Why switching to realistic fuels would make the game *EASIER*

[Northstar1989]

This probably isn't something you hear very often, but the stock "Liquidfuel/Oxidizer" system actually makes the game HARDER than a set of realistic fuels (hypergolics, Kerosene/LOX, and LH2/LOX). This is for 3 reasons:

(1) Realistic fuels aren't all the same density, and aren't required in equal or nearly-equal proportions (like stock LF/O). This means that you can adjust the Center of Mass of a spacecraft or (especially useful) spaceplane by changing the relative distribution of fuels. Craft too tail-heavy? Move the Liquid Oxygen up to the nose and the Liquid Hydrogen down towards the tail (LOX is 16 times denser than Liquid Hydrogen). Mass-distribution EXTREMELY important for aerodynamic stability with an aerodynamic system realistic enough that a full fuel tank falls faster than an empty fuel tank (and as the devs have already confirmed, the stock aerodynamics system *will* be getting an overhaul). Of course, to really take advantage of this, you need fuel tanks that hold just one fuel component of a bipropellant mix (like LH2/LOX, Kerosene/LOX, any hypergolic-pair, or yes even LF/O), either through tweakable tank configurations (so you can say this tank up here just holds LOX, and this identical tank down here just holds Liquid Hydrogen...) or dedicated parts. I suggest the tweakable fuel tank configurations.

(2) Some realistic fuels are capable of higher Specific Impulse (ISP) than the stock LF/O mix. Liquid Hydrogen (LH2) plus Liquid Oxygen (LOX), in particular (which can reach ISP values of 480 of greater with the right engine in vacuum). Sure, LH2/LOX is less dense than Kerosene/LOX, hypergolics, or the current LF/O- but you can always add BIGGER fuel tanks (especially if they're much lighter due to the reduced fuel density), and bigger rockets just look cooler anyways. Bigger rockets also have better ballistic coefficients (an aerodynamic feature measuring relative drag- that will necessarily show up in even the most basic aerodynamics overhaul- it's 100% of the reason a bowling ball falls faster than a feather in real life, but its absence is why that doesn't hold true in KSP...)

(3) Realistic fuels open up more interesting/intuitive In Situ Resource Utilization possibilities. Not only will it be more IMMERSIVE if you are mining ice from an asteroid to refuel your LH2/LOX fuel tanks than if you are harvesting some generic, imaginary resource- realistic fuels also open up types of ISRU that would be INCONCEIVABLE or INEFFICIENT with the stock LF/O system. In particular, any ISRU system that produces Oxidizer but not fuel in real life is EXTREMELY INEFFICIENT in stock, because LF/O burn in a nearly 1:1 mass ratio- whereas in *any* real fuel mixture, the Oxidizer component (LOX or N2O4 being the most common, and the only ones worth representing in KSP) is the MUCH more massive of the two (at an extreme, with LH2/LOX, Oxygen comprises roughly 8/9'ths of the total fuel mass)- meaning it becomes worthwhile to set up an ISRU system that can only harvest one. If you can set up a system that skims Oxygen off the upper edge of Kerbin's atmosphere, for instance (via a Propulsive Fluid Accumulator system), or electrolyzes it from Munar regolith (most Lunar regolith is comprised of Aluminum Oxides in real life...), it won't really be worthwhile unless you have a realistic mass burn-ration between your fuel and oxidizer.

It's also worth mentioning, though not strictly a part of having realistic fuels (although DEFINITELY part of a propulsion overhaul) that having a more realistic relationship between rocket TWR/ISP and atmospheric pressure (such that Thrust increases with decreasing atmospheric pressure, and Fuel Flow remains fixed, like in real life) actually makes efficient ascents to orbit easier, since you can build a craft with low TWR in the thickest part of the atmosphere, and have its TWR increase much more quickly as you ascend and get to the point where a higher TWR is ideal due to decreasing drag from the atmosphere (technically, a TWR of 2 would always be ideal over an infinitely-long ascent, but with any kind of a realistic climb-rate your TWR has to go higher and higher to keep up with terminal velocity as you ascend into thinner atmosphere...)

