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

[Hodo]

It‘s DRE's effect. The DRE's heating mechanism requires you to throttle down a little bit. I'll set HeatProduction=0 to all AJE engines next version.

Yeah it is definately DRE... now that I have broke my KSP, I am attempting to fix it.

[NathanKell]

Yes, 99% of what DRE changes in parts is giving them sane max temperatures. I invite you to find solar panels that can heat up fine to 3600C

Engines mostly get capped at ~1800C, and since that's about half their original max temp, their heat production is also halved.

[camlost]

Yes, 99% of what DRE changes in parts is giving them sane max temperatures. I invite you to find solar panels that can heat up fine to 3600C

Engines mostly get capped at ~1800C, and since that's about half their original max temp, their heat production is also halved.

I see what’s the problem. DRE’s config sets heat production to moduleengines not moduleenginefx that’s why f100 is having doubled overheating rate

[Hodo]

I just did a temp fix now that I know what the problem is.

I set this in the cfg for the F100

heatProduction = 175

[Shad0wCatcher]

@Fractal perhaps speed wall would be a more apt description? Either way the same effect occurs; rapid and immediate overheating of engines above a certain speed; causing rapid unplanned disassembly of the entire propulsion section as soon as any throttle is applied.

[Hodo]

Ok I have been testing and testing, but with .6 it seems most of the aircraft I built even ones that are nearly perfect in the FAR simulation don't have the power to get past mach 1 let alone mach 2 with any of the jet engines in this. I have tried using the F100, F79 and F119, all of them pretty much quit producing any usable amount of power around .965 mach.

I am testing between 7km-10km altitude, WELL within realistic test ranges for aircraft. I am using the mods in my sig. The newest ones are Real Fuels, RSS+Kerbin rescale (so it doesn't turn the Kerbin system into the Earth system), and engine config plugin for real fuels.

I know I can make supersonic and hypersonic aircraft in FAR, I have done it several times, but in this nothing seems to work. Shy of slapping 10 F100s on the back of something.

EDIT- Side note; Why did you rescale the B9 landing gear?

Edited February 27, 2014 by Hodo

[camlost]

Ok I have been testing and testing, but with .6 it seems most of the aircraft I built even ones that are nearly perfect in the FAR simulation don't have the power to get past mach 1 let alone mach 2 with any of the jet engines in this. I have tried using the F100, F79 and F119, all of them pretty much quit producing any usable amount of power around .965 mach.

I am testing between 7km-10km altitude, WELL within realistic test ranges for aircraft. I am using the mods in my sig. The newest ones are Real Fuels, RSS+Kerbin rescale (so it doesn't turn the Kerbin system into the Earth system), and engine config plugin for real fuels.

I know I can make supersonic and hypersonic aircraft in FAR, I have done it several times, but in this nothing seems to work. Shy of slapping 10 F100s on the back of something.

EDIT- Side note; Why did you rescale the B9 landing gear?

You made supersonic aircrafts in FAR because the stock engine performance is overpowered, which is the whole point of this mod. As you climb to high altitude the drag is reduced but thrust is not, making breakage of sound barrier very easy--you just climb up. However in real life the thrust also reduces as the air gets thinner. The thrust loss you report is altitude related, not velocity related. Actually for these turbojets and low-bypass turbofans the max thrust is around Mach 2.

An aircraft's speed is determined by thrust and drag, the latter part is done by FAR. I think FAR is a little bit more draggy than realism, but I was still able to reach Mach 1.6 with two F100s, and Mach 3 with two ramjets. Assuming your installation is correct this is a design-specifc problem.

[Fractal_UK]

In stock KSP, the aircraft are so overpowered they fly far more like rockets than like aircraft, you'll be hard pressed to find an aircraft that doesn't have TWR > 1, often it might be multiples of this. Realistically, you'd expect a fighter to have a TWR of ~1 (often marginally greater than 1) while an airliner might be ~0.3. To go a bit more space oriented, Skylon in atmospheric operation would be ~ 0.75. The fact that the thrust of the stock aircraft engines is so high is one reason that it appears that reducing the isp by ~16x isn't sensible. Once you bring the thrusts into a sensible regime and kick out the velocity curves, it all begins to make sense.

All this work here represents a much needed change in my opinion.

Edited February 27, 2014 by Fractal_UK

[Hodo]

You made supersonic aircrafts in FAR because the stock engine performance is overpowered, which is the whole point of this mod. As you climb to high altitude the drag is reduced but thrust is not, making breakage of sound barrier very easy--you just climb up. However in real life the thrust also reduces as the air gets thinner. The thrust loss you report is altitude related, not velocity related. Actually for these turbojets and low-bypass turbofans the max thrust is around Mach 2.

