Is Duna bugged?

[miklkit]

Years ago when I first broke out of the Kerbin SOI I went to Duna.  First I built a fuel depot on Ike, then dropped down to Duna.  I landed rockets and spaceplanes.  MK1,MK2, and MK3 all using stock parts.  I landed rockets and the only crashlanding was a rocket that I did not put enough retro rockets on and it landed too hard.  Then I moved on and forgot about Duna.

Well recently I decided to do a rover repair contract there and the rovers I left there years ago are small and unstable, so I decided to land a better one.  I have attempted to land 4 different spaceplanes there and none were successful.  One never made it close to landing.  Further testing showed the OPT wings made it very unstable and they were replaced with Big S wings. 

The problem is landing.  For the 3 that attempted to land they were fine until slowing to touch down.  My method is to glide in to the location, go vertical to kill all speed, and then back down like a rocket, touch gently, and fall onto the wheels.  This works everywhere.  Except that now on Duna they go unstable and start swinging side to side and touch down going sideways and fall apart.  I have found no way to keep them stable.  Not SAS, not SAS retrograde, not manually.  What is going on?

 

[king of nowhere]

2 hours ago, miklkit said:

Years ago when I first broke out of the Kerbin SOI I went to Duna.  First I built a fuel depot on Ike, then dropped down to Duna.  I landed rockets and spaceplanes.  MK1,MK2, and MK3 all using stock parts.  I landed rockets and the only crashlanding was a rocket that I did not put enough retro rockets on and it landed too hard.  Then I moved on and forgot about Duna.

Well recently I decided to do a rover repair contract there and the rovers I left there years ago are small and unstable, so I decided to land a better one.  I have attempted to land 4 different spaceplanes there and none were successful.  One never made it close to landing.  Further testing showed the OPT wings made it very unstable and they were replaced with Big S wings. 

The problem is landing.  For the 3 that attempted to land they were fine until slowing to touch down.  My method is to glide in to the location, go vertical to kill all speed, and then back down like a rocket, touch gently, and fall onto the wheels.  This works everywhere.  Except that now on Duna they go unstable and start swinging side to side and touch down going sideways and fall apart.  I have found no way to keep them stable.  Not SAS, not SAS retrograde, not manually.  What is going on?

 

hard to say without knowing the details, it may just be that those planes are unsuited to duna.

have you tried landing anything else? use the f12 menu to test and see if other stuff works

[miklkit]

Those planes were designed for Duna with more wings and more oxy.  I am building another MK3 now using all stock parts with Big S and mini big S wings.  I have tested them by landing on the Mun and Ike first where they did fine.  Except for that one with the OPT wings they all fly fine on Kerbin too.  It is only when they are backing down and get below 20m/s that they go unstable.

[magnemoe]

Never used planes on Duna, atmosphere is very thin so not sure how practical landing an plane is. 
20 m/s would be well below stall speed of any plane I flew so I assume you are trying to do an tail landing? Duna atmosphere is a bit to thin to be useful but too thick to ignore. 
One option might be to fly to destination then use parachutes not only to slow down but more to pull center of drag in-front of the plane, engines will point down and you can use it to slow down. 

[king of nowhere]

11 hours ago, miklkit said:

 I have tested them by landing on the Mun and Ike first where they did fine. 

...

what works on mun doesn't work on duna, and your first idea is "it's a bug" - rather than "i need better tests"?

 

duna has over twice the gravity of mun, three times that of ike. it has an atmosphere, affecting aerodynamics. you can't just "test something on mun" and assume it's going to work on duna. the higher gravity requires different solutions.

besides, regarding your concept of "land by tail, slam down with the wheels", i tried it, there's a good chance the plane is going to break apart when the wheels touch the ground. I made it to work, but it required a lot of save-scumming. i assume you are trying to play without reloading, because you sent 4 planes instead of just reloading until you manage to land the first one. if that's the case, i advise against the tail landing; too unreliable to make it work without save scumming. I absolutely advise trying it without testing in situ with alt-f12 (something you also seem opposed to doing). you are certainly not going to do it with only 4 testing iterations, which is what you actually had.

"instability" may be caused by many different things; my experience is that sometimes ships are unstable during the last phases of landing if the sas overcompensates, turning tiny deviations into huge ones. it may be caused by the higher gravity forcing more thrust, by the wings creating aerodinamic forces getting in the way, or by the ship getting bent under the higher gravity /aerodinamic forces, which confuses the SAS to no end.

 

[miklkit]

What has changed?  I landed many planes on Duna successfully without parachutes.  They did not break up on landing either.  I also landed many planes on Laythe without them breaking up.  They fly fine on Kerbin and can do tail landings there.  Something new is destabilizing them.  Nowhere else do they go out of control at speeds where the atmosphere should have no effect on them.

