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

[camlost]

I find it funny that building an SR-71-style plane in KSP w/ AJE and RealFuels is how I figured out how to fly the realistically-modeled one in X-Plane -- have to flatten out at 10km and build up speed before climbing up to cruising altitude.

Oh, I never passed M1.5

BTW, do you know if XP's supersonic aerodynamics' realistic or not

[jrandom]

Oh, I never passed M1.5

BTW, do you know if XP's supersonic aerodynamics' realistic or not

I'm no expert, but there's definitely mach tuck and other behaviors I've also witnessed in FAR, and FAR is designed by an expert.

[camlost]

Seems like in XP10 the SR71 max out at only M2? I looked at the engine setting interface in Planemaker.exe, their engine is probably less powerful than AJE's J58

[NathanKell]

It may well not support a variable Compressor Pressure Ratio. Been a while since I tried X-Plane...

[DaMichel]

@Damichel, I never thought that would worked! Because the SABRE S has a smaller TWR than SaBRE M. Also I found that the SABRE M had 2920kN in rocket mode, which is weird because it should be 1350kN. I corrected that in the dev version on github. Another thing is that I think the RAPIER should use LqdMethane instead kerosene (which is ridiculous)

It was a close call. I didn't realize that the Sabre M have higher TWR, but i wanted to build small anyways. I had DRE running, too. At some point this almost proved fatal as the forward tank temperature reached a critical level. It was already in rocket mode, ca. Mach 8 in 40 km altitude. No way to climb higher without accelerating ... Indeed, previously i burned up a couple of times Procedural Parts really need a heat shield.

I find it funny that building an SR-71-style plane in KSP w/ AJE and RealFuels is how I figured out how to fly the realistically-modeled one in X-Plane -- have to flatten out at 10km and build up speed before climbing up to cruising altitude.

It kind of makes sense though. The faster you fly the more air the engine gets to burn, so the higher the thrust, right?

I found if you climb real high there can be a state where your thrust equals drag so you cannot accelerate any more. But if you dive a little, thrust increases and you can actually go faster. Well actually i learned about diving here on the forum and tried to apply it to my space plane flying and it really worked.

For my last ascent i did it to go supersonic. But after that i monitored engine thrust and adjusted my climb rate so that it would stay between 100 - 125 kN per engine. That way i climbed slowly and never stopped accelerating. Not sure if most efficient (is it?) but it worked evidently.

Edited November 12, 2014 by DaMichel

[Iskierka]

The diving technique works (and is often more efficient, it was a common technique for breaking Mach 1 in both Concorde and the SR-71) because of something known as specific excess power, which is how much power the aircraft can deliver versus power required to maintain steady level flight. Around Mach 1 due to increased drag, there's effectively a throat of reduced SEP that gives a narrow and difficult gap to pass through. However, the aircraft can still get much excess power just a bit slower just before this throat - so it's often better to climb high while subsonic with plenty of power, then enter a dive, which will convert altitude to speed while your engines keep thrusting, pass through the throat quickly, then climb again after you are no longer restricted by the increased M=1 drag.

[jrandom]

The faster you fly the more air the engine gets to burn, so the higher the thrust, right?

I found if you climb real high there can be a state where your thrust equals drag so you cannot accelerate any more.

When I first installed AJE, that's the wall I kept hitting, until finally it clicked that "to go faster, first you must go faster".

[kcs123]

The diving technique works (and is often more efficient, it was a common technique for breaking Mach 1 in both Concorde and the SR-71) because of something known as specific excess power, which is how much power the aircraft can deliver versus power required to maintain steady level flight. Around Mach 1 due to increased drag, there's effectively a throat of reduced SEP that gives a narrow and difficult gap to pass through. However, the aircraft can still get much excess power just a bit slower just before this throat - so it's often better to climb high while subsonic with plenty of power, then enter a dive, which will convert altitude to speed while your engines keep thrusting, pass through the throat quickly, then climb again after you are no longer restricted by the increased M=1 drag.

Exactly my thoughts about it. That is how I was thinking when I was started to design aircraft. I didn't folow other peoples rules to put low profile delta wings some engines and control surfaces, all with high TWR. Instead I have made something that could be called as streched delta wing. Similar shape, but with lot more L/D ratio that suits better to some glider planes, rather then fighterplanes. MJ shows max TWR with empty tanks like 0.8 in SPH editor, but once in flight it wary a lot, depending on speed and altitude, so actual TWR is somwhere between 0.2 and 0.5 in airbreathing(jet) mode.

Problematic part is to accelerate enough on runway to be able to take off, flaps helps with that. Once I take off, 25-30% of throttle is enough for ~30kN of thrust. With that I can climb up to 8-12km, accelerating slightly on the way up, so when I got altitude, I don't need to wait much until I break sound barrier and L/D become stable again. Then comes confusing part, is it better to continue with full throttle to gain speed and altitude or it is more fuel efficient to go with lower supersonic speed and raise altitude and then again go with full throttle at high altitude to speed up.

Well, with latest test flight I found almost no difference in fuel efficiency with either of two aproach. When I was going with low supersonic speed until gain high altitude, when I was accelerating to gain speed at high altitude, I was forced to dive, because plane was lost lift due to higher speed until more dense atmosphere is reached, and when I was speed up at lower altitude, I was able to climb again. Have to do that several times until I reached enough speed/altitude for finall push to orbit.

