Rebalancing Jet Engines/Atmospheric Properties

[BowlerHatGuy3]

This is a very subjective topic, as well as one I don’t have that much expertise in. But hear me out. I think that many of the jet engines are too op, and the atmosphere simulation is pretty sucky in Kerbal.

From my experience once you get the jist of how aerodynamics works, it’s fairly easy to make a spaceplane in Kerbal. I don’t really have a problem that for the most part with the slower planes, what I have a problem with is the planes designed to go over mach 1 and SSTOs. The fact that you can just slap a couple of Whiplashes onto some stinky piece of junk and have it fly over mach 2 at SEA LEVEL is bonkers. Heck, I’d say that getting to mach 1 is too easy. Once I made a pretty bad, really heavy replica of an Airbus A320 and had it go 400m/s pretty easily.

So how would we fix this (I’m not an expert in aerodynamics so sorry for any broad metaphors)? First, at least early in game, going mach 1 should be like smashing through a brick wall. Not that it should be extremely hard, but it shouldn’t be a walk in the park; like getting your first rendezvous. Second, heat should be much more of a factor. Going mach 2-3 and having your plane being enveloped in plasma is kind goofy. I think that there should be new cooling systems in the game, and the ones that are already implemented should be much more important. This would also apply to the jet engines. Having engine failures due to heat would not only make high velocity spaceplanes more challenging, but also make room for some pretty spectacular crashes/disintegrations. 

And thats it. I’m a little paranoid about this not being implemented due to the game only being a little bit more than half a year from release (assuming there aren’t any more delays), but I’m optimistic. Would like to hear anymore things that some other people have come up with.

Edited June 27, 2022 by BowlerHatGuy3
Changed “subject” to “topic”

[Ember12]

I think this might tap a bit into the old "how hard should planes be" debate.  Personally I find plane design just as interesting as rockets, but from what I've seen a lot of people don't.   I love this idea and I think it would be fun for me to play, but many others could feel differently.

[t_v]

On the topic of thrust, I think there should definitely be a lead up to supersonic flight, because not every engine can support those speeds, but if you stick a powerful jet engine on something and then throttle up to maximum (which I think is pretty rare irl, you don’t want to be constantly accelerating as much as possible) you should be able to hit Mach even if your plane isn’t sleek, due to sheer thrust. On nicely designed planes with powerful engine, I can hit Mach 1 or even 2 without going at full throttle, which emphasizes aerodynamic plane design. In terms of my personal preference, I’d like it to become a little harder but still possible to slap engines on a brick and launch it at mach speeds. 
 

And on the topic of heating, I get red bars showing up consistently when going fast at low altitudes. Especially when designing ssto space planes, there is always a margin where you fly them too low and burn up. Once again, in terms of personal preference, I think that it could be made a little bit harder. 
 

Luckily, there are sliders, and if I want more heat, I can turn up reentry heating. I think if in KSP 2 there was a slider to increase the drag force (and therefore heat produced) in atmospheres this could work to satisfy everyone. 

Edited June 28, 2022 by t_v

[jastrone]

the thing is. that real life airplanes take several hours to go places. in ksp 2 you will have to move resources and you dont want to sit there for hours just going straight. a way to fix this problem would be making the early engines in the tech tree a lot weaker but that would be maybe even before you unlock  rockets like real life. but then the difficoulty curve fs up. therefore we need planes to be more powerful than their real world counterparts

[BowlerHatGuy3]

32 minutes ago, jastrone said:

the thing is. that real life airplanes take several hours to go places. in ksp 2 you will have to move resources and you dont want to sit there for hours just going straight. a way to fix this problem would be making the early engines in the tech tree a lot weaker but that would be maybe even before you unlock  rockets like real life. but then the difficoulty curve fs up. therefore we need planes to be more powerful than their real world counterparts

That’s not really the case. Kerbal 2 is going to have automated delivery routes as of now, so you won’t have fly every mission manually; its going to be handled by the computer. Planes shouldn’t get really powerful until about midway in the game.

[Bej Kerman]

15 hours ago, Ember12 said:

I think this might tap a bit into the old "how hard should planes be" debate.  Personally I find plane design just as interesting as rockets, but from what I've seen a lot of people don't.   I love this idea and I think it would be fun for me to play, but many others could feel differently.

