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Lo Var Lachland

Best NON NUCLEAR Liquid fueled engine?

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Posted (edited)

Well, the title said it all. I am building an interplanetary craft, and I need to find an efficient engine, Besides the LV-N "Nerv"

Anyone know what the best engine is?

(In terms of fuel consumption)

Edited by Lo Var Lachland

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1 hour ago, Blaarkies said:

Would it not be better to use 3 Darts at that point? 1t less mass and more TWR, and less part count...but that high tech tho

For the sake of comparison 2xPoodle VS 3xDart VS 9xTerrier:

P: 2600funds; 3,5t; 500kN; 350s; 4,5°;  Alternator. 

D:11550funds; 3t; 540kN;340s;no gimbal; no Alternator. 

T:3510funds;4,5t; 540kN ; 345s; 4°, no Alternator 

IMHO 3% difference in Isp is negligible,  thrust about the same,  gimbal/alternator not much relevant.  If not the case of milking just a ditch more deltaV,  is a choice among size,  cost or part count. 

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I like this website for these type of questions

http://meithan.net/KSP/engines/

put in your payload mass, your required delta-v and your TWR tolerance and it will give you a graph showing the best engine options.

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The Terrier, the Poodle and the Rhino. The dart comes next.

 

Which one you choose depends on your payload and desired thrust. Also, the Rhino may come from the central stack of the boosters you're using to lift off from Kerbin, so you may save an extra stage.

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24 minutes ago, Cpt Kerbalkrunch said:

If you put eight Terriers radially around a 2.5m core, you now have double the thrust of a Poodle without needing another 2.5m tank.

Would it not be better to use 3 Darts at that point? 1t less mass and more TWR, and less part count...but that high tech tho

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3 hours ago, Lo Var Lachland said:

Anyone know what the best engine is?

Kinda question to answer with a "for what?" OK,  you said it's a interplanetary craft and you are concerned about fuel consumption. 

However it depends on some factors,  some concerns may be burn time,  if the engine can also be used for landing at some celestial body,  cost,  size, total craft mass among others. 

But in the end it mostly boil down to what the rocket equation says (link below to an online calculator ). And,  to a considerable lesser extent, to your TWR (mostly for convenience) 

The rocket equation determine how much deltaV you will have based on: some constants,  your Isp and your wet/dry mass ratio. Everything being equal you want the engine with higher ISP but since different engines have different mass sometimes an engine with lower Isp can be better because is much lighter (e. g. For a satellite under 500kg with 1-2 Oscar-B tank worth of fuel nothing beats the Ant, not even close) 

The better idea it's to find out how much deltaV is needed for the mission and run the numbers. Just remember: 1) a vessel should be designed in the reverse order of use. 2) what you don't need/can go without,  it's often too heavy to carry. 

http://www.quantumg.net/rocketeq.html

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Ion engine :-P But that's not always practical - it's only suitable for relatively small craft in the inner system that won't be using ISRU.

Otherwise the Poodle is the most efficient chemical rocket and generally dominates for 0.33 TWR. The Terrier and Aerospike are alternatives which may be better in some cases (basically, when you'd ideally want a fractional number of Poodles). If you're looking for more like 0.5 to 1.0 TWR the Aerospike and Rhino show their advantage of having higher TWR, and the Rhino is a good choice on very large ships anyway to keep the part count down.

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Definitely depends on your ship. I don't use the Nerv myself, so it's usually Poodles or Terriers (the power of the pooch!). The Poodle is great because it's got a good gimbal and an alternator (big advantage over the Terrier). But I usually end up using the Terrier, anyway.

If you put eight Terriers radially around a 2.5m core, you now have double the thrust of a Poodle without needing another 2.5m tank. You can slap a Clampotron Sr on the bottom, and now it becomes extremely versatile. You can refuel it, or connect it to other modules. Combine that with an MK2 Lander Can and another Sr port on top and you can put it together however you want and it'll still be pretty stable under acceleration.

But for the trip home, you can't beat the Spark/Oscar B combo. If you put four radially around a 1.25m core, it'll get you farther than you'd ever think possible. Again, though; it all depends on your ship and what you wanna do.

