tetryds

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15 hours ago, AeroGav said:

What i mean is "aspect ratio" - the outboard sections have a much higher aspect ratio than the inboard section.    High aspect ratio wings have better l/d ratio but stall at lower aoa, so i was worried about my wing tips.    Stalls progress backward along the sweep of the wing, so again on a swept back design you got to worry about tip stall.   On your swept forward design the roots should stall first.

Lol, my fault, I was reading something else and didn't have a clue about what I'm typing.
I do know what aspect ratio means, though I did not know higher aspect ratios would stall faster. 
 

 

15 hours ago, AeroGav said:

Stall AoA increases with sweep angle too.   I wonder if the game is handling swept forward wings correctly?

Not sure if it's exactly correct but according to experience, even when I'm stalling at >70 deg AoA I still have some pitch/roll control without TVC, indicating a root stall, so I'd bet the game(or FAR)knows what it's doing.
 

 

15 hours ago, AeroGav said:

Could you just have them deploy with AoA like that slider in screenshot?   If the plane is at a larger AoA than 5 degrees it's probably not in cruising flight.    In fact above 5 degrees AoA, you'd probably get lower drag with trailing edge drooping since that increases lift and reduces the AoA needed?  The drag reduction from AoA reduction probably outweighs that from the flaps themselves at larger AoA

I'll try doing that tommorow, but one quick question, I suppose it's the same as leading edge droops, set the slider in -AoA% range?

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5 hours ago, Schwarz said:

@capi3101, the FBW mod you suggested was really good, can absolutely see just how many more micro adjustments it can make in a second compared to stock SAS. Flying this plane over long distances used be very annoying because of the pitch instability, I had to regularly steer the plane back on path. 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? Because sometimes banking and turning can be hard to execute with the plane constantly rolling in the other direction, and I don't have my stick with me to test if this was a keyboard problem or so.

There are a lot of the "under-the-hood" aspects of that mod that I don't really understand. What documentation there is on it is here. Just glancing through it, though, it does appear to have a built-in function to help the plane hold its attitude on the roll axis. You may want to check the "Roll angular velocity controllers" - more specifically the default snap angle (give it an increase). You may also want to try toggling the "coordinated turn" first if that's something you've not done (it's one of the standard options on the fly-by-wire GUI IIRC) and see if that helps.

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From my tests, Fly By Wire seems to have been built focusing on cruising, which makes sense given the nature of KSP.

If you want a control focused on combat you can try out my mod MAF (which I have to properly port to the latest KSP version... but I think it still works).

It also has a cruise mode, very good for bombing.

Do not use both mods together.

Shouldn't require tweaks unless your airplane is too weird or doesn't have a vertical stabilizer, which it uses to compensate for banks and sideslip.

@Schwarz yes set a negative AoA or a negative deflection, works either way.

Edited by tetryds

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16 hours ago, capi3101 said:

There are a lot of the "under-the-hood" aspects of that mod that I don't really understand. What documentation there is on it is here. Just glancing through it, though, it does appear to have a built-in function to help the plane hold its attitude on the roll axis. You may want to check the "Roll angular velocity controllers" - more specifically the default snap angle (give it an increase). You may also want to try toggling the "coordinated turn" first if that's something you've not done (it's one of the standard options on the fly-by-wire GUI IIRC) and see if that helps.

I'll look around more and see what I can find out about it, it's too good of a mod to pass.
 

 

15 hours ago, tetryds said:

From my tests, Fly By Wire seems to have been built focusing on cruising, which makes sense given the nature of KSP.

If you want a control focused on combat you can try out my mod MAF (which I have to properly port to the latest KSP version... but I think it still works).

It also has a cruise mode, very good for bombing.

Do not use both mods together.

Shouldn't require tweaks unless your airplane is too weird or doesn't have a vertical stabilizer, which it uses to compensate for banks and sideslip.

@Schwarz yes set a negative AoA or a negative deflection, works either way.

Ah yes, absolutely what I need, with keyboards it's impossible to do accurate minor adjustments - especially when using guns, which is made even more annoying when you're in an energy fighter.