This thread is to discuss these concepts, NOT to suggest an overhaul of the current fuel-system to something more realistic (which I believe has been suggested many times before, even though I didn't immediately spot it on the "Already Suggested" list...)

Regards,

Northstar

P.S. The topic of boil-off of realistic fuels, which actually makes the game a *little* harder (it's not that hard to assume the fuel tanks are all insulated- their mass rations are already terrible even for insulated fuel tanks, and a simple active-cooling part could eliminate boil-off entirely at the cost of ElectricCharge), is also a slightly separate topic- as it's entirely possible to imagine a set of 3 realistic fuels in KSP (LH2/LOX, Kero/LOX, and one hypergolic pair) without the inclusion of boil-off. Of course doing so would eliminate the main advantage of hypergolics- that they experience ZERO boil-off at most normal operating temperatures... (in real life, Venus or Mercury would be hot enough to cook off uncooled hypergolics)

Edited December 20, 2014 by Northstar1989

[r4pt0r]

Wouldn't lighter fuels and improved ISP's make most parts in the game way overpowered?

also I really feel "harvesting some generic, imaginary resource" is totally their plan.

[Captain Sierra]

I really like everything said here, and I think you just persuaded me to experiment with realfuels sometime in my near future.

Now I have to shoot you down and say I disagree. KSP already has a learning curve equivalent to a brick wall, and we don't need to increase that even more.

To play devil's advocate on my own comments, I would say I don't mind the idea of a more realistic fuel component/mass ratio, even if switching were not added. We can assume KSP liquid fuel is RP-1 kerosene since thats the only fuel I know which burns nicely in both turbofan and rocket engines. Since there is no boiloff (not that this is any sound basis), I think another safe assumption is that stock oxidizer is N2O4. That, however, complicates the resource mining side you talked about considerably. What kinds of readily available sources of those are there? (I ask because none come to mind.

[Red Iron Crown]

I don't think any of these suggestions make the game any easier.

1) Manipulating center of mass via differing fuel densities is not a simple concept, far less simple than simply varying the amount of a constant density fuel. This goal would be much better served with some sort of stock fuel balancing utility.

2) The specific impulse of the in game engines are arbitrary and chosen for game balance reasons, they could easily be set higher if desired without any change of the existing single fuel system.

3) Same deal with ISRU, Squad could easily make a single harvestable resource that produces LF and O in appropriate ratios for modest or no energy cost (Honestly, I think this is what stock ISRU will likely look like).

I get that you would prefer greater realism in fuel chemistry for a variety of reasons, but to say it will make the game easier in and of itself strains credulity. All the the things you suggest to make the game a bit easier in certain aspects are overwhelmed by the additional complexity and steeper learning curve that a variety of fuels would bring with it.

I would also argue that scaling thrust with Isp would not make the game easier at all, even though that is a change I would like to see. It gives lower thrust right when it is needed most, when the rocket is full of fuel and heaviest and trying to build its initial speed.

[Baythan]

I like the idea of better CoM control by having the fuels placed in more controlled locations, and using a better ratio of LF/O would help greatly with this. As Liquid Fuel and Oxidizer are generalized terms, we don't know WHAT kind of liquid fuel is being used and what sort of oxidizer either, but a more realistic ratio is a good idea.

I'd like airplanes to have their fuel flow from the top of the plane to the bottom rather than the front to the back, but that should be another discussion.

As it stands, I've started using the RCS Build Aid mod to see my Full CoM, Dry CoM, and Average CoM so I can better determine where to place wings and how to angle engines to create shuttles and spaceplanes. Having more control over these points by moving the heavier fuels forward or backward inside their tanks (or with two tanks attached, splitting the ratios up so one tank ends up heavier) would help with flight balance over the entire mission. I would guess that the ability to move two separate fuels around inside the entire vessel would be difficult, as would splitting the fuels unevenly across multiple tanks, so the best option then is your separate fuel tanks idea.

