Official FAR Craft Repository

[MightyDarkStar]

3 minutes ago, Van Disaster said:

If you want something more unusual to build have a look at the Hawker P.1121 - could have been absolutely stunning.

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https://itdoesnthavetoberight.files.wordpress.com/2012/06/hawker-p-1121.jpg

 

Oh that is larvely. I was thinking about building the Supermarine 508 (early Scimitar prototype) or the original Avro Vulcan flying wing concept. 

[MightyDarkStar]

@Van Disaster Here's the revised Scimitar

Spoiler

(can you see Minmus? :D)

And here's the Hunter with a revised wing and more accurate air scoops.

Spoiler

-> 

-> 

-> 

 

[Guest]

MiG-25

https://kerbalx.com/dundun92/MiG-25

[Schwarz]

For all you FAR experts out there, quick question about designing internal weapons bay. Been meddling around with them and can't seem to get them right.
Here's a picture of it:

The side bays are all right, the ventral bay is causing a lot of stability problems while open. With atmosphere autopilot the nose oscillates, and with stock SAS the plane stalls hard when banking.
I tried adding a retractable ramp at where the cursor is to direct the airflow over the bay while it's open, problem persists so I am suspecting something is wrong with the folding doors. Besides that I'm having no idea of what's causing the problem.
The slightest idea of how it can be fixed will be appreciated 
 

[capi3101]

15 minutes ago, Schwarz said:

For all you FAR experts out there, quick question about designing internal weapons bay. Been meddling around with them and can't seem to get them right. <snip />

Basics - can you give us a pair of screenies showing the debug voxels, one with the weapons bay doors shut and one with it open? Just want to eliminate that as a potential issue first.

While you're at it, go ahead and include the curves.

Edited December 5, 2017 by capi3101

[Schwarz]

27 minutes ago, capi3101 said:

Basics - can you give us a pair of screenies showing the debug voxels, one with the weapons bay doors shut and one with it open? Just want to eliminate that as a potential issue first.

While you're at it, go ahead and include the curves.

shut:

Open:


Debug voxels:

[Surefoot]

Others will comment better than i do, but i give a few hints: I see an aera ruling issue here, coupled with a distinct lack of vertical surfaces. You should first try and reduce the area behind the bay, or give extra width to the area around the bay (or move it backwards, that would reduce the impact). See that yellow line, it should be as straight as possible.

Then you seem to lack control surfaces, are you using flaperons for yaw control ? If not, try either adding control surfaces used as assymetric airbrakes for yaw control (there's a specific option given by FAR to allow this) or increase substantially your vertical tail fins, current ones are way too small, and way too tilted so they'll produce pitch/roll coupled with the yaw and have a very weak yaw lever.

(edit) also where is your CoM in relation with your CoL, what's happening probably is open bay doors add a hint of lift and move the CoL forward which would bring more instability.

Edited December 5, 2017 by Surefoot

[Schwarz]

49 minutes ago, Surefoot said:

Others will comment better than i do, but i give a few hints: I see an aera ruling issue here, coupled with a distinct lack of vertical surfaces. You should first try and reduce the area behind the bay, or give extra width to the area around the bay (or move it backwards, that would reduce the impact). See that yellow line, it should be as straight as possible.

Hmm, never thought it would be a big problem when opening doors. Thinning out the rear end would be hard, widening the bay might be the way to go.
 

48 minutes ago, Surefoot said:

Then you seem to lack control surfaces, are you using flaperons for yaw control ? If not, try either adding control surfaces used as assymetric airbrakes for yaw control (there's a specific option given by FAR to allow this) or increase substantially your vertical tail fins, current ones are way too small, and way too tilted so they'll produce pitch/roll coupled with the yaw and have a very weak yaw lever.

I am using flaperons for yaw control, but I suppose I can setup existing airbrakes for yaw control too. I'll try some different yaw control setups and see if it affects the issue.
It does feel a bit like a yaw control issue, if lucky I might be able to solve the problem right there
Quick question: Should elevators be excluded from yaw control?

38 minutes ago, Surefoot said:

(edit) also where is your CoM in relation with your CoL, what's happening probably is open bay doors add a hint of lift and move the CoL forward which would bring more instability.

