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

[Wolf_rt]

The issue is, i cant seem to get a model that has the same cd as it real life counterpart, the same weight, and the same thrust, to behave anything like it should.

The F-104 should be able to do at least mach 1.9 at 10000m

At the moment, is is only capable of Mach 0.95 at 3000m, and by the time you reach 10000m the J79 is only making around 20Kn of thrust, and the plane has slowed to Mach 0.4, no matter how gentle the ascent.

The J58-P-4 seems to be able to deliver the correct flight profile, but it delivers over 200KN at ground level, and 90KN at 10000m

The J79 never reaches its stated thrust of 79KN, and falls massivly as soon as altitude is gained. The J79 is the correct engine for the F104, so im wondering what has happened to the realisim, if everything is correct.

This has all been recreated on a fresh install, with FAR, AJE, B9, Tweak Scale, Procedural Tanks and KJR. I have made a new plane from scratch with no clipping.

Edited April 12, 2015 by Wolf_rt

[ThorBeorn]

Still there could be multiple reasons for this, besides the J79 underperforming (which camlost or someone knowledgeble needs to answer). For example cd varies with with several parameters, one being speed. Does your plane fly at a high AoA? Are the intakes facing the airstream at the AoA you flying at? Does your design use the area rule to reduce transonic drag? The J79 probably needs to go faster than subsonic to reach its maxthrust, a bit of a catch 22 there really.

Also are you using the latest verison of AJE and FAR and are you using RSS? Airpressure 10000m above kerbin is different than 10000m above earth.

Edited April 12, 2015 by ThorBeorn

[Wolf_rt]

No other mods than those stated, all latest versions, installed with CKAN.

plane flies at an AOA of around 2deg in general. Inlets are aligned. Current design uses the stock radial inlets, but i have tried all the others with no effect.

The area rule is implemented somewhat, as the plane is slightly narrower in the center of the fuselage where the wings are, and fuselage tapers further at the tail. The cd does rise to 0.03 around Mach 1 though. Not sure what i could do to make it more slippery though.

It should be able to hit Mach1 with 52KN of thrust (military power) It will basically do this at sea level (ie, there is 50KN of thrust available at sea level, and i can hit M 0.95) any increase of altitude absolutely kills it though.

I understand that kerbin is different to earth, but i thought this mod was to add realism? what is that realism measured against if i cant take this 'as realistic as possible' plane to any appreciable altitude without thrust dropping way more than in RL?

If i use the J58-P-4, i need around 55KN of thrust to reach Mach 1.9 at 10000m

Edited April 12, 2015 by Wolf_rt

[ThorBeorn]

Well looks like you have done what you can. I'm eagerly awaiting what camlost (ferram4 - if it's drag) has to say. Please let us know if you find a solution. I remember having the same issue with my own F104 replica in .25, one of the top 5 coolest planes in the world imo My problem was due to part clipping though. But I also remember thinking the engine should be more powerful with a super slippery design.

[Wolf_rt]

Cheers for your help.... For what its worth, a thrust of ~20KN at 10000M seems reasonable, im just not sure what is stopping the plane behaving as expected... The cd does rise to around 0.03 at Mach 1, then falls to around 0.022 at mach 1.5... Perhaps it is more an issue with FAR?

Wiki puts the F-104 cd at 0.048 http://en.wikipedia.org/wiki/Drag_coefficient

Where as another source i found put it at 0.017 (no lift)

Its got me stuffed....

[camlost]

Jet engines always lose thrust when you climb high, its thrust should be approximately proportional to ambient pressure. I believe the jet engines are working as intended and realistically, and your problem is likely to be drag. Does it have the exact dimension as the real F-104? What is the ref area and Cd provided by FAR?

[blowfish]

Jet engines always lose thrust when you climb high, its thrust should be approximately proportional to ambient pressure. I believe the jet engines are working as intended and realistically, and your problem is likely to be drag. Does it have the exact dimension as the real F-104? What is the ref area and Cd provided by FAR?

What about static thrust never reaching the specification? I think this has to do with the parameters being tuned with TPR=100% rather than what you get with real inlets, which is more like 85%.

[Wolf_rt]

For whatever reason, the engine is reaching its stated thrust at sea level now, with the fresh install and new model. No idea what would have changed...

It must be an aerodynamic issue.

I'm not sure what reference area refers to, but it is stated at 84.5m2 cd is 0.25 at mach 1. The model is actually around 75% of the size of the real thing. I have posted in the FAR thread, as im beginning to think that is where the issue lies.

[blowfish]

I'm not sure what reference area refers to, but it is stated at 84.5m2 cd is 0.25 at mach 1. The model is actually around 75% of the size of the real thing. I have posted in the FAR thread, as im beginning to think that is where the issue lies.

Total drag is equal to Q * Cd * Aref, where Q is dynamic pressure, Cd is the drag coefficient, and Aref is some reference area (usually total wing area). To compare how two craft will perform, it's useful to compare the Cd * Aref product.

[NathanKell]

And FAR uses all wing area, including horizontal and vertical tail, as well as in real life where only the area of the main wings is counted for reference area (when a Cd is stated). So for the same Cd*Aref, in FAR the Cd should be smaller since Aref is larger.

[blowfish]

I've been working on a GUI interface to provide useful information in-flight (with a little help from ferram's code).

