ORIGINAL: HO-229
How does one determine the angle of incidence for a scratch built design?
Does the designer need to partially build/estimate the weight/velocity of the aircraft first?
The full scale aircraft has a 4 degree root cord incidence?
Almost everything said before is true, but there is a bit more.
You basically do need to estimate or decide upon all the parameters needed in the formulas. Your second question suggests that you already know something about the formulas because you've listed some of what they requier. But then you also need a bit more.
For one thing you need to decide on the airfoil you're going to use and then find the plot or charts for the sucker. And then work them out for your wing design (since they're usually a report of the test results for the profile, not a wing) and that includes span and size (one place Reynolds effect comes into the mix) and a few others. Sound like an impossible task? Well, in recent years a couple of labs have produced really decent model airfoils and published their work. So something pertinent does exist. Finding it actually is the impossible task sometimes.
So yes, the designer needs to work out his design to know sizes, overall weight, and the speed range he expects to encounter. And then make a couple of choices.
But your 3rd questions suggests that there might be an easier option. If you're designing a model of a full scale, you can simply build it scale. If it might be judged in competition someday, you'll benefit from that possibly. And our models are very forgiving. They actually fly with almost any airfoil. And very few modelers have the skills to duplicate any profile with much accuracy, so a lot of this is moot.
What I know for sure is that it's fun to come close. Using a profile that gives the general impression of the full scale and plugging it into the fuselage within my ability to duplicate the full scale's incidence has always produced a pretty good flyer. What has often been the real problem has been pitch control using the scale numbers. The airfoil and incidence is no problem compared to that one.
And if fidelity to scale isn't a primary consideration, there really aren't any real problems.
BTW, have you started figuring out the tail? moments and areas?
And what's the model going to be?