[1.3.1] Ferram Aerospace Research: v0.15.9.1 "Liepmann" 4/2/18

[ymir9]

Ever since the update I find most of my smaller rockets are impossible to control in the transonic region.

I'd love to see some sort of tutorial or simple diagnostic tooltip that could help indicate stability.

It seems the margins of error have gotten very, very small.

[blu3wolf]

You can always use the stability simulation window to see what happens if its disturbed. Or you could look at the AoA sweep and Mach sweep graphs as well, which show lift and drag coefficients and the turning moment.

https://github.com/ferram4/Ferram-Aerospace-Research/wiki/Static-Analysis-with-FAR

[kcs123]

Ever since the update I find most of my smaller rockets are impossible to control in the transonic region.

I'd love to see some sort of tutorial or simple diagnostic tooltip that could help indicate stability.

It seems the margins of error have gotten very, very small.

Try to adjust max thrust on boosters/engines at early stages so you don't hit subsonic speeds while you are below 10km. After 10km transonic region is not much of issue.

Try to use engines with gimbals, with those and some fins it is easier to control your rocket trajectory. You will get better answer for building tutorial and examples in official FAR craft exchange thread.

You can find link for that thread in OP and in my signature as well.

[yithpistol]

Since the update my cat has exploded.... no wait... she's fine. BUT I noticed that pre-update my CoL was very difficult to keep low even with fairings off and fins with control surfaces. I could never get the CoL below my center of mass. NOW, the opposite is true. CoL is always near the engines, or over them, if not below them without fins, and CoM is about where it can be expected to be. The question is this: Is this normal (like exploding cats... no wait, that's abnormal).

Think of the cats, people, think of the cats.

[steve_v]

Heh, I've been too busy flying planes to bother with boring old rockets

Does your voxel debug show anything funny going on around the engines?

Ed: I'm seeing some strange behavior too - it's not below the engines, but the COL appears to move upward when adding fins below the COM:

Same deal with or without the engine.

3-way symmetry does funny things to the COL also, not sure if this is expected:

Am I seeing bugs or features here?

Edited May 23, 2015 by steve_v

[Shaman]

I'm having the exact same issue in the SPH. I installed a clean install of KSP and then installed FAR v.0.15.2_Ferri.

1. New Career mode game (with lots of science to beef of technical level)

2. Increase science to get to all the airplane parts

3. Build a plane and enable the CoM and CoL.

4. Watch the CoL mov far aft after adding an engine.

I've tried this with both jet engines and rockets and the same effect. I'm not sure if this is the intended result and I am doing something wrong or a bug.

Shaman

Edited May 24, 2015 by Shaman

[ferram4]

Considering that the reduced area of an engine should produce drag near the back, adding an engine is not a bug.

Now, the fins might be one. Alternatively, they're large enough compared to the rest of the rocket to produce a lot of nasty drag ahead of them, which would move the CoL up. I'll have to investigate further.

[blu3wolf]

Well, the one thing that the last few pages has convinced me of, is that I should stop using the CoL marker in designing. So far thats gone reasonably well (for the most part).

One thing I am having trouble with, is being able to work out using FAR's tools, which way around a craft will try to orient itself in airflow. I want to keep my reentry vehicles pointed away from the relative airflow, and Im not 100% sure how to simulate that with FAR's tools.

Help?

[Crzyrndm]

One thing I am having trouble with, is being able to work out using FAR's tools, which way around a craft will try to orient itself in airflow. I want to keep my reentry vehicles pointed away from the relative airflow, and Im not 100% sure how to simulate that with FAR's tools.

Static analysis graph, run it from 0-180 degrees (E: 0-90, flip the vessel to look at 90-180), look at Cm (yellow). Peaks (local maxima) indicate stable angles, troughs (local minima) indicate angles from which it switches from one stable position to another. The Cm slope into the peaks indicates how stable each position is (steeper slope == greater stability).

