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  1. A while ago there was this excellent discussion on air intakes and drag in KSP: This is still an important topic (would be even more so if the dev's could give us some larger airbreathing/jet engines, so spaceplanes are actually useful without massive engine-spam!) and I wanted to continue to draw attention to the idea, discuss it, and see if anything has changed. Also, there were some nuances to Right's graph (re-posted below for convenience) that I don't think really got any proper discussion- and couldn't be discussed there now without nero'ing a very old thread... Note, for instance, the shape of the Shock Cone Intake performance curve (or lack thereof). I think many players sub-optimally assumed the most efficient Spaceplane ascents involve keeping all your engines lit throughout your entire ascent. However I have increasingly found this is NOT the case-especially with the 2 stage spaceplane designs I have been experimenting with lately (a smaller Spaceplane optimized for high-altitude, high-speed operation rides piggyback atop a larger plane that breaks off. Awesome in Sandbox/Science, but requires a mod like Flight Manager for Reusable Stages so you can fly the lower stage back to actually be useful in Career...) Often it is better to have some engines- particularly Ramjet engines- you only ignite at higher altitudes and speeds, keeping your demand for IntakeAir (and Thrust production) relatively flat as you ascend... (this is even MORE true with modded parts like the Air-Augmented rockets from, I think, Mk2 Expansion: which, realistically for a ducted rocket, perform better at high speeds not only in terms of Thrust, but ISP...) If you have engines you only ignite at high altitude+speed (or simply don't throttle all the way up until you reach high speed/altitude due to heating issues, aerodynamic stability- particularly with dynamically unstable designs that become less stable at higher speeds, or not having your wings rip off due to aero forces in FAR!) then the Shock Intake curve suddenly looks a lot more appealing: note these curves are for constant altitude- the Shock curve ends up being flattened (in terms of rate of IntakeAir production) by reduced air density at higher altitude... Other things notable: - The Divertless Radial Supersonic Intakes appear to have the smallest performance-drop of any intake other than the Shock Intakes between Mach 3 and higher speeds (the slope of their curve is much more gradual, even controlling for their lower peak), making them often the second-best choice for high-speed planes (as well as great for fine-tuning *precisely* how much intake you have, so you don't have any more than needed...) - Engine Pre-coolers have, surprisingly (and unrealistically, given the whole POINT of using them in real life would be high speed+altitude performance) a steeper curve relative to the amplitude of their peak than the Adjustable Ramp Intake (aka the stock RAM-effect intakes). This makes them more poorly suited for high speed/altitude operations, at least as intakes (again, this is unrealistic- and the dev's ought to rebalance these to make them more useful). That being said, form-drag (from frontal cross-section mainly) becomes much more punishing at higher speeds, at least in FAR, so they actually do work well at high speed planes- but for all the wrong reasons (in real life, Pre-Coolers aren't even intakes at all, but allow you to cool/compress airflow before it reaches the engines so they "think" they're actually operating at lower speeds/altitudes. This would be easily simulated in KSP by simply having them decrease the airflow speed and altitude any engines they are connected too "see"- and indeed this is EXACTLY how they used to or still do work in KSP-Interstellar, which included special code to make pre-coolers work realistically: at least in older versions for sure...) In real life, they would produce a lot of intake Drag (as you slow the airflow more) and provide no direct intake functionality- yet be CRITICAL for a horizontal-takeoff spaceplane ascent... - On the topic of pre-coolers, again: there has been some mention that they are highly heat-conductive (wicking heat away from engines), yet this is somehow a BAD thing (as it causes them to absorb more heat from the atmosphere). It seems to me most players don't understand the Stock heat conduction system well, or how to use this properly. The best parts to attach pre-coolers to (on the other side of the engine) are large, heavy parts with a lot of cross-sectional area (so these parts in turn can pass the heat they absorb from the pre-coolers to other parts). This is entirely because the Stock heat model assumes an entire part is all at a constant temperature, to make the calculations manageable. Anyways, this makes good parts to attach Pre-Coolers to things like the long Mk2-Mk1 adapter, the Mk2 Bicoupler, the flat (rear) end of Mk3 parts, or especially large cross-section mod parts with inline 1.25 meter nodes (like the "Stail" to 2.5 meter adapter with shoulders in OPT Aerospace, or the Mk4 Adapters in Mk4 Expansion...) The parts they are attached to should, ideally, in turn be attached to even larger parts (like a Mk2-3 adapter in front of a Mk2 Bicoupler). The key is to wick heat away from the pre-coolers as quickly as possible so they can wick more heat away from the engines in turn. Not that engine overheating is THAT big of a problem in Stock (except for with the NERVA nuclear rockets- a part intake air precoolers would be USELESS for in real life, unless you were air-augmenting them... Or modded nuclear turbojets, like those in Mk2 Expansion- where at least the use of pre-coolers is realistic) - The Small Circular Intake has a relatively flat curve that LOOKS like it would be well-suited to high-speed operations: but in reality they tend to explode at high speeds, as they have terrible heat-tolerances...
