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Aircraft model 3D model origin point - questions

Ronald

Ronald

Resource contributor
Messages
974
Having completing Krispy1001's wonderful B2FSX tutorial series (thanks again Krispy1001) I'm now busy preparing and gathering relevant fact (like blueprints, aerodynamic data, background info) to build my very first FSX aircraft model - the F16 - in Blender:

After reading the FSX-SDK's article about:
- New Aircraft Procedures:
-> "Getting Started on a New Aircraft"
--> "Aircraft Center Point" (on the DC3 Example)
---> The green box in the image below is the aircraft’s center point.

A - I'm wondering what that "Aircraft center point" model exactly is:
medium.jpg

Is it just a geometrical modeling axis-origin point (X:0,Y:0, Z:0) of my 3D aircraft shape?
.. which can essentially be put anywhere inside / outside my model?

thumbnail.php

Does this point also need to be located on the exact Center Of Gravity of my aircraft model?
.. in order to have an correct mathematical effect on the aerodynamics of the model?

 
Before you launch into recreating a fairly complex aircraft as your first project I would make a suggestion.
Start with something less complex. In starting your modeling career with this plane you are trying to sprint before you can even crawl. The first plane is the hardest, and if you make that first plane easy you might actually finish it. Then you can work up to something like an F-16. :twocents:
 
It is the geometrical origin of your model. Depending on the data you have for building the model, you might want to put it at or near the centre of gravity. However if those cross-sections I can see in your blueprints are at distances from a manufacturer's reference point like the tip of the nose and loads and wheel positions are measured from that point then it would make sense to use manufacturer's data.

The decision is yours. It wouldn't matter if you modelled a house brick, it's the flight model that determines how that brick would fly in FS and part of the flight model is to tell FS where the CoG and model reference point are on your model.

Just make it easy for yourself and keep the model origin on the center line and in line with the jet exhaust!
 
Isn't the convention for the origin to be at quarter (or third?) MAC (or root chord)?
 
We are taught that usually your CG point (on the side view) is about 1/4 back from the wings leading edge.

Remember, building your plane in a 3D design engine is only the MDL file(s). Like Tom (HairySpin) says, the FD files (config and airfile) are what tell the plane (or brick) how to fly. Then panel and sound folders for those departments, etc, etc.

Have fun! The F16 is a beautiful bird. Nice choice.

I remember that F16 sim from years ago. Korea. Man, that was sweet. Made me fall in love with that fighter plane.
 
1.) Put the origin of the aircraft fuselage (middle of the airplane as viewed from the side) at center 0,0,0. (This ensures nice FSX view orientation within spot views and such)
2.) Define the reference datum in the .cfg as someplace in the front, or near the front of the aircraft. (Measured along Y from your center). Make this something you can easily measure FROM within blender. You might be able to find the real world datum location, which would help. In the case of my current project, it's the firewall.
3.) Define the actual aircraft Center of Gravity, enter into the cfg. This will be a measurement back from the above reference.

Take note that the rest of your measurements, in feet, will be FROM wherever you define the reference datum. The datum is just that, a reference from which you can measure things like C of G, contact points, payload weights, etc., etc.

So for example, within Blender your aircraft center origin will be Y0, your reference datum will be something like Y16, and your C of G will be like Y8.

- Joseph
 
The origin in your 3D program is where the camera is going to be focused, and it's also what FS is going to more or less treat as the 'center' of your airplane. As you have no doubt discovered, the reference data in manufacturer's data is usually at some random point in space.

These days, I build the model with respect to the manufacturer's datum, and then move the model so that the origin sits roughly in the CG range when I'm done.

Does anyone remember the original Ariane 737, where the origin was somewhere around the forward entry door (and therefore also the camera)? It also had paper-thin wings! Oh, boy...
 
Thanks everyone for your tips and very clear explanation of separation between the "3D modeling" and "flightdynamics-related" things. This is very useful information to me.
I've placed my 3D model's origin point:
- on the center-line of the aircraft and engine exhaust
- in the geometric middle of the plane-shape (in side view)

As for the F16's C.O.G: I've found the answer in F-16.net community, which lies just above the main landing gear:
- http://www.f-16.net/forum/viewtopic.php?f=23&t=52762&sid=560016da26afb6a275ff97601db2a19c
 
If the cog was directly above the main gear, it would be possible to push the nose up by hand and tip the aircraft on to its jetpipe: not good. Read that link further and someone else suggests further forward - about 10% of the distance between main and nose gear. That seems more reasonable.

