Eve ascent

[Cubfan]

Let me start by saying I don't use mods. KAC is the exception that proves the rule as it's essential to my style of play; which is this: Save game, build rocket, see if it works, reload. Tedious, as I have a dozen missions to several planets/moons that take years, but I like it. I've gotten pretty good at it. Even my first Tylo ship worked (2ND landing, though. First landing was at about 80 m/s). Eve, however, is evil. My lander worked and made orbit, so I reloaded and sent Jeb on his way. About a year later (game time), I came back to him. Meantime, 1.2 had come out. Landing went fine, but I cannot make orbit. Tweaked the fuel flow to normal, so that's not the problem. I do my own flying, so I'm obviously in a different spot. Fine. I will send a rescue ship, and rover to reach it. Money means nothing at this point. I want Jeb home. My method is this: Launch behemoth, refuel at Minmus, see if it works. So, finally, to my question: How do you test an Eve ascent vehicle without going all the way to Eve? I just set my engines to about 20% and see if I can make LKO. Any other suggestions? But please don't say hyper edit. It's an unholy abomination.

[Spricigo]

Unfortunately you already said uninterested in the possible suggestion, mods.

Anyway, maybe you consider this one reasonable: 

 

[Kerbital]

If you don't want to use Hyper Edit maybe you can at least tolerate using the built-in cheat to put your test ship in orbit around Eve? Seriously, I don't have that kind of time in real life to do a full interplanetary flight for every test ship. I just pretend it's "computer simulation" before doing an actual mission.

[AeroGav]

1 hour ago, Cubfan said:

. So, finally, to my question: How do you test an Eve ascent vehicle without going all the way to Eve? I just set my engines to about 20% and see if I can make LKO. Any other suggestions? But please don't say hyper edit. It's an unholy abomination.

If you need to take off from Eve, there is no substitute for taking off from Eve.  Sorry but that's the only accurate test.

I don't have hyperedit installed either, i just use the Alt-F12 menu, set orbit function to put me in  orbit of eve, then make a retro burn with infinite fuel/ignore max temperature /whatever other cheat i need to get it on the surface.  Then save,  turn off the cheats and hope to God it works.

 

[Cubfan]

1 hour ago, Kerbital said:

If you don't want to use Hyper Edit maybe you can at least tolerate using the built-in cheat to put your test ship in orbit around Eve? Seriously, I don't have that kind of time in real life to do a full interplanetary flight for every test ship. I just pretend it's "computer simulation" before doing an actual mission.

You hit the nail on the head. Time is the problem. I don't have much free time, and KSP eats up every bit of it. It's the most rewarding game I've ever played. I like your simulation idea, though. I fly every tough mission twice anyway, so that could work. Thanks.

1 hour ago, AeroGav said:

If you need to take off from Eve, there is no substitute for taking off from Eve.  Sorry but that's the only accurate test.

I don't have hyperedit installed either, i just use the Alt-F12 menu, set orbit function to put me in  orbit of eve, then make a retro burn with infinite fuel/ignore max temperature /whatever other cheat i need to get it on the surface.  Then save,  turn off the cheats and hope to God it works.

 

Jeb's rescue mission is already on its way, but I like this idea. If the mission flames out I'll use it to test the next one. And then I'm never going back to Eve again. Wait. Who am I kidding? Of course I'll go back. I love this game.

[Foxster]

A few tips that might improve your chance of making orbit from the surface of Eve:

It doesn't have to be big. My current smallest sea-level to orbit craft weighs in at a bit over 18t before lifting from Eve. About 40t or so is very practical. 

Streamlining is absolutely essential. Use the thinnest parts you can and the smallest number of stacks. 

Drop everything not needed to make orbit before lifting and have nothing at all on the craft that is not part of getting to orbit. So forget RCS, extra crew, landing struts, batteries, science experiments, parachutes, air brakes, ladders...

Have a high TWR throughout the lift, apart from your last stage that will be firing mostly in thin atmosphere and vacuum. You need to get up and out of the soup ASAP. 

Take just one Kerbal and use the mk1 capsule. 

Aerospikes for the first stages and a Terrier for the last stage are a good idea. 

If possible, aim for the highest landing spot you can. This will improve the dV margin a lot and allow for a less efficient lift if needed. 

A mod that shows TWR and dV is a very, very good idea. You think NASA put people into space without knowing this stuff?

