Until now, gas engines have not been designed for RC helicopter use, and have therefore they have been almost impossible to mount in a helicopter. And they have not come with the needed muffler system to extract maximum power, and they produced a lot of vibration because they were unbalanced. The folks at O.S. have tackled all of these problems and we now have a great alternative gas powerplant in the O.S. GT15HZ. However, gas engine operation is quite a bit different than what we are used to with a nitro engine. Here are some things to consider, but when you get used to these differences from a nitro engine, you can easily start it using a standard electric starter.
>When you set up a nitro carburetor, the throttle curve leads the pitch curve to ensure sufficient power to obtain the needed rotor speed. However, the instructions for this engine recommend hovering at only a 20 to 40% throttle opening.
>Initial high and low needle-valve settings are very sensitive and should be adjusted to factory specifications; just the slightest change to these settings will have a profound effect on the operation of the engine.
>This carburetor also has a choke lever, which we do not see on a nitro engine, and this is used to prime the carburetor with fuel before starting.
Initial flight tests in my Thunder Tiger Raptor 90 G4 have shown that this engine can produce more than sufficient power for everything but the most demanding 3D maneuvers. It appears to have more torque than a 91 nitro engine, making it very suitable for scale applications with multi-rotor heads and larger than normal rotor blades. Additional flight testing will be needed to find the optimum head speed and rotor blades for a particular application. Although changing to longer than normal rotor blades for your specific helicopter can interfere with the operation of the tail rotor, this can be compensated for by using rotor blades with a larger chord or thicker airfoil to produce the added lift/performance.