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


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1 hour ago, etheoma said:

Err know this was a long time ago but if anything the rocket ISP is too low on the wiki for the Skylon it says the Saber engines have a specific impulse of 460 the KSP Saber is 340... if anything the specific impulse for the air breathing mode is too high the specific impulse on the page for the air breathing engines is 4100, but I must admit the engines do not seem to really ever exceed 4100 Specific impulse in real usage at maximum throttle.so it's probably about right for the air breathing part.

 

I wondered my craft was having to weight 108 tons more than the actual skylon when I was cheating and increased the heat tolerance of procedural tanks and used cyro balloons so my craft should be lighter than the proposed Skylon  not heavier.

Like super seriously I'm having to carry 273 Tonns of liquid Oxygen if I only have to cut that by 1/3 that means I can cut back of the hydrogen as well and also the containers which effect my final weight which then give me much more bang for the bunk.

That difference in ISP is MASSIVE!!! I could probably get the hole craft down to 200 - 250 Tons after that point I would go to using the proper heat shielded procedural parts which would bring me back upto 325 tons~ which is still as lot better than 433 Tons

And who should I speak to about this inconsistency so I can at least get if fixed on my install if not just plain old just getting it fixed.

The ISP of 460s is on LH2.  For balance with denser fuels in a smaller solar system, 340 is about right.  If you're using a mod that changes to LH2 and not seeing a change in rocket-mode Isp, well, that's the responsibility of whatever mod is changing the fuel (not AJE)

What they give as the air-breathing Isp seems to depend on the source somewhat.  The most recent sources I've seen give 4000-9000s.

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I personally would love to see precoolers actually being usefull/ wouldbe needed to get anything to go faster then mach 3,  maybe have them cut off a sertate amount of heat from the engine when in use? But that might mean a whole rewrite of AJE's code sense last I heard AJE directly relates speed/ atmo density to heat 

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11 minutes ago, Tidus Klein said:

I personally would love to see precoolers actually being usefull/ wouldbe needed to get anything to go faster then mach 3,  maybe have them cut off a sertate amount of heat from the engine when in use? But that might mean a whole rewrite of AJE's code sense last I heard AJE directly relates speed/ atmo density to heat 

It doesn't make sense though.  Either the engine needs a precooler to operate at any speed, or it doesn't work with a precooler.  In the case of the SABRE, heat extracted in the precooler is a major component (and at higher speeds nearly all of) the energy that goes into driving the compressor (the helium loop extracts heat from the precooler and the preburner, dumps waste heat in the incoming fuel, and uses the resulting work to drive the compressor).  It might be possible to have a methane-powered engine where the fuel is pumped directly through the precooler, but AJE doesn't have anything like that currently.

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22 minutes ago, blowfish said:

It doesn't make sense though.  Either the engine needs a precooler to operate at any speed, or it doesn't work with a precooler.  In the case of the SABRE, heat extracted in the precooler is a major component (and at higher speeds nearly all of) the energy that goes into driving the compressor (the helium loop extracts heat from the precooler and the preburner, dumps waste heat in the incoming fuel, and uses the resulting work to drive the compressor).  It might be possible to have a methane-powered engine where the fuel is pumped directly through the precooler, but AJE doesn't have anything like that currently.

Aaaa dident know thats how it worked, thank you, so only the saber could use the precooler

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On 11/8/2016 at 4:56 PM, blowfish said:

The ISP of 460s is on LH2.  For balance with denser fuels in a smaller solar system, 340 is about right.  If you're using a mod that changes to LH2 and not seeing a change in rocket-mode Isp, well, that's the responsibility of whatever mod is changing the fuel (not AJE)

What they give as the air-breathing Isp seems to depend on the source somewhat.  The most recent sources I've seen give 4000-9000s.

@blowfish Yeah as you can see I posted on RO as you replied to me there. I hope someone does make the change because the engines are completely unbalanced with RO. With that changed I managed to get the craft almost exactly right, it's 7,000 kg over but that's probably just inefficiencies in my launch profile, plus to balance the craft I needed I needed to add 2,100 kg of lead ballast at the tip which the LH2 to carry that extra weight would easily account for the extra 4,900 kg.

If I could get rid of it I would probably be lighter than the actual craft.

Edited by etheoma
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@blowfish Also I would like to point out to a point you made a while ago to the a question I asked a while ago, the Skylon engines wouldn't actually explode or melt with a speed gained under there own power because before then the incoming air becomes faster than the hydrogen can burn inside the small area of the SABRE engine.

This is why proposed Scramjets that can reach orbit there hole bodies are used to burn the hydrogen because you need a long engine for the fuel to burn at like mark 20~ or you need to slow it down which the reduces the efficiency of the engine, Skylon does do this but there is a limit to how much you can compress the air before you have net 0 or negative thrust... ok not negative thrust but negative acceleration.  

If you were to say for example open the intakes and start the engine while de-orbiting maybe you would destroy the engine but it wouldn't blow up... that's just probably a limitation of the game that you can't just render parts inoperable but likely as long as you pre-chilled the engine with the hydrogen fuel you probably wouldn't even damage the engine as it has to be more heat resistant than the craft because as you might be aware hydrogen has a maximum burning temp of 2800C which the engine must be able to survive that at least and there for is more heat resistant than most heat resistant parts as long as your chilling it.

So yeah the reason they can't go faster than Mark 5.5 isn't heat it's that the thrust provided is not enough to speed you up any longer because the air is traveling into the engine too fast to allow the hydrogine to burn or you lose net thrust by having to slow down the air too much.

This is why they used hydrogen rather than kerosene both reasons for using it is because it burns faster, so it give your higher specific impulse and can produce more thrust at higher speeds.

