<s>
FlightGear	O
Flight	B-Application
Simulator	I-Application
(	O
often	O
shortened	O
to	O
FlightGear	O
or	O
FGFS	O
)	O
is	O
a	O
free	B-License
,	O
open	B-Application
source	I-Application
multi-platform	B-Operating_System
flight	B-Application
simulator	I-Application
developed	O
by	O
the	O
project	O
since	O
1997	O
.	O
</s>
<s>
It	O
has	O
specific	O
builds	O
for	O
a	O
variety	O
of	O
operating	B-General_Concept
systems	I-General_Concept
including	O
Microsoft	B-Application
Windows	I-Application
,	O
macOS	B-Application
,	O
Linux	B-Application
,	O
IRIX	B-Operating_System
,	O
and	O
Solaris	B-Application
.	O
</s>
<s>
FlightGear	O
is	O
an	O
atmospheric	O
and	O
orbital	O
flight	B-Application
simulator	I-Application
used	O
in	O
aerospace	O
research	O
and	O
industry	O
.	O
</s>
<s>
Its	O
flight	O
dynamics	O
engine	O
(	O
JSBSim	B-Application
)	O
is	O
used	O
in	O
a	O
2015	O
NASA	O
benchmark	O
to	O
judge	O
new	O
simulation	O
code	O
to	O
the	O
standards	O
of	O
the	O
space	O
industry	O
.	O
</s>
<s>
He	O
was	O
dissatisfied	O
with	O
proprietary	B-Application
,	O
available	O
,	O
simulators	O
like	O
the	O
Microsoft	B-Operating_System
Flight	I-Operating_System
Simulator	I-Operating_System
,	O
citing	O
motivations	O
of	O
companies	O
not	O
aligning	O
with	O
the	O
simulators	O
 '	O
players	O
(	O
"	O
simmers	O
"	O
)	O
,	O
and	O
proposed	O
a	O
new	O
flight	B-Application
simulator	I-Application
developed	O
by	O
volunteers	O
over	O
the	O
Internet	O
.	O
</s>
<s>
The	O
flight	B-Application
simulator	I-Application
was	O
created	O
using	O
custom	O
3D	O
graphics	O
code	O
.	O
</s>
<s>
Development	O
of	O
an	O
OpenGL	B-Application
based	O
version	O
was	O
spearheaded	O
by	O
Curtis	O
Olson	O
starting	O
in	O
1997	O
.	O
</s>
<s>
FlightGear	O
incorporated	O
other	O
open-source	B-Application
resources	O
,	O
including	O
the	O
LaRCsim	O
flight	O
dynamics	O
engine	O
from	O
NASA	O
,	O
and	O
freely	O
available	O
elevation	O
data	O
.	O
</s>
<s>
The	O
first	O
working	O
binaries	O
using	O
OpenGL	B-Application
came	O
out	O
in	O
1997	O
.	O
</s>
<s>
By	O
1999	O
FlightGear	O
had	O
replaced	O
LaRCsim	O
with	O
JSBSim	B-Application
built	O
to	O
the	O
sims	O
 '	O
needs	O
,	O
and	O
in	O
2015	O
NASA	O
used	O
JSBSim	B-Application
alongside	O
6	O
other	O
space	O
industry	O
standards	O
to	O
create	O
a	O
measuring	O
stick	O
to	O
judge	O
future	O
space	O
industry	O
simulation	O
code	O
.	O
</s>
<s>
Around	O
that	O
time	O
,	O
the	O
graphical	O
front	O
end	O
"	O
FlightGear	O
Launch	O
Control	O
"	O
,	O
also	O
known	O
as	O
"	O
FGRun	O
"	O
,	O
was	O
replaced	O
by	O
a	O
hard-coded	O
Qt	B-Language
launcher	I-Language
.	O
</s>
<s>
FlightGear	O
's	O
source	O
code	O
is	O
released	O
under	O
the	O
terms	O
of	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
and	O
is	O
free	B-License
and	I-License
open-source	I-License
software	I-License
.	O
</s>
<s>
Fluid	O
behaviour	O
is	O
often	O
characterised	O
by	O
eddies( 	O
Videos:aircraft	O
,	O
terrain	O
)	O
or	O
vortices	B-Application
on	O
varying	O
scales	O
down	O
to	O
the	O
microscopic	O
,	O
but	O
is	O
harder	O
to	O
observe	O
as	O
the	O
air	O
is	O
clear	O
except	O
for	O
moisture	O
phase	O
changes	O
like	O
condensation	B-Application
trails	I-Application
or	O
clouds	O
.	O