[king of nowhere]

1 hour ago, miklkit said:

What has changed?  I landed many planes on Duna successfully without parachutes.  They did not break up on landing either.  I also landed many planes on Laythe without them breaking up.  They fly fine on Kerbin and can do tail landings there.  Something new is destabilizing them.  Nowhere else do they go out of control at speeds where the atmosphere should have no effect on them.

if they can do tail landings on kerbin, then they should work. that's a much better test for landing than mun or ike.

still, just because you flew other, different planes on duna, it doesn't mean those specific planes you are trying to land now will work the same. i suspect the most recent ones will be bigger, for start.

regardless, i've never heard of a planet being bugged - except for the ground contact bug that occasionally comes with kerbalism. bugged vehicles, all the time, but you tried four of them.

it's much, much more likely it's faulty engineering anyway. sometimes things react differently in different gravity. i once had a lander for tylo, i tested it on kerbin, it could slam the ground at 10 m/s and survive. I went to tylo, i touched the ground at 3 m/s, it exploded. i couldn't get it to not explode on tylo, no matter how softly i touched down. i tried retracting the landing legs, and then it worked perfectly. things just get this weird occasionally.

[miklkit]

This is what has me puzzled.  Years ago I landed MK1, MK2, and MK3 planes just fine.  The MK3s were rover carriers that dropped them off and then went back to Kerbin, so they were in the 240-260 ton range.  All the ones I have tried now are lighter than that, in the 120-220 ton range. 

I'm still trying new designs trying to find any engineering mistakes, even copying old designs that I know worked before.  The latest one, a MK2 passenger plane was doing fine with SAS set to retrograde until I lit the engines to slow it down and it immediately flipped over and went nose first into the ground.  That is the weird part.  Once they decide to go over they can not be brought back in line.  They refuse to fly straight. 

[king of nowhere]

As i said, that can happen if sas overcompensates. Sometimes reducing engine gimbaling helps. Or it could be that the plane is getting bent, this screws up sas.

Else, i really have no idea.

If you landed those other planes "years ago", some updates changed some things, including sas and rigidity, and may result in finely tuned planes no longer being functional.

Edited November 10 by king of nowhere

[miklkit]

I no longer have any of those old planes, but did go through screenies of them and that jogged my memory a little bit.  I may be making them too stable.  The old ones were all short and wide.  I also remember how elated I was when I managed to build on that flew well in both Kerbin and Duna.  Most flew very well backwards in Kerbin. 

You keep mentioning rigidity.   To me if it falls apart on landing, then something is wrong with it and it needs to be rebuilt. Anyway, still building new designs.  On V7 now.

[king of nowhere]

On 11/10/2024 at 6:44 PM, miklkit said:

You keep mentioning rigidity.   To me if it falls apart on landing, then something is wrong with it and it needs to be rebuilt.

something is wrong with it, yes, but this is trying to figure out what is wrong.

you say that you lose stability at low speed, and i'm saying that it may be the result of the plane getting bent out of shape, which confuses SAS to no end. just a maybe

[miklkit]

Just got on here today.  Got a 504 error this morning. 

They seems to be just fine as far as rigidity is concerned.  Every part is auto strutted.  They just will not land on their tails.  I started taking off from KSC and flying up to 5000m, the altitude of Duna, and trying to get them to back down.  Nope.  Even tried parachutes which worked fine until the engines were lit to slow it down and it went completely bonkers.  I am out of ideas.

[king of nowhere]

11 hours ago, miklkit said:

Just got on here today.  Got a 504 error this morning. 

They seems to be just fine as far as rigidity is concerned.  Every part is auto strutted.  They just will not land on their tails.  I started taking off from KSC and flying up to 5000m, the altitude of Duna, and trying to get them to back down.  Nope.  Even tried parachutes which worked fine until the engines were lit to slow it down and it went completely bonkers.  I am out of ideas.

can you share pictures?

[miklkit]

This morning I just got a black screen instead of this forum.

 

Some.  I can get more of them in the SPH.  This is the MK3 with the OPT wings.

And at Duna.

[king of nowhere]

ok, but i meant, pictures about what goes wrong. trying to figure out what's the source of the instability

[miklkit]

Oh.  No screenies of that as I'm pretty busy trying to regain control.  In general terms they refuse to go straight.  The one above refused to fly straight once it got down into the atmosphere, but would fly sideways just fine. 

[king of nowhere]

21 hours ago, miklkit said:

Oh.  No screenies of that as I'm pretty busy trying to regain control.  In general terms they refuse to go straight.  The one above refused to fly straight once it got down into the atmosphere, but would fly sideways just fine. 

most of its mass is in the tail, so i'm not really surprised. i had planes with the same issue, and sometimes some atmospheres are less forgiving than others.

[miklkit]

I have found that Duna "needs" a less stable plane than Kerbin does, so moved the weight back a little on that one.  Also it is pretty well balanced and the COM does not move much.  I have tried them with the COM forward and back like that one and COM forward lets them fly better but they still crash. 

Here is the last one I built and tried on Kerbin.  It has the COM forward as well as parachutes.