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"Not A Number" (NaN) Trouble.
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TOPIC: "Not A Number" (NaN) Trouble.
#370
NP101
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"Not A Number" (NaN) Trouble. 12 Months ago Karma: 0
Hey all. I've been browsing around these forums for a couple days. A lot of helpful stuff on here - really liked the Digital DATCOM tutorial.

I've written up my input file for Digital DATCOM. It all seems ok. But when I run it there are a few results which gives NaN - most of the Aerodynamic coefficients (CL,CD,CM etc return NaN).

I have no idea why this is happening. Any help would be greatly appreciated!

I've attached my input file and I've also attached the MATLAB script for that DATCOM 3D plot script I found on here - which is awesome by the way!

The aircraft appears to be rendering correctly - so I'm still not sure why DATCOM is giving me NaN for standard stuff.

Thanks again.

Nick. (Final Year Aeronautical Engineering, Syd. Uni).
File Attachment:
File Name: input.txt
File Size: 1970
 
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Last Edit: 2011/05/24 09:33 By NP101. Reason: Working on upload.
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#371
NP101
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Re:"Not A Number" (NaN) Trouble. 12 Months ago Karma: 0
And the MATLAB script with my geometry in it:
File Attachment:
File Name: datcom3d_ACDC.txt
File Size: 6466
 
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Last Edit: 2011/05/24 09:34 By NP101.
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#372
wailo
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Re:"Not A Number" (NaN) Trouble. 11 Months, 3 Weeks ago Karma: 5
I am not familiar with DATCOM at all but I am moderate user of MATLAB. I looked at your m-file, and I couldn't find where the input file is linked to MATLAB workspace, can you please clarify the procedures you are following to get the results?

Wail
 
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#385
sncwhiz
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Re:"Not A Number" (NaN) Trouble. 9 Months, 3 Weeks ago Karma: 0
I am a veteran user of DATCOM, and have experience with the original code (instead of using the interface(s) listed on this website).

NaN's outputted by DATCOM can be for several different reasons, but one of the most common is that the geometry and/or flight condition you entered is simply not valid. That's not to say that in reality, there are vechicles that can do certain things, but you must remember that DATCOM is limited by method assumptions.

For instance, for hinge moments, there exists no high subsonic/transonic method. Therefore if you were to enter an aircraft geometry and told it to fly in the transonic region and spit out hinge moments, it would yield NaN's.

One way to get around this and a lot of other headaches: there are two commands called TSMACH and STMACH. They set the boundaries of what you consider to be subsonic/transonic/supersonic. If you try to fly in the transonic region and it outputs NAN's you can increase TSMACH (which is the upper limit that DATCOM considers to be valid mach numbers for subsonic methods) all the way to 0.99 which will basically tell datcom to use the subsonic methods even though you are in the transonic region. This is not really a great estimation technique since the sub-methods were restricted to a give flight condition, but it is a work around that will give you numbers in the ballpark.
 
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#390
BillGalbraith
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Re:"Not A Number" (NaN) Trouble. 9 Months, 3 Weeks ago Karma: 0
Okay, this thread is 2 months old, but for future reference....

You are getting NaNs for CM and XCP because of the propeller effects.

I don't know if you've gotten a copy of the free Datcom+ package, which has more information and tools. You can get it at www.holycows.net/datcom. There is also a professional version available
 
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#397
BillGalbraith
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Re:"Not A Number" (NaN) Trouble. 9 Months, 1 Week ago Karma: 0
There is a error in the code for propeller-driven models. The source code changes have been posted in this forum under the original-digital-datcom-source-code thread. This fix solves your problem.
 
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