SMA PLT IN LOSS OF ACFT CTL EVENT; SINGLE PLT IFR; IMC. SENSORY ILLUSIONS PREVAILED AFTER LOSS OF HSI.

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MY FRIEND AND I WERE ON AN IFR FLT IN CESSNA THAT LEFT ANOKA COUNTY; MINNESOTA TO MOBRIDGE; S DAKOTA ON FRI/SEP/94. WE WERE NE OF THE ABERDEEN VOR WHEN WE HAD COMS WITH CTR. CTR: 'WHAT IS YOUR HDG?' '2 -- (SOMETHING; I DON'T REMEMBER EXACTLY.)' CTR: 'TURN TO 240 DIRECT TO ABERDEEN VOR.' I TURNED THE ACFT TO 240 WITH THE HDG BUG; CHKED MY GAUGES AND STARTED TALKING TO MY FRIEND. HE WAS HOLDING THE VFR MAP. HE SAID ACCORDING TO THE DME WE WERE 5.1 FROM THE VOR. I SAID TAKE MY LITTLE YELLOW RULER OUT OF MY FLT BAG AND YOU CAN MEASURE WHERE WE ARE. HE PROCEEDED TO GET THE RULER AND PUT IT ON THE MAP. HE WASN'T HOLDING THE RULER OVER THE VOR SYMBOL SO I BEGAN TO POINT WHERE TO HOLD THE RULER. HE INDICATED WHERE WE WERE ON THE MAP AND I LOOKED BACK TO THE GAUGES. AT THIS TIME; THE AIRPLANE TOOK A VIOLENT SHARP L TURN AND A DOWN NOSE ATTITUDE. I IMMEDIATELY BEGAN TO PULL BACK ON THE YOKE. LOOKING AT THE ARTIFICIAL HORIZ; IT WAS 90 DEGS TO THE FIXED AIRPLANE. I FELT A G-FORCE ON MY BODY AND REALIZED THAT I WAS TIGHTENING THE TURN. I RELEASED THE AMOUNT OF FORCE I WAS APPLYING TO THE CTL AND IMMEDIATELY STARTED TO LEVEL THE WINGS. WHEN I GOT THE WINGS LEVEL I STARTED TO PULL BACK ON THE CTL. AGAIN THERE WAS A FAIR AMOUNT OF G-FORCE IN THIS PULL UP. WHEN THE AIRPLANE WAS IN THE CLB I LOOKED AT THE ARTIFICIAL HORIZON TO SEE WHERE I WAS AND THE GAUGE FLIPPED 180 DEGS FROM A R SIDE UP TO UPSIDE DOWN. WHILE STILL LOOKING AT IT; IT FLIPPED AGAIN 180 DEGS FROM UPSIDE DOWN TO R SIDE UP. I IMMEDIATELY LOOKED AT THE TURN COORDINATOR TO SEE IF THE WINGS WERE LEVEL (THEY WERE). I LOOKED AT THE DIRECTIONAL GYROSCOPE AND SAW IT WAS NOT TURNING. THEN I LOOKED AT THE VERT SPD INDICATOR AND SAW I HAD THE VSI PEGGED AT 2000 FPM ASCENT. I LOOKED AT THE AIRSPD INDICATOR AND SAW I WAS INDICATING VERY LOW AIRSPD. I PUSHED IN ON THE CTLR TO BRING THE NOSE DOWN AND IMMEDIATELY BEGAN A DSCNT. THE VSI PEGGED IN DSCNT. I PULLED THE CTL BACK AND FELT THE G-FORCE. I REMEMBER SAYING TO MYSELF I HAVE TO SLOW THE AIRPLANE DOWN OR I'M GOING INTO THE GND. CTR CALLED ON THE FREQ AND ASKED; 'WHAT IS YOUR ALT?' I RESPONDED; 'I AM TOO BUSY TO LET YOU KNOW.' SEATBACK HAD SNAPPED AND HE WAS LYING IN A PRONE POS. I IMMEDIATELY PULLED THE THROTTLE