Ok, Guru's

a friend is on a SPAD building terror!

He is going to build a Draco based spad, but he wants to sweep the wings back..... but not all the way from the fuse....

With a wing of the shape shown in the picture... how would we calculate CG???

Any help or insight would be great!!!



The leading edge at the Fuse is straight (90 degree from the fuse) then at the sweep (15" from centerline of fuse) he wants to sweep back approx 20 degrees......
the chord should be a 15" constant from fuse to wingtip.....

This site will handle any wing configuration....
http://perso.wanadoo.fr/scherrer/mat...glish/mce.html

Hmm...It looks like if I use that and then Geistware.com's CG calculator we can get in the ballpark.....

Thanks

Geistware's calculator is intended for conventional models. Your flying wing will need to depend on finding the MAC using that other site and then put the CG at 20% of the MAC as a starting point.

Depending on the airfoil shape you may find you need a LOT of reflex in the controls. To get it set roughly right I suggest some runs with the model held up and try to feel for any pitching up or down or a strong tendency for the model to try to lift or sit solidly in the hand. Set the reflex until it feels balanced and light but doesn't want to lift up on it's own. That should get the model through it's first flight but be ready on the elevator stick. Plank and near plank style wings are known for their sensitivity to pitch control inputs.

My buddies plan was to make the straight trailing edge (close to the fuselage) the Elevator control surfaces...and the swept back portion of the TE the aileron controls.......

We shall see

Try a c.g. about 15%, using Jean-Claude's computations.
That will probably be nose-heavy.
Your plane is basically a tapered plank, so it might let the c.g. get back some from there.
A little reflex won't hurt.