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Jan Hloušek on Space Engineer's developer team has a rather interesting thread on various third-party physics engines. In particular if you scroll down, Havok physics 2022 seems much better than the rest of the alternatives. If KSP 2 is still using Unity's PhysX underneath, would it be beneficial to swap it out during early access to see if there are performance and stability improvements? What are people's thoughts on his thread?

I already made a post about this issue, but it went sideways, and for readability reason I'm making a new post. KSP Version v0.1.1.0 Operating System and version Arch Linux x86_64, Kernel 6.2.7-arch1-1 CPU and GPU models, any other system information which could be relevant AMD Ryzen 5 7600X, AMD ATI Radeon RX 7900 XTX Description of the bug. Expected Behavior In level flight, the 4 forces acting on an aircraft are the following: Lift, is a force acting perpendicular to the flight path or the airflow; Drag, is a force acting parallel to the airflow or the flight path; Gravity, or weight, is a force acting toward the center of the celestial body, and should in level flight be acting parallel and opposite to the lift; Thrust, is the force produced by the propulsion system . Those 4 force in level flight should be in equilibrium. Source: NASA In order to simplify the calculation thrust will be assumed to be parallel to the airflow and opposite to the drag. With this in mind, in order to achieve level flight, the drag must be the same intensity as the thrust, and the lift should be the same intensity as the weight. In this case equilibrium is achieved and we can fly without losing altitude or accelerating. Observed Behavior In order to achieve level flight, the airplane require much more lift than it's weight. This requirement appear to be link to the longitudinal static stability margin of the aircraft. Steps to Replicate Use this aircraft. (I don't know how to upload save file so I copied the whole .json file in the following spoiler). Moving the main wing front and back should allow to change the longitudinal static stability margin by moving the relative position of the center of pressure in function of the center of mass. The design below has been chosen to simlify any calculation. The wing, horizontal tail, and vertical tail are square. The propulsion is aproximatly inline with the center of mass. Flying and trimming the aircraft while monitoring the aeroGUI should allow you to observe the same issue. Fixes / Workarounds (if known..) None. A list of ALL mods. If the list is long, please consider using a spoiler window. None. Other Notes / Screenshots / Log Files (if possible..) The test below show the effect described above. The airplane is flown and trimmed until it reach quasi level flight (easier said than done). This has been done for two postition of the wing, changing it's longitudinal static stability margin. Them the lift was recorded. The measurement was repeated at 4 second interval to assess the quality of the level flight. Wing position 1: Wing Position 2: Measurement: Wing position 1: Higher longitudinal static stability margin; Dry mass: 3.34t; Total mass: 3.98t; Mass: 3.78t; Weight: 37.069kN; avg Lift: 59.91kN; Ground speed: 179 m/s; Load factor: 1.62. Wing position 2: Lower longitudinal static stability margin; Dry mass: 3.35t; Total mass: 3.99t; Mass: 3.80t; Weight: 37.265kN; avg Lift: 50.93kN; Ground speed: 185 m/s; Load factor: 1.36. It is important to note that the load factor in level flight is supposed to be 1.0. It is also interresting to note that the thrust is higher than the drag. And if we look at Wing Position 2 the mach number slightly drop while the drag is lower than the thrust. It is also part of the problem. I'm unable to assess if this is an aeroGUI bug or an aerodynamic model issue. But issue there is. Thanks to @Buzz313th , who helped me understand that the issue might be linked to longitudinal stability. (Maybe) Linked issue:

I'm having a heck of a time getting a rather simple rocket into orbit. During my gravity turn, the rocket starts to swivel left/right, I have several stabilizers in the booster stage, and have stabilizer fins at the back to help with the turn. (I would post a list of parts, but I don't know how to do that in text form) Either way, when I do manage to get a craft's AP above 80km, I can't set the maneuver node while the game is "paused" so that I have time to adjust it. When I do get one (running at normal speed), when I start adjusting the prograde handle, the perigee doesn't change and I see two crash sites on the surface. I'm sure I'm doing something wrong, but I can't for the life of me figure out what it is. Any aid or suggestions would be greatly appreciated! Also, if you need anything from me to help solve my confusion, just let me know. Thanks!

