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This is my first post here. I was convinced by some friends to post the results of one of my investigations on this forum. It will be partly a question about things I have yet to fully discover, a bit of an explanation of how jet engines work. I will tell this investigation in chronological order explaining each step so if I have an error anywhere in my understanding feel free dear reader to point it out. I started this little investigation because of an unrelated efficiency calculation I wanted to do however it quickly spiraled into a bit of a rabit hole. I wanted to mathematically determine the most efficient jet engines for each flight regime but for this I needed a way to create a function for the thrust multiplier given the flight conditions(pressure and mach). To my understanding at the time the thrust was simply a function of two values those being the mach multiplier and the pressure multiplier. In other words: Thrust = mach_curve x pressure_curve Nice and simple right? The wiki shows these two curves as looking as follows for the whiplash: The data for these two curves are easy enough to find in the game files and look as follows (for the whiplash at least): velCurve { key = 0 1 0 0 key = 0.2 0.98 0 0 key = 0.72 1.716 2.433527 2.433527 key = 1.36 3.2 1.986082 1.986082 key = 2.15 4.9 1.452677 1.452677 key = 3 5.8 0.0005786046 0.0005786046 key = 4.5 3 -4.279616 -4.279616 key = 5.5 0 -0.02420209 0 } atmCurve { // definite 'kink' to the curve at high altitude, compared to flatter BJE curve key = 0 0 0 0 key = 0.045 0.166 4.304647 4.304647 key = 0.16 0.5 0.5779132 0.5779132 key = 0.5 0.6 0.4809403 0.4809403 key = 1 1 1.013946 0 } The way in which this is stored is not entirely obvious but through some googling i figured out it uses a technique called Cubic Hermite spline also known as Cubic Hermite interpolation [source for the curious reader: https://en.wikipedia.org/wiki/Cubic_Hermite_spline#:~:text=In numerical analysis%2C a cubic,of the corresponding domain interval.]. Each point (represented by a key) is defined by 4 properties which are the x, y coordinates and incoming and outgoing tangents in that order. To do this numerically in the program I was using(aka MATLAB) I had the option to either implement this interpolation from scratch or use one of the preexisting interpolation methods available to me. The functions that MATLAB had available were: spline() pchip() makima() I first decided on spline() and through that I aquired functions that produced the following curves: and: These curves look good but they differ slightly from the ones found in the wiki. This error could be through a number of reasons, it could be that i used the wrong interpolation function, it could be that the wiki is wrong or it could even be that both I and the wiki are wrong. I tried googling for which interpolation the devs used or which interpolation unity would use by default however very predictably this gave no results (Like many things in ksp odds are they implemented a custom interpolation method). Unable to find the answers I needed online i then proceeded to look at the functions themselves available to me. Each giving ever so slightly different behavior. If i am to show the difference in the interpolation method i am going to borrow an example from the online documentation for these functions:[image source: https://se.mathworks.com/help/matlab/ref/spline.html?searchHighlight=spline&s_tid=srchtitle_support_results_1_spline] As you can see from this image each interpolation method does it ever so slightly differently (though granted makima and spline are almost identical). The pchip() method seems most similar to the one used in the wiki however at this point I was through taking peoples word for it so i decided on a different course of action. To determine which of these methods I should use for my function I decided to conduct a little experiment. I slapped together a tiny test rig which would help me (with the aid of the autopilot mod) determine the properties of such a curve. The vehicle is seen below but there is not much to say about it: This vehicle flew on 100% throttle with infinite fuel turned on to limit the variables. The autopilot mod used was atmospheric autopilot [link: https://spacedock.info/mod/683/AtmosphereAutopilot]. This autopilot held 200m above sea level and flew only in the ocean east of the KSC. It held the speed asigned to it in mach and i confirmed the mach number both with the ingame aero data in the gui setting and through atmospheric autopilot. Then i sat down to record the data I needed. Here is a table (oh and since this whole journey started with efficiency I decided it could not hurt to record the fuel