Design Improvements for the Zenith 601 HDS: Cowl Air Intake and Alternate Air

Air Intake and Alternate Air

The air temperature inside the cowl on a hot summer day can be quite high. Thus, the engine does not perform well if the air within the cowl is used by the carburetors. Instead, an air intake next to the reduction gear box funnels cold air via two hoses directly to the carburetors. The system has been tested for rain by pouring water from a fully turned-on garden hose into the inlet, with no noticeable effect on engine performance. Nevertheless, the cold-air supply can be shut off, in which case the hot air within the cowl is used by the carburetors. The cold air intake has resulted in a dramatic increase of takeoff performance. At 10,000 ft density altitude, the plane takes off with 1,100 lbs gross weight in less than 3,000 ft of runway, with the Rotax engine turning 4,500 rpm and producing 42 hp.

The outside air is not forced into the carburetors, but is blown onto the air filters. If the outside air supply is turned off, the carburetors take in the surrounding air.

The choke lever of the carburetor has been safety wired in the off position. Instead of the choke, a primer is used. All fuel hoses in the engine compartment have a sleeve for fire protection.