Unless you have other considerations, I'd put the model's origin there too, on the centre line and jet thrust line as you say.
 
Last edited:
Roy Holmes is excellent with fighter aircraft FDE files. He might be able to guide you perfectly concerning the CG's on the Sixteen.
 
Thanks:
- Tom for the extra information on he F16 CoG
- Lionheart for the reference to Roy Holmes's skills
 
Ronald said:
Having completing Krispy1001's wonderful B2FSX tutorial series (thanks again Krispy1001) I'm now busy preparing and gathering relevant fact (like blueprints, aerodynamic data, background info) to build my very first FSX aircraft model - the F16 - in Blender:

After reading the FSX-SDK's article about:
- New Aircraft Procedures:
-> "Getting Started on a New Aircraft"
--> "Aircraft Center Point" (on the DC3 Example)
---> The green box in the image below is the aircraft’s center point.

A - I'm wondering what that "Aircraft center point" model exactly is:
medium.jpg

Is it just a geometrical modeling axis-origin point (X:0,Y:0, Z:0) of my 3D aircraft shape?
.. which can essentially be put anywhere inside / outside my model?

thumbnail.php

Does this point also need to be located on the exact Center Of Gravity of my aircraft model?
.. in order to have an correct mathematical effect on the aerodynamics of the model?
Click to expand...
Hi Ronald.
Since you are using SolidWorks, please update on the workflow and your success going from surface to mesh. I have experienced that SW have very little control over tesselation during export. The mesh becomes very messy. I have tried a few plug-ins but they did not work that well either. Any tips in regard of tools or workflow are welcome :)
 
Having completing Krispy1001's wonderful B2FSX tutorial series (thanks again Krispy1001) I'm now busy preparing and gathering relevant fact (like blueprints, aerodynamic data, background info) to build my very first FSX aircraft model - the F16 - in Blender:
Click to expand...
Hello Rotorhub, as you can read in the first line of my initial posting, i'm not using Solidworks, but i'm using only Blender.
I've merely used an clear image from an online Solid Works tutorial about F16 solid-modeling advertizement, which can be found over here http://www.solidworksf16.com/download-tutorial.php.
If you have any in-depth Solid works questions, look over here for more information, since I can not help you with that:
- https://forum.solidworks.com/
- http://my.solidworks.com/
- http://www.solidworkstutorials.com/
- http://learnsolidworks.com/
- https://www.youtube.com/channel/UCtwaWPOXEBysZLh1rrPzwFw

...please update on the workflow and your success going from surface to mesh
Click to expand...
I've already been busy, experimenting, practicing with 3D mesh modeling, animation, rigging which you can see some results over here, before following Krispy1001 B2FSX tutorials.
- http://s304.photobucket.com/user/indigowarrior9/library/BLENDER/F16-Project?sort=9&page=1

I will add more screenshots later
 
Ronald said:
Hello Rotorhub, as you can read in the first line of my initial posting, i'm not using Solidworks, but i'm using only Blender.
I've merely used an clear image from an online Solid Works tutorial about F16 solid-modeling advertizement, which can be found over here http://www.solidworksf16.com/download-tutorial.php.
If you have any in-depth Solid works questions, look over here for more information, since I can not help you with that:
- https://forum.solidworks.com/
- http://my.solidworks.com/
- http://www.solidworkstutorials.com/
- http://learnsolidworks.com/
- https://www.youtube.com/channel/UCtwaWPOXEBysZLh1rrPzwFw


I've already been busy, experimenting, practicing with 3D mesh modeling, animation, rigging which you can see some results over here, before following Krispy1001 B2FSX tutorials.
- http://s304.photobucket.com/user/indigowarrior9/library/BLENDER/F16-Project?sort=9&page=1

I will add more screenshots later
Click to expand...

Thank you! Looks very nice :)
 
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