AeroGav

Perfectly acceptable on my Ivy Bridge Desktop I5, though I've been watching the World Cup on my second monitor and the calculations make that stutter (thread priority?). Despite which I seem to do a better job spotting fouls than the V.A.R., but that's another topic. @linuxgurugamer very glad to see you're continuing the work, I thought it was a dead project because Google only brings up the old thread. You must have fallen out of favor with the Illuminati

OFF-TOPIC but someone really needs to come up with a replacement for @Boris-Barboris 's CorrectCoL mod. Andromeda has the noob error of insufficient pitch stability, especially when empty I'm ashamed to say. For me, we need something that takes account of drag from non-wing parts, and was also a big fan of the static stability graph. You could see at what AoA the airplane has neither a pitch up or pitch down moment, by where the line crossed the X axis. I was aiming for a very small positive AoA, being the one it would fly at with no hand on the controls. You can see whether the plane's nose down tendency gets stronger as the node continues to rise, or if it reverses and goes flip happy because the front wing stalls first. I've had to manually correct Andromeda by making countless test flights 1. move engines forward a bit , move fuel tanks aft a bit so that hopefully CoM doesn't shift when fuel burns off (have as much fuel behind CoM as in front of it) 2. Now make flight after flight , shifting the wings around so it's stable with the new CoM position, then dialling in the right amount of built in angle on the surfaces so it holds a small positive aoa with no input 3. tweak trim flap deployment angles so you get about 5 degrees +- with SAS off and +- 1.5 degrees with it on I've now got it so the plane flies at +1 AoA with SAS off and trim neutral, with trim up action group, it's 5 degrees nose up with SAS off and 1.5 with it on, -5 with nose down set and -1 AOA with nose down set on prograde hold. Full back stick gives about 15 degree nose up. That took 2 hours, would have been 5 minutes without test flights if i still had correct CoL. That's just the testing with full tanks. To do empty, i need to manually empty all those strakes by the same amount, or leave the nervs running with parking brake set on the runway for 20 minutes. I've updated the craft file just now and might do it again if i get time for more ksp next week.

Yes, that describes things :-) Kick ass mod, first time i've seen a flight envelope in KSP. Do try adding that orbital freefall thing though. You wrote this mainly to deal with the problem of getting supersonic , at such low speeds its not a factor and in any case, lift does not have to = weight when crossing mach 1, you can always go prograde for that bit of the flight even if it sends you arcing into a dive. During the speedrun, most of my planes, Andromeda included , have a bit too much wing, and especially when empty, trying to maintain 20km for the speedrun is like trying to hold a polystyrene block underwater. The graph doesn't really show this. Once you are done with airbreathing, i go prograde for best L/D ratio and the excess lift results in a positive rate of climb. It starts to run out of lift by 35km, but you're over 2000 m/s at that point which causes the climb rate to start increasing again.

It is a liquid fuel only cargo ssto. First stage starts both panther and both rapier together. Second stage starts the nukes. The rapiers are only ever used in air breathing mode and the oxidizer tank at the front is empty. But it can still put a full orange tank in LKO :-) I suspect the drag values are far too high - is it getting confused about whether the cargo bay is open or shut , or does the wing incidence upset things?

@Booots Awesome, the game really needs something like this. Sorry for not seeing the thread earlier but i haven't played KSP in a couple months. Anyway, I decided to see what it made of my last ship, Andromeda . In many ways, this is throwing your mod a curveball, it has two Rapiers and two Panthers, and the wings are angled up with 5 degrees incidence wrt to fuselage. Part count is quite high (look at all them strakes!) too. https://kerbalx.com/AeroGav/Andromeda According to the flight envelope it cannot bridge the gap to supersonic flight, though i think you can see the two sweet spot islands of excess thrust thanks to the two engine types.. In fact, if you care to download the craft, it goes supersonic at 8km in level flight with 2x as much thrust as drag = and that's without using its nukes. Lift drag ratio also seems a little off. The actual value depends on how close to prograde you can keep, since the wings are angled. However, at mach 6 and 30km+, on nuke power, it holds only about 0.25 degrees above prograde when sas is set to prograde lock (when empty.. payload distribution can effect this). At that AoA, I was getting over 3.7 to 1 lift:drag ratio in hypersonic flight. Also, does the flight envelope take account orbital freefall ? At the sort of velocities people are going closed cycle, over half the weight is being cancelled out by this, which reduces the amount of lift needed. With a payload onboard, it doesn't hold prograde as accurately.. but still getting decent hypersonic L/D/

