Which engines

[niceGuy]

I am new to the game, and tutorials do not cover that part but how do you find out which engines to use? Do you compare them by thrust (if yes than what's that) or fuels they require ?

[Space Alien]

basically the main factors you want to consider are 1-> is it the right size for your craft
2-> maximum thrust vs fuel efficiency ( you should probably ignore the fuel efficiency for now until you get better at the game). you almost always want a liquid fuel based engine, which for rocket engines will need oxidizer, which comes together in the same fuel tank. also something else to consider is not all engines generate electric charge. Another important thing is the amount of gimbal an engine has. Gimbal is basically the amount that the engine can rotate and change its thrust i.e steer. higher gimbal is better. for beginner rockets you cant go wrong with the lv909 as an orbital manouvre/ landing engine, and for take off you usually want the second engine you unlock

[niceGuy]

dude, thanks for detailed answer

[Spooky Lemon]

try & error. its part of the ksp experience.

[andylaugel]

For fuel efficiency, higher engine ISP is better. It's used in this formula:

delta v = ISP * g * ln( most mass / least mass )

Where ln() is the natural log function, g is about 9.806, and most/least mass refers to how massive the ship is with and without fuel.

For thrust, the formulas to know are:

F = ma
a.k.a.
a = F / m

Where a is acceleration, m is mass, and F is force (or thrust). If m is kg and F is kN, then a is measured in m / s^2 (or m / s / s). To take off, your acceleration must exceed the planet or moon's acceleration due to gravity.

Kerbal Engineer Redux (KER) is a nice mod that'll figure these numbers out for you, but you can do the math by hand if you want to. There is also a delta-v map out there that'll give you an idea of how much delta-v you'll need to get anywhere.

I'll generally use "Poodle" or "Terrier" engines after getting into orbit, due to their reasonable thrust and descent ISPs. LV-N "Nerv" nuclear engines are great for interplanetary burns, but are difficult to deal with (landing gear placement, no gimbals). "Dawn" ion engines are great for lightweight interplanetary probes, but their extreme low thrust often results in excessively long burns (40+ minutes).

[dwringer]

I'll just add that thrust vectoring is not always desired on engines if your craft already has got adequate reaction wheels at it's center of mass, control surfaces (if designed to fly within the atmosphere) or RCS (if you're willing to burn a little propellant to keep your ship lined up during burns). When it comes down to picking the Reliant or the Swivel, I will usually lean toward the Reliant (it is cheaper, lighter, and has slightly more thrust) even though it has no vectoring ability at all. Sometimes I will then replace reliants 1-2 at a time with swivels if I need more control.

[King_BR0K]

my primary launcher has a core with 3 large 1.25m tanks and a swivle and 2 boosters with 2 tanks and reliants feeding the core
sometimes i strap on thumpers for hevyer payloads

[ghpstage]

Originally posted by ARHC marcus232:

basically the main factors you want to consider are 1-> is it the right size for your craft
2-> maximum thrust vs fuel efficiency ( you should probably ignore the fuel efficiency for now until you get better at the game).

The mass of the engine can be just as important as the ISP.
Otherwise identical rockets that have lighter final stages tgat make use of the Spark, Ant or their radial versions will frequently have more dV than ones that use a LV-909, while also being cheaper!

[maestro]

I've found the wiki to be really useful for looking up graphs and good amounts of info about engines.