CoM on top of CoL, with CoL slighty towards the rear. I put quite some effort into making sure the relation changes as little as possible while opening/closing bay doors, draining fuel, firing weapons, etc, so it's definitely an airflow problem.
 

[capi3101]

Go ahead and show us screenies with CoL and CoM lit up, and while you're at it, let's see the pressure curve too. Again, for both states (shut/open).

[Schwarz]

48 minutes ago, capi3101 said:

Go ahead and show us screenies with CoL and CoM lit up, and while you're at it, let's see the pressure curve too. Again, for both states (shut/open).

Now that is reeeeeaaaally steep...........

[Surefoot]

4 hours ago, Schwarz said:

It does feel a bit like a yaw control issue, if lucky I might be able to solve the problem right there
Quick question: Should elevators be excluded from yaw control?

Yes, if possible you should have elevators near the center, and flaperons as far as possible on each side (see how the B-2 achieves it). It's not the guarantee of a perfectly stable aircraft though, if your CoL shifts too much when opening the bay (and that pressure curve doesnt look good...) that might be another cause for instability. I'd try to add more yaw authority first, in any case.

[capi3101]

I'd tend to agree - try and up your yaw authority first. If you don't want to mess too much with the design, you can try increasing the control deflection as a first step, though I couldn't say if that'd help you or make matters worse.

I guess a question I should've asked earlier on - you say you've got oscillations when the bay is open and atmosphere autopilot is running. Which axis? I'd assumed the pitch axis earlier; is it your yaw axis that's oscillating?

[Schwarz]

7 hours ago, Surefoot said:

Yes, if possible you should have elevators near the center, and flaperons as far as possible on each side (see how the B-2 achieves it). It's not the guarantee of a perfectly stable aircraft though, if your CoL shifts too much when opening the bay (and that pressure curve doesnt look good...) that might be another cause for instability. I'd try to add more yaw authority first, in any case.

Thanks, I'll try setting them up.

6 hours ago, capi3101 said:

I'd tend to agree - try and up your yaw authority first. If you don't want to mess too much with the design, you can try increasing the control deflection as a first step, though I couldn't say if that'd help you or make matters worse.

I think I'll have to work with both, maybe moving the bay more to the rear and use a narrower, longer bay.
Doesn't matter if it make things worse, because then you would learn it doesn't work, right?

6 hours ago, capi3101 said:

I guess a question I should've asked earlier on - you say you've got oscillations when the bay is open and atmosphere autopilot is running. Which axis? I'd assumed the pitch axis earlier; is it your yaw axis that's oscillating?

It is the pitch axis when I have FBW enabled.

[Schwarz]

The oscillation is pretty much gone after a revamp of the ventral bay:



It would stall under Mach 0.5 while banking hard, but the oscillations are long gone. Haven't setup the control surfaces accordingly for best results but it's already a bug improvement.
@capi3101 @Surefoot Thanks for the help! I will now experiment with different yaw control setups.

[maas1248]

How good are leading edge control surfaces at improving maneuverability? If they are, what's the best control scheme for their use on a air-superiority fighter?

cheers,

Maas

[blowfish]

14 minutes ago, maas1248 said:

How good are leading edge control surfaces at improving maneuverability? If they are, what's the best control scheme for their use on a air-superiority fighter?

cheers,

Maas

IIRC, their main purpose is to increase the stall angle so that you can perform higher AoA maneuvers without stalling.

[Schwarz]

54 minutes ago, maas1248 said:

How good are leading edge control surfaces at improving maneuverability? If they are, what's the best control scheme for their use on a air-superiority fighter?

I think they are important for fighters - you want every advantage, however small. Seems like the usual trick is to set them up to -AoA% in the right click menu(so they would be at a smaller AoA compared to the surface behind), delaying the stall on the following surface, usually the main wing. That said, I find overall design to be much more important, if you started out with a bad design, leading edge control surfaces aren't going to help you much. 
Leading edge extensions are more important in terms of delaying stall, like the ones you find on the F/A-18, which generate vortices that sticks to the main wing. The surfaces atop the F22, F35, or the more recent Chengdu J20 intake can also generate vortices, though I had little success in recreating them, mainly because they are so small in size an require intricate design. I would love to hear if anyone successfully incorporated those in their designs. 

