Official FAR Craft Repository

[kcs123]

Neither KAX or Firespitter prop engines were true "wing" rotating trough air. Prop engine types from both mods use mesh transformation, or in other words, once propeler start to spin at higher rates, propeler mesh is replaced with "blured disk" mesh that mimics high speed propeler rotation. But such "blured disk" is no longer real propeler made from small "wings" and as such it does not create any phantom torque, only forward thrust.

It is easy to test, just create craft with fuselage and engine, without any wings. Put landing gears in such way that craft is easy to tip over when rotated, or at least on very soft springs. If engine create any torque it will be visible trough whole craft behaviour with brakes ON and engine at full throttle.

Other, more accurate test can be made with IR mod and free move bearings. Create craft that stands on launch clamps and put bearing between fuselage and engine. You can put some small simetrical parts like thermometer or something to have some markings to observe possible rotation.

On the otehr hand, if you use powered bearings and "propeler" made from control surfaces or small wings, torque is more than noticable.

 

[Van Disaster]

Yeah, there may be an advanced prop engine mod I'm not aware of with torque, but traditional prop engine mods are just visual effects on top of normal engines - by which I mean fuel in, thrust out, end of matter. FS props were certainly like that, I've used KAX in the past but can't remember - the SXT props in my screenshots are certainly that way too.

Anyway you can check very simply by just replacing the props with small jets & checking if it still has aero issues. Or flipping the props to pushers, I suppose. However - you didn't accidentally thrust-reduce one engine at some point? I usually have mine slightly assymetrical so they sound like multiple engines if you start them seperately, but never more than a couple of % which doesn't really affect flight much.

Edit: and either I forgot how to delete posts with this board software or you can't, and I also forgot to quote again & you can't insert quotes to trigger notification later

Edited September 18, 2017 by Van Disaster

[capi3101]

2 hours ago, Drew Kerman said:

I have no idea if props can counter-rotate but from what I know they cannot, as I've already tried looking into this (should have mentioned). I'm not even sure if KSP models such effects even with FAR. I know it doesn't model prop torque because the Civvie design I linked to above does not have any tendency to yaw leftwards (except when I place a camera way out on the wing haha).

I should probably also have mentioned to help give you all an idea of how much roll is going on that I need to apply so much rudder to cancel it out my plane is sideslipping at 5°! That is way more rudder than should be needed to counteract asymmetric blade effect

 

28 minutes ago, Van Disaster said:

Edit: and either I forgot how to delete posts with this board software or you can't, and I also forgot to quote again & you can't insert quotes to trigger notification later

@Drew Kerman and @Van Disaster; this oughta cover y'all...

Try to see if any change happens when you replace the engines with stock motors, like Van Disaster suggested. If you notice a difference, turn on your voxels in FAR and take a screenie (might want to do that anyway; FAR doesn't play nice with every mod and if one of them is putting drag in a weird spot, that could also account for your issues). 

[Drew Kerman]

19 minutes ago, capi3101 said:

If you notice a difference, turn on your voxels in FAR

worth doing anyways, I actually submitted an issue on this for a previous FAR version and didn't think to check the voxelation this time around

55 minutes ago, Van Disaster said:

you didn't accidentally thrust-reduce one engine at some point?

nope, positive. I have a dual-throttle Saitek X-55 but I also fly w/the engine PAW open and record everything. At no point do any of the values in the two engine PAW disagree in the slightest.

Thx guys this should be enough for me to tackle once I get a chance to look at it in a few days

[kcs123]

27 minutes ago, Drew Kerman said:

I actually submitted an issue on this for a previous FAR version and didn't think to check the voxelation this time around

Might be worh to check that new configs: https://github.com/ferram4/Ferram-Aerospace-Research/blob/KSP_update/GameData/FerramAerospaceResearch/FARPartModuleTransformExceptions.cfg to see if all of exceptions are properly listed.

Although, in case of helicopters, large rotating disk on main rotor can simulate to some degree autorotation, if you run out of fuel that would allow you to land more softly. Even if it is not true autorotation feature and meant to be used for that.

[Kitspace]

On 16 сентября 2017 г. at 4:32 AM, capi3101 said:

Alright - so, I did make some minor tweaks to the design

Thank you for helping me!

As I understand it the main change regarding the pitch stability comes from moving the stabilizer higher and further aft.

Doing the same thing on my version gives an interesting effect. The craft becomes both more stable and more controllable simultaneously.

Can you please post a picture of your static stability page at the landing conditions with full pitch up input? What angle of attack is it capable of?

To me taking off and landing at 100 meters per second looks like a lot actually.

