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

[kcs123]

Keptin's Basic Aircraft Design thread is most probably first stop when comes to aircraft and spaceplane designs. Already mentioned Wanderfound's guides are also more then valid.

I have tried to cover gaps that I think is not covered up well in mentioned threads. You can find guide in pictures with my design steps with FAR few pages back in this thread.

More info and craft examples are in link in my signature.

[Undecided]

One other question: are persisting oscillations (pulling up, then down, ~10 degrees ad infinitum) when using the SAS in stability mode considered a quirk in the new SAS and/or Kerbal pilot skill levels? Or does it normally work fine with FAR and this just points to a flaw in my own plane design? SAS seems to work fine when in prograde mode -- it may drift somewhat, but it's smooth, not constantly wobbling up and down like in stability mode.

[BudgetHedgehog]

It's more of a quirk in SAS itself - at the moment, it doesn't quite know how to handle the improved atmosphere so overcorrections are common in many designs. Best bet is to disengage SAS and trim as necessary.

EDIT: That said, it may be a result of your design. It's impossible to say without see what FARs graphs and numbers say as there are certain designs that can produce a non-dampening oscillation, even without SAS.

[Crzyrndm]

One other question: are persisting oscillations (pulling up, then down, ~10 degrees ad infinitum) when using the SAS

SAS is using global parameters to decide how to respond to deviations. Craft with a lot of control authority (high speed, low altitude, lots of control surfaces, high control surface deflection) will oscillate because of this. This is more obvious in FAR because you can reach much higher speeds lower in the atmosphere.

There are several ways to alleviate this behaviour

1) Reduce speed at low altitude.

2) Reduce overall control authority by reducing surface area, deflection, or distance from Center of Pressure (smaller lever arm, reduced torque). 1) is obviously prefered over this

3) Tweak SAS behaviour. You need my mod "Pilot Assistant" for this, but you can change how aggresively SAS should respond in flight using it (WARNING: This is the advanced option. Slowing down is much easier to understand)

Edited February 14, 2015 by Crzyrndm

[cantab]

IMHO, 4) Don't use SAS. I find well-designed planes fly better using trim to control pitch and FAR's wing leveller to keep a straight heading, though I'll grant twitchy planes can benefit from SAS.

[trawum]

I'm seeing some unintuitive behavior with FAR and Procedural Wings, and I'm trying to figure out if it's modeled properly, or if there's something wrong with my FAR install. These two planes have the same fuselage, with different wings:

But where I expected the delta wing to have much less drag at Mach 4, its Cd is 50% higher than the other one at about the same AoA.

[NathanKell]

Drag = Cd * reference area (in this case wing are). Your wing area changes between the two craft as well as your Cd.

[IllicitMedic]

Just want to say thanks for your time and effort, this is the one and only mod I absolutely refuse to play without.

[Van Disaster]

Drag = Cd * reference area (in this case wing are). Your wing area changes between the two craft as well as your Cd.

Yes, but his canard delta has less wing area than the conventional layout, and considerably more drag.

Try building canards out of pWings instead of the stock ones, see what that does to the drag.

[Undecided]

3) Tweak SAS behaviour. You need my mod "Pilot Assistant" for this, but you can change how aggresively SAS should respond in flight using it (WARNING: This is the advanced option. Slowing down is much easier to understand)

Do the settings for Pilot Assistant need to be reconfigured on a per-plane basis, or will one configuration work for all planes in a given atmosphere/planet?

[Crzyrndm]

That's the entire crux of the issue, one size will never fit everything. Unless you go the way of calculating semi-optimal settings for every craft you launch, there are always going to be exceptions.

Generally speaking though, it's not that difficult to iron out the wobble. Open the SAS window, make sure it's set to the stock mode: (if it's not, toggle the Mode:, and then hit update defaults on the toolbar window. Then it will always open on the stock tab)

• If it's rapid vibrations (control authority too high), increase the value marked scalar on the relevant axis slowly until they dampen out
  
• If it's slow drunken flailing (control authority too low), decrease the value marked scalar until it becomes more controlled
  

Once again, there will be exceptions, but that will cover your SAS issues 95+% of the time

[NathanKell]

Van Disaster: yeah, 5.5 m^2 vs 7.4 m^2 frontal area. Huh.

[trawum]

Try building canards out of pWings instead of the stock ones, see what that does to the drag.

I tried removing the canards altogether, which had a negligible effect on AoA and a negligible effect on Cd.

I'm also seeing some very strange stalls on that first plane: The right control surfaces always stall before the left ones when I try to pitch up, no matter where my nose is pointed. Severely too: the right rudder and elevator goes completely red in the Aero Viz while the left ones have 0 stall.

[kcs123]

When comes to stable SAS, it depends much how steep your yelow line in FAR graph is, point where yelow line crosses x axis of graph and how much pitching authority your craft have.

For stable crafts, it is not possible to compleatly avoid some woobling whenever you change vertical speed(pitching), but it is possible to make to fade out quickly.

Study your static analysis, see at what AoA you will start to loose lift. I prefer to set pitching authority in way that no metter how you hold "S" key, AoA never exceeds 20 degree.

Trough test flight I found that in most cases I don't need more than 15 degree. Reason is that anything more than 15 degree will just produce more drag without significant gain in lift, still more than 15 degree is desireable when you want to slow down your plane in reentry from orbit, for example.

Perhaps this picture better explains it:

(Cm) yelow line is set in a way that will prevent craft going in AoA area much larger than 15 degree. Pitching authority have not enough force to push pitching further than 15 degree, that will prevent stall. More AoA is still possible on higher speeds and altitudes where you need it.

Steeper yelow line is near X axis will make plane stablilize quickly whenever you change pitching, but it will make plane less maneuverable at the same time.

You need to experiment with different steeps of yelow line and control authority to make controlable woobling with SAS.

[Guest]

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A whole bunch of new FAR projects (click pic to open thread):

Ferram4 do see any of this beeing worth adding to the other FAR's crafts bundle?

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Edited February 15, 2015 by RevanCorana

[smjjames]

How do I make the little FARtest box that appears in the SPH/VAB go away?

Also, the thing annoyingly does not remember it's position, it always goes to the top left corner the next time I come back to the SPH/VAB. So, please, how do I turn it off?

Edited February 15, 2015 by smjjames

[Guest]

How do I make the little FARtest box that appears in the SPH/VAB go away?

Also, the thing annoyingly does not remember it's position, it always goes to the top left corner the next time I come back to the SPH/VAB. So, please, how do I turn it off?

The FAR static analysis tool? You just click again on the bottom right "FAR" box

[smjjames]

The FAR static analysis tool? You just click again on the bottom right "FAR" box

No, I mean this little box called FARtest. Probably should have posted up a pic anyway, sorry:

[tetryds]

No, I mean this little box called FARtest. Probably should have posted up a pic anyway, sorry:

http://img.photobucket.com/albums/v214/smjjames/Untitled2_zpsenonvon8.png

Get a release version of FAR instead of the development version, that box is a debugger which is always needed for testing the latest features under development.

That's why it's a dev version, haha.

[smjjames]

Can't you guys at least make it remember it's position so that I can shove it off the bottom of the screen? I'm sure it's also annoying to those testing it.

[Svm420]

Is anyone able to help with this matter?

[Tarheel1999]

Is anyone able to help with this matter?

I looked at the posts you linked. Basically, FAR is giving you unexpected data in the editor when you do an aero analysis. It is, however, unclear from your posts whether you have observed the same thing in flight. So, have you tried to fly a plane with the part in question? How did it fly? Also, you should post a screenshot of the plane you are having trouble with.

[Svm420]

I havent so far. I mean I use the analysis tool to know when my build is right so if I can't rely on that being normal I don't know I it is my design or the part causing problems. I just don't see how curves like that could possibly be normal intented behavior. I am at work Atm but I will try to get a decent build to test and post up. Anyone have any other ideas or suggestions? Thanks!

[Tarheel1999]

I havent so far. I mean I use the analysis tool to know when my build is right so if I can't rely on that being normal I don't know I it is my design or the part causing problems. I just don't see how curves like that could possibly be normal intented behavior. I am at work Atm but I will try to get a decent build to test and post up. Anyone have any other ideas or suggestions? Thanks!

The reason I asked is that from time to time FAR's editor simulation will return data that is not entirely consistent with what happens in flight.

[Yemo]

Hey,

I looked over the last pages and did a google search (not easy searchinf for FAR, lots of hits).

The Basic Jet from stock has 150kN thrust, while all other air breathers are nerfed to 50% of their stock thrust values.

edit: Is there a specific reason why the basic jet engine is not nerfed with the rest of them?

Btw, this mod is absolutely great!

Edited February 15, 2015 by Yemo