Edited January 28, 2017 by Foxster

[Cubfan]

48 minutes ago, Foxster said:

A few tips that might improve your chance of making orbit from the surface of Eve:

It doesn't have to be big. My current smallest sea-level to orbit craft weighs in at a bit over 18t before lifting from Eve. About 40t or so is very practical. 

Streamlining is absolutely essential. Use the thinnest parts you can and the smallest number of stacks. 

Drop everything not needed to make orbit before lifting and have nothing at all on the craft that is not part of getting to orbit. So forget RCS, extra crew, landing struts, batteries, science experiments, parachutes, air brakes, ladders...

Have a high TWR throughout the lift, apart from your last stage that will be firing mostly in thin atmosphere and vacuum. You need to get up and out of the soup ASAP. 

Take just one Kerbal and use the mk1 capsule. 

Aerospikes for the first stages and a Terrier for the last stage are a good idea. 

If possible, aim for the highest landing spot you can. This will improve the dV margin a lot and allow for a less efficient lift if needed. 

A mod that shows TWR and dV is a very, very good idea. You think NASA put people into space without knowing this stuff?

Excellent points all. I appreciate the input. I call my current lander "light", but it's a couple hundred tons. To paraphrase Burnham, I "make no small rockets". I've yet to find a problem that couldn't be solved by more power. Except Eve, of course. This time I put wings and fins (which I haven't used in forever), because my last lander kept getting knocked sideways at about 11K. A layer of Jell-O I couldn't get past. Trying 16 Vectors for the bottom stage this time. I use Aerospikes for 2nd stage. If it doesn't work, I'll try going smaller.

[Zeiss Ikon]

I've just this evening watched a video showing a no-mods SSTO launch from Eve, starting around 7500 m above Eve sea level (still denser atmosphere and more height left above launch than Kerbin sea level).  It's a surprisingly small rocket, one of the 3.5 m 4-engine booster units, limited tanks, apparently a nicely shaped fairing, with a single Mk. 1 pod on top, and it looks like it will tolerate a small amount of imperfection in the launch profile (based on there being a little fuel remaining when it reaches orbit).  I presume you'd rendezvous with a return ship and Jeb could EVA across, since a docking port doesn't appear to be included (though you could probably add one if you use a multi-stage launcher).  If you can't start from that elevation (near the highest point on the planet, from my reading) you've got a heavy task ahead of you (or Jeb needs to start walking -- maybe you can parachute a rover down to him).

 

[Foxster]

8 hours ago, Zeiss Ikon said:

I've just this evening watched a video showing a no-mods SSTO launch from Eve, starting around 7500 m above Eve sea level (still denser atmosphere and more height left above launch than Kerbin sea level).  It's a surprisingly small rocket, one of the 3.5 m 4-engine booster units, limited tanks, apparently a nicely shaped fairing, with a single Mk. 1 pod on top, and it looks like it will tolerate a small amount of imperfection in the launch profile (based on there being a little fuel remaining when it reaches orbit).  I presume you'd rendezvous with a return ship and Jeb could EVA across, since a docking port doesn't appear to be included (though you could probably add one if you use a multi-stage launcher).  If you can't start from that elevation (near the highest point on the planet, from my reading) you've got a heavy task ahead of you (or Jeb needs to start walking -- maybe you can parachute a rover down to him).

 

There are a couple of similar designs kicking around for an Eve SSTO. I've made one and it is just about do-able with some luck and a fair wind. However, they are quite impractical and rely on using hyperedit to place them on the top of Eve's highest point. 

I think we talking here more about a practical mission where you can land and take off again from pretty much anywhere. 

Edited January 29, 2017 by Foxster

[Zeiss Ikon]

47 minutes ago, Foxster said:

I think we talking here more about a practical mission where you can land and take off again from pretty much anywhere. 

I did note that staging would allow for more payload -- but I think it's probably still possible to land an ascent stage(s) on Eve and get it back.  The video I saw (which is posted in the Eve SSTO thread) was specifically for version 1.2.2, with the latest increase in Eve's atmosphere.  Still, it might well be most practical to paradrop a rover to Jeb and plan to land the rescue mission in the highlands...

[Cubfan]

14 hours ago, Zeiss Ikon said:

I've just this evening watched a video showing a no-mods SSTO launch from Eve, starting around 7500 m above Eve sea level (still denser atmosphere and more height left above launch than Kerbin sea level).  It's a surprisingly small rocket, one of the 3.5 m 4-engine booster units, limited tanks, apparently a nicely shaped fairing, with a single Mk. 1 pod on top, and it looks like it will tolerate a small amount of imperfection in the launch profile (based on there being a little fuel remaining when it reaches orbit).  I presume you'd rendezvous with a return ship and Jeb could EVA across, since a docking port doesn't appear to be included (though you could probably add one if you use a multi-stage launcher).  If you can't start from that elevation (near the highest point on the planet, from my reading) you've got a heavy task ahead of you (or Jeb needs to start walking -- maybe you can parachute a rover down to him).