I hadn't considered that. You could make the fuel depot itself have only one tank (lock any others and just click on the transfer OUT button, but i agree it'd be easier with less tanks on the shuttle)

I build a lot of liquid fuel only SSTO space planes and they generally have 0.4 to 0.5 to 1 TWR in orbit, after the fuel used getting to orbit has burned off. A 2k DV burn to Duna or similar can take 8 minutes according to the maneuver node planner, so i start my burn 4 minutes early. As a result you do half of your burn before the maneuver node and half after it , so overall the burn happens "on time" more or less, and the craft takes the expected trajectory. Of course, if your burn times are long this can get in the way of making your burn close to PE to maximise Oberth effect. So it's generally better to do split burns - make a 900 m/s burn a few orbits before the ejection maneuver at PE, and do the rest of the burn at PE when the transfer window comes up - a much smaller burn is needed to put you on the interplanetary trajectory, since your AP is already on the verge of going out the system. For a single mk3 liquid fuel fuselage (long) I would use between four and six nukes,

That airplane has a massive, heavy fuselage and relatively small wings, of course it will have a high landing speed, though as you've not shared the craft file i can't check if problems with centre of mass and control assignments are making the problem worse. That front wing only has a small elevon on it, so you're either not going to be able to pitch up much, or if you do achieve large pitch angles it will be from the much larger elevons on the rear wings, however these get the nose up by pushing the tail down, and actually subtract from total lift. One other thing, wings have a much . much better fuel capacity to drag ratio than fuselage tanks. They also provide lift. Whilst they have a bit more dry mass than cylindrical tanks of the same capacity, the lower drag means less engines, which means less weight overall. With generous wing area you can climb subsonic after takeoff into thinner air before levelling off to bust the sound barrier, which allows you to reduce the number of engines still more. Matt Lowne tends to make extreme delta V flights (unrefulled to Eeloo, Moho etc) with negligible payload. Most of the fuel is burnt out of the atmosphere, and he usually has just a single nerv pushing the 100 ton ship around in space. So his priorities are different. Have a look at my crew shuttle, the Griffon. https://kerbalx.com/AeroGav/MK1-Griffon-Deep-Space-Crew-Shuttle Two NERVs, one rapier and one panther clipped together. No oxidizer required. Has 11 seats and makes orbit with over 3000dv when flown correctly. Has an inline clamp o tron and extra reaction wheels, but as it lacks RCS you're probably best off treating it as the passive partner in the docking maneuver and letting your orbital crew transfer vehicle/fuel bowser do the maneuvering. 42 m/s stall speed with full tanks on Laythe. Note that you can make large spaceplanes with good landing characteristics, but part counts get very high as you'll need to join lots of small wing parts together. Note 2 - I'd not taken this design to Laythe before and as expected, it would work better with a few small changes. Firstly, the trailing edge wing panels can bust off on landing if you pitch up any more than this. Maybe fit one of the small retactable landing gears at the back of the fuselage to prevent tail strikes, or a pair of them as outrigger wheels at the trailing edge near the wing tips. Second, there's not much sunlight out on Jool, so instead of solar panels in the service bay, fit an RTG (though in practice it has enough battery to handle re-entry , with the panels stowed and engines off, just fine. But its nice to have a bit of juice left to run the landing lights at the end of it)

