[Oops....today I learnt what "LAP" is.....and how do I fix my mistake?]

2 hours ago, paul_c said:

Next brain teaser is....what's the best altitude for a space station? It also has a pair of RA15 relay antennas, so its nice to have it high up? But not too high so that its reachable for craft possibly landed at Minmus on low fuel?

it depends on what you want to achieve, really.

for fuel considerations, it's better to put them low. it costs less to reach them from the surface, but also - for oberth effect, look it up if you're not familiar - it's going to be cheaper to reach them when coming from outside the planet, and it's also going to be cheaper to leave the planet from the space station, unless you are going very close.

still, they should be up high enough that a ship trying to make a rendez-vous can have a smaller orbit, to catch up to them (it can always go into a higher orbit and have the station catch up, but it's going to take very long if the station was ahead and have to go all the way around the planet). so, for minmus that good height should be around 20-30 km.

on the other hand, as you correctly pointed out (btw, nice to see a new player who already has a good understanding of stuff like gravity turn and antenna placement), on a low orbit minmus is going to block a lot of your antennae's path. so, to have the station act as relay, you would want to put it up as high as possible, so it won't be obstructed.

it really depends on what you want to prioritize.

[Best hope for Polar Orbital Insertion (the Mun)]

11 minutes ago, paul_c said:

What's the best (nearest 90deg, polar) inclination you'd normally hope to achieve if going from Kerbin to the Mun? I've done it a few times, initially not deliberately because my starting orbital plane on Kerbin was no where near zero (and it was just luck or lots of excess fuel to make the trip in the first place) but I deliberately wanted one this time, and achieved it:

 

38.4 degrees......could I hope for more? 90??

yes, you can get a mun insertion at 90 degrees, and it's not even very expensive. you don't even need to start from an inclined orbit either, that would be expensive.

just, when you make the intercept burn, fiddle with the normal/antinormal (pink direction) until you are not pointing at the equator but at the poles.

here is an image. do notice the directions in the manuever. it ended up costing 60 m/s more than a normal equatorial insertion.

 

But it's even better to make a course correction along the way, as shown here

the first manuever was a normal, all prograde manuever. the second manuever, in violet in the upper side of the image, is mostly normal to push your trajectory up, plus a little bit of radial to go exactly over the pole, and it is only 36 m/s. the cheapest place to make those manuevers is around halfway, and you can be more accurate.

[Real KSP Rockets?]

in theory, yes. in practice, it's all another matter

[the kerman club roving guide]

I like rovers and i spent a fair amount of time and effort building and driving them around. After leaving the kerbin system I quickly realized that every planet is a different driving experience, and I decided that someone should write a tourist review

Kerbin

Yes, you can drive a rover on your home world too. Kerbin is quite a nice planet. It has a wide variety of terrains and biomes, more than any other world. The giant quartz compete with Vall's criovolcanoes for the title of my favourite surface feature. On the down side, a habitable planet with large grassland but without trees feels a bit off. Also, the high gravity makes it difficult to go uphill with many of my favourite designs. All in all a balanced experience, three stars

 

Mun

Mun is a great place for rovers! The surface gravity is low enough to create stability problems, but still in the optimal window. The craters make the terrain interesting: if you have a cheap, frail rover, you can plan your way around them, while if you have a sturdy advanced rover you can use them for really cool jumps. The two canyons are great for racing circuits, and there are a lot of interesting places to visit. The gray surface would be a bit dull on any other place, but on kerbin's moon it gives a warm homey feeling. Definitely one of the best places to drive a rover

 

Minmus

Minmus has a nice coloring and nice terrain all around. The terrain is quite interesting, with all the big slopes up and down. Unfortunately, it has no special features worth visiting. But its major flaw is the gravity, too low to get any speed before capsizing. On the plus side, it is very easy to reach. Three stars, mostly because it looks good

 

Eve

The rating here is not for a rover but for a plane. But in the planet's thick atmosphere, a plane is actually much easier to use than a rover, and much faster. Most of the planet is dull, but some of the mountains are really wonderful, especially the massif around 30°S 150°W. I don't like the purple color, but twilight has the most beautiful green horizon.

