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

[blowfish]

[quote name='Van Disaster']Well, no, it won't necessarily disappear ( it doesn't ) above 1.2, but it it steady state. B9 pW uses it's own shader so I wasn't really expecting aero viz to work - although you can see an effect if you have an open wingtip. Mostly I was confirming my suspicions that it was showing wave drag in the first place, because that's the first supersonic thing I've recently built big enough for a specific effect like that not to not get lost in noise. Actually fixing the issue is another matter - I don't know much about shaping the back end of wings and I don't really want to add more wing panels. Sticking anti-shock bodies to the fuselage helped, but not a terribly elegant solution.

[url=https://flic.kr/p/BpYXyS][url]https://farm1.staticflickr.com/567/23243879486_4481411936_c.jpg[/url][/url]


Incidentally is this another one of yours, Ferram?
[code]
[ERR 08:06:31.687] The hull has more than 255 polygons. This is invalid.
[/code]

It's probably blowfish's cockpit which has a broken collider, but just checking.[/QUOTE]

It would be that ... I thought we talked about this on IRC though.

[Van Disaster]

[quote name='blowfish']It would be that ... I thought we talked about this on IRC though.[/QUOTE]

We did, but I checked the logs after & wanted to know if that was a recent FAR error report or a standard unity one, given I knew the likely cause first - just like the rather handy "your mesh is broken" message which arrived recently. There wasn't a tag to show what was generating it.

[Guest]

[quote name='Van Disaster']Well, no, it won't necessarily disappear ( it doesn't ) above 1.2, but it it steady state.
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[/QUOTE]

Lol I'm still a newb at this. Didnt know wave drag could occur at every mach.

[SpacedInvader]

Could someone please advise me on how to build smooth-sided (i.e. no fins near the bottom for drag / control) rockets where the center of lift is below the center of mass. I'm guessing this is a result of the new aero system, but since installing 1.0.5 + FAR, I've not been able to build a smooth-sided rocket that has been able to fly a proper gravity turn, instead, they always begin to tumble at some point. I've identified this as resulting from a center of lift / drag which is placed near the top of the rocket where the payload and fairings are, while the center of mass is far below with the fuel and engines. So far, I've been able to counteract this tendency easily by adding control fins near the bottom of the craft, shifting the center of lift / drag down below the center of mass, but at some point I would like to move on to launching without fins. The problem is, however, that absolutely nothing that I've tried up until now moves the center of lift down from the top of the rocket except adding fins down below. Is there anything I can do to fix this issue?

Thanks

PS: I guess I should mention that I'm using procedural fairings rather than the stock fairings and the diameter of the fairing is only slightly larger than the diameter of the rest of the rocket.

[Crzyrndm]

Heavier payloads (CoM forward), increasing the size of the base relative to the front end (cone shape), and thrust vectoring. Fairings might (if well shaped and blending into the remainder of the rocket) be good for drag, but they do tend to interfere with that second concept (either by being the fattest/draggiest part of the rocket, or by being so long that the shape of the rocket doesn't matter) Edited November 26, 2015 by Crzyrndm

[blowfish]

Rockets are naturally unstable, and are controlled by thrust vectoring. If the fairing isn't too much wider than the rocket, this should be enough (with SAS on). Just don't deviate more than 5ish degrees from prograde.

[SpacedInvader]

[quote name='Crzyrndm']Heavier payloads (CoM forward), increasing the size of the base relative to the front end (cone shape), and thrust vectoring. Fairings might (if well shaped and blending into the remainder of the rocket) be good for drag, but they do tend to interfere with that second concept (either by being the fattest/draggiest part of the rocket, or by being so long that the shape of the rocket doesn't matter)[/QUOTE]

I wish it were that simple... I've tried expanding the body of the rocket out to 5m with the payload staying at ~1.5m and the CoL didn't budge at all. As for the payload, I can only make it so heavy before I'm just adding parts for the sake of adding parts. Also, the CoL is firmly planted on the center of the payload fairing currently unless I add fins on the bottom of the rocket, so I don't think it even possible to shift the mass balance far enough forward to compensate without completely removing the drive section of the rocket.

[cantab]

Don't trust the CoL ball, it's bugged in FAR. Check the static stability chart instead.

[SpacedInvader]

[quote name='cantab']Don't trust the CoL ball, it's bugged in FAR. Check the static stability chart instead.[/QUOTE]

An interesting thought... what would I be looking for there?

[tetryds]

[quote name='cantab']Don't trust the CoL ball, it's bugged in FAR. Check the static stability chart instead.[/QUOTE]

False, it is not bugged, it's just not enough data to build airplanes properly.

[SpacedInvader]

[quote name='tetryds']False, it is not bugged, it's just not enough data to build airplanes properly.[/QUOTE]

So, this apparently brings me back to my original question...

