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FS2004 Station load question

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vololiberista said:
So explain the precise difference between aircraft.cfg empty_weight_CG_position= 5.300 / and airwrench -3.475776 (being 12.63MAC x 27.52%mac empty) then!! As they are both empty weight CoG.
Click to expand...

I don't use AirWrench because I've never needed it. Why not ask its developer what the difference is? However, they are not from the datums.
 
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I downloaded the VC-10 from DM website. Opened Airwrench on the balance page. CG positions are all negative percentage MAC. MAC is calculated as 23.3 ft
Opened the Dimensions page. Wing root chord is 34 ft, wing apex lon is 13 ft. This would be fine if the wing had no sweep angle, but sweep is 35°.
Basic problem is that the CG is ahead of the MAC so it is negative. Reason is apex lon needs to be quite a bit longer.
It is like WarpD said, LEMAC is wrong for the MAC. Not hard to fix, but needs the top view drawing and the entries in the CG calculator I referenced
Roy
 
AirWrench is making things up based on what it reads from your aircraft config. I have never found it to be 100% accurate. It is heavily subject to garbage in = garbage out.

Do you have a weight/balance sheet for one of these aircraft?
 
WarpD said:
AirWrench is making things up based on what it reads from your aircraft config. I have never found it to be 100% accurate. It is heavily subject to garbage in = garbage out.

Do you have a weight/balance sheet for one of these aircraft?
Click to expand...
No I don't :( I have all the other specs. Empty weight max fuel max traffic etc etc. But a real weight and balance sheet no. So essentially I'm relying on some figures that I know to be correct and others that seem to be off that I can't verify. My TPI settings are definately within operational range but the underlying calculations don't match up 100% with what the sim spits out.

That said weight distribution and indexes on the load sheet can be extrapulated to give the numbers I'm looking for.
SVC10_LOADSHEET.jpg
The important bits are circled. So from that I can get quite an accurate weight distribution for a full load.
On the one hand I have to get 2.71 inches zero fuel weight and on the other 3.82 deg TPI. It only works if the load is apportioned one way plus (in this case) 1,500kgs in the fin tank.
So I am certainly in the ball park!
 
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Volo,
You owe me one for this!
I found a 3-view of the RAF VC-10 and scaled it in ft/pixel. I used that image to get the data needed by the Aircraft Center of Gravity Calculator.
From that I found out that wing_pos_apex_lon should be 27.52 ft, it was 13.0

This is the distance from the wing LE to the reference point and since the DM VC-10 reference point and CG are both at 0,0,0 it is the same as "Wing root LE to CG" in the calculator.
From the Sweep distance to MAC, MAC itself and the wing root LE to CG I calculated the CG %MAC was 32.9%.
I changed the wing_pos_apex_lon to 27.52 in the aircraft.cfg and loaded the airplane into AirWrench. CG now looks reasonable at low 30's. Reasonable for a swept wing airplane and identical to the CG range for an F4.
bac_vc-10_90R.jpg COG.jpg AirWrench balance.jpg
Not a difficult exercise.
Roy
 
Thanks Roy,
I'll have a good look at that. I know the image but never trusted its accuracy.
The image is for the Standard 10. For the Super two fuselage plugs of 6ft6 have to be added either side of the wing. One question relating to wing tip chord. They are Kuchemann tips. I presume the measurement would be as if they are straight.
Take your pick just out of the fridge!!
beer.jpg
 
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I'll have a dozen Moretti, grazie.
There are always some approximations when trying to simplify dimensions. For example, the wing is not a simple shape and what value should one use for either root chord or tip chord. The trailing edge inboard on the wing is set up for high drag flaps and the wing tips are set up for low vortex drag. Sure this will affect the wing area calculations, but not have a huge effect of the CG calculations. The CG calculator has no fuselage size inputs so the wing area is reference area and includes the part within the fuselage. This is a commonly used convention which in fact has no impact on CG calculations.
The wing_pos_apex_lon dimension only affects the gauged CG and has no effect on flight characteristics since all of the necessary coefficients already exist.
Roy
 
I do have a couple of questions Roy,
first regarding wing_pos_apex_lon. I had a look at the payware VC10 (which has much to be desired to put it mildly!) and his wing_pos_apex_lon is 12
So both devs are working from the same reference point which is clearly different from the CoG calculator. The airerench version of the "rip-off ware" puts the fuelled CoG immediately in front of the wheels. Whereas your correction puts it correctly in relation both to the wheels and MAC but I'm not clear about the wing diagram in airwrench bcause it puts the wheels significantly behind the wing!

the other point is wing aspect ratio. In your correction it comes out as 6.5 whereas it should be 7.3. I presume that's just a question of more accurately drawing the wing. The CoG calculator allows for a three section wing so maybe it will correct itself. I have yet to fly your mod. It'll be interesting to see how different it behaves especially on final approach where the aircraft is essentially nose level.
 
