No record could be found showing the pilot received a weather briefing prior to takeoff. Unfavorable weather was in the vicinity. Several times the pilot had difficulties understanding and complying with instructions from clearance delivery, ground control, and departure control. After takeoff the pilot requested and received an IFR clearance. During the last five minutes of flight radar returns showed the airplane changing heading from 45 degrees to as much as 180 degrees about 10 times and descending or ascending several times from altitudes ranging from 4,500 feet MSL to 11,500 feet MSL. The altitude and heading changes were not directed by controllers. About 3 minutes before the accident departure control asked the pilot if he had a problem. The pilot indicated that he did and 'we're trying to get straight.' One minute later, the pilot said 'we're all right.' Shortly afterwards, radar data showed a loss of control. Radar and communications were lost and an on ground explosion was observed as the accident occurred. An FAA flight surgeon reviewed the pilot's medical records. Within one year of the accident the pilot had 3 physical conditions and was taking 3 separate prescriptions which would have prevented him from being medically qualified to pilot an aircraft.