Payload station locations

[davidvoogd]

I am still a bit confused as to where to place the payload station locations. It has only been explained as "relative to the center of gravity". This
doesn't make much sense to me as the center of gravity changes as weight is added, it is different depending how the aircraft is loaded.

Using this weight and balance example from an aircraft.cfg file, which values would I use for the seats / luggage in the FS Passengers Payload
configuration? Weight and balance makes a huge difference in the GA aircraft I fly so I would like to get it right.

[weight_and_balance]
max_gross_weight = 3663
empty_weight = 2564 //standard=2530
reference_datum_position = 7.4, 0, 0 //front cowling
empty_weight_CG_position = -6.625, 0, 0 //79.5in=6.625ft
empty_weight_pitch_MOI = 2784
empty_weight_roll_MOI = 2227
empty_weight_yaw_MOI = 4633
empty_weight_coupled_MOI = 0
max_number_of_stations = 7

station_load.0 = 220, -6.66, -0.9, -0.3, pilot
station_load.1 = 220, -6.66, 0.9, -0.3, co-pilot
station_load.2 = 100, -9.58, -0.9, -0.3, passenger 1
station_load.3 = 100, -9.58, 0.9, -0.3, passenger 2
station_load.4 = 0,-12.67, -0.9, -0.3, passenger 3
station_load.5 = 0,-12.67, 0.9, -0.3, passenger 4
station_load.6 = 15,-15.00, 0.0, -0.5, luggage



Thank you.

[KZLA-CH]

CG is a fixed location on the aircraft...on all AC scheamtic diagrams, it is shown with a CG symbol. Any station on the aircaft fuselage is always
listed as a +/- location in reference to it. Usually the CG is located on the apex of the wing root. But in swept wing aircraft it is a little aft
of that.

[davidvoogd]

As a pilot I know that the Center of Gravity is not fixed, it does move. One of the items you learn in ground school is how to calculate the location
of the center of gravity. This is accurately portrayed in the loading screen in FS Passengers.

Either way, technicalities asside it would be great if a demonstration could be made using the weight and balance data posted above. Again my main problem is knowing where to locate the stations in the payload configuration program.



Post Edited ( 09-05-05 18:53 )

[koyaan]

to my knowledge 'empty_weight_ cg_position' is the fixed one, relative to the 'reference_datum_position'. CG shifts back or forth when
payload comes in (pass,lugg,fuel)

Your aircraft.cfg is quite clear about it. Reference datum is at front cowling and the fixed CG is 6.625 ft behind that. The pilots are sitting
on it : ) About a meter behind there are 2 passengers and one meter further behind 2 more passngers. One meter more backward there
is the luggage.

I hope i'm correct about this : )

Let me know if it matches your aircraft : )

gerrit

[edit] so CG will shift back in your plane when it gets loaded.



Post Edited ( 09-05-05 21:44 )

[davidvoogd]

That is how I have been setting everything up so far, however this plane - the Beechcraft Bonanza A36 has quite affected by loading any cargo and
passengers, the aft C of G seems quite exaggerated, though perhaps this is true to the aircraft itself? I will ask that on the DF forums.

[davidvoogd]

Dan could you confirm or clarify if it is the proper practice to base station locations as distance from the empty weight Center of Gravity?

[DanSteph]

yes it's usually based on the "empty_weight_CG_position"

notice anyway that this value don't exist in memory so FsP calculate himself
the "empty CG position" it work like this:

When you click "start flight" FsP empty the aircraft and start to put various weight
at various points and test the CG until it find the center position...
This work for most aircraft but may fail on some...

So I have added in the latest payload editor a "don't recalculate the CG"
parameter, if you check it using the distance from the original aircraft.cfg
might work better.

Hope it help ?

Dan

[davidvoogd]

Yes Dan this does help a lot - thank you!

Just on the last item you mentioned. Do you mean that if I click on "Don't Recalculate the CG" it will use the aircraft.cfg's empty center of gravity pluse payload station locations to load the aircraft instead of the FS Passengers payload setup? As in with my example above it will use the pilot and passenger locations in the aircraft.cfg to place the pilots and passengers?

Thanks,
David Voogd.