An aircraft's speed is determined by thrust and drag, the latter part is done by FAR. I think FAR is a little bit more draggy than realism, but I was still able to reach Mach 1.6 with two F100s, and Mach 3 with two ramjets. Assuming your installation is correct this is a design-specifc problem.

I have tried slapping two SABRE S engines on a 15ton aircraft, with minimal drag and wing surface. A manned missile for lack of a better term. The aircraft on jet power of the SABRE engines topped out at mach 2.1 before needing to switch over to rockets at 18km ASL.

The same aircraft rebalanced for the F100s made it to mach 1.1. It was down to 20-25kn of thrust per engine at that speed using afterburner. Same altitude as above.

The RAMJET starts to lose part between mach .9 and 1.4. It will regain power if I use a rocket to push the aircraft past mach 2, but it does not maintain the thrust needed after the rocket is disengaged.

Do you have pictures or videos of your aircraft so I can compare them to what I have.

[camlost]

In stock KSP, the aircraft are so overpowered they fly far more like rockets than like aircraft, you'll be hard pressed to find an aircraft that doesn't have TWR > 1, often it might be multiples of this. Realistically, you'd expect a fighter to have a TWR of ~1 (often marginally greater than 1) while an airliner might be ~0.3. To go a bit more space oriented, Skylon in atmospheric operation would be ~ 0.75. The fact that the thrust of the stock aircraft engines is so high is one reason that it appears that reducing the isp by ~16x isn't sensible. Once you bring the thrusts into a sensible regime and kick out the velocity curves, it all begins to make sense.

All this work here represents a much needed change in my opinion.

Also the TWR people often talk about is the (static thrust at sea level)/(max takeoff weight). Actual thrust would change depending on altitude and velocity, and actual weight will reduce as fuel is burnt.

[Hodo]

Ok did some more testing after re-reinstalling KSP and all of my mods, now the F100 tops out at about mach 1.6 with the test craft, which is about right for the amount of drag that craft has. May have been a conflict somewhere in one of my mods killing the power based on speed.

[Hodo]

One minor bug I have found.

The all of the jet engines with after burner do not generate electricity when in non-afterburning mode.

[Azimech]

BMW 801!! Great! But, is in any way the single-stage two-speed supercharger taken into account?

In the Focke-Wulf 190 A-8 with the BMW 801 D-2, the service ceiling was 11,4 km. The top speed was 182 m/s at 6 km.

One of the most advanced engines of WW2, the 801 had mechanical fuel injection and a hydraulic/electrical/mechanical computer called Kommandogerät, which controlled propellor pitch, mixture, supercharger stage and ignition timing, the pilot only had one lever: throttle.

The Daimler DB601/603/605 in the Bf109 also had mechanical injection but used a very elegant and superior solution for the supercharger: a hydraulic clutch that worked with RPM, manifold pressure and ambient pressure.

Most british and american engines used carburators and manual operated superchargers, with the few exceptions of types using turbochargers (P38, P47) which were superiour to most other engines.

[camlost]

BMW 801!! Great! But, is in any way the single-stage two-speed supercharger taken into account?

In the Focke-Wulf 190 A-8 with the BMW 801 D-2, the service ceiling was 11,4 km. The top speed was 182 m/s at 6 km.

One of the most advanced engines of WW2, the 801 had mechanical fuel injection and a hydraulic/electrical/mechanical computer called Kommandogerät, which controlled propellor pitch, mixture, supercharger stage and ignition timing, the pilot only had one lever: throttle.

The Daimler DB601/603/605 in the Bf109 also had mechanical injection but used a very elegant and superior solution for the supercharger: a hydraulic clutch that worked with RPM, manifold pressure and ambient pressure.

Most british and american engines used carburators and manual operated superchargers, with the few exceptions of types using turbochargers (P38, P47) which were superiour to most other engines.

Ok apparently you know a lot so I'll tell you what the current approach is and maybe you can help me figure out a better way. RPM doesn't exists. The thrust is calculated according to the power-thrust relationship mentioned in the material I linked in the OP. Power is a constant value. Propeller efficiency is 85% at >40m/s. Below 40m/s the thrust is linear to speed.

In reality how does power change with altitude? How does turbocharger affect the power?

[Hodo]

In reality how does power change with altitude? How does turbocharger affect the power?

