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Mihara

Designing around LV-N

Question

Most of my spacecraft, owing to the absence of atmospheres on most of the Kerbol solar system bodies, are built with LV-N engines. Unfortunately, these engines are unwieldy long.

Most of the time one LV-N would be good enough, but the ship needs to land, and can't exactly land onto the nozzle, it's too fragile for this sort of thing. The solution I've been using most is mounting two of them on the sides of a lander on one or another 'shoulder' type of mount. Some special purpose ships use more than two, but for most, even two are kind of a waste. Trying to mount the landing legs on extenders, so that LV-N still hangs above ground level, doesn't result in very stable structures and the center of mass is way too high off the ground, it's too easy to tip over.

And yes, I know I can turn off clipping and squish the engine inside the tank, but that's a solution I'd rather avoid using.

The most bizarre variation I've come up with was a lander which had it's LV-N in the center, and four tanks hanging around it on a 3.75>5x1.25 extender, with the landing legs mounted to those tanks. I am not at all certain if the extra weight of the smaller tanks and fittings didn't make it worthless, as I abandoned that design for other reasons. I'm actually considering making a proper hollow cylinder fuel tank just to accommodate LV-N in such situations.

So I've been wondering, is there a clever solution I'm not aware about?

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You can do this without part clipping:

Place a Rockomax X200-16 tank somewhere where you can access the top of the tank and put two Radial Attachment points on top.

in6T5Ch.jpg

Flip a LV-N and put it on the point using 2x symmetry.

j4Wv7K9.jpg

Click a Radial Attachment point and flip it right side up and place it on the top of the tank.

nns4C9n.jpg

Pick up the tank and put it under either another fuel tank or what ever you what it under.

qNK5kwt.jpg

You can put a flat adapter under the tank to make it look better.

BaIPlMJ.jpg

You can also put some small trusses under the adapter to make it stackable.

YYH5c4z.jpg

Lots of clearance for landing legs.

pvGecxa.jpg

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I'm using the modular girder segments to have a place to put the landing legs. I take the short of the large one and places them outwards, and then the longer of them downwards with the landing legs at the bottom of them.

It's not beautiful, but it works. And as a bonus, if you touch down too hard and the landing legs gets destroyed, you can still land on the girder segments :)

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I've had success using radial tanks to mount the landing legs around a LV-N in the center. To avoid making it top heavy, just use the smallest 2.5m fuel tank and put the small engines on the bottom of the radial tanks. This should give you plenty of thrust to land on all but the heaviest of planets/moons, and if you need more you can attach radial engines. A stack of I-beams can be used to mount 1 or 2 ladders to let you reach the ground.

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You could just stick a couple of girder sections on to the side of your lander then mount the landing legs on those, it only takes a fraction to get them below your nuclear engine. If you're worried about stability, use the long girder section to add a very long outward section before adding a short downward section, then just add a few struts to secure it.

This skycrane I built doesn't use LV-Ns but in this case the wide landing legs are to accomodate the rover and allow it room to drive out from beneath.

p4OubQT.jpg

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This seems like it accomplishes the same thing as using no-clipping. You're not explicitly activating no-clip mode, but is the end result any different? I do enjoy finding these kind of strange exploits though.

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Docking with LV-N for transit and orbital adjustments and a proper lander engine for landing? There's also no sense in being concerned with the mass of decouplers (and smaller tanks have the same tank/fuel mass ratio as the large) if you're going to spam LV-N's. It's unusual that a single LV-N or perhaps a pair of them combined with a higher power, lower Isp engine isn't a better solution than larger numbers of them.

Otherwise, I also use the 3x struts combined with lander legs. It not only allows you to extend the legs downward to get past the bottom of the engines, it gives you a much broader base to land on so that you don't tip.

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LV-N's are so heavy, and produce so little thrust that it isn't really worth the trouble to land them. I prefer having a small lander that attaches to my interplanetary ship to land places. I would recommend the small LV-909 engine; while it does have less thrust than the LV-N, it has a tiny mass: 0.5t, which is as much as the landing gear! Hence, you can make your lander quite small, and still have a decent TWR.

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Other possibility for smaller landers is Rockomax 24-77

3 produce the same thrust but together weight only 12 % of LV-N.

They eat more fuel, sure, but for small landers the reduction in dry mass pays out.

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If you're landing things landercan-sized or larger, though, for Mun-class destinations and heavier, the extra delta-v on the lander from using LV-Ns as landing engines tends to be worth it. Doubly so, if you're using a wasteful landing procedure, or planning to check multiple locations out, or are simply going to leave the lander in orbit for the next mission to refuel and use. The more efficient the engines, the less fuel that the next mission has to brung to put in the lander when it gets there.

And it's not like you have to fly the lander to the distant planet on the same spacecraft you're sending the Kerbals on.

I've been using something similar the Side-attatch-point-clipthrough method posted upthread on the various landers I've been testing and using. overall, it works fairly well.

Some examples:

On Moho

D1eguApl.jpg

On Vall

iD57GU3l.jpg

On the Mun

opN7OxTl.jpg

The tankage on all three are significantly larger than they need to get to the surface and get back to orbit, but I figured I'd rather have a soft fluffy cushion than a knucklebiter.

