Swift UL94 at Airventure

[rwanttaja]

My understanding is that it is indeed that simple. If lead is needed as a lubricant, then we are all going to be in trouble when (and if) unleaded 100 octane is ever created and replaces 100LL.

It happened over twenty years ago, but this is how I remember it: I had bought a used Fly Baby with 25 hours on the overhauled engine, and immediately started running it on auto fuel. At the next condition inspection, one cylinder was leaking down a valve.

The guy who rebuilt the cylinder told me that this engine needed to run on leaded fuel (e.g., 100LL) for a while to establish a lead base, after which unleaded auto fuel could be safely run. There was also the option of installing special valves that were compatible with unleaded fuel right from the start. I did so, on the bad cylinder, but the other three were original style. So I ran about ~50 hours on 100LL then switched to alternating unleaded and leaded fuel. No valve problems in the last 20 years.

Though maybe that's the MMO. :-)

If I've remembered it correctly, existing 80-octane engines probably have a sufficient lead base to last then, and the right valves would just need to be installed at the next overhaul.

From the SWIFT website describing UL94:
"This proprietary unleaded fuel formulation is a blend of hydrocarbons designed to meet the fuel specification standards of ASTM D7592, D7547, and D4814. This fuel is FAA-certified for use in up to 65% of the US piston fleet; up to 100,000 aircraft are already certified to use the fuel based upon existing Type Certificates and/or Autogas STC's. An additional 25,000+ aircraft, those whose engines are rated for minimum Grade 91/96 Avgas, are eligible to purchase an FAA Supplemental Type Certificate (STC) for the use of Unleaded UL94 Avgas."

IIRC, lead is required if the fuel is to have an octane greater than ~94. So it sounds like the planes designed for 100LL (e.g. everything built since 1985) are going to be SOL.

Ron Wanttaja