consumption as well). I did a little tweaking to the PID parameters mid flight to ensure zero steady state error and also a fast enough response. Here is the raw data: Raw experimental data Mach Thrust [kN] fuel drain [u/s] 1 292.2 1.372 1.2 297.6 1.487 2 350.2 1.785 2.2 357.2 1.821 2.4 363 1.852 2.6 368.4 1.878 2.8 371.8 1.89 3 375.6 1.915 3.1 375.4 1.914 3.2 374.8 1.910 3.3 374.2 1.908 3.4 372.8 1.901 3.5 371.1 1.89 3.6 368.8 1.88 3.7 365.8 1.865 3.8 362.1 1.846 3.9 357.6 1.823 4 352.0 1.795 I would have sampled higher but this is where my poor slapped together craft reached its maximum velocity and at any rate I had enough data to work with. I took extra readings in the top of that "hump" to check if it is flat or curved. Something else stood out about this though which became all the more apparent when this data was subsiquently graphed: There seems to be quite a bit of thrust missing from this. In other words we have a mystery multiplier at play somewhere in the code. It is less simple than the equation for thrust I stated near the beginning. That said from the smoothness of this curve especially around the mach 3 region i can at the very least conclude that the interpolation method in the wiki is wrong. To Investigate the thrust discrepency further I decided to plot the theoretical data divided by the experimental data and the result looks as follows: The results of this show that our mystery multiplier is nonlinear making life difficult. That said I have tracked down the identity of this multiplier. It can be found in a seemingly unrelated spot in the data for the engine. The parameters section for this engine is as follows: // Jet params atmChangeFlow = True useVelCurve = True useAtmCurve = True flowMultCap = 2.0 machLimit = 2.5 machHeatMult = 6.0 Can you spot it? well it may not necessarily be obvious at first glance but looking back on the raw data it is curious that the fuel flow never goes above the flowMultCap set by the game. That is because this is our culprit. The specific impulse is tied to both thrust and fuel flow rate. The equation for which looks like this: Isp = T * (dm/dt)-1 *g-1 where: T is "thrust" expressed in newtons, dm/dt is the mass flwo rate of the fuel into the engine expressed in kg/s g is the gravitational acceleration at the surface (9.81 m/s2) The equation for Isp Ties the two values together and since the thrust can't rise without an increase in fuel flow rate and the fuel flow rate can't rise due to the limiter the end result is a situatuation where the thrust is effectivly capped at low altitudes. Just to show this equation is accurate i am going to take a random set of values (say, @mach 3 ) and confirm the fuel flow rate from the thrust value and Isp: For the whiplash at this point Isp = 4000 T = 375.6 [kN] = 375600 [N] Rarranging the equation for the specific impulse gives: (dm/dt) = T * Isp-1 *g-1 substituting in the values gives: dm/dt = 375600 / (4000*9.81) => (dm/dt)theoretical = 9.572 [kg/s] To convert this to u/s we need to know the density which can be found on the wiki [https://wiki.kerbalspaceprogram.com/wiki/Liquid_fuel] to be 5kg/unit so: (dm/dt)theoretical = 9.572 [kg/s] / 5 [kg/u] => (dm/dt)theoretical = 1.9144 [u/s] this value is similar to the experimental value: (dm/dt)experimental = 1.9148 [u/s] The discrepency in the last digit can be ignored due to me doing this calculation with values with up to 4 significant figures and the limiting value (g) has 3 significant figures. Thus the experimental and theoretical values can be seen as equal and thus the equation works. When I went in and changed the flowMultCap to a much higher number then the whiplash behaved as expected reaching its full thrust multiplier so it iscertainly the culprit here. When looking at the KSP API [source: https://www.kerbalspaceprogram.com/ksp/api/class_module_engines.html] the description for this is: This quote does not provide any actual details of how this tapering off multiplier is implemented or how it works in detail. I did a little more digging around this but found no actual answers so this is where this investigation of mine ends for now. For anybody still reading this i thank you for your time. I also shall ask the question I mentioned at the beginning but never actually asked throughout the entire text. Does anybody how this flowMultCap curve is implemented? maybe you have decompiled the code somewhere and you have it handy and can share? maybe you instantly know from the shape of the functions i have presented? maybe you are a dev and have the actual code infront of you? no matter how any answers to this are appriciated and would also appriciate the feedback to any errors you have seen me make during this investigation. Thank you for reading.

Hello there! I'm working at KSP mod that allows a player to upgrade parts. How to increase engine thrust by 15% or set a new value? Same with electricity generator. At the same time, also reduce fuel flow by 10% or set a new value. Here's an example: Basic engine Improved engine Thrust (kN) 200 230 Fuel flow (u/s) 16 14.4 EC generation (u/s) 10 12 Hope this information will be enough. Thanks in advance for your reply!

Hey guys, I have a good working RSS/RO modpack for the Version 1.10.1 Everything is fine only the fact that something seems wrong with the delta V maybe i am also just not good with RSS But the thing is I have a Rocket that uses 42000kN thrust for a payload of 18tons... that should end in an orbit 400KM aboth earth. SpaceX needs only about 10.000 kN thrust for 21Tons. But it makes also nearly no difference with the deltaV if I am on the surface of the earth or somewhere in space it changes only 1000 deltaV. I am new with Real Solar System so maybe it should be like that and I am just building wrong... I have uploaded my Modpack and the craft-file on Mega so you can check it out. I dont know if I am allowed to show the link to everyone for Copyright reasons but you can ask me to [email protected] hopefully you can help me

Hi everyone , I've got a little story to tell you that will end with a couple of questions on how the configuration of engines with multiple nozzles works. But before I start, here is a... TLDR: How can I configure an engine with multiple nozzles in KSP? And is it possible to tamper with the multi-nozzle configurations of stock engines by modifying their config file? If yes, how does it work? Okay, so I have been a little dissatisfied with the stock Launch Escape System for quite some time. It does its job when aborting mid-flight, even although in many such occasions it would also be sufficient to simply shut down all engines and decouple the command pod; but the LES's miniscule amount of propellant gives it far too little burn time to be useful for an abort on the launch pad. Instead, if it had more fuel, it could really be used in those situations where one builds a far too big and too unstable rocket that spontaneously disassembles itself right on the pad, to pull the capsule to a height large enough to deploy the parachutes and land safely back on the ground. Thus, in my KSP 1.8.1 install, I decided to give a look at the LES's config file and see what I could do to "improve" it. I have little to no experience with KSP modding, but still, increasing the amount of fuel in the LES was simple enough for me to manage that. However it then turned out that there is a problem created by the fact that the net thrust generated by the LES is angled with respect to its vertical axis. Once the burn time of the LES is more than fractions of a second, this will lead to the capsule spinning out of control quickly and stop it from gaining height after a pad abort. Therefore, I gave the config another look to figure out what I could do to reduce the amount of torque the LES induces. Unfortunately, I haven't been able to find anything that I can do to modify the center of thrust or the angle of the thrust the LES generates. My feeling is that the direction of the thrust the LES generates is computed internally by adding up the thrust of all its five nozzles, and therefore there is no single variable that determines the direction of the net thrust. Then, I'd only have to modify the configuration of the LES's off-center nozzle at the top to make it less off-center. Unfortunately, I haven't been able to find anything in the config file that seems to configure the multiple nozzles, their position, rotation, etc. and moreover, I also haven't been able to find any information on that anywhere else. So, in case someone reads this who knows how to configure multi-nozzle engines, I'd be very happy if you could explain it to me. Maybe it is configured somewhere else than in the LES's config file? Maybe it is not even possible to tamper with the multi-nozzle configurations of stock engines? Or maybe I'm just blind ? I just don't know and I'd appreciate any hints that you can give me. At least I am pretty sure that multiple nozzles have to be configured somewhere. I have RealPlume with stock configs in my install and for the LES it only configures a single plume which is automatically attached to each of the five nozzles. And here is a second issue that I am having: I find the plumes way to underwhelming for the thrust the LES generates, and I would like to make them much larger and longer. However, increasing the size of the plume also increases the size of the plume emerging from the little nozzle at the top, which I don't want. So I am guessing that what I could do, is to remove the top nozzle from the config and then manually add a small plume to it in a similar way it is done, for instance, with the turbopump exhaust plumes of various engines (like the ones in the ReStock mod for example). But before I can do that, again, I have to know where the multiple nozzles are configured. So, if you have any answers to my questions or any other suggestions you can give me on those problems, I'd love to hear them!

I tried to build a moon rocket but I have a graphics issue I think.. Just look! https://ibb.co/Pg2b56j https://ibb.co/P4Wx9cC https://ibb.co/DMwDyvp Sorry but the insert image button doesn't seem to work. Below is my installed mods list: https://ibb.co/xLnJ0vW Thank you!!

Assume a rocket is standing on the ground with mass = 1000 kg, and near the top of rocket we apply a force of 100 N for say 1 sec,now assume that this is sufficient to tip rocket over/start tipping over. If the rocket is mid air and accelerating at 30 m/s^2, then likewise how much force would be required to tilt it pi/180 rad or change its trajectory by some degree, please neglect the change of mass due to consumption of fuel because the value calculated with this assumption is going to be a a value higher than required, so that is not an issue. Will the force required mid air be the same as the force required on the ground with no acceleration ?

