Shaun

Kerbal Space Program's drag needs fixing.

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The x8 drag multiplier that KSP uses is astronomically high; so much so that jet planes have massive amounts of thrust, but can't gain speed at altitude, even when there should be sufficient thrust to do so. I could easily lower the drag multiplier, but that would knack up the game when I'm launching rockets. Surely there's a way to fix this.

Qualitive_variation_of_cd_with_mach_numb

I'm presuming the game uses a drag curve like the one above. Perhaps lowering drag below mach 0.9 by a factor of 4, or 8 would mean planes could act more realistically at subsonic speeds;  slow take-off rolls, and speed building up slowly as altitude increases. Past mach 0.9, the drag curve would remain the same, so rockets and supersonic flyers would act the same. This would mean that perhaps subsonic flyers could finally circumnavigate Kerbin with less fuel than hypersonic aircraft.

Alternatively, lowering thrust to jet engines and sticking the drag multiplier on 1 could sort the issue.

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KSP's brand of aerodynamics is fundamentally different from real physics. It's a reasonable gamified simulation, but it's not the same thing.

You're talking about fine-tuning the simulation, which is fine - suggest away. Just don't expect any of this fine-tuning to make it all 'act more realistically', because that is not due to any of the fine-tuning, it's due to how KSP calculates drag to begin with, at the very basic coding of it. For one: they'd first have to change the game engine to make drag only apply to the craft outline as a whole, instead of all individual parts by themselves as if atmosphere phases right through solid matter (selectively, to only hit each part individually).

 

As for the lack of performance you mention: that could have more to do with how you build your planes than with the game's parameters.

 

3 hours ago, Shaun said:

jet planes have massive amounts of thrust, but can't gain speed at altitude, even when there should be sufficient thrust to do so.

(...)

planes could act more realistically at subsonic speeds; slow take-off rolls, and speed building up slowly as altitude increases.

(...)

perhaps subsonic flyers could finally circumnavigate Kerbin with less fuel than hypersonic aircraft.

I'll admit that I've not specifically paid attention to that last point. I have on occasion built subsonic planes that could circumnavigate Kerbin on very little fuel (Wheesleys are amazingly economic, although Panthers in dry mode offer other advantages at almost the same fuel economy). It's just tedious to do in 3+ hours what can be done in under an hour if pushed supersonic instead, so not a lot of people do that out of habit. And I don't know for sure if it ends up using less fuel, but I do know that in the case of spaceplanes it's worth at times pushing right up or through supersonic in dry mode when using Panthers instead of lighting the afterburners from the very start. What you may be seeing is that in general, supersonic craft fly significantly higher than subsonic - and altitude definitely makes jets more economic in their fuel consumption.

I'm not sure what you mean by not gaining speed at altitude - if that were a fundamental problem in KSP,  none of us would be able to make working spaceplanes in the stock game. Jets do have imposed operating ceilings and power curves, yes, but that's a simulation choice and somewhat akin how real engines work. It's not that difficult to cruise at 10+ km on Kerbin with most stock jets - which if you consider Kerbin's scale compared to Earth is way higher than what most conventional or even experimental jets can do. 10km or 33000 feet is where jet liners tend to fly, but that's on a planet roughly 10x the size of Kerbin. On Kerbin, that'd be the equivalent of 1km (or 1.75km) up... all stock jets fly well at that altitude.

I also don't recognize the second point you make: slow take-off rolls are almost childishly easy to achieve in KSP, ironically in part due to high drag, which you are suggesting should be lowered. You almost have to be careful to not make your plane flip backwards at take-off. Or even before starting to roll... (just place your main gear a little too close to the CoM :D). And speed does generally build up as altitude increases, even for Wheesleys; atmosphere density drops faster in the first few km than the jet power curves, so for most planes it's immediately beneficial to get out of the lower draggy atmosphere.

There's a lot of well-performing (space)planes being shared every day; here, on KerbalX, on Steam. Which tells me a lot of KSP plane builders are not held back by the current stock parameters. Maybe check out how they are doing things?

Edited by swjr-swis
double dry is very dry

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46 minutes ago, swjr-swis said:

KSP's brand of aerodynamics is fundamentally different from real physics. It's a reasonable gamified simulation, but it's not the same thing.

You're talking about fine-tuning the simulation, which is fine - suggest away. Just don't expect any of this fine-tuning to make it all 'act more realistically', because that is not due to any of the fine-tuning, it's due to how KSP calculates drag to begin with, at the very basic coding of it. For one: they'd first have to change the game engine to make drag only apply to the craft outline as a whole, instead of all individual parts by themselves as if atmosphere phases right through solid matter (selectively, to only hit each part individually).

Most of this has been implemented by the Ferram Aerospace Research (FAR) mod, which admittedly hasn't been updated for quite some time.

While I'd definitely agree it'd be neat to have improved drag physics in the stock game that accounts for the overall craft outline, I'm concerned at the amount of time and effort to maintain the accuracy of that drag model for future game updates, which would mean SQUAD would have to hire someone of Ferram's caliber to understand the intricacies behind aerodynamics.

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FAR is still up to date.  Just look in the thread. There is a community update for 1.5.1. It doesn't really add anything new, just recompiles and whatnot.

Edited by Pds314

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