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

[NathanKell]

Sorry, is 1.6 built off master or the JSBProp branch?

EDIT: I committed a .25-compiled version of that branch.

EDIT EDIT: That's because you're trying my code without my files. (The extra cfg is there for a reason...)

I heartily recommend staying on the Master branch of the repo; JSBProp branch is not ready for prime time, nor for your average AJE user. I hadn't had a chance to rip it out, actually, into RealAirBreathers or whatever it should be called. Sorry about that.

Edited October 9, 2014 by NathanKell

[camlost]

Nevermind, found the problem. Yes, it was JSBProp branch

[NathanKell]

I think I edited after you posted >.>

[camlost]

Sorry, is 1.6 built off master or the JSBProp branch?

EDIT: I committed a .25-compiled version of that branch.

EDIT EDIT: That's because you're trying my code without my files. (The extra cfg is there for a reason...)

I heartily recommend staying on the Master branch of the repo; JSBProp branch is not ready for prime time, nor for your average AJE user. I hadn't had a chance to rip it out, actually, into RealAirBreathers or whatever it should be called. Sorry about that.

Quick question, can you make Turboprops with the current JSBprop implementation?

[NathanKell]

Not yet; that's waiting on ferram getting his jet code working (and, um, there was kind of an interruption called .25) since shaft power is needed. Once that's there though, it should work to hook up the JSBProp implementation as the way convert SHP to thrust (in addition to the exhaust thrust).

[Camacha]

Am I supposed to burn through my fuel like crazy and also encounter what feels like totally different behaviour? I can imagine the latter is caused by the former, shifting CoM and all.

Edit: oh, yeah, the shock cone does not seem to do much. Is that intentional?

[camlost]

Am I supposed to burn through my fuel like crazy and also encounter what feels like totally different behaviour? I can imagine the latter is caused by the former, shifting CoM and all.

Edit: oh, yeah, the shock cone does not seem to do much. Is that intentional?

I believe everything is behaving like before. you can calculate the fuel flow your self by Thrust/9.8*1000/Isp

Not yet; that's waiting on ferram getting his jet code working (and, um, there was kind of an interruption called .25) since shaft power is needed. Once that's there though, it should work to hook up the JSBProp implementation as the way convert SHP to thrust (in addition to the exhaust thrust).

How's it going? I haven't seen much activity on that project on github

[Camacha]

I believe everything is behaving like before. you can calculate the fuel flow your self by Thrust/9.8*1000/Isp

I kind of meant compared to stock. A vehicle that gladly flies around the world now barely makes it past the island runway. Is that what it should do?

Is the shock cone intake not behaving like an intake intentional? Of am I missing a minimum speed or something?

[NathanKell]

Can't speak for ferram. As for myself, weird, I've committed lots. I have things working pretty much spot on for 2-speed supercharger and for turbocharger piston engines; the problem is the R-2800, R-3350, and other latewar/postwar US engines with 2-stage *3* speed superchargers, but that just means I need to add a third boost mode. When I do that I'll also rework how intercooling/aftercooling works. Also I need to track how much ADI is used and have things overheat at high boost when it runs out, and get the temperature working right (probably have to model EGT, but JSBSim has good code for that).

What still needs work is mach effects on props. I have empirical data for helical tip mach vs Cp and vs Ct for NACA 16-series and Clark Y airfoil props, but nothing else, and also FAR doesn't model drag effects from propellers when the aircraft goes supersonic (and JSBSim models mach effects for helical *tip* mach, not across the blade). I just committed a hacky "extra drag at supersonic" thingie.

To test all this I've been making replica aircraft with 100% correct Cd0, so I can tune prop thrust to FAR's drag for an airframe of the correct Cd0.

Example:

and

F4U-4 and P-47D-22 for the record, although the latter needs some more tweaking and I need to find out its wet HP at altitude.

[NathanKell]

Camacha: Stock gives engines 16x the fuel efficiency they should have, for their rated Isp, because stock Isp->fuel flow calculations count "intake air" as part of fuel flow, whereas in real life one doesn't. So in effect non-AJE jets have 16x the Isp they should, since intakeAir makes up 15/16 of the used mass.

[Camacha]

Camacha: Stock gives engines 16x the fuel efficiency they should have, for their rated Isp, because stock Isp->fuel flow calculations count "intake air" as part of fuel flow, whereas in real life one doesn't. So in effect non-AJE jets have 16x the Isp they should, since intakeAir makes up 15/16 of the used mass.

