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


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The thing is, engines that are supposed to generate more thrust at higher speeds don't.

Like the RAMJET engine starts to generate thrust at .3mach, but then peaks out at mach 1 then sharply dies before mach 2. Which is not at all how that engine works.

The SABRE has the same problem, and the F100 gets to mach .9 before it starts to lose power and is a paper weight around mach 1.3. I can tell you now a F-15C can do a fair bit better than mach 1.3 with two of those engines. IMy test aircraft is the same weight as the F15C Eagle, and is roughly the same size, yet those two F100s which also power the F15C to mach 2+ barely get this aircraft over mach 1.5 at the same altitude.

When your intakeair is not enough KSP automatically throttles down engines to compensate that. Because we set the fuel flow to realistic values I had to make all intakes contain 100 units of intakeair. You need to re-install all intakes to make it work.

There was a bug with SABRE and I believe it's solved. I just managed to make an SSTO with 3 sabre S engines and B9 S2 fuselage.

As for realism this can never be accurate down to every kN, nor do I see any point. The overall performance of an aircraft depends on too many factors other than engine.

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When your intakeair is not enough KSP automatically throttles down engines to compensate that. Because we set the fuel flow to realistic values I had to make all intakes contain 100 units of intakeair. You need to re-install all intakes to make it work.

There was a bug with SABRE and I believe it's solved. I just managed to make an SSTO with 3 sabre S engines and B9 S2 fuselage.

As for realism this can never be accurate down to every kN, nor do I see any point. The overall performance of an aircraft depends on too many factors other than engine.

Ok that explains some of the air intake issues. I am going to install the latest update and test it out and see what changed and how it works.

EDIT, one last thing...

The downloaded patch has two Module manager files in it.

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Well I took that theory as a simple and relatively-realistic solution to model propeller thrust. Blade element theory is just beyond my capability. Even if what you proposed is done there's still important effects like induced velocity. I know propellers' been thoroughly studied and I would be cool if KSP could be like X-plane but I still don't see myself prioritize on that.

I would really like a decent propeller model, as I prefer those for a number of tasks. They are a lot more realistic than using rocket engines for relatively trivial tasks, and jets are not always suitable.

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@Camancha, compared to the model stock FS uses I think even the current apparently-over-simplified model is more decent. I would appreciate any specific suggestions on making a better model.

@m4ti410, in theory you can do a lot of tweaking of the cfg files to make it work without RF. But since this is supposed to be part of the "realism" thing I just find it too much trouble to maintain two sets of files.

@Hodo, The RO included rescaled B9. What I added is the friction correction provided in the 'B9 fix' thread. Besides the single-wheeled species are not rescaled. The two-wheels are rescaled 2x just following RO.

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@Camancha, compared to the model stock FS uses I think even the current apparently-over-simplified model is more decent. I would appreciate any specific suggestions on making a better model.

To be honest, I am not sure I am the most qualified person to do that - although I will think it over :)

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I'm really hoping someone will model a ballbearing and a cylinder/piston so in the future we can attach a "real" propellor to a working model of an internal combustion engine.

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xA2buKJl.png

It feels like something is wrong here. I'm using RSS and the SLT is around 1, but already at 5km I've lost most of the thrust and it doesn't break the sound barrier, even with afterburner. The thrust just keeps decreasing. Is this normal?

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I had the same problem MAKC, I unfortunately uninstalled it till it is a bit more stable.

I tested everything from the P&W F100s to the F119s and compared them to my resources, which include actual Air Force repair and specifications manuals for the F100, and JANES Information Service readouts.

The jets lose power way to fast, and are way under performing vs real life examples.

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@MAKC, I think the thrust decrease you experience is about right. The atmosphere density at your altitude is about 0.5 Sea level, that makes the air flow through engine ~1/2 sea level, hence the thrust is ~1/2 the sea level thrust. The thrust increased a little bit since you're flying at Mach 0.8. The static thrust at sea level is 53kN and you get 33kN.

The aircraft's performance is also determined by aerodynamics, so you should check if FAR has abnormally high drag on certain parts. A few days back I built an aircraft using 2x J79s and it was able to fly at M1.6 with AB and M0.9 without AB.

@Hodo, I don't think you have the same problem, nor is it caused by instability. You need to be more specific about what's your data and how do they compare to what you get in KSP. And you are complaining about thrust decreasing too fast with regard to what?

The only problem I can think of is when the intakeair is not enough, KSP automatically throttles down to compensate that, which results in thrust loss.

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@MAKC, I think the thrust decrease you experience is about right. The atmosphere density at your altitude is about 0.5 Sea level, that makes the air flow through engine ~1/2 sea level, hence the thrust is ~1/2 the sea level thrust. The thrust increased a little bit since you're flying at Mach 0.8. The static thrust at sea level is 53kN and you get 33kN.

The aircraft's performance is also determined by aerodynamics, so you should check if FAR has abnormally high drag on certain parts. A few days back I built an aircraft using 2x J79s and it was able to fly at M1.6 with AB and M0.9 without AB.