The difficulty with separate fuel tanks that I see is in teaching players how to place the two types of tanks in the proper ratios, because you DO need to make sure you have the right amount of both so that you don't run out of one while still having some of the other. A stock version of something like Kerbal Engineer windows in the VAB and SPH would help by highlighting which fuel you are short on. The tanks would, or should, be designed in pairs so that if you use one of the LF tanks, you place one of the corresponding O tanks. If the tanks larger versions are also designed to hold exactly double (or some other simple ratio) the amount, you could place one larger tank(LF or O) and two of the smaller tanks(O or LF) in other locations to keep balance and fuel ratios.

All in all, I like your ideas... provided the implementation remains as simple as possible in order to be fun while still being close to rocket science. If it become tedious rather than fun, Squad won't implement it.

[Bill Phil]

Actually, I would rather have nerfed LV-T 30s, 45s, Mainsails, Skippers, and the like.

Let's take a look:

LV-T 30: 370 vac ISP, high ish thrust.

LV-909: 390 vac ISP, low thrust

The gain in ISP is negligible, and 20s IRL wouldn't lose that much thrust.

[Northstar1989]

I don't think any of these suggestions make the game any easier.

Great thoughts from you, oh but they do! Consider the following...

1) Manipulating center of mass via differing fuel densities is not a simple concept, far less simple than simply varying the amount of a constant density fuel. This goal would be much better served with some sort of stock fuel balancing utility.

The two aren't mutually exclusive, first of all (uneven fuel tank distribution is a feature of the VAB/SPH, a fuel balancer utility is used in-flight to pump fuel around withing those tanks. Personally, though mods, I already use BOTH).

Second, there's NOTHING forcing players to utilize this feature. If a player doesn't feel comfortable changing around the distribution of fuel and oxidizer within their fuel tank sections (so that, say, the bottom fuel section in a 2-tank stage is all LH2, and the top section holds the remaining LH2 and all the LOX) they could leave it alone and stick with the "default" configuration for the fuel tank, where the fuels are present in their burn-ratios in equal amounts in all fuel tanks, without being any worse off for their decision than they currently are in stock KSP (which, admittedly, is not as well of as they *COULD BE* if they took advantage of this new, beneficial feature...)

Being able to tweak fuel-distribution would also open the door to a lot of cool gizmos or visuals in the VAB, or at the very least be aided by a KER-style informational screen where you could at least see your Delta-V, so you know if the fuels are still present in their burn-ratio (otherwise, your total Delta-V decreases as you have excess fuel or oxidizer all the way to the end of that stage's burn...) But once again, there would be nothing forcing less advanced players to utilize any of these features- they wouldn't harm players who ignore them, just make the game easier for players who learn how to use them! (which can already be said of a lot of features in KSP- admin strategies, anyone?)

2) The specific impulse of the in game engines are arbitrary and chosen for game balance reasons, they could easily be set higher if desired without any change of the existing single fuel system.

The ISP *could* be increased, but having a set of 3 different fuels with different densities and ISP ratings gives players more flexibility in their rocket-design. Hypergolics are the most dense, LH2/LOX has the best ISP, and Kero/LOX falls somewhere in the middle. Once again, these choices could be safely ignored by any player who wishes to- just set hypergolics or Kero/LOX as the default for all engines and fuel tanks (depending on whether Squad decided to simulate boil-off!), and leave it to players who are curious and want to play around to optimize their designs to discover how to use the other fuel modes!

Setting hypergolics as the "default" would also allow Squad to "nerf" the default rocket performance a little to make up for the reduced Delta-V to orbit by revising aerodynamics to get rid of the "soup-o-sphere" (a realistic aerodynamics model with the current size of Kerbin would mean 3.5 km/s to orbit instead of 4.5 km/s), as real-life hypergolics, while extremely dense, have inferior ISP to the current stock engines (which currently fall somewhere in an ISP range loosely centered on Kero/LOX levels of efficiency, but with densities more similar to hypergolics...)

