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[1.5.1] Advanced Jet Engine v2.12.1 (Nov 11)


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19 minutes ago, blowfish said:

Nope, nothing newer.  What do you mean "better works with FAR" anyway?  Are you seeing a particular issue?

Alright, thanks. Yea, it seems dual-engine configurations don't work. Im only getting thrust from one no matter the engines or setup.

EDIT: There seemed to be a issue with Enginelight mod, removing it seems to have fixed it.

Edited by Cratzz
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  • 2 weeks later...
On 11/11/2016 at 7:00 PM, blowfish said:

I'm not sure where you're getting this "thrust would become so low" part from.  Could you cite it?

And at any rate, it shouldn't matter.  Fuel flow and air flow will be roughly proportional regardless, so there's only so much heat you can extract from the incoming air (whereas incoming temperature will keep increasing as you go faster).  You will melt the compressor eventually, there's no way around that.

Sorry I took a long time to get back to you but that would be because the maximum burning temp of hydrogen is 2800 C which can only be achieved with a perfect hydrogen oxygen mix, with air it's only 20 odd percent so your burning temp is going to be significantly lower than that in air going through the engine even after being cooled through the pre-cooler at 1750 m/s is going to be a significant percentage of that. So thrust is caused by gas expansion if you cannot heat up the incoming air significantly you get little or no thrust, also due to dragging the air through the intake and pre-cooler you would actually get net negative thrust.

That's basic rocket science.

I'm not saying that the engine would never overheat because Precoolers but under the power of the engines it should never overheat as hard as you tried short of take a drive to pick up more speed or opening up the Intakes while in re-entry.

But in normal use it should never happen because the engine would become so inefficient and the thrust so low that it shouldn't happen, and the point of faluire would not be the compressor it would be the precooler if you took such drastic measures as going into a dive or opening up the intakes while in re-entry.

Because the pre-cooler is first in the engine... well the Intake could melt but the tolerances for the Intake are much higher than the pre cooler and yes the compressor tolarance for heat would be lower than the compressor, but the compressor is quite delicate it's self given how small and light it is and how much surface area you need.

And the SR71 shows you that compressors are not as delicate as you might think as it can reach mach 3.5 which is only 30% slower, and the Saber engines have the Precooler, which is there mostly for fuel efficiency and maintaining a good thrust to weight ratio as there is unmanned SR72 which can reach Mach 6 without a pre-cooler, which can reach those speeds because it's lighter, the engine technology hasn't been revolutionized that much since the SR71.

It's just with an UAV the weight for keeping people alive is removed which is a not insignificant, obviously part of it is engines getting better, but not by that much.

Edited by etheoma
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43 minutes ago, etheoma said:

the maximum burning temp of hydrogen is 2800 C

Where does that limit come from?  Recall that the SSME's chamber temperature is closer to 3600K, and that's pretty fuel rich.

43 minutes ago, etheoma said:

air going through the engine even after being cooled through the pre-cooler at 1750 m/s is going to be a significant percentage of that.

This doc puts the air exiting the compressor at 853K, which isn't anywhere close.  That's for the SCIMITAR, true, but there's no reason to believe that the cycle is any different in air-breathing mode.

According to the real engines I've seen, the compressor will likely overheat around 1200K or so.  I think the main limitation on the compressor is that it's quite hard to cool (whereas the precooler is actively cooled by helium passing through it).  At 1200K, you can still add quite a lot of heat by combustion before encountering limits on anything downstream of the compressor.

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30 minutes ago, blowfish said:

Where does that limit come from?  Recall that the SSME's chamber temperature is closer to 3600K, and that's pretty fuel rich.

This doc puts the air exiting the compressor at 853K, which isn't anywhere close.  That's for the SCIMITAR, true, but there's no reason to believe that the cycle is any different in air-breathing mode.

According to the real engines I've seen, the compressor will likely overheat around 1200K or so.  I think the main limitation on the compressor is that it's quite hard to cool (whereas the precooler is actively cooled by helium passing through it).  At 1200K, you can still add quite a lot of heat by combustion before encountering limits on anything downstream of the compressor.

Yes but the air is cooled before the compressor. Sabre_cycle_m.jpg

Ah my bad that was Oxyhydorgen, it's 3200 but the point still stands that with air it's going to be 2210C if for example if the air is coming out of the precooler is 926.85C your trust is going to be terrible because the expansion due to heating is going to be low, now heating from -150 C to 2210 C that will give you some thrust.

Edit, the number used an air temperature of 20C so it would be higher but I don't know the math to work out exactly how much higher, but you can't just add the 2.

Edited by etheoma
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1 minute ago, etheoma said:

Yes but the air is cooled before the compressor.

I know the cycle, no need to keep posting the diagram.

