From reading other threads, this bird came in 2 flavors, the f3a (retracts) version and the acro (fixed gear) version. The excelleron is a rebadged explorer (acro version). Do a search here, there are 2 decent sized threads on this bird and the excelleron. Also check out the huge thread on the Excelleron and aerobob's writeup on his website for the Excelleron (rcaerobats.net). I have the Excelleron (have yet to finish it) with a ys110.