Delta-V to orbit would go down (with improved aerodynamics), but so would ISP by making hypergolics the "default" (thus preserving the current stock balance)- and players looking to get better performance could switch to Kero/LOX or LH2/LOX, at the cost of fuel-density and possibly having to mitigate boil-off...

3) Same deal with ISRU, Squad could easily make a single harvestable resource that produces LF and O in appropriate ratios for modest or no energy cost (Honestly, I think this is what stock ISRU will likely look like).

Absolutely. But would Squad want to make this resource collectible in as many places as you can find Oxygen in the real solar system? I think not. Right now, there's talk about them just limiting it to asteroid-mining, in fact.

Having realistic fuels would make it more useful and believable to have places where you can obtain just LOX, but not other fuel components, for instance... (such as from ordinary Munar regolith, or from skimming the edge of Kerbin's atmosphere from orbit) It would also provide a guide (reality) on where to locate additional ISRU opportunities as time went on and the devs inevitably felt led to expand the ISRU system...

I get that you would prefer greater realism in fuel chemistry for a variety of reasons, but to say it will make the game easier in and of itself strains credulity. All the the things you suggest to make the game a bit easier in certain aspects are overwhelmed by the additional complexity and steeper learning curve that a variety of fuels would bring with it.

We're talking about adding a new feature, that currently doesn't exist (there is no stock ISRU system- yet), in a more realistic manner because a more realistic system is actually more useful/interesting. It opens up possibilities like Propulsive Fluid Accumulator satellites, Regolith electrolysis, or Sabatier Reactors on Duna (if Methane/LOX were added as a 4th fuel-mixture), that wouldn't really make sense with the stock resources.

Since ISRU is an entirely optional feature, *nothing* about this would make the game harder. And the complexity? Most of it you don't actually NEED to understand- for instance, you don't need to know WHY you can skim LOX (that is useful because it comprises 8/9th's of your fuel mass with a LH2/LOX rocket) off the top of Kerbin's atmosphere or extract it from almost any Munar regolith- only that you can.

The chemistry behind it may be complex, and interesting to some players, but for most, having the fuels called "LH2" and "LOX" instead of "LiquidFuel" and "Oxidizer" is an *entirely superficial* difference- and only *necessary* so that you can differentiate several different usable fuel-mixtures, and allow them to share components (for instance, a Kero/LOX and LH2/LOX engine both use LOX...)

I would also argue that scaling thrust with Isp would not make the game easier at all, even though that is a change I would like to see. It gives lower thrust right when it is needed most, when the rocket is full of fuel and heaviest and trying to build its initial speed.

Not at all. Most engines in stock KSP are DRASTICALLY underpowered in terms of Thrust. It wouldn't be that hard to set the current thrust values as the sea-level thrust values, and simply have the thrust climb higher as you ascend. The rocket engines would thus only become MORE powerful compared to their current state, making the game easier (especially when combined with realistic aerodynamics reducing Delta-V to orbit)- but balanced by a reduction in ISP by a switch to ISP levels and naming accurate for hypergolics for the default fuel mixture (with Kero/LOX and LH2/LOX available as higher-ISP, lower-density alternatives).

Regards,

Northstar

Edited December 20, 2014 by Northstar1989

[Northstar1989]

I really like everything said here, and I think you just persuaded me to experiment with realfuels sometime in my near future.

I hope you do! It's a great mod- and I've actually had some input into helping make it what it is today myself! (I helped get included new designs of Thermal Fin, and helped figure out the correct re-balance of the KSP-Interstellar Meth/LOX engine for the "Stockalike" engine config I also helped guide the creation of the current RealFuels/KSP-Interstellar built-in integration config, which is vastly superior to the one they had packaged with the mod before...)