  2. I down-loaded and flew @TheFlyingKerman 's Kerbus A380-400 this evening and, following the instructions, made an awesome discovery about the Panther. (Incidentally, I love the Kerbal Express Airlines -- Regional Jet Challenge. Always something interesting, educational and/or useful!) Whereas heretofore, I've always used the after-burner to climb to altitude where the dry mode won't work, I had concluded that the altitude limit for dry mode was somewhat less than 10km. However, dry mode is able to run as high as 15km (although probably better at about 13km[*]). The thing is that dry mode has a speed limit (somewhere in the 630-700 m/s bracket(?)). If you're going super-fast on the afterburner, you'll flame out switching mode to dry unless you first slow to a speed at which dry mode can operate... (Makes me wonder if there are some configurations in which wet mode is required to get to an altitude and speed at which dry mode can then sustain propulsion but could not have achieved alone...?) OK, so here is my first question: what else I don't I know about this marvelous, marvelous engine??? Please fill me in on all there is to know about the delightful Panther (dry mode)!! How high? How fast? Etc, etc? Second question is about air intakes as they perform in KSP: why would you want to close one? Is this only a drag-reduction measure (when the engine has been shut down)? Or does deeper magic lurk within? [*] Depending upon the aircraft, of course, but "as high as"...(?)
  3. Hi folks, I just completed a sandbox-mode dry run to Laythe with my six-kerbal, full-science SSTO, the Sojourner II: The dry run went pretty well - I got out of Laythe orbit with about 1100 delta-v left in the tank, which should work for my eventual plan to dock in Laythe orbit with a fuel pod. It would be nice if I could get back Kerbin without refueling but I have a feeling that's not going to happen, even if I improve my maneuvering a bit. In any event, I am always looking to optimize the plane for my career-mode run, and one area I'm unsure about is intakes. One preliminary note - due to my ruthless culling of extra jet engines to save weight, this thing can barely get out of its own way in-atmosphere. It has to launch half-empty on Kerbin (I refuel in orbit), then has to do a slow climb and then dive at around 7k meters to get velocity into the Rapier sweet spot. Laythe performance was a little better, but I still had to turn on my nukes for about 5 seconds on takeoff to make sure I didn't hit the ground right away. I don't care much about Kerbin efficiency as long as the darn thing makes it to orbit, since I will be refuling in LKO anyway. I do care about saving fuel on Laythe, though. But since so much delta-v is going to be expended in space, weight may be more important than atmosphere performance. As you can see, I've currently got 2 Ram Air Intakes on each of my Mk 1 nacelles. They generated way more than enough intake air throughout the journey, and are fairly light, but I hear their drag is not the best. Other options: -The shock cones. These seem to be the go-to choice in most planes I see. I do not need the extra air at all, but I do hear they have better drag than the Ram intakes. I did a test climb with shock cones and could see maybe a minor speed improvement, but it was overshadowed by inaccuracy in my climb profile. The extra weight shaved off about 20 of my plane's 5,800 vacuum delta-v versus the Ram intakes, which does not seem like a big price if there is a decent efficiency improvement on Laythe. -The precooler, which also seems pretty popular. I like the zero-drag factor, but between the weight of the part itself and the fact I'd have to put something else in front of my nacelles (maybe NCS adapter and tiny-size nosecone), it will likely end up heavier than the shock cones. It will also add bulk, being the size of a Mk LF tank but with much less fuel capacity. -The radial adjustable ramp intakes. These are very light, which I like, but they add a new source of drag and, again would require me to put a nose cone in front of my nacelles. Air supply seemed adequate (maximum draw with 2 of these guys was about 50% according to KER), except for a weird thing where my Rapiers flamed out 1 second after initial engine startup on the runway. This was remedied by starting at half throttle for the first few seconds, then maxing out once my plane was moving. None of the other intakes seem like good options. The subsonic ones would flame out, and the divertless intakes seem like worse alternatives to the precooler. I am tempted to just go with the shock cones, but was wondering if anyone else has any thoughts on what works best for a Laythe mission. At the end of the day I doubt there's a big difference, but half the fun of KSP is agonizing over the best part choice, right? Any other thoughts on ways to optimize the plane are welcome as well. I am tempted to remove the drone core, clamp-o-tron and/or RCS, but usually end up regretting those decisions. I'm only keeping 15 monopropellant. May also reduce the oxidizer capacity as I don't need it all to escape Kerbin, and didn't need any on Laythe. Final note - part cost is not an issue. Thanks!
  4. I know this question has been asked time and again, but I have dug deep and yet to find a clear cut answer to the question: Are pre-coolers capped with an aerodynamic nose (advanced nose or tail connector) less draggy than the same amount of shock cones per intake area? That seems to be the two greatest issues is intake area vs drag on any high speed vehicle. Testing the same vehicle with the same weight, does intake area even count towards drag on the pre-coolers that are streamlined? I guess what I'm asking is how the heck drag is calculated, especially if you can't directly tell from the debug part menu? This is the single most difficult issue preventing an SSTO to the outer planets is the drag on Kerbin.
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