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Strange Cm for BODY with first ZU=ZL != 0. #1

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ghost opened this issue Apr 29, 2019 · 0 comments
Open

Strange Cm for BODY with first ZU=ZL != 0. #1

ghost opened this issue Apr 29, 2019 · 0 comments

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@ghost
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ghost commented Apr 29, 2019

The manual does not make it clear whether the first point of BODY must be S=P=R=ZU=ZL=0.0, but get weird pitching behaviour if the first point of the fuselage is not defined as ZU=ZL=0.

I see strong positive Cm when lowering the nose cone ("Tu-144D cone 17.0" vs. "Tu-144D"):

https://gitlab.com/mdanil/Tu-144_src/blob/datcom_update/DATCOM/results_190426/Tu-144D.dcm
https://gitlab.com/mdanil/Tu-144_src/blob/datcom_update/DATCOM/results_190426/Tu-144D/output.dat

When I put an additional point with ZU=ZL=0, I get reasonable down pitching, at the same time CD and CL change a bit less:

https://gitlab.com/mdanil/Tu-144_src/blob/datcom_update/DATCOM/results_190429/Tu-144D.dcm
https://gitlab.com/mdanil/Tu-144_src/blob/datcom_update/DATCOM/results_190429/Tu-144D/output.dat

Is this a known limitation?

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