RE: Tiger 60 Kit Balance Point ??
Why is there a CG range described?
Because they wish to provide a safe range for the CG in case different people want different pitch stability from their model. The designer or developer has found that a 3.75" CG gives the most pitch stability with sufficient elevator response to be safe. And worked out that a 4.75" CG gives the most elevator response with sufficient stability to be safe. That's what CG ranges are about.
And then the designers test the elevator throws to find out what to recommend to match that CG range.
No matter what your airplane weighs after completion, the CG range fits. CG's are actually located by the size and shape of the wing versus the size, shape and location of the tail. My arf Tiger60 came out at 7'7oz. If your build comes out at 6lb 6oz, you can adjust battery or shift stuff to get the CG at 4.75" and your Tiger will fly just as agile as mine. My CG is right at 4.75" and mine is agile. Nice and agile. And both will have perfectly sufficient stability. They will have almost identical elevator response and recover pitch the same. You won't have to shift quite as much mass fore or aft to get your CG as I might, but a CG range is easy to predict and the prediction is dead reliable to do. Just measure the wing and tail and plug the numbers into the formulas that aeronautical designers have used forever. And if you're say the designer of the Tiger, you then go out with a safe CG located for the maiden flights. And if you WERE the designer, you then test fly with different CGs to prove the pitch response and pitch stability for your instruction manual.
BTW, my Tiger60 was preceeded by a TigerII. And with both models, I knew the CG ranges suggested were probably going to be conservative coming from a reputable company like Goldberg. And I knew I just might want more effectiveness out of the elevator than the suggested most aft CG probably would give. But I wanted to be sensible, so I measured both planes to get the numbers to plug into the formulas. And nowadays we don't have to work those formulas out with paper and pencil, or even a calculator. I ran them through the geistware.com application. I know from experience that some airplanes I've flown wound up with a CG WAY back, but no farther back than 10% Static Margin. So I ran the numbers through the geistware.com app with a 10% SM. It spit out that that CG would be at 4.75" Hey, that's what the manual gives. So when I took the sucker out with that CG, I knew it wouldn't be unflyable. It would be flyable. But I also knew the elevator throws would absolutely be sufficient, and with that CG would feel QUICK. Turns out they didn't feel too quick. With that CG pitch response that was really good. And elevator throws were ok. (look at how small the elevator is). Only bad thing I discovered, was that there was little need to test different CG locations. And I love to test stuff. So I'd cut myself out of some of the most fun testing.
CG ranges are starting points for the maiden flight. Then YOU can move it to suit with complete confidence of WHERE moving it would be safe.
That's what CG ranges do for you.