The most important thing is not to pitch the nose more than 5 degrees above prograde, because drag starts to get really bad when you do this If you're asking what altitude to go supersonic at, it depends. The two factors are 1. At altitude, there is less drag. 2. But, higher up, there is less lift and if you have to pitch the nose more than 5 degrees above prograde to get enough lift, then you need to stop climbing and go supersonic instead. So , a heavy plane with small wings might as well just fly level after takeoff and get supersonic first, before trying to climb, because if it tries to climb at low speed it will have to pitch the nose up excessively and that will create a lot of drag. Otoh something with more wing area relative to its weight will be able to avoid a bit of atmospheric drag by climbing a few km first, if you're patient. Whatever method you use, the main thing is that you reach hypersonic speeds (at least 1350 m/s) before switching to rocket mode. Very powerful airplanes might be able to bust that in a steep climb, others might not. For this reason I like to level off at 18-22km and fly level to make sure we hit our top speed. As @bewing says, making flight path changes at high speed like this can create major losses when using "all or nothing" keyboard control inputs. You need to make your corrections gentle, only moving the nose a few degrees away from Prograde. Probably the easiest way is just to set SAS to Prograde hold when you're halfway between your "supersonic" altitude and the 20km speedrun. For example, say you went supersonic at 6km altitude and started climbing steeply when the RAPIERs go nuts. 20km - 6km = 14km of climbing halfway point = 14km / 2 = 7km therefore at 6km + 7km = 13km, go to PRograde hold and the airplane should gradually start levelling off. In theory it will reach level flight somewhere near to 20km, as it levels off, go back to SAS attitude hold mode to stop this turning into a dive. My preference is RAPIERs and PANTHERs in a 1:1 ratio At mach 3.7, RAPIERS give 8x as much thrust as when static. Panthers have nice power at low speed and weigh half as much as a RAPIER. They loose power very abruptly after mach 2.5 but by that point the RAPIERS are boosting hard and it doesn't matter. Rule of thumb - One RAPIER, One Panther and Two NERVs will take a 50 ton spaceplane to orbit if it is very streamlined, has plenty of wing area, and is flown correctly. With mediocre aerodynamics, the same engine combo would only be good for a 25 ton airplane.

https://kerbalx.com/AeroGav/Andromeda Indeed, this mk3 cargo plane can put an orange tank in orbit with 2 rapiers and 2 panthers. It climbs to 5-7km (depending on weight) , then when the air is too thin for efficient subsonic flight, levels off to accelerate through the sound barrier. The Panthers cut out at mach 3, but by then the RAPIERs are really going some and bear in mind you can pretty much have two Panth for the weight of one RAPIER. In level flight at 20km it can still get 1400 airbreathing, after which I start up all 5 NERVs and off we go I reckon the combo of one Panther and one RAPIER can comfortably get 50-60 tons of well streamlined spaceplane up to hypersonic speed. Of course, that means either mounting them in pairs or clipping the panther onto the RAPIER to avoid thrust asymmetry problems. @dra321 Main thing - Don't use mk2 parts for fuel storage if you can help it. A mk1 LF tank holds the same fuel as a mk2 short LF tank, but has less than half the drag. However, wing parts are better still. The real champ is the Big S wing strake - 5 of them have the same dry mass and lift rating as a Big S delta Wing, but hold 500 fuel instead of 300. Now, wing parts do have more dry mass than LF tanks for a given capacity, but the difference is pretty tiny, and the lower drag means you need less engines , which weigh (literally) tons. So, build your wings and strakes out of fuel holding parts, and get rid of as many tanks as you can, especially the draggy mk2 sort. Also, you can construct tail fins out of strakes. Have a look at this one if you like https://kerbalx.com/AeroGav/MK1-Griffon-Deep-Space-Crew-Shuttle. Note that the cargo lifter i linked in the first pic uses no oxidizer, and keeps all its liquid fuel in strakes - the only fuselage tank is the adapter at the front, which you have to have. Minor thing - it looks like you're not doing rapier cones correctly. The rear attach node on the RAPIER is 1.25m in diameter, so you need to use a cone with a 1.25m attachment node. It looks like you're using 0.625m cones. Obviously , if you put a 1.25m cone on the back of the engine, that blocks the exhaust, but if you use the offset tool to move it forward, when the game checks the path of the engine's plume it will not see any obstructions. Sounds cheaty but all it does is reduce engine drag to be the same as an engine without a rear attach node, like a Whiplash.

