New Rocket Jockey SSTO Problems

[GoSlash27]

I still add them on principle.

In fact I think the rapier should require them

Nothalogh,

Different disagreement and parties, but same principle.

I don't concern myself with what "should" be or "principle". I merely focus on what works and what doesn't and build accordingly.

Objectively in KSP 1.04, precoolers aren't worth the mass, drag, or expense because they don't bring anything worthwhile to the table. You can make better SSTOs without them than you can with them. That, in itself, is enough reason for me to leave them on the shelf (though I agree that this means the game needs rebalancing)

Best,

-Slashy

Edited August 27, 2015 by GoSlash27

[Val]

...

Question: if you're looking for carrying the most dV to orbit, is there anything to be said for going with rapiers for the higher kick in the airbreathing phase and not carying a set of unused engines in either phase, or mix whiplashes with efficent rockets of some sort for a beter ISP in the none-breathing phase?

I forgot to reply to this one.

In my experience the Rapier is much more efficient than Jets, to the point of being unbalanced, like Slashy also seems to suggests.

I built this small (and mostly useless SSTL) for a thread about Is it even possible to make a <15t laythe roundtrip SSTO?

Before reaching the final design I'd first tried Jet+Nuke and Rapier w/Oxidizer+Nuke. But the final design ended up using Rapier only in Air-breathing mode + Nuke.

My guess is that, even though the Rapier has lower ISP than the Jet, it's higher thrust and top speed makes up for it. At least, when using a nuke as vacuum propulsion.

Edited August 27, 2015 by Val
Fixed incorrect plurals

[FyunchClick]

Here is an example of off-center air breathing thrust, I built for the Single Stage to Laythe challenge

[KSP 1.0.4] SSTL U-5 Dart Mk.6 [stock]

http://i.imgur.com/Sqa61p2.png

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http://i.imgur.com/I22Wosd.png

Take-off weight 24.935 t.

I think you also tilted the jet a bit to get the thrust vector closer to CoM again? And the wings as well to be parallel to the thrust vector and prevent it being pressed down?

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Oooo... good question. Sounds like my next ssto is going to be rapiers and nukes. How integral are the intercoolers to more advanced designs?

Apparently, not very... In theory they sound good; they come with fuel, intake air and cooling, but it didn't prevent the LV-Ns going all cherry. I'll give it a try without next time and see. LV-Ns do tend to run pretty hot but I've only rarely seen them blow up so it's probably not much of a need, although I do worry about my kerbals ability to procreate and create more victims, er test pilots; I put one on the end of a 1.25 liquid fuel fuselage and stuck some command seats on there as a little runabout for a science station I put in Minmas orbit, but the pilots get heat gauges almost as soon as I turn it on... pretty soon they'll be glowing in the dark.

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It's not Zen and it's certainly not minimalist but it will take you where you need to go... in style!

http://i.imgur.com/LJoAesu.png

http://i.imgur.com/SoTAJRt.png

Interesting use of the MK2 adapters as nacelles, I may just borrow that idea.

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My guess is that, even though the Rapier has lower ISP than the Jet, it's higher thrust and top speed makes up for it. At least, when using a nuke as vacuum propulsion.

Thanks, it's interesting to know that purely as a jet it may be a better choice than a whiplash for SSTOs.

[Val]

I think you also tilted the jet a bit to get the thrust vector closer to CoM again? And the wings as well to be parallel to the thrust vector and prevent it being pressed down?

Kinda. You're half right.

It is true that the Rapier is angled to thrust closer to CoM, but the wings are angled for a different reason. It is because the fuselage of a craft has much less drag if the wings have slightly higher AoA than the rest of the craft. You can see a more detailed explanation here.

[GarrisonChisholm]

Well... the physics are what they are, for better or for worse. There's quite a few people who understand them better than I do. The important thing is to accept them as they are and just roll with it. There are some things that are easier in KSP than real life and some things that are harder. You have to account for the reality you're dealing with.

The standard KSP mantra of "moar boosters" works well enough for rockets, but spaceplanes are all about efficiency so the reverse applies here. You always want less boosters, less struts, less dead weight... less stuff that's getting in the way and not adding anything to achieving the objective.

Instead of thinking "what do I need to add to make this work", you want to think "what can I get rid of that's getting in my way".

If you get into that mindset, spaceplanes are pretty easy. It's not really a matter of being smart so much as just having a proper state of mind.

Best,

-Slashy

I know this thread is aging, but I had to chime in on this point as I Absolutely came to the same conclusion over the last weekend. After designing "beautiful" space-planes that would not get to space, I started making each iteration simpler. Less less less, until you have something where clearly the Only fault is insufficient thrust. I am still learning, but Slashy speaks the Kospel here.

[GarrisonChisholm]

Kinda. You're half right.

It is true that the Rapier is angled to thrust closer to CoM, but the wings are angled for a different reason. It is because the fuselage of a craft has much less drag if the wings have slightly higher AoA than the rest of the craft. You can see a more detailed explanation here.

Hm. All of my designs are built with the wings perfectly "construction snap" aligned with the fuselage. Does this mean that if I tick the wings slightly "up" on any of them that performance would improve? How "global" is this effect when applied in-game?

[TheDarkMechanic]

Someone linked this the other day and it's too damn useful. Most of this we already know but there are definitely some nuances to be gleaned. Sorry in advance for how long it's going to make this post.

[Nich]

Really good pictograph but drag info is outdated

[Val]

Hm. All of my designs are built with the wings perfectly "construction snap" aligned with the fuselage. Does this mean that if I tick the wings slightly "up" on any of them that performance would improve? How "global" is this effect when applied in-game?

Yes, it will improve performance. There's a few things to watch out for, though.

If you have more than 1 Lift Rating per 10 t, then I'd recommend reducing wing area to that ratio. Otherwise you shouldn't angle all of your wings. At least not to the full 5 degrees, that is normally the minimum snap angle. More lift than 1 Lift rating/10 t will lift your prograde too much at high speed and just increase drag to the same or higher than what you had with un-angled wings.

It is harder to balance CoL if you mix angled and un-angled wings.

I don't count Mk2 Lift, nor angle it. You'll still get benefit from Mk2 lift when doing high-AoA maneuvers, landing, take-off, re-entry and attitude changes.