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LV-N vs LV-909


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After doing tests comparing the LV-N to the LV-909.

(tests done with a X200-16 fuel tank)

The LV-909 gets a deltav of 6245ÃŽâ€v (LV-909 had LFO in the tank)

Now if we replace the 909 with the nerva and remove the Oxidizer, the nerva gets 5063ÃŽâ€v. Thats 1km of ÃŽâ€v less!

This makes the Nerva seem inferior to the 909, not to forget the nerva overheats and explodes everything without proper heatsinks.

So these are just my tests done with kerbal engineer.

Id like to hear others opinions.

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Simply removing the oxidizer leaves too much empty mass in the fuel tanks - this is a bug with the stock Squad parts. There are mods which correct this, but with stock the only fair comparison would be to use the airplane tanks which are LF only.

That said, it must also be remembered that Nerva engines are heavy and designed to be used with a comparably significant mass of propellant - though again, this propellant must be housed in a liquid fuel ONLY tank, not an LFO tank with the oxidizer removed as that is currently bugged.

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Right, but the oxidizer has weight, so in total, wouldn't the LV-909 + tank combo weigh more than the Nerva + fuel tank sans oxidizer combo? If that's the case, then I imagine you're actually getting more delta-v/ton.

Nervas just require more fuel tanks if you're not going with spaceplane parts. They both have their strengths and weaknesses, so I think it's balanced.

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Use a Mk3 liquid fuel tank and a Mk 3 LFO tank. Because stock fuel tanks have no LF-only option, you're wasting a lot of volume of potential dV there.

I've taken to using the Mk 2 fuselages radially bolted to a 1.25m stack (usually of jet fuel tanks just for a bit extra juice).

Alternatively, grab Porkjet's Atomic Age pack, which a) adds some awesome new nuclear engine variations, and B) modulemanager patches stock tanks with firespitter fuelswitch, so you can fill a jumbo with pure LF.

The NTR is a bit different now, but not technically inferior. It just needs to be handled differently.

EDIT: Quadra-ninja? Really guys?

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Opinions aren't relevant. The LV-N is objectively a much more efficient engine. That doesn't mean it will be the best choice in every situation. You're setting up a test that favors the LV-909, so of course the LV-909 will win. The LV-N is designed to push heavy payloads between planets. That is what it excels at.... certainly not pushing light payloads around in LKO or short moon trips.

Problem #1) Your tank has dead weight in that you aren't filling the empty space once used by the oxidizer with more liquid fuel. That means there is empty tank mass... the LV-N is literally carrying an empty tank (ie, extra payload). You can use a mod to let you fill the empty space with more liquid fuel... the ideal solution... but the stock solution would be to use one of the liquid fuel only tanks.

Problem #2) LV-N has a high mass on its own. It also has a much better payload fraction. If you want to compare properly, give the LN-V more fuel in proportion to its mass, not its thrust.

This was already beat to death in a thread yesterday that is still on the front page and should give you all the info you need:

http://forum.kerbalspaceprogram.com/threads/121064-Are-LV-N-s-worth-the-trouble

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Alright I will check it out with jet fuel tanks.

After attaching the LV-N to a jet fuel tank (MK3 Liquid fuel tank)

it does get 12,315 ÃŽâ€v Yep I did it all wrong Can a mod please lock the thread.

Edited by Dooz
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Rocket fuel tanks emptied of oxidizer have a wet/dry ratio of 4.5. Rocket fuel tanks with oxidizer in have a wet/dry ratio of 9. That's huge, and given that the rocket equation relies on the ln(w/d) term, it's hardly surprising that that ratio would easily overpower the simply linear increase offered by the Isp.

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High ISP (low twr/high mass) engines result in high d-v only when the mass of the engine is small compared to the mass of the vessel (fuel tanks) that it is pushing. There is always a break-even point, the more efficient engine does not always get you more d-v.

So any high isp, low twr engine can result in less d-v than a lower isp, higher twr engine by putting it under a sufficiently small fuel tank.

For instance the 909 results in less dv than a 48-7S if it is put under a FL-T100 tank.

And conversely the LV-N does get more d-v than the 909 if you double the amount of fuel.

Edited by rkman
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The point at which the LV-n becomes better purely on mass terms than using a 909 depends on your required payload, delta v and what type of tanks you re going to use to store the LF for the LVN

if your required DV is greater than that shown below you are better of using the LV-N

[table=width: 500, class: grid]

[tr][td]payload (t)[/td][td]1[/td][td]2[/td][td]3[/td][td]5[/td][td]7[/td][td]10[/td][td]15[/td][/tr]

[tr][td]mk3 tanks[/td][td]4184[/td][td]3191[/td][td]2573[/td][td]1852[/td][td]1446.15[/td][td]1088[/td][td]769.88[/td][/tr]

[tr][td]mk1 tanks[/td][td]4390[/td][td]3367[/td][td]2721[/td][td]1960[/td][td]1530[/td][td]1151[/td][td]814[/td][/tr]

[tr][td]lfo tanks[/td][td]4536[/td][td]3494[/td][td]2826[/td][td]2037[/td][td]1590[/td][td]1195[/td][td]845[/td][/tr]

[/table]

This assumes you empty out the Oxidiser and that you can get tanks of exactly the size you require

Edited by tomf
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After doing tests comparing the LV-N to the LV-909.

(tests done with a X200-16 fuel tank)

The LV-909 gets a deltav of 6245ÃŽâ€v (LV-909 had LFO in the tank)

Now if we replace the 909 with the nerva and remove the Oxidizer, the nerva gets 5063ÃŽâ€v. Thats 1km of ÃŽâ€v less!

Oh look, another comparison that doesn't actually compare the engines. This is new and exciting.
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How snarky of you, regex. Excellent contribution.
Thanks! Also, I notice most everyone else in here has covered the main point, that being the 909 has roughly twice the reaction mass as the LV-N and thus this isn't, by any means, an accurate comparison.

E: Should I also point out that this is yet another redundant thread and that the previous one makes the same mistake?

Edited by regex
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E: Should I also point out that this is yet another redundant thread and that the previous one makes the same mistake?

Not to mention how often players overlook the LF only tanks...

These threads are not very useful when basic points are overlooked and conclusions are jumped to, the LV-N is still the most efficient non-ion engine if provided with enough fuel to do the job.

Moving to Gampeplay related stuff.

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Thanks! Also, I notice most everyone else in here has covered the main point, that being the 909 has roughly twice the reaction mass as the LV-N and thus this isn't, by any means, an accurate comparison.

E: Should I also point out that this is yet another redundant thread and that the previous one makes the same mistake?

To be fair to the OP he acknowledged his mistake and asked a mod to lock the thread. http://forum.kerbalspaceprogram.com/threads/121283-LV-N-vs-LV-909?p=1938849&viewfull=1#post1938849

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