This technique works ok with very high thrust aircraft and avoids having to make pitch corrections. In the stock game, without a good joystick or autopilot mod, or with an aircraft with poor handling characteristics, you are stuck with making "all or nothing" inputs that slam the control surfaces to max deflection or just leaving the nose locked on SAS . The above technique gets all the pitch adjustments done just after takeoff before speed has got high enough that you can loose a lot of velocity or cause structural breakup from it. But even within the stock aerodynamic model it's a gross oversimplification to call it "optimal". The problem with this technique is that if you climb too shallow, you will waste fuel fighting drag going too fast too low in the atmosphere. Of course, in jet mode you're still getting 4-10 times the ISP of rocket mode which lessens the impact, and fact if your SSTO doesn't have any nukes you want to use up all your excess jet fuel before switching to rocket mode or that leftover liquid fuel just becomes dead weight ! If you climb too steep you might never get supersonic, or climb out of the atmosphere and switch to close cycle mode prematurely before the air breathers have hit their top speed. For a version that's closer to "the truth" Keep your nose no more than 5 degrees above prograde. Drag increases very rapidly as angle of attack increases. Without autopilot mods, that probably means right clicking on the pitch control surfaces and lowering the authority slider for the flight to orbit, if you want to make small pitch adjustments that don't kick the nose far off prograde and cost velocity. Before landing, go right ahead and set them to full authority again so you can flare for touchdown properly. Whether you should skim just above the water after takeoff and go supersonic right on the deck or climb a bit first, depends on the design of your craft and how much wing it has. Climbing a bit, then levelling off to go supersonic in thinner air can work better if your craft can get enough lift to do that without the nose rising more than 5 degrees above prograde. If your plane is able to climb after takeoff without exceeding 240 m/s or letting the nose rise too far above prograde, let it! The thinner air will eventually rob it of lift and cause the flight path to level off, at this point, rather than fighting it by raising the nose further, let it level off or even fall slightly to penetrate the sound barrier. After 440 m/s, you are properly supersonic and can climb again, but it's best not to let her get too steep. If the nose goes much above 10 degrees above the horizon I set prograde hold on SAS to kill lift and minimise drag. Your aim is to level off about 20km for a speedrun to get as much velocity out of the air breathing engines as possible. I find it's a good idea to set prograde hold to begin the process of levelling off halfway between your supersonic acceleration altitude and your speedrun altitude. For example, it you went supersonic at 7km and want to speedrun at 21km, then set prograde hold at 14km to start levelling off at the latest. After engaging rocket engines, pitch the nose to 5 degrees above prograde and throttle back when AP goes over 70km. Unless your flying is absolutely perfect, it is normal to get slight porpoising or phugoids in the ascent profile (the sudden increase in thrust as you get supersonic is mostly to blame). Don't sweat these too much. They waste some time but only very little fuel, provided you don't make the mistake of making harsh corrections trying to straighten out your flight path or correct an overshoot - remember drag builds up severely when you get more than a few degrees off prograde, going way off prograde to make a harsh correction is counterproductive ! Zooming over 20km prematurely is also not a problem provided the RAPIERs aren't set to switch mode automatically - just let the plane come back down and the engines will relight. Piloting only really has two ways to hurt delta V By switching to rocket mode prematurely, before air breathing top speed has been reached By Climbing too steeply in rocket mode, causing cosine/gravity losses. You should be thrusting at (or close to the horizon) with a a climb angle less than 5 degrees. Let the wings do lift and engines do thrust. The OP got done over by the 1.4.1 fairing drag which no amount of piloting can overcome. Stock methods of "fine pitch control" Option One - Use Pitch Trim. https://kerbalx.com/AeroGav/Voodoo-Ray Craft file here with instructions. This video has annotations (turn on subtitles) that explains how to fly this to orbit using pitch trim and no SAS of any kind below the Karman line. If you're efficient , you can take this little plane surprisingly far. Method Two - Trim flaps bound to action groups Basically, fly the plane with SAS set to Prograde hold but have trim flaps bound to action groups that give you an amount of nose up trim that's good for an efficient climb as well as for the speedrun/supersonic acceleration. Example craft file here , with instructions https://kerbalx.com/AeroGav/MK1-Griffon-Deep-Space-Crew-Shuttle Note , this plane also has wings angled up as they attach to fuselage. So even when airplane itself is on prograde, the wings are still angled at 5 degrees to the airflow, making lift. You can use trim flaps to raise or lower the nose a couple degrees though when on prograde hold

