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a. Ultralight owners should remember that the
light-weight, thin wall tubing design of an ultralight
fuselage/wing structure is particularly susceptible to
metal fatigue. When aluminum tubing has been
stressed beyond its elastic limit, it takes on a chalky
white appearance (corrosion) at the point of highest
stress. Warpage and deformation are other signs of
high stress points and once discovered, the ultralight
should be grounded until the damaged is repaired.
b. The tolerance limit of a tube or fitting can
be significantly lowered by over-torquing a bolt. If
a bent or damaged support tube or structure is not
repaired, the bend or dent will become a crack, and
ultimately the crack will become a structural failure.
69
5/24/95 AC 90-89A
NOTE: If a used ultralight has been purchased,
it is highly recommended that the
owner perform a detailed acceptance inspection
on the aircraft assisted by an experienced
individual who is familiar with the
make and model aircraft. It is also recommended
that all existing hardware (e.g.,
nuts, bolts, springs) be replaced with new
aviation quality hardware.
c. If possible, remove the fabric envelope and
check the airframe structure underneath for dents,
cracks, and corrosion. Check the top and bottom of
the spars for compression (wrinkled metal) damage.
Double check all wings, landing gear, strut, engine,
and tail surface attach points for wear, elongated
holes, or damage.
d. If any previous repairs are found, check
with the manufacturer to see if damage in that area
can be repaired and if the repair that was made is
airworthy.
2. CHECKLIST. Each ultralight FLIGHT TEST
PLAN should include a pre-flight inspection
CHECKLIST. The CHECKLIST should include a
step-by-step approach to inspection that covers all
the manufacturer inspection items as well as the following
suggested items starting at the landing gear.
a. Landing Gear. The landing gear is the last
part of the light-weight aircraft to leave the earth
and the first part to arrive. Since the majority of
these aircraft fly from unimproved strips, the stress
on the gear is high. The checklist should include
inspection items recommended by the manufacturer
and inspection for the following:
(1) The condition of the landing gear attach
points and alignment of the landing gear and wheels
to the longitudinal axis of the fuselage. If the attach
points are mis-aligned, the landing gear will not track
in a straight line and this will affect take-offs and
landings.
(2) Elongated bolt-holes, loose AN hardware,
bent tubing, condition and attachment of
wheels, wheel bearings, tire inflation, tire condition
and brakes.
(3) Brake condition and operation, including
chafing of brake lines/cables against the gear
struts.
(4) Condition and operation of the steerable
nose gear, if applicable.
(5) Condition and attachment of the tail
wheel/skid, if applicable.
b. Wing Assembly. The vast majority of
ultralight aircraft use a man-made sailcloth material
stretched over a tubular frame. This type of fabric
is susceptible to ultra-violet radiation from the sun.
If left unprotected, it can become unairworthy in less
than 6 months. The checklist should include the following
inspection items:
(1) Ensure the sailcloth has not suffered
any tears, or abrasion, due to wear or foreign object
damage.
(2) Check the sailcloth for obvious ultraviolet
(UV) degrading of fabric strength by examining
the condition of the fabric on top of the wing.
Compare it to the fabric on the bottom of the wing.
If the top wing fabric shows a significant difference
in color (faded), the fabric should be tested for
strength with a fabric tester (Maule or Quicksilver)
to see if it tests within the manufacturer’s serviceable
limits. If no minimum service limits are listed, the
fabric should test out at 46 pounds, or 70 percent
or more, of its original tensile strength, whichever
is greater, to be considered airworthy. If the fabric
fails the tests, it must be replaced before further
flight.
(3) Flying and landing support cables
should be checked for tension, routing, attach points,
and condition. Scrutinize the swaged cable ends. It
is recommended that a red reference mark (nail polish
works fine) be painted on each of the cables abutting
the swaged end. If the cable is growing, i.e.,
a gap forming between the swaged end and the
painted referenced mark, there is an impending failure
of the swaged terminal. Do not fly the aircraft
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Amateur-built Aircraft & Ultralight Flight Testing Handb(42)
