This requirement is intended to establish standard design practices for the lubrication of the bearings and bearing surfaces used in flight control systems and all other mechanical subsystems installed in airframes except engines and their accessory drive gear boxes and helicopter transmission drive systems.

Unsealed rolling element bearings protected by an enclosure and periodically serviced with a proper lubricant unless they receive adequate lubrication from the lubricant of the unit in which they are installed.

Rolling element bearings which are permanently sealed are considered to be lubricated for the life of the bearing, unless a means of relubrication is provided. Rolling element bearings with replaceable seals shall be considered to be permanently lubricated for the life of the installation, unless service experience demonstrates the need for periodic lubrication.

Insofar as possible, provisions for lubrication and access to lubrication fittings shall not require the removal of adjacent fittings, structure, or the use of specialized equipment.

The recommended lubrication fittings to be used for grease lubrication are described in requirement 501.

The purpose of this requirement is to establish required criteria. Where there are no requirements in a specific area and guidance information may be included, the lack of requirements is so noted.

Aluminum, steel or titanium tubing may be swaged to an appropriate nipple diameter and tapped to receive a threaded rod end. Titanium tubing work hardens badly with rotary swaging and is more responsive to vail swaging. This process loses greater area in reduction and is therefore a poor candidate for control rod manufacture. The wall increase occurring in the taper is least for titanium, somewhat greater for steel and greatest for aluminum. However, all swagings elongate during swaging, universally having less cross sectional area at the nipple than the body. The further section loss from tapping the nipple requires accuracy in forecasting the appropriate nipple diameter and in the case of aluminum tubes, adds to the desirability of forming threads on the nipple I.D. as compared with cutting threads. Forming threads in steel or titanium tubing is not practical in that these swaged nipples lack ductility for the required thread imprinting. To obtain appropriate section for threading steel or titanium tubes, the unswaged blank may be precontoured or the center section after swaging may be turned off providing the appropriate wall tolerance is maintained.

Steel or titanium tubes for control rod assemblies may be required to support loads in excess of aluminum tubing capability. Abrupt sectional change as well as cut threads are sensitive to fatigue loading. Fatigue capability of these assemblies shall be established and shall be in excess of system requirements.

2024 aluminum tubing is most commonly utilized in manufacturing of control rod assemblies. Some swags reduction is possible in T3 temper, most swaging will require "O" (or annealed) material for swaging with subsequent heat treat to -T42 or -T62 in accordance with MIL-H-6088. The practical limit for reduction in 13 or 0 temper depends on equipment and technique. Reduction in T3 requires subsequent heat treat to T81. Drawing requirement should define acceptable micro-structure or fold depth in the critical area rather than prescribe manufacturing steps.

Many high strength alloys having desirable characteristics in a finished part are undesirable for swage fabrication. The physical characteristic most necessary to the swaging process is ductility. Materials having less than 10 percent elongation may be a poor candidate for swaging. CRES tube manufactured to MIL-T-6845 has excellent ductility, may be specially drawn to 100 KSI tensile strength and is inexpensive. Where loads or environmental considerations preclude aluminum tube, this CRES tube should be evaluated first.

Heat treatment of rods or rod components of alloy steel or heat treatable CRES shall be heat treated in accordance with MIL-H-6875.

An airframe requirement for a control rod assembly presumes assembly column loading in compression as well as tension. Where practicable the load in tension shall be the greatest. Tubes selected to support compression loads in a system are lightest if selected with large diameter and light wall. The limiting factors may be accomodation in the airframe or the largest diameter tubing economically reducible to effect an attachment to the desired rod end, i.e., an aluminum tube 1.37511 O.D. × .03511 wall to be threaded to receive a ⅜-24 rod end will require swaging to a nipple diameter approximately .525 inch.

This reduction of slightly more than 60 percent (1.525/1.375) approaches the practical limit. Reduction in excess of 50 percent will increase costs disproportionately.

Common terminology applicable to swaged tubes is recommended per figure 207-7.