 

Jeb's latest rescue was an utter disaster. I used 16 Vectors for the bottom stage. Asparagus'd to 8, 4, and 2. Didn't get to stage it once. Had insane power but flipped violently a couple of klicks up. Gotta go smaller. I neglected to mention Jonier Kerman is with Jeb. I needed an engineer for the original mission. Land, refuel, dump the mining equipment and go. Worked everywhere else (and in 1.1), but Eve's a different animal. I'm on the shore, near sea-level. I've gotta drop a rover. I've got 20 million in the bank, and I'll spend every bit of it if need be. I'll try 'til I solve it smash my laptop, whichever comes first.

 

[Cubfan]

5 hours ago, Foxster said:

There are a couple of similar designs kicking around for an Eve SSTO. I've made one and it is just about do-able with some luck and a fair wind. However, they are quite impractical and rely on using hyperedit to place them on the top of Eve's highest point. 

I think we talking here more about a practical mission where you can land and take off again from pretty much anywhere. 

Absolutely. I need one that'll work no matter what. A vector can get you just about anywhere if it has the fuel. The thicker atmosphere is killing me, though. I can only cut through it by slowing down. Whereby I quickly run out of fuel before getting anywhere near high enough. I've gotta streamline.

[Cunjo Carl]

KSP has been an on and off hobby for me for nearly half a decade and I can say, without a doubt, Eve is the worst! It's like the unfair last boss in old arcade games. So, if you're having a very hard time with eve, you're doing it right.

If you can, land on one of the big 1-3km high swaths. They're a big enough target and tend to have large flat-ish areas.

A huge breakthrough point for me was realizing just how good the Twin Boar is for eve ascent. During the initial ascent out of the soup, the most important aspect of an engine is its TWR, and since its recent buff, the Twin Boar surprisingly takes the cake at ~23@5atm, ~33 Vac (for comparison, the vector now comes in at ~18@5atm ~25vac). The advantage of vectors is they're very compact, so you can fit them in a more streamlined package. You'll often see Eve lifters with a single Vector on a 1.25m tank surrounded by droppable (asparagused) fuel tanks that get ditched early in the flight. If you can land it though, the twin boar is much simpler.

The next big question is how many stages to use, and I've found 3 has worked well, but I see a lot of people go with two . I'll echo what others have said, that the terrier makes an excellent upper stage for the long push from subortial to orbit. The middle stage has always been a tricky pick because there's not a lot of good 2 ton engine picks. To be honest, my favorite is a hammer SRB- it works great! If you insist on a liquid fuel rocket, you can put a couple aerospikes 'radially' on the bottom of a fuel tank, and a decoupler on the same tank shifted down. Thuds sadly remain a non-option.

 

    Shows 3 stages: A twin boar, hammer and terrier do the lifting.                       An alternative option for sneaking in aerospikes if they're your preference

Controlling ascent can be very tricky, but AV-R8 wings help a ton! Most ships I've launched from Eve can't handle more than a little gentle steering on the way up, but airplane control surfaces on the rear of the plane really help to keep you steady on that nice gravity turn. If your ship is suddenly flipping out during ascent, it's probably because as the fuel tanks up front empty, they become draggier relative to their mass and can get pulled back due to aero forces, a bit like on a weather vain. We could say that COM shifts back while COD stays forward. Control surfaces in the back help against this problem immensely. So does draining your bottom tanks first now that that's an option. Lastly, make sure you have atleast one reaction wheel with plenty of battery.... Neither the hammer nor the terrier have an alternator, so what you bring is what you got!

Coming back to aero forces, the drag along your rocket plays a huge roll in how much up going you do. Try cones, the pointier the better! When in doubt, the fuel carrying adapters tend to work much better than their structural counterparts. eg. C7 Brand Adapter - 2.5m to 1.25m >> Rockomax Brand Adapter despite looking roughly the same. This rule of thumb came from v1.05, so it may be different now. Also, ditch all of your parachute containers and landing legs before launch- you can mount them on radial decouplers.

