Darock is also right. You don't need formulas, and you do need them. It all depends upon the level you want to work at. If you're into building models that are yours, and yours alone, and not trying to get a particular level of performance, the general "rules of thumb" work very nicely...epecially if you're not too concerned about the "hows", and only want the "what works" part.

Using the general guidelines, you can whip out a piece of blank paper and draw a flyable model in an evening. You'll spend more time on the aesthetics than the actual design parameters. The resulting model will fly reasonably well, and your ARF-only friends at the field will consider you some kind of prodigy or genius.

Again, I have to stress that I only presented some very general guidelines that will enable you to build a successful model. If you're going for an airplane with very specific performance goals, then much more stringent "rules" apply. Study similar models of the type you want to design. Then go from there. Even so, after a bit of study, you'll find that those models will all conform to a set of guidelines that can be reduced to a similar set of "rules of thumb" as the very general ones I mentioned above.

Of course, if you go that route, you'll be copying ideas developed by other people, and you may not have a full understanding of the "whys" of how they work. If you're only interested in a flying model...then fine, just copy parameters and design your own aesthetics. If you want to know the "whys", then there's plenty of study for you to dig into.

It all depends upon what you want to do. The field's wide open....

OH...and be sure to build light, straight, and strong.