Some explanations on the various coefficent tables on the aircraft afm.dat file
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@frapes45 said in Some explanations on the various coefficent tables on the aircraft afm.dat file:
Thanks! you have been quite reaviling.
Another possible problem I have noticed is that on the F-18 file
the engine location relative to the noze on the .dat is a number something like -25 feet while the GC is something like -33Is this correct or is it a mistake? the engines on the F-18 are quite back
Maybe it is a mistake however if the z position of the engine is the same of the GC z the X position mistake will have zero influence on the FM
Edit : Hold on
I the OFM Dat file the engine position is relative to the GC , not the noze
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Alright, that makes sense then, Thanks.
You are the man and I really appreciate it!
I would love to help the team anytime in things considering flight models. Please consider me or don’t hesitate to contact me.
Also from studying the nasa fm document I understand that the tables represent various φ , θ angles and β angles. That would be the roll pitch and yaw axes if I am correct.
Now the flcs code on the f18 might be worth investigating as I can’t pull the Blue angels maneuvers correctly especially the inverted ones, of course at empty loads.
Also one last question is Tail Ht value of +7.6000 the tail distance from GC or from what exactly?
and what is the difference of the GC value with that on the .afm GC Designed (GC of the plane stability design). From your explanations, I understand that my only option is to alter the center of gravity. Until you perhaps come with an improved FLCS version for the FA-18 C/D.Kind regards!
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@frapes45 said in Some explanations on the various coefficent tables on the aircraft afm.dat file:
Alright, that makes sense then, Thanks.
You are the man and I really appreciate it!
I would love to help the team anytime in things considering flight models. Please consider me or don’t hesitate to contact me.
Also from studying the nasa fm document I understand that the tables represent various φ , θ angles and β angles. That would be the roll pitch and yaw axes if I am correct.
Now the flcs code on the f18 might be worth investigating as I can’t pull the Blue angels maneuvers correctly especially the inverted ones, of course at empty loads.
Also one last question is Tail Ht value of +7.6000 the tail distance from GC or from what exactly?
and what is the difference of the GC value with that on the .afm GC Designed (GC of the plane stability design). From your explanations, I understand that my only option is to alter the center of gravity. Until you perhaps come with an improved FLCS version for the FA-18 C/D.Kind regards!
No you misunderstood nasa TP1538 modeling , read again thé implemented aero model from page 30 to 33
Your have no option to try to fix the issue that you are seeing
This is FLCS related and nothing you can Do about itPlaying the wizard with GC will bring you massive problems in other flight domains
Your GC must stay close to 0.35c
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Sorry but 0.35c CG is reffering to F16 which has a C.G location Aft of the center of lift. I am talking about the F18 I am not sure its the same as the information is more limited.
Nevertheless there is no point in having an accurate C.g if the Center of lift is not calculated accurately. For example, an approximation for the f16 Center of lift would be somewhere 0.27c and 0.33c. Of course this changes dynamically.
In fact the max GC aft limit for f-18 is 28% mac
From the nasa technical paper 3111
S= 400ft2 (1.440ft2)
b= 37.417ft (2.245f-t)
c= 11.517ft (0.691ft)
c.g.= 25%c -
@frapes45 said in Some explanations on the various coefficent tables on the aircraft afm.dat file:
Sorry but 0.35c CG is reffering to F16 which has a C.G location Aft of the center of lift. I am talking about the F18 I am not sure its the same as the information is more limited.
Nevertheless there is no point in having an accurate C.g if the Center of lift is not calculated accurately. For example, an approximation for the f16 Center of lift would be somewhere 0.27c and 0.33c. Of course this changes dynamically.
In fact the max GC aft limit for f-18 is 28% mac
From the nasa technical paper 3111
S= 400ft2 (1.440ft2)
b= 37.417ft (2.245f-t)
c= 11.517ft (0.691ft)
c.g.= 25%cThe GC of the BMS f18 with current data shall be close to 0.35c
This is because the f18 aero data are derived from f16 data.
All f18 data are computed from the f16 data which means they share the same center of lift which means they must share the e same GC center
If you which to change the GC you will end up with major problems in the whole domain
if you which to recalculate all data by changing the center of lift in order to change the center of gravity feel free .However as you will be unable to change the FLCS all of this would be totally useless
But feel free to do what you want
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Ha!
That explains it all.
Anyway I ended up reducing the tail ht number. No idea what this exactly does(possibly something with the horizontal tail location?) but I think I got what I was looking for.
“if you which to recalculate all data by changing the center of lift in order to change the center of gravity feel free”
Provide me the tools and I would do so anytime, free of charge…
Any chance you will give the Fa18 Fm some love?
Also does the newest f15 also use the f16 FLCS?
Thanks for all the explanations.
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@frapes45 said in Some explanations on the various coefficent tables on the aircraft afm.dat file:
Ha!
That explains it all.
Anyway I ended up reducing the tail ht number. No idea what this exactly does(possibly something with the horizontal tail location?) but I think I got what I was looking for.
“if you which to recalculate all data by changing the center of lift in order to change the center of gravity feel free”
Provide me the tools and I would do so anytime, free of charge…
Any chance you will give the Fa18 Fm some love?
Also does the newest f15 also use the f16 FLCS?
Thanks for all the explanations.
https://www.microsoft.com/en-us/microsoft-365/excel
that is the tool we use , we dont have others
i dont know what you mean by tail Ht number, what is this ?
F18 FM not a priority at all for me , however, changing the center of lift and the center of GC will have zero impact overall , except at take off because then GC and wheel contact distance will be different
F15 does not use the F16 FLCS , as a matter of fact, i am actually putting some more love in it
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@Mav-jp said in Some explanations on the various coefficent tables on the aircraft afm.dat file:
i dont know what you mean by tail Ht number, what is this ?
aircraft.dat file
Physical data
----> # Tail Ht
So there is no GUI that @MaxWaldorf is referring too?
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@frapes45
Vertical stabilizer height. -
@ccc1tw Thanks must be Ixx inertia and area2span then cause I also reduced these numbers
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@frapes45 said in Some explanations on the various coefficent tables on the aircraft afm.dat file:
@Mav-jp said in Some explanations on the various coefficent tables on the aircraft afm.dat file:
i dont know what you mean by tail Ht number, what is this ?
aircraft.dat file
Physical data
----> # Tail Ht
So there is no GUI that @MaxWaldorf is referring too?
The tail Ht data is unused
The GUI is just a visualisation of the file, not a working tool
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@Mav-jp Indeed, I play with some values and see no notable difference . Its all on the FLCS hard coded which I have no power to change with excel…
Nevertheless some values are kind of off like inertia on all axes and indeed I see they affect the fm ,
also area2span ?