Swift Fuels’ 94 Octane Unleaded Avgas
Earlier this month I burned 25 gallons of Swift Fuels’ U94L unleaded Avgas in the 180 hp Lycoming O-360 in my 1960 Piper Comanche, Papa.
Swift Fuels of Lafayette, Ind. has submitted its 102 octane unleaded (102UL) Avgas to the FAA for testing in the Piston Aircraft Fuels Initiative (PAFI) program, but it also announced in mid-2015 that it was producing a 94 octane unleaded (UL94) Avgas.
In the last year and a half, UL94 hasn’t gained much traction even though it’s approved for operation in a wide range of GA engines and airframes.
UL94 is produced to ASTM Standard D7547, the specification for hydrocarbon unleaded aviation gasoline. This lead-free Avgas was developed at the request of the military in 1994 for use in its drone fleet. UL94 is a stable fuel with a “tank life” of two years.
I am looking forward to the day when Avgas will be free of tetraethyl lead (TEL), and when I saw that Swift offered a lead-free Avgas that I could legally use, I wanted to try it. What I found was very interesting.
By the end of my flight testing, I hadn’t seen one iota of discernible difference in any engine parameter—EGT, CHT, manifold pressure, rpm or oil temperature—between the UL94 and 100LL Avgas.
Data collection
The data I’ve captured is by no means an exhaustive test. I haven’t done an extreme heat or extreme cold temperature starting test. I haven’t done a high altitude (18,000 feet MSL) operational test. I haven’t done an in-flight restarting test. Nor have I done a fuel system compatibility test.
But thanks to the data collection feature of my Electronics International CGR-30P and 30C engine monitor, I could collect and plot the engine data gathered during the three test flights using EGView from EG Trends.
I also asked Joe Godrey and Savvy Analysis to check my plots. He verified my findings.
Preparing for the tests
There is one 30-gallon bladder-style fuel tank in each wing of my airplane. The fuel selector valve has three positions: left to the engine, right to the engine, and off. There’s no both position.
After flying the right tank empty and sumping the remaining unusable fuel out through the system low point drain, I paid Rabbit Aviation Services at the San Carlos Airport (KSQL) $118.37 to pump 26.6 gallons of UL94 into the right-wing tank.
I also topped off the left tank with 8.4 gallons of 100LL ($38.22). That crunches down to 100LL at $4.55 a gallon and UL94 at $4.45. (Vendors set the pump prices; when buying from Rabbit there are minimal direct cost savings.) The fuelers at Rabbit asked if my airplane was approved for autogas or UL94 Avgas before dispatching the UL94 truck.
Initial observations
UL94 smells different than Avgas and is clear. I checked the two fuels for weight. The UL94 is lighter at 5.79 pounds/gallon than the 100LL at 5.94 pounds.
I flew three one-plus hour flights, switching back and forth between the left and right tanks.
I switched during a full power climb; I switched with the mixture leaned to peak EGT on the first cylinder to peak; and I switched during my normal cruise power and mixture settings while level at 5,500 feet MSL. I also switched on descent and while idling before flight and after landing.
In addition to collecting the engine parameters digitally, I also watched for any EGT difference in the seconds following the switches. I never saw the numbers change.
Users’ reports
John Poppy at the Portage Municipal Airport (C47) in Portage, Wis., a popular fueling stop near AirVenture, said he’s heard “zero negative feedback” about UL94.
Poppy has a 1,000-gallon tank and says he pays two cents a gallon for shipping for the five-hour drive from the Swift production plant in Lafayette, Ind. Poppy sells UL94 for $3.35 a gallon—59 cents per gallon less than his 100LL.
Poppy told me that one customer who flies a Cessna 182 has been using it for over a year while commuting to another state. According to Poppy, the customer’s mechanic asked if he had taken his engine apart and cleaned it after pulling the cylinders for a top overhaul.
Rich Volker of RV Airshows burns it in the 600 hp Pratt and Whitney R-1340 that powers the Harvard Mk IV he flies in his airshow routine. Volker told me he flies his routines at full power and in his opinion, his engine can’t tell the difference.
Dennis Wyman runs the engine shop at G&N Aircraft in Griffin, Ind. Wyman told me that his experience is that running UL94 results in fewer deposits on pistons and valves. In his experience, the switch between the two fuels is transparent.
The only change Wyman has seen is that the combustion chamber of an engine that uses UL94 looks slightly darker than a 100LL chamber. Can you use UL94?
You can use UL94 is your airplane fits into one of the following options:
• Airframe/engine combinations that have an Auto Fuel STC (e.g., an STC from Petersen Aviation);
• Airframe/engine combinations OEM-approved for auto fuel (e.g., ultralights, LSAs, and experimental aircraft);
• Airframe/engine combinations Type Certificated to operate on Grade 80 (listed as Grade 80/87 in ASTM D910) or Grade UL91 (ASTM D7547) Avgas; (Note: If the fuel data plate on the engine lists 80/87 as the fuel, you can legally use UL94 without an STC. This includes Piper singles such as PA-18, -20, -22 and 150 hp PA-28s.)
• Airframe/engine combinations Type Certificated to operate on minimum 80 octane or lower (e.g., 73 or 65 octane) Avgas; or
• Airframe/engine combinations with an Avgas STC purchased from Swift Fuels.
The engine data plate on my Lycoming O-360-A1A specifies 91/96 octane fuel, yet my Piper PA-24 Comanche had never been approved for an auto fuel STC. My only avenue to use UL94 was buying an Avgas STC from Swift.
Where can you get UL94?
Per the user map on the Swift Fuels website, there’s only one public source for UL94 west of the Mississippi River, and it’s in California.
There are also 14 that are cited as “private users.” The 18 other public outlets for UL94 include three in Florida, one in South Carolina, one in Ohio, one in Missouri, four in Indiana, and eight in Wisconsin. (Note: If you would like to find out more about setting up a UL94 station, contact the folks at Swift. They have a team that will tell you how to get started.)
One of the potential roadblocks between availability and pumping UL94 at your airport is tankage. Most airports now have two tanks—one for jet fuel and one for 100LL. One option for adding a third is installing a box station from U-Fuel in Elk Mound, Wis.
U-Fuel offers a split tank—UL94 on one side and 100LL on the other. It appears that split models have the same footprint as existing single-fuel models.
UL94 is here now; PAFI fuel is a few years away
Since most privately owned and operated airplanes in the GA fleet can safely burn UL94, and since Swift sells it for less than today’s 100LL, Swift’s UL94 seems like a winner.
No one knows when the new unleaded 100-octane Avgas will be produced—it’s still being tested in the Piston Aviation Fuels Initiative (PAFI) program.
The PAFI program is scheduled to complete the fuels testing in 2018, but there could well be a time lapse between the approval date and the production and delivery to your local airport.
Based on my testing and my belief that TEL creates a wide range of problems in our air-cooled engines, I would be burning unleaded aviation fuel today if there was a pump with a Swift UL94 placard close by.
Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, Calif. with his wife Audrey. Send questions and comments to editor@www.piperflyer.com.
RESOURCES >>>>>