Finally, the path you take up is pretty critical. A proper gravity turn is even more important on Eve than it is on Kerbin, and @Kergarin did it right in this vid.... so..... try to copy that, and I will too! It's nearly impossible to guide the rocket cleanly during flight, so the trick is to try to line up on a well-chosen bearing and let your trajectory slowly drift down. Fortunately, this can be done by trial-and-error from a quick save rather than hyperedit. For reference, I found in v1.2 that 10-15 degrees at 3km and 45 degrees at 20km were good benchmarks. Mileage may vary pending your TWR. Somehow, it's always felt pretty low to me when done right. Also, keep it full throttle! You waste more to gravity than to drag. Don't worry about it being perfect, KSP is balanced nicely so as long as you're close it should work.

Finally, to keep the front end from burning off, I've heard the Clamp-O-Tron shielded docking port works a treat, but I've never tried it myself. I normally do cones these days. Fairings always gave me trouble.

Finally, use rigid joints. No one wants a floppy rocket. It helps to keep the oscillations down, at the expense of a bit off lost strength. For an eve launch the tradeoff is worth it in spades!

That's it, I hope something in there winds up being useful for you. Good luck getting off that monstrous purple rock!

Edited January 30, 2017 by Cunjo Carl

[AeroGav]

I've not done Eve before - my rockets are only occasionally successful, due to dumb luck - i haven't developed the "feel" and "rules of thumb" to design them successfully in the way i managed with aircraft.

But someone mentioned drag being important.  In which case i suspect you want to use mainly 2.5m stacks, since i found these to have the best fuel capacity to drag ratio of any type of tank, by quite some distance.

 

[Foxster]

29 minutes ago, AeroGav said:

I've not done Eve before - my rockets are only occasionally successful, due to dumb luck - i haven't developed the "feel" and "rules of thumb" to design them successfully in the way i managed with aircraft.

But someone mentioned drag being important.  In which case i suspect you want to use mainly 2.5m stacks, since i found these to have the best fuel capacity to drag ratio of any type of tank, by quite some distance.

Thinner is better. 2.5m is not good for keeping down the size of an Eve lander. 1.25m or, better still, 0.625m are better if you can figure out how best to use them. 

[Spricigo]

4 minutes ago, Foxster said:

Thinner is better. 2.5m is not good for keeping down the size of an Eve lander. 1.25m or, better still, 0.625m are better if you can figure out how best to use them. 

unfortunately this also result in something tall, thus more difficult to land...and its more difficult to have a good TWR because your engines have lower thrust to begin with... yay, compromises!

[Foxster]

8 hours ago, Cunjo Carl said:

KSP has been an on and off hobby for me for nearly half a decade and I can say, without a doubt, Eve is the worst! It's like the unfair last boss in old arcade games. So, if you're having a very hard time with eve, you're doing it right.

If you can, land on one of the big 1-3km high swaths. They're a big enough target and tend to have large flat-ish areas.

A huge breakthrough point for me was realizing just how good the Twin Boar is for eve ascent. During the initial ascent out of the soup, the most important aspect of an engine is its TWR, and since its recent buff, the Twin Boar surprisingly takes the cake at ~23@5atm, ~33 Vac (for comparison, the vector now comes in at ~18@5atm ~25vac). The advantage of vectors is they're very compact, so you can fit them in a more streamlined package. You'll often see Eve lifters with a single Vector on a 1.25m tank surrounded by droppable (asparagused) fuel tanks that get ditched early in the flight. If you can land it though, the twin boar is much simpler.

....

That's a neat vessel but more mass means an extra challenge getting it to Eve.

What, IMHO, you have going on is a bit of "mass creep". You add something and that leads to needing other stuff and before you know it the craft weighs more than you planned.  For instance, you have a lot of batteries because you have a lot of reaction wheels because you have a lot of mass. 

There's also the lack of asparagus and multiple stages. Yes, it makes for a neat craft but it means you are lifting engines that aren't being used and also have on-board a large/heavy tank for a long time. Having more stages and using asparagus staging to make use of all/most of the engines from lift-off makes a craft more efficient and so lighter. 

Oh and the Hammer for the 2nd stage is not really very efficient. It masses 3.562t, and gives 927dV (vac). If you used, for instance, a FL-T400 tank and an Aerospike it would mass 3.25t and give 1120 dV, and you'd have an alternator. 

[AeroGav]

20 minutes ago, Foxster said:

Thinner is better. 2.5m is not good for keeping down the size of an Eve lander. 1.25m or, better still, 0.625m are better if you can figure out how best to use them. 

