Engine Burn Times with RO, RF, etc.

[Grimm Spector]

I'm playing RP-0, and I keep seeing stuff about rated engine burn times, but cannot find that information anywhere inside the game. I know it's supposed to be the best way to ensure I get appropriate delta-v out of an engine, so I can load a good dry/wet ratio. Any information would be super helpful, thanks!

[FullMetalMachinist]

2 hours ago, Grimm Spector said:

but cannot find that information anywhere inside the game.

I'm not certain, but I believe you middle click on the engine while in the VAB. 

[Grimm Spector]

 

47 minutes ago, FullMetalMachinist said:

I'm not certain, but I believe you middle click on the engine while in the VAB. 

Some of the engines have an "Engine Configs" section, with Isp numbers and then a number of seconds. Some don't have these, I assume those are the times? But a tutorial NathanKell wrote indicates a rated burn time just under 2 minutes for the RD103 engine I think it was, but all configs are around 240s, much higher. So I'm feeling a bit lost.

[Starman4308]

You might try asking @NathanKell or the other RO folks directly, but my suspicion is that "rated burn time" is purely a real-world thing, where engines are only rated to run for a certain length of time before problems start to occur, such as excessive coking in the feed lines or injector*.

*Engines which burn hydrocarbons, particularly kerosene-based fuels like RP-1, don't burn clean; they tend to coke, and produce solid deposits that can clog up the works.

As to why it would be a good idea to match that rated burn time: those engines were designed for a specific purpose, and are rated for that specific purpose. If you're burning, say, an RD103 for less than the rated burn time, there's a good chance you could get more delta-V out of the system by adding more propellant and letting that RD103 burn longer. If you're burning longer, you probably over-loaded the stage with propellant. It'd be a rough rule of thumb to match that engine's real-world applications, not a hard requirement.

EDIT: Alternately, look up real-world engines on the Internet; rated burn times are probably out there somewhere.

Edited April 19, 2017 by Starman4308

[FullMetalMachinist]

42 minutes ago, Starman4308 said:

but my suspicion is that "rated burn time" is purely a real-world thing, where engines are only rated to run for a certain length of time before problems start to occur

Well, yes it is a real world thing. But it's also something that is implemented by RO (if you have test flight installed) that will cause engines to malfunction if you burn them longer than they're rated for. 

[michal.don]

I believe that i doesn't mean the time of burning to get the most delta-V, but rather for how long burn times the engine was designed. If you exceed that time, there is much higher risk of the engine failing, so I generally try to keep my burn times within the limits. And I had many failed launches in cases I did not check the rated burn time properly and exceeded it by a significant amount of time.

As to where to find these values, you have two options:

First, in the description of each engine, there is a list of the various configurations with the rated burn time in seconds

And second, if you right-click an engine already placed on rour rocket, click "show GUI", a window pops up where you can choose the desired engine config (some require a certain tech to unlock) and read the rated burn times as well.

I hope this helps,

Michal.don

[Red Iron Crown]

This is a feature of TestFlight, and the rated burn time shows in the part info pop-up when you mouse over an engine in the part list in the editor. You can sometimes exceed it, but you're rolling the dice if you depend on that. 

[Grimm Spector]

Alright, thanks folks.