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Full Version: What on earth is wrong with this Large Rudder on my ship.
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So ... I've been building a destroyer with a friend and I decided to try giving it a large rudder.

It works ... Very strangely.

It actually turns great and I love the idea, but anytime I try to turn the ship it basically lists 60 degrees away from the direction I'm trying to turn it. For obvious reasons, this is a big problem!
Usually this behavior would result from the rudder being vertically out of line with the center of mass, above. This is not true of this - I've tried many different rudder shapes and moved the spin block up and down to see if that's the problem and it reliably causes the ship to flop over away from the direction of turning. (Unless I extend the rudder far below the plane of the ship, in which case it jitters wildly instead.) Help, please?
The standard rudders apply their force perpendicular to the ship.

The big rudders, on a spinblock, apply their force perpendicular to the spinblock, not the ship. This resulting non-perpendicular force on the ship causes a drag on the ship at a complementary angle to your spinblock setting. It's probably the cause of your problem. I noticed it because my ship, with two of them, would slow down noticeably (>5m/s) when yawing. Mine's got lots of roll and pitch control and is a lot bigger than the one in your picture so it didn't get too squirrely.

Check the forces display (press \ in build mode).

EDIT: Your post got me thinking, so I looked into it some more.

The forces from the rudder are also applied at point where the spinblock connects to the vehicle, not at the rudder's location. This is a major problem and you should probably report it.

The forces also bounce around a lot.
Had a look on it: smart turret design Smile and this boat is unstable almost to the point of capsizing by design. Yes it has proportions close to real destroyer, but FTD physics is "somewhat" unrealistic, and scales badly with small builds.
Probably you better use old rudder instead, it's weird physics can compensate this, and rework your hull for more stability.
Attached one boat of similar size that was perfectly stable last time i checked.

btw,  Large Rudder's tendency to list the ship to outer side of the turn is actually pretty realistic, despite totally unrelated ingame case of such behaviour. If it lists too much, then your boat is too unstable, not the rudder's broken. And typical destroyer hull even in reality has stability issues. On earliest, smallest destroyers they even were forced to have short funnels and very light balcony instead of superstructure to compensate. And whole hull was built basically out of tin foil.
More investigation of rudder forces:

I took BioPhoenix's boat, added some hydrofoil outriggers to give it some stability, and then put a 16m metal pole to lower the Large rudder way down in order to make what was going on very obvious. I then disabled the steering ACBs and set and locked the rudder's spinblock at 10 deg. The forces are definitely applied at the spinblock, not the rudder. Here is the proof.

[Image: attachment.php?aid=52404]
It's a good test, but just thinking about it logically it was pretty obvious already.

the game treats a spin block as a separate entity scabbed onto your craft, just look at turret pop with explosions if it hits the turret the damage belongs to the turret no matter how much ship you put between the 2. Huge parts on tiny jets don't causing drag , many faction jests wouldn't be as fast as they are built without all all their major parts on spin blocks. Jet engines on spin blocks still apply force to the main craft in the direction they are facing, i would imagine code wise the large rudders are the same, except they don't provide thrust just direct it.

designing something with(or taking advantage of) a spin block , propulsion will always be applied to the spin block, but no other forces will matter.

now i'm interested in what other forces do apply and which ones don't.
If you read patchnotes, you'll discover that large rudder is designed to apply force at CoM's plane, regardless of where they actually placed.
In fact force's applied at globally horizontal plane containing the CoM of vehicle, regardless even of vehicle's tilting. You can test it by placing your spinblock at the end of that stick.
Listing appears if CoM is too high and hull's stability is bad.
In original modded version, there were two sets of rudder blocks. One worked similarly to current ingame version, other created their forces directly from blocks themselves, even if mounted on spinblock. Mixing ow these two allowed vertical balancing of rudder force. Would be good to have both sets ingame.
Go vote for suggestion! https://brilliantskies.customercase.com/...submarines

@BKCXb7, you're wrong about rudders, these also create magic force. Unlike old rudders (that created force strictly sideways and added to speed), these create force with noticeable forward component depending on rudder block's angle. This simulates correct rudder behaviour well enough, by "cancelling" part of the forward thrust that would be redirected with real rudder. Within game engine limitations, this is best way to do it.
(2018-11-11, 07:44 PM)Pastor of Muppets Wrote: [ -> ]More investigation of rudder forces:

I took BioPhoenix's boat, added some hydrofoil outriggers to give it some stability, and then put a 16m metal pole to lower the Large rudder way down in order to make what was going on very obvious. I then disabled the steering ACBs and set and locked the rudder's spinblock at 10 deg. The forces are definitely applied at the spinblock, not the rudder. Here is the proof.