When I used full throttle all the way up to highest speed/altitude after breaking 1 Mach, engine shows higher fuel consumption, but there was less diving until I reached point when I need to switch to rocket mode. And yes, I have established stable orbit with 30t payload and still 157 m/s of dV left for small orbital tasks and have fuel to deorbit and land on runway. Almost the same dV as I have left without AJE mod.

I didn't used real fuel mod with this, but is it any big difference besides calling fuels real life names ? If I use hydrogen, it is lighter, but I need more volume to store it, If I use kerosine, it require less volume, but it is heavier. Overall stored chemical energy in either fuel should be the same to provide enough dV for orbit. Probably I will give a RF a try, also deadly reentry, but my craft usualy crashes sooner from FAR aerodinamic failures then from too high temperatures.

I'm still researching available mods, what I should install and what to avoid to maintain stable game. I'm still in sandbox mode researching possibilities before I start new career.

[camlost]

RF is a big difference

" Overall stored chemical energy in either fuel should be the same"

No.

[Hyomoto]

The update for AJE just says, "Rapier change". Care to elaborate?

[camlost]

@Hyomoto, We use Liquid Methane now, which makes more sense. I don't know if you use RF, but you should if you're concerned about SSTOs

@Nathan, I find XP's jet model a good reference for BJE.

About the SR-71, their drag is also funky. In XP it was modeled as a delta-wing, with fuselage providing no lift

[DaMichel]

I saw you added a ramjet config. Thanks. I had to make a little mission devoted to it.

[Genius Evil]

I've been looking at the propeller config, trying to figure out how it works. It looks like some of the tables are coefficients calculated with Java Prop with respect to two parameters, but I have no idea what they are. My best guess was Cs on the Y axis and velocity on the x axis, but the x axis would only go up to ~70m/s. I have absolutely no idea what the four-column charts are. Could anyone shed some light on this?

Also, is ixxFTLB the moment of inertia?

[NathanKell]

Are you looking at the new code I wrote (based on JSBSim) or the old YASim code?

[Genius Evil]

I have 1.6.4, so the new code. I haven't actually looked at the code (no programming experience), just the "Propellers.cfg" file. I'm trying to create propellers for some high-powered post war engines (e.g. Wasp Major, Bristol Centaurus).

[Guest]

I see you're adding the RF VTOL engines. I've got a suggestion for the IR-based tiltjet pod: http://en.wikipedia.org/wiki/Rolls-Royce_RB145

The smaller one could be done as the J85: http://en.wikipedia.org/wiki/General_Electric_J85

The J85 was used in a similar configuration here: http://en.wikipedia.org/wiki/Bell_D-188A

[NathanKell]

Genius Evil: Use the HS60something propeller. That's the 13ft Hamilton Standard that the F4U-4 used, and is basically the same as the 13-footers all the late/postwar radials used. For the Wasp Major, you'll want to probably just use the R-2800-18W and increase the HP accordingly; alas I don't simulate three blower speeds yet, so you'll miss out on either low or high blower (neutral blower will always be the in as "low speed" because otherwise you won't get sufficient takeoff BHP). I think now I have the Double Wasps using neutral and high, skipping low, but at one point they were neutral and low, skipping high (which was kinda-simulated by increasing ram air recovery effectiveness).

[Genius Evil]

Ok, thanks! I'll post the cfgs when I've got them working well.

[NathanKell]

Genius Evil: use this excel sheet to generate the engine config. You can input the actual BHPs at altitudes and adjust things until the curves match.

[camlost]

I see you're adding the RF VTOL engines. I've got a suggestion for the IR-based tiltjet pod: http://en.wikipedia.org/wiki/Rolls-Royce_RB145

The smaller one could be done as the J85: http://en.wikipedia.org/wiki/General_Electric_J85

The J85 was used in a similar configuration here: http://en.wikipedia.org/wiki/Bell_D-188A

But the RB145 is weaker that J85. Having something bigger and weaker doesn't make sense?

[Guest]

I was going by the (apparent) size of the pods. If I was wrong about this, you can, of course, swap them. The basic idea was that I found two sets of engines which were used in pods like that. Certainly beats yet another R&R Pegasus config, and there aren't many jet engines that were used for VTOL applications.

Edited November 20, 2014 by Guest

[Genius Evil]

NathanKell: I got an early Wasp Major (built-in supercharger, no turbo; based on data from an old Flightglobal article) working. Power curve is pretty good, thrust is about what I expected (thanks for the Excel sheet; it was invaluable). However, for some reason it's causing an extreme amount of drag. I copied the mesh position, mesh scale, and FARBasicDragModel from the R-2800, but the Wasp Major has far greater drag. My Corsair with the R-2800 has a zero-lift drag coefficient of ~0.06-0.07; but with the R-4360 (same size, same drag model) it has a zero-lift Cd of ~0.1-0.11. With no engine, the zero-lift Cd was ~0.01-0.03. I also noticed that the maximum drag coefficient specified in the FARBasicDragModel for both engines was 0.04, indicating that the high drag isn't intended behavior.

Is this just a problem with my install, or is it intended behavior?

[NathanKell]

Can you post the config?

[Genius Evil]

Here it is:

https://www.dropbox.com/s/yuc6qx882p0c3t2/WaspMajor.cfg?dl=0

[NathanKell]

1. Remove FXModuleAnimateThrottle.

2. Remove ModuleResourceIntake.