Those are all the useful numbers I could think of, but I'm open to adding more. All can be turned on/off to reduce the size of the window, and the units can be changed (temperature in Celsius or kelvin and pressure in kPa or ATM).

[ThorBeorn]

What about static thrust never reaching the specification? I think this has to do with the parameters being tuned with TPR=100% rather than what you get with real inlets, which is more like 85%.

I would also like to know what the well versed people have to say about this.

Also good job on the gui blowfish!

[kcs123]

I've been working on a GUI interface to provide useful information in-flight (with a little help from ferram's code).

http://i274.photobucket.com/albums/jj251/blowfishpro/KSP/screenshot2_zpsxhmiekrf.png

Those are all the useful numbers I could think of, but I'm open to adding more. All can be turned on/off to reduce the size of the window, and the units can be changed (temperature in Celsius or kelvin and pressure in kPa or ATM).

Great work on this. Thing that I would like to see is current thrust that engine currently provide and fuel consumption rate.

In current release fuel consumption is in direct relation with ISP and ISP changes with thrust. For KSP 1.0 it will be oposite, fuel consumption will be constant with throttle, while thrust and ISP will change with speed and altitude.

In both KSP versions those values provide valuable information how to fly craft more efficiently.

[blowfish]

Great work on this. Thing that I would like to see is current thrust that engine currently provide and fuel consumption rate.

I was hesitant to include numbers that other mods already show (thrust, TWR, and Isp can be seen in Kerbal Engineer, TSFC can be seen in FAR), but I suppose the redundancy isn't hurting anyone, and anything unnecessary can be disabled if needed.

[Quiznos323]

Mike (Mu): It’s been another week of bug fixing and optimisation. There has been a lot more work put into balancing and tuning the aero system too. The jet engines have had another pass with respect to their characteristics. For those that don’t know, the airflow through jet engines (and thus fuel flow, and thus thrust) is now a function of mach and of air density giving them more interesting limitations and effects.

It looks as though Squad is implementing some more realistic jet behavior in 1.0. Just found this mod today, so I thought it was interesting that I'd read this in the dev notes in the same day haha

[blowfish]

It looks as though Squad is implementing some more realistic jet behavior in 1.0. Just found this mod today, so I thought it was interesting that I'd read this in the dev notes in the same day haha

It's certainly good news for removing one of the silly aspects of stock KSP physics, though it may eat into AJE's user base a bit. At the very least though, I expect some amusement coming from watching everyone trying to re-learn how to fly SSTOs

[Quiznos323]

It's certainly good news for removing one of the silly aspects of stock KSP physics, though it may eat into AJE's user base a bit. At the very least though, I expect some amusement coming from watching everyone trying to re-learn how to fly SSTOs

I agree I sucked at making them in the first place so better to learn correctly once 1.0 hits!

[NathanKell]

Just like FAR looks to be decent prep for New Aero, I'd say AJE is likely to be decent prep for New Jets.

[camlost]

From what's described above, what 1.0 is fixing is the Isp-scaling bug. However that alone will not make jet engine (or any air-breathing engine) performance more realistic. They need to fix two things 1) IntakeAir as a resource counts as fuel 2) Isp instead of thrust does not change with altitude. We're yet to know where the dev stands on this topic.

[blowfish]

From what's described above, what 1.0 is fixing is the Isp-scaling bug. However that alone will not make jet engine (or any air-breathing engine) performance more realistic. They need to fix two things 1) IntakeAir as a resource counts as fuel 2) Isp instead of thrust does not change with altitude. We're yet to know where the dev stands on this topic.

Based on what they said it looks like thrust will drop off with altitude.

[kcs123]

I was hesitant to include numbers that other mods already show (thrust, TWR, and Isp can be seen in Kerbal Engineer, TSFC can be seen in FAR), but I suppose the redundancy isn't hurting anyone, and anything unnecessary can be disabled if needed.

If I use your mod, and get more readable info in one window, I would most likely close other screens from FAR, Kerbal Engineer, TSFC or MJ. That is why those info while redudant with othe mods is not useless. That's just suggestion, not necessary that you have to agree with that.

[NathanKell]

From what's described above, what 1.0 is fixing is the Isp-scaling bug. However that alone will not make jet engine (or any air-breathing engine) performance more realistic. They need to fix two things 1) IntakeAir as a resource counts as fuel 2) Isp instead of thrust does not change with altitude. We're yet to know where the dev stands on this topic.

Actually, from what's described above, thrust becomes a function of density and mach. Given that, I'd be shocked if they didn't also fix both issues you described too.

[shoe7ess]

I love this mod, but I'm having a strange problem pop up. I use Realism Overhaul (along with RP-0) and the mods that surround it. All the parts work fine, but for some reason, the engine models textures are are all bugged for me. I believe the main cause is ATM caching the parts even though I changed the AJE ATM config to false, so they shouldn't be getting cached. The weirdest thing is that the parts aren't showing up as all white (which is what usually happens when there is an issue loading the models). Instead they have a strange red hue on one side.

Has this happened to anyone else? If it has, how can it be fixed?

I can screenshot the issue if needed, just let me know.

[NathanKell]

You can delete the AJE subfolder in your ATM folder / texture cache....?

[shoe7ess]

Not sure I made that fact clear enough in my original post, but I did that. For some reason it recreates and compresses the textures on launch each time. The only reason I can think why it would do this would be an outside config file that adds AJE to ATM, but their isn't one...