Well, that flat-bottom airfoil is just what I had readily available because I calculated my Telemaster. With some amount of work I replaced it by SD7037 what gave an airframe better suited to the task. Actually I think the OP really needs an airplane with something like a RG15 airfoil and a F3A drive as he already considered. It would not resemble a F3J machine but rather a F3C or even F5B one, but the drive would have the efficiency assumed for this project. It was just not what I had at hand data-wise.

I do have data for another F3A drive (AXI) which show that those 20x13 F3A props are really optimized. The Graupner CFK 20x12 is just not suited to such an application. Notice efficiencies well over 60%. The UAV would just climb with more than 20 m/s airspeed and more than 10 m/s climb rate, but why not with a RG15? The airframe could have less span and aspect ratio but should be a composite build for rigidity and accurate shape.