Getting Started
Before playing RealFuels-Stock for the first time you should know:
- Fuel - Different engines now have different fuels
- Ignitions - Engines now have limited Ignitions
- Ullage - Hold your Fuels stable before igniting!
Instead of having only LiquidFuel and Oxidizer there are now plenty of fuels, all with different pros and cons. Here's a quick run down on the most used fuel combinations
- Kerosene/LqdOxygen (K/LOx) - high thrust, low Isp,very few ignitions (mostly one), used primarily for Lifter Engines.
- LqdHydrogen/LqdOxygen (LH2/LOx) - low thrust, high Isp, lense dense, more ignitions than K/LOx, used for upper stage/orbital engine
- LqdMethane/LqdOxygen (CH4/LOx) - mix between K/LOx and LH2/LOx
- Aerozine50/NTO - Hypergolic Fuel, low thrust, high Isp, lots of ignitions, mostly used for orbital maneuvers due to high ignition count.
- MMH/NTO - same as Aerozine50/NTO
- UDMH/NTO - Hypergolic Fuel, used for Lifter- and Upper Stage Engines.
... and a lot more.
All Engines in RealFuels-Stock have limited "restarts" (ignitions), you will have to have a look which engines have enough ignitions for your mission to complete. To ignite an Engine, you need two things. The correct fuel types/ratio, with enough amount to run the engine and Electric Charge.
As soon as you turn off your engines the fuel in your tanks aren't under acceleration anymore, that means that your propellant in your tanks are now freely floating around and eventually move away from your engine, and it ends up "sucking" gas into your engines instead of your propellant. The solution for this is having a small acceleration burst before engine startup, so that the fuel can settle down the tank (at the aft bulkhead). For these small acceleration bursts you can use either ullage motors (small SRBs, higher thrust than RCS, primarily used in atmosphere where you will need a bigger acceleration burst), RCS thrusters or even use the rotation of your craft for your advantage.
Pressure-fed is often misunderstood, pressure-fed means just that you won't need any turbo pump machinery. Ullage is the concept of having to settle the fuel at the aft bulkhead. (see above) That means the pressurant gas could theoretically also settle on the aft bulkhead (microgravity, everything floats everywhere), so when you open the valves you're now pushing the pressurant out (instead of your propellant), so you'll have to make sure only fuel is sitting on the aft bulkhead.
So now you're asking, why don't I have to ullage RCS? RCS utilities "bladder-tanks", they a have a membrane which gets compressed by the pressurant, so the pressurant gas is never touching the fuel in the first place. This method is very inefficient at large scale, thus only used for RCS. See this image: