Sorry for the confusion. Yes the root and tip chord as well as the panel length of the arf are identical to the plan. I meant the shape of the tip is a little different than the plan. I wrote my own software to calculate the cg for given wing parameters many years ago. It still works and I can calculate the position for both the arf and the plan. My issue was with Tower using a starting cg of ~25% for a pattern model. I was wondering if there was a reason for the change in the recommended starting cg position. I'm going to disregard the arf directions and use the cg indicated on the plan version.
Thanks Much
Kevin
Originally Posted by
doxilia
K,
unless you have a rather strange looking Kaos (which I doubt if we're talking about the ARF), the root and tip chord cannot be identical. The Kaos is a double taper design with a tip chord which is shorter than the root chord. Also, the chord and the length for a wing section are the same - they are synonyms. The Kaos wing also has no sweep (like say the Blue Angel does) - it only has taper. A swept wing is one which has taper on the LE and the TE in the same direction. The Kaos wing is referred to as double tapered since the shorter tip rib is located somewhere along the length of the root chord with the LE and TE tapering toward the tip rib. A Dirty Birdy has LE taper only as the TE is straight with the TE of the root and tip coinciding. The shape of the actual wing tip is of little consequence and is primarily aesthetic.
In order to calculate the MAC properly and consequently find out where the CG should be located, you need to measure the chord (length) of the wing perpendicular to the spar at both the root (wing center) and the tip rib (where the wing tip begins). The LE taper is the offset distance between the front of the wing at the root and the front at the tip. The TE taper, as mentioned in my prior post, is the closure of the trapezoid shape of the wing. We're talking planform here (as viewed from above). The shape of the wing in terms of airfoil is of no importance in the CG calculation for this application.
It sounds like you might need to re-measure and make up a new sketch to confirm the positions of the MAC and the 28-30% CG position. If your drawing is off and you have located the MAC incorrectly, placing the CG at 30% of that chord could result in a model with the CG too far forward or backward - generally speaking.
I hope this helps,
David