THIS MIDAIR COLLISION OCCURRED APPROX 2 MI NE OF SAUK-PRAIRIE APT. THE PILOTS OF THE CESSNA WERE IN A CLIMBING RIGHT DEPARTURE TURN AT APPROX 1600 FT MSL HEADING APPROX 120 DEG WHEN A COLLISION OCCURRED WITH A PIIPER HEADING APPROX 270 DEG AND DESCENDING. ONE PILOT IN THE CESSNA WAS WEARING AN INSTRUMENT HOOD. THE PILOT OF THE PIPER WAS FLYING INTO THE SETTING SUN. ONE WITNESS SAW THE PIPER MAKE A SHARP EVASIVE TURN JUST PRIOR TO IMPACT. THE PILOTS OF THE CESSNADID NOT SEE THE PIPER UNTIL AFTER THE COLLISION. FOLLOWING THE COLLISION THE PILOT OF THE PIPER LOST CONTROL OF HIS AIRCRAFT AND CRASHED. THE PILOTS IN THE CESSNA LANDED SAFELY BACK AT SAUK-PRAIRIE EVEN THOUGH 3 FT 4 INCHES OF THE RIGHT WING AND 4 FT 4 INCHES OF THE RIGHT AILERON WERE MISSING. NEARLY FULL LEFT AILERON WAS REQUIRED THROUGHOUT THE RECOVERY AND LANDING.