(Image removed)

That would be helpful, but it's not what's going on.
I already tried what you tried. I also tried moving the actual spinblock's altitude around a bit to compensate. (You have to pull the ship out of play and put it back in for the ACBs to detect new spinblocks now, though.) To confirm that it's not that, I tried moving the spinblock again, but more so, so there's no way it could be above center of mass.
[attachment=52405]
If that was the issue, moving the spinblock's position up and down should fix it.
[attachment=52406]
It does not. The forces are clearly applying at the wrong altitude. They appear to always apply at the waterline.
[attachment=52407]
This leads to the same leaning effect happening regardless of the position of either the spinblock or of the rudder on the spinblock. I remember the old large rudders mod had rudders apply their force at the center of mass. Neither of these are very accurate but that would be better than this.

EDIT: You can also clearly see the forces aren't with the spinblock in any case, as the forces for different rudder segments are visibly applied at different positions along the forward-backward axis when there's only one spinblock.
EDIT2: Rephrased
what happens if the whole boat is under water???? fill it with lead and see if it list....... it could be interacting with buoyancy instead of center of mass

what happens if another one is added on top??? if it's ignoring its position and teleporting force to the waterline than another one on top would make it worse or counter it dependent on weather or not it cares about orientation.
(2018-11-11, 08:37 PM)DraWay Wrote: [ -> ]If you read patchnotes,  you'll discover that large rudder is designed to apply force at CoM's plane, regardless of where they actually placed.
In fact force's applied at globally horizontal plane containing the CoM of vehicle, regardless even of vehicle's tilting. You can test it by placing your spinblock at the end of that stick.
Listing appears if CoM is too high and hull's stability is bad.
In original modded version, there were two sets of rudder blocks. One worked similarly to current ingame version, other created their forces directly from blocks themselves, even if mounted on spinblock. Mixing ow these two allowed vertical balancing of rudder force. Would be good to have both sets ingame.
Go vote for suggestion! https://brilliantskies.customercase.com/...submarines

@BKCXb7, you're wrong about rudders, these also create magic force. Unlike old rudders (that created force strictly sideways and added to speed), these create force with noticeable forward component depending on rudder block's angle. This simulates correct rudder behaviour well enough, by "cancelling" part of the forward thrust that would be redirected with real rudder. Within game engine limitations, this is best way to do it.


(2018-11-11, 09:05 PM)BioPhoenix Wrote: [ -> ]
(2018-11-11, 07:44 PM)Pastor of Muppets Wrote: [ -> ]More investigation of rudder forces:

I took BioPhoenix's boat, added some hydrofoil outriggers to give it some stability, and then put a 16m metal pole to lower the Large rudder way down in order to make what was going on very obvious. I then disabled the steering ACBs and set and locked the rudder's spinblock at 10 deg. The forces are definitely applied at the spinblock, not the rudder. Here is the proof.

(Image removed)

That would be helpful, but it's not what's going on.
I already tried what you tried. I also tried moving the actual spinblock's altitude around a bit to compensate. (You have to pull the ship out of play and put it back in for the ACBs to detect new spinblocks now, though.) To confirm that it's not that, I tried moving the spinblock again, but more so, so there's no way it could be above center of mass.

If that was the issue, moving the spinblock's position up and down should fix it.

It does not. The forces are clearly applying at the wrong altitude. They appear to always apply at the waterline.

This leads to the same leaning effect happening regardless of the position of either the spinblock or of the rudder on the spinblock. I remember the old large rudders mod had rudders apply their force at the center of mass. Neither of these are very accurate but that would be better than this.

EDIT: You can also clearly see the forces aren't with the spinblock in any case, as the forces for different rudder segments are visibly applied at different positions along the forward-backward axis when there's only one spinblock.
EDIT2: Rephrased


This game has patch notes? Every now and then they get posted but it always stops getting done.

My test sure looked like the force was applied at the spinblock, and it made sense based on how other things in the game have worked before. I assumed it to be correct, and it was not. Sorry!

The irony is that the actual behavior (apply force at the waterline) is worse.

Applying the force at the waterline makes the large rudders only usable if your ship has the center-of-mass exactly at the waterline. If your ship does not meet this criteria, you cannot use large rudders without having stability issues unless you are willing to make big changes, which in many cases are probably not possible. Also, what happens with a submarine using large rudders?

Rudders should behave like you expect them to: they should apply a force at the center of the part of the rudder that is underwater. The magnitude of the force should be relative to speed, angle of attack, and the size of the rudder.

The rudders should work when mounted horizontally like diving planes, absolutely. I didn't even think to check that. I just assumed it would work, because it clearly should.

I wonder if this tying rudder force to the horizontal plane thing is why sideways-mounted old rudders used for pitch control do not work in the same manner ones used for yaw do. It stopped functioning as expected around the time the control surface lerper was added.

I didn't worry too much about the drag large rudders cause because a rudder should cause a drag. It's more weird that the old standard rudders don't.

This game doesn't need to be exactly realistic, it just needs to function more or less like the player expects it to and also be internally consistent.

Edit:
You can get ACBs to notice the new pieces by changing the affect range on the ACB down one and then back up one. You don't have to pull the craft out of play.
Well, with properly built ships these large rudders do not cause any issues, it's just barely anyone builds proper ships. But independently working variant must exist, absolutely.
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