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12 hours ago, Schwarz said:

If i want to turn quickly, I would have to 1.be able to point the nose in a new direction quickly and 2.do that while maintaining low AoA, is that correct? Supposedly I can delay the stall on the wings to a higher AoA, would that result in a quicker turn?

@AeroGav explained it:

4 hours ago, AeroGav said:

Yes because lift = airspeed x air density (altitude) x aoa x wing area

I can only add that "lift" is force that turn your plane during maneuver, it is not always used to cancel gravity force.

For quick turns you want to be able to turn nose in new direction quickly, you want high AoA to get as much lift (force) that will turn your craft as possible, you want to maintain high AoA for sustained turn as long as possible without loosing too much speed. Side effect of high AoA is high drag that will cause velocity loss. Therefore, you have find middle ground, how high AoA you want without having too much drag. And of course,  you want to prevent stall at high AoA, or if it happens, to be able to control craft behaviour when it stalls. But that is almost entierly different topic.

I didn't have time for proper KSP playgame for a while. I can only have screenshots of some test crafts created with KSP 1.1.2. and 1.2.2.
Too bad that I could not create some videos to show craft capabilities better, but I tried to catch some high turns on screenshots.

Links for imgur albums, have no idea how to embed those in forum properly, affter latest updates:

http://imgur.com/a/FJdeK

http://imgur.com/a/JxTtf

IYf1J2m.jpg

This picture probably shows in more decent way how tight turn can be. Craft on picture was perfectly controlable despite sustained high AoA and low speeds.

Edited by kcs123
Picture added to post

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We're inviting all you FAR specialists to take a look at stock turboprops. We're planning to organize events in the future to have BDA dogfights with the ultimate challenge: not just an airframe but you design the engine and propeller as well!

I you don't have experience with building an engine, take a look at the topic in my signature, also over here.

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On 12/09/2017 at 1:10 PM, Schwarz said:

Not sure if it's exactly correct but according to experience, even when I'm stalling at >70 deg AoA I still have some pitch/roll control without TVC, indicating a root stall, so I'd bet the game(or FAR)knows what it's doing

In as far as stalling from the correct direction for sweep, yes it does. You'll also find the right sort of instability issues due to sideslip.

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On 11 сентября 2017 г. at 4:54 PM, capi3101 said:

Might have to play around with it my own self - would you object to making the craft file available? Only mods you're using with this craft are Tweakscale and FAR, right?

Of course. The plane requires Tweakscale and B9 Procedural wings as flaps.

Here are the craft files. One is the full craft and the other is the identical one with the engines removed. That is because the original engines additionally require the Advanced Jet Engine and the B9 pack.

Original

No engines

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

Tsk0Awv.png

I didn't have the B9 engine, of course, so I had to improvise a little bit there with some stock parts - a structural pylon, Mk1 fuel tank, circular fuel intake and Wheesley engine port and starboard. I went ahead and reduced all the wing surfaces to 0.5 strength; the effect on the CoM was negligible. From Hangar Grid, I saw that your back wheels were tilted slightly forward. I went ahead and straightened them out , though I'm not entirely certain I got them back in the same spot. Tweaked the friction on both sets of landing gear for good measure. I went ahead and made the more inboard of the outboard pair of control surfaces on the main wing a set of spoilers and bumped them up to full deflection, and I also set up some action groups for flap control. The big change, as you can see from the screenie, is that I moved the stabilizer aft and up, and I did add some dihedral to it (despite my earlier advice). 

JmJlLZL.png

Flies like a champ - low takeoff speed, responds well to input both on FBW and stock SAS. AoA for level flight with no flaps is now between 4-5 degrees, says FAR.

Only trouble I have with the design is landing; every time I've tried to land it, it's bounced hard enough to rip off the tail - even at relatively low speeds. That might be more of a landing gear issue than anything else. 