Now I have to shoot you down and say I disagree. KSP already has a learning curve equivalent to a brick wall, and we don't need to increase that even more.

Please see my other explanatory post. None of these features increase the learning-curve: as long as Squad is careful to set the easiest/most intuitive options as the "defaults" (even fuel-distribution before tweaking, in this case). What they do is add additional options for players who want to play around with alternatives to the default, so as to squeeze higher performance out of their rockets- thus making the game easier for curious players who take the time to learn about the advantages of the more complex alternatives (uneven fuel distribution being used to improve arodynamic stability).

To play devil's advocate on my own comments, I would say I don't mind the idea of a more realistic fuel component/mass ratio, even if switching were not added. We can assume KSP liquid fuel is RP-1 kerosene since thats the only fuel I know which burns nicely in both turbofan and rocket engines. Since there is no boiloff (not that this is any sound basis), I think another safe assumption is that stock oxidizer is N2O4. That, however, complicates the resource mining side you talked about considerably. What kinds of readily available sources of those are there? (I ask because none come to mind.

The stock ISP values are currently centered around Kero/LOX, but as has been repeatedly pointed out, the current values might be OP'd with a more realistic aerodynamics system (which would mean only 3.5 km/s to LKO). It would probably be better to "nerf" them to those appropriate for hypergolics, so as to maintain game balance when revising aerodynamics.

In fact, Squad *could* (and probably *should*) re-name LF/O to that of a known hypergolic mixture (either MMH, Aerozine, or UDMH fuel; and N2O4 as oxidizer) and not add any other fuel mixtures for the moment, while reducing ISP levels to those appropriate for hypergolics. This would both pave the way for adding additional fuel mixtures in later updates, AND satisfy the realism-junkies (such as myself) without actually making any change to the gameplay that they didn't need to make anyways (reducing ISP to compensate for improved aerodynamics making getting to orbit cost less Delta-V).

Regards,

Northstar

[Northstar1989]

I like the idea of better CoM control by having the fuels placed in more controlled locations, and using a better ratio of LF/O would help greatly with this. As Liquid Fuel and Oxidizer are generalized terms, we don't know WHAT kind of liquid fuel is being used and what sort of oxidizer either, but a more realistic ratio is a good idea.

I'd like airplanes to have their fuel flow from the top of the plane to the bottom rather than the front to the back, but that should be another discussion.

As it stands, I've started using the RCS Build Aid mod to see my Full CoM, Dry CoM, and Average CoM so I can better determine where to place wings and how to angle engines to create shuttles and spaceplanes. Having more control over these points by moving the heavier fuels forward or backward inside their tanks (or with two tanks attached, splitting the ratios up so one tank ends up heavier) would help with flight balance over the entire mission. I would guess that the ability to move two separate fuels around inside the entire vessel would be difficult, as would splitting the fuels unevenly across multiple tanks, so the best option then is your separate fuel tanks idea.

I'm glad you see the value in being able to divide the duel mass unevenly. Note that I think the SIMPLEST and BEST option is to simply have the existing fuel tanks be tweakable as to whether they hold ONLY Liquidfuel (which should be re-named to MMH, UDMH, or Aerosize for the default fuel mixture), ONLY Oxidizer (N2O4 for the default- which should be hypergolics for their simplicity and lower ISP), or any arbitrary ratio of the two (assume the fuel tank is actually just an aero-shell with mutliple smaller tanks inside). Basically, something equivalent to the Modular Fuel Tanks mod.

Players would start off with both fuels present in the burn-ratio as the default (like in current stock KSP), and be able to change it with right-click tweaking in the VAB/SPH...

The difficulty with separate fuel tanks that I see is in teaching players how to place the two types of tanks in the proper ratios, because you DO need to make sure you have the right amount of both so that you don't run out of one while still having some of the other. A stock version of something like Kerbal Engineer windows in the VAB and SPH would help by highlighting which fuel you are short on. The tanks would, or should, be designed in pairs so that if you use one of the LF tanks, you place one of the corresponding O tanks. If the tanks larger versions are also designed to hold exactly double (or some other simple ratio) the amount, you could place one larger tank(LF or O) and two of the smaller tanks(O or LF) in other locations to keep balance and fuel ratios.