 

Gilly

I never expected to give a high mark to a small moon without enough gravity to do anything, but Gilly positively surprised me. It took me several minutes to get the hang of driving there, and it certainly does not resemble driving anywhere else. It's all in slow motion, 3 m/s is the top speed before going suborbital. But this lumpy rock is so small, even going slow you can still reach places faster than on other planets. And the terrain is very interesting, full of up and down

 

Duna
 

Duna has a variety of terrains, mostly hilly; there are canyons, but they are too big to be striking like those on mun or dres. The gravity is fairly high, so rovers are pretty stable. On the down side, going uphill is quite expensive. the sun is more distant, but still close enough to make effective use of solar panels. There are interesting features to visit. The atmosphere also make it much easier to land. All considered, it's a nice place to drive around, though it lacks striking features like the mun's canyons. The major factor preventing me from giving it full marks is that I find its red color dull after a while

 

Dres

There are very few reasons to go to Dres, and driving a rover is not one of those! the surface is full of angles, and coupled with the low gravity it makes a rover much more unstable - and much more prone to damage if it flips. The canyon looks good and it would have a lot of potential, but its bottom is too irregular to drive through. Definitely nothing to recommend here

 

Vall

Vall has a very nice environment, I like the blue color and the criovolcanoes are spectacular, not to mention the dance of Jool, Laythe and Tylo in the sky. The gravity is in that optimal range where it provides stability without making it too difficult to go uphill. There are nice mountains to climb and slopes to tumble downhill. its only real flaw is the distance from kerbol, making it very difficult to get energy. rover wheels are quite expensive to operate when running uphill, and even multiple rtg may not be enough to power a rover. Still, one of the best places. I'd give it 4 stars and a half if it was possible, but if I have to choose, I'll give it full marks

 

Tylo

A strange world, difficult to sum up. Different areas have very different characteristics. Gravity is very high, meaning it will be possible to reach high speed (and in lowlands at least the terrain is flat enough for it), but it's also going to be very difficult to go up a slope. or to brake down a slope. The combination of high speed, false sense of security, and difficulty to brake, makes for a very dangerous combination; I don't think i crashed my rover nowhere near this often anywhere else. The landscape is not bad, but nothing special either; the best thing is the dance of the other two moons in the sky, aside from that it's mostly an uninteresting rock. But the most damning feature of Tylo is the fact that its unique characteristics basically force you to pick up speed moving downward and conserve it moving upward, and zipping at high speed with very little control. It feels less like driving a rover and more like throwing a bowling ball.  I'm giving it a low score as i'm not liking it; however, i have to admit that Tylo brings out the worse weaknesses of my rover and negates most of its pros, so perhaps it would be a better experience with something designed more specifically for this environment.

 

Other worlds I didn't visit extensively enough to rate
 

Moho

Moho is just so distant from everything else, I never visited except in tests, though I would like to. there are some nice hills and the place looks good. The large amount of solar power is convenient, and the gravity is just right. Looks very promising overall.

Ike has a very rugged terrain. It could be potentially interesting, but it does not mesh well with the low gravity. That, and the lack of notable features, never gave me much reason to drive farther than the closest surface features.

Laythe

Laythe looks really good, but there's too little land for a rover. I think they should have made a "hydrotermal vent" surface feature that only spawns on the ocean floor, that would have been really cool. Anyway, I will soon explore Laythe in depth with an electric plane. Maybe i should expand this guide to generally include "suborbital vehicles"

Bop

The low gravity is just meh. Quite unremarkable except for a couple nice easter egg (cough cough kraken cough), and those are reached more easily by suborbital jumps.

Pol

A gravity even lowest than minmus does not bode well; however, the peculiar landscape and very rugged terrain may actually make it fun. If they don't make it even more miserable.

Eeloo

Nice gravity, nice surface features, looks good. Not much variety to the terrain, though. those canyons look good on the map, but they are quite unremarkable when you are inside. I did land there with a rover, but I wasn't compelled to explore further.

 

You are welcome to post your own review of driving on various worlds. Let's expand this guide

P.S. perhaps it would fit better under fan works?

 

 

[Career and contracts]

in addition to what others said, i like to make reusable stuff, so i can fulfill a contract and then go on a mission of my own.