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greetings Master FAR Builders :P

IBZmRpgl.png

having an issue with this aircraft, any help would be appreciated. KSA spoilerish stuff below

Spoiler

I'm currently working with the design on the right and for some reason it wants to roll to the left as soon as it leaves the ground. Noticeably. If I trim out for level flight and go stick neutral within 2-3 seconds I have winged over to about 45° of bank and am pitching downwards in a gradual death spiral. Recovery is easy and without any issue. I used to have red pitch values in the FAR analysis window and a yellow line heading upwards. The new design fixed both these issues, I have no more red values in any flight regime (60m/s+) and my yellow line goes downwards. But the craft still rolls and it's done this since the beginning. I'm fearing some fundamental flaw in how I put the whole thing together (I could swear those ailerons snapped on perfectly level) but before I re-build it from scratch I want to see if anyone else has thoughts. I'm using FAR with AJE and a joystick. I tried flying it without my joystick and without AJE and the roll persists as soon as it leaves the ground. it's not a yaw issue because the plane does not yaw in its takeoff roll at all and the FAR window shows only 0-0.5° of sideslip when its rolling over.

If any additional info is needed let me know

 

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It's still possible the issue is *starting* with sideslip and you just have enough vertical stab to point the nose into it fairly fast, but that means you're turning - try a little dihedral, and perhaps just a couple of degrees of sweepback, to start with. You might end up with dutch roll instead, but if you do at least that will keep you pointing roughly in the right direction. Also note symmetry isn't completely precise, and you do get some issues from that ( I suspect that is actually the problem here ). Analysing this properly is what the final FAR panel which hardly anyone uses is for. I have used it in the past to try & find oscillations, but I can't really remember what I'm doing with it at the moment. One last possibility is you added the wings in rotational symmetry mode by accident, added a degree of incidence on one wing which added a degree of opposite incidence to the other...

Going back to post/during stall controllability, I found this  in some screenshots:

Spoiler

22648740776_6da3f2f01b_b.jpg

Not sure if there's some washout on the tip panels ( I suspect so ) or if it's a result of the trailing edge controls on the centre panel stalling the whole panel, but 45 deg AoA, mostly stalled, and still mostly controllable is not terrible :P you can see the drooping leading edges aren't stalled, nor is the tail which I'd hope I'd left a little roll control in. That engine is the old Wheesley, which had no gimbal whatsoever.

Edited by Van Disaster

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23 hours ago, Drew Kerman said:

greetings Master FAR Builders :P

IBZmRpgl.png

having an issue with this aircraft, any help would be appreciated. KSA spoilerish stuff below.

If you share the craft file and the mod requirement list, there is probably a chance someone is tempted to nit-pick your design. It might be worth a try.

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1 hour ago, Rodhern said:

If you share the craft file and the mod requirement list, there is probably a chance someone is tempted to nit-pick your design. It might be worth a try.

well, I don't think anyone needs to go that far. I mean, I know there's a lot of experienced plane builders out there I'm really just looking to see if anyone has any theories on what could be causing a large left-roll tendency in an aircraft for me to look into further. I'm honestly out of ideas besides having put it together with something just a little bit out of alignment somehow. If anyone asks, I will gladly provide the craft file via KerbalX

Oh hey I see now @Van Disaster replied but didn't quote me or anything :P Yea general advice like that is what I am after thank you! You mention the FAR window but were you talking about a specific panel? Like I said as far as I know how to interpret things the Static Analysis and AOA/Mach graph look perfect. I haven't found a single good resource on how to use the simulation panel yet

Edited by Drew Kerman

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17 minutes ago, Drew Kerman said:

Oh hey I see now @Van Disaster replied but didn't quote me or anything :P Yea general advice like that is what I am after thank you! You mention the FAR window but were you talking about a specific panel? Like I said as far as I know how to interpret things the Static Analysis and AOA/Mach graph look perfect. I haven't found a single good resource on how to use the simulation panel yet

I didn't quote you because I was the next post :) anyway, the aoa/mach graph is all about pitch stability & the static panel assumes the craft is in the position it's in in the hangar as far as I remember, which is generally perfectly level unless you've tilted the entire craft yourself. I keep forgetting about the dropdown list & the transonic panel - previously the simulation tab was the last one from left to right & I always remember it there...

You have to preload the sim by hitting the calc derivatives button in the static panel ( I suspect a lot of people don't do this ), then you can set your starting state - the coefficients are the same ones as in the static derivatives, so the explanation of them is the same - & for a stable plane hope the graph trends towards zero rather than away. I generally don't touch the panel & try and eyeball problems, but if you're attempting to get the last bits of performance out of a craft, say for a contest, it's sometimes something to spend time in.

