Hydro-Mount-System "Pitts"
 
If you want a super quiet motor so you can hear the whistling noise from the air flow over the model, you should consider using our Hydro Mount System. The Hydro Mount System, or short HMS, as described here, is based on the two shock absorbers and very soft rubber mountings. This all produces a very efficient insulation of the engine from the fuselage. It would be impossible to use these soft rubber mountings without the two shock absorbers. The swing amplitude on the rubber mountings at tickover speeds would be 15?mm(!) and a low tickover speed would not be possible. A large proportion of the engines rotational energy would be absorbed by the soft rubber mountings and there would not be enough energy left in the propeller, to force the piston over the next compression stroke. If you use rubber mountings that are hard, that is to say stiffer, or even rubber grommets to keep the amplitude small, you will find these are only effective in the full throttle range, and then only partially so. At the low rpm range the system will run into resonance and the airframe´s vibration level will be even higher compared to a rigidly fixed engine.

The complete system contains four rubber mountings, two ready filled shock absorbers, one CNC milled engine mount, CNC milled shock absorber brackets, all necessary screws, nuts and washers, a length of special Bowden cable for the throttle linkage and a detailed set of instructions with full-scale drawings.