Compare the drag values of the x200-8 (2.5m) to the flt-800 (1.25m) and the mk2 fuselage - all 3 hold 800 units.   Of course , if drag is that important, you'll be putting reversed cones on the bottom of your lower stage engines, right?

[Foxster]

23 minutes ago, AeroGav said:

Compare the drag values of the x200-8 (2.5m) to the flt-800 (1.25m) and the mk2 fuselage - all 3 hold 800 units.   Of course , if drag is that important, you'll be putting reversed cones on the bottom of your lower stage engines, right?

It's not always as easy as comparing the shown drag numbers of the parts in that kind of scenario. How they are connected to the other parts with adaptors and where they fit into the stack makes a big difference. 

What you need to do is look at a craft made with, say, just 1.25m parts and one made with 2.5m parts. You also need to look at the drag when turning and also when flying with no angle of attack. 

It doesn't matter of course if you are happy carting some extra tonnage to Eve, but if you are keeping it light then I can assure you that in Eve's atmosphere thinner tanks mean less drag which means less losses and so less dV needed to reach orbit. 

Here is an extreme example of a Eve sea-level-to-orbit capable craft. Offset has been used "creatively" to split the drop tanks and keep the height down. Drag has also been reduced by clipping a shell into the lander can. Because of the extremely low drag, you can get away with really low total dV. You could build a less "cheaty" craft for just a couple of tons more.  

Edited January 30, 2017 by Foxster

[Cubfan]

8 hours ago, Cunjo Carl said:

 

That's it, I hope something in there winds up being useful for you.

Are you kidding? Pretty much everything you just said was useful. I'm a big fan of the Twin Boar, but I hadn't thought to use one on Eve. I like the Terrier in vacuum for sure, though lately I've fallen in love with Sparks and Oscar B fuel tanks for my return journeys.

I had heard SRB's were terrible on Eve, but I think that may be because people were using them for liftoff. I haven't heard of anyone using them second-stage like that. My takeoff angle is something I definitely have to work on. I haven't worried about aerodynamics since I unlocked mammoths. All great suggestions. I'm gonna go back to the drawing board. Building rockets is half the fun anyway. Thanks for the tips. Much appreciated.

[Cunjo Carl]

For sure! Happy it helped. And nice to see another Twin Boar fan- that engine needs way more love!

   I was just reminiscing on the bus home about the 1000 little things that went wrong on my early eve missions. I have no doubt you would conquer them too, but if you're in "Just get 'er done" mode, there's a few other things to mention that could make your road a bit smoother.

I like your min-maxing of the top stage. Using a Spark+OscarB as an extra top stage (in addition to the terrier) is a great way to get a ton of extra deltaV. Pretty much all of my missions have something like that tacked on. If you're willing, you can push the effectiveness of that final stage by replacing the command pod with a 1.25m service bay with a command chair in it. Throw in a tiny reaction wheel and a battery, and it's the lightest, toughest, most flame-retardant and maneuverable command pod out there! A small important detail,  putting the seat on the bottom of the service bay with its feat facing straight up makes the nav ball read correctly. OscarBs work great in this roll, but I eventually found I got the best results with FLT-100 or FLT-200 tanks instead. Regardless, any tiny top stage is a great idea.

The easiest way to attach a heat shield to the Twin Boar is using a radial attachment point or some form of strut attached right in the center on the bottom of the rocket. Sadly, it looks a little silly because the mesh makes it float a half-meter away. Fortunately, it's practical to truss the whole thing together with struts anyway, so it doesn't wind up looking too weird in the end! Just make sure to include a decoupler somewhere, or you'll find yourself with a very heavy anchor during final descent. Speaking of which, especially if you use a tiny top stage for extra deltaV, you should have plenty of extra fuel in the Twin Boar to make minor corrections to your descent after dumping the heat shield (in order to push your trajectory to flat ground) and also slow down your descent just before landing. Even with parachutes, I can never quite get it to fall slow enough without using a bit of thrust to help out. Maybe your design will wind up a bit easier, though.

I've also been surprised how often an SRB is a decent choice. It doesn't feel like they should be, but their high T/W can be critical trying to accelerate away from a massive planet like Eve, and deltaV-wise their low dry mass can nearly make up for their abysmal Isp when the payload is small. Even given this, I'd still wager dollars to donuts the twin aerospike option would give a better payload-to-orbit mass fraction than the SRB (at the expense of complexity), but as @Foxster pointed out even a single inline aerospike or skipping it all together may do the job. Speaking of which, if you're willing to asparagus you can apparently cut the lander mass by nearly half! Here's a group that went on an R&D mission to see how small they could make an eve lifter. Link.  I think I'll stick to simple in this case, though.

