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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.
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9.5.2 Structural Requirements. The structural integrity of a tow-hitch installation on an aircraft is dependent upon its intended usage.
9.5.3 Attachment Points. Tow-hitch mechanisms are characteristically attached to or at tiedown points or tail wheel brackets on the airframe. These are points where the design loadbearing qualities may be sufficient for towing loads. Keep the length from the airframe attachment point to the tow hook at a minimum as the loads on the attachment bolts are multiplied by increases in the attachment arm.
9.5.4 Glider Tow-Hitch Load Testing.
9.5.4.1 Towline Assembly. Protection for the tow-plane is provided by requiring use of a towline assembly that will break prior to structural damage occurring to the tow-plane. The normal tow load imposed on the hitch rarely exceeds 80 percent of the weight of the glider. Therefore, the towline assembly design load for a 1,000-pound glider could be estimated at 800 pounds. By multiplying the estimated design load by 1.5 (to provide a safety margin), we arrive at a limit load value of 1,200 pounds. The 1,200-pound limit load value is used in static testing or analysis procedures per paragraph 9.6 to prove the strength of the tow hook installation. When the hook and its attachment to the aircraft structure have been proven to withstand the limit load (1,200 pounds in this example), then the “maximum” breaking strength of the towline assembly is established at the design load of 800 pounds. Thus, the towline will break well before structural damage occurs to the tow-plane.
Figure 9-1. Glider Tow Angle Fig ure 9-2. Banner Tow Angle
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9.5.4.2 Load Carrying Capabilities. Another approach can be applied if the limit load carrying capabilities of a tow hook and fuselage are known. In this case, the known load value can be divided by 1.5 to arrive at the design load limits.
For example, if the tow hook and fuselage limit loads are known to be 1,800 pounds, divide this by 1.5 (1,800 ÷ 1.5 = 1,200) and we arrive at a design load value of 1,200 pounds. Thus, if a towline assembly rated at 1,200 pounds is used, it will break before reaching the structural limits of the hook and attaching structure.
9.5.4.3 Maximum Towline Breaking Strength. When considering tow hook installations, one may establish maximum towline breaking strength by:
1. Dividing the known limit load capabilities of the fuselage and tow hook installation by 1.5; or
2. Knowing the design load needs of the towline assembly and multiplying by 1.5 to arrive at a limit load. Then, through analysis or static testing, determine that the hook and fuselage are capable of towing the load.
9.5.4.4 Banner Tow Hitches. Install and test the hitch to support a limit load equal to at least two times the operating weight of the banner.
9.5.4.5 Multiple Hitches. Multiple tow hitches are sometimes used on banner tow aircraft. These installations should be evaluated individually for approval.
9.6 Structural Testing. When installations are made on an aircraft using brackets that have not been previously approved, some structural testing may be required. Adequacy of the aircraft structure to withstand the required loads can be determined by either static testing or structural analysis.
9.6.1 Static Testing. When using static tests to verify structural strength, subject the tow hitch to the anticipated limit load. Aircraft tow hitches used for banner towing shall be tested a minimum of two times the weight of the heaviest banner to be towed, using the cone angle shown in Figure 9-2. Aircraft towline used for glider towing shall be tested to a minimum load of approximately 80 percent of the weight of the heaviest glider to be towed using the cone angle shown in Figure 9-1. Static testing should be done in accordance with the procedures in paragraph 2.6.
9.6.2 Structural Analysis. If the local fuselage structure is not substantiated by static test for the proposed tow load using a method that experience has shown to be reliable, subject the fuselage to engineering analysis to determine that the local structure is adequate. Use a fitting factor of 1.15 or greater in the loads for this analysis.
9.7 Angles of Tow. Tests should be conducted on the system at various tow angles to ensure that:
1. There is no interference with the tail wheel or adjacent structure. Tow hitches mounted to tail wheel springs or trusses, as in Figures 9-6, Conventional Gear
9-4 A ircraft—Shock Strut Type Tailwheel, and 9-7 , Conventional Gear Aircraft— Tubular Spring Type Tailwheel, which travel up and down with the tail wheel, should be tested under load to ensure they do not contact any control surfaces.
2.
The towline clears all fixed and movable surfaces at the maximum lateral and vertical cone of displacement and full surface travel.
3. The tow hitch does not swivel. Experience has shown swiveling could result in fouling both the release line and towline during operations by the tow-plane.
4. The opened jaw of the hitch does not strike any portion of the aircraft.
5. The hitch is able to release under load at all tow angles.
9.8 Placards. A placard should be installed in a conspicuous place in the flight deck to notify the pilot of the structural design limits of the tow system. The following are examples of placards to be installed:
• For glider tow: “Glider towline assembly breaking strength not to exceed _____*______ pounds.” (*Value established per paragraph 9.5.4.)
• For banner tow: “Tow hitch limited to banner maximum weight of _____**_____ pounds.” (**Banner hitch limitations are one-half the load applied per paragraph 9.5.4.)
9.9 Installation Procedures―Types of Hitches. Two types of glider tow hooks are used in the United States: the American-made Schweizer and the European-made TOST brand.
The FAA has coordinated with Schweizer in developing detailed inspection procedures and identification of life-limiting parts. These procedures and specifications are identified in paragraph 9.9.1. The European-made TOST releases are German-manufactured and approved by the German Civil Aviation Authority (CAA). They are available in various types and configurations. Two types of TOST releases can be found on U.S.-operated gliders. The “E-type” release mechanism is commonly used as a nose release for sailplanes and as a tail release on towing aircraft. The “G-type” release mechanism is typically used as a CG release for winch launching. TOST has provided installation, inspection, and maintenance instructions for its systems. An overview of these systems is identified in paragraph 9.9.2. Regardless of the brand used, all tow hooks should be inspected for proper operation daily prior to tow activity.
9.9.1 Schweizer Hitch: Installation and Maintenance. The Schweizer is a simple over center L-hook type with a rubber tension block to preload the release lever. It is eligible for installation on several models of Cessna and Piper aircraft by STC and has been installed on many other aircraft using the field approval process. It uses a tow rope with a single round steel ring attaching to the hook. While this hitch is a simple mechanism, proper maintenance and frequent inspections are necessary to ensure proper operation. All initial installations should be proof tested. The proof test entails a total of two release-effort readings taken at the 1D112-8 arm assembly: one reading while a 600-pound load is applied to the hook and the other with a zero static load is applied to the hook. See Figure 9-10, Schweizer Type Hitch. The following additional procedures are