Moments of Inertia Switched?

Doing some research into how Moments of Inertia affects the FlightModel in the
MSFS2020 Aircraft, I stumbled onto a weird case of confuse Moment of Inertia
Attribution. In the Flight_Model.cfg it is stated: " empty_weight_pitch_MOI =
60000 ; Empty pitch moment of inertia, Jxx (SLUG SQ FEET)
empty_weight_roll_MOI = 13760 ; Empty roll moment of inertia, Jzz (SLUG SQ
FEET) empty_weight_yaw_MOI = 30090 ; Empty yaw moment of inertia, Jyy (SLUG SQ
FEET) " But this is not a correct mathematical convention, at least to the
material I Have? They state that Ixx = Moment of Inertia for Roll Iyy =
Moment of Inertia for Pitch
Izz = Moment of Inertia for Yaw I Wonder if
this is just a simple typo, or somethng that can be affecting internally other
areas of the sim? Worth checking anyway! Regards!

Well spotted Alexis ! Let’s see what they say…

Hey, I don’t know if that helps, but in the Flight Model Physics page, there
is a mention about the axes and referentials used by MSFS. Here is a
screenshot that might answer your question:

It’s a bit confusing since, from the original MS FS SDK documentation one can
get the following: Axis Longitudinal X Positive Forward Lateral Y Positive to
the Right Vertical Z Positive Down i9n FS9/X which agrees with the8old
conventional Ixx, Iyy, Izz notation and moments… Here’s an interesting (old)
post by Tom Goodrick on MOI estimates for MFS aicraft: Calculating MOI’s |
BGA Forums

where Tom advocates that in general and for most aircraft designs roll moi <
pitch moi < yaw moi The above example shows that the relation is not valid for
that model, but I really don’t know if it can be justified. Anyway the yaw moi
is lower…

Thank you all for the very good insights on the subject! This page on the SDK
saying MSFS doesn’t follow the usual convention might explain why there are
all swapped. I wonder if that was the case also in previous FSs, or something
that was implemented in Asobo’s Hands. Very good Link Jose! For sure, Yaw is
always bigger on all planes I have seen so far. Disregard my first example, as
that 60.000 in Pitch MOI is just me trying to break the system :smiley: