I was on the 2nd flight of the day.Everything was looking O.K.... 3 minutes after the takeoff ,i passed the transmiter to my 17 years old son (he flyies for 5 years now-mostly 3D ) to fly & feel the plane a little bit. He flew the Bear gently for 2 minutes, about 500-600 feet high and after a downwind leg and left turn, i saw the plane diving at full throtle .I thouht he was going to make a low pass over the runway- the plane was flying str8 to the ground on a 70 deg angle with the wings level and no respont to throtle, aileron or elevator inputs. I said """"uppppppppppppp""""""" but there was nothing that could be done.As if the receiver was locked !!! There was only 1 more flyer on the field on 40.150Mhz , i was on 35230 Mhz.,so no problem from him...
The plane fall in a very very mudy field, so i saved the engine ( found 20 cm under the surface).
I still can not undersand what happened. There was not pilot error. No crack or brake on the stabilizer/elevator. Everything was working normaly when i got there and took the photos. Battery ( i use 2- 6volt/2500 ma Nimh with two switches -http://www.rcbatteryclinic.com/parallel.html ) was O.K. , each one gave me 1500ma on the discharger...at 0.8 A.
Now i have put the receiver and crystal aside ,and will not use it again. If any friend has some answer ,i 'ld be glad to hear.
By the way, the last modification on the retracts ,was to put a 2mm ply, under the base plate close to the wings center, so that the wheels,moved when open about 1 inch to the front and away from the C.G. That gave even better ground handling.[][][]