Murph

Boosters, lots of boosters! Then booster-boosters, lots of them too! Best bet is probably to spend a little time watching some of the excellent tutorial videos out there. There's also the Tutorials on the wiki. Oh yeah, and welcome!

It's not a bad idea, although I personally rate it as low priority. There's a "RCS Build Aid" mod out there which you may wish to check out in the short term. Have you tried keeping SAS enabled while RCS-translating? I find that works reasonably well for me (not claiming perfect, just ok), combined with just instinctive RCS port positioning. Movement of the CoM due to fuel usage is going to mean that it's rarely perfect, no matter how carefully the ports are positioned.

Yes, that would be my #1 issue with them. The performance is really poor from the runway up to maybe 12,500m or 15,000m. Combined with not that great fuel economy, the total fuel burnt really kills them for me, compared to just sticking with the turbojets and aerospike. The thrust and fuel efficiency in rocket mode are not a major issue for low orbits, as there's pretty much too much thrust and ok-ish efficiency there. It's the first half of the ascent that really kills them for me, but add in less efficiency than the aerospike in the second half, and they are basically all round mediocre at best.

Cherry picking just a couple of issues, as I don't have the energy to respond to everything here. You're landing too hard. You need to have a vertical speed of less than -5 m/s (approx) at touchdown, or things will break. Either that, or it's a tail strike due to having the nose too high. Slam a F18 into the runway with high vertical speed, or at too sharp an angle, and I promise you that you'll cause serious damage to it. Ok, the damage is probably going to be quite different on the real F18, but the plane is not going to be flying again in the short term. Having been around real fighter jets stripped down to subassemblies and component parts, I can assure you that it's quite possible for bits to fall off if you put enough force into them, it just won't be quite as comical as it is in KSP. Visualise how tall 5m is (hint, it's over twice the height of a modern home/office ceiling). How long is 1s? Combine the two. That's how quickly (and therefore how hard) the plane is hitting the runway. Various forms of spin are entirely possible in the real world, and can be unrecoverable. It's hard to be certain, but it's very likely that your plane's centre of mass (CoM) is ending up behind the centre of lift (CoL). When that happens, the plane loses aerodynamic stability and becomes uncontrollable. If it only happens after fuel has been used, it's quite possible that the CoM is starting out ok, but moving to an unstable position as it changes with fuel use. These are real issues from the real world. The solution is to manage the fuel weight, and/or ensure that the CoM and CoL positions prevent it happening too easily. That's not true. The Mainsail actually has a moderately poor ISP, and it's quite possible to use other combinations of engines to equal or exceed its performance (both TWR and efficiency). Long term, KSP likely will get a broader selection of engines, tanks, and other key components. If you're willing to put a little effort into hunting them down, there's actually a massive range of parts out there as mods, many of equal or better quality than the supplied ones. A short list of mod packs I'd suggest looking at are: B9 KW NovaPunch Firespitter Taverio's …and many more… I don't want to claim that all of your concerns are invalid, there's still plenty of things which need to improve with KSP. I hope that the above is of some help to you.

Remember that overheat should generally be ignored unless it's getting close to 100%. It will depend just how you have attached them, but I didn't see the overheat being problematic on them (although all of the testing I've done has been with small craft to LKO, so fairly short burns, possibly insufficient to know for sure).

It's not related to the size of the craft. It's all about the TWR (thrust to weight ratio). If the TWR is excessive, 100% throttle will be inefficient due to the drag from significantly exceeding terminal velocity. If the TWR is just right (approx 2.0), 100% throttle will keep you on terminal velocity until you are out of the thick part of the atmosphere (approx 25–30,000m).

Yes, the O2 and H used in real world rocketry is typically liquid in cryogenic tanks. It's not explicitly defined in KSP, as far as I'm aware, but I'd guess our liquid fuel is mostly meant to be kerosine, as it's the same used for both jets and rockets (which both use kerosine in the real world, just different grades of it and different additives).