</s>
<s>
The	O
aircraft	O
surface	O
interaction	O
works	O
with	O
the	O
same	O
dynamics	O
,	O
but	O
on	O
a	O
limited	B-Algorithm
range	O
of	O
scales	O
.	O
</s>
<s>
Atmospheric	O
water	O
is	O
modeled	O
by	O
FlightGear	O
ranging	O
from	O
state	O
changes	O
such	O
as	O
condensing	O
into	O
cloud	O
or	O
haze	B-Device
layers	O
,	O
along	O
with	O
energy	O
provided	O
from	O
latent	O
heat	O
to	O
drive	O
convective	O
fluid	O
flow	O
,	O
through	O
to	O
precipitation	O
as	O
rain	O
droplets	O
,	O
snow	O
,	O
or	O
hail	O
.	O
</s>
<s>
The	O
process	O
of	O
generating	O
lift	O
creates	O
turbulence	O
with	O
vortices	B-Application
,	O
and	O
FlightGear	O
models	O
wake	O
turbulence	O
with	O
shedding	O
of	O
wingtip	O
vortices	B-Application
by	O
flown	O
craft	O
as	O
well	O
as	O
AI	O
craft	O
.	O
</s>
<s>
FlightGear	O
also	O
has	O
a	O
less	O
physically	O
accurate	O
model	O
that	O
uses	O
METAR	O
weather	O
updates	O
of	O
differing	O
frequency	O
,	O
designed	O
for	O
safe	O
operation	O
of	O
aerodromes	O
,	O
to	O
dis-continuously	O
force	O
atmosphere	O
based	O
on	O
attempted	O
guesses	O
of	O
processes	O
that	O
are	O
fundamentally	O
constrained	O
by	O
the	O
closeness	O
or	O
density	O
of	O
observation	O
stations	O
,	O
as	O
well	O
as	O
the	O
small-scale	O
,	O
limited	B-Algorithm
,	O
rounded	O
off	O
,	O
non-smoothly	O
varying	O
,	O
and	O
need-to-know	O
precision	O
of	O
information	O
.	O
</s>
<s>
There	O
is	O
a	O
model	O
of	O
gravity	O
based	O
on	O
a	O
non-spherical	O
Earth	O
,	O
and	O
craft	O
can	O
even	O
experience	O
differing	O
gravity	O
across	O
their	O
bodies	O
which	O
will	O
exert	O
twisting	B-General_Concept
force	I-General_Concept
.	O
</s>
<s>
FlightGear	O
supports	O
multiple	O
flight	O
dynamics	O
engines	O
with	O
differing	O
approaches	O
,	O
and	O
external	O
sources	O
such	O
as	O
MATLAB/Simulink	O
,	O
as	O
well	O
as	O
custom	O
flight	O
models	O
for	O
hot	O
air	O
balloons	O
and	O
spacecraft	O
.	O
</s>
<s>
JSBSim	B-Application
is	O
a	O
data	O
driven	O
flight	O
dynamics	O
engine	O
with	O
a	O
C++	B-Language
core	O
built	O
to	O
the	O
needs	O
of	O
the	O
FlightGear	O
project	O
from	O
1996	O
to	O
replace	O
NASA	O
's	O
LaRCSim	O
,	O
and	O
integrated	O
into	O
FlightGear	O
as	O
the	O
default	O
from	O
1999	O
.	O
</s>
<s>
Flight	O
characteristics	O
are	O
preserved	O
despite	O
low	O
frame	O
rate	O
,	O
as	O
JSBSim	B-Application
physics	O
are	O
decoupled	O
from	O
rendering	O
and	O
tick	O
at	O
120Hz	O
by	O
default	O
.	O
</s>
<s>
This	O
also	O
supports	O
high	O
time-acceleration	O
as	O
rendering	O
does	O
not	O
have	O
to	O
be	O
done	O
faster	O
causing	O
the	O
GPU	B-Architecture
to	O
be	O
a	O
bottleneck	O
.	O
</s>
<s>
Mass	O
balance	O
,	O
ground	O
reactions	O
,	O
propulsion	O
,	O
aerodynamics	O
,	O
buoyant	O
forces	O
,	O
external	O
forces	O
,	O
atmospheric	O
forces	O
,	O
and	O
gravitational	O
forces	O
can	O
be	O
utilized	O
by	O
JSBSim	B-Application
,	O
the	O
current	O
default	O
flight	O
dynamics	O
engine	O
supported	O
by	O
FlightGear	O
,	O
to	O
determine	O
flight	O
characteristics	O
.	O
</s>
<s>
JSBSim	B-Application
supports	O
non-terrestrial	O
atmospheres	O
and	O
has	O
been	O
used	O
to	O
model	O
unmanned	O
flight	O
in	O
the	O
Martian	O
atmosphere	O
by	O
NASA	O
.	O
</s>
<s>
JSBSim	B-Application
