I was going to title this, "WE DON'T NEED NO STINKING FORMULAS", but figured someone's feelings might get hurt. (but then, the title was so kewl, I had to mention it)

The idea is that we don't need to use formulas to "design". And the way we do that is basically to copy somebody else's design. Or we just build using some basic "ideas". (Don't call them formulas, 'cause we ain't using formulas.) And that list of ideas actually lead us to "create" what? Just what those other things are that can be described simply without "formulas". Hey, that works. To build another whatever.

But what if you actually want to understand what's going on aerodynamically? Why do people want to design airplanes? I guess there are those who really just want to say they designed their own airplane and want the easiest way and figure copying works for them. But what if they really do want to explore. Or to understand. And about this idea of "no formulas"...........

Hey, just make your fuselage 80% of the wing span. Hmmmmm..... And use 4 or 5 for your aspect ratio for your tail. Hmmmmmm....

Say, how does one come up with a value of 4 or value of 5 for an aspect ratio? Isn't an aspect ratio the result of a formula? But I guess you could explain it without having to use symbols and pretend it's not a formula. But isn't an aspect ratio sorta like this: AR = S / C

Is the whole idea to not use algebraic symbols when stealing.... uh, designing your airplane and it'll somehow be a better design effort?

Lf = .80 X Sw
"Your fuselage length should be 80% of the wing span" is another way to talk about that formula.

BUT I'M NIT PICKING, right? No, I'm actually making a point. The point is, that the formula (or description in words) for the tail volume of the horizontal tail actually is worth knowing and using.

Not everyone wants to steal a successful model design, change the wingtips, and call it their new design. Some people want to design something new. That might be impossible or very difficult, but that might be the motive. And they might want to learn something from the effort. Sure, just changing a successful model might teach you something, but what? Use the most basic formula for success and what do you learn? That build something to the simplest formula that's like the majority of existing popular models and it'll fly like them.

Take the formula for tail volume for example. What does it tell you? It not only sorts out some design details, but it also tells the designer what dimensions are important to pitch stability and how. Would you have inherently known that Cw (the chord of the wing) has something to do with pitch stability? The wider the wing chord the less pitch authority the tail will have. Did you know that the Aw (the area of the wing) works the same way? Everyone probably would guess that the area of the tail (Aht) is good for pitch stability, but it's only about as good as the distance it is aft.

Tail Volume = (Aht / Aw) X (Tail Arm / Cw) actually tells you something.

And it actually is good to know for understanding what is happening when your new design takes to the air. And it's good to know if your design doesn't do what you wanted. It gives you both understanding and a way to work out a solution if you have a problem or if you only want to enhance something. Say you don't have the pitch stability you were hoping for. From that formula, you can see that if you increase the distance the tail is from the wing, OR increase the area of the tail, OR decrease the area of the wing, OR decrease the chord of the wing, you can change that lack of pitch stability. And you can run the numbers again and again to get a feel for how much you'd have to do each individual change.

You'll actually learn something. And understand what's what.

We actually don't need no stinking formulas, but they sure are useful if you wan't to actually design. and learn what does what......

Which is what most of the designers I know do it for. I'm guessing that greenskintau was sorta figuring he'd learn something with his effort, but I really don't know for sure. Just trying to help him.