AEROBATIC ACFT CLIPS TREE ON APCH TO LNDG.

Narrative

MY INSTRUCTOR AND I HAD JUST FINISHED SOME AEROBATIC PRACTICE IN AN SMA BIPLANE AND WERE IN THE TFC PATTERN TO DO A FEW LNDGS. I OCCUPIED THE REAR SEAT; MY INSTRUCTOR WAS IN THE FRONT. THERE WAS NO OTHER TFC IN THE PATTERN. I WAS FLYING THE DOWNWIND LEG APPROX 3/4 OF A MI FROM THE RWY. I WAS AT 800 FT AGL (PATTERN ALT); 15 INCHES MANIFOLD PRESSURE; AND 110 MPH. ABEAM THE APCH END OF THE RWY; MY INSTRUCTOR PULLED THE THROTTLE ALL THE WAY BACK TO SIMULATE AN ENG FAILURE. I BEGAN AN IMMEDIATE L DSNDING TURN TO THE RWY AT 100 MPH. TURNING TO FINAL; FROM MY VANTAGE POINT; LOOKING OUT ALONG THE L SIDE OF THE ACFT; IT APPEARED TO ME THAT WE WERE CLRING THE TREES OFF THE APCH END OF THE RWY; BUT THAT WE WOULD NEED PWR TO MAKE THE RWY ITSELF. AT THAT POINT MY INSTRUCTOR ADVISED ME TO ADD PWR; WHICH I DID. ALMOST IMMEDIATELY THERE WAS A JOLT. WE APPARENTLY HIT THE UPPER BRANCHES OF A TREE THAT WAS BLOCKED BY THE NOSE TO MY LINE OF SIGHT. MY INSTRUCTOR TOOK CTL OF THE AIRPLANE AND LANDED WITHOUT FURTHER INCIDENT. THERE WERE NO INJURIES BUT THE AIRPLANE REQUIRES EXTENSIVE REPAIR. I WAS SO INTENT ON MAKING A NICE GLIDING TURN TO THE RWY; THAT I FORGOT THE AIRPLANE'S POOR VISIBILITY CHARACTERISTICS. MY ATTN SHOULD HAVE BEEN MORE EVENLY DIVIDED AMONG ALL OF THE FACTORS AFFECTING THE FLT.