@herbal space program As well as not getting a Rapier engine snagged after jettison, I have another way to improve the design. I've been torn by the need to save weight and lower drag. The problem is there are no mk3 decouplers , so if you use some kind of mk3 to 2.5m adapter on both ends of the mk3 tank, you can only jettison the bits forward and aft of these adapters. Thus , a majority of the streamlining part mass is carried all the way to and from Tylo. But, if you offset the 2.5m nose cone so it's partially inside the mk3 to 2.5m adapter, after firing the decoupler, the 2.5m cone and mk3 adapter will be occupying the same space and this should trigger an explosion that destroys both. Ship is likely to flip out severely, but out of the atmosphere there should be plenty of time to bring that under control. Also, my design had 6 nukes. Dropping to the optimal 5 will give better delta V as well (after punching off 3 engines i gained 2k delta v in orbit)

This is the airplane and here is an exploded view of the mk1 fuselages attached either side of the main body On stock settings, unless you're re-entering at 5000 m/s from a Jool trajectory, only the Kerballed bits are at risk and the cockpit in particular. Clipping stuff inside the structural fuselages does not hide them from drag or heat, the game still sees them as radially attached stuff on the outside of the ship, regardless of how you offset. And that stuff will make huge drag btw. Just swap to an inline cockpit and if that's not enough, increase wing area so you can make more lift and drag on re-entry. Lift keeps you out of the thickest atmo till you've slowed up a good amount, and drag obviously reduces your speed and therefore heat too.

Helecopters can never manage a particularly high forward speed - possibly you are encountering "retreating blade stall" which is why it loses control. That said, if you can get up to 30-40km the ISP of stock engines dramatically improves. I built a NERV spaceplane that could make the ascent from these altitudes to orbit if hypereditied there. However, nuclear turbojets make it all much easier.

I'd be interested to see what your design looks like @Lego_Prodigy I never use the pointy cockpits (like the one in your avatar pic) because the part at the front gets most of the heat and the cockpit is the most sensitive to heating. In 1.3 heating effects made pointy cockpits more or less useless for Spaceplanes, in 1.4 heating levels have been reduced but still the first thing i'd try is to swap to the mk2 inline cockpit with a mk2 to mk1 adapter in front then a nose cone or intake on the front of that. In fact you could even put a mk2 clamp o tron ahead of the cockpit. For re-entry profile, I usually come in pitched up moderately with the nose 10 degrees above prograde. That way you're not completely stalled and are still making lift, which keeps you in the thin air longer. You also have more control that way and can fine tune your arrival point by pitching up for more drag (if overshooting) or lowering pitch to 5 degrees for best glide ratio (if coming up short). This all works better when you have a lot of wing. I normally retro burn until my PE goes to ground level somewhere in the desert continent west of KSP, my planes have good / lift drag ratios and when they encounter significant atmosphere the impact point inevitably starts moving downrange. BTW, are you dumping your payload after launch and immediately re-entering, or are you orbiting in orbit a little while first? It is harder to re-enter if the cockpit is still heat soaked from the launch process. This video demonstrates the landing point aim process mostly - but you can see how even a mk1 design has no problems with heat when using inline cockpit. Make sure you have subtitles / captions enabled for the text (think that only works on a pc tho)

Interstellar is a huge mod that takes a lot of supporting, and i think it has balance issues. But if you want to go to Eve, it has something you absolutely need for this - dual mode nuclear thermal engines that can function as nuclear turbojets (running off eve's atmosphere below mach 3.5) and then operating as a traditional nerv in close cycle mode. Use a 2.5m pebble bed reactor and hydrazine or ammonia fuel for best results ! Stock, I have various spaceplanes able to land on Duna. Pure aerodynamic lift like a Fieseler Storch - https://kerbalx.com/AeroGav/stol I have not actually flown this to Duna but I'd be amazed if it couldn't land there. As for getting there, it took off from the rooftop and got to orbit with enough Delta V to reach Duna, if not come back without some refuelling Here is a 5 seater IRSU plane that could straight shot Duna in 1.3. I haven't tried it in 1.4 since fairing drag is bugged, it might not go so well.... This one uses Vernier lift engines to reduce landing speed on Duna, as you can see from the first part of this video, you can also land on Minmus flats with them. https://kerbalx.com/AeroGav/Starsailor

