Design Improvements for the Zenith 601 HDS: Radiator

Oil Cooler

A 2in. NACA inlet supplies air to the oil cooler.

The amount of air supplied to the oil cooler suffices when ambient air temperature is below 85 deg F. For higher air temperatures, an electric fan has been installed on the outlet set of the oil cooler.

The fan produces a high-volume air flow while drawing 2.5 A. The fan has been tested for 1,000 hr in 230 deg F air, and thus can be expected to be very reliable. It is so effective that the oil temperature does not go above the green 190-230 deg F range even if ambient air temperature climbs past 100 deg F. Indeed, with the fan running, the oil temperature rarely goes beyond 210 deg F. This is a good thing, as argued in the article Points for Pilots: Cool Oil is Cool.

A red switch with internal LED light, positioned just below the instrument cluster, activates the fan. When turned on, the lit switch reminds us constantly to monitor the oil temperature.

The fan is also turned on during steep climb-outs, since then the NACA inlet becomes ineffective due to the low speed and the large angle between the NACA inlet axis and the direction of air flow. This option allows climb-outs at 60 kts, the speed for fastest rate of climb. This is important in high temperature environments where we want to reach cooler air as quickly as possible.

It is important that the fan does not windmill when power is turned off, since a windmilling fan would impede airflow. We checked that the fan does not windmill in normal flight by measuring the voltage produced by the fan in the off position. Except for airspeeds near red line, that voltage is zero, proving that the fan does not windmill in normal flight.