I have a plane with the following main body, from nose to aft: Mk1 cockpit Mk1 LF tank Three material bays 1.25m service bay Radially attached to this are two Mk0 tanks with an intake and a Juno each. Rounded nosecone The problem with this setup is that if the Mk1 fuel tank is at the rear, the CoM moves forward a lot as the fuel is used up, which makes parachute positioning tricky (aside from the fact that I never build a single plane without enough chutes to come back down safely, the plane has the starting landing gears and is already overweight as it is, so the gears explode instantly if I try to land normally). So I put the tank in the front which stabilized the CoM, but now I have a different problem: the CoM is so far ahead in the front that if I put the rear landing gear near enough to it for the plane to even take off (if so, it takes off at ~87 m/s), the plane becomes impossible to land with parachutes when the tanks are full because even though it noses down while hanging from the chutes, the moment the front wheel touches ground, the plane's rear whips down and tailstrikes hard enough to destroy the rearmost material bay. So then. Depending on where I put the wheels, either I can't even take off or I can take off but need to fly for at least an hour before I can parachute down without breaking anything. For visual reference, this is the plane in question: The CoM is in the Mk1 fuel tank just behind the cockpit, both when full and when empty; the rear landing gear is attached to the material bay immediately behind the fuel tank because, again, putting it any more backwards makes the plane unable to take off. Fuel transfers from the Mk0 tanks at the rear cause negligible CoM movement.

I hope you can forgive me asking a question that has almost certainly been asked many times before, but I don't know the best search terms to find it. This problem has shown up in my other large surface stations using all stock parts. I just downloaded Kerbal Planetary Base Systems and it seems to do the same thing when my base gets big. The only other mods I use are Mechjeb and Kerbal Alarm Clock, so I doubt it's a mod-induced issue. It seems to only happen some of the time and only within the first few seconds after switching to the base. I end up holding my breath hoping it will be stable when I first switch to it. If it doesn't start flailing and explode in 30 seconds or so, the base seems to remain fine until the next time I switch to it. Is there a mod (or some other solution) that will keep my oversized bases intact? https://i.imgur.com/3A7PJPv.mp4 *Edited because I'm new to this whole imgur link business*

This rocket has been having stability problems on its 2nd stage. I have checked everything that normally makes rockets unstable. The center of mass is way above the center of lift, I checked for clipping parts, I strutted everything together. It hasn't helped. Through making the winglets into an entire wing, I managed to make the 1st stage only just stable, however no matter what I've done, the 2nd stage is still unstable. I've moved the wing as far down as possible, but it still flips. I have no idea why, and would like some help. I don't know how to upload the craft file, so I cant do that, but I will if i figure out how to. Thanks for any help.

Okay. I've got a shuttle-esque replica that flies... sort of. I've got a problem with it I've never encountered before: At low speeds, it flies fine and normally (tested at manual launch from runway and low-speed approach from orbit). At high speeds, however, any deviation more than about 10 or 15 degrees off vector results in it flipping. After which time, it flies perfectly happily... backwards. Attempts to slow in reverse, then bring it back to forward flight are 50/50, but I suspect it's at least partially my piloting in that. COM and COL are appropriately placed.

The problem is that in the last days when I launch a rocket it keeps stable for the first 7km more or less, but then it stars to flip over. I have tried wings but they dont help. I don´t know what to do. I love this game but i tilt everytime I play it

I give up ! All I want to do is make an airplane that has a tendency to return to wings - level if disturbed to a few degrees of bank angle, one that does not constantly need to have uncommanded roll angles taken out by hand, and can stay on a steady 90 degrees due east heading without continual course corrections. I build a simple test plane big tail fin, yaw stability plenty of dihedral Despite the above, roll angle gets bigger the longer i leave it uncorrected, plane would spiral dive into the ground if i let it. However, the smallest elevons are having trouble putting any bank on that i do ask for, it's almost impossible to turn this plane at all without the rudder - so maybe it is doing something after all?

I've been flying planes without SAS more frequently to obtain a smoother flight, and now with 1.1 there's an option to dedicate the reaction wheel control to SAS only, Pilot only, and normal. However a few things are missing I believe. 1) Ability to set Pilot control, SAS control, or Normal control to control surfaces. 2) Ability to change Reaction wheel mode to Dampener, allowing you to dampen your rotation along the x,y, and z axis. This would allow for smoother craft turning, without the jerky movement we have currently. 3) Ability to adjust the dampener of reaction wheels (along x,y and z axis individually or as a whole),engine vectors, steering wheels, and control surfaces so you're not forced to change your attitude quickly and suddenly if you dont want to. I know how stubborn you are. 4) Ability to set the Vector control of engines to Pilot only and SAS only, as well as Normal. 5) Ability to create presets for control surfaces and bind them to an action group.

