Plane & Pilot
Tuesday, January 28, 2014

A Natural Gas To Fly

A Husky takes the alternative route to the skies

We started the motor on CNG power, which, by the way, is immune to hot-start problems, another of its, "But wait, there's more!" benefits, and shortly, we're taxiing to runway 27, the Lycoming blissfully ignorant of what it was being fed. Besides the visceral thrill that always comes with operating in or out of Oshkosh during AirVenture, the takeoff and climbout on CNG power were un-noteworthy, except for the realization that we were wasting lots of the CNG's 138 octane power.

As noted, the only modification to the engine for this installation was the switch to high-compression 10:1 cylinders from the standard 8.50:1 set, but as Horn had pointed out, "The standard Lycoming is set up to be efficient at 100 octane, so technically the engine can't take advantage of that [extra] energy."

We leveled at 2,000 and switched to avgas for air-to-air photos, conserving the CNG for cruising the countryside. Changing from CNG to avgas or vice versa in the demonstrator creates a slight, transitory burble, but nothing that raises the heartbeat.

When flight-testing the system, the Aviat team found exhaust gas and cylinder head temperatures ran about 20 degrees cooler with CNG than with avgas power. Cruising on CNG at 24-squared and 95 knots indicated that after the photo shoot, oil temperature was 164 degrees, oil pressure was 77 psi and CHTs were in the 340-degree range—all well within normal operating parameters. The fuel flow gauge read "0." (As CNG is consumed, the four vertical lights on the CNG gas gauge turn from green to red in sequential order starting at the top; the bottom light is always red.)

The Future Of CNG Power
Not much else in the aircraft needed to be demonstrated, so I was free to wander over the countryside (which to a Husky all looks like one big landing strip) and imagine a CNG avfuel future. A dual-fuel system like N15NG's would add about $12-$15,000 to the cost of a new aircraft, according to Aviat.

The company will also pursue Supplemental Type Certificates (STCs) for retrofits on other aircraft types, Horn said. Thus, the system could pay for itself in a few hundred hours of flight time through fuel savings and reduced maintenance. True, CNG fueling systems aren't common, but that's hardly a reason to cross it off the list of potential avgas alternatives.

Labels: Piston Singles


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