ON LNDG ROLLOUT RPTR LOST DIRECTIONAL CTL DUE TO PARTIAL GEAR EXTENSION.

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I WAS MAKING A FAMILIARIZATION FLT WITH MY CO-PURCHASER IN A NEWLY ACQUIRED AIRPLANE. AT THE TIME OF TKOF TENSION LEVELS BTWN MYSELF AND MY PARTNER WERE AT A PEAK DUE TO CONSTANT DISAGREEMENTS PERTAINING TO THE AIRPLANE. AFTER TKOF I SELECTED GEAR UP AND NOTICED A DOWN AND LOCKED LIGHT ON THE NOSE GEAR INDICATOR. I ADVISED MY PARTNER OF THE CONDITION AND HE CONFIRMED IT. WE ATTRIBUTED IT TO A FAULTY WARNING LIGHT BECAUSE WE HAD HEARD THE GEAR CYCLE NORMALLY SO WE CONTINUED ON WITH THE FLT. DURING THE FLT ANOTHER DISAGREEMENT AROUSE BECAUSE I FELT WE WERE NOT STICKING TO THE FLT REGIME AGREED TO ON THE GND. UPON RETURNING TO THE ARPT AREA I SELECTED GEAR DOWN AND STILL NOTICED I STILL ONLY HAD A NOSE GEAR DOWN AND LOCKED INDICATION. I CYCLED THE GEAR AND NOTED NO CHANGE IN THE INDICATOR LIGHTS. AIR PRESSURE IN THE TANKS WAS NORMAL AND THE REDUNDANT EXTERNAL INDICATORS DID SHOW A DOWN AND LOCKED POS FOR THE GEAR. I INFORMED MY PARTNER THAT I WAS GOING TO DO A LOW APCH AND CHK THE 'SHADOW' OF THE AIRPLANE. MY PARTNER DISAGREED AND WANTED TO LAND THE AIRPLANE. I PERFORMED THE LOW APCH AND DID NOTE THAT THE SHADOW OF THE AIRPLANE SHOWED THE GEAR DOWN. ON THE NEXT APCH I TRIED TO DEPLOY THE FLAPS WITH NO RESULT. I INFORMED MY PARTNER THAT 'WE HAVE NO FLAPS.' HE RESPONDED TO 'LAND NORMALLY;' WHICH IS WHAT I DID. AS THE AIRPLANE SLOWED DURING ROLLOUT IT DEPARTED TO THE L OF THE RWY. UPON DEPLANING WE DISCOVERED THAT THE MAIN GEAR WAS PARTIALLY RETRACTED (MORE ON THE L THAN THE R). 1) VALVE THAT FED AIR TO THE LNDG GEAR WAS ALSO DISCOVERED TO BE IN THE CLOSED POS. 2) NO CHKLIST SUPPLIED WITH THE AIRPLANE. 3) PLT NEW TO THIS AIRPLANE AND SYS. 4) COCKPIT RESOURCE MGMNT NON-EXISTENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE TYPE EXPERIMENTAL ACFT WAS A WAK-52. THE PROB WITH THE GEAR AND FLAPS WAS THE AIR SELECTOR VALVE WAS POSITIONED TO OFF. THE VALVE IS IN THE FRONT COCKPIT AND COULD HAVE BEEN MOVED BY THE PLT IF HE HAD KNOWN. THE GAUGE READING GIVES THE AIR TANK PRESSURE. THE ENG STARTS ON AIR PRESSURE; THE FLAPS ACTUATE ON AIR PRESSURE AND THE GEAR ACTUATES ON AIR PRESSURE. THERE WAS ENOUGH RESIDUAL PRESSURE EVEN WITH THE VALVE OFF TO START THE ENG; RAISE THE FLAPS AND PARTIALLY RAISE THE GEAR. THE RPTR WAS JUST NOT FAMILIAR ENOUGH WITH THE SYS; AND HAD AT THAT TIME NO PLTS HANDBOOK AND; IN FACT; WAS IN THE PROCESS OF EDUCATING HIMSELF. FOR AWHILE AMERICANS COULD PURCHASE THE YAK 54 AS A FULLY CERTIFICATED ACFT; BUT NOT SO ANYMORE (YAK 54 IS TAILDRAGGER VERSION). THE ARPT WAS A PVT STRIP NEAR W PALM BEACH CALLED WELLINGTON. BECAUSE THE STRIP WAS GRASS AND WET THERE WAS NO DAMAGE AT ALL TO THE ACFT.