How to put jet engines back the way they were in 0.90

[Alshain]

I really miss back when it was possible to do SSTO planes. I'm kinda feeling nostalgic for it. Does anyone know of a mod or if there is a way in-game to revert the engines back to where they didn't lose thrust in high altitudes similar to 0.90. I'd like to use the stock atmosphere and heating, but I want Jet engines that can get fast enough to make it to space.

Edited October 12, 2015 by Alshain

[Gaarst]

I guess you could go and download the 0.90 version still available on the KSP website, and copy-paste old configs into your 1.0.4 folder. Though as general engine behaviour was completely changed in 1.0 I doubt that will work.

On the other hand, I think I found the lines in the config responsible for the loss of thrust with speed and atmosphere:

// Jet params
atmChangeFlow = True
useVelCurve = True
useAtmCurve = True
machLimit = 2.5
machHeatMult = 6.0
velCurve
{
    key = 0 1 0 0
    key = 0.2 0.98 0 0
    key = 0.72 1.716 2.433527 2.433527
    key = 1.36 3.2 1.986082 1.986082
    key = 2.15 4.9 1.452677 1.452677
    key = 3 5.8 0.0005786046 0.0005786046
    key = 4.5 3 -4.279616 -4.279616
    key = 5.5 0 -0.02420209 0
}
atmCurve
{
    // definite 'kink' to the curve at high altitude, compared to flatter BJE curve
    key = 0 0 0 0
    key = 0.045 0.166 4.304647 4.304647
    key = 0.16 0.5 0.5779132 0.5779132
    key = 0.5 0.6 0.4809403 0.4809403
    key = 1 1 1.013946 0
}

Taken from: KSP_win\GameData\Squad\Parts\Engine\jetEngineTurbo\jetEngineTurbo.cfg (for the Whiplash Ramjet).

There should be similar blocks in jetEngineBasic (Wheelsey) and rapierEngine (Rapier); though I suspect Rapier to be a bit more difficult to edit due to the dual mode (at least the config file looks more complex), but you can still find a similar code in there.

Then you'd have to edit these values. I haven't tried and am not sure but I think that the lines means this:

• atmChangeFlow: should allow the engine to use different amounts of fuel depending on thrust (unlike rocket engines)
  
• useVelCurve: should allow to modify the thrust depending on velocity
  
• useAtmCurve: should should allow to modify the thrust depending on altitude and air density
  
• machLimit: should define the max speed of the engine before its thurst drops
  
• machHeatMult: no idea what this does
  

atmCurve and velCurve should define how thrust varies with height or velocity respectively, supposing useVelCurve and useAtmCurve are enabled. I don't know what all 4 values mean though, neither in what units they would be expressed (m/s, Mach, kN, % of max thrust, m...)

To completely delete thrust changes with speed and height, setting useVelCurve and useAtmCurve to false should be enough; but completely delete any thrust variation is maybe not what you're looking for. Then you'd have to try editing the other lines, or the numbers in the Curve functions.

[Alshain]

On the other hand, I think I found the lines in the config responsible for the loss of thrust with speed and atmosphere:

Unfortunately this is all very over my head. I was hoping someone as frustrated with the end of SSTO planes as I am had already done this. It just sucks they finally gave us a decent atmosphere and screwed up the engines, so it's still better to play 0.90 with FAR than stock if you want to fly planes into space.

[Svm420]

Unfortunately this is all very over my head. I was hoping someone as frustrated with the end of SSTO planes as I am had already done this. It just sucks they finally gave us a decent atmosphere and screwed up the engines, so it's still better to play 0.90 with FAR than stock if you want to fly planes into space.

I hope you know all of that is like your opinion man. Many have no trouble making jet ssto

[Alshain]

I hope you know all of that is like your opinion man. Many have no trouble making jet ssto

Good for them, whats your point?

[hab136]

It just sucks they finally gave us a decent atmosphere and screwed up the engines

Good for them, whats your point?

The point is that you're framing it as the engines are somehow broken, when in fact Squad actually fixedthe jet engines in 1.0, going from "ridiculously overpowered" to just "overpowered". They're still way more powerful than real life, even scaled to Kerbin's size.

There's nothing wrong with wanting the ridiculously-overpowered engines from 0.90, but the current ones are not "screwed up", as evidenced by people making SSTO spaceplanes.

If you want to try to bring them back yourself: http://forum.kerbalspaceprogram.com/threads/117038-Reverse-engineering-Jet-Engines-how-do-velCurve-and-atmCurve-work

If you just want easier-to-get-to-space space planes, check out Mark IV and/or OPT

[Alshain]

The point is that you're framing it as the engines are somehow broken, when in fact Squad actually fixedthe jet engines in 1.0, going from "ridiculously overpowered" to just "overpowered". They're still way more powerful than real life, even scaled to Kerbin's size.

That isn't what this thread is about. I say they are broken, ridiculously weak and incapable of getting any decent payload to orbit, it's my thread and my mod request I can frame it how I want.

I've seen the velocity curve thread but I'm afraid it's still too far over my head.

Edited October 13, 2015 by Alshain

[Guest]

Maybe try this (you do have ModuleManager, right?)