E: IIRC, when peaks become +ve the stable locations are the points where Cm becomes +ve (eg. deploying flaps typically makes Cm +ve at zero degrees and 0 at 2-3 degrees, vessel will stabilise at that 2-3 degree point, not the peak at zero).

I should ammend what I said above based on that. The stable positions (0 torque, deviation causing torque that applies torque back towards the point) will be 0 crossings with a -ve slope. Peaks with a -ve magnitude will be the most stable locally (lowest torque) but may not actually be stable. Troughs are the points with the highest torque

Ignore me, listen to ferram >.>

Edited May 24, 2015 by Crzyrndm

[ferram4]

NOOOOOOOOOOOOOO THAT'S NOT HOW THE CM GRAPH WORKS

Alright. The stable orientation on the Cm graph is where the graph crosses 0 and is sloping downwards with increasing AoA. A Cm of 0 indicates no pitching moment, so everything is balanced out. A downward slope ensures that if the AoA decreases slightly, there will be a pitch-up Cm, bringing it back to 0; likewise for slight AoA increase. Where the Cm slope goes to 0 is a point of neutral stability where the dynamics switch from stable (where the line slopes down) to unstable (where it slopes up).

Many rockets will not be stable. This is intentional, because most rockets aren't. Use thrust vectoring to keep them under control.

[blu3wolf]

Is it possible to overlay onto the Cm graph, the Cm points assuming that full stick back and full stick forwards commands are made? So 3 Cm lines plotted?

[kcs123]

You have probably missed this picture that I posted long time ago:

And this one too:

All of that is available in this post.

Although it was for planes, same thing is valid for rockets too.

[taniwha]

kcs123: Close: in flight, the CoM is the fulcrum and the "CoL" is the point of application of net force.

That said... oh, so that's how flaps work. Thank you .

[kcs123]

kcs123: Close: in flight, the CoM is the fulcrum and the "CoL" is the point of application of net force.

That said... oh, so that's how flaps work. Thank you .

Nope. I meant what I said. Main wing only could be considered as "fulcrum" and COM is weight on one side of leverage, while other lifting sufaces on tail provides "counterweight".

I know that is not exactly a true, but it is good simple explanation without complex math to provide you way of thinking when you design craft.

When you want to fine tune how steep yelow line need to be to provide you stability and pitching control without excesive authority from control surfaces.

You are welcome.

[taniwha]

kcs123: actually, thinking about it that way, it does make sense. I was thinking more of rockets, I guess, because yes, it is the wings that hold up the plane. Sorry.

[Kitspace]

How to affect the slope of the pitch moment line?

To my current experience with usage of this mod adjusting the stabilizer and main wing placement and angles affects the point of neutral stability where the line crosses the graph zero but does not greatly affect how steep the line is.

Also the line tends to have steps or changes in slope. This makes the aircraft slightly bounce up and down while increasing angle of attack due to an applied pitch control input even if that input is smooth and constant. Something makes me think that those bouncy steps are stalling points of some local parts of the airframe.

That behavior applies for example to the airplane shown some pages above in the airspeed pictures as well as most other my airplanes.

With the real airplanes a sufficiently strong but gentle pull back on the controls usually leads to a certain increase of the gee force and a smooth increase in angle of attack until a stall happens or there is no more control authority. There are no jumps or oscillations in the angular velocity up until a stall point. How to affect and fix that bit?

[kcs123]

@taniwha, no need to apologize, I just clarified something that you misunderstand. I was not offended in any way.

Hopefully that picture will allow you to build aircrafts in more efficient way.

@Kitspace, move main wing closer to CoM. With that you will move CoL from main wing ("fulcrum") closer to CoM. That way large amount of weight is on shors side of leverage. At the same time move lifting surfaces on tail further away from COM(further away from "fulcrum" too) and add slight angle on tail lifting surfaces to push down tail.

With CoM distance from main wing CoL(or "fulcrum") on one end, and amount of force provided by angle of lifting surfaces on tail with needed larger distance from CoM you can control slope of pitch moment line.

When you figure that out, you experiment also with slight angles on main wing too. With few trials and errors you will soon be expert on this.

