8-2 Figure 8-1. Location of Cargo Release in Relation to the Rotorcraft’s Center of Gravity
8.4.1.2 Thus, any attachment method or location that decreases the length of the arm will reduce the distance that the combined CG will shift for a given load (F) and line of action angle (see Figure 8-1, Illustration D).
8.4.2 Maximum External-Load. The maximum external-load (including the weight of the cargo sling) for which authorization is requested may not exceed the rated capacity of the quick-release device.
8.5 Fabrication and Installation.
8.5.1 Static Test. The cargo sling installation must be able to withstand the static load required by 14 CFR §§ 27.865(a) and 29.865(a). Conduct the test as outlined in Chapter 2, Structural Data. If required during the test, supports may be placed at the landing gear to airframe attach fittings to prevent detrimental deformation of the landing gear due to the weight of the aircraft.
8.5.2 Sling-Leg Angles of Cable-Supported Slings. The optimum sling-leg angle (measured from the horizontal) is 45 to 60 degrees. Minimum tension in a sling leg occurs with a sling-leg angle of 90 degrees, and the tension approaches infinity as the angle approaches zero. Thus, larger sling-leg angles are desirable from a standpoint of cable strength requirements. Slings should not be attached in such a manner as to provide sling-leg angles of less than 30 degrees.
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8.5.3 Minimum Sling-Leg Cable Strength.
8.5.3.1 An analysis that considered the effects of 30-degree sling angles showed that the minimum cable strength design factor required would be 2.5 times the maximum external load for each leg regardless of the number of legs.
Although this is the minimum strength required by 14 CFR part 133, it may be desirable to double this value to allow for the deterioration of the sling-leg cables in service. This will result in a cable strength equal to five times the maximum external load.
Example: Maximum external load 850 pounds Minimum required sling-leg cable strength 850 x 2.5 = 2,125 Minimum desired sling-leg cable strength 850 x 2.5 x 2 = 4,250
8.5.3.2 A 3/16-inch, nonflexible 19-wire cable (MIL-DTL-87161G) provides a satisfactory cable strength. For convenience, the cable sizes desired for various loads have been calculated and are tabulated in Table 8-1 based on a factor of five:
Table 8-1. Cable Load Table Maximum External Load (pounds) Aircraft Cable Size for Each Cargo Sling Leg MIL-DTL-87161G Type II Carbon Steel MIL-DTL-83420N Carbon Steel MIL-DTL-83420N Corrosion Resistant Steel 100 1/16 3/32 3/32 200 3/32 3/32 1/8 300 7/64 1/8 1/8 400 1/8 1/8 5/32 500 5/32 5/32 3/16 600 5/32 3/16 3/16 700 3/16 3/16 3/16 800 3/16 3/16 7/32 900 3/16 7/32 7/32 1,000 7/32 7/32 7/32 1,200 7/32 1/4 1/4 1,400 1/4 1/4 9/32 1,600 1/4 9/32 5/16 1,800 5/16 5/16 5/16 2,000 5/16 3/8 3/8
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8.5.4 Sling Installation.
8.5.4.1 Attach the cargo sling to landing gear members or other structure capable of supporting the loads to be carried. Install the quick-release device in a level attitude with the throat opening facing the direction as indicated on the quick-release device. When cables are used to support the quick-release device, make sure the cables are not twisted or allowed to twist in the direction to unlay the cable.
8.5.4.2 Some cargo release devices are provided with a fitting to permit installation of a guideline to assist in fully automatic engagement of the load target ring or load bridle. Secure the guideline to the quick-release device with a shear pin of a definite known value that will shear if a load becomes entangled on or over the guideline. Provision should also be made for cable-supported slings to be drawn up against the fuselage into a stowage position to prevent striking or dragging the release on the ground when not in use.
8.5.5 Installation of Release Controls. See Figure 8-2, Typical Cargo Sling Wiring Diagram, for a typical wiring diagram of the electrical controls.
