TM 1-1500-204-23-5
b. Types. Common types of tail rotor hubs are
described in the following paragraphs.
(1) Delta hinge type. This type of tail rotor
hub assembly has a preconed or split cone arrangement
with a flex-beamed-type or grooved yoke and a delta
hinge mounted on a trunnion which is splined to the tail
rotor gearbox shaft. Rotor blade pitch change occurs at
the attach points to the spherical bearings.
(2) Flapping action tail rotor. On this type of
tail rotor hub, the blade assemblies telescope over the
hub and are bolted to an interconnecting tension-torsion
strap assembly within the hub. Blade angle is controlled
by the pitch control assembly.
(3) Articulated tail rotor. The articulated tail
rotor head has two forks. Each fork has a hub with two
blades. The resilient mounts allow each hub and blade to
move in and out in a seesaw motion. Blade twist is
controlled by a stainless steel strap pack that passes
through each hub.
39. Tall Rotor Blades. The following paragraphs
describe the types and construction of tail rotor blades.
Balancing and trammeling are also discussed.
a. Types. Tail rotor blades are the same basic
types as main rotor blades.
(1) Metal. Aluminum is the most common
metal used in tail rotor blades. It is found in the skin and
spars. Stainless steel is used in spars and on leading
edges.
(2) Fiberglass. Fiberglass tail rotor blades
can be crossply fiberglass or graphite composite types.
Fiberglass is used for spars and skin.
b. Construction. Use of metal and fiberglass
components in the construction of tail rotor blades is
contained herein.
(1) Metal. Metal tail rotor blades typically are
all-metal bonded assemblies with a stainless steel spar
and honeycomb core or an all-metal shell bonded to a
honeycomb core.
(2) Fiberglass. Fiberglass tail rotor blades
typically have graphite composite spars running from tip
to tip. In some uses, the spars are covered with crossply
fiberglass to form the airfoil shape.
c. Balance. Balance is critical to tail rotor blades
because of their high rotational speed, compared to the
main rotor blades. Tail rotor blades can be balanced in
both the span and chord directions.
(1) Spanwise. Spanwise balancing of the tail
rotor blades involves adding or removing weight at the
blade tip. A balancing kit should be used with adapters
for the specific type blades.
(2) Chordwise. Chordwise balancing of the
tail rotor blades involves adding of removing balance
washers to the pitch arm. A balancing kit with adapters
should be used for the specific blades being balanced.
NOTE
· Always try to balance the blades by
deleting weights or washers. Keep
over-all weight at a minimum.
· Consult the applicable maintenance
manual for the particular model of
helicopter.
d. Trammeling. Trammeling is the method of using
a trammel bar to adjust or set the adjustable control rod or
tail rotor pitch change link A trammel bar is a precision
tool with adjustable trammel heads. The shaft pins on the
trammel heads are put in the clevis holes of the control
rods or change links to get the exact dimension of the part
being replaced.
3-10. Blade Balance. Blade balance is very important to
safe operation of a helicopter. Methods used to balance
blades are discussed in the following paragraphs.
a. General. Out of balance blades can cause a
flutter which affects helicopter operation. Even though
rotor blades are balanced against a master blade during
manufacture or overhaul, they occasionally need to be
rebalanced because of wear or damage.
Change 2 3-9
