renhanxue

Well, once you've escaped from Minmus you're (presumably) in a highly elliptical orbit with a sub-100km periapsis and an apoapsis somewhere out around Minmus or beyond, kinda like the one you started your journey to Minmus from. Unless I've misunderstood something about orbital mechanics, lowering apoapsis and raising periapsis or vice versa is equivalent from an energy standpoint, so circularizing at periapsis is gonna cost you just as much dV as raising the apoapsis up to Minmus did. The only reason it may be cheaper is because of the Oberth effect. So, yes, it's normal, I think. edit: this thread has some interesting discussion on the topic:

I was wondering how I could get my impression of how thrust occlusion actually worked so wrong, so of course I had to test it, and the results explain perfectly why I came to the wrong conclusions. Everything in the game (including right clicking on the engines) will tell you this thing is producing around 230 kN of thrust, while in reality it is producing zero thrust (the speed of 0.3 m/s is only caused by the runway not being completely flat): However, the heating caused at this range is almost completely negligible and won't show up on the thermal overlay. I have the KER thermal window open here, and there you can notice something is going on - after a while. I think the rocket part was just because the thrust "column" is so narrow that I just happened to miss the wings with the rocket engines.

Yep, it's thrust occlusion. A very confusing phenomenon, because there is nothing in the game that will explain to you in any way what's going on - IIRC even things like KER show that thrust levels are normal, you just notice that you're going really really slowly. The stuff that's occluding the nozzle doesn't heated up by the exhaust, either, and just to make it even more inconsistent I'm pretty sure it only happens with airbreathing engines, not with rocket motors. I spent long while scratching my head just last week trying to work out why a variant of this design that had wing panels extending much further inboards aft of the engine flew like a brick even when empty: Some of my ramjets were doing basically nothing except produce noise and fancy lightning effects. Spent a good ten minutes looking for misattached nodes causing drag, until finally the other shoe dropped. (docked the mk2 mun/minmus commuter successfully and brought it back down - it was bad, and mistakes were made, leading to it ending up in a retrograde orbit, so I decided I didn't want it anymore)

The aerospike's good for spaceplanes when you haven't unlocked the RAPIER yet - good thrust to weight ratio, same stack size as the ramjets and decent - if not great - ISP. Moving on to things I no longer use, though... Autostruts and the new fuel feed priority system made me completely abandon the use of both struts and external fuel lines, and the stock fairings made me almost completely abandon fins. Then there's the new aerodynamics making the old ways of building really wide asparagus stacks far less viable, and suddenly KSP rockets actually look like rockets rather than like a scattered heap of junk and steel rods on top of a forest of fuel tanks. Which is awesome! I mean, the Kerbal-y aesthethics of it all are somewhat diluted, but there's still so much disparity between different parts that it hardly matters. The orange tank is comforting in its complete refusal to blend in with anything whatsoever. The spaced radial decoupler is also pretty pointless these days, but I think that's more due to me learning how to place decouplers for proper separation than due to anything changing in the game. Then again maybe the new aerodynamics helped.

It's not, but if you have access to the 88-88 you also have the RA-100. If you put a single RA-100 on craft 2 instead of the RA-15 and 88-88 you could get away with putting quite small antennas on anything else you send to Jool.

