The O.S. Engines FS-120S III Surpass Pumped is a high-performance, single-cylinder 1.20 cubic inch (20cc) four-stroke glow engine engineered for large-scale radio-controlled (RC) aircraft. It is widely recognized for its integrated fuel system designed to deliver steady, position-independent power, though it has now been discontinued by the manufacturer.
The engine features a ringed piston construction and an optimized aluminum alloy body built for longevity and continuous high output.
According to the O.S. Engines Factory Specs:
Displacement: 1.218 cu in (19.96 cc)Bore & Stroke: 30.4mm (1.197 in) x 27.5mm (1.083 in)
Power Output: 2.1 PS (2.07 HP) at 12,000 RPM
Practical RPM Range: 2,000 to 12,000 RPM
Weight: 32.5 oz (921g) without muffler; 35.3 oz (1000g) with muffler
Crankshaft Thread: 5/16 – 24 UNF
Suggested Propellers: 14×9, 14×10, 14×11, 15×8, 15×9, 15×10, 16×6
The Fuel Injection System:
Pump & Carburetor
The defining characteristic of this version is its dedicated fuel regulator system:PD-07 Fuel Pump: A rear-cover mounted diaphragm pump operated by crankcase pressure pulses. It ensures consistent fuel delivery regardless of the fuel tank’s physical placement relative to the engine centerline or your aircraft’s orientation during extreme aerobatics.
Type 70N Carburetor: Features a built-in atmospheric pressure regulator to manage the pressurized fuel fed by the PD-07 pump, keeping the air-to-fuel ratio perfectly balanced.
The O.S. FS-120 III Manual lists strict maintenance guidelines for the fuel mixture to protect the internal components:
Fuel Composition: Standard methanol-based glow fuel with 5% to 15% nitromethane.
Oil Content: A minimum of 18% total lubricant consisting of high-quality synthetic oil, castor oil, or a synthetic/castor blend.
Glow Plug: Optimized for use with the traditional O.S. Engines Type F long-reach four-stroke glow plug.
