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gear bearings.
(5) Eccentricity of the driving, or driven,
pulley will cause variations of belt tension with rotation,
possibly leading to rapid failure of the belt and
engine or propeller shaft bearings. Remove the spark
plugs and rotate the engine slowly by hand for several
turns in small steps (approximately 45 degrees
of engine rotation per step). There should be no
noticeable change in belt tension at any position. Any
noticeable change must be investigated further (e.g.,
by measuring the run out of the engine pulley and
propeller shaft pulley with a dial indicator).
SECTION 2. FUEL SYSTEMS
1. GENERAL. Many problems with lightweight
aircraft engines can be directly traced to the
type of fuel used. Many states allow automotive fuels
to be sold containing 10 percent alcohol without
requiring a label stating so. Alcohol can cause serious
problems in aircraft engines so first ensure that
the fuel source is a reliable one.
73
5/24/95 AC 90-89A
a. Test for Alcohol in Automotive Fuel.
Take a thin glass jar, mark it one inch from the bottom
of the jar with tape or indelible ink, and fill
the jar with water up to that mark. Fill the jar to
the top with a sample of the fuel to be tested. There
is a clear separation between the water and the fuel.
Put the lid on the jar and shake. Let it settle for
about a minute and check. If the ‘‘water’’ line is
now above the first mark, the fuel has alcohol in
it. Try another source for fuel and do another test.
b. Fuel Primer System. Perform a careful
inspection of fuel primer bulbs fitted in suction lines
because they deteriorate over time and are a possible
source of air leaks, resulting in a lean mixture. Primer
bulbs with plastic one-way valves have been known
to break loose and completely block the fuel in the
fuel line. Positioning the fuel line so the fuel flows
upward through the primer bulb will help minimize
the possibility of this problem occurring. A permanently
fitted fuel pressure gage is recommended
because it can check fuel system operation during
engine break-in and fuel flow during extreme angles
of attack.
c. Filters, Fuel Lines, and Throttles.
(1) Finger screens in fuel tanks should be
checked every 10 hours for debris or varnish build
up from fuel. Nylon mesh fuel filters are preferred
with 2 cycle engines. Paper element filters should
be avoided because they may severely and invisibly
restrict the fuel flow. This is due to a reaction
between water and oil detergents. The fuel filter
should be distinctly located, between the fuel pump
and the carburetors, to facilitate pre-flight inspection
and avoid the possibility of air leaks on the suction
side.
(2) Check plastic fuel lines for age hardness,
discoloration, and over all condition. Fuel line
attach points should be checked before each flight.
Always clamp a fuel line at the inlet and outlet. A
slip-on line might slip off in flight. Leave a little
slack in the fuel lines to minimize cracking from
vibration.
(3) If the 2 cycle engine has two carburetors,
make sure the throttles are exactly synchronized.
If not, one carburetor will run rich while
the other runs lean, causing cylinder overheating and
a possibility of the piston seizing or being holed.
d. Causes of High Fuel Consumption
(1) Dirty air filter causes a rich mixture.
(2) Propeller is not matched to the engine.
(3) Carburetor float improperly adjusted.
(4) Fuel pressure set too high.
(5) Wrong carburetor jets installed.
(6) Defective float valve.
(7) Extreme vibration (propeller/engine)
that keeps float valve open.
74
AC 90-89A 5/24/95
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75
5/24/95 AC 90-89A
CHAPTER 10. ULTRALIGHT TEST FLYING RECOMMENDATIONS
‘‘Hurrying is a visible sign of worry.’’ Arnold H. Glascow
SECTION 1. THREE RECOMMENDATIONS
1. OBJECTIVE. To list additional items
applicable to ultralights that will need to be
addressed in the FLIGHT TEST PLAN
2. RECOMMENDATIONS.
a. Even if the builder/owner or pilot is an B-
747 airline captain with 20,000 hours in type, he/
she should NOT climb into an ultralight without first
receiving flight instruction from a properly certified
or authorized ultralight flight instructor. This must
be done in a two-seat ultralight trainer operated in
accordance with the EAA or USUA exemption to
FAR Part 103.
b. Ultralights by their very nature are highly
susceptible to winds above 15 mph. All ultralight
aircraft test flights should be conducted in light or
　
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