The HB-25 version with extreme cooling head for helicopter models manufactured or modified by HB. This engine was the series recommendation for the Graupner RC-helicopter BELL-47G.

Single-cylinder 2-stroke engine with glow plug ignition, rotary valve crankshaft, side outlet for special silencer, piston with piston skirt, double crankshaft bearing in the front bearing housing, crankshaft housing with additional rear mounting holes, Perry throttle carburetor type 76 with cylindrical throttle plug and mixture control plate.

In rendering, this was my first version with rendered cast textures to get as close as possible to the original surface texture.

Other engines