[1.0.5] Advanced Jet Engine v2.6.1 - Feb 1

[camlost]

The issue is that the air intakes aren't feeding enough air into the engine in both cases, which causes them to throttle down, since it's still above the flameout threshold. I suspect that it might just be that the intake's resource pool isn't capable of holding enough air, in which case it can be fixed by simply increasing the resource pool for all intakes.

And don't go with the solution of giving IntakeAir density = 0. ModuleResourceIntake uses the density of the air it's flying in and the density of the resource to determine how many units of the resource to create, so under that solution a single intake produces an infinite quantity of that resource. So engines are never able to run out of thrust at that point.

The engines are not flaming-out, just that its thrust is reduced. I wonder how did that happen?

[ferram4]

A change in the ModuleEngines / ModuleEnginesFX code to change a bug where engines would not respect the "ignition threshold" parameter. Basically, an engine was supposed to automatically throttle down to use the resources available, unless the ratio of resources available to resources requested was below the ignition threshold; by default all the engines have an ignition threshold of 0.1, so the engine will throttle down to 10% of the thrust requested if necessary, but if it needs to throttle further it will flameout. Basically, not having enough fuel / air results in less thrust, until it drops below a threshold, at which point the engine flames out.

Take a look at the FAR Flight Data window; it has a section that handles air requirements, and it should tell you that you're slightly low on air when the engines spool up.

[Fractal_UK]

And don't go with the solution of giving IntakeAir density = 0. ModuleResourceIntake uses the density of the air it's flying in and the density of the resource to determine how many units of the resource to create, so under that solution a single intake produces an infinite quantity of that resource. So engines are never able to run out of thrust at that point.

The other problem with using IntakeAir density = 0 is that ModuleEngines uses the fuel density to calculate thrust so setting IntakeAir density = 0 makes a jet engine require IntakeAir for operation but prevents expelling it from actually producing any thrust. That means all the requested thrust is instead produced by LiquidFuel and that changes the fuel flow behaviour further.

[Hodo]

I am considering getting this mod and starting over my career mode. But I have a couple of questions.

-How stable is it?

-Does it conflict with any of the parts mods listed in my sig?

-Does it work with DRE-C?

[DoubleOSeven1]

I am considering getting this mod and starting over my career mode. But I have a couple of questions.

-How stable is it?

-Does it conflict with any of the parts mods listed in my sig?

-Does it work with DRE-C?

1.) As far as I can tell

2.) No

3.) As far as I can tell

[ferram4]

The other problem with using IntakeAir density = 0 is that ModuleEngines uses the fuel density to calculate thrust so setting IntakeAir density = 0 makes a jet engine require IntakeAir for operation but prevents expelling it from actually producing any thrust. That means all the requested thrust is instead produced by LiquidFuel and that changes the fuel flow behaviour further.

Well, that's intended. The Isps are supposed to function based on mass flow rate of fuel, not total mass flow rate. If Isps were defined for total mass flow rate we'd see the Isp for turbojets and turbofans listed in the realm of 50 s - 350 s, depending on how much mass flow of air gets pushed through, rather than the 3500 s - 10000 s that the specifications give in real life. The way things are currently coded up, the stock turbofan engine with an Isp 2400s actually propels its exhaust 3 times as fast as the nuclear engine's 800s; I know from experience that the exhaust of a jet engine isn't going at 23,500 m/s when it leaves the nozzle, so what we have currently is jet engines that are horribly, horribly overpowered in the efficiency department.

[Fractal_UK]

Well, that's intended. The Isps are supposed to function based on mass flow rate of fuel, not total mass flow rate. If Isps were defined for total mass flow rate we'd see the Isp for turbojets and turbofans listed in the realm of 50 s - 350 s, depending on how much mass flow of air gets pushed through, rather than the 3500 s - 10000 s that the specifications give in real life. The way things are currently coded up, the stock turbofan engine with an Isp 2400s actually propels its exhaust 3 times as fast as the nuclear engine's 800s; I know from experience that the exhaust of a jet engine isn't going at 23,500 m/s when it leaves the nozzle, so what we have currently is jet engines that are horribly, horribly overpowered in the efficiency department.

