Tom Haines

Saving $4,000 in the real world

July 28, 2008 by Thomas B. Haines, Editor in Chief

My August “Waypoints” column “Saving $4,000 in Fuel,” has generated a number of questions and comments from readers also curious about running their engines lean of peak. I just landed this afternoon at Appleton, WI, after flying LOP from Frederick, MD. Brutal headwinds kept our groundspeed in the 140s all day, stretching our flight time to about 4.4 hours. As usual en route to OSH, I stopped for fuel, this time at Mason Jewett Field near Lansing, MI, where avgas was a reasonable (by this week’s standards) $5.05. Nice airport, but completely deserted this beautiful Sunday morning. My fuel burn LOP was about 12.5 gph while true airspeed at altitudes of 6,000 and 8,000 feet was around 160 knots. Rich of peak, I would usually see about 17.2 gph and maybe 165 KTAS.

A big difference today was that I could have made the trip nonstop, even with the strong headwinds of about 25 knots on the nose. That wasn’t even an option when operating ROP. The Garmin GNS 530 showed that we could have landed at ATW with an hour and 16 minutes of fuel nonstop from FDK. Because of the uncertainties of traffic flows associated with AirVenture, I chose to stop. On a “normal” flight I would have charged ahead and made the trip nonstop.

To answer a few of the questions from members: You can expect exhaust gas temperatures LOP to be in the 1,400s, depending on conditions. As for fears about burning exhaust valves, George Braly of General Aviation Modifications, Inc., reminds that the exhaust valves spend 75 percent of their time seated, allowing heat to be wicked away into the engine. Also when seated, they are not exposed to the combustion process, which can run 4,000 degrees F or so–making 1,400 degrees seem downright chilly. Those operating LOP properly with good monitoring equipment shouldn’t see problems with exhaust valves.

One member reports running the Lycoming in his Cessna 182 25 degrees LOP and shaving about 3 gph off his fuel burn, but costing him 9 knots. That’s a larger speed decrease than most Continental engine drivers will see, especially when running only 25 degrees LOP.

Keep sending your questions and sharing your experiences. Everyone benefits.

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