The people who don't shouldn't be too affected by new aerodynamic models, then.

[Ember12]

What I meant was, with what was suggested, it would be harder to create an orbit-capable spaceplane, and some players might want that to be easy.

[BigStar Aerospace]

Very odd that you all are only hitting mach 1 or 2.... On PS4 all of my planes tend to go over mach 5.9, it's not even hard. But take this info with a grain of salt, I had a period of time where I was just trying to make my planes as fast as possible without using any bugs or tricks so now all of those building techniques are stuck in my head. Still though, it is too easy now to hit mach 5.9. I would also like to raise the point that it's harder to go above mach 4 when you reach more than 10-15 Km in altitude where as in real life it would be easier to get to mach 4 or 5. Another thing to take into point is that for me to hit mach 5.9, I hold at 30 meters above the ocean, when in real life I would barely be able to hit mach 1 at that altitude.

3 hours ago, BowlerHatGuy2 said:

Planes shouldn’t get really powerful until about midway in the game.

You must remember that KSP2 is based in the future tense of the KUniverse so if anything RAPPIERs and all the other jet engines and early engines of the first game would be pretty close to the beginning of the tech tree.

Edited June 28, 2022 by BigStar Aerospace

[Ember12]

One issue is that, in KSP, planes aren't that useful unless they go to space.  You can putter around Kerbin and get a bit of science from each biome, but it's a tiny amount and the flights are long.  In many of my career & science mode games I don't even bother with non-space planes.

One way to encourage use of atmosphere-only planes would be if certain resources were much more highly concentrated at locations far from KSC.  The player's first automated transports could be subsonic airplanes delivering ore and fuel from remote locations on Kerbin.

[t_v]

19 minutes ago, Ember12 said:

One issue is that, in KSP, planes aren't that useful unless they go to space.  You can putter around Kerbin and get a bit of science from each biome, but it's a tiny amount and the flights are long.  In many of my career & science mode games I don't even bother with non-space planes  

I’d like to dispute this, because I make use of planes whenever I can, especially when not leaving an atmosphere. On Kerbin you can just recover a vessel from anywhere on the surface, but if you have interplanetary infrastructure, crashed ships or ships low on fuel will need a way to get to a fuel depot and shipyard, and I am definitely not using a rover to circumnavigate Duna. Planes in KSP 2 will be even more important because they will provide a very efficient way to move around a planet with speed and ease. Not to mention, they can be fun to fly.

[JadeOfMaar]

On 6/27/2022 at 7:38 PM, BowlerHatGuy2 said:

This is a very subjective topic, as well as one I don’t have that much expertise in. But hear me out. I think that many of the jet engines are too op, and the atmosphere simulation is pretty sucky in Kerbal.

From my experience once you get the jist of how aerodynamics works, it’s fairly easy to make a spaceplane in Kerbal. I don’t really have a problem that for the most part with the slower planes, what I have a problem with is the planes designed to go over mach 1 and SSTOs. The fact that you can just slap a couple of Whiplashes onto some stinky piece of junk and have it fly over mach 2 at SEA LEVEL is bonkers. Heck, I’d say that getting to mach 1 is too easy. Once I made a pretty bad, really heavy replica of an Airbus A320 and had it go 400m/s pretty easily.

So how would we fix this (I’m not an expert in aerodynamics so sorry for any broad metaphors)? First, at least early in game, going mach 1 should be like smashing through a brick wall. Not that it should be extremely hard, but it shouldn’t be a walk in the park; like getting your first rendezvous. Second, heat should be much more of a factor. Going mach 2-3 and having your plane being enveloped in plasma is kind goofy. I think that there should be new cooling systems in the game, and the ones that are already implemented should be much more important. This would also apply to the jet engines. Having engine failures due to heat would not only make high velocity spaceplanes more challenging, but also make room for some pretty spectacular crashes/disintegrations. 

And thats it. I’m a little paranoid about this not being implemented due to the game only being a little bit more than half a year from release (assuming there aren’t any more delays), but I’m optimistic. Would like to hear anymore things that some other people have come up with.

