HELI IN PATTERN AT CHD; PRACTICING AUTO ROTATION TO TXWY; EXPERIENCED NMAC WITH ACFT ON SHORT APCH TO PARALLEL RWY.

Narrative

WE WERE CONDUCTING PATTERN WORK ON A TXWY PARALLEL TO THE RWY IN USE (RWY 4R). THIS WAS PROBABLY OUR 8TH PATTERN; R TFC. WE WERE SETTING UP FOR AN AUTOROTATION AND MAINTAINED AN ALT OF 500 FT AGL ALL THE WAY TO FINAL. AS WE WERE FINISHING OUR TURN FROM BASE TO FINAL; THE PITTS PASSED RIGHT IN FRONT OF US ON A STEEP DSNDING TURN. WE WERE BOTH IN R TFC; HE PASSED R TO L. THE PITTS HAD NOT BEEN CONDUCTING PATTERN WORK; I BELIEVE THEY HAD TRANSITIONED IN FROM THE S FOR LNDG. UPON SEEING THE ACFT; I TOOK CTLS FROM MY STUDENT AND CONTINUED A HARD R TURN TO PASS BEHIND. ONCE CLR; WE REALIGNED OURSELVES WITH THE TXWY. WE NOTIFIED THE TWR THAT A BIPLANE HAD PASSED ACROSS OUR FLT PATH ON FINAL. THE TWR ACKNOWLEDGED THAT THEY HEARD US; BUT DID NOT MAKE ANY FURTHER STATEMENT. AS THE INSTRUCTOR; I WAS IN THE L SEAT. WITH R HAND TURNS; THIS MADE IT DIFFICULT TO SEE TFC TO THE R AND NEARLY IMPOSSIBLE TO SEE TO THE R AND ABOVE. BOTH ACFT WERE CLRED TO LAND. NORMAL PATTERNS SHOULD HAVE KEPT US SEPARATED; HOWEVER; THE BIPLANES HAVE A HISTORY OF CUTTING INSIDE THE STANDARD HELI PATTERN AT THIS ARPT.