tetryds

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I am not talking about the pilot, I am talking about the airframe itself.

Anyway, 12deg. Ok are you flying with SAS turned on?

Always. It's been giving me a bit of oscillation but nothing too bad.

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If I were at home I would post my exact PID tuner settings I use for almost everything. And I dont have that rocking anymore on any aircraft unless it is at its edge of flight envelope.

I know the real Flanker has leading edge slats that auto deploy on low leading edge pressure situations. This helps it maintain control in high AoA situations, there is also an audible alarm that goes off in the cockpit that warns the pilot of an impending stall.

I would also suggest running and using Kerbal Joint Reinforcement, it will help for structural strength without over abundance of struts.

As for the take-off and landing speeds, the trick I use is leading edge slats and flap use. Again the real Flanker uses both for take off and landing.

Your take off speed should be around 140-180kts depending on load of craft. I use knots for my increments of speed it is easier to find that information.

Landing speed should be about 120-140kts again depending on the current load on the craft.

Almost all of my craft take off and land at those speeds except my Mig-21 SSTO, it has a 200-230kts take-off and a 180-200kts landing speed, much like the real Mig-21.

That'd be great :)

I use negative AOA settings for the leadingedge controlsurfaces, so its kinda like that. I Noticed when I increase the deflection the craft stays controlable longer, so I guess that's some improvement ;D

I know that bitching betty warning for the SU27 because I played DCS SU27 :) The struts you see are only there to counter wobble under high G, even with KJR the wobble still persists under high G loads.

Tried flaps and spoilers but there wasnt any difference, I have the feeling flaps don't do much in FAR, could be wrong tho.

I used km/h because metric and the HUD for the russian planes used metric aswell, but I switched to knots and the plane lifts just after reaching 180knots under normal load. I think I'm gonna do some part customization to get the weight of the craft a bit lower and to get the right amount of fuel in there. Real SU27 weights around 16 metrictons with 9.4 tons of fuel capacity which brings it to 30tons fully loaded.

Mig21 isn't even a plane ... it's a rocket with an identity crisis thinking it's a plane. :D

- - - Updated - - -

Internet stick, and if I pass a certain ammount of download volume it puts a limit on my connection.

Pictures usually aren't a problem, just takes a while to load. But vids... not a chance.

Anyway, I know it's annoying with Adjustable Landing Gear, but calculating stuff with raised gear is usually a good idea (except for calculating performance for landing approach, etc. ofcourse).

The stability issues do sound and look alot like an asymmetric stall -> snap roll (wouldn't call it spin unless it keeps spiraling down, instead of instantly recovering). Thick wings allow you to pull higher AoAs, but would prob skyrocket the wave drag area on your design. Otherwise, what Hodo said (it kinda is possible to do automatic "slats" though, just need to set the leading edge to negative AoA deflection).

However, do you actually pull 70° AoA? Or do you pull till less, and then the nose suddenly lifts? If so, your tail stalls first, loses lift, and now that your tail wings aren't countering anymore, your wings will pull the nose up. Possible solutions would be thicker tail wings, or tail wing slats. Or not pulling that tight.

With B9PW it shouldn't be a problem to add slats/make the slats bigger. Same for flaps.

Set the leading edge control surfaces (if I'm not mistaken your leading edge is already a control surface) to either spoilers, or flaps, then modify the custom action groups so you can control them. They should deflect up at 0° AoA, and then deflect towards the airflow (-AoA deflection, I think you already use that) so they don't cause a stall. That should increase your lift a bit. Don't expect too much though.

EDIT: You could ofcourse also rotate the slats, instead of letting them deflect as flaps/spoilers.

Data volumes suck :/

Wait raising the gear in the hangar actually effects the calculations? ... Ups :D

I could try to increase the thickness a bit, there is still room for that.

I use negative AOA deflection, I found out about that from one of BahamutoDs videos, that inspired me to revisit this design, since the SU27 is an inherently acrobatic plane.

And yes I pull till it snaps basically. If I could get a good PID setting that would not start to oszillate when I reach the setpoint, but instead would just keep me under it so that I could pull the stick back as hard as I want without worrying to lose control. That'd be great :D

I will play around with that a bit, I could also use negative deflection for spoiler and flaps.

Edited by VentZer0

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Always. It's been giving me a bit of oscillation but nothing too bad.

I have to suggest you get the PID tuner for FAR. It is handy and fixes a lot of those issues.

That'd be great :)

I use negative AOA settings for the leadingedge controlsurfaces, so its kinda like that. I Noticed when I increase the deflection the craft stays controlable longer, so I guess that's some improvement ;D

I know that bitching betty warning for the SU27 because I played DCS SU27 :) The struts you see are only there to counter wobble under high G, even with KJR the wobble still persists under high G loads.

Tried flaps and spoilers but there wasnt any difference, I have the feeling flaps don't do much in FAR, could be wrong tho.

I used km/h because metric and the HUD for the russian planes used metric aswell, but I switched to knots and the plane lifts just after reaching 180knots under normal load. I think I'm gonna do some part customization to get the weight of the craft a bit lower and to get the right amount of fuel in there. Real SU27 weights around 16 metrictons with 9.4 tons of fuel capacity which brings it to 30tons fully loaded.