Consider that a lot of the stock physics is geared towards easily getting to orbit and granting that gameplay satisfaction to fresh players, but also to trying to compensate for the smallness of stock scale. Much of the OP of the stock jet engines imo is that orbital speed is only Mach 7, not Mach 22+, and that we're able to freely attempt things with technology in the game that can't be done IRL because of issues like funding, the efforts of engineers to build the things, and risking human lives when something goes wrong mid-flight. Intakes are OP too, or rather, it's just the intakes that are OP, not the engines. They provide too much air and there isn't much of a tangible gameplay dynamic to them other than that. I'm sure you know that 1 shock cone and 0 precooler can feed 2 maybe 3 RAPIERs and at near-zero velocity.

A fair portion of the answer to your argument lies in the reasons that FAR (Ferram Aerospace Research) and DRE (Deadly Reentry) exist:

• FAR makes it so that planes are less draggy (the stock fuselage parts that have lift surface are actually double-draggy) but that more IRL physics are added such as: Clipping and hiding wing boards doesn't work; You can optimize for 1 or 2 of these but can't have all 3 (subsonic, supersonic, hypersonic) and will be penalized accordingly; Forward wings can occlude and stall rearward ones if you build wings as usual and don't know their fluid dynamics.
• DRE: Many parts in KSP are actually excessively resilient against heat and so can be presumed to be built out of a Handwavium. With DRE installed, you wouldn't dare attempt a Mach 4+ flat run at sea level, or if you do you won't last long. Mach 2+ might be fine as we have things like "Supersonic Low Altitude Missiles."

Intakes have speed curves and become better or worse at given speed ranges because of it. That makes them fairly diverse already. But these fixes and additional dynamics can possibly float your boat:

• Fix: Ram and shock intakes should be poor or useless when subsonic.
• Add: Choke and starvation could occur when going too fast in thicker atmosphere. This may somewhat already be paralleled by suffering extreme drag when transsonic in thicker atmosphere.
• Add: Air temperature limit when received by engines, and the precooler exclusive ability to (try to) keep the air cold... If your inlet temperature matches or exceeds exhaust temperature then you're not adding useful energy and you get no thrust. The AJE (Advanced Jet Engine) mod makes you care about closing your intakes to prevent reentry plasma getting into your turbines and exploding things. KSPI-E also makes a big deal out of SABRE-alike precoolers and SABRE-alike engines. Such an engine without a compatible cooler will quickly threaten to overheat and explode.

 

[Domonian]

I can agree that KSP1 aerodynamics and atmospheric flights aren't... good. Some things are too fast while others are too slow, its just all over the place sometimes.  Hopefully KSP2 has a more well-rounded and consistent atmospheric and aerodynamic system, and maybe we'll see stuff like ramjets or scramjets for true hypersonic flight. I know I'll be spending most of my time in atmospheres where jet engines work, since that's what I enjoy most. 

[BowlerHatGuy3]

On 7/13/2022 at 7:14 PM, Domonian said:

I can agree that KSP1 aerodynamics and atmospheric flights aren't... good. Some things are too fast while others are too slow, its just all over the place sometimes.  Hopefully KSP2 has a more well-rounded and consistent atmospheric and aerodynamic system, and maybe we'll see stuff like ramjets or scramjets for true hypersonic flight. I know I'll be spending most of my time in atmospheres where jet engines work, since that's what I enjoy most. 

There are already ramjets in the game; that’s why I’m looking forward for scramjets. Ramjets could be reduced to mach 3 and scramjets would keep your plane going until in disintegrates. 

[JadeOfMaar]

8 hours ago, BowlerHatGuy2 said:

There are already ramjets in the game

There are no pure ramjets, though. At stock scale, you almost can dodge having an LFO engine for your SSTO plane or have a perfect air-breathing hypersonic plane that never needs Oxidizer. A stock jet engine that works between Mach 2 and 6.5 would be pretty sweet. Sadly, because KSP2 is obviously inheriting stock scale for its game scale, there isn't going to be a stock scramjet. There's literally no room for it because you're already orbital before you reach peak cruising speed with it.

On 7/13/2022 at 7:14 PM, Domonian said:

like ramjets or scramjets [snip] I know I'll be spending most of my time in atmospheres where jet engines work, since that's what I enjoy most.

Sounds like me. Unfortunately, most of the atmospheres you can encounter won't allow chemical jet engines so what about... nuclear thermal turbos and rams? Your Eve taxi and Jool skipper would be happy for sure.

