tell by the picture did half of my landing struts break on impact and the entire rocket fell to the side, Im using Lt-2 landing struts

Well, it's a very tall rocket, which is not very stable for a lander. Main rule of thumb for landers to stay upright is to keep center of mass as low as you can, and the base (distance between landing legs) wide. A table can't fall over on to its side very easily, but a stool only needs a little shove.

If your payload is intended as a lander, you need to consider building it wide and low.

[officernickwilde]

The reason I want it to be able to land on bodies is to refill the fuel tanks to get even further

Looking for other solutions than rebuilding my entire rocket to allow it to land on (at least smaller) bodies.

Would apricate some ideas <3