I want to make a mun landing but i'm only paid for bringing tourists in mun orbit? i make a ship with two modules, in mun orbit i detach them, the tourists stay in orbit and the lander lands.

i want to make an eve probe but i'm paid to put a satellite in orbit around minmus? i send the eve probe with plenty of extra fuel, i place it in minmus orbit to fulfill the contract, then i go on to eve

after i unlocked isru, that was magnified exponentially, because i could keep reusing my stuff infinitely. shortly after, i stopped playing the career as it was not challenging anymore.

[visualize CoM and thrust on a ship in flight?]

2 hours ago, Snark said:

Well, at least at a very rough level, just look where the camera is pointing (i.e. at the middle of the screen).

Unless you manually set the camera to focus on sometihng else, by default the game always points the camera at the CoM of the current vessel.  So you can just look at the center of your screen and that's it.  (It's easier to see where the spot is if you rotate the camera back and forth a bit-- the CoM is the part in the middle that doesn't move when you rotate the camera, because it's at the center of rotation.)

Dunno if that's good enough for your purposes, but it can give you at least a rough idea.

it's not good enough for my purposes, as the push can be off-center by just a little bit and it will already set the ship rotating. even with a dozen large reaction wheels.

and while this game has a mod for everything, i am reluctant to install them.

ultimately, i solved this by trial and error. deactivate sas, turn on rockets at full speed, see which way the ship deviates. shut down one of the engines on the opposite side, and repeat the process. i was able to find a good enough balance that sas could keep me stable by shutting off two of my 24 engines. with that i was able to land on minmus and refuel, and with full tanks the ship is balanced.

[Attitude control and SAS - Tutorial Orbiting 101]

i've done challenges where i had to launch stuff without sas because i could not afford a module and i had to prioritize other things than sending a pilot. including doing mun landings without sas, keeping manually aligned retrograde.

so, i can testify that managing without sas is indeed something that may turn out useful

[Attitude control and SAS - Tutorial Orbiting 101]

yep. actually, the main skill there is being able to focus on the navball. if you will just look at the tumbling spacecraft, it will be hopeless. look at the navball, and try to figure out just one motion at a time. ok, the ship is wildly out of control, but let's ignore that and focus on seeing if it's actually spinning on its axis. let's fix that, then continue with another axis. if you can focus on one movement at a time, you'll do it

[The Ultimate Jool 5 Challenge Continued]

2 hours ago, JacobJHC said:

The propellers are fine, although the science bay needs to have the clipped science parts and RTG moved. I also think the roverarm needs to be moved so it isn't clipping as well

ok, i worked on it. i added another cargo bay, and i arranged the stuff around. the science bay has no parts clipped in it.

As for the rover arm. i can't fit it into a cargo bay because there isn't a bay large enugh. i even tried to remake the whole plane as a Mk2, and there the cargo bay works, and it also flies very well, and it has exceptional resistance to reentry. but it's much heavier and it has no chance of taking off from water. too much drag.

But! I moved the three non-propellers cargo bays together, and I placed the robotic arm in a way that is entirely contained in the bays and it's not clipping anything else. In my mind, those three bays would be joined by a hole where the robotic arm would pass. It's a tight fit, but there's no clipping for any piece, except the arm is going through the cargo bay walls.

It's the best I can do with the lack of a longer cargo bay. Will that be acceptable?

[The Ultimate Jool 5 Challenge Continued]

44 minutes ago, JacobJHC said:

The propellers are fine, although the science bay needs to have the clipped science parts and RTG moved. I also think the roverarm needs to be moved so it isn't clipping as well, although I am not sure what I would suggest you do with it.

 

ok. another question, since i'm going for science. the orbital scanner adds another 20 science when scanning a planet. do those 20 science count even if they don't generate a report?

if they do, can i get them by launching a few disposable probes (which will separate from the main ship in jool orbit) that i will never recover?

[The Ultimate Jool 5 Challenge Continued]

On 3/17/2018 at 12:03 AM, JacobJHC said:

2. No part-clipping of functional parts (fuel tanks, batteries, crew pods, engines, science parts, SAS) into each other. It is okay to clip structural and non-functional parts, wings, and heat shields.

Question: I built a spaceplane for this challenge that uses some moderate clipping. I thought it was fine, but I'm not sure anymore, and I'd rather find out before spending weeks on a science run and then being disqualified

this is the plane. looks good. which is why i resorted to some clipping to make it look like this

I put the mystery goo and 2 rtg inside the science jr. but hey, the science jr has a lot of empty space inside, i thought it was fair game. isn't it?