@PART[turboFanEngine]
{
	@MODULE[ModuleEnginesFX]
	{
		@useVelocityCurve = True
		@atmChangeFlow = False
		@useVelCurve = False
		@useAtmCurve = False
	}
}

Also, could the rest of the "realism defenders" here just back off? It's not like OP is in Suggestions trying to get something changed, they're asking for help modding their game. Whether you like it or not isn't relevant.

[Alshain]

Maybe try this (you do have ModuleManager, right?)

@PART[turboFanEngine]
{
    @MODULE[ModuleEnginesFX]
    {
        @useVelocityCurve = True
        @atmChangeFlow = False
        @useVelCurve = False
        @useAtmCurve = False
    }
}

Also, could the rest of the "realism defenders" here just back off? It's not like OP is in Suggestions trying to get something changed, they're asking for help modding their game. Whether you like it or not isn't relevant.

Thanks! I'll give that a try.

[Kerbas_ad_astra]

Alshain, part of the difficulty you're having is that core engine behavior (never mind the configs) changed in 1.0. It used to be that we would set an engine's thrust directly with the throttle. If the engine was in a speed or atmosphere regime where it had a reduced Isp, the engine would guzzle more fuel to compensate and keep thrust up. (This is why people would make statements like "burn time is 90 seconds in vacuum, 60 seconds at 1 atm".) Now, the throttle controls fuel-flow, so reducing Isp reduces thrust (as it should) as opposed to increasing fuel consumption. I suppose someone could write a "ModuleEnginesIspCompensator" or something that reproduces the old behavior, but it's probably easier to tinker with configs to make an engine that has better performance at high speeds and altitudes.

velCurve
{
    key = 0 1 0 0
    key = 0.2 0.98 0 0
    key = 0.72 1.716 2.433527 2.433527
    key = 1.36 3.2 1.986082 1.986082
    key = 2.15 4.9 1.452677 1.452677
    key = 3 5.8 0.0005786046 0.0005786046
    key = 4.5 3 -4.279616 -4.279616
    key = 5.5 0 -0.02420209 0
}
atmCurve
{
    // definite 'kink' to the curve at high altitude, compared to flatter BJE curve
    key = 0 0 0 0
    key = 0.045 0.166 4.304647 4.304647
    key = 0.16 0.5 0.5779132 0.5779132
    key = 0.5 0.6 0.4809403 0.4809403
    key = 1 1 1.013946 0
}

The first value in each curve is the Mach number (in velCurve) and pressure in atmospheres (in atmCurve). The second number is a multiplier that scales thrust. So, a ramjet flying at Mach 3 at ~11 km altitude (~0.16 atm) at maximum throttle will have a thrust of 130 kN * 5.8 * 0.5 = 377 kN. The second two numbers are slopes that change the shape of a curve (to the left and the right, respectively). These produce shapes like this (made with the Amazing Curve Editor):

(Bear in mind that the velCurve, left, increases in speed from left to right, but atmCurve, right, decreases in altitude from left to right.)

To make engines suitable for SSTOs, we need an engine with a velocity curve that doesn't drop to zero at high speeds (orbital velocity is about 2.5 km/s = Mach 7.3, while the ramjet peaks at Mach 3 and cuts off at Mach 5.5), and having good performance at high altitude is also a bonus. Instell Incorporated Experimental Technologies makes some scramjet parts that have curves like this:

They have no thrust until you get to about 850-900 m/s (because they rely on ram air pressure at supersonic speeds to do the compressing), but then have consistently high thrust throughout the hypersonic regime, as well as high thrust at low air pressures (except for the very last 0.002 atm or so -- between 60,000 to 70,000 meters). (Even up to Mach 20+, so they're probably good for RSS SSTOs, where orbital velocity is in the neighborhood of Mach 26.)

If you want a magic all-range super-jet for SSTOs, you might try a velocity curve like this:

Like the Instell XE-202, its thrust really picks up at hypersonic speeds, to give you a kick out of the atmosphere. Unlike the XE-202, it has some nominal thrust at lower speeds to get off the ground.

To replace the ramjet's velCurve and atmCurve with that set of curves, you can use this patch (if regex's suggestion doesn't work):

@PART[turboFanEngine]
{
    @MODULE[ModuleEnginesFX]
    {
        -velCurve{}
        -atmCurve{}
        velCurve // modified from Instell XE-202
        {
            key = 0 0.5 0 0
            key = 0.2 1 0 0
            key = 0.5 1 0 0
            key = 1 1 0 0
            key = 3 1 0 0.9064457
            key = 6 3 0.1908697 0.1780635
            key = 25 0 -1.75369 -4.279616
        }
        atmCurve // from Instell XE-202
        {
            key = 0 0 0 3.700989
            key = 0.002308854 0.4496168 49.44624 15.83227
            key = 0.008248772 1.493585 3.667849 1.200267
            key = 0.3508157 1.556122 -2.350542 -2.14261
            key = 0.5718389 0.6684216 -0.9174542 -0.8193923
            key = 1 0.3 -0.03553883 0
        }
    }
}

Edited October 14, 2015 by Kerbas_ad_astra