DRG TAXI AFTER A X-COUNTRY FLT, A PROP BLADE WAS NICKED BY FLYING GRAVEL. THE PLT HAD THE PROP DRESSED BY A MECH, THEN HE MADE AN ENG RUN-UP & TOOK OFF ON A TEST FLT. WITNESSES RPRTD THAT AS THE ACFT WAS DEPG, IT REMAINED AT A LOWER ALT THAN EXPECTED, BUT THE ENG SOUNDED SMOOTH. THE ACFT WAS TURNED DWNWND & MNVRD FOR FINAL APCH TO THE SAME RWY. HOWEVER, IT OVERSHOT THE TURN & COLLIDED WITH TREES AT THE EDGE OF THE CLEAR WAY ABOUT 1200' SHORT OF THE RWY. THE ACFT REMAINED AIRBORNE FOR ABOUT 500', THEN IT COLLIDED WITH THE GATE OF A HI FENCE, CRASHED & BURNED. NO PREIMPACT PART FAILURE OR MALFUNCTION, OF THE ACFT OR ENG WAS FND, BUT THE MIXTURE CTL WAS FND AT A MID-RANGE PSN, RATHER THAN FULL FORWARD. FOR TAKEOFFS BELOW 17,000' IN THIS ACFT, THE MIXTURE SHOULD HAVE BEEN FULL RICH. THE PLT HAD BEEN ISSUED A 3RD CLASS MED CERT ON 3/14/91, BUT IT WAS RESCINDED LTR, WHEN A CARDIOVASCULAR ABNORMALITY OF THE PLT WAS NOTED. A CHECK OF THE PLT'S BLOOD SHOWED A CHLORPHENIRAMINE (ANTIHISTAMINE) LEVEL OF 0.073 UG/ML. DENSITY ALT WAS ABT 9300'.