[Boris-Barboris]

"Proper gravity turn" requires autopilot, it's not a task for human pilot. Precise and optimal thrust and pitch\yaw control is required. Least you can do is provide good control authority to counter the instability of the rocket, by using powerful gimbals (vectors), or fins. Most you can do is to learn KOS\C# and take a deep dive in control theory. If you're interested in fly-by-wire, wich will try to keep your rocket in controllability AoA region, you can find it in my signature - I implemented "Rocket mode" for my career save to solve this problem for me. Edited November 26, 2015 by Boris-Barboris

[Dermeister]

IS it normal that the debug voxels are not updating as I build my Rocket? I keep doing display debug voxels because my COL is not moving when i change lift surfaces. Far feels bugged for COL. SO i checked the Debug voxel thing and only part of my rocket is in pink the rest seems like it's not registering. :(

[kcs123]

[quote name='Boris-Barboris']"Proper gravity turn" requires autopilot, it's not a task for human pilot. Precise and optimal thrust and pitch\yaw control is required. Least you can do is provide good control authority to counter the instability of the rocket, by using powerful gimbals (vectors), or fins. Most you can do is to learn KOS\C# and take a deep dive in control theory. If you're interested in fly-by-wire, wich will try to keep your rocket in controllability AoA region, you can find it in my signature - I implemented "Rocket mode" for my career save to solve this problem for me.[/QUOTE]

Creating KOS autopilot that also works reasonably well is on my "to do" list for quite long time.
Your mini mod is highly appriciated, but I looking more towards KOS because it will "force" me to learn more about control theory.

More difficult aproach, but also more rewarding on the end of road. Knowlage learned trough KOS can also be used elsewhere, not only for atmosphere autopilot.

Too bad that I don't have enough free time for any of this right now, but it is good to know where to look when I start this for myself.
If not for mod, you have earned some reputation points for provided detailed documentation for this.

[SpacedInvader]

[quote name='Boris-Barboris']"Proper gravity turn" requires autopilot, it's not a task for human pilot. Precise and optimal thrust and pitch\yaw control is required. Least you can do is provide good control authority to counter the instability of the rocket, by using powerful gimbals (vectors), or fins. Most you can do is to learn KOS\C# and take a deep dive in control theory. If you're interested in fly-by-wire, wich will try to keep your rocket in controllability AoA region, you can find it in my signature - I implemented "Rocket mode" for my career save to solve this problem for me.[/QUOTE]

In the old aero model, I used to be able to pitch 2.5-10 degrees at about 100m/s, turn off SAS, and the rocket would fly pretty close to a proper gravity turn, with only minor corrections needed, and no requirement for control fins. In the new model, the center of lift / drag / pressure sits in the nose of the rocket for some reason without the fins, so the above method always results in tumbling in one direction or the other. I do use MJ, so ascent autopilot is an option, but I have never really been happy with its implementation and have up until now gotten better results with the unguided method.

[ferram4]

[b]@SpacedInvader: & Dermeister: [/b]Well, you're both going to have to recreate the issue with as few mod parts as possible and post the resulting craft files. Things should be updating, but I need reproduction steps if there's a problem. I don't get these issues, so you need to tell me how to cause them.

[SpacedInvader]

Ok, so Stock only:

[IMG]http://i.imgur.com/QvuDW1f.png[/IMG]

Stock plus FAR only:

[IMG]http://i.imgur.com/Xt4hDzQ.png[/IMG]

Basically the same craft, with only a small variation in the fairing. I should note, however, that neither was able to hold an ascent without tumbling, but the Stock + FAR tumbled much sooner than Stock, beginning at ~65m/s compared to Stock's 150m/s or so. It seems FAR is definitely doing something strange with the CoL that is having some effect on the performance of craft, but where I'm lost is that this vehicle should fly, and in previous versions of KSP (0.90 and before), I've flown very similar rockets, not to mention the fact that most real life examples follow this profile...

Thrust vectoring, while an improvement, doesn't overcome the tendency to tumble. So far, the only successful rockets I've been able to launch in 1.0.5 have had fins at the bottom...

[tetryds]

@SpacedInvader: I cannot see any problems with how FAR would handle your craft and the COL is right where it should be.
Before KSP 1.0 the transonic effects were not as accurate as they are now.
Check the pressure distribution yourself, you will see a huge bump on that region.
Just add some tailfins and you will be good to go.
Real life rockets implement complex control systems and everything is precalculated.
It's not because something changed that it's wrong, FAR only gets better and more accurate.

