LV-N what's it good for

[kBob]

So I get a contract to test the LV-N nuclear engine: "nifty," I think, "never really played with them before and it will be awhile before I reach that tech level," so I jump at the contract.  I replaced the poodle on my run-about with it and head for the Mun.  If it works out I'll just be careful not fulfill that contract for awhile.  But hmmm, it's way slower, heavier and seems to use about the same amount of fuel (though I'm just eyeballing the fuel gauge not doing detailed flow rate comparisons).  What is this engine best for?

[Parv Kerman]

I think for it's efficiency

[Atlas2342]

I've never used them before so I don't really know but I think they are more efficient than other engines aside from the fact that they only use liquid fuel. Probably great  for interplanetary transfers...

EDIT: ninja'd lol

Edited May 31, 2016 by Atlas2342

[The Aziz]

Yup, much more efficient than poodles, much lower thrust, and don't forget to put some radiators, as they heat up really fast. And yes, used for interplanetary transfers.

[Foxster]

Yes, good for big inter-planetary stages. 

For small craft they don't make a lot of sense because of their high mass but if you have to push a big payload to the outer planets then nukes are the way to go due to their very high Isp (MPG). 

[Harry Rhodan]

16 minutes ago, kBob said:

I replaced the poodle on my run-about with it and head for the Mun.

You also have to replace the tanks or drain them of oxidizer if you don't want to carry araound tons of dead weight.

[SchweinAero]

In general, a Terrier will do better for Delta-V if you have less than about 5 tons of fuel. The Nerv is also 25.6 times more expensive than a Terrier for the same vacuum thrust.

[mk1980]

it doesn't use the same amount of fuel. it uses less than half the amount of fuel compared to the Poodle. And that's also its main selling point - you get a lot more mileage out of your fuel reserves, so you can get to places with much less fuel (or get to places easily that would be very difficult to reach with much less efficient "normal" rocket engines).

Note that the LV-N only burns the Liquid fuel and has no use for oxidizer, so you should use LF-only tanks (airplane fuel tanks) for nuclear ships.

The downsides of the LV-N are low thrust, heavy weight and high cost, so it may not be the best choice for relatively simple tasks like going to the Mun. It's very good for interplanetary transfers, though.

[kBob]

Ah, good to know.  I didn't notice it's different fuel requirement, back to the drawing board.  I didn't think to right click on the tank itself, I see now all that wasted mass.

Thanks for the quick replies!

[Slam_Jones]

If you're going interplanetary, it's a great choice.  Make sure to put radiators near it.

 

If you're just taking a single Kerbal to the moon, just use a Poodle.  For that short a distance with that small a payload, the LV-N will be too heavy to be worthwhile.

[kBob]

^Yes, I'm just playing around with it.  The actual contract wants it in orbit of Minmus however.  So I guess they don't want it's real abilities tested.

[Brainlord Mesomorph]

I use them for non-atmospheric LANDERS!

I have single and dual engine nuclear landers that also work as interplanetary ships, or as engine pods for larger ships.

Why carry LFO landers when the engines come off and ARE landers?

[Kertech]

16 minutes ago, Brainlord Mesomorph said:

I use them for non-atmospheric LANDERS!

I have single and dual engine nuclear landers that also work as interplanetary ships, or as engine pods for larger ships.

Why carry LFO landers when the engines come off and ARE landers?

I like this idea, problem is most of my interplanetary vessels are built long before the window and the landers sent closer with newer science stuff!

[magnemoe]

2 hours ago, Foxster said:

Yes, good for big inter-planetary stages. 

For small craft they don't make a lot of sense because of their high mass but if you have to push a big payload to the outer planets then nukes are the way to go due to their very high Isp (MPG). 

They are also nice for heavier tugs and tankers for the low orbit to Mun or Minmus, tanker has oversized fuel tanks and is designed to  take lots of fuel from mining on minmus down to low orbit for other ships to use. Tugs is reusable transfer stages designed to move stations, they are also nice to give an interplanetary ship extra TWR in the start. 

And yes engines are heavy with low twr so don't use for small landers and probes. 

