Cessna 150K - Bulkheads; Repair after Hard Landing; Replacement of Hi-Shear Rivets; Firewall Damage

18-57. REPAIRABLE DAMAGE. Fuselage skin re-
pairs may be accomplished in the same manner as
wing skin repairs outlined in paragraph 18-14.
Stringers, formed skin flanges, bulkhead channels
and similar parts may be repaired as shown in fig-
ure 18-5.
18- 58. DAMAGE NECESSITATING REPLACEMENT
OF PARTS. Fuselage skin major repairs may be
accomplished in the same manner as the wing re-
pairs outlined in paragraph 18-15. Damaged fittings
must be replaced. Seat rails serve as structural
parts of the fuselage and must be replaced if damaged.
18-59. BULKHEADS.
18-60. LANDING GEAR BULKHEADS. Since these
bulkheads are highly stressed members, irregularly
formed to provide clearance for control cables, fuel
lines, etc., the patch-type repairs will be, for the
most part, impractical. Minor damage, consisting
of small nicks or scratches, may be repaired by
dressing out the damaged are, or by replacement
of rivets. Any other such damage must be repaired
by replaCing the landing gear support assembly as an
aligned unit.
18-61. REPAIR AFTER HARD LANDING. Buckled
skin or floorboards, and loose or sheared rivets in
the area of the main gear support will give evidence
of damage to the structure from an extremely hard
landing. When such evidence is present, the entire
support structure must be examined, and all support
forgings must be checked for cracks, using a dye
penetrant and proper magnification. Bulkheads in
the damaged area must be checked for alignment,
and deformation of the bulkhead webs must be deter-
mined with the aid of a straightedge. Damaged sup-
port structure, buckled floorboards and skins, and
damaged or questionable forgings must be replaced.
18-62. REPLACEMENT OF HI-SHEAR RIVETS.
Hi-shear rivet replacement with close tolerance
bolts or other commercial fasteners of equivalent
strength properties is permissible. Holes must not
be elongated, and the Hi-shear substitute must be a
smooth push fit. Field replacement of main landing
gear forgings or bulkheads may be accomplished by
using:
a. NAS464P* Bolt, MS21042-* Nut and AN960-*
washer in place of Hi-shear rivets for forgings
with machined flat surface around attachment holes.
b. NAS464P* Bolt, ESNA2935* Mating
Base Ring, ESNA LH2935* Nut for
forgings (with draft, angle of up to a maximum of
8°) without machined flat surface around attachment
holes.
*Dash numbers to be determined according to the
size of the holes and the grip lengths required. The
bolts grip length should be chosen so that No threads
remain in the bearing area.
18-63. FIREWALL DAMAGE. Firewalls may be re-
paired by removing the damaged material and splic-
ing in a new section. The new portion must be lapp-
ed over the old material, sealed with Pro-Seal #700
(Coast Pro-Seal Co., Chemical Division, 2235 Bev-
erly Blvd, Los Angeles, California), compound or
equivalent, and secured with stainless steel rivets.
Damaged or deformed angles and stiffeners may be
repaired as shown in figure 18-12, or they may be
replaced. A severely damaged firewall must be
replaced as a unit.
18-64. ENGINE MOUNT.
18-65. DESCRIPTION. The mount for the aircraft
engine is constructed of 4130 chrome-molybdenum
steel tubing. A truss structure, fastened to the fire-
wall at four points, supports a cradle arrangement.
This cradle arrangement with its supporting lugs,
forms the base for rubber shock mounted engine sup-
ports.
18-66. GENERAL CONSIDERATIONS. All welding
on the engine mount must be of the highest quality
since the tendency of vibration is to accentuate any
minor defect present and cause fatigue cracks. En-
gine mount members are preferably repaired by
using a larger diameter replacement tube, telescoped
over the stub of the original member using fishmouth
and rosette type welds. However, reinforced 30-
degree scarf welds in place of the fishmouth welds
are conSidered satisfactory for engine mount repair
work.
18-67. ENGINE MOUNT SUPPORT CRADLE DAM-
AGE. Minor damage such as a crack adjacent to an
engine attaching lug may be repaired by rewelding
the cradle tube and extending a gusset past the dam-
aged area. Extensively damaged parts must be re-
placed.
18-68. DAMAGE INVOLVING ENGINE MOUNTING
LUGS
AND ENGINE MOUNT TO FUSELAGE ATTACH-
ING FITTINGS. Engine mounting lugs and engine
mount-to-fuselage attaching fittings should not be re-
paired but must be replaced.
18-69. BAFFLES. Baffles ordinarily require re-
placement if damaged or cracked. However, small
plate reinforcements riveted to the baffle will often
prove satisfactory both to the strength and cooling
reqUirements of the unit.
18-70. ENGINE COWLING.
18-71. REPAIR OF COWLING SKINS. If extensively
damaged, complete sections of cowling must be re-
placed, Standard insert-type skin patches, however,
may be used if repair parts are formed to fit. Small
cracks may be stop-drilled and dents straightened if
they are reinforced on the inner side with a doubler
of the same material.
18-72. REPAIR OF REINFORCEMENT ANGLES.
Cowl reinforcement angles, if damaged, must be
replaced. Due to their small size they are easier
to replace than to repair.
18-73. REPAIR OF ABS COMPONENTS. Rezolin Re-I
pair Kit Number 404 may be obtained from the Cessna
Service Parts Center for repair of ABS components.
Change 2 18-5