SMA PLT RUNS OUT OF GAS IN 3 1/2 HRS OF FLT WHEN ENDURANCE SHOULD ALLOW 4 1/2 HRS.

Narrative

AFTER 3 1/2 HRS OF SIGHTSEEING; THE ENG QUIT. THE FUEL TANKS HOLD 55 GALLON AND HAD BEEN TOPPED-OFF IMMEDIATELY PRIOR TO TKOF. THE ENG PWR SETTING FOR THE FLT WAS 22 INCHES/2300 RPM; WHICH WOULD BURN 10 1/2 GALLONS /HR. AT A MAX CRUISE PWR SETTING OF 23 INCHES/2450 RPM; FUEL CONSUMPTION IS 12 GALLONS/HR. WITH FULL FUEL; I SHOULD HAVE HAD A MIN OF 4 1/2 ENDURANCE HRS AS STATED IN THE SMA OWNERS MANUAL AND BASED ON MY OWN EXTENSIVE EXPERIENCE WITH THE ACFT. WHEN THE ENG STARTED CUTTING OUT; I DECIDED TO RE-RTE TO MARTHA LAKE AIRSTRIP WHICH WAS THE CLOSEST LNDG STRIP. UPON LOSING TOTAL PWR; APPROX 5 MI S OF MARTHA LAKE; I IMMEDIATELY LOCATED AN ALTERNATE LNDG SITE AND MADE A SAFE LNDG IN A BALL AND TRACK FIELD. I WAS INDICATING 1/4 TANK OF FUEL WHEN I LOST PWR. INSPECTION OF THE ACFT UPON LNDG REVEALED NO CONTAMINATION IN THE LINES; FUEL TANKS WERE EMPTY; AND FUEL DISPERSION PATTERN STAINS UNDER THE R WING AROUND THE FUEL TANK VENT. THE A&P MECH WHO INSTALLED THE FUEL TANKS A FEW MONTHS AGO HAS BEEN SCHEDULED TO MAKE A THOROUGH INSPECTION AND MAKE THE NECESSARY REPAIRS.