8.5.5.1 Install a cargo release master switch, readily accessible to the pilot, to provide a means of deactivating the release circuit. The power for the electrical release circuit should originate at the primary bus. The “auto” position of the release master switch on some cargo release units provides for automatic release when the load contacts the ground and the load on the release is reduced to a preset value.
8.5.5.2 Install the cargo release switch on one of the pilot’s primary controls. It is usually installed on the cyclic stick to allow the pilot to release the load with minimum distraction after maneuvering the load into the release position.
8-5 Figure 8-2. Typical Cargo Sling Wiring Diagram
8.5.5.3 Install the emergency manual release control in a suitable position that is readily accessible to the pilot or other crewmember. Allow sufficient slack in the control cable to permit complete cargo movement without tripping the cargo release.
8.5.5.4 The manual ground release handle, a feature of some cargo release units, permits ground personnel to open the cargo release.
8.5.5.5 Label or placard all release controls as to each function and operation.
8.5.6 Functional Test.
8.5.6.1 Test the release action of each quick-release device release control with various loads up to and including the maximum external load. If the necessary load can be applied, this may be done in a test fixture or while installed on the rotorcraft.
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8.5.6.2 If the quick-release device incorporates an automatic release, the unit should not release the load when the master switch is placed in the “automatic” position until the load on the device is reduced to the preset value (usually 80 to 120 pounds).
Figure 8-3. Typical Cargo Sling Installation No. 1
8.5.7 Supplemental Flight Information. The aircraft may not be used in 14 CFR part 133 external-load operations until a Rotorcraft-Load Combination Flight Manual (RLCFM) is prepared in accordance with 14 CFR § 133.47. Appropriate entries should also be made in the aircraft’s Weight and Balance (W&B) data, equipment list, and logbooks. The FAA Form 337, Major Repair and Alteration (Airframe, Powerplant, Propeller, or Appliance), should also be executed as required by 14 CFR § 43.5(a) and (b).
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8.5.8 Inspection and Maintenance. Inspection of the complete installation should be accomplished prior to each lift for security and functionality. Maintenance should be accomplished in accordance with the manufacturer’s instructions.
Figure 8-4. Typical Cargo Sling Installation No. 1 (Showing Fuselage Attachment Fitting)
8-8 Figure 8-5. Typical Cargo Sling Installation No. 1 (Showing Fore Aft Limiting Stops) Fig ure 8-6. Typical Cargo Sling Installation No. 2 (Cargo Hook Attached Directly to Underside of Fuselage)
8-9 Figure 8-7. Typical Cargo Sling Installation No. 3 (4-Leg, Cable Suspended) Fig ure 8-8. Typical Cargo Sling Installation No. 3 (Showing Cable Sling Leg Attachment to Landing Gear Crosstube Fitting)
8-10 Figure 8-9. Typical Cargo Sling Installation No. 3 (Showing Cargo Sling in Stowed Position)
8-11 Section 2. Cargo Racks
8.6 General. This section contains structural and design information for the fabrication and installation of a cargo rack used as an external-load attaching means for a Class A rotorcraft-load combination operation under 14 CFR part 133.
8.7 Fabrication of Cargo Racks. The type of construction and method of attachment depend upon the material to be used and the configuration of the rotorcraft involved.
Figures 8-10 through 8-14, Typical Cargo Rack Installation No. 3, illustrate typical construction and installation methods.
Figure 8-10. Typical Cargo Rack Installation No. 1
8.8 Static Test. The cargo rack installation must withstand the static test load required by 14 CFR § 27.865(a). Conduct the test as outlined in Chapter 2.
8.9 Supplemental Flight Information. The aircraft may not be used in 14 CFR part 133 external-load operations until an RLCFM is prepared in accordance with 14 CFR § 133.47.
8-12 Figure 8-11. Typical Cargo Rack Installation No. 1 (Showing Attachment Detail) Fig ure 8-12. Typical Cargo Rack Installation No. 2
8-13 Figure 8-13. Typical Cargo Rack Installation No. 2 (Showing Rack Partially Installed) Fig ure 8-14. Typical Cargo Rack Installation No. 3