All in all, I like your ideas... provided the implementation remains as simple as possible in order to be fun while still being close to rocket science. If it become tedious rather than fun, Squad won't implement it.

The simplest way to ensure new players have the correct burn ratio is simply to make the default fuel tank configuration the burn-ratio of hypergolics (which never boil-off, so even if boil-off were added, players won't need to add excess quantities of the more cryogenic component to maximize Delta-V), and force players who want to use anything else (such as Kero/LOX or LH2/LOX, or move the fuel-distribution around like we were talking about) to have to manually adjust the fuel contents through tweakables.

So, players could place the heavier hypergolic in the nose and the lighter once in the tail through tweakable, switch over to Kero/LOX or LH2/LOX and do the same ting, or just stick with the default burn-ratios.

I suggest if you've never played with RealFuels before, you go and download it as soon as it's updated for 0.90, as it has basically the system I am describing (although actually selecting the fuel contents there is overly-complicated due to a huge bloat of weird Cold War Era fuels that almost nobody ever uses except people with Real Engines installed...)

Regards,

Northstar

[Carmoldu]

Maybe it would make the game easier in terms of designing efiient rockets and having alternative solutions to some problems, but in terms of gameplay it would be a lot harder (just because it is a more complex system, which makes it less intuitive). I'm studiing space engineering and I think that'd be great fun, but maybe for my little brother or my father or anyone else would be too much to try to learn how to design rockets, learn how to fly them and in addition having to know which fuel is the best for each situation... This would increase the learning curve and, in my opinion, would throw back a lot of potential players.

Personaly I'd like it: yes. I think it would be good for the game: nope.

Thankfully this game is open to mods and you can customize your experience thanks to them. There ara a bunch of mods which already introduce realistic fuels and I think that is the solution to those of us who want more and more hahaha

[Ziff]

I don't think any of these suggestions make the game any easier.

1) Manipulating center of mass via differing fuel densities is not a simple concept, far less simple than simply varying the amount of a constant density fuel. This goal would be much better served with some sort of stock fuel balancing utility.

This is exactly what I was going to say. We have players who can't even figure out which way their contract orbit is going even though it has flashing lights moving around it and you can read the exact inclination in the [+]Notes section of the contract. And you want them to balance fuel in their craft?

I would also argue that scaling thrust with Isp would not make the game easier at all, even though that is a change I would like to see. It gives lower thrust right when it is needed most, when the rocket is full of fuel and heaviest and trying to build its initial speed.

It would make for some pretty awesome slow liftoffs though.

[King Arthur]

Alright, this has been itching at my OCD too much after it's been incorrectly repeated too many times.

Of course doing so would eliminate the main advantage of hypergolics- that they experience ZERO boil-off at most normal operating temperatures...

The primary reason for using hypergolic rocket fuels is because they spontaneously combust when they come into contact with each other, requiring no external source of ignition and meaning they are simple and reliable. Being liquid at room temperature is a handy secondary trait that most hypergolic rocket fuels tend to have.

A hypergolic rocket propellant combination used in a rocket engine is one where the propellants spontaneously ignite when they come into contact with each other. The two propellant components usually consist of a fuel and an oxidizer. Although hypergolic propellants tend to be difficult to handle because of their extreme toxicity and/or corrosiveness, they can typically be stored as liquids at room temperature and hypergolic engines are easy to ignite reliably and repeatedly.

https://en.wikipedia.org/wiki/Hypergolic_propellant

[Bill Phil]

Even so... KSP engines can ignite at will. Plus they are reliable. Sounds like a hypergolic fuel mixture. Maybe it's propellium.

[King Arthur]

There are cryogenic engines that can restart like the RL-10 and J-2/J-2X, so KSP engines having the capability to restart on demand doesn't exempt cryogenic fuel mixes.