The "core heating" system of the ISRU's and drills is kinda separate from the regular skin/internal heating mechanic, and it took me a while to understand what was going on. If you look at the stats of the radiators in the VAB/SPH, there's a number called "max core xfer", expressed in kW. This is how much "core heat" (which, again, is a different thing than "regular" heat) the radiator can extract from things which produce core heat. It has nothing to do with how much heat (any kind of heat) the radiator can dissipate into space; that's a completely different thing and it's usually (always?) much greater than the heat it can extract via core transfer, so actually getting rid of the heat once you've gotten it into the radiator is almost never a problem. Now, if you look at the stats of the drills/ISRU's, there's one "required cooling" and one "max cooling" number, also expressed in kW. Required cooling is how much core heat you need to remove from it with radiators to keep it at optimal temperature, while max cooling is how much core heat it is actually possible to remove from it with radiators. On drills, these two numbers are the same, so you just need to match radiator core transfer to drill cooling 1:1. The converters on the other hand are more complex. First off, they use the number stated as required cooling multiplied by the number of processes running, so you can max out at four times that number if you run all four processes (LF+OX, LF, OX and monoprop) at the same time. The small converter is designed to always overheat since it requires 100 kW of core cooling but has a max cooling of only 50 kW, while the big converter has 200/500 so you can run two processes indefinitely, but not three. There used to be some weird things going on with foldable radiators, drills and converters, which led to fixed radiators being the preferred way of cooling (you wanted to separate the core transfer "circuits" so the drills and the converters didn't interact), but I don't know if that's been fixed or not. Either way though, I like using one large radial mounted radiator (the fixed, non-folding one) to cool two drills, or two to cool one big converter. I tend to do my mining on bases where there's truss or girders parallel to the ground, so I just put the radiators on the underside of the piece(s) the drills/converter is mounted to - discreet, takes no useful space, stays in the shade. Open questions: - I'm not sure how engineers interact with this - they reduce heating, don't they, but by how much? - Can the core transfer stat be reduced by the radiator getting too hot? - Does core heating actually cause regular internal heating these days? If it does it's gotta be a pretty small effect, but I haven't really tested it - I don't have any mining bases at the moment in my current save. - Is there anything in the stock game other than mining equipment that produces core heat? RTG's?

The HG-5 has absolutely pitiful range - to reach it at all from LKO when it's at apoapsis in that eccentric orbit you need a DTS-M1/RA-2 or better. Max range between two antennas - assuming you only have one on the craft in each end - is the square root of the product of their ratings (in other words, sqrt(rating_a * rating_b)). If you have one antenna each on the relay and the craft that you want to communicate with, you can use this simple table (all ranges are in meters): As you can see, a HG-5 trying to talk to a Communotron 16 will lose signal completely at just over 1581 km. You're nowhere near reaching the Mun from LKO with that, much less the edge of the SOI. I did the exact same mistake you did when first setting up my Kerbin relay network (the exact same polar setup, too - I still use it). The HG-5 just isn't useful for that kind of work, but nobody will tell you that. It works for Apollo-style missions and for very short range relays (like around moons for example, when you have bigger relays around the planet), but for everything else it's too weak. For the eccentric polar orbit setup to really work you need at least the RA-15 but preferably the RA-100, unless you want to drag around DTS-M1's on everything you fly inside the Kerbin SOI.

I considered doing that but since it has no problems at all breaking the sound barrier and tail end drag basically disappears for all practical purposes above Mach 1.1 or so, I decided against it.

That thing of yours is really cool :V If there's one thing I don't like about mine it's that there's a bit too much unused tank mass (and a pair of structural fuselages for balance reasons). This is in part due to part number limits, but I think it might be fixable if I just let go of some design orthodoxy...

Mucking around with dinky little Panther-powered things again. This here thing is completely stock, 28 parts, takeoff weight <16 tons, requires only two 160 science nodes (Supersonic Flight and Advanced Electrics), ferries 3 Kerbals to or from LKO with ~350-400 m/s dV to spare. I'm quite satisfied with of the aerodynamic part of the design - it handles really, really well and is very stable. https://kerbalx.com/renhanxue/Everything-I-Know-About-Spaceplanes I wrote a lot of words about everything I've learned about spaceplane design in the KerbalX description. Some of it is empirical, but I've also learned a lot from reading things written by the members of this forum - thank you, guys!

Well, having tested it I can report that KSTS works perfectly together with Configurable Containers - recorded a mission with a dummy payload, then used the profile to deployed a craft with a regular fuel tank edited to have a little bit less LF/O in favor of a little bit of monopropellant. No problems at all, craft appeared in orbit with everything in the right place. Thanks for a great mod!

Interesting mod! In the OP it is mentioned that it is not compatible with Modular Fuel Tanks. Is the incompatibility conceptual, or just related to something Modular Fuel Tanks does in a particular way? The reason I'm asking is that I'm using a mod that does a very similar thing (Configurable Containers) and was wondering if anyone had used that together with KSTS.

The OP is good, and I like it, but I read it several times and the aerodynamic center still made no sense to me (not an engineer, solely basing this off of my hazy memories of high school physics). So then I read Wikipedia and some "basics of aerodynamics" texts by NASA and others, as well as old forum posts where @Boris-Barboris argued with people about the difference between center of pressure and the aerodynamic center, and it makes a little more sense now, maybe? And I find the best way of actually improving your understanding of something is to try to explain it to someone else, so, I'll give it a shot. When our aircraft is in flight, the aerodynamic forces acting on it are usually separated into two component forces: our familiar friends lift and drag, where the lift is perpendicular to the direction of the airflow and drag is opposite to the direction of motion through the airflow (although, in KSP I think lift might actually be perpendicular to the lifting surface instead, which probably has a whole bunch of implications that I do not fully understand the extent of). When you consider the sum of these aerodynamic forces, you find that they produce a torque on the aircraft. For the aircraft to maintain a constant attitude, the control surfaces need to be arranged such that this torque is zero (or, well, we would also also need to consider any torque caused by the engine thrust not being aligned with the center of mass, but let's disregard that here). What we're interested in here for the purposes of this discussion on "CoL behind CoM", or in fancy terms "static longitudinal stability" is obviously only the longitudinal torque, or the pitching moment. Now, what we must avoid in order to achieve static longitudinal stability is a situation where an increase of the AoA leads to a positive pitching moment (that is, in the nose-up direction, or more strictly speaking in the "increasing AoA" direction), because this causes a positive feedback loop where the pitching moment causes a further increase of the AoA, which causes a further increase of the pitching moment, and so on. Going by the rule of thumb, we know that ordinarily the greater deal of the aerodynamic forces is lift (because our lift to drag ratio is usually greater than one), that lift is directed roughly upwards-ish, and that lift tends to increase with AoA, so going by the seat of our pants it seems obvious that if we place the center of lift behind the center of mass (around which the aircraft rotates), we'll be home safe and the resulting torque will be negative (acting to decrease AoA) and grow with increasing AoA, more the further the CoL is from the CoM. Remember, the magnitude of the torque is the force multiplied by the length of the lever arm, and this is why people say that aircraft with the CoL closer to the CoM are more maneuverable - the counter-torque caused by any AoA that differs from the equilibrium is smaller, so you need less force, that is smaller control surface deflections, to maintain the attitude you want. And all that is true - it's just that lift is only one component of the aerodynamic force, so considering only the center of lift doesn't tell us the whole story. So, what do we do? You'd think that it would be useful to try to find the center of pressure instead, because just like we can think of the gravitational force as a single force acting through the center of mass, we can think of the total aerodynamic force as acting through the center of pressure. The problem with this though is that when the AoA changes, not only does the total aerodynamic force change considerably (both in magnitude and direction), the center of pressure also moves (it can in fact move outside the aircraft in certain conditions). So, while it is certainly possible to analyze stability based on the center of pressure and the total aerodynamic force, it is much more complex than "place center of lift behind center of mass". There is an easier way, though. Remember, what we're interested in is the pitching moment, or torque, and how it changes with AoA. It turns out that if we disregard the center of pressure and play around with where the total aerodynamic force is applied, considering it as a force which varies in direction and magnitude with AoA plus a pitching moment which varies in magnitude with that force and the length of the lever arm (that is, the distance between the point through which the force acts and the point where we choose to apply that force) it is possible to find a fixed, AoA-independent point such that if we apply the aerodynamic force there, the pitching moment about that point is constant (well, almost) regardless of AoA. This point is called the aerodynamic center, and that is what we want behind the center of mass. It accounts for the total aerodynamic force regardless of AoA and as long as it's behind the center of mass the torque about it acts to push the nose in the direction we want. You can't actually see this point in KSP, of course, but the center of lift is reasonable substitute in many cases, at least for eyeballing purposes. We've talked about why already, but additionally contributing to why this is the case is that the pitching moment produced by the lifting component of the aerodynamic force tends to be much greater than the pitching moment produced by the drag, since the lift is perpendicular to the direction of motion while the drag is parallel to it. You can of course construct craft where this assumption goes right out the window by giving the drag a very long lever arm, especially one that isn't parallel to the longitudinal axis of the craft, but if you do that, well, I hope you know what you're doing. Adding angle of incidence to the wings does shift the aerodynamic center away from the center of lift, since the wings and the body now have different angles of attack and thus differing aerodynamic torques, but for the most part the difference is pretty small. If you just want to make stable craft in KSP without worrying about all of this, just install the Correct CoL mod and if it says your plane is stable, it almost always is. Does that make any sense at all? By all means, please point out where I'm wrong here. I'm sure there's mistakes - again, just working with hazy memories of high school physics, so terminology might be wrong, I may have misunderstood concepts completely etc. I think I understand what's going on better, but philosophizing all by yourself can lead you into weird mental sinkholes.

I've been away from the game for a while but I've had it and played it for years and it's certainly better now than it has ever been before, make no mistake about that. The original purpose of this small scale experiment was really to try to improve the way I design spaceplanes, since I noticed odd roll tendencies just like in the thread you linked and was wondering what caused it. The original spaceplane design I was investigating uses pretty heavy wing-mounted fuel/engine nacelles which I figured could cause weird things if there was some joint flexing going on, so I turned on autostruts thinking "hey, it can't hurt". Then I figured I should experiment at a smaller scale to make sure I actually understood the effects of wing positioning and angling in KSP (consulting the literature - that is to say, digging in forum threads - was inconclusive), and the rest of the story is in the OP. The actual spaceplane testbed consistently rolls about 0.3°/s or so towards the left with all autostrutting (other than the landing gear's forced one) turned off. Not too bad, but maddening when I couldn't understand why. Either way, judging by the thread you linked it does seem like this is a known issue that has been around for a while, so that does settle the question in the OP. I guess I should try KJR to see if that improves things - I was thinking I really wouldn't need that with this new nice autostrut feature, which sure seemed to help a lot with stabilizing space stations for example. Absolute and relative does seem like reasonable explanations for the labels on the rotation rate numbers, so thank you for clarifying that too.

Further observations: if you grab the offset gizmo and move the wings laterally inwards towards the fuselage so far that they end up swapping places and the "root" of the wing is now the tip (but on the other side of the aircraft), like so: Then the roll tendency inverts and the plane wants to roll right instead. I think the effect is somewhat less pronounced, though. As an aside, the elevons work fine in this scenario and still get the roll direction right (even if you don't reattach them after offsetting the wings), but for some reason the roll authority is considerably decreased. There might be something weird going on with the moment arm calculations, I guess? Another - tangentially related - question: in the AeroGUI, next to the pitch, roll and heading readouts, there is a readout in parentheses that seems to be related to the rate of change in some way. Two numbers are shown, one labelled R and one A. What exactly do they mean?

I was playing around with a simple plane with infinite fuel enabled, in order to test the effects of dihedral and high vs low wing, but I was getting some extraordinarily weird results. I was expecting the high wing dihedral arrangement to counteract sideslip disturbances and make the plane not tend to bank into level turns, but that wasn't what was happening at all. This was my test craft: It is, as far as I can tell, completely symmetrical around the longitudinal axis. Reaction wheels were disabled and I was flying without SAS. Ignore the radial parachutes on the bottom, I was trying to balance out the high wings to neutralize torque from the engine thrust axis being off center mass, but they have no effect on the test and I just removed them. After taking off and trimming pitch neutral, I was getting a very noticeable and annoying roll tendency to the left, and I just couldn't figure out why. I could trim it out, sure, but where was it coming from? On my actual planes I was planning to fly with SAS on (for autotrim, mostly) and I find that making the plane as stable as possible without SAS on helps a lot with making it fly well. After investigating if there was asymmetric drag or lift going on somewhere and scratching my head for a bit I discovered this little bit of weirdness: if the wings are set to autostrut to heaviest part (the engine), the plane consistently rolls to the left. If they are set to autostrut to the root or grandparent part (the cockpit in both cases), the roll tendency is much less pronounced but still there. With autostruts disabled, the wing configuration does what I expected, and the plane is quite well-behaved in level turns - just bank it over 20-30° in either direction and it will quickly stabilize in a clean turn with no sideslip by itself with no input other than the pitch trim, and it has a weak tendency to bank out of the turn and return to wings level regardless of turn direction. Rigid attachment of the wings seems to have a similar effect of making the plane tend towards to rolling left, but the effect is quite weak and it could easily be a mistake on my part (my testing methodology is hardly all that scientific and the testing environment isn't exactly controlled). What is going on here? Why does this happen? Surely autostruts don't actually have drag (even if they did, I don't think that would cause this). I've seen some discussion of some old symmetry joint rigidity bug that could have similar effects but I couldn't find it on the bug tracker. Here is the craft file for the test aircraft (with autostruts and rigid attachment off) in case you want to play around with it yourself. To reproduce my test conditions, take off (it is pretty nose heavy at low speed but you have more than enough pitch authority to counteract that) and get into stable level flight, without SAS, with nose pointed at horizon. Adjust pitch trim so that the plane maintains level flight. I did my tests at quite low AoA - around half a degree. Bank the aircraft left or right and observe how it behaves in a turn. Now, while you're in such a turn, autostrut the wings to the heaviest part and observe the roll tendency. It's more noticeable in a right hand turn because then the high-wing dihedral tendency to return to wings level combines with the tendency to roll to the left. It is also more noticeable at higher speeds.

Yep, works fine in 1.2.2. The static stability analysis tool is the greatest thing to ever happen to stock spaceplane design.

Many people play around with Panther powered SSTO's in career mode because they don't have the actually useful parts (Rapiers) yet. I mucked around with them so much that I forgot to actually go anywhere other than LKO for days on end. I finally did unlock the Whiplash so I guess I need to go do grownup things now but I did get a Panther powered "let's get two free kerbonauts from LKO in one launch" vehicle preeeetty optimized. While it is somewhat anathema to the spirit of the Kerbal Space Program, it is a fact that how you use your thrust is just as important as how much you have. When I started out with this whole spaceplane thing I watched a Youtube tutorial where some guy used two Panthers and two Swivels for the same payload. His plane weighed somewhere just over 30 tons, I think. This thing weighs 15,186 kg on the runway and that's including 120 kg monopropellant that I really just should replace with regular fuel. That single Panther gets it to around 790m/s at 17500m, and from there the Terriers comfortably get it to an 80km orbit with around 250m/s dV to spare. Then you have another couple dozen m/s in the RCS thrusters but again, that's strictly worse as far as ISP goes and I should just replace it with regular fuel. Other than the 1000 unit battery it's all stock parts that cost 160 science or less (battery could be trivially replaced by a payload bay and some smaller ones, plus a probe core or something). I also did use the configurable containers mod to muck around with LFO to liquid fuel proportions in regular liquid tanks and add a tiny bit of monopropellant so I could hide RCS thrusters under the nosecone and the Panther, but that's hardly mission critical - I just like getting really close before EVA'ing over. It could easily be made completely stock with no meaningful performance degradation. It flies pretty well and reenters and lands at the KSC just fine, although the airbrake is overkill, really. The center of mass is essentially completely static during flight because the Terriers are mounted so far back, but I did discover after flying it last time that the tail cone mounting is definitely not as aerodynamically efficient as I thought it was when I built it. I should probably just extend the intake nacelles backwards with structural fuselages instead.

On the other hand, I find external fuel lines to look ugly and they add a surprisingly big amount of drag. I don't find it a problem to keep track of when to stage - just right click the tank and see when it's empty.

First of all, thanks for a great mod that would be hard to live without! I do have a feature request, though. Since the new fuel feed system was introduced, I no longer use external fuel lines at all. There's simply no need, since the game does the right thing for you automatically now (by default, without you having to touch anything, tanks staged to drop first are also set to be emptied first via the fuel feed priority system). The problem with this though - as far as staging and dV calculations go - is that while KER does understand and account for crossfeeding through decouplers, it does not agree with me on when I'm going to use those decouplers. With external fuel lines set up and crossfeeding through the decouplers disabled, it correctly calculates fuel drain and very reasonably assumes that tanks attached to decouplers will be dropped when they are empty. On the other hand, if I implement the exact same thing without external fuel lines and instead just enable crossfeeding through decouplers, from what I can tell it just assumes I'll be hanging on to everything until the entire tank pool is empty, which is obviously not what actually happens. I can work around this easily enough, but it would be nice if KER did it automatically. Again, thank you for your work! edit: I guess things are complicated by the fact that although the tanks on decouplers are emptied first, fuel can still flow "backwards" from the inner stages to the outer engines. The dV calculations seem correct if I don't put engines on the tanks that are going to get decoupled.