[Strawberry]

While SLAM aircraft sound amazing, I dont want all non off station jet engines to be nuclear hellburners going at several mach, I want there to be "slow" and versatile air breathing engines that work on all atmospheres, without the use of fuel directly. Fortunately, we have that in real life, using electricity to convert air directly into thrust. The most simple are propellers, assuming that there isnt robotics in ksp2, having propellers as preexisting engines as very early game flight tech seems fitting. Honestly you really only need one engine of this type, but a thunderscreech style engine seems amazing. Early game these would be used for early science gathering on kerbin, and for vehicles on laythe and eve (duna presumably has too light of an atmosphere for these engines).  For a mid game electric "all air" engine just before you leave kerbin, an ionic wind airplane engine seems good as a highly energy efficient yet slow engine, these should be energy efficient enough to run on solar panels to make "eternal" airplanes (since I assume the way different types of procedural wings that have different materials work for things like heat shields is by having them all be the same part with a setting you can love with, an option for solar wings seems cool mostly for this engine). Finally, for your late game electric you have plasma aircraft engines. This is an incredibly niche technology that has yet to taken off (both literally and figuratively). These work by using microwaves to ionize gas. With current technology, these engines can achieve similar thrust density to jet engines (the gas is really hot though so its a bit out of reach under current engineering designs). These would serve as both highly energy efficient (though energy intensive) and fast electric engines, capable of acting in any atmosphere (maybe have a ramjet style one that can work in thin atmospheres at very fast speeds, or just have a single plasma thruster with all those niches) with high efficiencies and no need for fuel. Plasma aircraft engines could also easily serve as an advanced RAPIER engine which can use any fuel (no need to carefully manage ratios of oxygen and jet fuel anymore!) and can air breath, however at the cost of electricity consumption. 

Edited July 16, 2022 by Strawberry

[BowlerHatGuy3]

3 hours ago, JadeOfMaar said:

There are no pure ramjets, though. At stock scale, you almost can dodge having an LFO engine for your SSTO plane or have a perfect air-breathing hypersonic plane that never needs Oxidizer. A stock jet engine that works between Mach 2 and 6.5 would be pretty sweet. Sadly, because KSP2 is obviously inheriting stock scale for its game scale, there isn't going to be a stock scramjet. There's literally no room for it because you're already orbital before you reach peak cruising speed with it.

Sounds like me. Unfortunately, most of the atmospheres you can encounter won't allow chemical jet engines so what about... nuclear thermal turbos and rams? Your Eve taxi and Jool skipper would be happy for sure.

I think nerfing the whiplash to make room for a ramjet would be the best option. The Whiplash would have a top speed of mach 3 and the scramjet would have a top speed of mach 4-5. The Whiplash is already op as it is. Revamping the way that you turn on the ramjets/scramjets would be nice as well.

[Domonian]

On 7/16/2022 at 12:13 AM, BowlerHatGuy2 said:

I think nerfing the whiplash to make room for a ramjet would be the best option. The Whiplash would have a top speed of mach 3 and the scramjet would have a top speed of mach 4-5. The Whiplash is already op as it is. Revamping the way that you turn on the ramjets/scramjets would be nice as well.

Maybe instead of nerfing engines themselves, changing efficiencies at specific speeds for engines and air intakes could be a decent compromise. Possibly increasing drag values for intakes as well, so even if you have a powerful engine, the reduced efficiency from low-speed optimized intakes (as well as the drag at higher speeds) would limit the top speed severely. That might open up room for high-speed optimized intakes and engines, such as ramjets or scramjets.

The scale of KSP is still an issue, but reducing the max speeds of traditional turbine engines and intake combinations from KSP1 might help as well. Ignoring mods, its always possible that they may add a planet so massive that, provided it has an atmosphere, hypersonic aircraft are not only viable, but required if you want to get anywhere in a reasonable amount of time. 

Just a few thoughts of mine. I'm still an advocate for these types of engines being in KSP2, but I understand that there simply may not be any room (literally and figuratively) for them. 

[JadeOfMaar]

On 7/16/2022 at 12:13 AM, BowlerHatGuy2 said:

I think nerfing the whiplash to make room for a ramjet would be the best option. The Whiplash would have a top speed of mach 3 and the scramjet would have a top speed of mach 4-5. The Whiplash is already op as it is. Revamping the way that you turn on the ramjets/scramjets would be nice as well.