[SpacedInvader]

[quote name='tetryds']@SpacedInvader: I cannot see any problems with how FAR would handle your craft and the COL is right where it should be.
Before KSP 1.0 the transonic effects were not as accurate as they are now.
Check the pressure distribution yourself, you will see a huge bump on that region.
Just add some tailfins and you will be good to go.
Real life rockets implement complex control systems and everything is precalculated.
It's not because something changed that it's wrong, FAR only gets better and more accurate.[/QUOTE]

I can give you that FAR is more accurate, as I would expect it to be, and if that's where the CoL is supposed to be, then I can live with that, but I've yet to fly a successful rocket in 1.0.5 where I didn't add fins which moved the CoL below the CoM. Where I keep having the disconnect is that I've never NEEDED fins in the past. Here is an example of a launch vehicle I used to launch around 15 missions last year in RSS on 0.90:

[IMG]http://i.imgur.com/95B7R4N.png[/IMG]

No tail fins, and only small reaction wheels on the payload that wouldn't be able to stabilize a vehicle of this size and mass, yet this rocket was always rock solid stable. I have tried to rebuild something similar, albeit smaller, on my new install and it can't get more than a couple of thousand meters into the air before it tumbles and tears itself apart. Edited November 27, 2015 by SpacedInvader

[tetryds]

On 11/27/2015, 5:09:29, SpacedInvader said:

I can give you that FAR is more accurate, as I would expect it to be, and if that's where the CoL is supposed to be, then I can live with that, but I've yet to fly a successful rocket in 1.0.5 where I didn't add fins which moved the CoL below the CoM. Where I keep having the disconnect is that I've never NEEDED fins in the past.

You did not need them because of the lack of proper area ruling, which is implemented now.

It was wrong before, it's right now, try to make the tip of your rocket smoother, it's much taller than the one you said you were failing to fly properly.

Going slower also helps.

[sashan]

Is it just me or does the new FAR refuse to extend flaps in hangar and do proper simulations of them extended? Can't find my stall speed with flaps extended till I fly...

[ferram4]

That was noted as an issue a few pages back.  It'll be fixed in the next release.  I don't blame you for not reading back though given the state the forums are in though.

[Matt77]

On 23/11/2015, 22:20:24, Motorsheep said:

This is probably a dumb question and would be answered by reading the material thoroughly, but it's late and I'm tired and counting on the kindness of the forum folks, especially since I usually figure everything out for myself and hardly ever ask questions:


Is my capsule supposed to go supersonic in free fall?

I just got back into KSP after a long break and started off with the latest FAR installed right away.

Now in free fall, my MK1 capsule will easily reach supersonic speeds and keep accelerating right down to sea level. This makes for some very interesting parachute brake maneuvers going from 400+m/s to 8m/s within seconds, subjecting poor Jeb to 15+g's in the process. I can't imagine that it's working as designed for me?

I've got the same issue.  From a 100km orbit, I reduce the peri to re-enter.  I've tried 30, 40 and 50km for this.  The capsule decelerates nicely, only loses about 10 ablative, but minimum speed is 410m/s.  Then it starts to accelerate again as gravity overcomes drag. The acceleration continues until impact at sea level.

My re-entry vehicle is a Mk1 Pod, stock heat-shield with 50 ablative, a Mk16 chute, and two goo containers stuck to the sides.

If I disable FAR, the landing goes as expected.

[SpacedInvader]

On 11/29/2015, 11:45:27, tetryds said:

You did not need them because of the lack of proper area ruling, which is implemented now.

It was wrong before, it's right now, try to make the tip of your rocket smoother, it's much taller than the one you said you were failing to fly properly.

Going slower also helps.

Hmm, I'm just now getting to a stage where I'm building big rockets again, so I guess I'll see if that has an effect on the situation, though so far it seems the answer is no and all rockets will need added drag at the bottom in the form of fins or wings.

 

On a somewhat different note, I noticed my game getting choppy in the VAB whenever I open or close something meant to open or close in space (like a Universal Storage wedge or folding parabolic dish). Upon checking my KSP.log, I'm greeted with thousands of lines like this:

 

Error in mesh triangle; triangle plane components are NaN or triangle is degenerate; FAR unable to use this triangle

 

Is this an error in the part's model, or does it have to do with the way FAR handles moving parts?

 

EDIT: After some additional poking, the errors are continuing to be thrown any time I do anything to the craft. So if its just sitting there, no new errors, then if I move the craft up or down in the VAB, thousands of new lines of errors.

Edited November 30, 2015 by SpacedInvader

[SpacedInvader]

So in poking around looking for a possible cause / effect of the above problem, I think I found an issue with FAR and Procedural Fairings. I had noticed that the debug voxels weren't showing up on the outer surface of my fairings when I turned them on, so, on a hunch, I exited the VAB, returned, and then turned them on, along with the cross-sectional area curve.

 

This is what I got:

 

Then I removed and then re-added the fairings and this is what I got:

 

While both cases seem odd to me (shouldn't the voxels only follow the outer surface of the fairing and not completely fill its internal space), the latter is clearly wrong as it completely ignores the fairing, instead following the contours of the protected parts. The only way to revert the voxels to the former condition from the latter is to leave the VAB and return. Even this only works about 50% of the time by my estimate, as the other 50% of the time, attempting to show the voxels or the cross-sectional area curve lead to an NRE related to those activities.

 

I have checked whether this can be replicated on a bare bones install (Stock + FAR + PF only) and it indeed can. FAR + Stock fairings are updated properly as you add or change each piece, but FAR + Procedural Fairing displays this behavior. Searching hasn't indicated that this is a known issue, but that doesn't mean I haven't just missed something along the way, but is there a way around this behavior and / or is this affecting aerodynamic characteristics at all?