A REPUBLIC RC3 SEABEE PLT PERFORMS A FORCED; EMER OFF ARPT LNDG IN A CORNFIELD WHEN HIS 1 ENG FAILS TO PRODUCE PWR 1 MI SE OF DLL; WI.

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AM00 LCL; LIGHT WINDS AND CLR SKIES. ACFT HAD RECEIVED MAINT AFTER A PRECAUTIONARY LNDG DUE TO ROUGH RUNNING ENG. MECH DISCOVERED FAILED MAGNETO ON L SIDE (PLT'S SIDE) OF ACFT. MECH AND OWNER BELIEVED THIS WAS THE CAUSE OF PWR LOSS THAT PRECEDED PRECAUTIONARY LNDG. MAGNETO WAS REPLACED. ACFT WAS THOROUGHLY PREFLTED WITH VISUAL EXTERNAL CHKS OF ENG AND AIRFRAME. ALL FLUIDS AND FUEL WERE TOPPED OFF AND VERIFIED FULL. FULL RUN-UP WAS DONE TO VERIFY ENG PERFORMANCE BEFORE TKOF. MAGNETOS AND CARB HEAT CHKED IN NORMAL RANGES BY MECH PRIOR TO DAY OF FLT. ON FLT DAY PLTS STARTED ACFT AND DID SAME PREFLT CHKS. ACFT PERFORMANCE SEEMED GOOD. AFTER ROTATION ON DEP RWY 19 BARABOO DELLS; WI; ACFT ACCELERATED TO 75 MPH (NORMAL CLB SPD) AND VERT SPD OBSERVED AT GREATER THAN 250 FPM. AT ABOUT 200 FT ABOVE ARPT THE CLB PERFORMANCE AND AIRSPD BEGAN TO DECAY RAPIDLY. NO CHANGE IN ENG SOUND WAS OBSERVED. MIXTURE; PROP; THROTTLE AND CARB HEAT WERE VERIFIED FULL FORWARD; NO INCREASE IN PERFORMANCE NOTED. ACFT PITCH ATTITUDE WAS REDUCED TO MAINTAIN FLYING SPD AT 65 MPH. AN ATTEMPT TO REVERSE COURSE WAS BEGUN IN HOPES TO RETURN TO RWY 1 FOR LNDG. HOWEVER; PITCH ATTITUDE HAD TO BE FURTHER REDUCED TO MAINTAIN AIRSPD AT NO LESS THAN 55-60 MPH. ENG SEEMED TO BE LOSING PWR BUT CONTINUED TO RUN. AIRPLANE COULD NOT COMPLETE TURN FOR ARPT; I JUDGED WE WOULD CONTACT GND FIRST. SO I TURNED TO DIRECTION OF WIND (COMING FROM ABOUT 230 DEGS) AND LANDED IN AVAILABLE CORNFIELD WHILE MAINTAINING CONTROLLABLE AIRSPD INTO FLARE AT TOPS OF CORN STALKS. NO CONFIGN CHANGES WERE ATTEMPTED. I COULD NOT ANTICIPATE EFFECTS ON ACFT AT SUCH LOW SPDS AND WITH SO LITTLE TIME TO PUMP HYDS WHILE FOCUSED ON CHOOSING LNDG SURFACE WHILE MAINTAINING ACFT CTL. AFTER LNDG; ENG WAS SECURED (IT RAN UNTIL AFTER LNDG) BOTH OCCUPANTS OF ACFT DEPARTED WITHOUT INJURY. I BELIEVE THAT ENG FAILURE WAS BEYOND MY ABILITY TO PREDICT. ALL INDICATIONS (BASED ON MY LIMITED EXPERIENCE WITH THIS SPECIFIC TYPE RC3) WERE THAT ACFT SHOULD HAVE PERFORMED NORMALLY. RECENT MAINT SHOULD HAVE RESOLVED PREEXISTING PROBS (AS KNOWN PRIOR TO THIS FLT). I WOULD NOT VOLUNTEER TO FLY AN ACFT OF THIS AGE AGAIN UNLESS I HAD 1) MORE EXPERIENCE IN THAT SPECIFIC TYPE AND 2) THE ACFT HAD MORE RECENT FLT TIME (IT HAD PREVIOUSLY BEEN FLOWN LESS THAN 3 HRS SINCE 1960'S) AND/OR 3) FULL ENG MAINT AND OVERHAUL HAD BEEN CONDUCTED BY TECHNICIANS FAMILIAR WITH THIS SPECIFIC AIRPLANE. THE PRELIMINARY DIAGNOSIS IS ENG FAILURE AFTER TKOF IN MY OPINION.