19 minutes ago, etheoma said:

Ah my bad that was Oxyhydorgen, it's 3200 but the point still stands that with air it's going to be 2210C if for example if the air is coming out of the precooler is 926.85C your trust is going to be terrible because the expansion due to heating is going to be low, now heating from -150 to 2210C that will give you some thrust.

Except that

  1. after being compressed to 15 MPa, the temperature is going to be more like 400K (lower bound based on quick calculation - incoming air is cooled just above boiling point of ~82K then compressed).
  2. According to REL, the temperature of the incoming air at sea level is too low for the helium loop to drive the compressor, so heat has to be bled off after the preburner (HX3 in the diagram you posted).
  3. The ambient pressure when the vehicle is going mach 5 is going to be much lower then when the vehicle is at sea level.  Thrust increases as the ambient pressure falls away.

There's definitely somewhat of a loss in headroom, but it's not going to be as much as you say, and definitely not enough that you'd loose thrust before other things start breaking.

And I realized I didn't address some of your points from the last post, so here they are:

1 hour ago, etheoma said:

And the SR71 shows you that compressors are not as delicate as you might think as it can reach mach 3.5 which is only 30% slower, and the Saber engines have the Precooler, which is there mostly for fuel efficiency and maintaining a good thrust to weight ratio as there is unmanned SR72 which can reach Mach 6 without a pre-cooler, which can reach those speeds because it's lighter, the engine technology hasn't been revolutionized that much since the SR71.

Mach number alone can be somewhat misleading here, as total temperature actually increases with the square of mach number.  At mach 5 it's about double what it is at mach 3.5 (in kelvins).  The SR-71 managed to go as fast as it did by only compressing the air a little, and is limited by the temperature of the air exiting the compressor.  At mach 5, the air is hot enough that it would melt the compressor at the entry point (hence precooling).  The SR-72 would use a scramjet, which relies only on ram compression (although the cycle is somewhat different).

These are both aircraft intended for use in-atmosphere.  They can burn a lot of fuel if need be.  The Skylon would need to generate ~6 km/s in rocket delta-v after changing modes, so the cost of low efficiency in air-breathing mode is much higher.

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@blowfish, I've noticed that with AJE engines don't care about IntakeAir. First, I can place an intake everywhere on the vessel, even on 90 degrees rotated girder, the cosine (what is it, though?) still shows 0.98 and engines work.
Second, I've used MM to replace intake's generated resource from "IntakeAir" to a new "Uncompressed air" resource and was surprised that engines still work. Stock engines flameout in that case with "Insufficient Intake Air" reason. But with AJE they flameout only if intake is closed or absent with the reason of "Insufficient intake area", otherwise they work regardless what does intake produce.
So it seems that it is enough to have any hole of sufficient diameter anywhere on the vessel for engines to operate, and that's not right I think. Is it possible to check at least the fact that an engine has access to IntakeAir resource? I want to force a player to put a special "Turbine" part between an intake and an engine that would convert "Uncompressed air" into the old IntakeAir resource for the engine to operate, but the fact that engines don't care about IntakeAir ruins my effort.

Edited by Ser
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Correct, they don't care about intake air.

An intake rotated 90 degrees should work fine at a standstill, but the cosine should rapidly decrease as you gain speed (so eventually you will flame out).  Is this not the case?

In real jet engines, the intake and engine aren't separate components.  At subsonic speed, the engine can suck however much air it needs through the intake, although if the opening is small enough you will run into issues of course.  At supersonic speed, the shape of the intake does determine how much air it lets in, but then also many supersonic intakes adjust their shape to match flow to the air requirement of the engine.

As far as adding a "turbine" part (isn't that really a compressor), I think that would be something along the lines of procedural engines, and I've thought about that in the past but it proves to be quite complicated.

So unfortunately it looks like the way AJE works is incompatible with what you want to do at the moment.  Sorry!!

Edited by blowfish
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3 hours ago, blowfish said:

An intake rotated 90 degrees should work fine at a standstill, but the cosine should rapidly decrease as you gain speed (so eventually you will flame out).  Is this not the case?

Haven't pay attention to that, but I was able to drive along the runway about a minute with no flameout. I will be able to test that a bit later.

3 hours ago, blowfish said:

As far as adding a "turbine" part (isn't that really a compressor), I think that would be something along the lines of procedural engines, and I've thought about that in the past but it proves to be quite complicated.

So unfortunately it looks like the way AJE works is incompatible with what you want to do at the moment.  Sorry!!

