DEN83FA114

Before departing, the plt received a wx briefing & was advised that VFR flt was not recommended thru western Nebraska & eastern Wyoming. A frontal wx sys was forcasted to produce thunderstorm activity with associated turbulence & rain. Reportedly, the plt was anxious to make the flt so he could deliver needed parts for a machine that was to be used in a publicly advertised demonstration. Additionally, he felt he could help his partner complete the project in time for the demonstration. The plt elected to file a VFR flt & then departed as planned. While en route, the acft encountered wx & subsequently crashed. Just before impact, the acft was seen spiraling after it came out of a low overcast with no right wing or tail section. After the plane crashed, a witness saw the right wing 'drifting down.' An exam of the wreckage revealed evidence that both horizontal stabilators failed from positive airloads & the right outboard wing section failed from negative airloads. No evidence found of a malfunction/failure before inflt breakup.