I can answer that part pretty easily as I deal with cars a lot. Turbos are nothing more than exhaust gas driven compressors. They can increase the air pressure inside the intake manifold to above ambiant pressure to maintain or increase power with a good air to fuel ratio (usually around 14.7:1). A supercharger works pretty much the sameway but is mechanically driven and often robs power from the engine because of the mechanical linkage to the engine to work the compressor blades. Granted it isn't a great deal of power loss compaired to the power gains. But superchargers have a much more straight power curve than a turbocharger. But you have several types of superchargers and really only one type of turbo. There are twin screw, centrifigual, and roots style superchargers. While the one type of turbocharger is the centrifigual style.

In short,

Turbos increase boost over atmospheric pressure based on exhaust speed. More exhaust = more power

Superchargers increase boost over atmospheric pressure based on crankshaft speed and gearing. Faster the engine turns = more power.

[Pds314]

Actually, the default jets are NOT 15 times as efficient as they could realistically be. Remember that even a turbojet only pulls in 20% O2, 80% inert gas. Jet fuel+O2 is only 1/4th the overall mass exiting the back side of the engine, but what does go out comes out at half the exhaust velocity as it would in a pure O2 atmosphere. So overall, they are 4x as efficient as a rocket in a pure O2 atmosphere, and 8x as efficient as a rocket in Earth's atmosphere. In other words, the maximum possible exhaust velocity of a 100% efficient turbojet is about 2300 m/s, as opposed to 4600 m/s for pure jet fuel and O2 (yes, jet fuel, not H2. Most jets and rockets aren't quite that efficient however.)

So the maximum functional Isp is 2300/9.8*16=3755.

And of course, there are bypass engines that are more efficient, if an engine took 143 units of air in for every unit of fuel burned (much higher than most bypass engines), the maximum Isp should be 11265 or so (and the actual exhaust velocity would be up to 766.667 or so).

So realistically, turbojets are 3 or 4 times as efficient as they should be, but not 15.

[camlost]

A jet engine's thrust is not equal to exhaust vel/g

[ferram4]

The reason that the jets are 16 times as efficient as they should be (not 15) is that the jet engine burns 1 unit of fuel for every 15 units of intake air, both of which have the same density in this setup. Isp for jet engines is defined based on mass flow of fuel. The ModuleEngines and ModuleEnginesFX code defines Isp based on total mass flow through the engine. So due to the difference in the definition of Isp used in real life (which was also used for specifying the jet's Isps) and the definition of Isp used by the ModuleEngines code, the code is burning 1/16 the amount of fuel it should be burning, since it's counting the mass flow of air in the calculations even though that's supposed to be taken for granted.

The error is due to the fact that the Isp numbers reported by the jet engines(stock at least) are bogus. They run off of a different definition of Isp than that used to rate air-breathing jet engines, and that's why the engines are more efficient than they should be.

[Azimech]

But superchargers have a much more straight power curve than a turbocharger.

True for a car, totally opposite for an airplane.

In a car you choose your speed with changing your RPM. In a plane you choose a fixed RPM (maximum torque) and change your speed by changing manifold pressure and propellor pitch. An increase in altitude makes a supercharger running at low gear less efficient, you see a drop in manifold pressure. That's why they used gears to increase the RPM of the supercharger above a certain altitude. The turbocharger provides a near constant boost from sea level all the way up, until max RPM is reached (around 10K during the 1940's) after which manifold pressure dropped as well.

[Azimech]

Ok apparently you know a lot so I'll tell you what the current approach is and maybe you can help me figure out a better way. RPM doesn't exists. The thrust is calculated according to the power-thrust relationship mentioned in the material I linked in the OP. Power is a constant value. Propeller efficiency is 85% at >40m/s. Below 40m/s the thrust is linear to speed.

In reality how does power change with altitude? How does turbocharger affect the power?

It's best to have it visually, these charts provide a lot of info: http://www.wwiiaircraftperformance.org/fw190/fw190-a8-level-speed-13nov43.jpg

It roughly translates as "horizontal speed at altitude"

Drehzal means engine RPM

Ladedruck means manifold pressure, "ata" is a non SI unit roughly the same as atm.

The decrease in speed between 1 and 3 km is the result of the supercharger having less ambient pressure to compress and feed to the engine, but too much ambient pressure to be able to switch to second gear. It would increase boost above safety level and causes engine damage.

More charts: http://www.wwiiaircraftperformance.org/fw190/fw190a8.html

The same basic principles are valid for the Rolls Royce Merlin, of course.

[Hodo]

True for a car, totally opposite for an airplane.