It's a change I would suggest making because I'm sick of my engines blowing up because I'm not paying attention to the speed of the craft because I'm already trying to balance a car on a needle for the sake of "realism" when it's not realistic.

Edited by etheoma
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As for avoiding explosions, there are a couple of features I've thought of.  One is auto-throttling to avoid compressor overheat, another is (specifically for the SABRE) auto-switching the engine mode when the compressor temperature gets close to the limit.

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10 hours ago, blowfish said:

Actually the sources I've seen suggest that the SABRE's is limited to about Mach 5.5 by compressor heating.  Temperature rises a lot with Mach number and the cooling loop/fuel can only absorb so much heat.

Erm well I know it was one or the other but in both cases it's not that the engine would break it's that the thrust becomes non existent due to either the heat being so high that the burning of the hydrogen become a small amount of the heat that is in the engine so therefore the thrust become non existent or that the air is traveling through the engine too fast, I can't remember which one it is but either way it's not because the engine will break.

I may have got the reason why they didn't use kerosene mixed up with the reason the craft could only go so fast on air breathing mode. But as said I am sure either way that the engine would not become inoperable under it's own power, because the thrust would be so low at that point that it wouldn't matter.

Edited by etheoma
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53 minutes ago, etheoma said:

Erm well I know it was one or the other but in both cases it's not that the engine would break it's that the thrust becomes non existent due to either the heat being so high that the burning of the hydrogen become a small amount of the heat that is in the engine so therefore the thrust become non existent or that the air is traveling through the engine too fast, I can't remember which one it is but either way it's not because the engine will break.

I may have got the reason why they didn't use kerosene mixed up with the reason the craft could only go so fast on air breathing mode. But as said I am sure either way that the engine would not become inoperable under it's own power, because the thrust would be so low at that point that it wouldn't matter.

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.

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5 hours ago, notgoogle said:

Is it purposeful that I can never seem to get even close to idle on any of the engines? With the TF34 on zero throttle (confirmed by right-clicking engine) I can never seem to get lower than 10 kN.

Welcome to the forums!  Yes, it's purposeful.  Jet engines need to have air flowing through them even at idle, meaning that they will produce thrust.

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4 hours ago, Ser said:

@blowfish, it's heard that there's some stable dev version of FAR on GitHub. Is the AJE version from KSP_1.2 branch worth a try with it or it's not advised?

It was working the last time I checked.  You'd need to do the same for SolverEngines to make it work though.

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  • 3 weeks later...
36 minutes ago, Murican_Jeb said:

So how excatly do you guys covert kW to kN for realistic preformance?

There is data on various propellers in AJE, which converts the shaft power and rotational speed into thrust.  @ferram4 would probably know more about that than I would though.

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Just now, blowfish said:

There is data on various propellers in AJE, which converts the shaft power and rotational speed into thrust.

Okay but my question was

40 minutes ago, Murican_Jeb said:

So how excatly do you guys covert kW to kN for realistic preformance?

 

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9 hours ago, Murican_Jeb said:

So how excatly do you guys covert kW to kN for realistic preformance?

There is no universal equation that can be used for each propeler engine. You need to know length, width, AoA of each blade and number of blades used in propeler to calculate useful thrust. While propeler rotate, raw energy from engine is used to create longitudinal thrust force, but at the same time you have lateral drag force that is actualy unwanted and it is lost energy from engine.

Pretty much same thing as it is with aircraft wing AoA. More AoA on wing gives you more lift upward, but also at the same time cause drag in longitudinal direction of motion.

At the same time raw engine power is not constant on each altitude. More you climb up, less power you can have from piston engines due to lack of air(oxygen). Usage of turbochargers in piston engines helps with that to some degree, but there is still limit in altitude where it can help to maintain raw engine power.

On top of that, as you climb up and air density(preassure) become lower and lower and propeler become less and less efficienty simply because there is not enough air particles in air "to grab" and push in longitudinal motion.

I haven't closely inspected code and table data provided by blowfish, so I can only assume that data in table represent curvature points how propeler blades perform at some altitude and craft speed.

I assume that you need that info to find out how much thrust very first planes were able to provide. Unfortunately there is not enough data (usualy from wikipedia) for their propelers to be able to calculate thrust in a way it is done in AJE code (only for some engines). What you possible can do is very rude estimation if you assume that early planes were have TWR ratio somewhere between 0.15 and 0.30. TWR ~0.30 is actualy extremly good one for more modern aircrafts post WWII area. So, using craft weight data and rude assumption of TWR you can calculate how much of useful longitudinal thrust some craft possible have.

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  • 3 weeks later...
4 minutes ago, Murican_Jeb said:

@blowfish Wait. FAR isn't updated.

How will it work?

 

On 5/15/2016 at 6:49 PM, blowfish said:

AJE does not explicitly depend on Ferram Aerospace Research but has not been tested without it, and you will probably think that your engines are very underpowered in stock aero.

There are beta builds of FAR available, and while I can't recommend them for general consumption, some may want to go that route.  Also as a general matter of getting RO's dependent mods up to date I thought it was a good idea to release changes that I had mostly been sitting on for months.

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  • 2 weeks later...
On 2016-11-16 at 4:17 PM, blowfish said:

It was working the last time I checked.  You'd need to do the same for SolverEngines to make it work though.

Hello, i have tried the devbuild of FAR with the correct version of MFI, and it works with the AJE v2.7.3 and SolverEngines v3.0 but is there a devbuild for those latter that's newer, that better works with FAR? Thank you.

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5 minutes ago, Cratzz said:

Hello, i have tried the devbuild of FAR with the correct version of MFI, and it works with the AJE v2.7.3 and SolverEngines v3.0 but is there a devbuild for those latter that's newer, that better works with FAR? Thank you.

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

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