AOPA Turbine Pilot Magazine - November 2024 - 85

Piper PA-31-T() with MTV-27
it makes perfect sense that the engines
are producing a bit more power and a bit
greater airspeed on G100UL. "
G100UL has a vastly different chemical
composition than avgas, and that's
obvious at the fuel pump. The unleaded
fuel looks like apple juice, smells like turpentine-and
it has some bothersome
traits that avgas doesn't.
First, G100UL tends to stain paint,
hangar floors, and anything else it touches.
Pilots and aircraft owners can take precautions
by applying protective coatings,
but G100UL doesn't wipe away or evaporate
like avgas. Inadvertent and relatively
small fuel spills must be cleaned immediately
and thoroughly to avoid staining.
The top of the fuel caps on the Baron's
left wing have yellowed during its year
of exposure to G100UL, while the fuel
caps on the right wing show no noticeable
change.
George Braly, co-founder of General
Aviation Modifications Inc., the
Oklahoma firm that developed G100UL,
said pilots can avoid paint staining with
" good fuel hygiene, " and pretreating aircraft
surfaces with ceramic coating and
thoroughly wiping away fuel spills right
away will avoid stains.
" If the fuel is left on the surface and
exposed to the UV from sunlight, then
that will cause some brown discoloration, "
he said.
Also, G100UL produces black soot
that lines exhaust pipes and spark plugs.
This fine black ash is easy to wipe away
from the exterior. Inside the engine compartment,
cleaning the spark plugs with
pressurized shop air, for example, blows
away the sooty residue immediately.
Braly says the black ash is the product
of an excessively rich fuel/air mixture and
can be minimized by leaning.
" If pilots do not consistently follow
standard good engine management practices
with respect to leaning...then there
will be accumulations of that black soot
in the tailpipe and spark plugs, " he said.
The most important and most vexing
question about G100UL is whether
it harms other aircraft components it
touches such as O-rings, fuel tanks, and
fuel lines. GAMI has done extensive
tests and says it's safe. In June, however,
Cirrus Aircraft warned customers that
it won't honor warranties for aircraft
using G100UL because of concerns about
" materials compatibility. "
At EAA AirVenture this year, the
AOPA fuel demo Baron unintentionally
became part of the debate when
leaks from fuel bladders in the left
wing stained the ground under the aircraft
with a dark puddle of G100UL.
There was a great deal of speculation
that G100UL may have weakened or
destroyed the rubber bladders.
After AirVenture, AOPA had all four
bladders from the aircraft removed and
inspected by Kurt Hartwig of Eagle Fuel
Cells in Wisconsin. Hartwig reviewed
aircraft records and pressure tested the
bladders. He said the Baron's main fuel
bladders were produced in 1974 and
1978 and overhauled in 2023 before the
unleaded fuel demonstration began.
Hartwig found small leaks in both the
left main bladder containing G100UL and
the right main bladder containing avgas.
He didn't make any determination about
why the leaks occurred, or why they were
more numerous in the left tank than the
right. But he suspects improperly torqued
bolts holding the gaskets to the left wing
were the main culprit.
" Old cells, under torqued bolts, and
unbelievably bad timing led to the leaks
and drama at AirVenture, " he said.
All four of the bladders were replaced
with newly manufactured ones, and those
are made from newer materials resistant
to the solvents contained in both G100UL
and avgas.
Although this demonstration has
reached its conclusion, much work
remains to be done. One of AOPA's highest
priorities is working with industry
stakeholders to ensure the national
availability of an unleaded aviation fuel
that works in every piston engine aircraft
by 2030. The association remains
interested in demonstrating other
100-octane unleaded aviation fuels as
they become available.
Thanks to AOPA supporters Greg
Herrick and Dan Shewmaker for providing
the Baron and allowing AOPA to
gain experience with GAMI's pioneering
unleaded aviation fuel.
AOPA PILOT / November 2024
85
- General performance improvement
(5% take-off & climb, 3kts
cruise with 1900 rpm)
- No propeller speed restrictions on
ground while operating in low idle
- More ground clearance for less
FODs
- Significant noise and vibration
reduction
- Unlimited blade life
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AOPA Turbine Pilot Magazine - November 2024

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