RWY EXCURSION IN AN L19 AFTER LOSS OF ACFT CTL.

Narrative

ON FOURTH AND FINAL LNDG; STUDENT MADE GOOD LNDG JUST R OF CTRLINE. ACFT STARTED DRIFTING R. STUDENT APPLIED L RUDDER AND L BRAKE. ACFT CONTINUED R DRIFT AND DEPARTED RWY. AFTER ABOUT 40 FT THE GND BECAME VERY SOFT AND THE MAIN WHEELS SUNK IN A DECELERATED ACFT. IT TIPPED UP ON ITS NOSE AND HUNG FOR A MOMENT AND THEN TOPPLED OVER ON BACK. MINOR DAMAGE TO TAIL; L WINGTIP; 1 TIP OF PROP AND ENG COWLING. NO INJURIES TO PLTS. SUSPECTED CAUSE: A THERMAL OR PROP WASH FROM T28'S THAT HAD LANDED AHEAD OF US. THEY HAD ALREADY TURNED OFF SOME 3000 FT DOWN RWY BEFORE WE WERE OVER THE OVERRUN. I HAD ADVISED PF THAT WE MIGHT HAVE TO GO AROUND UNLESS WE HAD SUFFICIENT SPACING BEHIND LNDG T28'S. AFTER THEY CLRED THE RWY I TOLD HIM WE HAD SUFFICIENT SPACING AND TOLD HIM TO CONTINUE THE APCH. INSPECTION OF RWY SHOWS L RUBBER MARKS FROM BRAKING FROM JUST L OF CTRLINE SLOWLY CURVING R FOR SOME 200+ FT. R WHEEL BRAKING MARKS START APPROX 50 FT PRIOR TO EXITING RWY -- THEY WERE LIGHTER AND NOT AS WIDE AS THOSE AT THE L. IN THE FIRST SENTENCE I SAID STUDENT PLT; BUT THE PF HAS EXTENSIVE FLYING EXPERIENCE AND CERTIFICATES. HE OWNS AND FLIES A T28C AND A C421B. HE HAS PREVIOUS TAIL DRAGGER TIME; BUT HAD NOT FLOWN THEM IN A LONG TIME AND HAD NEVER FLOWN O-1'S.