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Other possibility for smaller landers is Rockomax 24-77

3 produce the same thrust but together weight only 12 % of LV-N.

They eat more fuel, sure, but for small landers the reduction in dry mass pays out.

Sorry, but it doesnt, unless you have the smallest ship imaginable.

24-77 has amazing TWR, and makes an excellent probe lander, but here are the hard figures:

deltaV_zps0f7eb351.jpg

As you can see, even with this small ship, the NERVA has better dV. As the 'dry mass' increases, it gets more and more significantly different:

deltaV2_zps3d1223e3.jpg

All i've done here is swapped out the T400 fuel tank for its double-size T800, and you can see how much more dV you get from the NERVA.

It's only when you get the really small stuff that it starts to matter:

deltaV3_zpsc0eb9986.jpg

And even then, there isn't much in it.

CONCLUSION:

NERVA engine is superior in almost every situation. (assuming vacuum)

Edited by kahlzun

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I use cube struts for landing gear, or at least to make a scaffold on which you can put landing gear.

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2272dXi.jpg

Using side mounted NERVAs gives me good TWR, high efficiency, well balanced RCS, AND the ability to tow little robots along for the ride. Without clipping I don't see how you would otherwise go about making a compact ship.

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Using side mounted NERVAs gives me good TWR, high efficiency, well balanced RCS, AND the ability to tow little robots along for the ride. Without clipping I don't see how you would otherwise go about making a compact ship.

I like this design, it's sort of the opposite of my Tylo lander. The rover rode in below the nuclear engine, which I only needed for the ascent.

Tyloposed.jpg

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Sorry, but it doesnt, unless you have the smallest ship imaginable.

.

Dunno how you did the equations but

Mtotal = (FuelRatio-1)/(FuelRatio-exp(dV/g/Isp))*(Mengine+Mpayload)

.

where

tank FuelRatio = Mfull/Mempty = 9

g = 9.81

dV required = 1500 (Mun orbit up and down with some reserve)

Mpayload = 3 ton

gives for

Isp = 800

Mengine = 2.25

Mtotal = 5.392 ton

but for

Isp = 300

Mengine = 0.27 ( 3 * 0.09 )

Mtotal = 3.566 ton

= given the same performance ( TWR dV Mpayload ) you can build a much lighter lander using 24-77.

.

either that, or my calculations are wrong :wink:

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empirical test :

Payload = 3 ton, dV = 1339 m/s, TWR= 5.78, Mass = 6.375 ton

jj6h8Hz.jpg

.

Payload = 3 ton, dV = 1324 m/s, TWR= 6.67, Mass = 5.04 ton

a29nmcc.jpg

= you really saved 1.335 ton, but there seems to be something off with my equation

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Most of my spacecraft,

And yes, I know I can turn off clipping and squish the engine inside the tank, but that's a solution I'd rather avoid using.

The most bizarre variation I've come up with was a lander which had it's LV-N in the center, and four tanks hanging around it on a 3.75>5x1.25 extender, with the landing legs mounted to those tanks. I am not at all certain if the extra weight of the smaller tanks and fittings didn't make it worthless, as I abandoned that design for other reasons. I'm actually considering making a proper hollow cylinder fuel tank just to accommodate LV-N in such situations.

So I've been wondering, is there a clever solution I'm not aware about?

This kind of problem, and your thougts, are full filled my mind a long time ago, till present day!!

Some feelings like: Why?! Why I can not simply put the already heavy and big nuclear engine radially?! And this was feel it in such high level that I change cfg, adding a 3th node for nuclear engine, almost the same of long 1,25m tank. But, just 3 days behind, when I must use, just one engine in normal way (stacked below some part) I realize that he are attachment in some other piece, or the fairings when jettisoned are destroying the node and messy with my entire lander + last stage!!

I dont know why, and can't find a razonable solution, but I find a mod with shuttle engines, shoulders engines and ordinary ones, but I not try yet.

By the way: it because I create a topic talking about this problem Nuke problem, and a friendly person paste the link of this thread, so I am some way "happy" that I am not alone in this "cruzade" to find a logic way for build a good ship/lander/lifter/plataform!!

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This kind of problem, and your thougts, are full filled my mind a long time ago, till present day!!

Some feelings like: Why?! Why I can not simply put the already heavy and big nuclear engine radially?! And this was feel it in such high level that I change cfg, adding a 3th node for nuclear engine, almost the same of long 1,25m tank. But, just 3 days behind, when I must use, just one engine in normal way (stacked below some part) I realize that he are attachment in some other piece, or the fairings when jettisoned are destroying the node and messy with my entire lander + last stage!!

I dont know why, and can't find a razonable solution, but I find a mod with shuttle engines, shoulders engines and ordinary ones, but I not try yet.

By the way: it because I create a topic talking about this problem Nuke problem, and a friendly person paste the link of this thread, so I am some way "happy" that I am not alone in this "cruzade" to find a logic way for build a good ship/lander/lifter/plataform!!

...you do realize the last post before yours was in May, right?

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