Could it be that the difficulties you are experiencing with landing are due to the high speed? In terms of the actual lifting force the thing can lift off the runway at 70-80 ms.

The only difficulty I found is making it pitch up high enough for that.

It can be done with stabilizer incidence angle but then it requires a lot of forward pressure on the stick in order to prevent pitching up in flight. A movable stabilizer would probably solve the problem but it seems to be quite difficult to make a kerbal version of one. Anyways an adjustable stabilizer is used to allow for a bigger range of center of gravity as far as I know. And in this plane the center of gravity does not move a lot if at all.

By the way cheers for the flag. 

Edited September 18, 2017 by Kitspace

[capi3101]

15 hours ago, Kitspace said:

By the way cheers for the flag. 

The flag came from the forums all the way back in v. 0.20, a contribution by @Volodyuka. The original post/image is here, if it's one you want...

I'll get to the rest of your post later today. I had hoped to respond to it properly before I had to begin my paying job this morning; alas, it was not to be...

[capi3101]

On 9/18/2017 at 4:40 PM, Kitspace said:

As I understand it the main change regarding the pitch stability comes from moving the stabilizer higher and further aft.

Doing the same thing on my version gives an interesting effect. The craft becomes both more stable and more controllable simultaneously.

Can you please post a picture of your static stability page at the landing conditions with full pitch up input? What angle of attack is it capable of?

Yes, all I did was move the stabilizer back and aft, thereby increasing the length of the "lever arm" on the pitching axis, providing more torque/pitch authority. 

Here's the image you requested:

That's what I'm getting at 100 m/s. Here's 80 m/s:

And for good measure:

I did a little fiddling with the upper and lower bounds; the yellow line crosses the graph at just over a 7.1-degree angle of attack. It's about the same for both speeds; for some reason the F1 key doesn't always take a screenie when I want it to.

On 9/18/2017 at 4:40 PM, Kitspace said:

To me taking off and landing at 100 meters per second looks like a lot actually.

Could it be that the difficulties you are experiencing with landing are due to the high speed? In terms of the actual lifting force the thing can lift off the runway at 70-80 ms.

The only difficulty I found is making it pitch up high enough for that.

It can be done with stabilizer incidence angle but then it requires a lot of forward pressure on the stick in order to prevent pitching up in flight. A movable stabilizer would probably solve the problem but it seems to be quite difficult to make a kerbal version of one. Anyways an adjustable stabilizer is used to allow for a bigger range of center of gravity as far as I know. And in this plane the center of gravity does not move a lot if at all.

One thing here is that I'm generally used to flying spaceplanes, which is a different type of animal entirely. My designs usually have wing loading in the 0.4-0.5 tonnes/square meter range, which means higher takeoff and landing speeds than an subsonic aircraft like this one. I'm also used to a negative AOA gear configuration (going all the way back to the topic in keptin's discussion), which once again lends itself to higher takeoff and landing speeds. So it's probably just how I was flying the plane/how I typically handle landings. Incidentally, I did try replacing the back gear with extra-large gears (so I'd get the negative AOA gear configuration), and was able to land the plane just fine at around 90 m/s. The plane still wanted to bounce, but the fuselage was higher up off the ground so I didn't slam the tail into the ground in the process.

That all said, my observations concur with yours, in that the plane doesn't want to pitch up at speeds in the 80-100 m/s regime. Increasing the length of the horizontal stabilizer a little bit (i.e. improving pitch authority/torque/leverage by increasing the amount of force the tail generates) might help with that.

 

In case you were curious. Not a bad set of curves at all.

This last screenie shows how the CoM moves - the red "dry center of mass" marker (courtesy of RCS Build Aid) actually shows it going forward and upwards. Forward moving CoM makes the plane more stable; a CoM above the CoL makes the plane maneuverable. Couldn't tell you if those two effects would cancel one another out or not as your fuel drained. As a diagnostic test that I'm thinking about just now, you might want to try reducing your plane's fuel load to 5% to see what that does to your stability figures. I'm not sure if there's a potential issue there or not.

[kcs123]

1 hour ago, capi3101 said:

I'm also used to a negative AOA gear configuration (going all the way back to the topic in keptin's discussion), which once again lends itself to higher takeoff and landing speeds.

I use landing gear configuration like that on almost each craft design, never have issue that I need higher craft speed for lift off just because of that. If you need more speed for takeoff with craft configured with nose pitching down on runway vs same craft but landing gear configured for zero nose pitch, you have issue elsewhere.

As for your craft on picture above, you simply don't have enough control surface authority. If you don't want to use procedural wings for whatever reason, try to use all moving control surfaces for elevators. Not enough surface area for elevators is one part of issue.