Oh dear, it seems my kerbals will lose their legroom to an extra tank of fuel. It feels like realistic craft are not even possible this way, but it probably means I will need to fiddle a bit more.

Wat about the shock cone intake?

[camlost]

Camacha: Stock gives engines 16x the fuel efficiency they should have, for their rated Isp, because stock Isp->fuel flow calculations count "intake air" as part of fuel flow, whereas in real life one doesn't. So in effect non-AJE jets have 16x the Isp they should, since intakeAir makes up 15/16 of the used mass.

Seems like in 0.25 not only this is not fixed, but further buffed 5x

I kind of meant compared to stock. A vehicle that gladly flies around the world now barely makes it past the island runway. Is that what it should do?

Is the shock cone intake not behaving like an intake intentional? Of am I missing a minimum speed or something?

The shock cone's part name got changed, You can find the fix in the github.

You don't compare it to stock, that stock is ....e. In reality airplanes designs are very sensitive on these parameters: weight, fuel, wingload and engine. Because in stock the engines are overpowered vastly in every way, the other parts don't need to be fine-tuned at all. As a result, you get very poorly and arbitrarily-defined weight, fuel capacity and dimensions for the cockpit, fuselage and wings. But you can still put together a behemoth and still fly it, because the engines are soooooo powerful and efficient.

Now you can specify your problem by posting a pic and tell us what kind of fuel percentage, and runway TWR your design has. At least one of the two must be ridiculous.

[NathanKell]

camlost: I have not seen that in .25, and nothing in the cfg's (or testing) has shown that. Or did they tweak the jet's Isps themselves?

[camlost]

camlost: I have not seen that in .25, and nothing in the cfg's (or testing) has shown that. Or did they tweak the jet's Isps themselves?

I found that with IntakeAir stripped, the fuel flow in the engine's context menu is always 5x the real fuel flow(used to be the same value AFAIK). So I had to add a 0.2 multiplier in AJE in the late build

[Camacha]

Now you can specify your problem by posting a pic and tell us what kind of fuel percentage, and runway TWR your design has. At least one of the two must be ridiculous.

I thought I'd do an experiment. I took a Ram Air Intake, Mk1 Fuselage for Jet fuel and Pratt & Whitney F11-PW, strapped those to a big weight and ran it on full power on the runway under AJE. The tank drained in a little under 38 seconds with a thrust of 115 kN. After that I did the same without AJE, but now with a Basic Jet Engine instead (default replacement), with a thrust of 150 kN. This time it took 26:28. That's about 1:42 factor, or 4300% without compensating for thrust. When you do compensate the difference is about 1:55. Does that line up with the numbers you are seeing?

I will see if I can upload pictures the two relevant craft I was talking about later. Any specific values you need to see?

[camlost]

I thought I'd do an experiment. I took a Ram Air Intake, Mk1 Fuselage for Jet fuel and Pratt & Whitney F11-PW, strapped those to a big weight and ran it on full power on the runway under AJE. The tank drained in a little under 38 seconds with a thrust of 115 kN. After that I did the same without AJE, but now with a Basic Jet Engine instead (default replacement), with a thrust of 150 kN. This time it took 26:28. That's about 1:42 factor, or 4300% without compensating for thrust. When you do compensate the difference is about 1:55. Does that line up with the numbers you are seeing?

I will see if I can upload pictures the two relevant craft I was talking about later. Any specific values you need to see?

You also need to compensate for Isp. But like I said above, the engines becomes EVEN MORE powerful in 0.25. Whatever Squad is doing I do not understand.

[Camacha]

Right, a picture is worth a thousand words. These are the craft I was working on before. The first picture is a craft with four engines and just one fuel tank with 600 fuel. The second and third segment are inverted bays with a couple of BahamutoD cluster bombs as a payload. The two round sidepods are made of structural fuselages. If flies well, but under AJE it drains its tanks by the time it reaches the island runway, even when reducing throttle after take-off.

To mitigate the problem in my second craft I removed two engines, reverted to a more frugal engine type, added a hull tank and replaced the structural fuselages for liquid fuel tanks. I tried to reduce FAR drag by adding a tail rather than a blunt end. I then tried dialling back thrust as much as possible, helping the craft getting airborne by an altered nose-up stance, with added flaps and a different AoA for the tail fins, but despite my best efforts, I still need more than 75% thrust to make it off the runway at all. If it does it flies like a pig. Total fuel load is now 2835 and about 25% of that has been burned up as soon as it is airborne. I try to cruise at about mach 0,5-0,8 and not much more.