Edited May 24, 2015 by kcs123

[Enceos]

Guys, is there a way to disable voxel calculation ticks while in space? Big structures in orbit turn into a slideshow because of that...

And do we really need voxels in vacuum?

Edited May 24, 2015 by Enceos

[blowfish]

Guys, is there a way to disable voxel calculation ticks while in space? Big structures in orbit turn into a slideshow because of that...

And do we really need voxels in vacuum?

Vessels aren't re-voxelized constantly, only after staging events and every so often during animations. If you're getting a slowdown, it's probably not FAR.

[Enceos]

Vessels aren't re-voxelized constantly, only after staging events and every so often during animations. If you're getting a slowdown, it's probably not FAR.

For some reason I get this log spam 2 per second while in space, with lagspikes on each take:

[blowfish]

For some reason I get this log spam 2 per second while in space, with lagspikes on each take:

http://i.imgur.com/7MOohyK.png

Okay, so there's definitely a problem, but FAR doesn't usually do that so there must be something telling it to voxelize constantly (not sure what it is though).

[NoPersona]

I was getting bad slowdown with DRE. Since I removed it, things started to work right again.

*Edit*

Although obviously, now that I want to repro it, I can't.

So in the interest of doing this right. Before I changed my mod configuration, I had the issue that when Deadly Re-entry went in, all of a sudden it would slow down to a crawl. After I removed it, then the game would go fine again. So it seemed as if DRE and some mod configuration that I have totally forgotten was the cause.

I have updated some things since then, so I would say, make sure all of your mods are up to date and try to round it down into a reproducible configuration. Copying your entire KSP directory somewhere else and using the copy to test things out in if needed. I am also aware that this isn't a case of do what I do.

Edited May 25, 2015 by NoPersona

[Demuder]

Just a quick update (for closure's sake) regarding the no-drag bug I had encountered.

After several launches and re-entries of various shapes and sizes during the weekend, I didn't encounter the bug again. All I did was switch from the CKAN version to the manual installation and kept the FAR details window open all the time when in atmosphere to check on drag - I would have uninstalled all my other mods and do some proper bug hunting, but my game-time available was so little that it was either that or play at all, so I selfishly chose to just play :-)

So, I can't say if CKAN is the culprit (it seems identical to the manual install) or if it's just too sporadic or if it's some other mod interacting, but I am pretty confident that if it is an actual bug with FAR, it is so sporadic that there's no real problem - in my book at least. I will try of course to hunt it down if it rears it's ugly head again.

Once more, thanks for the wonderful mod, it adds so much to gameplay.

[ArchmageNydia]

I seem to be getting a bug involving B9's procedural wing addon. It appears voxelization is not happening more on one wing than the other, causing that wing to lift and not the other. It's affecting my designs as they do not get enough lift and there is a constant roll to one side. A bunch of images here, so watch out. I couldn't figure out how to do a spoiler :/.

^My plane and the lift it is receiving. vs. CoM.

Debug voxel mode. Voxels are much stronger(?) on one side than the other.

It may also be a B9 PWings problem, so I will post there as well, but since it seems more related to FAR, I posted here first. Help, please?

[Recon777]

There's a bug (ironically) in the Debug Options window.

If you go to the Aerodynamic Failure tab, there are large mode buttons on the left side of the window. Next to each of these buttons is a smaller [-] button.

If you press the [-] button next to the selected mode button, the entire debug menu becomes irrecoverably broken for that savegame.

[edit]

After a whole lot of frustrating reloading and reinstalling and restoring, trying to get the debug window to come back, I just about gave up on it. Then, I found this in a file called FerramAerospaceResearch\Plugins\PluginData\FerramAerospaceResearch\config.xml

Yikes, that doesn't look good.

So, the question is: Why are there "break the mod" buttons in the debug window?

[edit 2]

*sigh* Okay, that doesn't actually fix anything. I'm actually stuck!! I can't get my debug window back now no matter what I do. Help.

Edited May 25, 2015 by Recon777