Not here

Hi guys! Annoying thing happens on my try to build space station. It was pretty stable before I switched to Space Center and back. Any recomendations or is it bug? YouTube Video Also, I am using 1600x900 resolution. So, you can see a bug at Tracking Station UI on video.

Applies to KSP versions: 1.0.4 and newer. TL/DR: Among other things, this post explains why your reentering Space Shuttle replica and other winged craft can be unstable even though you built it with Center of Lift (CoL) behind Center of Mass (CoM). It also explains how you can improve general stability of any winged craft with Angle of Incidence (AoI), while at the same time making the craft very SAS friendly, and able to fly straight without SAS. The difference between CoL and Aerodynamic Center Longitudinal Stability, the ability of the aircraft to self stabilize, is attained by having the Aerodynamic Center+ behind CoM. +) The wikipedia explanation for how to calculate the Aerodynamic Center for an aircraft is in the spoiler below. I find it useful to imagine the Aerodynamic Center as an arrow that pulls backward in your craft, relative to it's movement, while the CoL pulls perpendicular to the direction of movement. Lift influences the Aerodynamic Center because, among other things, lift creates drag, but it is only a dominant part while the craft is pointed near prograde. When the craft points away from prograde other types of drag become dominant. CoL actually has less effect on stability, than either Center of Drag and Aerodynamic Center. The CoL actually needs to move to be able to control the craft. To pitch down it needs to move behind CoM. To pitch up the CoL needs to be moved in front CoM. Left and right for roll. And that is exactly what control surfaces do*. You can see this in action in the SPH. Create a simple aircraft mockup, with a handful of structural fuselage. Select the root part and Shift+S, to give it a little AoA, because that's needed for the wings to create lift. Add a couple of small wing panels with control surfaces in mirror symmetry as elevators, either at the front or back. Turn on CoM and CoL and add a couple of larger wing panels with control surfaces in 2x radial symmetry, and place them so CoL is on top of CoM. Using the Rotate Gizmo you can now directly see what really happens to the CoL, when control surfaces move, by rotating them slightly up or down. *) I'll ignore yaw for now. It doesn't contribute to CoL in the same way, because it's a vertical surface. In the SPH yaw is shown as a rotation of the CoL marker. As long as the Aerodynamic Center stays behind CoM, designing your craft with CoL in front or behind of CoM doesn't change aircraft stability much, even in KSP, it just changes how much control input you need to apply, to fly straight. And keeping the Aerodynamic Center behind CoM is the hard part. We can't see the Aerodynamic Center, and for many designs it is close enough to CoL, because large control authority can move the CoL to CoM, so that the CoL works OK as a stand-in for Aerodynamic Center, during design. But the closer then CoM is to the rear of the craft, the worse it gets. The Aerodynamic Center is now significatly in front of CoL. So even if CoL at design time is behind CoM, the Aerodynamic Center might be right on top of CoM or in front of it. This is why most people believe CoL needs to be behind CoM. And with the available information it is the right thing to do. Except it's not always enough. This is also one of the reasons why Shuttles in KSP are so hard to get stable, even when the CoL is far behind CoM. If the Shuttle isn't built to account for the invisible Aerodynamic Center, the mass and wings are often concentrated in the back, but that long fuselage, with lots of drag, pulls the Aerodynamic Center in front of CoM. The result is a lawn darting shuttle, because of CoL too far back, which at the same time spins out of control, because of Aerodynamic Centre being in front of CoM. This has led people to accuse the aerodynamics or the cargo bays of being bugged. Which is understandable given the information available at design time. Angle of Incidence (AoI) Most of us were taught how lift works with pictures like this. Pictures showing lift from cambered wing profiles without Angle of Attack. It's not completely wrong, but it's missing a big part. Most of the lift comes from Angle of Attack, not from the cambered shape. But because of how we were taught, we all have a tendency to imagine wings mounted parallel to the fuselage. On top of that KSP defaults to wings mounted that way. When really we shouldn't. And to make things even worse, KSP does not model wings as cambered profiles. Which means: Wings in KSP always need