In a car you choose your speed with changing your RPM. In a plane you choose a fixed RPM (maximum torque) and change your speed by changing manifold pressure and propellor pitch. An increase in altitude makes a supercharger running at low gear less efficient, you see a drop in manifold pressure. That's why they used gears to increase the RPM of the supercharger above a certain altitude. The turbocharger provides a near constant boost from sea level all the way up, until max RPM is reached (around 10K during the 1940's) after which manifold pressure dropped as well.

I am not sure if I said it in my previous post but each style of supercharger is different in how it creates boost and when. A twin screw setup is very flat and controled and will go up with the RPM of the engine till it reaches its max gear limited speed. The Roots style is very much like the twinscrew but suffers from a much lower top end production of boost than the twin screw.

The Centrifugal is very much like a turbo, and many WWII aircraft used this style of supercharger as it was the smallest most compact design but has a very sharp power curve. Which can be akin to the turbo lag of a turbocharged engine.

On the topic of these engines, I feel I may have to alter the cfgs in this mod because after doing some more reading I confirmed what I had feared, the engines in this are outdated in specs. The current as of 1989 PW-F100-229 which is used by the F-15E and the F-16s now creates 80kn of dry thrust and nearly 130kn of thrust in afterburner. And the F119s create to little thrust also, they are listed at over 150kn of thrust in afterburner.

I have also run into another issue. My test aircraft I mounted a SABRE S engine on it. I know they are not fully supported yet but I can repeat the same problem with the Turbojet/ramjet. I climb under the power of the two F100s to my test altitude of 10-15km ASL. I then level off to level flight, and accelerate to 300m/s or better on the F100s, engage the SABRE-S or the turbojet engine. They both create power as the aircraft accelerates till it hits mach 1.7-1.9. Then they begin to sharply drop off in power. So bad in fact that it begins to slow down the aircraft and that reduces the power created by those engines. I have tried switching over to closed cycle on the SABRE-S and using it as a rocket to accelerate passed mach 3, and then switch over to the jet mode again, and it goes from creating over 200kn of thrust to less than 10kn of thrust.

I use a pair of divertless intakes on the sides of the body of the aircraft as a source for air for the engines. The airflow speed on inlet is over 600m/s when the ramjet or the SABRE is engaged in open cycle.

Edited March 2, 2014 by Hodo

[kellven]

Only read the Op, and the one above, just wanted to mention a couple things. First, that link to the workthrough of propeller operation probably isn't really what you want, you should probably be using combined blade element and momentum theory if you're trying to get any values in flight. It ends up being a non-deterministic equation, but it can be reasonably well solved running it twice in a newton iterator loop. Find a good book on helicopter aerodynamics if you want the full equations.

Second thing was that jet engine thrust is supposed to fall off when you exceed their operational velocity curve same as any other real atmospheric engine, not sure what exactly you were expecting Hodo.

Almost forgot, back when they came out, I dug around the air intakes, and at least back then, they were creating a magical 100m/s induced velocity without requiring power, and had a very loose interpretation of intake vs orientation.

[Hodo]

The thing is, engines that are supposed to generate more thrust at higher speeds don't.

Like the RAMJET engine starts to generate thrust at .3mach, but then peaks out at mach 1 then sharply dies before mach 2. Which is not at all how that engine works.

The SABRE has the same problem, and the F100 gets to mach .9 before it starts to lose power and is a paper weight around mach 1.3. I can tell you now a F-15C can do a fair bit better than mach 1.3 with two of those engines. IMy test aircraft is the same weight as the F15C Eagle, and is roughly the same size, yet those two F100s which also power the F15C to mach 2+ barely get this aircraft over mach 1.5 at the same altitude.

[camlost]

Only read the Op, and the one above, just wanted to mention a couple things. First, that link to the workthrough of propeller operation probably isn't really what you want, you should probably be using combined blade element and momentum theory if you're trying to get any values in flight. It ends up being a non-deterministic equation, but it can be reasonably well solved running it twice in a newton iterator loop. Find a good book on helicopter aerodynamics if you want the full equations.

Second thing was that jet engine thrust is supposed to fall off when you exceed their operational velocity curve same as any other real atmospheric engine, not sure what exactly you were expecting Hodo.

Almost forgot, back when they came out, I dug around the air intakes, and at least back then, they were creating a magical 100m/s induced velocity without requiring power, and had a very loose interpretation of intake vs orientation.

Well I took that theory as a simple and relatively-realistic solution to model propeller thrust. Blade element theory is just beyond my capability. Even if what you proposed is done there's still important effects like induced velocity. I know propellers' been thoroughly studied and I would be cool if KSP could be like X-plane but I still don't see myself prioritize on that.

[Hodo]

Just noticed there is a more updated version out, I will try that out tonight before I go and start fiddling around with cfgs.