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1 minute ago, Van Disaster said:

I didn't quote you because I was the next post :)

yea but best to quote/tag people so they get notified, otherwise I don't even ever visit the subforum this thread is in. Yea the static panel goes based on the position of the aircraft, which I keep level as that is the position I am in when the craft starts to roll. Well I mean it rolls regardless but if I level out the aircraft in flight and let off the stick it rolls more noticeably so that's where I've kept the plane in the SPH for the static analysis. I haven't even tried playing with the sim because I'm not even sure I'll understand the results but thx for the tip of having to run the static analysis first

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20 minutes ago, Drew Kerman said:

yea but best to quote/tag people so they get notified, otherwise I don't even ever visit the subforum this thread is in. Yea the static panel goes based on the position of the aircraft, which I keep level as that is the position I am in when the craft starts to roll. Well I mean it rolls regardless but if I level out the aircraft in flight and let off the stick it rolls more noticeably so that's where I've kept the plane in the SPH for the static analysis. I haven't even tried playing with the sim because I'm not even sure I'll understand the results but thx for the tip of having to run the static analysis first

I don't ever get notified anyway, so I don't think of that...

Before you start fiddling with the sim I'd try some simple tests with wing shape first. Dihedral would be a start - actually perhaps pulling the wings off & reattaching might be the place to start just in case it's a symmetry error. Back sweep is self-stabilising in yaw because the inner wing is temporarily less swept than the outer one, so it has a little more lift & rolls the plane out of the sideslip ( the fun corollary is that forward swept wings roll *into* the sideslip ) which is why I suggested a tiny bit of sweep, but try dihedral first.

Most of my planes seem to ( slowly ) fall off their heading if I don't trim them or use a course-hold tool like pilot assistant, I suspect we're never going to get it absolutely perfect.

Edited by Van Disaster

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56 minutes ago, Drew Kerman said:

yea but best to quote/tag people so they get notified, otherwise I don't even ever visit the subforum this thread is in. Yea the static panel goes based on the position of the aircraft, which I keep level as that is the position I am in when the craft starts to roll. Well I mean it rolls regardless but if I level out the aircraft in flight and let off the stick it rolls more noticeably so that's where I've kept the plane in the SPH for the static analysis. I haven't even tried playing with the sim because I'm not even sure I'll understand the results but thx for the tip of having to run the static analysis first

Hey Drew Kerman,

It's never a good idea to have an aircraft with no dihedral/anhedral on the main wings. This is because changing the angle of the wings slightly will provide a lot of longitudinal stability. Imagine viewing the aircraft from the side, orthographically (without perspective). With a slight up or down tilt to the wings, you'll notice that the lifting area you can see from the side will increase dramatically. This is because as wing surfaces get more vertical, they act more like rudders/vertical stabilizers. In addition to controlling Yaw, the Rudder also passively helps control Roll. Thus, by increasing the dihedral/anhedral, you can also improve roll stability and yaw stability.

Other possibilities:

1) you've accidentally loaded fuel in one wing but not the other

2) you've done something in the editor that caused the other wing's FAR properties to be messed up.

3) the wings are not connected to the fuselage rigidly enough

4) you have a controller plugged into your computer that is providing a constant input that you don't know about

5) I'm not familiar with KAX anymore, do the props generate torque?

6) the physics engine has glitched and a wing mesh is "colliding" with some other mesh on your vehicle, causing it to be slightly out of alignment

7) your wings may be slightly out of alignment with the rest of the craft

You have to remember that in KSP, wings are perfectly symmetrical airfoils that produce no lift at 0o AoA. As a result, you get weird properties that in reality you wouldn't experience. It may be that your wings are aligned such that when they are both at 0o AoA, any small disturbance of the vehicle will cause each wing to gain opposite AoA. That's just a theory and I don't know how realistic that is.

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2 hours ago, Nixod321 said:

You have to remember that in KSP, wings are perfectly symmetrical airfoils that produce no lift at 0o AoA. As a result, you get weird properties that in reality you wouldn't experience. It may be that your wings are aligned such that when they are both at 0o AoA, any small disturbance of the vehicle will cause each wing to gain opposite AoA. That's just a theory and I don't know how realistic that is.