Angle of Attack to provide lift. By giving the wings "built-in AoA", Angle of Incidence, the craft can be pointed prograde while still creating lift. That reduces fuselage drag greatly. If you mount wings with no Angle of Incidence, then the fuselage has to point away from prograde (the direction of movement) in order to get the wings to create lift. This creates a lot of drag. Even in real life, wings are mounted with incidence. For the same reason: Less drag from fuselage. There is no one AoI that works for everything and it isn't necessarily most optimal to have the fuselage pointed directly prograde, because the fuselage can also contribute to lift (not just Mk2). But in my experience it is always better to have at least 1° AoI than none. Personally I use between 1-5° Angle of Incidence on my designs. I don't have any set rules, but fast craft and/or big wings, needs smaller AoI, and high altitude needs bigger AoI. For SSTO spaceplanes, I've had good experiences with designs that can fly at 0° pitch, without losing or gaining altitude near sea level at 350-400 m/s. That also means the fuselage is close to 0° AoA at the critical phase just above supersonic where drag is highest and the engines haven't reached maximum performance yet. My Solutions Until KSP is able to show the Aerodynamic Center, I use the rule of thumb, that CoM of the craft needs to be as close as possible to midway between nose and tail, and never closer than 2/3 of the craft length towards the tail. Not a very accurate solution and doesn't work for all designs, but it has worked OK for me. Additionally, I design my crafts so the forward most wing has more Angle of Incidence than those behind it. That works effectively as if the elevator has built in pitch, which you can use to move the CoL on top of CoM, without compromising stability. Here are some examples. A stable conventional design (craft file) The conventional straight wing design with CoM forward of the middle. It's a breeze to get stable with CoL on top of CoM, because the Aerodynamic Center is most often behind CoL. Nonetheless, this design has 2° AoI on the main wing to reduce fuselage drag, and no AoI on the tail plane. A stable canard design (craft file) Canard designs, the most prevalent type in KSP, probably due to the way engines are massed in KSP for the LEGO™-modularity and gameplay balance. CoM is often way behind the midpoint, which means the Aerodynamic Center will most likely be in front of CoL. If the CoM isn't too far behind, you might get away with initially designing it with CoL a good bit behind CoM, using CoL as a stand-in for Aerodynamic Center. Once you've tested that it flies stable, you can then add a little more** AoI to the Canard than the main wing, to move CoL up to CoM. If the CoM is far behind the midpoint, see the Shuttle designs. It will now be possible to fly the craft without you or the SAS having to constantly apply pitch-up. It won't reduce drag, but it will make it easier for you or an autopilot to control the craft. The shown craft has a fixed canard with 4° AoI and the main wing has 2° AoI. **) Only very rarely will it be required to have more than 2° difference between main wings and tailplane/canards in KSP. An unstable shuttle design A stable deltawing design (craft file) Shuttles and other pure deltawing designs, are the hardest to balance and require great care taken during design to make sure the CoM doesn't fall too far back. If the CoM is far behind the midpoint, you may be forced to redesign it. It might not be possible to stabilize it without adding dummy weights near the cockpit. Moving the fuel tanks forward might help initially, but instability could re-emerge when the fuel is spent. If the CoM isn't too far behind, you might be able to do something similar as with a Canard designs, by initially designing it with CoL a good bit behind CoM, using CoL as a stand-in for Aerodynamic Center. Again, once you've tested that it flies stable, you can then use the Rotate Gizmo to prebake the elevons with some pitch up, to move CoL up to CoM, to get the craft to fly without you or the SAS having to constantly apply pitch-up. The deltawing jet shown here, has 2° AoI om the main wing and the elevons have been angled up 2° from their default attachment angle. Additionally, the big wing strake has also been angled up 1° more than the rest of the wing. Test showing increased stability with AoI Edit 2016-03-01: Fixed some grammar and clarified a few sentences. Edit 2016-11-03: Added applicable KSP version. Edit 2016-12-01: Added AoI image. (source) Edit 2020-10-21: Format fixes as the new forum software made it apparant, that lots of old style formattings have been mixed over many, many edits.