Yes, that in fact is a compressor. The word "Turbine" just sounds more epic for a regular player :) I don't understand why it is that complicated. I'm not going to simulate a real compressor with all the air compression maths. My one is just a ModuleResourceConverter that converts uncompressed air into Intake Air needed for engines at the rate 1/1. All that is needed is that engines require some insignificant amount of IntakeAir resource just to check if it is available, all the rest may work as it currently does. So an engine would require that 1. Intake area is enough 2. the engine has any amount of IntakeAir, doesn't matter how much. Otherwise it flameouts. That will be more an emulation than simulation of a jet engine but still more realistic than having a fuel tank between an intake and a nozzle. What do you think?

EDIT: doing so will have an additional effect: engine would automatically require a proper flow of intake air, not allowing to place an intake on any strut connected to the vessel.

Edited by Ser
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1 hour ago, blowfish said:

You could write a patch that adds a nominal amount of intake airback to all AJE engines.  I think that would have the desired effect

Ok, if it doesn't break AJE functioning. I guess I should filter by ModuleEnginesAJEJet?

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5 minutes ago, Ser said:

Ok, if it doesn't break AJE functioning. I guess I should filter by ModuleEnginesAJEJet?

Yeah, it should be fine.  AJE removes IntakeAir because it's no longer required but adding it back in should be fine.  And yes, you'd want to target ModuleEnginesAJEJet

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On 1/25/2017 at 6:20 AM, Me1_base said:

Does AJE support QuizTechAero engines? I saw MM patches of QuizTechAero in the mod but it just doesn't work properly.

I wrote configs a while back, but they might be out of date at this point.  Haven't actually looked at them in quite some time.

5 hours ago, Inflectrum said:

A quick question about the CR-2 ramjets. What thrust are they meant to put out at minimum ignition speed?

At this point I would consider the ramjet to be broken.  I have plans to redo it, but haven't gotten around to it yet.

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16 hours ago, blowfish said:

I wrote configs a while back, but they might be out of date at this point.  Haven't actually looked at them in quite some time.

At this point I would consider the ramjet to be broken.  I have plans to redo it, but haven't gotten around to it yet.

Does this include the J58?

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4 hours ago, Inflectrum said:

Does this include the J58?

No.  At the moment the J58 is modeled as a pure turbojet.  This does mean that it's behavior at higher Mach numbers isn't perfect - it should have somewhat more thrust than it does, but I haven't found that to be a problem in the craft I've build.  It's still mostly a turbojet anyway, only ~20% of the air bypasses the main combustion chamber.

1 hour ago, Me1_base said:

I saw 4 types of air inlet in the cfg, what are the differences between them? Thrust of engines are affected by the type of inlet significantly.

It's what speed they're optimized for.  If you right click the part in the part list, the info display should tell you what flight condition they work best at.

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  • 2 weeks later...

@blowfish, is there any chance for AJE to be compatible with RealPlume? I tried to find that out by looking at AJE MM patches and RealPlume's ones but couldn't understand whether the mods were compatible some day or not. Currently RealPlume eats up all the ModuleEngines* including ...AJEJets and turns them back into ModuleEnginesFX thus killing AJE functionality. The only thing I could do about that is to manually add NEEDS[!AJE] to every RealPlume's turbojet patch. Maybe there's a solution that would let me keep AJE functionality and RealPlume effects for the same engines?

Edited by Ser
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12 minutes ago, blowfish said:

If RP is converting back to ModuleEnginesFX, then the fix needs to be on RealPlume's side.  I'll build for compatibility where possible, but trying to fight other mods' patches is going to lead to issues.

I try to understand is it worth to bother with. What I like about RealPlume is engine sounds and plumes. I saw that AJE patches do something with engine effects too so does AJE already implement proper afterburn plumes and engine sounds or should I still use RealPlume to increase coolness?

Edited by Ser
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2 minutes ago, Ser said:

I try to understand is it worth to bother with. What I like about RealPlume is engine sounds and plumes. I saw that AJE patches do something with engine effects too so does AJE already implement proper afterburn plumes and engine sounds or should I still use RealPlume to increase coolness?

AJE mostly just modifies the stock effects to work better with AJE.  It doesn't change how they look.

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Just now, blowfish said:

AJE mostly just modifies the stock effects to work better with AJE.  It doesn't change how they look.

Ok, I've got it. I guess if I keep ModuleEnginesFX modified by RealPlume along with AJE's ModuleEnginesAJEJet that would most likely mess the things up because of re-enabling stock engine behavior, right?

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50 minutes ago, Ser said:

Ok, I've got it. I guess if I keep ModuleEnginesFX modified by RealPlume along with AJE's ModuleEnginesAJEJet that would most likely mess the things up because of re-enabling stock engine behavior, right?

Well you can't have both.  A module can only have one name (I think if there are multiple then it will use the first).  But yeah, now that I think about it, RealPlume would need to be configured specifically to work with AJE (at least for anything with an afterburner).

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