36 minutes ago, Brainlord Mesomorph said:

I use them for non-atmospheric LANDERS!

I have single and dual engine nuclear landers that also work as interplanetary ships, or as engine pods for larger ships.

Why carry LFO landers when the engines come off and ARE landers?

I did this here, Duna transfer stage, lander module with science equipment on top. Over 4km/s dV so I can go from Ike to Duna, jump around a couple of times and return to ike surface, no its not fuel efficient but the Ike base has mining. 
 

[Brofessional]

They can be useful for SSTO spaceplanes.  Their low thrust and high mass means they're not ideal for all designs, but in some cases the extra mass of the engine is offset by the fact that they don't need oxidizer.

I also like to use them to ferry fuel from mining operations on low-gravity moons to orbiting fuel stations.

Due to their heavy weight you'll quickly lose efficiency when using more than one of them.  It takes careful planning to make sure you have enough TWR to carry out your mission with as few of them as possible.

[KerikBalm]

3 hours ago, kBob said:

it's way slower, heavier and seems to use about the same amount of fuel (though I'm just eyeballing the fuel gauge not doing detailed flow rate comparisons).  What is this engine best for?

This is deceiving... if you're just lookin at liquid fuel per unit thrust compared to looking at total mass of fuels (liquid fuel and oxidizer) per unit thrust.

The poodle has an Isp of 350, compared to the LV-N's 800. to produce 1 kN of thrust, the poodle uses 800/350 = 2.286 x more fuel mass per second than the LV-N. The poodle's fuel mass consists of liquid fuel and oxidizer in a 0.9: 1.1 ratio... so only 0.9/(0.9+1.1) = 0.45 of its fuel mass is actually liquid fuel.

Soooo.... 2.286 * 0.45 = 1.0287... it uses 2.87% more liquid fuel per second to produce 1 kN of thrust... so that may not seem like a lot if you just look at liquid fuel, and completely forget the oxidizer that is over half the fuel mass... the poodle consumes more than twice as much "propellant mass" per second to produce the same amount of thrust as an LV-N.

If you use a LV-N without emptying the oxidizer... you're carrying around useless mass, and you'll end up worse than if you used the poodle which could get rid of that oxidizer mass (since the game won't let you jettison it). Empty the oxidizer... and better yet, use LF only tanks.

The LV-N is much more efficient than the poodle, although its TWR is not so good.

by the way... when talking about "atmospheric"... duna might as well be a vacuum as far as Isp is concerned... same with Kerbin after 10 Km... just don't use it below 10km on kerbin/laythe (well, ou could go lower on laythe)... and... somewhere between 20 or 30km on eve... I forget.

TWR is relative... even if it got vacuum Isp on Eve... it would barely lift itself, let alone fuel for it... on Duna... its TWR is almost 6.67... and its got enough thrust to lift fuel needed for orbit and a payload...

It works as a lander engine pretty much everywhere except Eve, Kerbin, Tylo, and Laythe... although lighter engines can be attractive alternatives for landers.

[cantab]

In general chemical engines make a lighter ship overall for Mun and Minmus trips, unless you're doing repeated landings and refuellings then the LV-N can shine. "Break even" is more or less Duna, you can go chemical or nuclear and the ship mass ends up about the same. For trips to Dres and Jool the LV-N will be much more mass-efficient. Moho too, though you might also consider ions for extreme delta-V because Moho missions can use a lot of it if you aren't careful.

Ship mass is a factor too. On small probes and even lightweight Kerballed ships the LV-N is just too heavy itself, so chemical or ion propulsion is the way to go. On very large ships the LV-N doesn't provide enough thrust and you'd need to spam too many of them, so instead consider the Rhino, one Rhino provides as much thrust as 33 LV-Ns.

Edited May 31, 2016 by cantab

[BeeGeenie]

As Edwin Starr might have sung it:

LV-N! Hooah! Good Kraken, y'all! What is it good for?

Absolutely efficient burns. Say it again, Yeah!

LV-N! Huh! Yeah! What is it good for?

Absolutely lower oxidizer weight! Uh-huh!

 

I use them generally for interplanetary transfers, where high TWR isn't as important as it would be on landers or orbital capture at small bodies like Moho or Dres.

