Center of lift makes no sense on my ship..

[OscarWilde]

Hey all,

Not 100% sure if I'm in the right section.. my issue is more gameplay related than the actual game itself so I posted here instead of the support section!

As the title says: the center of lift on my ship is way off from where I imagine it should be and I don't understand why... Screenshot:

As you can see, the CoT and CoM are both perfectly centered but the CoL is under the one corner.. As a result that side flips over. Very confusing as the ship is essentially symmetrical.

Or at the very least the CoM could have been off as the two sides aren't the same. For the record I don't have any mods for Aerodynamics (ie. FAR or the like).

Any ideas? Tips? I thought maybe it had something to do with the OKTO on that corner, but I tried adding one to the opposite corner to absolutely no change. It's not like there is a wing or anything there..

so why the extra lift?

Also I'm afraid I don't know how to make my images smaller on here... my apologies if they are to large!

Thank you!

Oscar

Edited January 21, 2015 by OscarWilde
Typo

[cantab]

You appear to have no wings at all. That means the centre of lift is undefined, and it just gets shown on the bottom of the VAB as a "default" location.

I can't see where your propulsion is, but if it's flipping in flight the design looks sound so I'd suspect pilot error.

[capi3101]

Which part is your root? Grab it, move the whole structure around until the CoM, CoT and CoL are aligned and see if that sorts out the problem. I've seen this sort of thing before, but not since 0.19.

[OscarWilde]

Corrected the flip with a bit of SAS but I'm still wondering why it would do that anyway if the first two (Mass/Thrust) are centered.. Why would the third (Lift) be pulling so hard on that one corner? When it isn't any different than it's neighboring corner.

Only really a problem in atmosphere anyway.. which isn't an issue as this is a mun lander (1 of 4 pieces to be docked in space and landed together) but still irritating.

- - - Updated - - -

Did not know it would leave it undefined! (I never build space planes so I rarely use CoL) I guess pilot error... I've been playing a long time (600+ hours according to steam...where the hell did they all go) so I'm a good enough pilot.. but my design did not lead me to expect to flip the way it does.

For the record: there is an LV-909 at the bottom of each corner for thrust.

Tried moving the other two over the CoL now Capi and it didn't change anything; thank you though!

Also on the note of Pilot error: I should say this is an immediate 180 degree flip within ~150m of the launchpad... it's like my mass is WAY off center. But clearly it isn't. It happens so fast I don't think any level of piloting skill would ever fix it.

Edited January 21, 2015 by OscarWilde
Update

[pellinor]

I don't see any lift arrow. If the lift is zero, it has no well-defined point of attack, so the CoL marker has no meaning. Also note that the CoL is different from the center of drag, which unfortunately is not accessible at all.

[pincushionman]

I agree, that CoL location appears to be the center of the build floor, nothing more. You also appear to have a "loop" of sorts going on, which isn't actually supported by the vessel definition format. Have you strutted across the ends to connect them or used a docking port pair to link them in-engine? Otherwise floppiness may cause control problems.

[OscarWilde]

I agree, that CoL location appears to be the center of the build floor, nothing more. You also appear to have a "loop" of sorts going on, which isn't actually supported by the vessel definition format. Have you strutted across the ends to connect them or used a docking port pair to link them in-engine? Otherwise floppiness may cause control problems.

Definitely not a lift problem. You're all correct, I honestly had no idea that it just left CoL undefined when you had no wings. I assumed all parts generated some lift. And yes, the corners are all supported by struts. So no floppiness!

I'm starting to think glitch or something maybe..?

[Kesa]

does the fuel symetrically flows? I guess yes since you said this does not happen in space, but check it in space until the fuel tanks are empty.

- - - Updated - - -

in stock aero only wings and some (mk2) fuselage generate lift.

If fuel flow is your issue, check the fuel flow rules to know how to balance fuel consumption, or use a fuel balancer mod. AFAIK, the rules in the link still apply (despite dating from 0.24.2)

[OscarWilde]

Fuel consumption seems normal in space.. I've pretty well given up on fixing it now.. SaS bandages it enough for my use (and there isn't an issue once its attached to the launch craft and sent to orbit) The issue only exists when I try to take off with no SAS from the launch pad.

Is it possible for me to change the post title to "answered"? Or does a Moderator have to do it? Essentially my original question about the CoL was answered; as it was just showing the default position of lift as I had no wings.

Thanks for all of your help everyone! If anyone else has any added input I would still be glad to hear it.

[technicalfool]

Is it possible for me to change the post title to "answered"? Or does a Moderator have to do it?

It's been a while since I edited a thread without the green username. I'm pretty sure you can change the prefix. But in any case, consider it done.

And have fun!

[capi3101]

Is it possible for me to change the post title to "answered"? Or does a Moderator have to do it? Essentially my original question about the CoL was answered; as it was just showing the default position of lift as I had no wings.

For future reference, you just have to go and edit the initial post, go into advanced mode and flip the little pull-down menu option to set the thread as answered.

Do you use TAC Fuel Balancer or something similar? If not, I'd recommend grabbing it and installing it, and then seeing how the fuel drains in flight (don't necessarily have to keep it afterwards if you don't want to; I'm just suggesting using it to run a diagnostic). If that's the underlying cause, you can set TAC to balance all tanks and you're good to go. If not, at least you eliminated fuel imbalance as a cause. Or you can just let SAS handle it; nothing wrong with that.

[flashcactus]

While the actual question seems to have been answered, I'd like to point out that it's not the center of lift you're looking for, but the center of drag. In the stock souposphere it tends to be in the exact same spot where the CoM is, but with Ferram's aerodynamics mods (and probably in the next versions of KSP, too) it's usually somewhere else. Unfortunately, the editors don't have an indicator for it, so you'll have to try and judge where it'll be by yourself.

[Janos1986]

You didn't mess with thrust limiters, did you?

[OscarWilde]

You didn't mess with thrust limiters, did you?

I thought maybe I'd messed one up by accident, but after checking they are all 100% thrust... Great suggestion though! I now have all four corners of this lander in space and connected together; still flips without SAS on ! Pretty strange!

FlashCactus Unfortunate that there is no indicator for CoD! Maybe something someone could mod? It'd be interesting to see sometimes.