By measuring the drag Seriously, the only practical way of doing this is to find a university handy that has an aeronautical thread and a tunnel big enough to put the whole model in. Knowing the tunnel corrections they can the measure all the parameters at various airspeeds and come up with Cd and Cl for the model. They can do lots of other things, stall speed and stall aoa etc. Could be a useful trade off here, it gives the students a practical set of problems, and you all you need to know about your model, and the cost of doing this, which could otherwise be horrendous, may be within some sort of bargaining reach. It may mean you lose the model for a month or two, but the results could be well worth the time. Based on what you find, the answers could be extrapolated across a wide range of models, and answer quite a few questions.
Evan, WB #12.