Volo,
Enjoyed the beer.
Some of the aircraft.cfg [airplane geometry] parameters are eye candy and have no effect of the flight characteristics in the sim. Like the sdk says:
This section has been added mainly for reference. Although you can edit these values by hand here in the aircraft.cfg file, modification of some of these variables will have little to no effect on airplane performance, as the flight model aerodynamic coefficients are all located in the .air file.
A few years back some of us in this forum removed most of the airplane geometry parameters from some long-suffering small airplanes and listed what is actually required for the beast to fly. It was a small list.
http://www.fsdeveloper.com/forum/threads/aircraft-returning-to-level-bank.107248/
If you look through Zskowski's paper for the inputs used in the aerodynamics calculation, the only airplane geometry parameters listed are:
Wing surface area.
Wing mean geometric chord.
Wingspan.
Horizontal tail incidence angle
Elevator deflection
Aileron deflection
Rudder deflection

Wing sweep is eye candy. The sim essentially considers the wing to be a rectangle based on wing area and wing span.
From the aerodynamics standpoint wing_pos_apex_lon is also eye candy, but the sim uses it and wing sweep to calculate CG position.
The CG position affects things like ground behavior. Get the CG too close to the main wheel position and you may be surprised by what happens with reverse thrust going backwards.
However, it does not affect the flight characteristics because they are the result of the flight model aerodynamic coefficients in the air file.

What this is all about is that you can put wing_pos_apex_lon at 25% of the the wing root chord and it will be OK as long as there is no sweep angle in the aircraft.cfg. (and of course assuming that the reference and CG points are at 0,0,0)
But if you want to be more accurate and include wing sweep, you need to have wing_pos_apex_lon correct or WarpD will shout at you!
Roy
 
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Roy Holmes said:
Volo,
Enjoyed the beer.
Some of the aircraft.cfg [airplane geometry] parameters are eye candy and have no effect of the flight characteristics in the sim. Like the sdk says:
This section has been added mainly for reference. Although you can edit these values by hand here in the aircraft.cfg file, modification of some of these variables will have little to no effect on airplane performance, as the flight model aerodynamic coefficients are all located in the .air file.
A few years back some of us in this forum removed most of the airplane geometry parameters from some long-suffering small airplanes and listed what is actually required for the beast to fly. It was a small list.
http://www.fsdeveloper.com/forum/threads/aircraft-returning-to-level-bank.107248/
If you look through Zskowski's paper for the inputs used in the aerodynamics calculation, the only airplane geometry parameters listed are:
Wing surface area.
Wing mean geometric chord.
Wingspan.
Horizontal tail incidence angle
Elevator deflection
Aileron deflection
Rudder deflection

Wing sweep is eye candy. The sim essentially considers the wing to be a rectangle based on wing area and wing span.
From the aerodynamics standpoint wing_pos_apex_lon is also eye candy, but the sim uses it and wing sweep to calculate CG position.
The CG position affects things like ground behavior. Get the CG too close to the main wheel position and you may be surprised by what happens with reverse thrust going backwards.
However, it does not affect the flight characteristics because they are the result of the flight model aerodynamic coefficients in the air file.

What this is all about is that you can put wing_pos_apex_lon at 25% of the the wing root chord and it will be OK as long as there is no sweep angle in the aircraft.cfg. (and of course assuming that the reference and CG points are at 0,0,0)
But if you want to be more accurate and include wing sweep, you need to have wing_pos_apex_lon correct or WarpD will shout at you!
Roy
Click to expand...

Thanks Roy,
I certainly don't want WD40 to shout at me :duck:
I'm trying out certain numbers from the web CoG page. I did do a quick hop from LIMZ to LIMF using your figures and there was a change to the V speeds all 2-3 kts lower which is actually good as they were always a little higher than they should be before. I didn't tip up when I applied RT. But during finals The nose was more than 1deg nose down so I'm trying out wing_pos_apex_lon= 27.35 which is a little further forwards. This number also works well with the TPI take-off settings as well.
So the sim actually uses far less parameters than expected. Is P3d the same?
An interesting point regarding the Super VC10 wing is that it is super critical. The wing root form appears to be upside down. And was designed by the boffins at the RAE in Farnborough. The upshot of that is that the VC10 cannot super stall. I've often wondered if that could be set up in the sim but imagined that it would be unlikely.
 
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