Post Edited ( 09-06-05 12:46 )

[DanSteph]

Sorry If I'm unclear, I'll try to explain better....

well lets take an example:

you set in payload editor cargo station to be at +20 feet

If you let FSP calculate the center position:

FsP empty the aircraft and found the center position to be +10ft (internally relative to Fs9 model's center)
you "CARGO station" will be moved to 30ft...
This method fail on aircraft as PMDG because the center position of the empty aircraft is way off.

If you forbid FsP to recalculate:

Your cargo will be at +20ft whatewer happen.

I know the difference might look subtle...

Just one important things: FsP don't look at all aircraft.cfg station position or weight, as long as it have the correct number of them.
in brief whatewer you write in the station point of an aircraft.cfg doesn't matter, FsP overwrite position and wight in memory
as written in the payload editor.

Pffff I hope my explaination doesn't suck to much ?

Dan

[davidvoogd]

No your explaination does make sense, sorry if I appear to be very picky but I just want to fully understand how this works so I can setup my payload
configurations properly. It appears that I have been setting them up properly so far. I do understand how the PMDG 747 differs for C of G locations as
it has the reference point at the nose rather than around the center of the aircraft. Since I mostly fly General Aviation aircraft and they generally use the standard FS2004 conventions for weight and balance this isn't really an issue for the payload setups I am making.

So just to make sure I totally understand this now with this example...

I have an aircraft.cfg file for an aircraft with

Empty Weight Center of Gravity = 1 (feet)
Station1 (2 Passenger Seats) = -2 (feet)

I would set up Station 1 in the FS Passengers Payload Editor as
Passenger seats (2) = -1 feet (2 back from the empty weight C of G)

So when I am in Flight Simulator and load passengers into my plane with FS Passengers it will place them at a station 2 feet back from the Empty center of gravity, and then recalculate the C of G from there to reflect the load. Is this correct?

If this is correct perhaps it would really clear things up if you changed the description for that station locations in the Payload Editor to
"Distance from Empty Center of Gravity".

Thank you for your patience Dan, I really appreciate your help in this!



Post Edited ( 09-06-05 15:42 )

[JaWood]

here' what I do to make my payload models in the editor. It's not nesecarilly the right way, but it works well for the simulator.

First, I put in all of the stations in my, lets say, 737. There would be a first class, an economy class, a front cargo and a rear cargo. Now
chances are the numbers that are typed in for "distance from CG" are inittially waaaay off. I hit the calculate button and sure enough, the CG is too
far out of whack.

So I first reset all station weights to 0. CG will go neutral. I turn on ONLY the cargo weights, and look up what kind of cargo weight a real 737
might have (Google is great for this) and then start typing in values to match this. I swap capacities back and forth between the cargo stations, and
nudge their possitions back and forth until my calculated CG looks centered. "Great! Good enough for simulated flight" I say to myself.

I then turn off the cargo weights, knowing that they by themselves are balanced, and turn on ONLY the passenger stations. I configure the seating
capacities, then again start nudging their possitions back and forth until the pax stations by themselves are centered. Now if I turn on pax
stations, cargo stations, or all stations together, everything is always balanced.

I can load my planes in FsP with very good CG results using this technique. The idea behind this is to keep the adjusted CG as close to the empty CG location no matter what the weight.



Post Edited ( 09-07-05 04:16 )

[koyaan]

another question about this, i tried a payload model for the B1900C and not as much as David's plane, the weight of the pilots matters. I
just renamed location one from VIP to Pilots and set them No Price. Now in the Start flight menu the pilots are also waiting at the gate
with the other passengers. What exactly does this No Price mean?

i forgot to search the forum, maybe this has been answered. Sorry bout that than.

Gerrit

[JaWood]

no price means charter flight, sorta, I guess. If you want to add the pilots' weight, add it to something a litle more permanent. Tack on an extra
350 lbs for two pilots into the empty weight number. I think it's in the aircraft.cfg file somewhere.

[koyaan]

Thks JaWood,

i did that before but FSP doesn't read the weights from the aircraft.cfg if FSP payload is enabled.
When i understand Dan correctly, when starting a flight the weights from aircraft.cfg are disregarded
and the FSP weights next are written into memory.