ORIGINAL: Bozarth
Please, somebody tell me the value of knowing the EXACT location of your cg, assuming it falls somewhere between 25 to 35% back along the mac? And after you tell me, I will simply ask you ''how does it fly?''
Kurt
No problem.
I do it for every airplane I design, build from a kit, or assemble as an ARF. I run the numbers to find out where I wish to locate the CG in order to have a safe maiden. OK, that's actually the reason just for my designs. The reason I run the numbers for a kit or ARF is also based on experience however. I don't really trust the present ARF 'designers'. Their documentation often has fatal flaws in it and I've seen way too many that were screwed. I run the numbers on them and use that number. So anyway.....
I have found out from experience almost every model I like flies the way I like when the static margin is 5% or thereabouts. I can run the numbers ahead of time and find out EXACTLY where that would be. Do I need it exact for any other reason? Nahhhh. But why not use science to my advantage. Why not cut out the fiddly fiddling around and come out of the gate running. Could I use the ARF recommendations? lol..... I do, when they match the numbers I ran.
As for everyone else.... if they choose to start with a recommended CG location, actually flying with it makes sense. If they want to use the mfg's recommended CG, then it doesn't take a genius to accurately adjust for it, and it most certainly doesn't take any longer to do it accurately than it does to do it sloppy. Almost everyone will benefit from flying the maiden with a correct CG. It's easily done accurately for sure. So why 'assume'. Find out where it is suggested and put it there. Almost everyone is going to approach the maiden flight with confidence knowing they've got a safe CG and it is where it's supposed to be. They won't need you to ask how it flies. They'll know ahead of time and it will fly safely, without any nose heavy or tail heavy problems.
But you're correct about one thing..... The CGs don't ever have to be in only one exact spot. They've got a range that is safe and reliable. But you really do need to know where that range is, and it's good to use a balancing technique that is accurate enough to be worth the time you spend employing it.
With every model of mine I've built in the last 50 years, I could tell you BEFORE I flew it, how it was going to fly. And every one did. At least how their pitch stability was going to be, which is about all the CG is going to help with.