My first F1A models were from a kit Sija. It is easy to build model kit. The wing is based on a tube longerons. It flies well, but the wing construction is not very stiff.
My most successful models ware MD4 and MD5. They contain two functions clockwork timer. One function for DT operation, the second for rudder delay after release. This system is very reliable for thermal weather.
Drawing of fuselage with 2 functions timer: fuselage_2f.pdf