Cessna 172 Maintenance Manual page 32

1. General
A. Fasteners used in the airplane are generally solid aluminum rivets, blind rivets, and steel threaded
fasteners. Usage of each is primarily a function of the loads to be carried, accessibility and frequency
of removal. Rivets used in airplane construction are usually fabricated from aluminum alloys. In
special cases, monel, corrosion-resistant steel and mild steel, copper, and iron rivets are used.
2. Rivets
A. Standard solid shank MS rivets are those generally used in airplane construction.
fabricated in the following head types: roundhead, flathead, countersunk head, and universal
head. Flathead rivets are generally used in the airplane interior, where head clearance is required.
MS20426 countersunk head rivets are used on the exterior surfaces of the airplane to minimize
turbulent airflow. MS20470 universal head rivets are used on the exterior surfaces of the airplane
where strength requirements necessitate a stronger rivet head than that of the countersunk head
rivet. Hi-Shear rivets are special, patented rivets having a high shear strength equivalent to that of
standard NAS bolts. They are used in special cases in locations where high shear loads are present,
such as in spars, wings, and in heavy bulkhead ribs. This rivet consists of a cadmium plated pin of
alloy steel. Some have a collar of aluminum alloy. Some of these rivets can be readily identified by
the presence of the attached collar in place of the formed head on standard rivets. Blind rivets are
used, where strength requirements permit, where one side of the structure is inaccessible, making it
impossible or impractical to drive standard solid shank rivets.
Replacement Of Hi-Shear Rivets
3.
A. Replacement of Hi-Shear rivets with close tolerance bolts or other commercial fasteners of equivalent
strength properties is permissible.
(1) The hardware used for the Hi-Shear rivets is determined according to the size of the holes and
the grip lengths required.
(2) Bolt grip length should be chosen so that no threads remain in the bearing area.
(3) Holes must not be elongated, and the Hi-Shear substituted must be a smooth, push-fit.
B. Field replacement of main landing gear forgings on bulkheads may be accomplished by using the
following hardware:
(1) NAS464P, NAS436P, and either: NAS1103 through NAS1120, NAS1303 through NAS623 or
NAS6203 through NAS6220 bolt, and either:
(a) MS21042 nut and AN960/NAS1149 washers in place of Hi-Shear rivets for forgings with
machined flat surfaces around the attachment holes.
(b) ESNA2935 mating base washer and ESNA RM52LH2935 self-aligning nut with forgings
(with a draft angle of up to a maximum of eight degrees) without machined flat surfaces
around the attachment holes.
4. Substitution Of Rivets
A. When adapting the typical repairs shown in this manual to suit actual conditions, it may be necessary
to use different fasteners than those originally used. This may be due to non-availability of a particular
fastener, restricted access, or other difficulties. When replacing rivets, it is desirable to use rivets
identical to the type of rivet removed. Countersunk head rivets are to be replaced by rivets of the
same type and degree of countersink. When rivet holes become enlarged, deformed, or otherwise
damaged, several options are available.
(1) The simplest solution is to install a 1/32 inch (0.032 inch) larger size rivet as a replacement. This
solution uses the designed repairability of the structure, and is the quickest repair.
(2) Repair rivets are available.
(a) Repair rivets have a shank that is 1/64 inch (0.016 inch) larger diameter than a standard
rivet but have the same size and shape heads.
(b) NAS1241 repair rivets replace MS20426 rivets if they have the same suffix.
NAS1242 repair rivets replace MS20470 rivets if they have the same suffix.
(c)
CESSNA AIRCRAFT COMPANY
SINGLE ENGINE
STRUCTURAL REPAIR MANUAL
FASTENERS
© Cessna Aircraft Company
They are
51-40-00
Page 1
Jun 1/2005