KintakeAir Wonky

[Geschosskopf]

Using 0.7.4. The KintakeAir provided by the KE-J65 behaves so unpredictably that using this engine is pointless. At least in testing on Kerbin. The plane is intended for Duna but it's not going there until I know it works. I'm using the TAC Fuel Balancer to load the tanks with Kethane before flying.

The plane has 2 engines. When it spawns on the runway, the resources tab shows it has 2.0 units of KintakeAir. So I take off and start climbing. Unlike regular jet intake air, the KintakeAir does not slowly decrease with altitude. Instead, at some highly variable altitude, suddenly the KintakeAir goes from 2.0 to 0.0 all at once. Instant flameout with no warning. But at least both engines flameout simultaneously so no tumble results.

Also unlike regular intake air, the KintakeAir does not gradually increase again as the plane glides lower. It stays at 0.0 until you reach some highly variable lower altitude, then suddenly jumps back up to 2.0 all at once. So now you can go back up but again the KintakeAir goes to zero all at once again, and at a different altitude than before.

On my last test flight, starting at the KSC runway, I 1st lost KintakeAir at about 12100m. It came back at 6900m, then disappeared again at 9500m, came back again at 1200m, and this time lasted to over 14000m, where I gave up on it started searching for information and previous bug reports about this issue. Finding none, I posted this.

Note that most of Duna's terrain is 3000m or more, which is like 16000m on Kerbin. So at present, I'm not even sure the KE-J65 will even work on Duna. Is it supposed to?

[Majiir]

This is intended behavior, although the exact implementation could use tweaking.

The KE-J65 intake performance improves with engine thrust and suffers from excessive airspeed, so sudden throttling-down or climbing too high will result in a loss of intake power. The engine does work on Duna, but it's challenging to use there. In all cases, the KE-J65 works much better when it's behind a slow and heavy plane so it can run at full throttle. It's a freighter engine, not a supersonic high-altitude fighter engine.

I'll look into improving the implementation so the intake behavior is more intuitive.

[Geschosskopf]

I fail to understand the reason why making a part behave in an entirely unpredictable and unreliable manner would be working as intended.

I am not trying to make a "supersonic fighter". I'm trying to make a big, slow, long-range, STOL exploration plane for Duna. But this is impossible because the engine cannot be made to work. It kicks out for no apparent reason regardless of either speed or altitude It's useless for any application.

[Geschosskopf]

OK, the above sounds a little harsh, but I was mad because I was doing my civic duty in reporting what I thought was a legit problem (the totally unpredictable behavior) only to be told it's working as intended and having this thread immediately closed. I took that as a sign no further discussion was wanted. But I hope Majiir accepts my apology for this misunderstanding.

Anyway, now I know this engine has a very specific purpose and apparently works fine for that. OK, that's great. Too bad that's not the job I wanted it to do. So I think it would help avoid future misunderstandings if the intended role of this engine was specified in the part description, so folks like me would know not to bother with it for anything else, and then think it's bugged when it doesn't work.

But that brings up the subject of the basic desire to use a Kethane-burning engine for other purposes. I would assume there are far more folks like me who don't want to move hugely heavy stuff with this engine. Instead, they want to use it on light scout planes to explore places like Eve and Duna in more safety and comfort, and at higher speed, than is possible in a rover, and without having to use a Hooligan blimp (especially now that they're so much bigger)..

So it seems to me that the Kethane pack should include smaller engines for these purposes. Given that the atmospheres of Duna and Eve are polar opposites, they each would probably need their own specialized engine. Or at least add extra intake parts so you could air hog on Duna. Then, if you want a middle-weight airiplane, you can just add more of these smaller engines.

[Majiir]

I agree with your analysis of the problem. I'd rather not introduce new parts, since Kethane is fundamentally a resources mod, not an engines mod. I'll probably do some reworking of the engine behavior and also make things more obvious and intuitive. There's also a tutorial series coming, but a jet engine tutorial might not make it into the first round.

FWIW, this has been on my radar for a while now, which is why I closed the issue.

[Geschosskopf]

Is it OK if I try my hand at tweaking the engine's parameters to make it work better for the job I want?

[Majiir]

Sure. You can modify Kethane however you want for personal use.

[Geschosskopf]

Well, if it's successful, I will send the resulting files on to you to do with as you wish.

Anyway, I think it's the intake that needs tweaking for my application so can you please explain what the parameters "BaseFlowRate", "PowerFlowRate", and "SpeedFlowRate" do? I don't see those callouts in the stock intake files.

[Majiir]

The intake produces resources at a rate proportional to BaseRate + (PowerRate * engine power) + (SpeedRate * air speed).

You can see in detail how they're used here: https://github.com/Majiir/Kethane/blob/master/Plugin/OrthogonalIntake.cs

[Geschosskopf]

Hmm....

I keep thinking that somehow that formula is double-dipping either altitude or airspeed due to using those curves, given experience on Kerbin. This, however, is complicated by the fact that the intake is always 90^ to the fuselage axis and 45^ to the left as viewed from behind. This means that effective air flow is much dependent on angle of attack. The higher you go the higher the angle of attack you need at any given airspeed. As airspeed increases, angle of attack reduces. This cycle seems to have an effect on KintakeAir.

Also, the engine lacks a rear attachment node so you can't use it singly within a stack The engine is totally unsuited to an SSTO so to get it anywhere, you need stages below it. This means you must have at least 2 engines with a central fuselage between them to attach the lower stages to. But this means you have twice the thrust you really wanted so you have to throttle even further back than you would with 1 engine, which makes KintakeAir cut out even sooner.

Provided there's any KntakeAir at 0m/s at 3000m altitude on Duna ,then the engine will at least crank up on the ground. If that's possible, then the only viable flight profile that comes to mind for a light plane is a vertical ascent at full throttle followed by a glide for however far you can get, repeat. Thus, it might be that air hogging on Duna is the best bet, modding a standard intake to provide KintakeAir instead.

What do you think?