George Shell's Downdraft Cooling System

Long-EZ N10LZ

[Text: George Shell and Wayne Hicks, photos: George Shell]

N10LZ's downdraft cooling system uses ram air inlet scoops for engine cooling and the NACA scoop for carb air and accessory cooling.

The two inlet scoops have 4-inch circular openings to feed ram air into two separate high pressure plenums. Shaped from urethane foam, the scoops are glassed onto the top cowling directly in front of the cylinders. The plenums are typical sheet aluminum fabrication using standard gasketing for sealing to the top cowl. The installation is simple, uses mostly factory-supplied holes, without the need for complicated ramps or diverters. A Kevlar manifold is installed over the entire NACA scoop opening to funnel air to the carburetor, oil cooler, fuel pump, and alternator. A Brackett filter is mounted in the manifold for filtered air to the carb. 3-inch scat tubing is used for the carb and oil cooler. Note the customer Kevlar air channeler upstream of the oil cooler. 1.5-inch hoses are routed to the fuel pump and alternator diodes. Carb heat is provided by two half-shell muffs on port exhaust stacks. Exhaust stacks exit straight, avoiding hot air blast to prop. Except for the cooling scoops, the only cowl modification was to install a slight bubble to the lower cowl for clearing the carb air/heat box. Original exhaust cut-outs in lower cowl will be reshaped and glassed over later.

N10LZ uses the Audio Flight Avionics AV-10 and 4-line display for engine monitoring. CHT bayonets are installed in the factory ports on the bottom side of the cylinders. EGT bayonets are located 3 inches below the exhaust ports.

Cooling performance has been outstanding. Even at high angle climbout (98 MPH IAS), CHT is 340 F, EGT is 1100, and OIL is 170. Airflow in the plenums is well balanced. CHT spread amongst cylinders is never more than 20-25 degrees. EGT spread is 100-150. Cooling numbers are lower during cruise flight. Still in primer only, N10LZ is a fast bird and sees no adverse effects from these cooling mods. Performance is 225 MPH flat out, 200 MPH at high cruise, and 180 MPH at economy cruise (2400 RPM @ 4,000 feet). Paint, wheel pants, and spinner should gain another 10-15 MPH.

N10LZ's engine is an O-320 E2A (160 HP), outfitted with Klaus Savier's LSE electronic ignition and propeller.