@Hodo, I don't think you have the same problem, nor is it caused by instability. You need to be more specific about what's your data and how do they compare to what you get in KSP. And you are complaining about thrust decreasing too fast with regard to what?

The only problem I can think of is when the intakeair is not enough, KSP automatically throttles down to compensate that, which results in thrust loss.

He is at 6km, or about 19kft, which is pretty low when talking about aircraft.

And I did over 50 tests, with the same airframe, at the same altitude, 10km (33kft), and would accelerate with a F100 it would be useless at any speed above mach 1.9-2.1. Meanwhile the real F-15C Eagle which runs those very same engines, can go to mach 2.5+. When tested with a single F100 it would barely break mach 1.2, while a F-16C which runs that engine can go faster than that at the same altitude. I built my test aircraft to be roughly the same mass of the F/A-18 which is a good middle ground for the F-15 and F-16.

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If you're flying on stock-sized Kerbin then the atmosphere is slightly shortened, with a scale height of 5000m rather than Earth's 7500m; so that works out to you flying at an Earth equivalent altitude of 15km (49.5kft), while MAKC was flying at an Earth equivalent altitude of 9km, or 28.5kft. You're a lot higher up than you think you are, and so you're getting less thrust than you expect because you're comparing the wrong things.

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If you're flying on stock-sized Kerbin then the atmosphere is slightly shortened, with a scale height of 5000m rather than Earth's 7500m; so that works out to you flying at an Earth equivalent altitude of 15km (49.5kft), while MAKC was flying at an Earth equivalent altitude of 9km, or 28.5kft. You're a lot higher up than you think you are, and so you're getting less thrust than you expect because you're comparing the wrong things.

I was testing in the RSS scale Kerbin, which if I am correct is the same size as Earth and scales about the same.

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He is at 6km, or about 19kft, which is pretty low when talking about aircraft.

And I did over 50 tests, with the same airframe, at the same altitude, 10km (33kft), and would accelerate with a F100 it would be useless at any speed above mach 1.9-2.1. Meanwhile the real F-15C Eagle which runs those very same engines, can go to mach 2.5+. When tested with a single F100 it would barely break mach 1.2, while a F-16C which runs that engine can go faster than that at the same altitude. I built my test aircraft to be roughly the same mass of the F/A-18 which is a good middle ground for the F-15 and F-16.

Again, an aircraft's performance is not solely determined by engine performance. You cannot build an airplane that looks like F-15, find out it doesn't fly as fast as F-15 then immediately blame the engine. I built the engines so their static thrust at sea level matches what wikipedia says. If you think the engine thrust curve against altitude is far from reality then you need to present the exact numbers. Otherwise I can only trust whatever NASA's program says.

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Again, an aircraft's performance is not solely determined by engine performance. You cannot build an airplane that looks like F-15, find out it doesn't fly as fast as F-15 then immediately blame the engine. I built the engines so their static thrust at sea level matches what wikipedia says. If you think the engine thrust curve against altitude is far from reality then you need to present the exact numbers. Otherwise I can only trust whatever NASA's program says.

Not saying you did it wrong, or that it is a bad plugin, just saying that they don't seem to match up with the real counterparts. And I didn't make an aircraft that looks like a F-15, or an F-16, I just went with the lowest drag profile aircraft I could make that has the same mass as an F/A-18 for test reasons. It isn't built to turn on the dime like the F-16 or climb to 60kft in 60seconds.

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Is the small sabre engine supposed to burn as much kerosene on air mode as five ( maybe more ) F119s?

It burns hydrogen. And yes, I made the sabre in a way that their Isp roughly matches the reference I linked in OP.

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@MAKC, I think the thrust decrease you experience is about right. The atmosphere density at your altitude is about 0.5 Sea level, that makes the air flow through engine ~1/2 sea level, hence the thrust is ~1/2 the sea level thrust. The thrust increased a little bit since you're flying at Mach 0.8. The static thrust at sea level is 53kN and you get 33kN.

The aircraft's performance is also determined by aerodynamics, so you should check if FAR has abnormally high drag on certain parts. A few days back I built an aircraft using 2x J79s and it was able to fly at M1.6 with AB and M0.9 without AB.

@Hodo, I don't think you have the same problem, nor is it caused by instability. You need to be more specific about what's your data and how do they compare to what you get in KSP. And you are complaining about thrust decreasing too fast with regard to what?

The only problem I can think of is when the intakeair is not enough, KSP automatically throttles down to compensate that, which results in thrust loss.

1011593

You were right. Drag's the culprit.

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1011593

You were right. Drag's the culprit.

I think drag maybe the issue. That would explain the power to weight ratio that I was having issues with.

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  • 2 weeks later...

How would I go about adding other engines like, say, the D-30F6 used in the MiG-31? What parameters would I have to find? Do any of the parameters require calculations of my own?

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How would I go about adding other engines like, say, the D-30F6 used in the MiG-31? What parameters would I have to find? Do any of the parameters require calculations of my own?

You need to find the thrust, weight, compression ratio, specific fuel consumption with or without afterburner, turbine temperature. Some of these might not be public but get as much as possible. Then you can, or I can, use EngineSim to guess the rest of the parameters

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