One of the hardest parts of Eve missions for me is getting the Kerbal back up to their command pod / command chair. A nice alternative to coating your rocket with ladders is placing command pods on cubic struts on radial decouplers near the bottom and (optionally) top of your ship. Instead of climbing, simply (never simple in practice) get your kerbal into the bottom pod and then transfer them straight up to the top! If you're using a command seat for your launch and so have a decoupling top command pod, it will probably need a couple sepratrons to help it decouple without ruining your day. Just make sure the top command pod is close enough to the command seat that your Kerbal can 'board' the seat easily from the pod's ladder. I remember once my Kerbal couldn't quit make it, so I needed to bring the detachable pod halfway up to orbit and transfer in freefall. My mission had the margins, but it was very silly.

Well, I think that's everything, though I'm sure Eve will still contrive something to make your experience a Kerbal one. Good luck, have fun!

 

[Cubfan]

9 hours ago, Cunjo Carl said:

And nice to see another Twin Boar fan- that engine needs way more love! 

Couldn't agree more. I love that they have great power and a large built-in fuel tank. The lack of an underside attachment point presents a challenge, but from experience I think you have to get creative with shielding to survive Eve anyway. You have to be really small or really slow or you just burn up. At about 2300 m/s regular heat shields usually overheat and explode spectacularly. Inflatable shields work even at about 3500 m/s, which is perfect, but you can't get rid of them without blowing up half your ship. I'm not worried about shielding, though (I'll bring enough fuel to slow down to a crawl if I have to), and I think the Twin Boar will provide the power I need. It's the aerodynamics on Eve that are killing me. I haven't used fins or winglets in so long, my attempt at using them was disastrous. I've gotta work on it. I like your idea of draining tanks backwards, as well. I think it'll help. No matter what, I will slay the purple dragon.

[Cubfan]

23 hours ago, Foxster said:

It's not always as easy as comparing the shown drag numbers of the parts in that kind of scenario. How they are connected to the other parts with adaptors and where they fit into the stack makes a big difference.

I think you're right-on here. A great engine doesn't help much with a crappy design. I think AeroGav make great points and that you're actually both right. You need power to get your speed an altitude up in a hurry (I love Cunjo Carl's idea about using the Twin Boar for liftoff), but you have to get small in a hurry if you wanna make orbit. The design is what I need to work on. I've got 2 Kerbals to pick up, so my payload will be larger than I'd like. I think if I get the right parts in the right sequence I'll get it done. Or I'll just drop a rover and drive to the mountain tops like Zeiss Ikon said.

[Gordon Fecyk]

On ‎1‎/‎30‎/‎2017 at 1:48 AM, Cunjo Carl said:

If your ship is suddenly flipping out during ascent, it's probably because as the fuel tanks up front empty, they become draggier relative to their mass and can get pulled back due to aero forces, a bit like on a weather vain. We could say that COM shifts back while COD stays forward.

What about adjusting fuel flow priority on the upper tanks? Assuming you have something like a Twin Boar with an orange tank stacked on top...

If you turn on Advanced Tweakables in KSP 1.2 (I forget where that is though) you can instruct a given stage to draw its fuel from certain tanks first. Give tanks near the bottom a higher priority than those on the top, and you keep centre of mass higher up as you ascend. You can adjust priority on the fly as well.

--

[Cunjo Carl]

14 minutes ago, Gordon Fecyk said:

What about adjusting fuel flow priority on the upper tanks? Assuming you have something like a Twin Boar with an orange tank stacked on top...

If you turn on Advanced Tweakables in KSP 1.2 (I forget where that is though) you can instruct a given stage to draw its fuel from certain tanks first. Give tanks near the bottom a higher priority than those on the top, and you keep centre of mass higher up as you ascend. You can adjust priority on the fly as well.

--

Absolutely, that is the handiest new feature. I made reference to it (though not by name) in the post, but it was a huge text block so I'm not surprised it went unnoticed!

As it turns out, the Twin Boar has about the right amount of fuel in it already for a first stage on Eve. That Lg-Sm adapter tank I've got on there is mostly for aerodynamics, and only carries as much fuel as one of the Rockomax pancake tanks. That said for launches from Kerbin, I agree that fuel feeding from the Twin Boar first and then the tanks above it should help stability fantastically. Emergency fuel flow adjustments 'on the fly' sounds hugely nerve wracking and very Kerbal. I'm looking forward to it!