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7 hours ago, Blaarkies said:

Would it not be better to use 3 Darts at that point? 1t less mass and more TWR, and less part count...but that high tech tho

You definitely could, just depending on personal preference and what you have planned. I've taken to using Darts on larger landers. The short cone gives you good clearance no matter where you put the legs. And their atmospheric power is great. They'll get you off Duna or Laythe with ease.

Their biggest drawback, to me, is their lack of a gimbal. I know you can use more reaction wheels, but it still irritates me. I usually combine them with Twitches (to get a little gimbal), but that presents its own problem. If you put your solar panels or rcs thrusters too close, the Twitch exhaust blows 'em off. You have to switch back from map view to see what just blew off. Oh, well. It's all give and take.

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Posted (edited)

6 hours ago, Cpt Kerbalkrunch said:

I usually combine them with Twitches (to get a little gimbal), but that presents its own problem. If you put your solar panels or rcs thrusters too close, the Twitch exhaust blows 'em off. You have to switch back from map view to see what just blew off. Oh, well. It's all give and take.

Is it that hard to make sure not stick a part under your engine ? lol 

Anyways, back on topic, as has been mentioned earlier, the Poodle has the best isp, and is reasonably light. Though if your payload is light (just a couple tons), the dart spark or ant would probably be best. For about 7-10 tons I'd recommend the terrier. I could test using math to see where the crossover points are.

Edited by EpicSpaceTroll139
Getting my engines mixed up

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Posted (edited)

1 hour ago, EpicSpaceTroll139 said:

Is it that hard to make sure not stick a part under your engine ? lol 

 

Ha. I guess not, though radial parts and radial engines do tend to fight for space sometimes. And I'm tellin' ya, the Twitch's exhaust travels a bit further than you would think. I'll think I'm safe, but then I'll hear an explosion during a burn and think "did I lose a thruster or a solar panel this time?"

But I agree with your conclusions. Poodles for larger ships, Darts for ships that need more power, and Terriers for everything else. But again, if your ship is small enough (returns usually) the Spark is awesome.

Edited by Cpt Kerbalkrunch

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Posted (edited)

22 minutes ago, Cpt Kerbalkrunch said:

Ha. I guess not, though radial parts and radial engines do tend to fight for space sometimes. And I'm tellin' ya, the Twitch's exhaust travels a bit further than you would think. I'll think I'm safe, but then I'll hear an explosion during a burn and think "did I lose a thruster or a solar panel this time?"

But I agree with your conclusions. Poodles for larger ships, Darts for larger ships that need more power, and Terriers for everything else. But again, if your ship is small enough (returns usually) the Spark is awesome.

I guess I never come across the problem because I have this OCD thing that I never put a part where it looks like it could possibly lie along an infinite line from a thruster's nozzle. Even RCS ports which lack actual occlusion detection. :P*

I also realized I was mixing up my engine names. I meant to refer to the Spark engine when I said Dart. I must say I haven't used the Dart much in space since it (for good reasons) got whacked with the nerf bat, as I generally favor isp over power in my designs. Though from its stats, it definitely would be good for more power.

* Except when building turboshaft vehicles, in which this is kind of necessary for the turbines to work!

Edited by EpicSpaceTroll139
*
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17 hours ago, Cpt Kerbalkrunch said:

I usually combine them with Twitches (to get a little gimbal), but that presents its own problem.

It sounds like Vernors will do you better, since you are already using bad Isp engines for the gimbaling they provide. Place them almost on the sides of the engine itself and launch with RCS, then you have even more gimbal at 70-90' angles without constantly using fuel through them

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On 4/19/2017 at 11:00 AM, tomf said:

I like this website for these type of questions

http://meithan.net/KSP/engines/

put in your payload mass, your required delta-v and your TWR tolerance and it will give you a graph showing the best engine options.

This, basically... except I have a spreadsheet to show me my options.

 Which engine is "best" depends on what you're doing. What's the payload mass and DV budget?

Best,
-Slashy

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