On the topic of restartable engines, that's another avenue of realism that can merit an entire thread of its own.

[Bill Phil]

Well, the tanks don't boil off, the engines fire an infinite umber of times, it's probably hypergolic. Maybe not toxic hypergolic, but hypergolic.

[King Arthur]

I personally attribute fuel not boiling off to reasons of development simplicity just like how the LV-N runs off LF/O despite being an NTR. Basing arguments of what LF/O actually is on gameplay mechanics that aren't likely fully implemented isn't going to mean much.

And even presuming that fuel (LF/O) not boiling off is fully working as intended, there still remains the question whether "room temperature" on Kerbin is "Earth room temperature" or "room temperature that still maintains Earth-cryogenic fuels in a liquid state".

Basically, Kerbals aren't launching from Earth. What is cryogenic for us might not be cryogenic to them, anything we debate right now is essentially unfounded guesswork.

[Baythan]

As far as fuel boil off, I very much doubt this will ever be added to the game, as that is needless realism that would make the game less fun. One can assume that the fuel listed in the tanks is what is available after such things are taken into account. I see no reason to force the players to have to worry about that extra percentage of fuel.

[Northstar1989]

This is exactly what I was going to say. We have players who can't even figure out which way their contract orbit is going even though it has flashing lights moving around it and you can read the exact inclination in the [+]Notes section of the contract. And you want them to balance fuel in their craft?

Like I said, advanced concept for advanced players. But making it part of the stock game wouldn't DETRACT anything from the experience of newbies (provided the fuel tanks came pre-configured with the fuels in the correct burn-ratio as the "default"), while it WOULD add to the experience of experienced players and particularly advanced newbies (personally, I was landing on Duna within a week or two of staring KSP- I would have loved more advanced content without having to install mods, which I was initially reluctant to do as I didn't know how hard/safe it would be to add mods- I had some bad experiences with modding in Minecraft back in the day...)

It would make for some pretty awesome slow liftoffs though.

Indeed.

As for those getting super into discussing re-naming LF/O as hypergolics, keep in mind that while it *IS* true you can have highly reignitable cryogenic engines, and can theoretically even store cryogenics with little to no boiloff with the right equipment, the point was that it's the most *believable* replacement for LF/O as the "default" fuel (all the cryogenic fuels should be more advanced alternatives that players would have to know how to switch to via tweakables to use). Sometimes believability and ease of use is more important than realism (which is why I suggested making hypergolics the default, even though Kero/LOX is more widely used in real life...)

Hypergolics have a lower ISP than the current LF/O mix, but the ISP of the default stock engines needs to be nerfed a bit anyways when they overhaul aerodynamics and it starts taking only 3.5 km/s to get to LKO with well-designed rockets... That hypergolics provide a convenient measuring-point to match up against with about the right ISP and fuel-density for what the new (nerfed) balanced should be is simply convenient and a great way to enhance realism without harming gameplay...

Sometimes you CAN have your cake (realism) and eat it (balance/fun) too.

Regards,

Northstar

[Kesa]

Of course, playing with real world rocket on planet 10 times smaller than ours whith the corresponding tiny atmoshpere would be easy.

[Capt Snuggler]

This is exactly what I was going to say. We have players who can't even figure out which way their contract orbit is going even though it has flashing lights moving around it and you can read the exact inclination in the [+]Notes section of the contract. And you want them to balance fuel in their craft?

Like I said, advanced concept for advanced players. But making it part of the stock game wouldn't DETRACT anything from the experience of newbies (provided the fuel tanks came pre-configured with the fuels in the correct burn-ratio as the "default"), while it WOULD add to the experience of experienced players and particularly advanced newbies (personally, I was landing on Duna within a week or two of staring KSP- I would have loved more advanced content without having to install mods, which I was initially reluctant to do as I didn't know how hard/safe it would be to add mods- I had some bad experiences with modding in Minecraft back in the day...)