I can easily fix that if needed. I only put them like this because a scientist in eva can restore both experiments without needing to leave the cockpit

I did a little bit of clipping with the propellers to fit two in a single cargo bay. Only a little bit. I suppose I can rearrange that too if needed, though it would be a lot less convenient.

the inside of the science and electricity cargo bays are a huge mess, but as far as i can tell, there's no clipping inside. except...

the rover arm is just spanning multiple parts. but there was no cargo bay large enough to accomodate it using the mk1 size, and i wanted it to be inside a cargo bay. mostly for aesthetics, because the extra drag from putting it outside would be negligible, and if i put it behind the cockpit, it would be shielded for atmospheric reentry. The alternative would be using Mk 2, but everyone around here says they are evil

 

I've spent one week  building and optimizing this spaceplane for this challenge. I avoided clipping of engines, fuel tanks, and most other parts. I certainly never abused clipping. I've mostly done it for practicity, or to make the plane look better. at worst i'd have to put in an extra cargo bay, which would not be a huge deal; this thing can ssto from kerbin with 2 tons of fuel left, it would still be able to perform all its tasks

Please tell me the plane is fine as it is; I'm already in jool system, having performed the gravity assist for capture; having to go back would cost me several hours of gameplay.

If the plane is not fine, please tell me which of those licenses I took are acceptable, and which are not

 

[visualize CoM and thrust on a ship in flight?]

while in the VAB, we all know to visualize the center of mass and the thrust vector. but i know no way to do so in flight.

i just assembled in orbit a complicated monstruosity; i had checked that all its parts would be balanced before the flight. but that was with full tanks. the thing on the top was balanced with the rest of the ship, provided its fuel tanks were full. now they are half full, and the ship is tilting to the side. and i have no idea how to check the new CoM.

I can fix the problem. I have 24 engines radially, i can turn off a few of them until they compensate the imbalance. but trying to estimate the deviation by eye is a nightmare. that's why i'd really need to see the CoM. and i can't really do that in the VAB.

 

P.S. imgur is not letting me upload stuff at the moment, so no picture. not that it would be particularly relevant anyway, i'm just asking ways to see my CoM

[Flea contract??]

6 hours ago, AlexanderTheGreat said:

Just started this game recently,  and I'm trying to do a contract to run the flea engine in suborbital flight at 220,000-230,000 meters, I met all requirements before running the test, and it didnt complete the contract??

hoe do you meat the requirements "before" the test?

anyway, generally those contracts also sepcify a target speed. check that.

[negative air resistance???]

34 minutes ago, fourfa said:

I’m muddling through half-remembered Italian in the screenshot... could the “total resistance’ figure be including thrust?

No, it cannot. I normally always get a positive number, even though i am accelerating with rockets. only exception, as i mentioned, is when i accelerate with propellers, because the thrust from propellers is counted as negative resistance. but that's not what's happening here

Quote

Does the number remain negative if you shut off the engines?

i didn't check when i shut down the engines - i was more concerned about not screwing up the ascent. but i have plenty of experience of using rockets and getting positive - and high - resistance

[negative air resistance???]

1 hour ago, J O N said:

That is quite odd! Is AeroGUI a mod?

No, it's just the window that pops open if you open the debug menu and go on physics-aerodinamics-show aerodinamic data

Quote

If it is maybe its just a glitch? But if not you could have found one hell of an exploit! A reaction-less, 0 energy input space craft! You should try it again to see if it is reproduceable!

alas, as i said, it does not generate actual propulsion. the plane slowed after shutting down the engines

[negative air resistance???]

I was launching a plane, when i noticed something very strange: negative air resistance

now, i know of a case when you get negative resistance, and that's when you use propellers. i made many things with propellers (it's basically infinite fuel without cheating), and in this case the effect of the propellers is rendered as negative resistance. which incidentally makes it awfully hard to figure out how your plane is doing aerodinamically, but i'm going on a tangent here.

anyway, i'm not using propellers here. this thing has propellers, but at the moment they are safely enclosed inside a cargo bay. they wouldn't be able to work at this speed anyway.

for the sake of science, i tried to shut down the engines; if the resistance is negative, i should keep accelerating without it. but didn't happen, as i shut down the engines i started decelerating. unsurprisingly.

anyone has any idea what the hell just happened with the resistance data?