It's likely actually possible for the Whiplash to operate at up to Mach 5 like in-game. The SR-71 never went that far because it would melt if it tried. In KSP2, who's to say we can't legit have the material science necessary to build a plane to survive Mach 5? (The same material science that allows any MetallicHydrogen engine to not melt itself!) So I don't believe in nerfing the Whiplash........Or at the very least, not that far. I'd take down to Mach 4.5 if I really had to and still have the ramjet reach Mach 6 as you actually need to reach roughly Mach 7.5 to be orbital speed. That last stretch (Mach 6+) still leaves a solid opening for an LFO engine.

The Whiplash would be redundant and pointless next to the Panther if you nerfed it that far, and the Panther isn't a ramjet.

1 hour ago, Domonian said:

The scale of KSP is still an issue

This. Absolutely this. Build an SSTO spaceplane while playing 2.5x scale, and involve the scramjet from Mk2 Expansion and you'll feel right at home.

1 hour ago, Domonian said:

Maybe instead of nerfing engines themselves, changing efficiencies at specific speeds for engines and air intakes could be a decent compromise. Possibly increasing drag values for intakes as well,

I went into detail on this earlier. Intakes have "mach curves" that control how well they work at a given speed, but there are still some obvious faults like how you can use the stock shock cone alone, at zero velocity and can still feed a RAPIER or two. There's no "shock" at the hovering speeds of a VTOL plane but many of us use this exploit.

The air-breathing engines have the ability to change their Isp as the vessel's velocity changes. I've tuned a few engines to be like this and it's pretty nice to look at in the engine's PAW.

I'm against making intakes noticeably draggy just for "balance" sake. This defeats the basic necessity of any frontal aerodynamic component and it encourages the plane to be draggy towards the front and flip over at high AoA.

[Domonian]

2 hours ago, JadeOfMaar said:

I'm against making intakes noticeably draggy just for "balance" sake.

Fair enough. I also figured heat could play a bigger role in a planes performance, either by changing the performance in relation to current engine temperature (idk if that's realistic, I've never really explored that topic) or by general overheating and destruction of parts. In KSP1 it just seems like I could push a plane as fast as the engines allow, which is generally pretty dang fast already. 

2 hours ago, JadeOfMaar said:

I went into detail on this earlier. Intakes have "mach curves" that control how well they work at a given speed, but there are still some obvious faults like how you can use the stock shock cone alone, at zero velocity and can still feed a RAPIER or two. There's no "shock" at the hovering speeds of a VTOL plane but many of us use this exploit.

I'm not sure if there is a relation between Mach-optimized air intakes and air compression, but I figured air density of the atmosphere would play a major role in both aerodynamics (duh) and the viability of ram/scramjets. I don't know if there is a limit to how MUCH air could actually be pushed into an intake built for hypersonic speeds, but when it comes to KSP, more is better, right? 

I'm finding that there's just a lot more to air-breathing engines than I originally thought, and a lot of it I don't really know about. Balance via drag on intakes is a bit silly, I'll admit, but balance via engine and airframe overheating, engine thrust, fuel usage, and overall size of atmospheric planets are what I think could be  explored more to allow for scramjets and ramjets to have a place in the game. 

[BowlerHatGuy3]

3 hours ago, JadeOfMaar said:

It's likely actually possible for the Whiplash to operate at up to Mach 5 like in-game. The SR-71 never went that far because it would melt if it tried.

Yes I know, but then there would be no point for a scramjet. Many of Kerbal’s engines are less powerful & less efficient than their irl counterparts for gameplay reasons. This should be no different for aircraft.

[Bej Kerman]

I think the RAPIER shouldn't be a jet and rocket in one, that's a bit silly. Or at least the current RAPIER should be shunted forward in the tech tree with the following proposed engine taking its current place: a hybrid jet containing a jet capable of reaching Mach 2/3 and a scramjet (as opposed to a rocket) for reaching higher velocities in atmosphere once the temperatures needed to operate the scram are attained. Being able to "paint" on heat-resistant tiling a la SR-71 would help.

