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AOPA fuel demo Baron surpasses 150 flight hours

AOPA has logged more than 150 flight hours in a Beechcraft Baron with unleaded G100UL in the left engine and avgas (100LL) in the right, and the most remarkable aspect has been how similar the performance between the two fuels really is.

This composite of two different photos taken in flight shows the engine instrumentation readout during lean-of-peak operation on the left, and rich-of-peak operation on the right, with the Beechcraft Baron running G100UL in the left engine, and avgas in the right. At both mixture settings, the cylinder head temperature of the left engine (G100UL) was lower than the right engine (avgas), and the fuel flow on the unleaded side was also lower. Photos by Dave Hirschman.

If pilots didn’t know the airplane was using different fuels, they wouldn’t be able to tell from the way the two engines behave during start, runup, takeoff, cruise, or descent and landing. Beyond the obvious differences between G100UL and avgas in terms of color and smell, however, a few trends are becoming well established.

First, G100UL fuel flow is consistently about a half-gallon less per hour than avgas at the same power settings in the AOPA fuel demo Baron’s Continental IO-520 engines. The difference is less when the engines are operated lean of peak exhaust gas temperature and consuming less total fuel, and more when rich of peak EGT and burning more total fuel—but always proportional.

“That difference in fuel consumption is attributable to G100UL’s higher energy density,” said George Braly, a principal at General Aviation Modifications Inc. (GAMI), which developed the unleaded fuel. “It weighs slightly more than avgas, and it puts out more energy per gallon.”

G100UL weighs 6.3 pounds per gallon compared to 6 pounds per gallon for avgas.

Cylinder head temperature (CHT) is slightly higher in the AOPA Baron’s left engine using G100UL than the right, and EGT is slightly cooler. The differences are typically quite small, however.

I’ve flown the AOPA fuel demo Baron on several long trips and typically try to match fuel flow in the two engines for maximum range and a balanced fuel load.

I was present at GAMI’s maintenance hangar in Ada, Oklahoma, when technicians performed compression checks and borescope inspections, took oil samples, and cleaned the spark plugs after 150 flight hours. Those inspections showed excellent compression in both newly overhauled engines, clean exhaust valves and spark plugs in the G100UL-running left engine, and normal lead deposits in the right.

Oil filters in both engines were clean and devoid of any visible amounts of metal. Oil samples from both engines were sent out for analysis and we’re awaiting the results. The oil itself seemed remarkably clear even though it had been in the engine for more than 50 tachometer hours at the time it was changed. GAMI expects G100UL will increase the time between oil changes, allow for synthetic engine oil, and perhaps increase the required time between engine overhauls.

The AOPA fuel demo Baron will be on display at the 2024 Sun ’n Fun Aerospace Expo at Lakeland, Florida, where GAMI expects to offer G100UL to airplanes with the appropriate supplemental type certificate to try out for themselves.

Dave Hirschman
Dave Hirschman
AOPA Pilot Editor at Large
AOPA Pilot Editor at Large Dave Hirschman joined AOPA in 2008. He has an airline transport pilot certificate and instrument and multiengine flight instructor certificates. Dave flies vintage, historical, and Experimental airplanes and specializes in tailwheel and aerobatic instruction.
Topics: Advocacy, Avgas, Supplemental Type Certificate

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