I've played career games this way, but with standard difficulty it is harder to get tech than to get funds, and what funds are required are mostly spent on upgrading facilities than on vehicles. For any given mission, it requires a larger (more facilities) or higher tech vehicle to accomplish with re-use rather than 100% disposability. Plus, landing all those re-usable craft eventually becomes a chore in itself. Suggest you create a custom difficulty game and Lower Funds Rewards to 30%, as well as Funds penalties to 30%, then give yourself just enough starting tech to unlock aviation. Lowering Funds Penalties reduces cost of building upgrades , so they are no longer the major expense , and cuts down the grind. However lowering Funds Rewards means you get less money per contract and have to shoot for 100% re-use on most flights if your space program is to be profitable. As for the airplanes I use : Juno / Terrier https://kerbalx.com/AeroGav/Juno-basic-ssto 4 junos and a terrier, just gets to orbit with tight margins. Panther / Terrier Still rubbish payload fraction, but a lot less sweaty. Simple 30 part low orbit tourist ship https://kerbalx.com/AeroGav/Basic-Tourist-SSTO Something that can actually tow station components to orbit behind itself (no cargo bay) https://kerbalx.com/AeroGav/Aero-Tug-1 Panther and Poodle, self launching science lab - https://kerbalx.com/AeroGav/lowtec-flylab2 Panther / N.E.R.V Now you're in business. Worthwhile performance possible. Here's the basic Voodoo Ray https://kerbalx.com/AeroGav/Voodoo-Ray possibly able to put flags on Minmus, it will certainly do Munar flybys with ease. It is very stable aerodynamically and can be flown by non-pilot Kerbals. Here's a stretch version of the above, with larger wings and fuel tanks. A bit slower getting to orbit but enough fuel to get you to the Mun surface and back. https://kerbalx.com/AeroGav/Stretch-Ray I To reduce drag and to make the lower TWR easier to manage, the wings and control surfaces are angled such that you just use Prograde Hold in Surface mode for the flight to orbit, minor adjustments to climb rate can be accomplished by action groups 1-3 which deploy nose/up down trim flaps. Whilst none of the parts are higher tech than the basic Ray, it requires a trained pilot for the Prograde hold mode and that your Hangar supports custom action groups. The longer wingspan may not be launchable on the basic runway either. The final Panther/NERV jet is this dinky little mk2 with a small cargo bay. Can deploy small satellites but with an auxilliary fuel tank, could also get you to the surface of Minmus pretty easy (then drive it as a rocket rover over multiple biomes to max your tech tree) https://kerbalx.com/AeroGav/Firefox-I Whiplash / DART / N.E.R.V The NERV is a 500 tech point part, and overall i can do more with a Panther/ nerv than i can with a Whiplash/Terrier. But If you have both 500 tech nodes, you can make something nice like this - https://kerbalx.com/AeroGav/X949-Xanadu-B

The Russians converted an airliner to run an engine off one, search for "cryoplane". Jet engines can run off any combustible fluid, I've seen some youtube videos from a Canadian guy who refurbishes old jets for use as ground power plants, if you want to run off Natural Gas, Gasoline, Kerosene, Diesel or even waste vegetable oil (how good would that smell) you just change the fuel injector nozzles to account for the viscosity of what you're injecting and that the engine gets the right amount of fuel. Certainly less involved than converting in internal combustion engine to run off a different fuel - lower octane ratio, would have to put a spacer between engine block and cylinder head to lower compression ratio, something with higher boiling point than gasoline? would need to worry about your carburettor failing to vapourize the fuel etc. Biggest problem with liquid fuel being hydrogen, is that you'd never get a worthwhile amount in big s wings and strakes like you can in game. Also with that huge surface area to volume ratio, boil off rates would be insane. also , ice forming on wings of aircraft is generally considered a bad thing, so filling the wings with cryo propellant probably not smart,

