Fastest startup engine?

[Foxster]

Which of the non-jet engines get up to max thrust the quickest?

[Norpo]

I think all rocket engines (and solid rocket boosters, though those only stay at 100%) automatically respond to throttle instantly.

That is, they don't need any start-up time.

[Foxster]

Umm, I'm not sure about that. Yes, the throttle needle jumps up at the same rate but the actual thrust catches up after and this delay is, I believe, different for each engine.

[WhiteKnuckle]

Right click on the engine, you can watch it's thrust rating in real time.

Pretty sure all non-jet engines are instantaneous, or so close to that as not to matter.

[Starwhip]

No, rockets are instantaneous. Jets, on the other hand, are not.

If you hit "Z" you jump to max thrust (on the throttle, anyway) instantly.

[Foxster]

Oh, OK. Thanks for clearing that up.

[michaelsteele3]

Whatever it is, it is the opposite of cliche horror movie cars.

But on a serious note, they have no "start up time" from what I can tell. If anyone finds anything else, let me know.

[Pecan]

I'd never thought to look and am intrigued enough to check ...

... and, yes, rockets reach full (or whatever the throttle/thrust limiter is set to) thrust instantly.

Edited February 4, 2015 by Pecan

[KerikBalm]

The Basic jet (for an example of the jet engines) has this in its .cfg file:

heatProduction = 350

useEngineResponseTime = True

engineAccelerationSpeed = 0.12

engineDecelerationSpeed = 0.21

useVelocityCurve = True

fxOffset = 0, 0, 0.74

While the LV-T30 (for an example of the rocket engines) has this:

heatProduction = 400

fxOffset = 0, 0, 0.8

They don't even bother to have the line about engine response time in there set to false... its just left out completely.

Rocket engines have no response time delay.

[Red Iron Crown]

Interestingly, rocket engine spool up is one of the effects that Realism Overhaul adds to the game. Makes launch clamps much more important.

[DuoDex]

Interestingly, rocket engine spool up is one of the effects that Realism Overhaul adds to the game. Makes launch clamps much more important.

Rocket engine spool up? I can't really see that being SUPER realistic unless it's very minor. Rocket's don't really spool up in real life-you mix the propellants in the correct amounts and proportions and either get a very kerbal boom or some thrust. I mean, yes, the things do have to be moved from the fuel tank, but...

[Red Iron Crown]

Rocket engine spool up? I can't really see that being SUPER realistic unless it's very minor. Rocket's don't really spool up in real life-you mix the propellants in the correct amounts and proportions and either get a very kerbal boom or some thrust. I mean, yes, the things do have to be moved from the fuel tank, but...

It's all about the turbopump that feeds the fuel to the combustion chamber. The pump is powered by the combustion of propellants, and once combustion is started it takes time for the turbine that drives it to spool up to full speed.

Of course, some rocket engines don't work this way (pressure-fed hypergolic engines are a good example), but RO simulates that, too.

[DuoDex]

It's all about the turbopump that feeds the fuel to the combustion chamber. The pump is powered by the combustion of propellants, and once combustion is started it takes time for the turbine that drives it to spool up to full speed.

Of course, some rocket engines don't work this way (pressure-fed hypergolic engines are a good example), but RO simulates that, too.

I've already learned not to question RO too much. And why is the pump not electric? It seems that would provide more thrust quicker than a turbopump, especially seeing as a turbopump would have to be kick-started if no combustion was taking place.

Disclaimer: I am not an aerospace engineer. I just try to apply common sense. Actually, that'd be a nice thing to put in my signature...

[godefroi]

Because real rocket engines don't have alternators, I believe. The turbopumps they use are big, heavy, and move a LOT of propellant very quickly. While electric pumps are (probably) up to the job, they'd consume a lot of electricity. The turbopump on the Rocketdyne F-1 produced 41 megawatts, or 55,000 brake horsepower.

The SSME high pressure fuel turbopump produces 23,260 hp (17.34 MW).

These are SERIOUSLY POWERFUL pumps.

Edited February 4, 2015 by godefroi

[Red Iron Crown]

A turbopump is lighter, simpler, and more powerful than an electric pump, especially one that can deliver the flow rates required for a good-sized rocket engine. You're right that some external power is required to start up the pump in the first place; I believe this is done with external power supplied from the launch tower for most launchers and ullage-fed ignition for upper stages.

[DuoDex]

Indeed. Now moving into the hypothetical, why don't we use hybrids? They start at full using electric power, and as the combustion increases they augment that until they're running off of it entirely? It would provide (almost) 100% thrust on demand, instead of a slow cycling up.

[KSK]

Indeed. Now moving into the hypothetical, why don't we use hybrids? They start at full using electric power, and as the combustion increases they augment that until they're running off of it entirely? It would provide (almost) 100% thrust on demand, instead of a slow cycling up.

I'm guessing the performance gain wouldn't be enough to justify the added complexity? 'Slow' is also relative - even the F1 didn't take more than a few seconds to hit full thrust.

[cerberusti]

Interestingly, rocket engine spool up is one of the effects that Realism Overhaul adds to the game. Makes launch clamps much more important.

Anything I attach clamps to in the last patch with RO shreds itself as physics loads. I let them sit on the pad now.

I never noticed the spool up, it must be pretty fast. They really do like even tiny details, which is what makes the mod great!

[peadar1987]

41 megawatts?!!!!

[Srpadget]

Because real rocket engines don't have alternators, I believe. The turbopumps they use are big, heavy, and move a LOT of propellant very quickly. While electric pumps are (probably) up to the job, they'd consume a lot of electricity. The turbopump on the Rocketdyne F-1 produced 41 megawatts, or 55,000 brake horsepower.

The SSME high pressure fuel turbopump produces 23,260 hp (17.34 MW).

These are SERIOUSLY POWERFUL pumps.

Minor nit. You quoted the stats for the LOX turbopump. The SSME fuel turbopump is quite a bit more powerful. IIRC, I believe it produces MORE power than the F1's turbopump.

But, yes, the take-home message is absolutely true: SERIOUSLY POWERFUL pumps.

[godefroi]

Minor nit. You quoted the stats for the LOX turbopump. The SSME fuel turbopump is quite a bit more powerful. IIRC, I believe it produces MORE power than the F1's turbopump.

But, yes, the take-home message is absolutely true: SERIOUSLY POWERFUL pumps.

Indeed. The HPFTP (High Pressure Fuel TurboPump) produces 71,140 hp, or significantly MORE power than the F1's turbopump. And this is just the high-pressure fuel pump. There's low-pressure pumps in there too (one for fuel and one for oxidizer) that produce non-negligible amounts of power.

[John FX]

Indeed. Now moving into the hypothetical, why don't we use hybrids? They start at full using electric power, and as the combustion increases they augment that until they're running off of it entirely? It would provide (almost) 100% thrust on demand, instead of a slow cycling up.

Weight. Also, as already pointed out, even the F1 got to full power in something like 6 seconds.

[Falcon Coupe]

The engines from KW rocketry have an acceleration time. Yes I only know about this due to explosions!