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

[ferram4]

@Suzie's Brother Max: The current changelog is in the readme included with the download.

Here's a non-exhaustive list of things modeled in FAR right now; most of this is using approximations rather than exact solutions since the latter would be painful for the processor:

Wings

• Effects of aspect ratio, taper ratio, wing sweep, camber (not intrinsic to any piece; must camber wing with multiple wing pieces placed at angles), and flaps accounted for.
  
• Subsonic flow based off Prandtl lifting line theory, with stall above a given angle of attack.
  
• Supersonic flow based off a combination of linear approximations for wings and shock-expansion theory for airfoils (using 10% thick diamond airfoils).
  
• Transonic flow approximated as a smooth blending of the above.
  
• Drag is a combination of the induced and wave drag factors predicted by the above, along with a simple approximation to account for transonic wave drag and a constant base friction drag.
  

Bodies

• Effects of taper ratio and fineness ratio are considered. Sudden changes in cross-sectional area produce more pressure drag.
  
• All flow regimes are approximated using simple potential and viscous flow calculations.
  
• Extra drag added for unused attach nodes, which indicate a very un-aerodynamic surface exposed to the airflow; nodes facing the flow are assumed to have a stagnation pressure coefficient across the entire surface while nodes facing away from the flow are assumed to have half of the minimum pressure coefficient in that flow.

Most of the above stuff is based off of the 1965 Stability DATCOM that I managed to get my hands on. Not all of it is completely exact, but it does seem to provide a decent flight model.

Other stuff

[*]Payload fairings and cargo bays will properly detect parts inside them and shield them from the airflow, making them useful for decreasing drag.

Hope that was helpful!

@Taverius: Hmm... I'll look into that then.

Edited October 28, 2013 by ferram4

[Surefoot]

- If i have a composite wing (with overlapping joints) does it count as one wing, as in there is only one leading edge ?

- Are leading edge mobile surfaces accounted for ? (i guess it counts in the wing camber does it)

- Wingtips have exposed nodes (always, even with pwings), how do they count in your drag model ?

- Do you model flow separation at transonic speeds ? (that would explain some weird behaviours i have seen at these speeds)

- Are the hypersonic plasma effects any indication of what is happening in FAR ? Or are they totally unrelated

[softweir]

It could be the debug log, which is somewhat resource intensive. It could also be all of the calculations necessary to figure out the aerodynamic properties of the vehicle. I can try things on my end and see if I can make things better.

Could you at least inhibit the calculations while the FAR dialog is minimised (and the CoL display is turned off!), and re-do them on scene transitions such as going to launch? I don't mind choppiness while I am working on CoL or using the FAR dialog, but when I am just throwing parts on a large station layout it seems redundant that FAR is busy calculating all the aerodynamics of an object that will never launch as one piece!

Edited October 23, 2013 by softweir

[ferram4]

@Surefoot: Composite wings will be treated as essentially one wing. The method isn't perfect, but it is close.

Leading edge slats / flaps are accounted for.

No, those aren't the types of nodes I was talking about. I don't know of any wing part that includes the teal sphere stack node on it. And anyway, the wing aero model doesn't account for those at all.

I don't model flow separation at transonic speeds (mostly because the wing model isn't sophisticated enough to handle it), but I do shift the CoL forward a bit at those speeds.

Reentry effects aren't changed by FAR and are just pretty effects, just like in stock.

@softweir: I've looked at not dumping things to the log, and that seems to make things a lot smoother.

[Senshi]

Removing the log dumping would be nice. Even better: Make a toggle-able debug mode (in a .ini/.cfg file, maybe?) which can enable these dumps that are useful for troubleshooting after all would be even better, I think.

Additional thanks for making the GUI remember its place: I was just about to complain about the VAB/SHP GUI being minimized to the top-left corner of the open GUI upon re-entering the VAB/SHP or using the "New" button and placing a new FARed part, but it seems your latest update fixed that.

[lipatden]

@ferram4: I noticed something last night while doing !!SCIENCE!! to kerbin with this bay:

That is one tidy little science bay you have there

[Miller]

I am having a problem reentering with command pods. They just tend flip out at the top parts of the atmosphere even though the "heat shield" is facing prograde. Not sure if this is caused by FAR or i am simply missing something.

[softweir]

@softweir: I've looked at not dumping things to the log, and that seems to make things a lot smoother.

Excellent! (Senshi's idea of a .cfg option sounds convenient - but yet another code-path for you to maintain. )

[Barb0]

Hello. First of all, im sorry for my bad english, its not my natal language.