Most of the cost issue is down to people using NTR for deep space probes. Obviously if you're not recovering the part, the price hurts. That said, since the NTR will be on the upper stage, it really should be possible to recover the entire upper stage at the end of the mission , though the re-entry aerodynamics and parachute landing attitude will need careful design. I only really use them on space planes and shuttles, so the recovery of the engine is a given (and necessary delta v would be hard to achieve otherwise). Though some of these nuclear spaceplanes aren't SSTOs, discarding jet engines or riding up to 20km on SRBs

But Methane leads to soot deposits within the reactor doesn't it, which precludes us from using the engines the way we do in KSP (over and over with no maintenance, for decades on end, in an IRSU grand tour) The values given for Ammonia and Hydrazine as NTR fuels vary a lot depending on what source you're quoting and on the reactor temperature (degree of dissociation). Remember though, we're not comparing their values with Hydrolox, an Ammonia/Hydrazine NTR is competing against storable chemical propellants, that give between 310 sec (Space Shuttle OMS) and 375 (SpaceX Raptor, as yet unbuilt, if you treat mild cryo Methalox as "storables")

You can see why the RAPIER is such a good jet engine even if you're not using close cycle mode. The thrust multiplier remains above 3 till mach 5.5, given that orbital velocity (at stock scale) is about mach 7, you only need 1.5 mach's worth of rocket delta V. The Whiplash may have 20% better fuel consumption in the air breathing phase, but it drops to a multiplier of 3 by mach 4.5, which means you need 2.5 machs worth of rocket delta V. Even if you are using LV-Ns, rocket mode fuel consumption is 4x that in air breathing, so you can see why the Rapier's higher top speed always wins. Well, there are other fuels that an NTR can run off than LH2. For example, Ammonia (which can also be used in jet engines). Liquid ammonia is a storable propellant. It won't give you anything like the ISP of NTR / LH2 (though it does partially dissociate to hydrogen in the heat of the reactor) , but it's still heaps better than storable chemical propellants. The main thing is that large LH2 tanks mean drag, which is worse on a space plane than a rocket. BTW, in this game rocket engines correctly attached give very little drag, even if you don't clip nose cones into their rear attach nodes. The vast majority of the drag is coming from the fuselage, ie. the LFO tanks of your thirsty closed cycle RAPIERS. Sounds like the best compromise would be to give it the Vacuum / Atm closed cycle ISP values of the Dart aerospike, and to reduce this flow multiplier to 1.5. People will have to use a proper flight profile. You can still hit the same airbreathing top speed, but you'll need to do that in level flight at high altitude, not while passing through 8km in a steep climb. Flights to orbit will take a minute or so longer, but if you don't like flying, why are you building space planes. I'll have to redesign my craft to incorporate more RAPIERs, but will probably start using Oxidizer again and fit fewer NERVs/Panthers.

You are correct in that the SABRE, unlike the RAPIER, has a plug type nozzle that gives decent performance across a wide range of air pressures, purportedly not far below the state of the art in terms of vacuum isp. The problem is you are going to hard time attracting support from the community because it is already seen as one of the most OP engines in the game. You'd really have to package this up with a set of nerfs to address the following : The Rapier should require liquid hydrogen. LH2 has more heat absorption per KG than even water, no other fuel comes close in this regard. This means to have a RAPIER you have to deal with boil off and more importantly, very bulky (draggy) fuel tanks. Without LH2, the use of fuel to pre-cool the intake air - the thing that differentiates it from a Whiplash - is not viable. The Rapier gets this crazy ramjet boost to max thrust at high speed, peaking at over 8 times the static thrust rating at mach 3.7. This is not a feature of the real SABRE and seem to ignore flow limits of the intake/precooler/compressor systems, rpm limits of the turbines and max chamber pressures. This banzai surge from mach 1.5 - 4 makes possible the blatantly unrealistic flight profile of flying level after takeoff and accelerating to mach 4/5 at sea level, before pitching up and holding a constant pitch angle till clear of the atmosphere. The fact that thrust goes to near infinite levels, allows the massive drag to be overcome. In reality no aircraft has gone more than a hair over mach 1 at sea level. Any airframe that generates enough lift to get airborne before the tyres explode will be too draggy to push high speeds at sea level. At altitude, it's a different story. Same with the SABRE engine - the ram air effect of increasing speed compensates for the thinning air at altitude, but will not allow it to greatly exceed its sea level thrust due to choke limits. The pre-cooling deals with adiabatic heating, up to a point. Doing both of those would require major changes, but they should perhaps give the RAPIER a much flatter thrust curve in its config files, to at least acknowledge the above, if they're going to buff the vacuum ISP like you suggest. That will still break a load of legacy craft files, but then that's something with come to expect with version updates ! My preferred propulsion is now one Rapier , one Panther and two NERVs per 40 tons of craft weight. I don't use the close cycle mode at all. Can only see it making sense in edge cases like what Matt Lowne does with RAPIER SSTO lifting an ION system into orbit. I can get better payload fraction going liquid fuel only (mass of the nervs more than offset by absence of massive LFO tanks) but RAPIER only gives lowest dry mass, which enables the Xenon drive payload to get more delta V.

