O.S. FX Series Engines

The FX series engines from O.S. are also very good and reliable engines. Properly tuned and maintained they will provide the modeler with years of trouble free operation. I have sever years old 61FX - it is the very first engine I owed, and seven years later it still runs like a Swiss watch

The 61FX is a great engine for use in your first plane, assuming you are getting a 60 size trainer. Not only will it have enough power to haul it around, but you will probably be able to use it in your second plane - usually a low wing model. I used mine to power my first plane - Hobbico Hobbistar 60MKIII - it flew great. The 61 was very "happy" spinning a 12x8 prop.

I've had two of the 91's - great engines. Very easy to tune, just like the 61, great runner. I used 14x6 and 14x8 props on my engines, and found that they plenty of power to haul my models.The one major difference from the 61 is that 91 is a ringed engine - the brake in prosedure is more impartant to seat the ring correctly....

Specifications for O.S. 91FX

Displacement: 14.95cc (0.912 cu in)

RPM range: 2,000 - 16,000

Bore:   27.7mm (1.090")

Stroke:  24.8mm (0.976")

Compression Ratio: 10.1 : 1

Weight: 550g (19.42oz)   24.3oz w/muffler

Horsepower: 2.8 BHP at 15,000 RPM

Props: Hobby Services recommends 

a 13x8 or 13x9

Specifications for O.S. 61FX

Displacement:  9.95cc (0.607 cu in)    

Bore: 24mm (.945")                    

Stroke: 22mm (.866")

Horsepower: 1.90 BHP at 16,000 RPM    

Weight: 19.4oz, 23.6oz w/muffler

RPM range:  2,000 - 17,000

Props: Tuned Pipe: 12x9, 12x10, 12x11

Sport: 12x6, 12x7, 12x8, 13x6, 13x7

Break-In: 11x7

I've used a pair of the 25's to power my Hobbico Twinstar. Swinging APC 9x6 props made the plane a lightning in the sky. The only draw back was the small size of the fuel tanks, which only allowed for about five minutes of wide open throttle flight....

Just like the AX series engines my FX series engines seemed to perform best on Morgan Fuel Cool Power 15%. I've also tried Wildcat 10% and 15% and Omega 15%.... I got best idle and transition with Cool Power.

Specifications for O.S. 25FX

Displacement:  4.07cc (.2485 cu in)

Bore:   18mm (.708")

Stroke: 16mm (.630")

Horsepower: .84 BHP at 18,000 RPM

Weight: 248g (8.8oz)  10.8oz w/muffler

Recommended Props: Pattern Flying: 9x5, 9x6

Pattern Flying if a tuned pipe is used: 9.5x5

Sport Flying: 9x5, 9x6, 9.5x5, 10x4, 10x5

Practical RPM Range: 2,500 - 19,000 RPM

160FX engine is a power house - it will turn 18x8 prop with ease. I had mine in the 140 size Extra 300s and it was a great combo. I did fine the 160 hard to flip start, especialy on the first start of the day - even after primed it did not want to start. If you have a strong starter I'd recommend to use it in lieu of flipping...

Specifications for O.S. 160FX

Displacement:  26.23cc (1.60 cu in)

RPM range: 1,800 - 10,000

Bore:  33.6mm (1.32")

Stroke:  29.6mm (1.17")

Weight: 930g (32.8oz)

Horsepower: 3.7 BHP at 9,000 RPM

Suggested Props: 

Aerobatic: 15x12-14, 16x10-14, 16.5x10-13

Sport:     17x10-13, 18x10-12