It would make for some pretty awesome slow liftoffs though.

Indeed.

As for those getting super into discussing re-naming LF/O as hypergolics, keep in mind that while it *IS* true you can have highly reignitable cryogenic engines, and can theoretically even store cryogenics with little to no boiloff with the right equipment, the point was that it's the most *believable* replacement for LF/O as the "default" fuel (all the cryogenic fuels should be more advanced alternatives that players would have to know how to switch to via tweakables to use). Sometimes believability and ease of use is more important than realism (which is why I suggested making hypergolics the default, even though Kero/LOX is more widely used in real life...)

Hypergolics have a lower ISP than the current LF/O mix, but the ISP of the default stock engines needs to be nerfed a bit anyways when they overhaul aerodynamics and it starts taking only 3.5 km/s to get to LKO with well-designed rockets... That hypergolics provide a convenient measuring-point to match up against with about the right ISP and fuel-density for what the new (nerfed) balanced should be is simply convenient and a great way to enhance realism without harming gameplay...

Sometimes you CAN have your cake (realism) and eat it (balance/fun) too.

Regards,

Northstar

its... beautiful...

Edited December 20, 2014 by Capt Snuggler

[King Arthur]

the point was that it's the most *believable* replacement for LF/O as the "default" fuel

If we're going that way the only real answer to what LF can be is kerosene since kerosene is used both as rocket fuel and jet fuel just like our LF is used by both our rocket and jet engines.

And since LF can only be answered as kerosene, the natural answer to our oxidizer is LOX.

[Northstar1989]

If we're going that way the only real answer to what LF can be is kerosene since kerosene is used both as rocket fuel and jet fuel just like our LF is used by both our rocket and jet engines.

And since LF can only be answered as kerosene, the natural answer to our oxidizer is LOX.

Actually, both Kerosene and Liquid Hydrogen can be used in jet engines. While Kerosene-jets are MUCH more common, hydrogen-jets CAN be built or at least designed (see the SABRE engine, for instance).

I wouldn't mind having jet engines burn a different fuel than the standard rocket-fuel mixture. Honestly, when I first started playing the game, the only rocket fuels I was familiar with were hypergolics and LH2/LOX. I was *surprised* to see rocket engines and jet engines burning the same fuel resource.

I think making MMH/N2O4 the default rocket fuel, and Kerosene the default jet fuel; but having Kerosene/LOX available as a viable (higher ISP, but lower-density) alternative for rockets along with LH2/LOX (and possibly LH2/IntakeAir for a jet engine alternative), would be the best solution.

Regards,

Northstar

P.S. Yes, basically I think that making RealFuels stock, without all the weird alternative fuels, and with *either* MMH/N2O4 or UDMH/N2O4 (one, but not both) being the *ONLY* hypergolic fuel-mixture, and the default for EVERY rocket engine (regardless of this being unrealistic) would be the best choice...

Fuel tanks should also be made a good bit cheaper in Career Mode, at the same time as reducing ISP, so as to not add *too much* to game difficulty- and this would also simultaneously increase the realism (fuel tanks are currently far too expensive in relation to rocket engines, especially compared to real life) and eliminate the need to adjust standard contract monetary rewards with the reduced ISP.

Edited December 22, 2014 by Northstar1989

[thereaverofdarkness]

I would like to see some sort of fix for aircraft engines. Real aircraft engines may be a large chunk of the weight of the whole plane, but they extend throughout its whole body (in small aircraft) or are at least pretty long. In KSP the engines are just little exhaust nozzles you attach to the back of your plane which drag the center of mass way back and make it difficult to put the wings far enough back to actually fly the plane. You have to start loading up the nose with multiple tons of weight just to make the plane stable, whereas in real life planes with that much weight on the nose would fall flat, and probably couldn't carry the weight even if it were distributed evenly.

[CaptainKipard]

Could someone please start writing bullet point summaries of all points? With links to posts for those who want to read more.