Mig21 isn't even a plane ... it's a rocket with an identity crisis thinking it's a plane. :D

.

Flaps work just set them to a much lower angle then FAR sets them when you first set them. I like to have my flaps between 10-15deg of deflection at max setting. And my leading edge slats at no more than 7.5deg, usually they are set around 5deg at most.

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70deg AoA? not surprising you have issues there given that's very likely stalling one wing, and at 650kts I'm not sure if thrust vectoring is going to manage to hold onto the craft.

One thing you can try is adding control surfaces to the wing leading edges and link them to AoA so the leading edge is pointing along the velocity vector - if FAR is still using the old wing model ( I think it is? ) an unstalled leading edge should help keep the surface behind unstalled also. You don't need to link them to any control deflection if you don't want to ( although one day I'll try some craziness with that ). If you go back probably a couple of hundred pages in the main FAR thread to roughly just before 1.0 release you'll find a lot of discussion on supermanoeverability.

16613167570_b0391c996c_z.jpg

That was my over-exaggerated test example craft.

Edited by Van Disaster

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Anyone want to do a brief rundown of vertical stabilizer function? When is two better than one? If using two, how does their lateral distance from each other and relative angle affect their performance?

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Anyone want to do a brief rundown of vertical stabilizer function?

Keeps your plane from being yaw instable. Usually also adds dihedral effect (if mounted above CoM), and yaw control.

When is two better than one?

If a single one would need to be ridiculously large, you need a better field of view or field of fire for the gunner, or if you have an engine mounted on the back that would damage a tail fin if mounted in the middle. Also if you want to avoid 90° angles for stealth reasons.

If using two, how does their lateral distance from each other and relative angle affect their performance?

The further away from each other, the better I'd say.

And relative angle would end in a V-tail, right? AfaIk that's less effective at keeping you yaw stable, but does ofcourse add pitch stability, and possibly more dihedral effect (if mounted far from each other) (not too sure about the dihedral effect though).

No money back if anything of the above is only semi-correct

Edited by FourGreenFields

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General rule of thumb I go with for the vertical stabilizer is to have its area somewhere between 10-12% of the total main wing area, with its root length roughly 25% the length of the main wing root (or, if I'm building a craft with a tail-plane, I want the fin to be roughly half the total area of the tail). If the configuration of a single stabilizer with those numbers gives me a fin length greater than the height of the plane (wheels down), I split it into twin tails.

Take that advice for what it's worth - I usually build SSTO cargo planes, not fighters.

A too-tall vertical surface can start giving you excessive roll couple, it'll show up in the derivatives.

And conversely, one that's not tall enough will give you yaw instability at high speeds (and as a result your plane will want to fly backwards). Lost a good many of my early FAR craft on account of insufficient fin...

Edited by capi3101

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Two small tails also have a smaller radar cross-section.

You can also angle them to affect your roll stability.

That is not all, there is a huge difference between using one and two vertical stabilizers, from storage to structural integrity, it's up to you to find out what fits your design the best.

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Anyone want to do a brief rundown of vertical stabilizer function? When is two better than one? If using two, how does their lateral distance from each other and relative angle affect their performance?

Repeating what some others have said:

The main function is to control yaw instability. Amount of control is a product of vertical fin area and distance from CoM. More fin, further back = more stable. If you're accustomed to building in stock, you're going to need a lot more tailfin than you're accustomed to, especially if you build rearward weight-biased ships (e.g. most deltas).

Twin fins are for when the needed single fin would be excessively large, or when there is some design logistics issue discouraging a central tailfin placement. Angling the fins out will provide some lift and dihedral, but will reduce the vertical fin area. Lateral spacing doesn't matter much; centralised is better from a weight distribution PoV, but if you can manage central, you probably wouldn't need two tails.

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Lateral spacing doesn't matter much; centralised is better from a weight distribution PoV, but if you can manage central, you probably wouldn't need two tails.

Oh, well, it actually matters, but all you want is them not being too close together.

If they are closer they become less efficient.

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Oh, well, it actually matters, but all you want is them not being too close together.

If they are closer they become less efficient.

I was trying to avoid excessive complication. :)

But, yeah; not so close together that they block each other's airflow once you start to yaw.

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70deg AoA? not surprising you have issues there given that's very likely stalling one wing, and at 650kts I'm not sure if thrust vectoring is going to manage to hold onto the craft.

One thing you can try is adding control surfaces to the wing leading edges and link them to AoA so the leading edge is pointing along the velocity vector - if FAR is still using the old wing model ( I think it is? ) an unstalled leading edge should help keep the surface behind unstalled also. You don't need to link them to any control deflection if you don't want to ( although one day I'll try some craziness with that ). If you go back probably a couple of hundred pages in the main FAR thread to roughly just before 1.0 release you'll find a lot of discussion on supermanoeverability.

https://farm8.staticflickr.com/7617/16613167570_b0391c996c_z.jpg

That was my over-exaggerated test example craft.

Where's that propeller mod from? I didn't see that engine in Firespitter nor KAX...