That's not so much a feature of the RAPIER. The resources system was re-worked to fix the case where the last few units didn't drain out of tanks properly (intakes are self-refilling fuel tanks, effectively). The result is that flame out from intake air starvation is at higher altitude for all engine types, as long as you have good air speed driving the intakes (and a small angle of attack). I'm not certain, but I think the air/fuel ratio for RAPIERs is either the same or roughly the same as for jets.

You already have to use either reaction wheel torque or RCS thrusters. The movement of control surfaces in space does not have any effect on the craft's attitude (and it's a very limited effect above around 25–30,000m, diminishing as the atmosphere thins, as far as I'm aware).

Nope, just tried twin turbojets + twin aerospikes, and the twin RAPIERs still lose by a significant margin. I even used a bi-coupler when doubling up on the aerospikes, to try to make it as fair a test as possible. I also don't agree that it's a better comparison, as it's not about having the same number of engines during both ascent phases, but delivering everything in front of the engines into orbit with the most fuel remaining (using that as a metric for payload delivery capability). I guess the RAPIER is ok for newbies, for lazy inefficiency, and possibly micro-planes, but that's about it from my point of view. I'm just disappointed that it's basically useless for me. I strongly disagree that it's well balanced  well balanced would be providing an alternative option which gave roughly comparable results, not significantly worse results which push it close to being relatively useless for any practical purpose. To me, the RAPIER has been crippled due to excessive concern about preventing it from being overpowered, which is actually worse than if it had been slightly overpowered. It's meant to be state of the art technology, but what we have today certainly doesn't live up to that for me. As for the 48-7S, that's not a disaster to me, it's a perfectly reasonable little engine.

It's small by my reckoning, fighter-style/size/weight. Medium to me is 50-100t, large 100-250t, huge 250t+.

Possibly for micro-planes, but I'm not convinced that they are even remotely competitive for small planes. The testing I've been doing is on a close-to-stock Aeris 4A, which I'd call fairly small. For non-RAPIER, I've been using a twin turbojet + single aerospike config. For RAPIER, twin with no middle engine. In practical terms, the RAPIER version has about half the spare fuel once it is established in a 100x100 orbit, so significantly less overall capability. I guess their winning case might be something tiny enough that a single 100kN engine works well for atmospheric flight.

The turbojets may be a little overpowered, but not ridiculously so. Look up the numbers for the 1960s RR Olympus 593s used on Concorde, for example. Even if the turbojets are overpowered, they are what the RAPIER has to compete with in air-breathing mode, and it just doesn't come close to competing. As far as bigger/smaller, lighter/heavier goes, I'm not convinced that the RAPIER actually wins there, or even comes close to competing, since you're going to need more fuel for the same overall capability. The mode switching is irrelevant to me, as it's so simple and easy to get right once you know how to fly your plane.

Great concept, great potential, but sadly the current implementation is mediocre at best. They are horribly underpowered compared to turbojets, at all air-breathing altitudes. They are also worse for fuel efficiency than turbojets and aerospikes, in their respective modes, so any weight saving is negated by needing more fuel for the same overall capability. All of the testing I've done has shown them to be significantly worse than turbojets and aerospikes in pretty much every regard, at least for small spaceplanes (but I can't see how they would be any better for big spaceplanes). I'm very disappointed with them, can't see myself using them as-is for any practical purpose. Auto mode switching doesn't come remotely close to making up for their poor performance and fuel efficiency. They do work, but you're just better off using turbojets and aerospikes, or use the B9 SABREs instead.

That's ok, it wasn't a bad suggestion, just not the right solution for all cases. For rockets, I'd argue that you're better to keep the fuel until just before the parachutes fully deploy, if you're on a ship which is a bit marginal for landing. That fuel is probably best used for a braking burn just before the chutes fill, and possibly some continued thrust after they fill, to give control over touchdown speed.