Monopropellant Hydrazine fits the bill, unless anyone can think of a reason to look further Liquid Fuel It's far too dense to be Hydrogen It doesn't give nearly enough ISP to be Hydrogen (450 top end chemical, over 1000 NTR) It can be stored indefinitely It does not cause soot clogging of NTRs with prolonged use (so not Methane or Kerosene) It can be used in jet engines Not particularly explosive. No sustained ground fire when the container is destroyed My theory is that it's Liquid Ammonia. This stuff can burn in air in air breathing engines (though it only has half the calorific value of kerosene) and it can be reacted with storable oxidizer in a chemical rocket. In an NTR, some of it dissociates to hydrogen, giving moderately high ISP. In a crash, you really don't want be breathing the vapours of this stuff, but then the same goes for Hydrazine. It probably helps our little green friends wear space suits, but then again they seem to be made of strong stuff all round. Oxidizer Storable Nitrogen Tetroxide?

Max deflection does not come free. The higher the angle of attack of the control surface, the more drag it produces. Eg. Airplane is at 3 degrees angle of attack Wing is mounted to fuselage with 5 degrees of incidence Aileron on wing deflects 10 degrees That aileron is now at 3 + 5 + 10 = 18 degrees At small angles, you get mostly lift, but after a point lift starts to max out but drag goes up exponentially. This is especially important with regard to ailerons because the drag at the wingtip torques the nose away from the direction you're trying to turn in (adverse yaw/sideslip). Of course, you can take a surface with a low max deflection angle and crank its "authority limiter" slider up to 150% if you want to turn it into a highly deflecting one, or take a highly deflecting surface and turn the authority right down. I love Big S wing strakes, i try to keep all my fuel there if i can. Orange tank to orbit on a really dinky liquid fuel lifter - ...and yes, if your computer can bear the part count, don't use real tail fins, mount big S strakes vertically like in the above example then put elevons on the end for the active part of rudder functions. Here's another convert to the Way of the Big S Strake p

This is overall the best spaceplane i've built so far, tested in 1.4.2. https://kerbalx.com/AeroGav/MK1-Griffon-Deep-Space-Crew-Shuttle 11 Seats and 3000dv in low kerbin orbit. Has an inline clamp o tron and twin reaction wheels, but it wouldn't be particularly easy to dock to a station. Since i'm bad at docking, i'd probably put some kind of tender in orbit next to the station, some non aerodynamic thing with docking ports and 4 way rcs blocks to move the crew the last 100m from the station to the airplane. You could try to improve the docking maneuverability of the airplane but RCS ports add a lot of drag - if you must do this use one Vernier or linear RCS port for each axis, mounted on the CG, not the draggy and melty 4-ways. Even then , the inline clamp o tron makes it better as a thing to be docked to , rather than a thing doing the docking. Yes, people put shielded clamp o trons on the front of spaceplanes but that adds even more drag. You can overcome that drag with the raw power of a chemical fuelled ship where every engine is a rapier, but then running out of fuel becomes the issue. SSTO rockets are a few minutes quicker to orbit than a space plane, but it ultimately turns into a race against your fuel gauge the margins are so thin.