Yes but the fundamental problem in KSP is that we are using specific impulse to define a mass flow rate rather than the reverse. We also have the problem that while there are different definitions for exhaust velocity (effective and actual exhaust velocity) there is no such distinction for specific impulse - KSP hasn't really got its definitions right. I would say the solution is to simply divide the atmosphere curve values by the intake air:fuel ratio then perform a corrected isp calculation and write that to the realIsp field so that the player sees the correct value.

We know from our previous testing that the turbojets are also seriously overpowered in terms of thrust as well as having dodgy velocity curves that stealthily affect the isp and that both need to be corrected before we have a realistic fix but I presume this mod can handle both of those changes.

[camlost]

having dodgy velocity curves that stealthily affect the isp

Eh, what do you mean?

[Fractal_UK]

Eh, what do you mean?

Let me explain in more detail, the default turbojet engine contains this:

	velocityCurve
	{
		key = 0 0.5 0 0
		key = 1000 1 0 0
		key = 2000 0.5 0 0
		key = 2400 0 0 0
	}

See the 0,0.5 and 1000,1.0 lines? They mean that at 0m/s the engine produces half the thrust compared to the thrust produced at 1000m/s *but* if you watch the fuel flow rate when transitioning between these velocities on a test flight in KSP, you will see that that although the thrust changes by a factor of 2, the fuel flow rate doesn't change at all. That means, using a real world definition of specific impulse, the specific impulse has also changed by a factor of 2 but the game does not report this to the player. The game will tell you the engine is achieving the same specific impulse in both circumstances, even though they differ by a factor of 2 by definition.

Specific impulse is thrust/mass flow rate so if you double the thrust without changing the mass flow rate, specific impulse should double.

In other words, at 0m/s the specific impulse is only half what the game is claiming (or only 8x greater instead of 16x greater once you take its poor handling of intake air in isp calculations into account).

Edited February 25, 2014 by Fractal_UK

[camlost]

Really? Anyway that's not my problem since AJE turns velocitycurve off.

[Hodo]

So I was testing your mod out, with the Real Fuels mod and several others. (See sig for list) And I found that the basic Pratt & Wittney jet engine, over heats like crazy. If run at 100% throttle for anything over 30seconds odds are it will overheat. Not sure if this is an intended design or not. I also took your code for the heat pumps and put them in the B9 SABRE intercoolers just so they at least pseudo function.

The other problem I ran into, and I am not sure if it is this mod or real fuels, but the RAPIER does not use anything in the real fuels mod, it runs on liquid fuel and oxidizer. But the RAPIER runs pretty much like the stock KSP RAPIER does, no real changes there. Haven't tested the SABREs yet.

[camlost]

So I was testing your mod out, with the Real Fuels mod and several others. (See sig for list) And I found that the basic Pratt & Wittney jet engine, over heats like crazy. If run at 100% throttle for anything over 30seconds odds are it will overheat. Not sure if this is an intended design or not. I also took your code for the heat pumps and put them in the B9 SABRE intercoolers just so they at least pseudo function.

This largely depends on your design. Read the general guidance section in blue in the first post. It has nothing to do with the throttle. What heat pumps? I've done nothing with no heat pumps.

I haven't touched RAPIER yet and SABRE is done in a pseudo-realistic way, so if you don't like it just delete B9_sabre.cfg for now

[Hodo]

This largely depends on your design. Read the general guidance section in blue in the first post. It has nothing to do with the throttle. What heat pumps? I've done nothing with no heat pumps.

I haven't touched RAPIER yet and SABRE is done in a pseudo-realistic way, so if you don't like it just delete B9_sabre.cfg for now

The only thing I have had an issue with is the basic jet engine. The Pratt & Whitney F100 Turbofan, it overheats faster than any engine I have tested yet. Even at subsonic speeds at reasonable altitudes it overheats pretty fast.

EDIT- was just testing the F100 Turbofan, the aircraft is 9tons total on take off. With one intake and based on a modern fighter design the aircraft is topping out at mach 1.189 around 9km alt. I am also running the RSS Kerbin mod.