Second thing to improve take off, try to adjust control surfaces in a way that yellow line cross x axis at ~15 degree of AoA with 100% of pitch.
With zero pitch input from pilot, try to set yelow line to cross x axis at ~1-2 degree of AoA. Try to do that first and if it does not help try with all moving wing control surfaces for elevators.

EDIT:

Because you need ~5 AoA for leveled flight, you might also try to set inclination on main wings for 1-2 degree.
It can also be major changer in craft behavious, but dont forget to re-adjust engines too.

For a little more info, post a screenshot like the last picture, with COM and COP indicators, but with removed elevators from tail.

Edited September 20, 2017 by kcs123

[Van Disaster]

I noticed Kitspace's craft has reaction wheels enabled by default. Anyway, made a fresh install & grabbed the engineless one, disabled reaction wheels, emptied the monoprop, built some engine pods out of the nacelles & some wheesleys, realigned the rear wheels & took off. As has been said, in it's default state it's rather lacking pitch authority - this was as slow as it'd fly level.

Spoiler

So, I moved the horizontal tail back & up, and added 5 deg more max deflection, and now this is roughly as slow as it will fly level - this is also roughly it's takeoff speed, a bit hard to tell when it accelerates so fast.

Spoiler

AoA graph seems to agree:

Spoiler

It doesn't help that the outboard flaps are inducing pitch-down moment which is why I used flaps 1 there ( actually in flight it won't stay in the air with flaps 1 at 67m/s, though ). And of course at a reasonable speed it's still having to pitch back a bit to stay trimmed level - if this thing has a cruising speed, you might want to pitch the entire horizontal tail so it self-trims at that speed.

Spoiler

Most of this can be fixed by adding mass to the tail so it's static balance is better. I just made the horiz tail stabs as heavy as possible and added a bit to the vertical fin, moved the wheels back a bit, and hey presto:
 

Spoiler

 

 

These wings are quite swept back, you could just unsweep them a bit & clip the leading root into the fuselage slightly, or use some other pieces to blend the root.

[Boris-Barboris]

On 12.09.2017 at 10:38 AM, Schwarz said:

Quick question: The standard FBW seems to automatically roll the plane keep the plane horizontal(does not happen with pitch controls), was that meant as a function, or am I missing something?

If anyone has the same problem: no, FBW does not do this. There is a "level snap" that snaps wings to level when your roll is very small, like a degree or so, but nothing more.

Usual suspect: FAR wing leveler you somehow activated previously.

[Van Disaster]

Has anyone found a way to measure drag caused by roll combined with aileron deflection in the SPH? you can set ailerons up as spoilers, but that is not the full story.

[Cratzz]

Decided to celebrate a fresh 1.3.1 install with all the must-have mods, and did a stockalike Shuttle where focus is on low partcount and *cough efficiency.

Can take of both from Runway or from Pad. Just enough Delta-V to orbit i one go! Arent't there suppose too be new parts, with 1.3? I haven't found anything new yet

Edited October 11, 2017 by Cratzz

[Surefoot]

I'm having a lot of fun with the new version of FAR and that AA mod (fly by wire) that allows unstable designs to be flown !

I'm still strugging with delta / elevon designs (cant get a decent level flight AoA for some reason, i'll look into that later) but that unstable fighter design is a total success:

I named it KU-57.

It flies beautifully, it's a bit twitchy on roll (should tweak deflections here and there), can manoeuver at high AoA / low speed.

Took me about 5 hours of work, the original design is full of tricks, what with the anhedral lifting body and leading edge AoA elevons. The wing design is very intricate and everything was done using B9 procedural wings.

I doubt this can fly with stock SAS, it wont react fast enough.

This will be my kerbin atmo research platform, next project is a VTOL...

Edited October 11, 2017 by Surefoot

[capi3101]

17 minutes ago, Surefoot said:

I'm having a lot of fun with the new version of FAR and that AA mod (fly by wire) that allows unstable designs to be flown !

I'm still strugging with delta / elevon designs (cant get a decent level flight AoA for some reason, i'll look into that later) <snip />

You gotta love Atmosphere Autopilot - turns KSP flying from a chore into something that's actually fun, IMHO. Plane looks really good too.

 

I assume you're talking about a tail-less delta in your second sentence there. In general, those require larger pitching control surfaces with higher deflections than tailed deltas to offset the reduced leverage.