I understand this shape of craft requires speed, so it is relatively inefficient, but I cannot imagine real craft ever getting out of the country with this kind of fuel consumption, not to mention fly around the world. The thing is practically a flying fuel tank and still the useful range is quite limited. Is there some kind of major flaw in my design, like too little wing surface perhaps, or is something else going on?

You also need to compensate for Isp.

I figured as much.

[camlost]

@Camacha,

In real world a SR-71, which has two J-58s, takes off with around 30tonnes of fuel, so 600L for 4 x J-58 I would say that's not generous enough. Nothing is wrong with AJE, It's KSP's wrong engine model gives people illusion that 600L fuel is a lot. Needless to say in .25, they're about 80x more efficient (compared to 16x from before).

So in general, everyone should pack more fuel into a fuselage. The mk1 fuselage, which only contains 100L fuel and weighs 1.2ton, is vastly underpowered

Also Kerbal engineer and alike addons cannot display data from AJE, never trust it. Thrust and Isp always depends on altitude, speed and temperature

Edited October 9, 2014 by camlost

[Camacha]

In real world a SR-71, which has two J-58s, takes off with around 30tonnes of fuel, so 600L for 4 x J-58 I would say that's not generous enough. Nothing is wrong with AJE, It's KSP's wrong engine model gives people illusion that 600L fuel is a lot. Needless to say in .25, they're about 80x more efficient (compared to 16x from before).

I can see why the first craft might not perform as well under real world circumstances/AJE as it does in stock KSP. However, I did everything I could to improve those factors in the second aircraft including using more frugal engines and adding a huge amount of fuel, yet the range only improved marginally. I have trouble believing that this is how real aircraft would perform, because it would pretty much mean that airliners would barely make it to the border of a small country

So in general, everyone should pack more fuel into a fuselage. The mk1 fuselage, which only contains 100L fuel and weighs 1.2ton, is vastly underpowered

So if I understand correctly the engine values are right, but the contentx of the tanks are way too small for their size and weight? That would indeed explain the silly range. I must admit I assumed AJE would also fix this. Is there any mod or configuration that can be used to rectify this?

Don't take this the wrong way, I am not criticising your mod, I am merely trying to work out how I can get KSP to act as realistically as possible without being impossible

Edited October 9, 2014 by Camacha

[camlost]

Airliners usually pack 30% its weight's fuel, and they have very efficient (6000s+) turbofans, while the F110 with afterburner is only ~2000s, and they also cruise at very high altitude. Believe me I've made airliners that can cruise for 14hrs.

You should believe me about this, as I was very careful about it, unless you can shoot me numbers to prove the fuel consumption is wrong. On the other hand, you shouldn't believe in the stock at all.

[Camacha]

You should believe me about this, as I was very careful about it, unless you can shoot me numbers to prove the fuel consumption is wrong.

Again, it is not my intention to prove anyone wrong and not a matter of believing. I would just like to know how to deal with what I am seeing. Do I need different engines? Do I need different tanks with more fuel? Or are the tanks properly balanced against the engines and do my designs simply need improving?

Believe me I've made airliners that can cruise for 14hrs.

Great! Could you provide pictures or a parts list? It might help me along.

[camlost]

The simple thing is to look up some real airplane data on wikipedia, know their dimension and weight, and choose the right engine. which is also a nice learning opportunity. Generally you always need RF, or write some cfg for yourself.

I plan on writing some RO patches to bring along 'real' cockpit and fuselage data, as many of the mods out here are not well balanced.

[camlost]

camlost: I have not seen that in .25, and nothing in the cfg's (or testing) has shown that. Or did they tweak the jet's Isps themselves?

Nevermind, I made a mistake by assuming 1Unit=1L=1kg liquidFuel . Don't remember when's the last time I played without RF.

[miyuruasuka]

Again, it is not my intention to prove anyone wrong and not a matter of believing. I would just like to know how to deal with what I am seeing. Do I need different engines? Do I need different tanks with more fuel? Or are the tanks properly balanced against the engines and do my designs simply need improving?

Great! Could you provide pictures or a parts list? It might help me along.

Sorry if it's a stupid question, but do you have FAR installed? The stock aerodynamics has *MUCH* more drag than in real life.

[mdosogne]

The OP has a link to a GitHub page with the sources, but... I'm not seeing a link to download a release.

Perhaps I need another coffee?

EDIT: Never mind; it seems the "Source Code (zip)" button on GitHub contains more than the source code!

Edited October 11, 2014 by mdosogne