I've made this kick-ass SSTO that could get up to 20 people to Laythe. In previous tests, I managed to get to LKO (and Minmus' surface for refueling) and re-enter with no problem. However, after I was done with the ALT-12 Laythe tests, for some reason the Poseidon started to fail. More specifically, it lost thrust and speed as it got to Mach 1 and never got past 400 m/s during the initial ascent. For more details regarding the previous Poseidon tests, read my "Neptune Mission Files" post about them. SPH image of the latest variant CORRECTION ATTEMPT 1 Tried the "low-angle" approach to get to a high enough velocity so that the engines can't stop working CORRECTION ATTEMPT 2 Tried to ascend as fast as possible at a 30-degree angle. Backfired miserably How do I fix this? This plane used to be awesome, and now for some reason it's a "massive flop."

Don't you hate it when you have too much fuel/oxidizer laying around? Which you could change the mixture ratio that your engines use (like the J-2 did in real life)? Want no more. Introducing: EMRController With this mod, you can configure your engines to use different oxidizer/fuel mixtures, and have the ISP and thrust adjust accordingly. You can even set up your engine to run in "Closed Loop" mode, emptying your tanks at the end of a burn. This mod does not contain any configurations, but if you use Realism Overhaul, you'll see that the J-2 does have configurations that work with this mod. Download: Github View the Source cfg changes powered by sarbian & ialdabaoth's ModuleManager plugin. Changelog:

Hello. Nuclear engines on my SSTO produce no thrust, while using fuel in vacuum. In atmosphere it works fine. I understand the low TWR, and it's my second flight with this issue. Right clicking the engine shows regular parameters, ISP, thrust, fuel usage. Technicly they are fine, but not phisically. (IDK how to spell that). Hope you'll help me! Have a nice day!

Simply, I am working on my physics thesis and I need to observe the effects of gradual change in mass of a rocket in orbit without any force being applied, namely thrust. For this I need fuel consumption, the rate of which I can modify but no thrust. The only thing that comes to my mind is using a 0 Isp engine but I don't know how to change the files. Do you have any suggestions other than a modified engine? If not, how do I change the Isp and thrust values of engines in the game? Is there a mod I can use?

I created an SSTO which works fine in Kerbin atmosphere, has plenty of fuel to get into orbit, however, when trying to circularise the orbit and using the nuclear engines in orbit, the SSTO keeps on pitching up, even when all control surfaces are turned off. Any help please? The SSTO has a mass of 56.3k kg, 4900 units of liquid fuel and 880 units of oxidiser, with 4 rapier engines and 2 nuclear.

In a plane the Centre of mass is just ahead of the centre of pressure, so it is stable. When elevator movement is given, it does go nose up but it doesnot climb. Instead in it tries to come down. How to make it climb. P.s Rhodes34 airfoil if used inclined at 8deg Basically I want to know what affects the rate of climb and vertical velocity

Hey all, so I've been trying to build a mars tranfer vehicle somewhat in the vein of Hermes (from The Martian). For me, it's an 80 ton, crewed, ion propelled spacecraft. Unfortunately, when I got it assembled and fueled in orbit, I discovered that my mod install had reduced the thrust of the engines from 2 kN to 0.25 N which is 8000 times less thrust, and KER told me a 10 m/s burn would take 4 hours and change (8 engines). I am obviously going to have to rethink my plan, but that's actually not my main point of interest. \ All this got me wondering, how would a real world ion rocket leave earth orbit for an interplanetary transfer? I am very experienced with using multiple perigee kicks to make low thrust escapes, but the thrust of real life ions is SO low that this isn't possible. Even if I halved the mass of my rocket to 40t and tripled the number of engines, it'd still be more than half an hour for 10 m/s. At that rate, it'd take more than 300 kicks to reach escape velocity. I know that all real world ion spacecraft to date have been lauched into heliocentric orbits using chemical rockets, so I'm not sure it's actually possible to use such a low thrust system for earth escape. There are however, several hypothetical vehicles, both fictional and real concept designs, that do appear to exclusively use ion propulsion once in orbit. Does anyone know what kind of trajectory would be used? The only one I can think of is a very long spiral up to very high orbit, and from there on to deep space. However, I imagine this would eat up an absurd amount of dV, so it doesn't seem like a good option for anything except maybe a solar sail vehicle. Ion drives in stock are time consuming, but you can basically treat them the same way you would small chemical rocket engines like the LV-1. With realistic ion drives though, I don't have the first clue how to use them. Thoughts? Ideas?