Let me explain - torque is defined mathematically as the cross-product of a position vector and a force vector, which comes out to the magnitude of the position vector times the magnitude of the force vector times the sine of the angle between them. Increasing any one of those three values increases torque, which in an aircraft means more authority along any given axis. That's why in a typical tailed design you want the tail as far up and as far back as you can get it; by doing so, you've increased the length of the lever arm (the distance between the control surface and the CoM of the plane, which acts as the fulcrum) and the angle between the two vectors. In a tail-less design, those control surfaces are in-line with the wing, which means there's a greater tendency for the two force vectors to line-up, which you don't want (sin0=0). So, to offset, your control surfaces need to be able to generate more force (hence the reason I suggest larger surfaces). The part about suggesting higher deflection values is also because maths. Higher thrust can also help, of course.

I could be completely wrong here; sure would appreciate being refuted by a more senior FAR veteran if I am.

[Surefoot]

Yeah i have 700 hours of FAR KSP under my belt, i used to nail tailless delta SSTOs but i seem to have lost my mojo I stopped playing for about a year and just started again, exactly thanks to Atmosphere Autopilot which allows exploring new flight characteristics. I do have enough pitch authority on those delta wings, but the plane wants to fly at a ridiculous 20°AoA where my usual working designs were between 2° and 4° under nominal conditions (flying straight on, cruise altitude). Probably CoM issues, or wing loading, or subtle angles i missed. I'm still fighting with the editor to get correct wing profiles, on that fighter it was "easy" because wings are mostly flat (well they are polyhedral but cross section is flat), whereas on a delta we should put some camber somewhere in there, i have to remember my bag of tricks

Some Kronal Vessel Viewer views:

  

That one has a near perfect CoM / CoL alignment (with the CoM a few centimeters ahead), i'll balance for empty tanks later but it has plenty of room for tweaking.

(edit) oh, missed that:

Quote

In a tail-less design, those control surfaces are in-line with the wing, which means there's a greater tendency for the two force vectors to line-up

It's not the issue, it's about having a lever against the CoM and CoL so the greater the distance between your elevon / elevator and the pivot axis, the greater the moment (as in rotational force) it will have. The real issue of having a tailless design and why in many designs tails are elevated is shadowing, as in the wing in front will separate the airflow so as the elevator / elevon will not get any (or just turbulence) and thus will lose its acting power. Delta wings are supposed to mitigate that effect, but given the CoM is rearwards (due to the nature of the design itself) you need bigger surfaces to get the same force.

Edited October 11, 2017 by Surefoot

[Joseph Kerman]

https://kerbalx.com/The_Kerbal_Way/KP-37-WarBird

[Van Disaster]

7 hours ago, Surefoot said:

It's not the issue, it's about having a lever against the CoM and CoL so the greater the distance between your elevon / elevator and the pivot axis, the greater the moment (as in rotational force) it will have. The real issue of having a tailless design and why in many designs tails are elevated is shadowing, as in the wing in front will separate the airflow so as the elevator / elevon will not get any (or just turbulence) and thus will lose its acting power. Delta wings are supposed to mitigate that effect, but given the CoM is rearwards (due to the nature of the design itself) you need bigger surfaces to get the same force.

Shadowing would be a reason to have the tail *below* the wing - otherwise you end up with conditions like deep stall. Somewhat awkward to arrange, sure ( although a lot of combat aircraft have quite high wings & do this - obvious examples, Tornado, F-15 ) but it'll only get blanketed at high negative AoA ( when are you going to do that? ) and the higher the AoA, the less likely it is to be in turbulent air.

Edited October 12, 2017 by Van Disaster

[Surefoot]

On 10/12/2017 at 2:11 AM, Van Disaster said:

Shadowing would be a reason to have the tail *below* the wing - otherwise you end up with conditions like deep stall. Somewhat awkward to arrange, sure ( although a lot of combat aircraft have quite high wings & do this - obvious examples, Tornado, F-15 ) but it'll only get blanketed at high negative AoA ( when are you going to do that? ) and the higher the AoA, the less likely it is to be in turbulent air.

I suppose that's mostly due to air combat manoeuvers involving high positive G's and almost never negative G's which are way more difficult to counter for the pilot (the pressure suit will work on legs, but not on the head). So the aircraft will be mostly encountering positive AoA situations, makes sense to have this high wing / low tail design, also structurally speaking it makes it easier to design for resistance against high positive G's.

Also on newer designs (such as the SU-57 i copied here) they use moving slats or canards to keep the wing from stalling at high AoA. Look how the horizontal tail surfaces are in line with the main wing on the SU-57 for example, i think the front slats (and those "canards" above intakes) allow for this to happen. The Rafale is using canards for the same reason.

Well at least on the KU-57 it works It can manoeuver fine with 90° AoA and recover from a stall without any issue. I set up the slats/canards in counter-AoA mode, i dont know exactly how they are set up on the real thing but on KSP+FAR they do their job.

