Poodle more efficient than LV-N atomic motor

[OrangeGills]

Everybody holds the LV-N in high regard, but from my understanding the poodle is more efficient. If the LV-N generates 60 thrust at 800 isp, and the poodle Generates 250 thrust at 350 isp, then wouldn't the Poodle be more fuel efficient? It generates more than 4 times the thrust the LV-N achieves, at only less than half the isp
Please corret me if I am wrong, or if my math is not done correctly

[Rioka]

No, the LV-N uses less fuel for the same level of thrust, just because it's max thrust is lower doesn't change that. However, the Poodle can be a more efficient choice, depending on how big your craft is, because the LV-N is heavier.

Basicly, if you to put the two side by side and limited the thrusts so they were the same, the LV-N would use less fuel. Also, since it only need Liquid Fuel, and not Oxidizer, your craft will be lighter for the same Dv.

[R.A.W.R.]

Poodle needs oxydizer (sp?) and liquid fuel, but i think the atomic motor just needs liquid fuel.

Which is why it might be more efficient .

I think.

[OrangeGills]

I was wrong, my understanding of ISP was incorrect. Isp factors thrust and fuel consumption into its number, thus isp represents overall efficiency including thrust

[ghpstage]

ISP is purely the efficnecy of fuel to thrust however, for the efficiency of a rocket the mass is critical too.
This means that despite its huge ISP the LV-N is frequently a less efficient propulsion method than many other engines, Poodle included purely because of its enormous dry mass!

[OrangeGills]

Originally posted by ghpstage:

ISP does however only make up a part of a crafts efficiency, the mass is critical too.
This means that despite its huge ISP the LV-N is frequently a less efficient propulsion method than many other engines, Poodle included purely because of its enormous dry mass!

Because of the law of diminishing returns, the engine is better used on larger stages where its 3 tons of mass wont make much of a difference

[kesat]

As far as i know your math is wrong. The Isp is efficiency per used fuel. Thrust-to-Isp ratio is used to get Fuel Rate = Thrust / Isp. A bigger value for fuel rate is less efficient (Poodle 0.71 vs LV-N 0.075).

But you also have to look at engine masses to get the "real efficiency". A engine with bigger mass is less efficient for light payloads (read: less fuel amounts), but more efficient for higher payloads. Landers e.g. are sometimes better off with a small engine with less thrust or Isp due to their low mass.

Due to this, the LV-N isn't a good choice for small upper stage rockets compared to engines like the Terrier. You need quite a lot of liquid fuel to outrun the Terrier (0.5t mass vs. 3t mass) in that case.

If you want to see the best choices for your rockets during design take a look at some mods which show you generated Delta-V per stage.

[Rioka]

Originally posted by Gills:

Because of the law of diminishing returns, the engine is better used on larger stages where its 3 tons of mass wont make much of a difference

Exactly, and it doesn't stop there, I have a probe I use for satellite contracts that uses the 'Ant' engine, and if I swap it it for a Terrier, it loses almost half it's Dv due to the added mass.