Edited June 1, 2016 by BeeGeenie

[KerikBalm]

NR-V? its the LV-N

or, in real life, NERVA

[Mjarf]

1 hour ago, cantab said:

In general chemical engines make a lighter ship overall for Mun and Minmus trips, unless you're doing repeated landings and refuellings then the LV-N can shine. "Break even" is more or less Duna, you can go chemical or nuclear and the ship mass ends up about the same. For trips to Dres and Jool the LV-N will be much more mass-efficient. Moho too, though you might also consider ions for extreme delta-V because Moho missions can use a lot of it if you aren't careful.

Ship mass is a factor too. On small probes and even lightweight Kerballed ships the LV-N is just too heavy itself, so chemical or ion propulsion is the way to go. On very large ships the LV-N doesn't provide enough thrust and you'd need to spam too many of them, so instead consider the Rhino, one Rhino provides as much thrust as 33 LV-Ns.

This is very true, I've found the Rhino to be an excellent engine for that midstage to get a large interplanetary ship out of Kerbins SOI, and then use NERV's for the rest of the trip. I love the NERV's efficiency, it's very good at turning fuel into delta-v, one thing I dislike is the length, it's a bit awkward for smaller ships IMO.

[Renegrade]

I generally don't use 'em anymore.  ISRU bases basically cut round-trips in half delta-v wise, and the miserable TWR means really long, inaccurate burns, or spamming nukes until you have a craft every bit as inefficient as a chemical one.  Plus the stock system is kinda small vs. the specific impulse of chemical engines... it's not necessary.

Besides, sending my Duna station to Duna on four Skippers at 1.85-3.35g was a lot more fun than drooling it out there at 0.2g on a nuke-based platform.  And cost about 20k less

I made a DunaBus-N crew carrier as a test - the LV-N "all the way there and back" model is actually bigger and slower and more expensive and requires more fuel than the Poodle-based "refuel via ISRU" model.

[awfulhumanbeing]

Deep space.

[DD_bwest]

I find they are good for trips to dres and beyond.   Duna and Eve are close enough that the poodle will meet your needs unless you have a really large ship.  Moho is close enough to the sun that you can get away with using a couple handfulls of ions without having to really worry about power.

 

really wish we had some 2.5m  liquid fuel only tanks.  Sure there are mods, but im doing a stock only career right now, and not havng any gets frustrating

[AeroGav]

They are good for spaceplanes because they don't need as much thrust/weight ratio as rockets, also it's really nice having one fuel type for both your jet and rocket engine.  Especially so when you can put liquid fuel in a lot of the airplane essentials - intakes,NCS nose cone, wings, strakes.  You'll need one LV-N for every 15 tons of airplane mass, lots of lift and very low drag, also having a fuel balancer mod like GPO SpeedFuelPump + ModularFuelTanks makes design a lot easier.

30 ton spaceplane with 2 nerv and 1 whiplash, takes 5 kerbals to minmus and back -

And here's how the Space Shuttle might have turned out, had the military not insisted on a cargo capacity that made the carrier plane too big/expensive to develop.

 

[Violent Jeb]

between 10-50 tonnes, you can't beat the LVN which is almost 3 times more efficient than anything else IIRC.

LVN only uses liquid fuel, so you can ditch your oxidizer if you have tanks with both. The limiting factor is the low thrust, which means you'll usually need at least 2 to land on something as large as duna. Anything larger or with more atmosphere and the lvn isn't going to be a good match.

So, they're great for interplanetary stages, or for lander on small-to-mid sized planets. An interplanetary LVN stage can usually get any payload pretty well anywhere in the system

It took me a good year to figure out how to use them effectively.

Now, My 18t Terrier munlander can achieve ~3500 dv with LFO
vs
My 25t LVN munlander which has more than double the range with ~7000 dv with liquid fuel only. This machine can easily land and re-orbit at least 3 times around the mun.

I strongly encourage trying to get used to them. It's one of the only ways to get crews round trip to places like moho without ISRU or some other very complex designs.

Edited May 31, 2016 by Violent Jeb