Experimenter

April 2013

Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.

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flight, so there's no real use for the excessive power for extended periods. The Conversion A required mod for the engine conversion is the addition of an oil circulation system. As mentioned, the engine was only designed to run for four minutes, just long enough to start the big engine, so there is just enough oil in the engine to accommodate this function. Running it longer will require a system that will circulate the oil through a filter and a cooler. So a three-stage dry sump was added, with two of the stages dedicated to evacuating the oil out of the two gearboxes, with the third stage removing oil from the holding tank and pressurizing it before running it through a pair of aluminum coolers, then two filters and then back into the two gearboxes. The pump is custom made by Peterson Fluid Systems, using components designed for a single-stage NASCAR differential oil pump. Why two oil coolers? The primary one is for cooling the engine of course, but the second one is for cabin heat. At high altitude, it's nice to have warm toes. The starter motor used on the little turbine is rated at 24 volts, as is the previously mentioned igniter. So to use it with a 12/14-volt electrical system, they call on a second 12-volt battery that can be switched from parallel to series (and back again) with the primary 12-volt battery. So when it's not called upon for starting the engine, the second battery becomes the backup for the avionics system. Both batteries are maintained by the B&C; 40-amp alternator that was custom installed on the engine. In the stock starter motor configuration, the fuel controller manages the engine up to an optimum rpm for spinning the jet engine it's trying to start. But as an airplane engine, it has to be modified for variable rpm. On this particular 701, the throttle operation is controlled by an electric servo (fly-by-wire if you will) from a momentary-on DPDT toggle switch on the stick grip—no actual throttle lever in the cockpit. Same for the propeller adjustment. So with one hand on the stick, the pilot can operate the throttle, prop, and pitch trim from three different switches, including a hat switch for the trim. Scott also used the stick to control the mouse on the laptop that is used for in-flight data acquisition from the stick grip as well. The EIS Horizon screen reads out the engine as well as flight information. A Garmin 696 provides navigation info as well as weather. A Grand Rapids autopilot is installed to handle the pitch and roll axis and tracking duties as assigned from the Garmin. The Propeller The propeller is a vintage NSI unit. The NSI CAP 140 prop is in-flight adjustable (electric) and uses three Warp Drive composite blades that have been modified by the addi- Scott in front of his turbinepowered Zenith CH701. EAA Experimenter 21

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