 

P.S. I was uncertain if i should put this under gameplay questions, but then, this is not a question about gameplay.

[How do I make this rocket wobble less??]

did you autostrut the various parts? from what i can see without downloading the craft file, your ship inside the fairing has a narrow attachment. it doesn't have much strenght, so it wobbles. autostrut all the parts (or at least the heavier ones) inside the fairing and it may fix.

if the problems are the boosters, put more struts on them

[Show off your awesome KSP pictures!]

i went to test a rocket to see if it could land on vall, and i just caught a jool eclypse

[Toroidal Aerospike Engine overhaul]

On 10/29/2020 at 7:10 PM, desert said:

Well, it doesn't work great in this application. Eve has 5atm pressure. I've found good plots with engine comparison in different pressure: https://github.com/mueslo/KerbalPlot

Even at 5atm Mammoth (and hence Vector) has better ISP than Aerospike.

no, it has not. aerospike has by far the best Isp at eve sea level.

the problem is the low TWR. you need a crapton of darts to get off of eve, so the weight of the extra engines more than compensates for the fuel saving. not to mention the aerodinamic problems caused by so many engines.

personally, i like it for ssto planes, they can get by with a low twr and the dart works better in vacuum than other ssto engines.

[liquid fuel rocket fuselages]

I am mightily annoyed that all the liquid fuel fuselages are Mk 2 and 3, with shapes meant for airplanes. The nuclear engine is real. I want to make a large rocket with nuclear propulsion, i must use a plane fuselage. The only rocket-friendly piece of liquid fuel tank is the 1.25 m part, which is mostly pointless because nuclear engines only make sense on large rockets

I'm posting this because i'm making a 2.5 m rocket, but i have to slip in a mk 3 fuselage, with one adapter in front and another behind. horrible. I'll try to put a structural tube and some mk 1 fuselage clipped inside. i'm sure someone fixed it with a mod, but that would be just one more reason to make it official

[about plane stability]

you know what, guys, after some more extensive testing i realize the plane is perfect as it is, for my purpose.

it is supposed to grab science from laythe in every biome, both on the ground (well, water) and flying over it. this means making a lot of distance over the sea, while still keeping enough fuel to orbit. so my choice of propellers is the correct one.

at this point, i must be able to land on water. that, i discovered, can be done even with the new version, it's just a matter of figuring out the technique. i was trying to hit the water as slowly as possible and absorb the impact with the wings, which have a decent impact tolerance; this worked with the lighter model, not with this. but then i discovered that if i enter water very carefully touching only with the wheels, those wheels will slow the plane enough to safely enter with the fuselage too, and i can do it at 70 m/s reliably. i've done it 5 times in a row without crashing, and while i'll still want to save the game before landing, it's a fairly safe manuever.

taking off from water is not strictly necessary, but it is highly desirable.  i can use my propellers to move around on the water surface and pretend i'm a boat, but i'm limited to around 70 m/s top speed. I can go above 200 m/s in the air, it's gonna make things much faster. And to take off from water, a rear CoM is desirable; it helps me tilt the plane upwards for take off. i tried to move the CoM forward by moving the big fuel tank in front of the command pod, and i discovered that I couldn't take off anymore; when i tried to tilt the tip up, the back of the plane would sink in the water, slowing me down. I also need the huge elevons, to help me get off the water.

I tried to add a third pair of wings to improve manueverability at low speed, but they didn't work as well, and they apparently created all sorts of issues. plus they pushed the center of mass way too forward.

So I'm basically going with my first model, just with 2 tail fins and the elevons closer to the center.

Your input was useful, though. it made me realize that while I could make this plane fly better, I could only do it by sacrificing something else. So there are no engineering mistakes in my design, only trade-offs.

3 hours ago, jimmymcgoochie said:

If I read this thread right, you want to use this plane as an SSTO for Laythe? Jet engines would be the best choice, a hybrid of Whiplash ramjets and a NERV would most likely be enough to get into orbit due to Laythe’s low orbital velocity and fairly thin atmosphere and would also have the big advantage of using solely liquid fuel and no oxidiser. Since that plane already has an ISRU in it (I think, looking at the screenshots) it would be easier to refuel it with just one fuel type- you could easily game the system by adding one small tank with oxidiser to run a fuel cell or with a drain valve to dump it, then run the ISRU for both LF/Ox and LF only to refuel faster.

