I am days away from putting on the first flight on my 1/2A profile DO 335.  The question is where should I start with the CG?  Right now I have it just in front of the main gear whitch places it at the LE of the wing tips.  The LE has a lot of sweep so I think this may be about right.

            

John,

The really safe way to go would be to place the CG at 20% of the mean aerodynamic chord (MAC).  On the Dornier with those different sweep angles of the wing leading edge, the calculation of the MAC is a bit complicated.  So a close approximation would be to just determine the average chord line, take 20% of that and you will have a safe CG location for the first flight.  (I would run a straight line LE from the root to the tip, go to the mid point and that is where to take the aveage chord.  Actually, because of the wing planform of the Dornier, that calculation will be very close to the MAC anyway.  The MAC of a wing is always just slight larger than the average chord.)

Another way would be to run a line 10 or 15 degrees up and forward from the main gear axles on your scale drawing.  I would imagine that would be probably close to that 20% MAC point.

Since the Do 335 wing has virtually no sweep (as measured by the 25% chord line) the average chord and the MAC chord will be very close and the 20% position of each of those chord lines will be even closer.  Close enough to get you a safe first flight.

(edit for typos)

Keith

Hope for no rain in the next few days. I am ready to pit John, just call. Ty

Ty I need to test run the engines and make up some lines.  It probbly will be next week befor I am ready.  Besides I want to bring it to the club meeting before it has its first crash (I mean test) flight.

I will call thanks.