UmbralRaptor changed the topic of #kspacademia to: https://gist.github.com/pdn4kd/164b9b85435d87afbec0c3a7e69d3e6d | Dogs are cats. Spiders are cat interferometers. | Космизм сегодня! | Document well, for tomorrow you may get mauled by a ネコバス. | <UmbralRaptor> egg|nomz|egg: generally if your eyes are dewing over, that's not the weather. | <ferram4> I shall beat my problems to death with an engineer. | We can haz pdf
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<galois>
title: Principia significantly affects the handling of a significant portion of the aircraft · Issue #2808 · mockingbirdnest/Principia · GitHub
<oeuf>
are you aware of cases where the rigid body dynamics of an aircraft matter for its handling characteristics?
<WeylandsWings>
i mean only in cases of flutter i thought
<oeuf>
(the bug is very poorly phrased, but essentially the attached and pictured aircraft are mostly-stable in stock+FAR and mostly-unstable with Principia; flyable, but nervous and could really use FBW)
<WeylandsWings>
maybe principa is causing issues because there are bodies contacting each other
<oeuf>
nah, we handle this well; this has something to do with our handling of rigid body rotation
<oeuf>
(I mean rigid body dynamics in the Джанибеков effect sense, not as in nonrigidity of the aircraft)
<WeylandsWings>
maybe it is an issue because forward swept wings then? as those tend to be crazy unstable
<oeuf>
yeah I think the aircraft is close-to-unstable in stock and with Principia it becomes less stable
<oeuf>
but it is somewhat odd, because Principia doesn't do aerodynamics obviously; so assuming no stupid bugs the explanation would be that the rotational behaviour is different enough to push it on the other side of stability
<oeuf>
which is not entirely unbelievable, but still a bit odd
<WeylandsWings>
also could be a matter of stock vs principa slightly changing axis/location making it silly unstable
<WeylandsWings>
but yeah that one is a head scratcher
<WeylandsWings>
i would say ask Ferram
<oeuf>
(e.g. a freely-spinning aircraft will tend to convert pitch into roll, assuming that the intermediate axis is pitch, and then depending on how close the axes are it may behave differently)
<oeuf>
(but most aircraft aren't freely spinning because then you call them spacecraft)
<WeylandsWings>
my knowledge of plane stability is having spent a day or two in undergrad on it
<WeylandsWings>
so not the best
<oeuf>
and then a bit more than that in KSP I suppose :-p
<oeuf>
(but obviously that doesn't help where we wonder about the limitations of KSP+FAR)
<WeylandsWings>
i mean there are many limitations of KSP
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<_whitenotifier-9244>
[Principia] RCrockford opened issue #2811: Crash while descending towards the surface of a body - https://git.io/JIsmq
<_whitenotifier-9244>
[Principia] RCrockford edited issue #2811: Crash while descending towards the surface of a body - https://git.io/JIsmq
<_whitenotifier-9244>
[Principia] RCrockford edited issue #2811: Crash while descending towards the surface of a body - https://git.io/JIsmq
<_whitenotifier-9244>
[Principia] RCrockford edited issue #2811: Crash while descending towards the surface of a body - https://git.io/JIsmq
<_whitenotifier-9244>
[Principia] pleroy commented on pull request #2809: Fix tolerances for Linux and remove a check - https://git.io/JIssv
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<SnoopJ>
ha
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<egg|laptop|egg_>
smkz: whitequark: speaking of aerospace techniques with military origins, one I quite like is trimming by moving fuel around in the Concorde, originating in the Mirage IV strategic bomber
<egg|laptop|egg_>
smkz: whitequark: yeah the rear trim tank is at the base of the tail in the Mirage IV: 104. килевой топливный бак-кессон
<egg|laptop|egg_>
uh s/base/front/ probably
<egg|laptop|egg_>
Looks like the A330, 340, and 380 had trim tanks too, but not the 350; Boeing designed the 747 to support having that but it’s not clear to me from cursory googling if it was used
<umbralraptop>
something something early 747s contained ballast that was waste from nuclear weapons production
<umbralraptop>
well, "waste"
<whitequark>
DU?
* oeuf
finds trim tanks eggstremely entertaining for no discernible reason
<umbralraptop>
DU
<oeuf>
tired: control the aircraft using control surfaces; wired: control the aircraft using differential thrust; inspired: control the aircraft by moving fuel around
<smkz>
is the thing with trim tanks and CG just the thing that the tail stabilizer thingie (idk what it's called) provides downforce in stable flight and reducing the downforce it needs to produce is useful because it reduces the amount of drag involved in producing that downforce?
<smkz>
i dont actually know much about how airplanes or wings work
<oeuf>
smkz: my understanding is that in the transonic regime the aircraft needs to be trimmed differently in pitch, and you don't want to fly with control surfaces deflected to do so because drag