Nevermind this, I saw a thing called Firespitter. I know the engine and engine fx modules already exist but what do I put in my plugin code to make a part produce thrust? I'm trying to figure out how the stock engine module works but I'm having issues with that because I can't see the source for it. I at least know it increments/decrements a vector based on throttle and fuel input somehow and the api documentation at the wiki isn't showing the somehow.

Hi, I am currently modding the J404 Engine to fit it to my SU27 replica (might release as part mod eventually). I noticed something weird when I was editting the engine curves and trying them out ingame and this is true for Stock KSP engines aswell. The static thrust of the J404 is 130kN, @ Mach 2.5 it is supposed to be 219.5kN okay that is as advertised when you try it out. However when I look at the curves the thrustmultiplicator of the J404 at mach 2.5 is 3.5. 219/130 is a mere 1.8-ish of the thrust that the curve says. I thought the atmospheric curves play a role in this and might explain the vastly lower thrust, but nope even with a constant atmospheric curve the engine still is not producing the amount of thrust. What variable am I missing? What else is playing into the calculation of the thrust? I really don't want to make totally ridiculous thrust curves and have multiplicators like 6 or higher in there. (I hope this is the correct subforum to ask this)

with a v simple craft using the MK1 cockpit. after going eva I realised that the craft was spinning. (when it wasn't before hitting the EVA button) so i got back inside and stopped the spin with some SAS. then the moment i hit EVA and my kerbal is holding the ladder the craft is spinning again. so i checked the map and notice that my PE and my AP are going down together at about 20meters a second. I've tested this out with a few similar craft but with no luck recreating it. but this one craft always does it. https://dl.dropboxusercontent.com/u/92121741/broken 1.craft this craft is all stock parts but the install does have mods this is the Ckan file. https://dl.dropboxusercontent.com/u/92121741/ckan list2.ckan Edit, I've been unable to recreate the problem with a brand new craft but if I use craft that was having the problem to begin with its always there even when I reorganise the parts of the lander and remake it with new bits it still spins. I also saved it under a different name and change the root part.

I'm fairly new to the game and play on Xbox. I saw a video where someone set the max thrust of his solid rocket booster so that he had a thrust to weight ratio to his liking. When he left clicked on the booster to lower its thrust, there was a pop up that showed (among other things) his TRW. He was on a PC. Is there a way to view your TRW while you build your project on the Xbox version? Clicking on a booster only displays the Thrust Limiter and amount of solid fuel.

Greetings all. This is going to sound stupid but, is there anywhere else that can cause thrust to show backwards in the game? I know its correct in Unity, I exported it and another part with the same thrustTransform rotation and the other one works fine. Any ideas? I might have been refrencing the wrong .mu. Any mod is free to delete this.

Hi all, I've got a bit of an odd question regarding engine thrust. I'm designing an asteroid "puller" to bring in a Class E. I have my nuclear engines out on 4 radially-symmetrical nacelles, which were angled at about 45 degrees to try to clear the asteroid for unimpeded thrust. On my first attempt, the angle was not sufficient, and I had some of the engines (but not all) obstructed by the asteroid, leading to more asteroid-spinning and less asteroid-moving. So to address this, I tried to increase the angle of the engines (i.e., make them closer to perpendicular to the main axis of the ship). I tested out the new design on the launchpad, with gravity hacked and with just the core ship, not the orbital-launch rig. Results were not good- I was barely getting any thrust! In other words, it seems there's a thrust penalty for having your engines angled. I've looked on the forums for info on this and not seen much, but one person suggested the end-thrust is a function of the cosine of the engine angle. My question, I guess, is why. My (probably wrong) understanding was that, if you have two symmetrically balanced engines, as long as there was SOME angle in one direction, they would put full thrust forward regardless of the angle. Those engines' energy has got to go somewhere, and I presume it's not being lost to deformation or heating of the ship in between. If not, the only place the energy could go was forward. The analogy that comes to mind is: squeeze a wet bar of soap between your hands, it will shoot out straight up or in some direction. Not because you pushed it in that specific, but because it's got nowhere else to go when you apply a squeezing force. Can anyone explain what's causing the observed thrust loss? Is there just extra heat generation? Is the specific impulse of the engine affected somehow? Is it just something else? (By the way, if major engine angling is not the answer, I will probably fix my rig by either extending the "tail" so the ship is further in front of the asteroid, or putting the engines out on longer pylons). Thanks for any info you might have!