was	O
used	O
by	O
NASA	O
in	O
2015	O
with	O
other	O
space	O
industry	O
simulation	O
code	O
,	O
both	O
to	O
establish	O
a	O
ruler	O
to	O
judge	O
future	O
code	O
for	O
the	O
requirements	O
and	O
standards	O
of	O
the	O
space	O
industry	O
,	O
as	O
well	O
as	O
check	O
agreement	O
.	O
</s>
<s>
The	O
verification	O
tested	O
both	O
atmospheric	O
and	O
orbital	O
flight	O
in	O
6-degrees-of-freedom	O
for	O
simulations	O
like	O
JSBSim	B-Application
that	O
supported	O
both	O
.	O
</s>
<s>
The	O
results	O
from	O
6	O
participants	O
consisting	O
of	O
NASA	O
Ames	O
Research	O
Center	O
(	O
VMSRTE	O
)	O
,	O
Armstrong	O
Flight	O
Research	O
Center	O
(	O
Core	O
)	O
,	O
Johnson	O
Space	O
Center	O
(	O
JEOD	O
)	O
,	O
Langley	O
Research	O
Center	O
(	O
LaSRS++	O
,	O
POST-II	O
)	O
,	O
Marshall	O
Space	O
Flight	O
Center	O
(	O
MAVERIC	O
)	O
,	O
and	O
JSBSim	B-Application
were	O
anonymous	O
as	O
NASA	O
wanted	O
to	O
encourage	O
participation	O
.	O
</s>
<s>
By	O
contrast	O
,	O
offline	O
approaches	O
like	O
JSBSim	B-Application
can	O
incorporate	O
windtunnel	O
data	O
.	O
</s>
<s>
They	O
can	O
also	O
incorporate	O
the	O
results	O
of	O
computational	O
fluid	O
dynamics	O
which	O
can	O
reach	O
computable	O
accuracy	O
only	O
limited	B-Algorithm
by	O
the	O
nature	O
of	O
the	O
problem	O
and	O
present	O
day	O
computational	O
resources	O
.	O
</s>
<s>
This	O
allows	O
saving	O
of	O
CPU	O
and	O
GPU	B-Architecture
resources	O
by	O
letting	O
unimportant	O
parts	O
of	O
the	O
simulation	O
,	O
like	O
visuals	O
or	O
less	O
time-sensitive	O
aircraft	O
systems	O
,	O
run	O
at	O
slower	O
rates	O
.	O
</s>
<s>
Separate	O
clocks	O
are	O
available	O
for	O
JSBSim	B-Application
physics	O
,	O
different	O
parts	O
of	O
aircraft	O
systems	O
,	O
as	O
well	O
as	O
environment	O
simulations	O
at	O
large	O
scale	O
(	O
celestial	O
simulation	O
)	O
and	O
small	O
scale	O
(	O
weather	O
physics	O
)	O
.	O
</s>
<s>
Layering	O
of	O
hazes	B-Device
is	O
rendered	O
by	O
FlightGear	O
,	O
such	O
as	O
low	O
lying	O
ground	B-Device
haze	I-Device
with	O
3d	O
structure	O
,	O
smog	O
related	O
to	O
human	O
activity	O
,	O
and	O
dust	O
.	O
</s>
<s>
Several	O
networking	B-Architecture
options	O
allow	O
to	O
communicate	O
with	O
other	O
instances	O
of	O
.	O
</s>
<s>
A	O
multiplayer	O
protocol	O
is	O
available	O
for	O
using	O
on	O
a	O
local	B-General_Concept
network	I-General_Concept
in	O
a	O
multi	O
aircraft	O
environment	O
.	O
</s>
<s>
Since	O
version	O
2020.1	O
it	O
is	O
possible	O
to	O
connect	O
to	O
VATSIM	O
by	O
using	O
the	O
open-source	B-Application
swift	O
pilot	O
client	O
.	O
</s>
<s>
Several	O
instances	O
of	O
can	O
be	O
synchronized	O
to	O
allow	O
for	O
a	O
multi-monitor	B-General_Concept
environment	O
.	O
</s>
<s>
Although	O
not	O
developed	O
or	O
typically	O
analyzed	O
solely	O
as	O
a	O
game	O
in	O
the	O
traditional	O
sense	O
,	O
has	O
nevertheless	O
undergone	O
reviews	O
in	O
a	O
number	O
of	O
online	O
and	O
offline	O
publications	O
,	O
and	O
received	O
positive	O
reviews	O
as	O
a	O
flight	B-Application
simulator	I-Application
game	O
.	O
</s>
<s>
Linux	B-Application
Format	O
reviewed	O
version	O
2.0	O
and	O
rated	O
it	O
8/10	O
.	O
</s>
<s>
MathWorks	O
FlightGear	O
to	O
Simulink	B-Application
interface	O
.	O
</s>