 

Propellers are better. laythe has way too little land to make isru reliably (unless i can mine ore from water? i never tried), and anyway i realized i don't need it. i land on laythe, move around with propellers (fueled by 8 RTG), then i use the fuel only to go back in orbit. I will have a mother ship waiting me, and it will have isru capacity from the smaller moons. not that i will actually need a refueling, since for the other moons i will use a rover.

the mission actually has another part earlier, where i dip inside jool atmosphere enough to reach the low atmosphere, do science there, and start again. for this, i coupled this plane with another, bigger thing that will brake during descent (thanks to an inflatable thermal shield used as a parachute, i already tested the concept) and will then propel me in orbit again. this plane then will be the last stage, the one reaching jool orbit. there it will couple again with the main ship to get refueled and explore laythe.  my choice of engine works for jool ascent too.

the final version i picked

and the jool ascent stages. the jool ascent is a pretty poor flyer, but it does its job, and since i intend to only use it once - and it has two vectors to help stability - then it's fine

[about plane stability]

11 hours ago, Wobbly Av8r said:

@king of nowhereDon't know if anything I posted was significant in your mind, but those really large "elevons"  are the kind of thing that will cause you to have a wild ride; when you state that "this thing flies pretty well, as long as i never touch the control since leaving the runway" that's where I'd *start* to make it more stable.

Keep in mind that every time you press one of the control keys (WSAD) you are giving a "full deflection" instruction to those controls - if you "tap" the control key, it may be less of an input only due to the fact that the key press duration was shorter than the time it takes the control to fully deflect. Furthering the problem is that as you get faster, the effect is increased.

A couple of solutions to try: limit the total deflection of the controls, make them smaller or place them further inboard to limit their roll authority and see if that makes it a bit more manageable.

[Edit: One additional observation, below]

i reduced the maximum angle to 20 degrees already, because i know the highest deflection level is very inefficient. i didn't want to do all the way down to 15, though, in case i needed some harsh manuever.

you are right that the elevons were oversized, in fact i distinctly remember swapping out those bigS for something smaller already in the past. probably i messed up with saving games and i got stuck with the old oversized elevons without realizing.

8 hours ago, FleshJeb said:

I suspect that when it departs from perfectly forward flight, it's not stable at all.

wrong. of course if i pull all up suddenly it will capsize, but moderate deviations (say, up to 10 degrees away from prograde even in the worst aerodinamic conditions) are handled just fine.

Quote

If I were to modify that to make it fly better, I'd make the elevons flat (no AoA) to pull the COL back a little. I'd also double or triple the vertical tail, because the yaw stability is currently minimal--Especially with AoA on the wings.

huh? by making the elevons flat, it pulls the CoL forward, not back

increasing the vertical tail instead worked,

8 hours ago, Wobbly Av8r said:

Apologize, but after looking it over one more time I recognized also that (contributing to instability with any maneuvering) the amount of area you have in FRONT of the CoM is considerable - while wings and vertical fins can stabilize things, when you give it enough 'yaw', the airplane will act just like a rocket with a huge payload on top with little or no fins on the bottom (i.e. it will want to "swap ends"!) What @FleshJeb mentioned "I'd also double or triple the vertical tail, because the yaw stability is currently minimal" (more vertical fin-nage) will help solve the issue...

how would I reduce the amount of area in front of the CoM? All i have there is part of the wings, and I can't exactly move the wings around without messing with the CoL...

 

anyway, i implemented the changes suggested: I swapped out the big elevons for smaller ones and i put them closer to the body, and i swapped out the single vertical fin for two of them. It is, indeed, somewat more stable. I am able to manuever around and then find again a trajectory that won't require constant correction. though that's not always easy, sometimes i point prograde and leave the controls and it keeps flying straight, and sometimes the nose starts going down and i have to manually correct until i find a new stability. So my original doubt "why, when i stop touching the controls, sometimes it keeps flying perfectly straight and sometimes it will not?" is still without answer. i guess it would depend on complex aerodinamic parameters determined by the exact trajectory and pressure

Since I was there, i also attached the lateral tanks to the main body.

 

EDIT: what the....?

i went back to trying some water landing, and i'm finding out it doesn't fly well anymore. I didn't touch anything since saving the plane after it did fly well... and i can't find stability anymore. and suddenly i have no roll-pitch control

it's like the game wants me to revert all the changes i made. but why was it flying correctly the first time i tried them, only to fail the second?

EDIT 2: I figured out why i needed the big elevons: it's to land on water. water landing requires careful manuevering at low speed; smaller elevons are more effective at high speed, but they're no good if i can't land. generally speaking, this plane's major goal is exploring laythe, and I can now recognize that some of the things I did that were a bit less effective for flying were meant to improve water landing survivability

EDIT 3: i am unable to land on water anymore. to check if it was the new changes, i tried with an old model, and i discovered i also can't land on water anymore. maybe i checked water landing before adding extra fuel tanks. or maybe the game is inconsistent again. anyway, while i was piloting the old plane, i found it behaved well too; i could find stable trajectories easily enough. all things considered, the only improvement is the double fin tail. anyway, i need to alter the project to land on water again. possibly without screwing up flying and going to orbit while at it

[about plane stability]

6 hours ago, Snark said:

So, this plane, then?
 

It looks to me like the CoM is probably too far to the back of the plane.  Could you post a SPH screenshot that has the CoM display turned on?  (yellow-and-black checkered sphere).  (Especially with all the changes you mention, since that could have a major effect on the plane's stability depending on what you've got where.)

I have some suggestions if my hunch is correct, but I don't want to make assumptions without actually getting an accurate picture of the CoM placement.

Also... is there any chance the plane may be bending?  You've got a long narrow plane with only 1.25m stack and a whole bunch of stacked parts, meaning a lot of part joints-- that's the sort of scenario that can easily lead to bending under stress.  If the part of the plane in front of the CoM with the front wings is bending, that could cause bad instability at speed.  Are you using anything to stiffen the plane, such as autostrutting the engine and rear wings to the cockpit?

here it is. yes, the CoM is a bit back, which is unavoidable when the heaviest parts are the nerv engine, which must go on the back, and the wings, which must generate lift behind the CoM and so must be put fairly backwards themselves.

still, I remark that this thing flies pretty well, as long as i never touch the control since leaving the runway.

regarding autostrutting, i did indeed autostrut everything I considered also adding manual struts, especially for the lateral tanks. they would probably be a bit more stable, and they would definitely be more stable if i attached them to the central body instead of the wings. but i like the shape now, and in all my simulations it has never been a problem

[How to prevent my car from rolling over when turning (and how to tune the wheels)]

i would never try to make a steep turn above 10 m/s on a low gravity, even with a rover i consider stable.  my rover stops at around 40 m/s, and at that speed i would never try to turn except by the smallest possible increments. and it would take a huge amount of time braking.

it's normal. it's how physics work.

[about plane stability]

48 minutes ago, Snark said:

Longer explanation below, but the excutive summary is:

• CoM should be towards the front of the plane
• Pitch and yaw controls (e.g. on the aircraft tail) should be as far behind the CoM as possible
• Vertical stabilizer on the tail shouldn't stick up high above the fuselage, and should have roll authority disabled
• Show us a screenshot and we may be able to offer advice

 

yes, i know the basics. and i wouldn't say it's exactly "having difficulties". it flies fairly well, it has ssto capacity, it can go cruise around on propeller power alone and can even take off from water, all on propellers.

I just would like to understand why it has that strange behavior

 

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If you could post a screenshot of a plane that's having difficulty, then we could critique it for you ("oh, see, there's your problem right there-- you need to move this thing over there," that sort of thing).  Ideally, a shot of it in the SPH with the CoM display turned on would be best.

i already asked regarding this plane for a problem on the ground (which was fixed), and the pictures are there.

i made some changes since that model; i swapped out the liquid fuel tanks with rocket fuel, and i added some extra tanks under the wings, and i added two aerospikes, because i realized going to orbit on a nerv alone was too ambitious. and since the plane was much heavier i added another couple of propellers, and a few more rtg inside the cargo bays to support it.

but it makes no difference. it always does the same, sometimes starting perfectly, but losing stability as soon as i try to manuever, to never recover it

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