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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
8-4
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
9-1 CHAPTER 9. GLIDER AND BANNER TOW-HITCH INSTALLATIONS
9.1 Purpose. This chapter contains design and installation information for banner and glider tow hitches. Guidance for inspection, service, and continuous airworthiness requirements for the hitches are also addressed in this chapter.
9.2 Hazards and Warnings. The direction and maximum arc of displacement of banner towline loads occur within a more limited rearward cone of displacement than do glider towline loads (see Figures 9-1, Glider Tow Angle, and 9-2, Banner Tow Angle). Hitches that meet the banner tow criteria of this chapter may not be suitable for glider towing.
Due to the basic aerodynamic differences between the two objects being towed, glider and banner tow-hitch installations are treated separately with regard to loading angles.
9.3 References. This chapter will occasionally reference manufacturers’ documents, certain parts of 14 CFR, and certain FAA ACs. It is the installer’s responsibility to ensure the latest revisions of these documents are used as reference material. Refer to Civil Air Regulation (CAR) 6, Rotorcraft Airworthiness; Normal Category, and Order 8900.1, Volume 8, Chapter 5, Section 2, Changes to Special Purpose for Restricted Aircraft.
9.4 Installation Considerations.
9.4.1 Weight and Balance (W&B). In most cases, the weight of the tow-hitch assembly will affect the aft center of gravity (CG) location. To ensure that the possibility of an adverse effect caused by the installation has not been ignored, enter all pertinent computations in the aircraft W&B records in accordance with the provisions contained in 14 CFR § 43.5(c). The requirements of 14 CFR § 43.5(a) and (b) should also be addressed for maintenance record entries and repair and alteration forms.
9.4.2 Equipment List. The aircraft equipment list should be updated to reflect any tow equipment installations. Consideration should also be given to adding appropriate revisions to the aircraft’s pilot’s operating handbook (POH) or flight manual, as required.
9.4.3 Corrosion Protection. Tow hitches are traditionally simple mechanical devices; however, improper care may lead to hazardous conditions for the aircraft operator. The aft, external location of tow hitches expose them to the elements, and proper corrosion protection methods should be employed to prevent improper operation or malfunction. Refer to the manufacturer’s documents or AC 43.13-1, Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair, Chapter 6, Corrosion, Inspection, and Protection, for some additional corrosion protective measures that may be used.
9.5 Fabrication and Installation Procedures.
9.5.1 Methods. Accomplish the installation of tow hitches using the manufacturer’s data or that data previously approved by a representative of the Administrator, when available, such as a Supplemental Type Certificate (STC) or a field approval. Installations requiring fabrication of brackets, parts, fittings, etc., should be accomplished using data in the form of ACs, such as AC 43.13-1, to determine material requirements, load requirements, and the type and size of hardware used.