No, that's the wrong solution for spaceplanes, as it's only the oxidiser that you want to get rid of early, keeping the fuel for use in the turbojets once you're back below 20,000m, for the flight in to the runway. You might also want to dump some fuel if you've got significantly more than you require, or are going for a glider landing, but it's not as simple as just burning it away. Dumping excess fuel is the correct solution.

That would be great if it was true, but it's not true if you want to achieve the same overall capability. For example, changing from 2 turbojets + 1 aerospike to 2 RAPIERs requires additional fuel for the same capability, negating the weight saving, and possibly negating the part saving. In some cases, more RAPIERs will be required than you would need with turbojets due to the very lacklustre performance in air breathing mode. It should be great, the concept is great, the current implementation is mediocre at best.

Ahhh, ok. Yeah, I did know about that behaviour, just didn't connect it with the OP's description  I was thinking of a specific dump option. Simple solution, use TAC Fuel Balancer  it lets you shuffle fuel around more easily, dump fuel you no longer need, etc. It seems to work ok in 0.23.

I don't spam intakes. Excessive intake:engine ratio is cheating, pure and simple, in my book. It takes the skill and achievement out of designing a good plane, might as well just hack the part.cfg for the engines and/or intakes, or debug yourself infinite fuel. Multiple intakes per engine is not necessarily spam in my book, if they are attached in a reasonably realistic manner, and the total number is reasonable (more or less max 2 axial ram intakes, or 1 axial + 2 radial ram intakes, per engine). If there's cubic struts jammed onto them, I'm likely to consider that spamming and hate it. Each to their own, however. KSP rules are whatever each individual wants them to be, so spam all you like (if that's your thing). Just don't bother trying to convince me that your intake-spam design is anything other than a cheat, or that it's actually a good design, or that intake spam is actually necessary.

Maybe I missed something, but there wasn't any way to dump oxidiser in stock 0.22 that I ever noticed. How were you dumping it?

Yeah, that's the concept, but it doesn't even have that going for it when you have to add an extra fuel tank for the same overall capability, negating the mass saved by having fewer engines. For reference, most of the testing I've done with it so far has been on a close-to-stock Aeris 4A. Comparing the Aeris with an Aerospike in place of the standard LV-T30, and the Aeris with twin RAPIERs replacing the standard turbojets (and no middle engine). The Aerospike Aeris hits a 100x100 orbit with plenty of spare fuel. The RAPIER Aeris hits 100x100 with much less spare fuel.

That's the thing. What I'm saying is that I feel that the RAPIER actually doesn't fill a niche, unless there's a niche for a fuel-hungry, underpowered engine. It's early days, I'll grant you, but the testing I've done so far tells me that I'm better off ignoring the RAPIER and sticking to turbojets combined with Aerospikes. I'll gladly put up with having to use a couple of action groups compared with poor power and excessive fuel consumption (and those 2 attributes combine horribly, since needing to carry more fuel with less power isn't exactly great).

Well, to be honest, I'm kinda feeling that it falls short of its niche, when twin turbojets combined with an Aerospike outperform twin RAPIERs. I love the concept, but it gives significantly lower performance and worse fuel economy, so it's hard to justify using it.

Yeah, I'm somewhat underwhelmed by the thrust and impulse of the RAPIER. In fact, I think I'd go as far as to say that I'm actually significantly disappointed by it. I'm very glad that they have added the engine concept, just not very happy with the current performance of it.

Yeah, adding some sort of ILS or runway targeting is something which should definitely be in the long term plans. The trick I use myself is to plant a flag at each end of the runway, on the grass, as a very crude runway position and alignment indicator. That, and MechJeb's ILS target marker. I don't see anything above that really comes close to that, to be honest. We're talking about adding features which could easily be ignored by newbies, and add to the overall richness of KSP. I could just as easily say "why does every other suggestion end up with someone crying that it will be too difficult for newbies, so shouldn't be done?".