Unless something has changed recently, that is not true for FAR - the aerofoil section is a mashup of several NACA profiles suitable for supersonic flight ( which is why they're not fantastic for flying very slowly - we had a bit of that last page ). Ferram mentioned which ones they are somewhere in the main thread, I'm not about to dig through that behemoth again though.

What dihedral actually does is worth reading up on (spiral mode & divergence in general too ) - it's far more complicated than the wing having a vertical component, and anhedral will tend to promote rolling into sideslip unless there's a compensating factor like the wings being shoulder-mounted & the fuselage quite heavy, or a lot of sweep, etc.

Edited by Van Disaster

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3 hours ago, Van Disaster said:

Unless something has changed recently, that is not true for FAR - the aerofoil section is a mashup of several NACA profiles suitable for supersonic flight ( which is why they're not fantastic for flying very slowly - we had a bit of that last page ). Ferram mentioned which ones they are somewhere in the main thread, I'm not about to dig through that behemoth again though.

What dihedral actually does is worth reading up on (spiral mode & divergence in general too ) - it's far more complicated than the wing having a vertical component, and anhedral will tend to promote rolling into sideslip unless there's a compensating factor like the wings being shoulder-mounted & the fuselage quite heavy, or a lot of sweep, etc.

I was not aware of this, thank you for informing me. Sorry to @Drew Kerman for the incorrect info.

While it is far more complicated I tried to keep it simple and stick with basic, general ideas that can be used to get desired results. 

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6 hours ago, Nixod321 said:

I was not aware of this, thank you for informing me. Sorry to @Drew Kerman for the incorrect info.

no problem. Will be trying these things out in a little while. In the meantime.... my aesthetics!! Noooooooooo!!!!! (in regard to non-straight main wings haha :wink: )

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2 hours ago, Drew Kerman said:

no problem. Will be trying these things out in a little while. In the meantime.... my aesthetics!! Noooooooooo!!!!! (in regard to non-straight main wings haha :wink: )

 

 

Spoiler

 

37133307022_fd12f38ea9_b.jpg

36492476993_9fbca8e7aa_b.jpg

36492478903_78e869c305_b.jpg

37143443331_47237eeaca_b.jpg

 

Sweep does not have to look like an EE Lightning :P

I'm going to say you will probably never tune all roll/spiralling out of your aircraft - this is not something we've ever tuned out of real aircraft completely, which is why we invented autopilots instead of just using trim controls. That it's this bad *is* a build problem.

Edited by Van Disaster

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On 9/16/2017 at 5:06 PM, Drew Kerman said:

greetings Master FAR Builders :P

IBZmRpgl.png

having an issue with this aircraft, any help would be appreciated. KSA spoilerish stuff below

  Hide contents

I'm currently working with the design on the right and for some reason it wants to roll to the left as soon as it leaves the ground. Noticeably. If I trim out for level flight and go stick neutral within 2-3 seconds I have winged over to about 45° of bank and am pitching downwards in a gradual death spiral. Recovery is easy and without any issue. I used to have red pitch values in the FAR analysis window and a yellow line heading upwards. The new design fixed both these issues, I have no more red values in any flight regime (60m/s+) and my yellow line goes downwards. But the craft still rolls and it's done this since the beginning. I'm fearing some fundamental flaw in how I put the whole thing together (I could swear those ailerons snapped on perfectly level) but before I re-build it from scratch I want to see if anyone else has thoughts. I'm using FAR with AJE and a joystick. I tried flying it without my joystick and without AJE and the roll persists as soon as it leaves the ground. it's not a yaw issue because the plane does not yaw in its takeoff roll at all and the FAR window shows only 0-0.5° of sideslip when its rolling over.

