Second to none is the quality of the Japanese built OS Engines. Their 91 size engines have been World Championship winning for many years, and used by many competitive 3D pilots to win multiple XFC and 3D Masters events.
My newest Vibe 50 helicopters are equipped with the popular OS Hyper 50 heli engine. I am using them stock and have experimented with regulated and pumped OS carburetors. This engine works best with gear ratios of 9.3:1 down to 8.5:1. Keep the headspeed and engine RPM high for best power. I run my vibe 50 at 1950RPM head speed in stunt mode. I use a Model Avionics Throttle Jockey REV MAX limiter to keep the RPM stable.
When tuning the mixture needles on this engine keep in mind that the low speed cam will affect mixture nearly all the way up to 50% thottle opening and hover range. Use the Main needle solely to adjust the overal mixture at full power climbouts.
- Displacement: 14.95cc. (0.912cu.in.)
- Bore 27.7mm (1.091in.)
- Stroke 24.8mm(0.976in.)
- Weight 635g (22.4oz.)
- Output: 3.4ps/15,000r.p.m.
Practical RPM .2,000 - 16,000r.p.m.
OS has offered more versions of a 91 Engine than any other manufacturer. With this vast experience, they have produced a winning engine for years. Their latest being the 91HZ-PS. The HZ incorporates many new internal features from years of testing and pilot input. I use this engine un-modified in all of my 3D competition helicopters and in my F3C World Championship machines. The HZ runs smoother, with more power than any of its competitors.
The new pump and regulator system delivers constant fuel flow at any flight attitude and any fuel level. The carburetor features new needle valve designs and internal changes making the mixture easy to adjust and perfect for the best all-round performance.
Internal modifications include low weight piston and rod assembly, high flow porting and intake improvements.
OS 91HZ, SZ, and C-Spec engines operate at their best with good cooling systems fitted tightly around the cylinder head. The Vibe 90 type helicopter fan and shroud as well as many new models on the market feature well designed cooling shrouds that are key to stable and powerful running of the OS 91. I have fitted the Vibe cooling system to my World Championship models to maximize power output and consistency. Many comments from competitors and spectators at the last two World's in Spain and Poland about my engine are a testament to the power they can put out in the right conditions. I attribute this to the cooling system and fuel selection.
Optimal OS 91 Engine settings:
• SZ / C-Spec 0.012" head shimming; HZ stock head shim only
• OS#8 or new OS#7 Glow plug (medium to medium hot heat range)
• High volume, close fitted cooling shroud system
• 8:1 gear ratio
• 15,500 - 16,000 Max Engine RPM (1950-2000RPM Main Rotor)
• 3D Fuel - Cool Power 30% Heli fuel
• F3C Fuel - Cool Power 30%/15% 1:1 Mix Multi Viscosity fuel combination
OS Engines benefit and run best with lower viscosity oils at higher contents in fuel. The oil acts also as a coolant and is expelled from the engine easily if lower viscosity. I do not recommend low oil content low smoke type fuels as these often will affect the longevity of any engine.