Rotor Blade Sections

Main ROTOR. TUBULAR SPAR BLADES. DESCRIPTION. Each main rotor blade is an airfoil with a point of attachment at one end which is the "root" of the blade. The extreme opposite end is the "tip". The distance between the root and tip is defined as the "span" of the blade. The advancing edge in the direction of rotation is the "leading edge". The "trailing edge" is parallel to the leading edge and laterally opposite it. The lateral distance between the leading and trailing edges is the "chord". Each main rotor blade is constructed of a step-tapered chrome molybdenum supporting boom extending from root to tip, termed the "spar", and serves as the main span wise support. Cycle welded to the spar is sheet metal collars to which spruce plywood true ribs are bolted. The true ribs extend chord wise from the leading to trailing edges. Between the true ribs, a number of intermediate ribs are located starting at the tip to about 40 percent of the blade span. The intermediate ribs are partial, or false ribs, which extend from 65 percent aft of the leading edge to the trailing edge. The area span wise between true ribs is the "inter coastal area". The skin covering in this area is supported by small wood blocks, or intercostals, cycle welded to the spar and a semi-round stringer extending from root to tip of the blade at 65 percent of the chord. A Wood's metal strip is inserted along the leading edge for chord wise balance and a cable fastened by stainless steel clips to the aft ends of the true and intermediate ribs forms the trailing edge. A partial spruce plywood skin covering extends from the leading edge to 65 percent of the chord from the edge.

The blade is completely covered with two fabric envelopes, or covers. The first, or inner cover, is doped and sewn to the ribs. Pinked tapes are doped over the sewing. The second, or outer cover, is doped over the inner cover, and a pinked tape doped over the leading edge seam. A stainless steel leading edge strip consisting of three pieces is cemented and nailed to the leading edge to complete the hide.

CLASSIFICATION OF DAMAGE.

NEGLIGIBLE DAMAGE. Small dents due to tracking accident or other causes that may be restored to contour by a slight tapping with a hammer are considered negligible.

DAMAGE REPAIRABLE BY PATCHING. Small tears or punctures that occur in the fabric between the trailing edge and the plywood skin may be patched.

DAMAGE REPAIRABLE BY INSERTION. Damage to plywood skin (0.070 inch thick) forward of the inter coastal area may be repaired providing the damaged area is confined to the space of two inter coastal areas. The plywood skin aft of the inter coastal area of the blades may be repaired by insertion, providing the repair is restricted to the area between ribs number 1 through number 10. Cracked or broken true and intermediate ribs may be repaired by insertion only, providing there are no more than four true ribs damaged in one blade or the damage is not to two or more adjacent ribs.

DAMAGE NECESSITATING REPLACEMENT OF PARTS. Damage necessitating replacement of parts is not permitted in the field due to the lack of equipment for extensive overhaul.

REPAIRS NOT PERMITTED.

Note: Repairs are not permitted to the following damages. Due to the critical nature of the damages they are beyond field repair.
a. Cracks in the leading edge block, such as caused by a "quick start".
b. Broken trailing edge clips.
c. Damage to the blade between the inter coastal area and 65 percent of the chord where the plywood skin ends, other than the area between ribs number 1 through number 10.
d. Damage to the trailing edge cable. This may be detected by a local sagging.
e. A damaged true rib that necessitates replacement.
f. When two or more adjacent true ribs are damaged.
g. When more than four true ribs are damaged in one blade.