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Datum line

D

drmax

Well Known Member
70" from leading edge. Measuring from wing root leading edge fwd, comes out roughly 4-5" fwd of spinner. Am I looking at this correctly? Thx DM
 
The datum line can be any point you want. It's just a reference.
I personally use the leading edge of the wing. In level flight attitude the leading edge of my wing is exactly in line with my wheels. Makes the math really easy. Anything multiplied by "0" is "0".
 
Mel said:
The datum line can be any point you want. It's just a reference.
I personally use the leading edge of the wing. In level flight attitude the leading edge of my wing is exactly in line with my wheels. Makes the math really easy. Anything multiplied by "0" is "0".
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Using what builder used, and is what is in paperwork. Just making sure I'm reading it correctly
 
drmax said:
70" from leading edge. Measuring from wing root leading edge fwd, comes out roughly 4-5" fwd of spinner. Am I looking at this correctly? Thx DM
Click to expand...

Yes, the datum is generally located somewhere forward of the aircraft spinner so that all 'arms' are positive numbers.
 
Note that the CG range is expressed in reference to the designers datum. If you change the datum, you must change the envelope reference dimensions similarly.

+1 with Walt.
 
drmax said:
Ok. Thank you
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Also be careful to measure the actual landing gear axle distances from the datum, rather than just using the book numbers. Mine were different enough that it made a noticeable difference in the CG calculations.
 
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