[Surefoot]

They seem to work, at least the flight model of my KU-57 seems realistic enough, although i have limited elements of comparison (SU-33 simulation in DCS or other flight sims). I know the SU-33 (it's basically an SU-27 with canards) is not the same design as SU-57 but it takes from the same bag of tricks and is also naturally unstable. On my flight tests with FAR i notice the leading edge AoA slats will definitely improve handling at high AoA and delay stall. With thrust vectoring i can even throw the plane around at such high G's i'll just disintegrate the airframe from the stress. Putting a G limiter on AA makes it fly mostly like an agile SU-27. The real world SU-27 has also very wide flight characteristics and is able to pull damaging G's if you override the joystick limiter, to pull aerobatic figures like the "cobra".

 

Quote

Seems like the usual trick is to set them up to -AoA% in the right click menu(so they would be at a smaller AoA compared to the surface behind)

Yeah that turns out to be similar to how they work on real models, you can watch them in DCS for example on SU-27 you'll see the leading edge slats countering AoA. Same goes for the F-15 "side pods" extensions, they do move counter to AoA (although in a very limited manner). And yeah on that F-22 photo you can see them clearly too.

(edit) on that very nice SU-57 photo they are also quite obvious:

Edited December 9, 2017 by Surefoot

[Van Disaster]

18 hours ago, maas1248 said:

How good are leading edge control surfaces at improving maneuverability? If they are, what's the best control scheme for their use on a air-superiority fighter?

cheers,

Maas

Parts behind stalled parts are also stalled, so if you can keep the leading edge part unstalled then it's possible the wing behind will be too. Wing parts also stall from the back eventually:

Not how it works IRL because the wing flow model isn't near complete yet.

[AeroGav]

I installed FAR again and decided to limit myself to stock engines and not use procedural wings, hoping to keep things simple.

That failed.    Admittedly it was a simpler design before the addition of high lift system, which i eventually persuaded to work.   You can now mash full nose up with full flaps and wallow along at under 80 m/s, it used to depart without warning below 130 m/s.     

 

I still had a couple of self disassembly events - it seems running AoA below 3 at supersonic speed causes something to happen so suddenly i am unable to describe the event, suffice to say it disassembled the airplane.

If you avoid such pitfalls, it eventually gets to orbit, more or less.    Hypersonic lift/drag ratio of less than 2 however i am not happy with.  In stock aero i can beat that even with a mk2,  some of my mk1 / 2.5m ships have over 4:1 at this point.     It does produce somewhat more realistic looking aircraft, though in this case i have to wonder  - tandem wing?

With high lift devices

https://www.dropbox.com/s/3t45vn6oh1sb28q/fa5.craft?dl=0

Without high lift devices

https://www.dropbox.com/s/mqutrh4kjvilfob/fa4.craft?dl=0

Fuel fraction needs to be increased,  i fell about 50 m/s short of circularising my orbit (could remove a cabin for more fuel i suppose)

 

[Surefoot]

Procedural wings is a must have, keeps part count a lot more reasonable.

[NSEP]

So, this is a little off-topic, but im trying to make FAR craft in realism overhaul, but there is this slightly well know problem and thats the bumpy terrain bug. How do i avoid this problem? Any ideas?

[Gordon Fecyk]

On ‎12‎/‎12‎/‎2017 at 6:27 PM, Surefoot said:

Procedural wings is a must have, keeps part count a lot more reasonable.

Have procedural wings and procedural tanks been tested against the current FAR? I have a heavy lifter that could stand some part count reduction. Tried Ubizor Welding but that seriously messed up the properties of the welded wings parts.

[kcs123]

B9PW works just fine. Can't tell much about procedural parts, but if coliders are set properly it should work fine too. Easy to see if you turn on voxelization in SPH on craft that have procedural parts.

[Surefoot]

I use both B9PW and Procedural Parts, they work fine in 1.3.1.