The pilot said that he was departing in his airplane from the downhill-sloping (east) runway at 9AK with a slight tailwind. He said that, as the airplane tried to become airborne, the tailwind increased considerably, and the airplane would not climb. The airplane struck brush that encroached the east end of the runway area and veered left into brush and small trees. He stated that no mechanical failures or malfunction of the airplane precluded normal operation. Damage included the separation of the right outboard elevator. (Note: Photographs of the airstrip provided by the pilot showed that 9AK was a short, narrow, rough-surfaced airstrip with brush growth encroachment.)