Swags angle should be limited to close tolerance only if structure or installation dictates.

Effective definition of a swaged tube should define nipple diameter, length, minimum wall allowable swags angle, and concentricity relative to tube body.

Tube cross section area reduction is inherent in the swaging process. The wall increase occurring in the taper coincides with an increase in length. The approximate wall thickness (W2) remaining in the nipple and available for attachment may be calculated as follows:

Where D₁ = original tube diameter, D₂ = nipple diameter and W1 = original wall thickness.

Where an integral clevis or threaded nipple is required to have greater material thickness or cross section than the tube body, manufacture should be allowed from larger diameter and heavier wall tubs at supplier option. As illustrated in figure 207-8, the integral formed clevis tube is traced turned to the dimensions shown from 1.375 O.D. × .188 wall stock size. The clevis end is then formed from the original material size to meet the .178/.183 clevis ear thickness requirement. The threaded nipple can be either mandrel swaged, turned and swaged, or swaged and turned to obtain the material thickness at the threaded end(s). When the detail drawing indicates "Tube Body" as shown, tolerances per FED-STD-245 will be maintained.

Types I, II, and III rod ends are for use in aerospace systems in many difference applications and environments.

This requirement is intended to establish engineering criteria and requirements for the selection and application of bushings for aerospace systems. These design requirements are peculiar to these bushings and are to be used as a supplement to requirements specified in Requirement 201. This requirement also identifies the presently approved bushings for aerospace applications.

This requirement is intended to establish engineering criteria and requirements for the selection of self-lubricating metallic sleeve bearings for aerospace systems. These design requirements are peculiar to these types of bearings and are to be used as a supplement to design requirements specified in Requirement 201. This requirement also identifies the presently approved lined sleeve bearings for aerospace-applications.

Sleeve bearings are designed to be installed and retained using a press/interference fit. Recommended housing and shaft fits for installation of the bearings shall be as specified in Requirement 202. Adhesive can be used to aid in the retention, but care shall be taken to avoid installations which rely on adhesive as the sole means of retaining the bearing in an oversized hole. Adhesive brittle failure may occur in such cases.

This requirement is intended to establish the nuts and locking-devices for use in assembly of rod end bearings, control rods, and associated hardware.

MS 14227 was developed to provide a stronger rod end lock for use in existing design and which would be compatible with NAS 513 and NAS 559 lug slot dimensions in threaded sizes up to 1.125 inch diameter. For larger diameters, the MS 14198 locks are compatible with NAS 513 and NAS 559 lug slot dimensions and offer a retrofittable lock having greater strength.

Use of NAS 559 Type A locks in sizes smaller than the 4 (9/16" thread size) should be discontinued because of poor strength. Mechanically formed locks, such as NAS 559 Type B, and stamped-out (not machined) NAS 513 locks should also be discontinued from service because of poor strength and susceptibility to installation damage which may go undetected.

This requirement is intended to establish standard design practices for the use of fittings required to provide grease lubrication of bearings and bearing surfaces as described in Requirement 203.

All suggestions are covered in applicable areas herein or in requirement 206.

This requirement, MIL-P-7034, and the supporting documents are intended as an outline of the availability and requirements for control pulleys used in aircraft

Table 604-I is presented as an aid in the selection of self-retaining bolts. Table 604-1. Selection of self-retaining bolts.

Head Style Drawing Procurement Material Temperature Finish Bolt Types Number Specifications Limit --------------------------------------------------------------------------------------------------------- Hex MS3369 MIL-B-23964 CRES 450°F Passivated Positive Locking Pan MS21125 MIL-B-23964 CRES 450°F Passivated Positive Locking Flush MS21130 MIL-B-23964 CRES 450°F Passivated Positive Locking Hex MS27476 MIL-B-83050 CRES, 450°F Passivated Impedance STEEL Cadmium Type Plated Flush MS27577 MIL-B-83050 CRES, 450°F Passivated Impedance STEEL Cadmium Type Plated