Others estimate 70 percent of the
fleet will be unaffected. Some mod-
els may be able to operate on a new
unleaded fuel with simple changes. A
manufacturer could reduce the maxi-
mum cylinder head temperature via
an airworthiness directive or a type
certificate revision. Other engines
depend on the detonation protection
of 100LL and can’t easily compensate
for a lower octane. If the fuel-to-air
mixture inside a piston engine com-
busts at the wrong time, it would cre-
ate holes in the pistons and cause the
engine to tear itself apart.Technol-
ogy does offer hope. Full authority
digital engine controls (FADEC) and
other electronic timing controls are
capable of pinpoint monitoring and
adjustments not normally possible.
Lycoming’s iE2 (integrated electronic
engine) was designed to power the
leading high-performance pistons of
today with multiple fuels. “By moving
to an adaptive, closed loop, cylinder-
by-cylinder control system, you can
compensate for some loss of octane,”
states Michael J. Kraft, Lycoming vice
president of research, development,
and engineering. “Going further up
the ‘trick’ line, you could include the
go-fast gizmos that we’ve placed on
Jon Sharp’s Nemesis NXT engine.”
Kraft believes a 100-octane unlead-
ed fuel, or 100UL, may come to
market. “What would happen if we
were faced with very low octane rat-
ings…say 91UL or lower? Possibly a
change in engine technology would
be needed. Remember, today’s high-
performance aviation engines were
designed around the then-available
fuel. If the fuel changes, the engine
will need to change either in control
methods or mechanical configura-
tion,” he says. “There are limits as
to how far down you can go without
impacting the power rating.”
Rhett Ross, the president of Tele-
dyne Continental, said last spring
that the company was developing an
engine for either diesel or jet fuel to
be certified by 2010. Spokesperson
Mac Little won’t comment on exist-
ing prototypes. “You’ll probably have
to follow up with us every six to eight
months,” he says. “We have 1,800
types of specifications, and we have
to test each and every one of them.”
What about modification kits that
could adapt today’s engines for tomor-
row’s fuel? “It’s an active program,”
Little hints, adding, “We won’t get
Comparison of Fuel Possibilities
FUEL
AIRCRAFT
AVAILABILITY
Petroleum-based unleaded
similar to 100LL without
the lead
Significant modifications for high-compression and turbocharged engines.
No effect on 70 to 80 percent of the fleet.
Transparent for producers, distributors,
FBOs. Same cost as today’s 100LL.
SwiftFuel biomass
hydrocarbon fuel
or other possible
specialty fuel
Dual-fuel interim
transition approach
(unleaded for most existing fleet & all
new aircraft; leave 100LL in market for
remaining high-performance aircraft)
Could possibly satisfy the needs of
the current high-performance fleet.
Initial engine testing by FAA Tech
Center has had positive results.
Transparent for existing fleet.
Significant modifications for new
production high-performance
engines/aircraft.
Still in the uncertain research and
development phase. Proprietary and
patented biochemistry process. No
demonstrated production. Unknown cost.
Infrastructure costs and handling issues
for two fuels. Cost of leaded fuel likely to
rise faster than unleaded. FBOs may
choose to only offer one fuel.