If any additional info is needed let me know

 

@Drew Kerman first thing I'll suggest is to put the plane out on the runway and set the brakes, then begin playing with the roll controls (Q and E) to see which way your ailerons deflect (a little "is it plugged-in?"-esque diagnostic test). Two things I can think of that would cause the behavior you're describing - either one of the ailerons has been set to -100 control input (causing it to deflect in the wrong direction) or your wing surfaces were attached in radial mode instead of symmetric mode. That's just what I can think of off the top of my head. Some screenies with the parameters you've set up for the control surfaces would be nice. Also, one or two with your CoM, CoT and CoL turned on (top downs and side view) would be helpful.

As far as the dynamic stability simulator is concerned, what you're looking for there are oscillations. Plug in a starting value for the parameter you want to test (a value of 1 works for me) after you've got your static parameters for the altitude and velocity you wish to test, and then mash go. If the graph oscillates from left to right but it dampens with time, you're fine. If the oscillation stays the same amplitude, you're probably okay. If it increases with time or if it flies wildly off, you've got a dynamic instability problem that you'll have to address with your craft.

http://code7700.com/aero_stability_and_control.htm

...which leads me to want to see a front-end screenie as well, to see how you've set up your vertical stabilizer. Your craft may have a tendency to roll if the vertical stabilizers are slightly tilted to one side. Just something else to check.

Edited by capi3101
added the link to the code7700 site. They've changed it on me since the last time I was there, but all the content is still in place...

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45 minutes ago, Van Disaster said:

I'm going to say you will probably never tune all roll/spiralling out of your aircraft

I agree, but this roll is very excessive and immediately noticeable as opposed to this craft which flies perfectly and for which I twitch the ailerons every few seconds as it slowly lolls from side to side like I would expect from an aircraft (I've flown MSFS since before it was MSFS). For the most part I can sit back and let this little Cessna analog fly itself (I don't yet use any AP mods for role play reasons)

44 minutes ago, capi3101 said:

Two things I can think of that would cause the behavior you're describing - either one of the ailerons has been set to -100 control input (causing it to deflect in the wrong direction) or your wing surfaces were attached in radial mode instead of symmetric mode

Not sure how this applies since as I said the roll occurs at stick-neutral so I have no control input working the ailerons to induce a roll. Already tried w/o joystick plugged in just in case it was sending slightly off-center signals to the game due to bad calibration

44 minutes ago, capi3101 said:

to see how you've set up your vertical stabilizer

They are a bit hard to notice, someone else also pointed this out, but the vertical stabilizers are there atop the tail as seen from the rear shot

Edited by Drew Kerman

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1 hour ago, Drew Kerman said:

Not sure how this applies since as I said the roll occurs at stick-neutral so I have no control input working the ailerons to induce a roll. Already tried w/o joystick plugged in just in case it was sending slightly off-center signals to the game due to bad calibration

They are a bit hard to notice, someone else also pointed this out, but the vertical stabilizers are there atop the tail as seen from the rear shot

Hmm...here's a question: are your props counter-rotating? By which I mean that if you're looking at your plane nose-on, is the prop on the left spinning clockwise and the one on the right spinning counter-clockwise? If not, can you set them up that way and see what happens? You may have a yawing effect going on due to asymmetric blade effect, and yawing can induce rolling. It's something I didn't consider before; I'm too used to working with the stock KSP engines. Just a thought.

I did notice your stabilizer placement; I was more interested in making sure they weren't twisted five-degrees to one side or the other. A mod that could help with that determination is Hangar Grid, which (incidentally) is also a good one for making sure you've got your landing gear on straight.
 

I'm trying to think what else might induce a roll with no control input, and how to go about fixing it. I might suggest adding some dihedral to that wing, if it wouldn't mess up the aesthetic you're going for there (looking back at the thread, I can see that Van Disaster already suggested that - and it's good advice). Larger ailerons wouldn't hurt either (a brute force solution, I know). But try the propeller thing first, if possible. And double-check all the numbers on your control surfaces for good measure.

Edited by capi3101

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8 minutes ago, capi3101 said:

Hmm...here's a question: are your props counter-rotating? By which I mean that if you're looking at your plane nose-on, is the prop on the left spinning clockwise and the one on the right spinning counter-clockwise? If not, can you set them up that way and see what happens? You may have a yawing effect going on due to asymmetric blade effect, and yawing can induce rolling. It's something I didn't consider before; I'm too used to working with the stock KSP engines. Just a thought

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

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