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And conversely, one that's not tall enough will give you yaw instability at high speeds (and as a result your plane will want to fly backwards). Lost a good many of my early FAR craft on account of insufficient fin...

Area is not the same as height - you can make it longer & still get your yaw stability but without increasing roll moment so much, just as you can have narrow span wings with large area.

Where's that propeller mod from? I didn't see that engine in Firespitter nor KAX...

Retrofuture - haven't checked if it's updated for 1.0 yet - the static parts will probably be fine, engines I suspect not.

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Retrofuture - haven't checked if it's updated for 1.0 yet - the static parts will probably be fine, engines I suspect not.

It hasn't yet... the nodes on most of the parts are off unless you do a cfg edit.

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Area is not the same as height - you can make it longer & still get your yaw stability but without increasing roll moment so much, just as you can have narrow span wings with large area.

True - you can increase the area by making either the root length or the height longer. Poor choice of words on my part in my prior post.

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Yeah but remember that changing the aspect ratio heavily affects the lift characteristics, a wider shorter vertical stabilizer is not as strong as a narrower taller one with the same area.

Edited by tetryds

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What is a good aspect ratio for the vertical stabilizer, anyways?

(Yes, I know - it. depends. on. the. craft. Just in general, though, what do you guys typically shoot for?)

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I have a weird thing happening to my craft: Pitch input over Mach 1 and without SAS on the plane will roll to left or right while pitching, not extreme but very noticable. With BD Armory ordanance it's worse.

The Craft is totally symetrical how can this be? There's no wobble under normal G loads ( < 12G)

Enlighten me pls?

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@capi3101: what is the fun of having it as a rule of thumb?

As I don't like other people having fun... usually 3/2 (rectangle)

Even though there is a lot to them, vertical stabilizers are not that big of a deal, you just need enough.

If going too fast too low or it's too big you need two, that's all.

IMO it's something that you can save for area ruling.

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What is a good aspect ratio for the vertical stabilizer, anyways?

(Yes, I know - it. depends. on. the. craft. Just in general, though, what do you guys typically shoot for?)

I generally choose my tailfins based on aesthetics, then tweak as necessary if yaw stability is an issue (usually only a problem on tail-heavy deltas). Mk1 ships normally get a Tailfin or similar (AV-R8, Delta Deluxe, etc,) Mk2’s a tapered swept wing piece, Mk3's one of the new large tailfins. Like so:

lnW0yBv.png

FZqIzbp.jpg

KhnMolx.jpg

Edited by Wanderfound

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@capi3101: what is the fun of having it as a rule of thumb?

As I don't like other people having fun... usually 3/2 (rectangle)

Well, I like having a place to start. Most of the time, my design process for the fin goes like this:

1) Carefully determine what I think the area of the fin should be.

2) Carefully determine the length of the root and the span based on that area and the shape I want it to have.

3) Build the tail to those carefully determined specifications.

4) Throw out the whole damn thing because it looks like dreck and exchange it for some random thing that may or may not work on the first go.

3/2, eh? I can probably handle that...

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3/2 looks something like I use, although mine are usually heavily swept. Looking back on 0.90 builds apparently "about the size of my canards". I will tend to build up the root first if that isn't sufficient, or throw the lot out and add two fins rather than make something excessively tall.

I also used to heavily use vertical-ish wingtip surfaces - which is probably *not* a good idea for canards generally - but some of that was to help with the oddities of sideslip/yaw you get with forward sweep ( the craft will tend to roll into a sideslip - given how canard craft like slipping their nose off heading already, adding that on top gets amusing ).

Given one of the most awkward areas of spaceplane flight seems to be 20km-30km at high AoA when it's heavily loaded I'm wondering if ventral tails might not be a better idea. At least supplementary ventral tails. I'm not sure how much occlusion of the tail FAR does, but at the sorts of AoA we fly at we'd be occluding most of it if it was real life...

Edited by Van Disaster

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I generally choose my tailfins based on aesthetics, then tweak as necessary if yaw stability is an issue (usually only a problem on tail-heavy deltas). Mk1 ships normally get a Tailfin or similar (AV-R8, Delta Deluxe, etc,) Mk2’s a tapered swept wing piece, Mk3's one of the new large tailfins. Like so:

http://i.imgur.com/lnW0yBv.png

http://i.imgur.com/FZqIzbp.jpg

http://i.imgur.com/KhnMolx.jpg

You can get away with smaller vertical stabilizers than what Wonderfound has shown.

h10XsCr.jpg

That aircraft is strictly atmospheric and operates just fine with those tiny fins in the back as a tail.

oMkClOO.jpg

Same for this craft... which is a cranked arrow delta wing design.

isWhT2Z.jpg

m6QPLKD.jpg

I tend to go with smaller vertical stabilizers because I found the larger ones are not only "ugly" but also cause drag that I would rather not deal with.

zNGUx0j.jpg

96E3VvD.jpg

Both of those last two are different tail designs, one is more of a traditional vertical stabilizer design the other is a more split V tail, like the YF-23.

But ultimately the best vertical stabilizer is the one that does its job without causing unwanted side affects.

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