center of gravity?

S

smilo

Charter Member
so, i was wondering, how does one determine
the forward/aft center of gravity
for a multi-engine aircraft model?

for the sake of argument, let's just say
that specifications are next to nil,
except that, there are decent 3 view drawings
with height, length and wing span dimensions.
 
smilo said:
so, i was wondering, how does one determine
the forward/aft center of gravity
for a multi-engine aircraft model?

for the sake of argument, let's just say
that specifications are next to nil,
except that, there are decent 3 view drawings
with height, length and wing span dimensions.
Click to expand...

You could start with the center of the wings tip to tip. now this isn't perfect but could be a starting point. with out the weight at the tail and at the wheels its a best guess. what plane are you looking for?
 
It;s unfortunate that Firestriker's site is no longer available as he had lots of examples of different aircraft types to give you a feel for this.

For FS however, it is pretty simple to set the CoG in order for the flight model to work its best.

Longitudinally, you set the model on the design program at centerline of course.
Laterally, the model should be set at 1/4 wing root cord, at 25% back from the wing's root leading edge.
Vertically, set the model at or near the prop spinners, or an average of them on a 3 or 4 engine model.

I usually set the model (and indicate such in the aircraft.cfg engine parameters) just below the spinner so that thrust would give a slight nose down moment.

Attaching some examples

For swept wings (like jets), use 1/4 cord at the root measured back from where the leading edge meets the fuselage.
 
Hi Smilo,
Seems to me that you are getting some pretty good advice so far. Let's see if I can change that! :wiggle:

While I believe that Milton Shupe is technically correct, I prefer to do things just a little differently:
Instead of using 1/4 of the wing chord, I usually start with 1/2 chord and adjust slightly forward if it has a trycycle gear and slightly aft if it is a tail dragger.
The reason I do this is to make the aeroplane balance a bit better on the ground. It doesn't matter so much with a tricycle gear, but with a tail dragger, you might want to make a nose-over a bit more difficult.
Real aeroplanes have wheel brakes that can be controlled a bit more precisely than the simple on/off that we see in CFS.

The value you are actually interested in is not really the chord at the wing ROOT, but something called the "Mean Aerodynamic Chord". With a good drawing and a straight edge, you can do a fairly precise estimate, but to be honest, I have never bothered to go that far. Eyeballing it seems to be as accurate as we need for our purposes.

Another way that I believe would work pretty well is to check where the bomb bay is if you are building a bomber. The chances are pretty good that the original designer was smart enough to put the bomb bay on the Longitudinal CoG. If there are external bomb racks or drop tanks, they would also most likely be on the CoG or pretty close.

Have Fun!
- Ivan.
 
to say that i am pleased with the replies
would be a gross understatement.
many thanks gentlemen.

at the risk of getting Dave too excited,
i have, at least, 4 aircraft on my to do list.
for starters, and most likely,
a complete start over of my old A-20 project,
which was so rudely interrupted by an ar196.
sorry Dave, just pulling your chain.
a Do17 and my latest interest, the forgotten bomber,
the Martin 187 A-30 Baltimore.
then, one that's way down on the list,
the Kawanishi H6K Mavis.

while i'm dreaming, how about my long time fantasy
of better visual models of the stock cfs aircraft.
nothing terribly complex, just better ai models.

just thinking about it a little,
i can't help imagine how cool it would be
if we cfsers could do a collaborative project
much like the way Milton and company does for fs9 and fsx.
anybody up for it or am i just dreaming, again?

okay, go relax Dave.
at the current production rate,
all of that should keep me busy
for the next ten to twenty years.
 
Hi Smilo,

I was debating on whether or not to tell you about my build list.
I suspect you already know that the A-20 and Dornier 17Z-2 are already on my list and started because I have posted a few screenshots.
What I don't believe I ever told you about is that the Martin 167 Maryland and the Kawanishi H8K Emily are also on the list though I have never gotten beyond information gathering on those two.

That's some pretty good overlap, huh?

Regarding replacements for the stock aircraft, you know I have a pretty decent P-47D Razorback and a FW 190A AND a Spitfire Mk.IXc, right?
The Hurricane and P-51D are also on the build list though not very high.

- Ivan.
 
as i may have said before,
my interest in the a-20 and do17
both come from cfs itself.
when installing the game or auto playing the disk
the picture has an a-20 with D-Day stripes.
i thought, what the hey? how come, no a-20?
as for the stock do17, what's up with that thing?
would saying, "i hate the stock do17!"
be too harsh? i think not.
cfs is in dire need of one better than what we have.
frankly, i'm surprised one has never been done.

the mavis...because it was the first
on the long list of p-38 victims.
and i like planes that can float, too.

up until this past month,
i had never heard of the martin 167 or 187.
i subscribe to a magazine called Aviation History.
the May issue had an article, The Forgotten Bomber
about the Martin A-30 Baltimore.
apparently, the Brits worked her a$$ off in the Med and Italy.

i do remember your fw190, p-47 and spitIX.
they are top candidates for the job.
although, the spit isn't finished yet, right?

i have a pretty nice hurri mkI and spit mkI
that i use instead of the stockers.
sorry, i can't remember the authors right now.
i'd have to fire up my game machine to look.

apologies...gotta run.
i've got to finish getting the place in order.
out of town company arriving in the morning.
 
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