 

(edit) VTOL done

 

About to land on top of KSC

 

Mach 1.7 low altitude flying

Of course i'm using TCA (edit: used to have trouble with horizontal flight transition, looks like i missed i can assign an action group to both TCA on/off and engines toggle, also 'cruise' mode seems to be the right one for controlling main engines..)

That aircraft flies nice, is mostly stable actually, i added front slats so i can do high AoA stuff with the vector thrust engines... it's not as nimble as the KU-57 but it will do well for tasks needing a VTOL !

Edited October 13, 2017 by Surefoot

[Van Disaster]

On 12/10/2017 at 1:32 PM, Surefoot said:

I suppose that's mostly due to air combat manoeuvers involving high positive G's and almost never negative G's which are way more difficult to counter for the pilot (the pressure suit will work on legs, but not on the head). So the aircraft will be mostly encountering positive AoA situations, makes sense to have this high wing / low tail design, also structurally speaking it makes it easier to design for resistance against high positive G's.

Also on newer designs (such as the SU-57 i copied here) they use moving slats or canards to keep the wing from stalling at high AoA. Look how the horizontal tail surfaces are in line with the main wing on the SU-57 for example, i think the front slats (and those "canards" above intakes) allow for this to happen. The Rafale is using canards for the same reason.

Well at least on the KU-57 it works It can manoeuver fine with 90° AoA and recover from a stall without any issue. I set up the slats/canards in counter-AoA mode, i dont know exactly how they are set up on the real thing but on KSP+FAR they do their job.

Yeah, I've been using AoA-controlled leading edges since they appeared, although they don't really do much work providing lift - I've had craft at near 40deg AoA with unstalled wings, which to be fair is a bit of a cheat based on how FAR's wings work :D. Not sure what else the variable leading edge next to the inlet on the SU-57 actually does ( presumably vortex generation similar to close-coupled canards is one thing, but Sukhoi are far more clever than I am... ).

[Surefoot]

1 hour ago, Van Disaster said:

 Not sure what else the variable leading edge next to the inlet on the SU-57 actually does ( presumably vortex generation similar to close-coupled canards is one thing, but Sukhoi are far more clever than I am... ).

The amount of trickery on Sukhoi planes is insane The shapes they use, the sleek profile of engine nacelles (thanks to clever gear box positioning... specific to russian jets), the small aerodynamic details on every surface.. I had a lot of fun reading litterature on the SU-27. They are on top of the game in terms of aerodynamics as of today, IMHO.

At least those inlet "canards" on SU-57 from what i read on various military publications are pure AoA coupled, where i'm a bit fuzzier is the wing edge slats and the inner control surfaces which i've assigned to flaps, given their positioning not far from CoM, and the slats went to AoA but that's pure guesswork here. In any case with FAR this is a beast in flight, it doesnt need so much control authority to be thrown around in high G's and does your exact bidding from any flight mode, and this for a quite heavy plane (we're talking MK2 base here, not a light MK1). Makes me think the real thing will be quite fearsome since they also seemed to improve a lot upon SU-27 family avionics.

[Van Disaster]

To be fair, western ACM doctrine does not include deliberately stalling so that type of trick aero is limited to research - I've no doubt someone could build something like that, the cost of an actual combat aircraft would probably bankrupt nations though...

I tend to build combat craft for BDA, which doesn't like regaining energy much - so I try not to lose it in the first place.

[Surefoot]

The Rafale is also built for high AoA, so far in combat exercices it's superior to most alternatives, be it BVR or dogfight. The Russians may be thinking in similar ways, that once the BVR exchange of formalities is done, it's high G time, and there whoever can manoeuver the best has a much easier time. If you play a bit on DCS World you can see the strengths of SU-27 vs F-15 for example, it's quite interesting.

[maas1248]

What are the most effective ways of decreasing takeoff speed when already using flaps? Are slats the next step, or are there other options out there? Also, is reducing wing sweep a viable way to reduce it?

cheers.

Maas

[capi3101]

1 hour ago, maas1248 said:

What are the most effective ways of decreasing takeoff speed when already using flaps? Are slats the next step, or are there other options out there? Also, is reducing wing sweep a viable way to reduce it?

cheers.

Maas

Decreasing your wing loading will have a measurable effect on decreasing takeoff speed - you either need to reduce the takeoff weight of your plane or increase the size of your wing area. All things being equal, wing sweep affects performance at high speeds; the higher the degree of sweep, the better the craft performs at high speeds. If I understand it correctly, sweep shouldn't have the kind of effect you're looking for.