Edited February 26, 2014 by Hodo

[Hodo]

Noticed one more thing. The F100 Turbofan makes very little if no noise when the afterburner is off. I have my sound down to 35% in game and I can't hear the F100 at all without the afterburner on.

[camlost]

The only thing I have had an issue with is the basic jet engine. The Pratt & Whitney F100 Turbofan, it overheats faster than any engine I have tested yet. Even at subsonic speeds at reasonable altitudes it overheats pretty fast.

EDIT- was just testing the F100 Turbofan, the aircraft is 9tons total on take off. With one intake and based on a modern fighter design the aircraft is topping out at mach 1.189 around 9km alt. I am also running the RSS Kerbin mod.

I just made an aircraft with RSS, FAR, RF, KJR, AJE and nothing else. With two F100s, it reached Mach 1.4 at 8km. What do you mean by "topping out"? F100 should be able to tolerate heat until ~Mach 2 at high altitude. Check your mod versions. Better show some pictures if you think the problem is with a specific design.

[Hodo]

I just made an aircraft with RSS, FAR, RF, KJR, AJE and nothing else. With two F100s, it reached Mach 1.4 at 8km. What do you mean by "topping out"? F100 should be able to tolerate heat until ~Mach 2 at high altitude. Check your mod versions. Better show some pictures if you think the problem is with a specific design.

I am using a single F100, and at 5-8km running 100% throttle it overheats really fast. Could it be that I am running DRE?

[Xarian]

I love me some realism mods. This will go well with realistic fuel tank weights and rocket engine TWR.

[camlost]

I am using a single F100, and at 5-8km running 100% throttle it overheats really fast. Could it be that I am running DRE?

Does't matter what your throttle is, overheating is not related with throttle. DRE's effect on engines are overwritten

[camlost]

I love me some realism mods. This will go well with realistic fuel tank weights and rocket engine TWR.

Right now the RF and RO simply treat fuselage as rocket segments, which is not so realistic. In other words a 2m x 1.25m x 1.25m fuselage segment should weigh more than 0.03t

[Hodo]

Does't matter what your throttle is, overheating is not related with throttle. DRE's effect on engines are overwritten

Here you go....

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As you can see the F100 overheats within 60seconds.

[camlost]

That's definitely not caused by AJE. Make sure you have the correct installation of RF 4.3 and MM. Since I cannot reproduce your problem, you can troubleshoot with the following questions one by one:

1. What if you delete DRE

2. What if you throttle down at say 200m/s, sea level?

3. What is the part's temperature shown in the right click menu

4. What about other engines? Does the J85 have a similar problem?

[Hodo]

That's definitely not caused by AJE. Make sure you have the correct installation of RF 4.3 and MM. Since I cannot reproduce your problem, you can troubleshoot with the following questions one by one:

1. What if you delete DRE

2. What if you throttle down at say 200m/s, sea level?

3. What is the part's temperature shown in the right click menu

4. What about other engines? Does the J85 have a similar problem?

All of the jet engines have the same problem. Except the SABREs and RAPIERs..

Temp is showing 1750C before it blows.

And i have uninstalled DRE and reinstalled it. I can't imagine that is causing the issue.

Edited February 26, 2014 by Hodo

[Shad0wCatcher]

@Hodo Is your Modlist up to date? I can't see what type of intake you're using; but if a) you're running KSPI and using a B9 radial intake this may not be overwriting KSPI's heating code and you could be hitting KSPI's heat wall.

[Fractal_UK]

@Hodo Is your Modlist up to date? I can't see what type of intake you're using; but if a) you're running KSPI and using a B9 radial intake this may not be overwriting KSPI's heating code and you could be hitting KSPI's heat wall.

Interstellar doesn't have a heat wall, it sets part temperature based on velocity to a proportion of the part max temperature. In any case, he's not going anywhere near fast enough for that to be a problem.

I have a theory however, I recall hearing that DRE halves max temperatures for some parts, assuming this hard sets part temperature, a halved or reduced maximum could be a real problem.

[camlost]

It‘s DRE's effect. The DRE's heating mechanism requires you to throttle down a little bit. I'll set HeatProduction=0 to all AJE engines next version.