Now the question. After starting both PW125B engines in C130 and trying to
both centered). When gliding in the air without engines, the plane flies
well - no yaw.
Aircraft config is attached.
Post by Jim WilsonFrom: "Correu PelDavid"
Hi,
I'm studying theory control, and I'd like to play a bit with
helicopter's capabilities.
I'd like to work on their model.
Flightgear works with YAsim, JSBsim and LaRCsim.
I've take a look at the LaRCsim manual. It says it uses "a set of
equations of motion for a rigid-body aircraft in atmospheric and
low-earth orbital flight".
In fact, using the equations of a 6D rigid-body is where I would have
started if I were to choose without more info.
I wonder how the other models work.
For instance, I know the X-plane engine considers the aerodynamic
planes. A totally different point of view from LaRCsim, but still
accurate and working.
Where could I get some info on YAsim and JSBsim?
Could you draw me a shot of the main ideas?
It would be helpful if there was some documentation readily available in
the source or base package that gave a nutshell description of each flight
dynamics model library. This sort of question gets asked now and then.
JSBSim is fairly well documented. I'm not sure if Andy Ross is reading
and will answer but I'll give a brief description of what I understand
about YASim.
The parts of the code that I've worked on (doing very minor fixes) seem to
be using a collection of well known (as in I could find some of them on
the Internet) formulas for calculating things like lift, drag, thrust,
prop rpm, etc. based on weight/mass and geometric data. Some of the
calculations use very general data points about performance capabilities
of the aircraft (e.g. stall speeds, cruise speeds) that are readily
available for just about any model airplane.
You can get an idea of the scope of these calculations by examining some
of the configuration files for the Aircraft that are currently using the
YASim FDM. My unskilled assesment is that the YASim can reasonably
simulate a wider range of Aircraft operations better than JSBSim but a lot
depends on how much data you give JSBSim. In the end a JSBSim flight
model is potentially much more faithful to the original aircraft given
detailed enough data.
A very general distinction between using the two FDMS, in my view would be
this: If you want to make a very accurate simulation of a single
aircraft for which you have access to a fair amount of information on
(especially wind tunnel tests) then JSBSim is definately the way to go.
If you want to put together a reasonable simulation fairly quickly and/or
the data you have is limited to general performance and geometric
measurements, YASim is definately the way to go. The laws of diminishing
returns seem to kick in a little quicker refining YASim model
configurations, but you can get something quite reasonable with less.
JSBSim models can be refined and tweaked and with greater attention and
time can be made quite accurate. If neither of those senarios matches
exactly what you want to do, then do a little more research and see what
you can get for data, and how you wish to approach your project.
At the moment it seems that YASim is further ahead in terms of Helicopter
simulation. And I would even suggest that if one were interested in
examining control (as opposed to flight dynamics) with maybe a variety of
helicopter configurations, that YASim might be better suited anyway.
As you know from previous discussion, the helicopter simulation isn't all
that accurate. In my opinion, the biggest problem (from a control
perspective) is the lack of ground effect modeling. The effect of the
collective control (rate of accent/decent) should be significantly
influenced by distance from the ground during landing, takeoff (or any
extended hovering close to the ground).
On the issues of transational lift modeling, I must confess it has been a
while since I've experimented with the helicopter simulation so I cannot
remember exactly what was wrong. The lift effect is basically working.
Also I think the tendency for the aircraft to rotate goes away as you
transition to ETL as it should. I do not think asymmetrical lift (the
side where the blades are moving forward produces more lift) is modeled.
Just to check for basic operation, you might try some of the obvious
things like pitching the aircraft up and down to see if it climbs/falls
and decelerates/accelerates in response. The accuracy of these effects
might require a little improvement but if translational lift is working
you should at least see something reasonable happening.
In my opinion the other issues, like the lack of autorotation, pale in
importance compared to the omission of ground effect modeling. This is a
critical element for fixed wing aircraft modeling, and it is just as or
even more so for helicopters because the behavior of that cushion of air
is so central to their operation.
Best,
Jim
--
Jim Wilson
Kelco Industries
PO Box 160
Milbridge, ME 04658
207-546-7989
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