ORIGINAL: da Rock
ORIGINAL: billd76
All very interesting. I plan on using the formula I read in AM to find the CG, which is based on wing area and finding the neutral point.
There is a better, easier way. 9 measurements with a yardstick and choice of static margin:
http://www.geistware.com/rcmodeling/cg_super_calc.htm Run it with a 5% then a 15% and you've got a safe, reliable CG range. It includes everything on the airplane that affects the CG. And tells you where the NP is along with a lot of other things.
You do understand that the problem is the CG affects both how the plane flies and how it handles on the ground also. Since it matters more how it flies, that's the deciding factor on where the CG get's moved to. With planes like the Decathlon, you then have to arrange the gear to match. And that's where the guys who've moved CGs forward to be extra safe have screwed their ground handling.
I installed a 13 X 6 APC for the break in and flight prop. What do you think? To big or should I go with a 12 X 6 first?
13x6 too big? They were for my 55AXs. My planes that have 55AXs on them have done best with smaller. I did a prop test session awhile back with the help of a buddy who ran the stopwatch. That's when I had just retrofitted a new 55AX on my Calmato Sport that'd had a 46AX on for a couple of seasons. So I was pretty experienced with how that plane flew. The watch was for vertical comparisons.
The two 13x6s tried gave the least rpm on the ground (as expected) and did the poorest in the vertical tests. RPM figures won't mean anything much and especially since the DensityAltitude on that day was abnormally high, highest of any tests so far.
Anyway, the 13x6s both gave rpms under 10k and shortest climbs.
A 12x6(3) was next slowest to those two. As expected, it still turned in the 3rd highest climbs.
A wooden Zinger 12x6 was about as slow and did average climb numbers.
An identical Zinger cut down to 11.5x6 was slightly better but still average.
A wooden 12x5 made from a cut down 13'' prop was the star of the show. RPM was around 11.8K but the climbs times were significantly higher than next best.
An 11.7x6(3) was next best and 2nd overall. Interestingly, it gave the about the same RPM as the 12x5. They probably have the same overall blade areas. It was made by slightly trimming a 12x6(3) identical to the one that'd done the 3rd highest climbs (but was at least 1K slower, which shows how little you can tell from ground rpm).
The climb times aren't the deciding factor, btw. But they're almost always good for the props that show up best in the maneuvers part of my tests. They're subjective