Im experiencing one issue with FAR and the largest wings of B9 aerospace mod. When my plane is reaching over 120 m/s the wings starts to wobble and becomes uncontrollable. I only have this problem when using these wings, because when i change them the problem fades away. When SAS is ON, it only encourages the issue.

The plane is a simple cargobus with the MK5 cabin, 8 or 9 metres of fuselage, tail, stabilizers and two turbofan engines... nothing special.

Thanks to all and sorry again for my horrible writing.

[softweir]

Hello and welcome!

You could try using several of the "EAS-4 Strut Connector" to make the wings more rigid. Attach one end of a strut to the body and the other end to a wing. That will make the wings much less wobbly.

[Guest]

Since you're using B9, don't use stock EAS-4, instead, use the special B9-made struts. They look better and are somewhat stronger.

[ferram4]

@Miller: If the pod gets too far off of retrograde it will flip around due to the way that drag is worked out on it. Another possibility is that a lot of stuff is attached to the top of the pod, shifting the CoM further back and making it less stable in a traditional reentry configuration.

@Barb0: Struts. Lots of struts, like Softweir said. The same problem occurs if you create any large-span wing and look at where it attaches to the fuselage.

[NathanKell]

I have to say re: pods, they behave somewhat strangely, and adding even a single parachute to the top node doesn't change the CoM, but it massively changes the CoP (at least as shown in VAB). Probably because of node drag? Anyway, I've had to use CoM Offsets on most pods to get them to fly right with stuff on top. And even then they often want to fly at a three-quarter angle to the airstream.

[123nick]

how does this mod work with non-ferram compatible wing pieces? like the nova-punch fins?

[ferram4]

Wing pieces that don't have FAR modules defined will behave exactly as they do in stock. This means that lift will be proportional to velocity, rather than velocity squared (so don't trust them to keep your vehicle pointed the right way). The CoL indicator is calculated differently for the stock wing pieces than for FAR wing pieces, so combining them on a rocket or plane will make the CoL indicator absolutely worthless.

[Simmer22]

Hey, can anyone point me to a FAR compatible fairings mod?

[ferram4]

I would advise KW Rocketry or Procedural Fairings.

[Surefoot]

Procedural wings are a must have with FAR, imho. More flexibility, without the flex (heh).

[p1t1o]

Has anyone added FAR to the configs for Cepheus's "Component Space Shuttle"? I'd have a bash myself but I'd have to guess at the wing dimensions...

[Spanier]

I have a problem with this ship:

Whenever I try to roll it pitches, not that the ship reacts to the actions of the wings by pitching, the wings pitch as I'm pressing [Q] or [E].

What's wrong?

Edited October 25, 2013 by Spanier

[Surefoot]

If you have roll coupling (from what i understand) i may hazard a guess that your control surface relative area is big enough that you lose significant lift upon roll inputs - in other terms you are using these canards for lift, and they represent a large part of your total lift. Its only a guess :-) you could try using smaller canards, and/or larger wings.

In any case this will always happen to some degree, just like yaw-roll coupling, you can only mitigate it only.

Edited October 25, 2013 by Surefoot

[Ciber]

Is there anyway to calculate areobraking while using this mod?

[p1t1o]

I have a problem with this ship:

Whenever I try to roll it pitches, not that the ship reacts to the actions of the wings by pitching, the wings pitch as I'm pressing [Q] or [E].

What's wrong?

Where is the CoM? Is it forward far enough of the CoL? If the craft is on the edge of stability, a roll input can push it over the edge and start to pitch uncommanded.

Were the wings attached with symmetry?

[Surefoot]

@Ciber: Since the amount of aerobraking depends on a huge lot of parameters, i dont think so - just your AoA during approach will totally change the outcome (as i learned recently trying to aerobrake on a direct entry on Laythe). You can run the AoA simulation with FAR in the VAB/SPH to know your aerodynamic parameters, then i guess you could compute the aerobraking amount from the derived Cd for a given AoA, and then try to hold that (with SAS) during actual aerobraking.. Of course you need to know your entry speed (e.g. like mach 216 for Jool). Good luck

Edited October 25, 2013 by Surefoot

[smarky55]

Hi, I've run into a bug with how the game remembers the position of the button to toggle the FAR CAS window in the editors, if the window is minimised and the editor is left and then returned to the button will be shifted to the left a bit and appears behind the editor UI assets such as the top menu bar. This does not happen if the window is open when the editor is left. When the button is clicked after returning to the editor it returns to it's correct location and the window opens correctly. This happens when only FAR is installed and on a ship that is only a command pod. This is with FAR 0.9.7 and KSP 0.22.

Screenshots:

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KSP.log

config.xml

You can work around the issue by using the CAS window in a place where it won't become inaccessible when you come back.