Just now, BowlerHatGuy2 said:

3 hours ago, JadeOfMaar said:

It's likely actually possible for the Whiplash to operate at up to Mach 5 like in-game. The SR-71 never went that far because it would melt if it tried.

Yes I know, but then there would be no point for a scramjet. Many of Kerbal’s engines are less powerful & less efficient than their irl counterparts for gameplay reasons. This should be no different for aircraft.

And that's why I propose a velocity ceiling of Mach 2/3 instead of something more realistic - KSP isn't meant to be a simulation of reality, it's supposed to be an emulation from which people can learn about how reality works. Using a lower velocity ceiling means being able to demonstrate why scramjets are needed for these high velocities, otherwise you'll end up with players thinking a jet is sufficient to attain suborbital velocities. That's not true, and in order to get a more true-to-life behavior that also gives scramjets room for actual use, jet engines need to be nerfed.

[BowlerHatGuy3]

2 minutes ago, Bej Kerman said:

And that's why I propose a velocity ceiling of Mach 2/3 instead of something more realistic

I don’t think they should be THAT slow. Theres something special about seeing your plane glow up from the speed it’s at. IMO Mach 4 should be the breaking point where going any faster is a death wish.

[Bej Kerman]

10 minutes ago, BowlerHatGuy2 said:

18 minutes ago, Bej Kerman said:

And that's why I propose a velocity ceiling of Mach 2/3 instead of something more realistic

I don’t think they should be THAT slow. Theres something special about seeing your plane glow up from the speed it’s at.

A jet shouldn't be capable of getting you fast enough to make your aircraft glow. You should need scramjets for that.

[BowlerHatGuy3]

21 minutes ago, Bej Kerman said:

A jet shouldn't be capable of getting you fast enough to make your aircraft glow. You should need scramjets for that.

Oh sry I thought you said that everything flying should be limited to mach 3.

[JadeOfMaar]

36 minutes ago, Bej Kerman said:

I think the RAPIER shouldn't be a jet and rocket in one, that's a bit silly. Or at least the current RAPIER should be shunted forward in the tech tree with the following proposed engine taking its current place: a hybrid jet containing a jet capable of reaching Mach 2/3 and a scramjet (as opposed to a rocket) for reaching higher velocities in atmosphere once the temperatures needed to operate the scram are attained.

RAPIER is fine as-is. That's how theSkylon's SABRE engine is. It's a "turborocket" -- a jet that supplements its air intake with LOX so it can perform at even higher altitudes. It's a ramjet -- the ring of nozzles are where excess air from the intake is combusted for upper supersonic performance. It's a proper rocket -- this is what provides powered flight from Mach 5 up to orbit.

The hybrid engine you're describing is nearly a "Turbine Based Combined Cycle" -- turbojet, ramjet and scramjet in one. But I notice you didn't clearly suggest ramjet, only the other two.

1 hour ago, Domonian said:

Fair enough. I also figured heat could play a bigger role in a planes performance, either by changing the performance in relation to current engine temperature (idk if that's realistic, I've never really explored that topic) or by general overheating and destruction of parts. In KSP1 it just seems like I could push a plane as fast as the engines allow, which is generally pretty dang fast already. 

I described earlier in this thread 3 mods that exist and provide for this intention (DRE, AJE, KSPI-E), and what I believe is a decent application (to the stock game) of heat as a limiting factor to how far and how long you can push a jet engine.

On 7/9/2022 at 7:48 PM, JadeOfMaar said:

DRE: Many parts in KSP are actually excessively resilient against heat and so can be presumed to be built out of a Handwavium. With DRE installed, you wouldn't dare attempt a Mach 4+ flat run at sea level, or if you do you won't last long. Mach 2+ might be fine as we have things like "Supersonic Low Altitude Missiles."

On 7/9/2022 at 7:48 PM, JadeOfMaar said:

Add: Air temperature limit when received by engines, and the precooler exclusive ability to (try to) keep the air cold... If your inlet temperature matches or exceeds exhaust temperature then you're not adding useful energy and you get no thrust. The AJE (Advanced Jet Engine) mod makes you care about closing your intakes to prevent reentry plasma getting into your turbines and exploding things. KSPI-E also makes a big deal out of SABRE-alike precoolers and SABRE-alike engines. Such an engine without a compatible cooler will quickly threaten to overheat and explode.