BACK AND DROPPED THE LNDG GEAR. I WAS NOSE HIGH AND STARTED TO LOSE AIRSPD. AT THIS TIME; I PUSHED THE NOSE OVER AND STARTED TO FREE FALL GETTING A LOT OF NEGATIVE G-FORCE. EVERYTHING IN THE AIRPLANE THAT WASN'T STRAPPED DOWN WAS ON THE CEILING. AS THE AIRPLANE CAME OVER AND STARTED TO PICK UP SPD; I STARTED TO APPLY A LITTLE BACK PRESSURE ON THE CTL AND I CAME OUT OF THE OVCST IN AN APPROX 60 DEG ANGLE TO THE GND. I IMMEDIATELY LEVELED THE AIRPLANE AND LOOKED AROUND FOR GND REF. I SAW THE HWY ON MY L AND KNEW IT SHOULD BE ON THE R. I TURNED 180 DEGS AND IMMEDIATELY PICKED UP THE ABERDEEN ARPT. I FOUND MY CHARTS AND DIALED IN THE FREQ OF THE ARPT TO LET ANYONE KNOW I WAS IN THE VICINITY AND WAS LNDG RWY 13. I HEARD ON THE FREQ; 'CESSNA LNDG ABERDEEN; LET ME KNOW WHEN YOU ARE ON THE GND; WE ARE IN A HOLD.' I COMMUNICATED BACK THAT I WOULD AND PROCEEDED TO LAND. WHEN I LANDED AND CLRED THE RWY I CALLED BACK ON THE FREQ AND TOLD THEM I WAS CLR OF THE ACTIVE. THE ACFT ON THE FREQ IDENTED THEMSELVES AS A COMMUTER AND ASKED ME TO MEET THEM ON THE GND BECAUSE THEY HAD A PHONE NUMBER FOR ME TO CALL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR REVEALED THAT THE ACR DH-8 WAS INBOUND TO THE VOR AS HE WAS XING THAT SAME VOR. HE; AND OTHERS THAT WERE INVOLVED IN THIS POST FLT ANALYSIS; THINK THAT THERE WAS A CHANCE ENCOUNTER WITH WAKE TURB FROM THE DH-8. THE DH-8 WAS A 7000 FT; ABOVE HIM AND INBOUND INTO THE VOR OR IN A HOLD. WHEN THE RPTR CONTACTED THE CTLR; THE CTLR WOULD NOT OR COULD NOT GIVE HIM SPECIFIC INFO REGARDING THE POS OF THAT OTHER ACFT. AUTOPLT WAS CHKED AND NOTHING WAS FOUND WRONG WITH THAT EQUIP. THE GYRO; HSI; WAS REPLACED AFTER FAILING ON A GND CHK AFTER THE INCIDENT. IT WAS DISCOVERED TO BE AN 'OLDER' TYPE; WITH A DIFFERENT SERIAL NUMBER THAN THAT ON THE ACFT'S LOG AND REGISTRY. IT IS ASSUMED THAT THE PREVIOUS OWNER SWITCHED HSI'S WHEN THE ACFT WAS SOLD TO THE FLYING CLUB. THE TURN AND BANK INDICATOR/COUPLER TO THE AUTOPLT WAS FOUND TO HAVE A SPURIOUS PLUS OR MINUS VOLTAGE TO 1 SIDE AND WAS THEREFORE CHANGED. THE ACFT SUFFERED DAMAGE DURING THIS EVENT; HAVING EXPERIENCED 3 STALLS OF A VIOLENT NATURE. THE WINGS WERE BENT SO THAT 2 RIBS AND THE REAR SPARS HAD TO BE REPLACED. THE FAA SUBJECTED THE RPTR TO A FLT CHK FOR PROFICIENCY DETERMINATION. PASSED OK. RPTR KNOWS HOW HE FAILED IN HIS BASIC ATTITUDE FLYING AND IS GETTING MORE PRACTICE TIME.